tr-110083

EPRI Project ManagerP. Frattini

EPRI • 3412 Hillview Avenue, Palo Alto, California 94304 • PO Box 10412, Palo Alto, California 94303 • USA800.313.3774 • 650.855.2121 • [email protected] • www.epri.com

Surface Chemistry Interventions toControl Boiler Tube Fouling

TR-110083

Final Report, December 1999

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THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS ANACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCHINSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THEORGANIZATION(S) BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM:

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ORGANIZATION(S) THAT PREPARED THIS DOCUMENT

Atomic Energy of Canada Limited

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Copyright © 1999 Electric Power Research Institute, Inc. All rights reserved.

iii

CITATIONS

This report was prepared by

Atomic Energy of Canada LimitedChalk River LAboratoriesChalk River, Ontario, Canada K0J 1J0

Principal InvestigatorC. W. TurnerD. A. GuzonasS. J. Klimas

This report describes research sponsored by EPRI.

The report is a corporate document that should be cited in the literature in the following manner:

Surface Chemistry Interventions to Control Boiler Tube Fouling, EPRI, Palo Alto, CA: 1999.TR-110083.

v

REPORT SUMMARY

This report summarizes results of a detailed investigation of surface chemistry on colloidalmagnetite and hematite exposed to absorbing amines. It is part of a multi-year study to determinehow amines used for secondary-cycle pH control in pressurized water reactors (PWRs) affectcorrosion product deposition rates onto steam generator tubes.

BackgroundPrevious research conducted at Chalk River Laboratories determined that the surface chemistryof corrosion products has a significant influence on the particle deposition rate under flow-boiling conditions [TR-108004]. Researchers postulated that the difference between depositionrates of magnetite and hematite was due to differences in the surface charge of these oxidesunder the test conditions (magnetite is negatively charged at pHT=6.2 and hematite positivelycharged). As Inconel 600 also should be negatively charged under these conditions, magnetiteparticles will tend to be repelled from Inconel 600, while particles of hematite will be attracted.To explain observed deposition rate increases under flow boiling conditions, researchers alsohypothesized that amines used for pH control increase the particles’ surface potential (surfacepotential will become more positive) by adsorption onto the particle surface.

ObjectiveTo characterize the impact of amine adsorbate surface chemistry on iron oxide deposition onsteam generator tubes.

ApproachThe work scope for this project included measuring adsorption’s effect on the surface potentialof corrosion products. Atomic Force Microscopy (AFM), which measures the force exerted bythe surface of Inconel 600 on a particle as the two are brought together, was used to characterizesurface potential.

ResultsAECL Chalk River Laboratories measured the adsorption of ammonia, morpholine,ethanolamine, and dimethylamine onto the surfaces of colloidal magnetite and hematite at 25qC.They quantified the effect of the adsorption of these amines on surface potential by measuringthe resulting shift in the isolectric point of the corrosion products and by the direct measurementof the surface interaction force between the corrosion products and Inconel 600. Thesemeasurements support the hypothesis that adsorption of amine affects the magnetite depositionrate by lowering the force of repulsion between magnetite and the surface of Inconel 600.

vi

Researchers also identified a mechanism to account for enhanced deposition rates at highmixture qualities (>0.35), which has been shown to predict behavior that is consistent with bothexperimental and plant data. As a result of this investigation, several criteria are proposed toreduce the extent of corrosion product deposition on the tube bundle. To minimize adsorption,the amine should have a high base strength and a large “footprint” on the particle surface. Toprevent enhanced deposition at high mixture qualities, the study proposes that a modified aminebe used that will reduce the surface tension or the elasticity of the steam-water interface.

EPRI PerspectiveReducing degradation of steam generator thermal performance is one of the principal goals ofPWR secondary-side water chemistry control. Corrosion product deposition resulting in thicktube scales may lead to less effective steam generator heat transfer. Furthermore, deposition ofiron oxide corrosion products in tube-to-support plate crevices facilitates stress corrosioncracking (SCC) of the tubing from boiling concentration of impurities in the packed crevice.Specific studies, such as this report and the EPRI report, “Effects of Morpholine on the SurfaceCharge Properties of Magnetite [TR-110082], which detail the effects of amines used as pHcontrol agents on surface charges of iron oxides, provide evidence for determining how theseamines impact deposition rate. Ultimately, EPRI’s goal is to give utilities the capability to tailortheir amine choice based on plant-specific tube fouling concerns in addition to balance-of-plantbasicity and volatility needs.

TR-110083

KeywordsCorrosion productsMagnetiteHematiteSurface chargeAmine

vii

CONTENTS

1 EXPERIMENTAL METHODS AND ANALYSES.................................................................. 1-1

1.1 Adsorption Isotherms................................................................................................... 1-1

1.2 Electrophoretic Mobility................................................................................................ 1-2

1.3 Atomic Force Microscopy (AFM).................................................................................. 1-3

1.4 Surface Tension .......................................................................................................... 1-9

1.5 Loop Deposition Tests............................................................................................... 1-10

2 RESULTS ............................................................................................................................ 2-1

2.1 Adsorption Isotherms................................................................................................... 2-1

2.2 Electrophoretic Mobility................................................................................................ 2-4

2.3 Atomic Force Microscopy ............................................................................................ 2-5

2.4 Surface Tension ........................................................................................................ 2-14

2.5 Loop Deposition Tests............................................................................................... 2-15

2.6 Deposition Mechanism at High Steam Quality ........................................................... 2-22

3 DISCUSSION....................................................................................................................... 3-1

4 SUMMARY AND CONCLUSIONS....................................................................................... 4-1

5 IMPLICATIONS FOR CONTROLLING TUBE-BUNDLE FOULING..................................... 5-1

6 REFERENCES .................................................................................................................... 6-1

7 NOMENCLATURE............................................................................................................... 7-1

A AMINE ADSORPTION ISOTHERMS ON MAGNETITE AND HEMATITE...........................A-1

REFERENCES...................................................................................................................A-2

B CALCULATION OF FORCE-DISTANCE CURVES FROM NANOSCOPE II RAWFORCE DATA ..................................................................................................................... ...B-1

viii

C FIX ME ................................................................................................................................C-1

Magnetic Field Inside I-600 Test Section..........................................................................C-17

D THERMOHYDRAULIC PARAMETERS UNDER TWO-PHASE FLOW WITH FOCUSON STEAM GENERATOR FOULING.....................................................................................D-1

STEAM QUALITY...............................................................................................................D-1

SUPERFICIAL MASS FLUX, VELOCITY, AND REYNOLDS NUMBER .............................D-2

FLOW PATTERNS.............................................................................................................D-3

VOID FRACTION ...............................................................................................................D-5

SLIP RATIO .......................................................................................................................D-6

TWO-PHASE DENSITY .....................................................................................................D-7

VELOCITY OF THE PHASES ............................................................................................D-7

SINGLE-PHASE SHEAR STRESS, FRICTION VELOCITY, FRICTION FACTOR,AND PRESSURE DROP....................................................................................................D-8

TWO-PHASE PRESSURE DROP......................................................................................D-9

INCEPTION OF DROPLET ENTRAINMENT....................................................................D-10

DROPLET ENTRAINMENT RATE ...................................................................................D-11

DROPLET DEPOSITION RATE .......................................................................................D-12

ENTRAINED FRACTION .................................................................................................D-12

TURBULENCE INTENSITY IN THE GAS CORE .............................................................D-13

DROPLET SIZE, VELOCITY AND DISTRIBUTION..........................................................D-14

FILM THICKNESS............................................................................................................D-15

NOMENCLATURE ...........................................................................................................D-16

REFERENCES.................................................................................................................D-17

E SEM MICROGRAPHS OF TUBE DEPOSITS......................................................................E-1

ix

LIST OF FIGURES

Figure 1-1 Raman spectrum of 1000 mM ethanolamine solution in the absence of addedmagnetite, showing the various CH stretching modes. The gradual sloping baselineis the shoulder of the OH stretching mode of water. ........................................................ 1-2

Figure 1-2 SEM micrograph of a typical magnetite sintered agglomerate glued to anAFM cantilever ................................................................................................................ 1-4

Figure 1-3 AFM image of a 10-Pm-by-10-Pm region of the Inconel 600 coupon used inthe force measurements (bottom), and a representative surface roughness profilemeasured from this AFM image (top). ............................................................................. 1-5

Figure 1-4 Comparison of surface potentials obtained from AFM force curves and fromelectrophoresis of magnetite particles used in the AFM experiments. All potentialsare for a zero concentration of amine. ............................................................................. 1-8

Figure 1-5 Comparison of surface potentials obtained from AFM force curves and fromelectrophoresis of hematite particles used in the AFM experiments. All potentialsare for a zero concentration of amine. ............................................................................. 1-8

Figure 1-6 The assembled cell, showing the orientation of the Inconel 600 and magnetitecoupons and the location of the liquid meniscus.............................................................. 1-9

Figure 1-7 Cell configuration used for the contact angle measurements ............................... 1-10

Figure 1-8 Schematic of the loop used for measurements of particle deposition undersingle-phase forced-convection and flow-boiling conditions........................................... 1-11

Figure 1-9 Schematic of the test section showing 3 heated and 4 unheated regions............. 1-12

Figure 2-1 Adsorption isotherms for dimethylamine, ammonia, ethanolamine, andmorpholine onto magnetite at 25qC. ................................................................................ 2-1

Figure 2-2 Adsorption isotherms for dimethylamine, ammonia, ethanolamine, andmorpholine onto hematite at 25qC. .................................................................................. 2-2

Figure 2-3 Temperature dependence of the adsorption of dimethylamine onto thesurface of magnetite ........................................................................................................ 2-3

Figure 2-4 Effect of 5 mM solutions of amine on the surface potential of magnetite ................ 2-4

Figure 2-5 Effect of 50 mM solutions of amine on the surface potential of magnetite .............. 2-4

Figure 2-6 The effect of additions of morpholine and ammonia on the surface potential ofhematite, determined from the electrophoretic mobility.................................................... 2-5

Figure 2-7 Successive force curves measured using the same particle–tip combinationunder the same solution conditions. Filled circles are advancing measurements,open circles are retracting ............................................................................................... 2-6

Figure 2-8 Force curves measured between a magnetite particle and an Inconel 600surface using 3 different particle–tip combinations. (Dimethylamine series: -

x

diamonds; Morpholine series: - open squares; Ethanolamine series; - filledtriangles). ........................................................................................................................ 2-6

Figure 2-9 Some representative force-distance curves, showing the behaviour of theadvancing (filled symbols) and retracting (open symbols) parts of the force curve:(a) pH25 9, hematite particle, no amine; and (b) pH25 8, hematite particle, noamine. ............................................................................................................................. 2-7

Figure 2-10 Best fit of Equation (1-6) to the force-distance data for magnetiteapproaching the surface of Inconel 600........................................................................... 2-8

Figure 2-11 Best fit of Equation (1-6) to the force-distance data for hematite approachingthe surface of Inconel 600 ............................................................................................... 2-9

Figure 2-12 Plots of the best fit of the force curve versus separation for the systemmagnetite/Inconel 600 as a function of morpholine concentration, at pH25 6 to 10.Units of the abscissa are mN/m. Upper, middle, and lower lines are for 0, 5, and 50mM amine. .................................................................................................................... 2-10

Figure 2-13 Plots of the best fit of the force curve versus separation for the systemhematite–Inconel 600 as a function of morpholine concentration at pH25 6 to 10.Units of the abscissa are mN/m. Upper, middle, and lower lines are for 0, 5, and 50mM amine. .................................................................................................................... 2-11

Figure 2-14 Photograph of the interior of the cell used to measure the contact angles (θ)of a morpholine solution on Inconel 600 and magnetite, taken at 25°C.......................... 2-14

Figure 2-15 The effect of temperature on the wetting angle of the Inconel-600–solutionand the magnetite–solution interfaces ........................................................................... 2-15

Figure 2-16 Normalized deposition rate as a function of steam quality. � indicateslocations along the heated (diabatic) test section. � indicates locations on theunheated (adiabatic) test section. .................................................................................. 2-16

Figure 2-17 Normalized deposition rate vs. mixture quality. � indicates locations alongthe heated (diabatic) test section. � indicates locations on the unheated (adiabatic)test section. ................................................................................................................... 2-17



Figure 2-20 Build-up of radioactivity resulting from the deposition of magnetite onto thesurface of Inconel 600 under flow-boiling conditions. The suspension of magnetiteparticles was traced using 59Fe so that the build-up could be followed using a γ-raydetector, as described in Turner et al., 1997.................................................................. 2-22

Figure 2-21 Flow regimes under flow-boiling conditions ........................................................ 2-24

Figure 2-22 Steam–liquid velocities and film thickness vs. mixture quality ............................ 2-25

Figure 2-23 Calculated droplet deposition rate vs. mixture quality......................................... 2-25

Figure 3-1 Comparison of typical deposition behaviour versus steam quality from the H-3 loop tests with deposit loadings measured on tubes pulled from Oconee-1 andOconee-3 ........................................................................................................................ 3-9

xi

Figure 4-1 Effect of surface coverage of amine on the average deposition rate ofmagnetite under flow-boiling conditions........................................................................... 4-1

Figure 5-1 Trends in magnetite and hematite deposition rate with water chemistry underflow-boiling conditions ..................................................................................................... 5-2

Figure A-1 Raman intensity versus amine concentration for dimethylamine, ammonia,ethanolamine, and morpholine. Linear fits to the data constrained to go through theorigin are shown. .............................................................................................................A-1

Figure B-1 Typical raw data output from atomic force microscopy (AFM). Regions ofzero force and of constant compliance are indicated .......................................................B-1

Figure B-2 Fits of F/r versus separation for the system magnetite–Inconel 600 as afunction of ammonia concentration for pH = 6 to 10. The concentration of addedamine is indicated in units of mM. Units for F/r are mN/m. Energy required by a 1-µm particle to surmount a force barrier of 0.04 mN/m is 49kT..........................................B-3

Figure B-3 Fits of F/r versus separation for the system magnetite/–nconel 600 as afunction of ethanolamine concentration for pH = 6 to 10. The concentration ofadded amine is indicated in units of mM. Units for F/r are mN/m. Energy requiredby a 1-µm particle to surmount a force barrier of 0.04 mN/m is 49kT...............................B-4

Figure B-4 Fits of F/r versus separation for the system magnetite–Inconel 600 as afunction of dimethylamine concentration for pH = 6 to 10. The concentration ofadded amine is indicated in units of mM. Units for F/r are mN/m. Energy requiredby a 1-µm particle to surmount a force barrier of 0.04 mN/m is 49kT...............................B-5

Figure B-5 Fits of F/r versus separation for the system hematite–Inconel 600 as afunction of ammonia concentration for pH = 6 to 10. The concentration of addedamine is indicated in units of mM. Units for F/r are mN/m. Energy required by a 1-µm particle to surmount a force barrier of 0.04 mN/m is 49kT..........................................B-6

Figure B-6 Fits of F/r versus separation for the system hematite–/Inconel 600 as afunction of ethanolamine concentration for pH = 6 to 10. The concentration ofadded amine is indicated in units of mM. Units for F/r are mN/m. Energy requiredby a 1-µm particle to surmount a force barrier of 0.04 mN/m is 49kT...............................B-7

Figure B-7 Fits of F/r versus separation for the system hematite–Inconel 600 as afunction of dimethylamine concentration for pH = 6 to 10. The concentration ofadded amine is indicated in units of mM. Units for F/r are mN/m. Energy requiredby a 1-µm particle to surmount a force barrier of 0.04 mN/m is 49kT...............................B-8

Figure C-1 Normalized deposition rate as a function of steam quality. � indicateslocations along the heated (diabatic) test section. � indicates locations on theunheated (adiabatic) test section. ....................................................................................C-5




xii







Figure C-11 Normalized deposition rate as a function of steam quality. � indicateslocations along the heated (diabatic) test section. � indicates locations on theunheated (adiabatic) test section. ..................................................................................C-10





Figure C-16 Normalized deposition rate as a function of steam quality. � indicateslocations along the heated (diabatic) test section. � indicates locations on theunheated (adiabatic) test section ...................................................................................C-12




xiii






Figure C-25 Magnetic flux density from axial and transverse direction .................................C-18

Figure D-1 Schematics of the steam quality change during a non-equilibrium 2-phaseflow. Re-printed from Tong and Tang (1997) should the reference be Hsu andGraham (1986)?. .............................................................................................................D-2

Figure D-2 Hewitt and Roberts flow pattern map (Whalley, 1987) for vertical upwardsflow inside a tube.............................................................................................................D-3

Figure E-1 Morphology of surface deposits created under magnetite/morpholinechemistry, Experiment D097............................................................................................E-2

Figure E-2 Morphology of surface deposits created under magnetite/morpholinechemistry, run D119 ........................................................................................................E-3

Figure E-3 Morphology of surface deposits created under magnetite/ammoniachemistry, run D120 ........................................................................................................E-4

Figure E-4 Morphology of surface deposits created under magnetite/dimethylaminechemistry (D100 and D105).............................................................................................E-5

Figure E-5 Morphology of deposits created under magnetite/potassium hydroxidechemistry.........................................................................................................................E-6

Figure E-6 Morphology of surface deposits created under magnetite/pyrrolidinechemistry control .............................................................................................................E-7

Figure E-7 Morphology of surface deposits created under magnetite/3-methoxypropylamine chemistry (experiment D102) .........................................................E-8

Figure E-8 Morphology of surface deposits created under magnetite/4-aminobutanolchemistry.........................................................................................................................E-9

Figure E-9 Morphology of surface deposits created under hematite/ethanolaminechemistry, D108 and D111 ............................................................................................E-10

Figure E-10 Morphology of surface deposits created under hematite/dimethylaminechemistry, hydrazine present, no oxygen, experiment D106..........................................E-11

Figure E-11 Morphology of surface deposits created under hematite/potassiumhydroxide chemistry D113 and D115.............................................................................E-12

xiv

Figure E-12 Morphology of surface deposits created under hematite/3-methoxypropylamine chemistry, experiment D110 ........................................................E-13

Figure E-13 Morphology of surface deposits created under hematite/3-methoxypropylamine chemistry, experiment D112 ........................................................E-14

xv

LIST OF TABLES

Table 1-1 Surface potentials determined for Inconel 600, magnetite, and hematite fromelectrokinetic data ........................................................................................................... 1-6

Table 1-2 Nominal loop conditions for the deposition tests................................................... 1-10

Table 1-3 Concentrations of amine required to achieve pHT = 6.2 at 270qC ......................... 1-11

Table 2-1 Amine adsorbed at concentrations of 5 and 50 mM................................................ 2-3

Table 2-2 Surface potential of magnetite in mV, determined by fitting Equation (1-6) tothe AFM force-distance data.......................................................................................... 2-12

Table 2-3 Surface potential of hematite in mV determined by fitting Equation (1-6) to theAFM force-distance data ............................................................................................... 2-13

Table 2-4 Surface charge density (mC/m2) calculated for magnetite from Equation (1-7). ..... 2-13

Table 2-5 Surface charge density (mC/m2), calculated for hematite from Equation (1-7). ...... 2-14

Table 2-6 Listing of loop deposition tests performed in this investigation.............................. 2-16

Table 2-7 Summary of loop deposition results for magnetite ................................................ 2-18

Table 2-8 Summary of loop deposition results for hematite .................................................. 2-21

Table 3-1 Comparison of trends in amine base strength, molecular size, and the relativeamount adsorbed onto corrosion products for 5 and 50 mM concentrations of amine...... 3-2

Table 3-2 Calculated change in surface charge density with adsorption of amine for thesecond limiting case ........................................................................................................ 3-4

Table 3-3 Summary of deposition results for magnetite. Results of the currentinvestigation are shown in bold, and the other results are from Turner et al. (1997) ........ 3-6

Table 3-4 Relationship between surface coverage of amine and the average magnetitedeposition rate under flow-boiling conditions ................................................................... 3-7

Table 3-5 Summary of deposition results for hematite. Results of the currentinvestigation are shown in bold, and the other results are from Turner et al., 1997.......... 3-8

Table C-1 Loop chemistry and operating conditions for each test ...........................................C-2

Table C-2 Database of all the H3 loop deposition results for magnetite, Fe3O

4........................C-3

Table C-3 Database of all the H3 loop deposition results for hematite, Fe2O

3..........................C-4

1-1

1 EXPERIMENTAL METHODS AND ANALYSES

1.1 Adsorption Isotherms

Adsorption of the amines onto suspensions of magnetite or hematite particles was determined bymeasuring the amount of amine removed from solution in contact with the corrosion product.Four amines were included in the investigation: morpholine, ammonia, ethanolamine, anddimethylamine. The magnetite was synthesized using a procedure developed by Sugimoto andMatijevic (1980), whereas the hematite was reagent-grade chemical purchased from FisherScientific Co. Both oxides were thoroughly rinsed in solutions of acid and base and then indistilled water, before measurements were made.

A measured amount of oxide (approximately 4 mg) was added to a fixed volume of solution witha known concentration of amine, and the suspension was adjusted to pH 10 using potassiumhydroxide. The suspension was then thoroughly mixed in an ultrasonic bath for 1 h and then leftfor 24 h to equilibrate. After equilibration, the suspensions were filtered and the concentration ofamine in the filtrate was measured using Laser Raman spectroscopy. This method of analysiswas chosen because it can be applied over a range of temperatures. Surface areas for themagnetite and hematite particles used in these experiments were determined by nitrogenadsorption using the Brunauer–Emmett–Teller (BET) method (Brunauer et al.,1938). Values of3.98 m2/g and 9.62 m2/g were obtained for magnetite and hematite, respectively.

A typical Raman spectrum from a solution of ethanolamine is shown in Figure 1-1. Ramanspectra were excited, using the 514.5-nm line of an Ar+ ion laser with an incident power of about1.5 W. The scattered light was collected and analyzed using a SPEX 1.0-m monochromator andcharge-coupled-device detector. The spectra were stored on a PC running SPEX DM3000software. Detector integration times ranged from 1 to 40 s, depending upon the amineconcentration in solution. Sixteen scans were averaged for each measurement. Data werefurther manipulated using GRAMS/386 software (Galactic Industries). For room-temperaturemeasurements, the spectra were acquired in square silica cuvettes, having a path length of1.0 cm. The high-temperature measurements were made using a Graseby–Specac heatedinfrared cell, with silica windows and an automated temperature controller. For measurementsat elevated temperatures, the particles were allowed to settle out of the beam beforemeasurements were made.

Calibration curves of Raman intensity as a function of solution concentration were prepared bymeasuring the Raman spectra of amine solutions at concentrations of 1, 10, 100 and 1000 mM.For quantification, the CH stretching and bending modes of the amines were selected becausethey are intense, occur at frequencies free of interference from water bands, and their intensitieswere not expected to be significantly perturbed by changes in concentration. Plots of the Raman

Experimental Methods and Analyses

1-2

intensity versus concentration for each of the 4 amines are linear over the 3-decade concentrationrange examined, as shown in Figure A-1 of Appendix A of this report.

For the adsorption isotherms measured at room temperature, the spectra of both the startingsolution and of the solution + oxide were measured sequentially. For each solutionconcentration., the water bending mode at ∼1600 cm-1 was used as a reference to compensate forthe small variations in laser power, sample alignment, and spectrum acquisition times1. Thesame cuvette was used to measure all the Raman spectra. The spectrum of the solution + oxidewas subtracted from the spectrum of the starting solution, and the intensity of the difference bandwas used to determine the amount of amine adsorbed, as described in Appendix A of this report.

0

2000

4000

6000

8000

10000

12000

2500 2600 2700 2800 2900 3000

Raman Shift (cm )

Ram

an In

tens

ity (

coun

ts)

-1

Figure 1-1Raman spectrum of 1000 mM ethanolamine solution in the absence of added magnetite,showing the various CH stretching modes. The gradual sloping baseline is the shoulderof the OH stretching mode of water.

1.2 Electrophoretic Mobility

Stock suspensions of the corrosion products used for the measurements of electrophoreticmobility were stored in clean stainless steel vessels, to avoid possible contamination by silica.Dilution of the suspensions and final adjustments for pH and amine concentration were doneusing a dedicated set of glassware that had been washed with potassium dichromate andthoroughly rinsed with de-ionized water. All water used in this investigation was purged withultra-high-purity argon to remove dissolved oxygen and carbon dioxide and was stored in asealed glass carboy.

1 At high amine concentrations in solution, only short detector integration times were used during data acquisition toavoid saturation of the detector. As the amine concentration in solution decreased, longer integration times wererequired to achieve adequate signal-to-noise ratios.


1-3

Electrophoretic mobilities (velocity per unit electric field) of particles in suspension weremeasured at room temperature in a commercial apparatus supplied by Zeta-Meter, Inc2. Forthese measurements, a suspension of particles is placed in a quartz capillary, and an electric fieldis then applied along the axis of the capillary. The sample is illuminated from the side so that themotion of the particles can be observed with the aid of a low-powered microscope. Velocity isdetermined by measuring the time taken for a particle to cross a calibrated grid.

Many factors can influence the electrophoretic mobility and isoelectric point (IEP) of a colloidalsuspension. Thus for each amine concentration, a fresh suspension of magnetite or hematite wasprepared from the concentrated stock suspension, and all samples (i.e., 4 different amines plus areference with no amine added) were processed and measured batchwise. For each sample, analiquot of the stock suspension was diluted in a 0.5 mM solution of potassium nitrate. Therequired amount of amine was then added, and the pH was adjusted by the addition of eitherKOH or KClO4. The samples were then agitated in an ultrasonic bath for 20 min and left for24 h to equilibrate. Previous experience has shown that in the absence of the amine thesuspensions reached equilibrium within 1 or 2 h of adjusting the pH, but longer times wererequired in the tests for which an amine was present.

Electrophoretic mobilities were measured for pH ranging from 5 to 10 in the presence of 5 and50 mM concentrations of amine and were compared to the mobilities measured in the absence ofamine. From 12 to 14 particles were tracked, and their electrophoretic mobilities were measuredfor each set of conditions. Duplicate measurements were made on freshly prepared samples toensure the reproducibility of the method. Electrophoretic mobility was converted to zetapotential, defined as the potential at the plane of shear between the particle and the solution,using the equation developed for the case where the particle radius is large compared to thediffuse layer thickness (Hiemenz, 1977):

uD

=ε ζµ

0 (1-1)

For all intents and purposes, the plane of shear is so close to the surface of the particle that thezeta potential is generally equated with the surface potential, which is the practice that will befollowed in this report. The validity of this assumption will be discussed later in this report.

1.3 Atomic Force Microscopy (AFM)

Interaction forces between the surfaces of Inconel 600 and either magnetite or hematite particleswere measured using a Nanoscope II Atomic Force Microscope (AFM). Agglomerates ofmagnetite and hematite colloidal particles, suitable for force measurements, were prepared bysintering magnetite and hematite particles at 750°C for 1 h. Magnetite was heated under anatmosphere of ultra-pure argon to prevent oxidation, whereas hematite was heat-treated in air.The diameters of the agglomerates were measured by scanning electron microscopy (SEM) at thecompletion of the experiments. An SEM micrograph of a typical sintered agglomerate ofmagnetite particles is shown in Figure 1-2. The agglomerates were roughly spherical and had

2 Zeta-Meter System 3.0


1-4

diameters in the range 2 to20 µm. The magnetite or hematite agglomerates were glued to the tipof a standard AFM cantilever, using the method of Ducker et al. (1991).

Inconel 600 coupons were polished to a 0.06-µm finish using alumina and were then autoclavedat pH25 9 with morpholine at 250°C for several days to grow an oxide film. The resulting surfacewas relatively smooth, as shown in Figure 1-3. The average surface roughness of the Inconel600 substrate was measured by AFM to be ∼25 nm. The same coupon was used throughout themeasurements. Between each set of measurements, the surface was lightly polished with0.06 µm alumina and then was agitated in an ultrasonic bath for 30 min in methanol.

The force curves were measured at 25 °C in aqueous solution using the manufacturer’s fluid cell.The entire AFM assembly (head, fluid cell, tip) was allowed to come to thermal equilibrium for 1to 2 h before starting the measurements. The addition of fresh solution to the cell required aminimum of 15 min before thermal drifts had stopped. From 6 to 10 force curves were measuredfor each solution. Thus about 100 force curves were acquired for a single set of measurementswith either magnetite or hematite and 1 amine at 2 different concentrations.

Figure 1-2SEM micrograph of a typical magnetite sintered agglomerate glued to an AFM cantilever


1-5

Figure 1-3AFM image of a 10-•m-by-10-•m region of the Inconel 600 coupon used in the forcemeasurements (bottom), and a representative surface roughness profile measured fromthis AFM image (top).

A single agglomerate–tip combination was used to measure force curves at 0, 5 and 50 mMconcentrations of each amine. The force-distance curves were measured in the fluid cell over thepH25 range 6 to 10 in increments of 1 pH unit. After the addition of amine, the solutions wereadjusted to the appropriate pH by additions of KOH and KClO4. For each new solution, 10 mLof solution were passed through the cell before adding the final aliquot. This 10-mL aliquotrepresents several cell volumes and ensured that all traces of the previous solution were flushedfrom the cell. After allowing time for adsorption, a fresh aliquot of solution was added to thecell just before the measurements were taken, to ensure that the solution in contact with thesurface was not depleted in amine.

The Nanoscope II software does not directly provide an output file containing the force-curve data.A discussion of the process used to convert the Nanoscope II output to force-distance curves ispresented in Appendix B of this report. The total force of interaction between the agglomerate andInconel 600 coupon was converted to an interaction energy per unit area by dividing the total forceby 2πr. For 2 charged surfaces that are not in contact with one another, there are 2 maincontributions to the total interaction energy: one arising from the van der Waals interaction and theother from the overlap of the diffuse layers of ionic charge in solution adjacent to a chargedinterface (see, for example, Hiemenz (1977) for a full discussion of both interactions). The van derWaals force is generally attractive with a magnitude that is dependent upon both geometry and the


1-6

Hamaker constant for each of the component materials. The diffuse-layer interaction results in arepulsive force if both surfaces have the same sign of charge. The magnitude of the repulsive forcedepends upon the ionic strength of the solution and the 2 surface potentials.

A complete analysis of the force curves requires knowledge of the Hamaker constants andsurface potentials for each of the materials involved. Under the circumstances, however, severalassumptions could be made that greatly simplified the analysis without significantly changing theresult. The first assumption was that the surfaces had potentials of similar magnitude in theregion of interest, i.e., pH25 > 7. Table 1-1 lists surface potentials deduced by variousmeasurements for the 3 surfaces involved. The surface potential of Inconel 600 was determinedfrom measurements of the streaming potential (P.V. Balakrishnan and C.W. Turner, Chalk RiverLaboratories, unpublished results), whereas surface potentials for magnetite and hematite weredetermined from the electrophoretic mobilities reported in Section 2.2. It is clear from the tablethat all 3 surfaces are negatively charged and have potentials of approximately the samemagnitude for pH25 > 7. Thus the simplifying assumption that all 3 surfaces have similar surfacepotentials is justified, at least in the absence of adsorbed amine.

Table 1-1Surface potentials determined for Inconel 600, magnetite, and hematite from electrokineticdata

pH25 ψ (mV)

Inconel 600 a Magnetite a Hematite b

4.1 +7.5 0b

4.7 -6.6 0b

5.8 - - -25.5

6.0 - +11.0

6.8 - - -27.6

7.0 -19.2 -26.0 -

8.0 - -31.0 -

8.5 -39.5 -28.6 -

9.2 -47.2 -

9.6 - -35.6 -32.7

a from streaming potential measurementsb from electrophoresis measurements (Section 1.2)

The second simplifying assumption made was that the Hamaker constants (see Equation 1-5) forthe 3 surfaces are approximately the same. Since the Inconel 600 coupons had been autoclaved,it is the Hamaker constant of the surface oxide film that is important and not that of the


1-7

underlying metal. A Hamaker constant of 9 x 10-20 J was used for the magnetite–water–Inconelsystem, determined from previous measurements of the interaction force between magnetiteparticles and the surface of a single crystal of magnetite (D.A. Guzonas, Chalk RiverLaboratories, unpublished results). For the hematite–water–Inconel system, a Hamaker constantof 5 x 10-20 J was used because hematite is a less conductive oxide than magnetite.

The third simplifying assumption made for the analysis of the force data was the “linearsuperposition approximation” to calculate the total repulsive potential between the surfaces as afunction of separation. This approximation is good for separations for which κh >>1, where

κ πε

228=

e zn

D kTo

(1-2)

κ is related to the ionic strength of the solution and is a measure of the thickness of the diffuseionic layer of charge in the solution adjacent to the charged interface. (To a good approximation,the diffuse layer of charge decays exponentially with increasing distance from the chargedsurface, with a decay constant equal to κ). For the AFM measurements, κ ranged from 0.14 to0.25 nm-1, which corresponds to diffuse layers that extend 20 to 30 nm into the solution from thecharged surface (Hiemenz, 1977). The diffuse layers are, thus, thin enough compared to the sizeof the agglomerate on the AFM tip that the force of repulsion between the agglomerate and thepolished Inconel 600 coupon can be calculated on the basis of repulsion between 2 flat surfaces.In this case, the principle of linear superposition leads to the following expressions for therepulsive potential:

WnkT

hdl = −64 2

κγ κexp( )

(1-3)

γψψ

=−+

exp( / )

exp( / )

ze kT

ze kT

2 1

2 1 (1-4)

Because interaction potentials in water generally only become significant for separations that aresmall compared to the sample dimensions, the expression for the van der Waals attractivepotential between flat surfaces was used in the analysis. Thus,

WA

hvdw = −12 (1-5)

The total interaction potential between the 2 surface is given by the sum of Equations (1-3) and(1-5):

Wtot = Wdl + Wvdw . (1-6)

Finally, the surface potential, ψ, is determined by fitting Equation (1-6) to the force-distancecurves using the assumptions discussed above.

Values for the surface potentials determined by fitting Equation (1-6) to the force-distance dataare compared to those obtained by electrophoresis for magnetite and hematite in Figures 1-4 and1-5, respectively. The zeta potentials and the surface potentials derived from AFM data aregenerally in good agreement above pH25 7, suggesting that the simple treatment of the surface-


1-8

force data, described above, is sufficient. One exception comes from the analysis of thehematite–Inconel 600 force curve for the morpholine series of measurements, where the derivedsurface potential is zero between pH25 6 and 8. This behaviour was peculiar to the particularhematite particle chosen for this series of measurements.

-40

-30

-20

-10

0

10

20

30

40

4 5 6 7 8 9 10

pH

Sur

face

Pot

entia

l (m

V)

no amine, ammonia expt.

no amine, morpholine expt.

no amine, ethanolamine expt.

zeta potential

Figure 1-4Comparison of surface potentials obtained from AFM force curves and fromelectrophoresis of magnetite particles used in the AFM experiments. All potentials are fora zero concentration of amine.

-40

-30

-20

-10

0

10

20

30

40

4 5 6 7 8 9 10

pH

Sur

face

Pot

entia

l (m

V)

no amine, ethanolamine exptno amine, dimethylamine exptno amine, morpholine expt.zeta potential

Figure 1-5Comparison of surface potentials obtained from AFM force curves and fromelectrophoresis of hematite particles used in the AFM experiments. All potentials are for azero concentration of amine.


1-9

From the surface potentials, the surface charge density can also be calculated:

σ ε ψ=

820

0D kTe

kTsinh (1-7)

1.4 Surface Tension

A relatively simple method was devised for measuring the interfacial tension of water at the Inconel600–water and magnetite–water interfaces as a function of temperature. The same high-temperaturecell that was used for the laser Raman measurements was also used to determine the interfacialtension by measuring the wetting angle at selected temperatures. A coupon of Inconel 600—identical to the one used for the AFM measurements—and a single crystal of magnetite were placedinto the cell, which was then filled with a solution of morpholine at pH 9.5. The 2 flat surfaces of theInconel 600 coupon and the magnetite single crystal were arranged parallel to one another so that thewetting angle of the morpholine solution could be recorded by photography at a magnification of10X through the quartz window of the cell. Photographs were taken at selected temperatures from25°C to 140°C, and the wetting angle on each surface was measured from the photographs. Aschematic showing a view through the quartz window of the filled cell and the menisci at the water–Inconel 600 and water–magnetite interfaces is shown in Figure 1-6.

Figure 1-6The assembled cell, showing the orientation of the Inconel 600 and magnetite couponsand the location of the liquid meniscus

Figure 1-7 shows the configuration of the windows and spacers used to contain the liquid and themagnetite and Inconel 600 coupons for the measurements. A rectangular Inconel 600 couponmeasuring 10 mm x 20 mm was cut and polished on one side to a mirror finish using polishinggrits down to a final grit size of 1 µm. A thin, near-rectangular magnetite coupon measuring10 mm x 15 mm was cut from a sample of magnetite of geologic origin (Bentley Lake, Ontario),and polished to a 1-µm finish. The magnetite and Inconel 600 coupons were placed between thequartz windows of the cell (within the 10-mm Teflon spacer) and held apart by a Teflon plug.About 2 mL of the solution of interest was then added to the cell, and the loaded cell was placedin the stainless steel holder and was bolted.


1-10

Figure 1-7Cell configuration used for the contact angle measurements

The contact angle (θ), defined as the angle measured in solution between the solid-liquid andliquid-vapour interfaces, is determined by the surface tensions of 3 interfaces: solid-liquid, solid-vapour, and liquid-vapour. Their relationship is given by the equation of Young and Dupre(Vold and Vold, 1983):

cosθγ γ

γ=

−SV SL

LV

(1-8)

If the contact angle at the liquid-solid interface (measured within the liquid) is less than 90°, thenthe liquid will spontaneously spread over the surface, whereas if the contact angle is greater than90°, the liquid is said to be non-wetting. Equation (1-8) states that the liquid will spreadprovided that γSV > γSL, whereas it will be non-wetting if γSV < γSL. Where the liquid is water, the2 surfaces would be referred to as hydrophilic and hydrophobic, respectively. Equation (1-8) canbe used to compare the relative hydrophobicity of 2 different surfaces for measurements with asingle liquid, or it can be used to measure trends in the surface tension of a series of liquids orsolutions for measurements made on a single surface.

1.5 Loop Deposition Tests

The experimental test procedures are discussed in detail in Turner et al., (1997), and will not berepeated here. A schematic of the loop used for the deposition tests is shown in Figure 1-8, andthe nominal conditions used for the deposition tests are listed in Table 1-2. Theoreticalconcentrations of amine required to achieve pHT = 6.2 at 270°C are listed in Table 1-3.

Table 1-2Nominal loop conditions for the deposition tests

Pressure Heat Flux Mass Flux Tsaturation QualityMPa kW/m2 kg/m2s °C -

5.6 230 300 270 -0.28 - +0.55


1-11

Figure 1-8Schemat ic of the loop used f or measurements of part icle deposition under si ngle-phaseforced-convect ion and fl ow-boiling conditions

Table 1-3Concentrations of ami ne required to ac hieve pHT = 6.2 at 270°C

pH Control Reagent (asanhydride)

RelativeMolecularMass, - pH270°C pH25°C

Concentrationof Free Amine,

mg/kg

ConcentrationFree Amine,

mole/kg

Morpholine 87.12 6.20 9.26 10.7 1.2 x 10-4

Ethanolamine 61.08 6.20 9.53 4.3 7.5 x 10-5

Ammonia 17.0 6.20 9.64 2.6 1.5 x 10-4

Dimethylamine 45.08 6.20 9.14 0.63 1.4 x 10-5

3-Methoxypropylamine 89.14 6.20 9.70 7.3 8.2 x 10-5

4-Aminobutanol 89.0 6.20 9.44 2.9 3.3 x 10-5

Pyrrolidine 71.12 6.20 9.13 0.96 1.4 x 10-5

KOH 56.1 6.20 8.93 0.47 8.4 x 10-6


1-12

A typical test consisted of bringing the loop to stable operating conditions and holding it therefor a period of approximately 48 h while the suspension of corrosion products was beingequilibrated with amine at the required pH. Corrosion products used in the deposition tests werefrom the same source as those used for other parts of this investigation, i.e., measurements ofadsorption isotherms, electrophoresis, and AFM. The suspension of corrosion products wastraced using 59Fe, to facilitate on-line measurement of the deposition rate. The deposition phaseof the test was initiated by starting the injection of the suspension of corrosion product into theloop. Particles were injected upstream of the test section and were filtered downstream, so theparticles in suspension made just a single pass through the test section.

A schematic of the test section with 3 heated and 4 unheated regions is shown in Figure 1-9. Thedirection of fluid flow is now upwards in all regions where deposition rates are measured. Thismodification is an improvement over the test section used for the previous investigation wherethe flow direction was downward in the unheated regions. The steam qualities in the 4 unheatedsections are approximately - 0.28 (single-phase forced convection), 0.03 (2-phase forcedconvection), 0.23 (2-phase forced convection), and 0.50 (annular flow).

Figure 1-9Schematic of the test section showing 3 heated and 4 unheated regions


1-13

Additional equipment was installed on the loop to improve the measurement of electrical powerdissipated in each region of the test section. This upgrade permits a more accurate evaluation of localheat flux, steam quality, and heat-transfer coefficient. The temperature at the inlet to the test sectionis now regulated using a by-pass valve connected to a temperature controller on the loopinterchanger. This modification has eliminated drift in the inlet temperature and has improved thestability of the tests. An 18-L stainless steel tank was manufactured to hold the concentrated slurriesof magnetite and hematite that are injected into the loop during each test. The replacement of theglass carboy with a stainless steel tank eliminates the concern over silica contamination of thecorrosion products. The data acquisition system was expanded from 30 to 80 channels. The heat-transfer coefficients can now be evaluated at several locations during each test. A commercial Hall-effect probe was acquired, and its sensor was modified to make it suitable for measuring themagnetic field inside the test section. The results of these measurements, which are included inAppendix C of this report, show that the intensity of the magnetic field in the fluid inside the testsection is too small to influence the particle deposition rate. The electrical conductivity of the loopwater is now monitored continuously during each test. Although not a specific test parameter, thisapproach provides an additional check on the chemistry control from one test to another.

These upgrades to the main loop and test section were completed before starting the current setof loop tests, and have resulted in an improvement in the reliability and quality of the loop testdata.

2-1

2 RESULTS

2.1 Adsorption Isotherms

Adsorption isotherms for the 4 amines examined are shown in Figures 2-1 and 2-2 for magnetiteand hematite, respectively. The isotherms for adsorption of amine onto magnetite show a steeprise in the amount adsorbed over the concentration range 1 to 100 mM, followed by a moregradual increase between amine concentrations of 100 and 1000 mM. Adsorption per gramoxide was converted to adsorption per unit area using the specific surface area of the oxides (seeSection 1.1). Adsorption onto magnetite at 25°C decreases in the following order:ammonia > dimethylamine > ethanolamine ≈ morpholine.

0

2

4

6

8

10

12

0 200 400 600 800 1000

[D imethylam ine] (mM)

Dim

ethy

lam

ine

Ads

orbe

d

(mm

oles

/g)

0

10

20

30

40

0 200 400 600 800 1000

[Am monia ] (mM )

Am

mon

ia A

dsor

bed

(mm

oles

/g)

0

2

4

6

8

10

12

0 200 400 600 800 1000

[Ethano lam ine ] (mM)

Eth

anol

amin

e A

dsor

bed

(mm

oles

/g)

0

2

4

6

8

10

12

0 500 1000

[M orpholine] (mM)

Mor

phol

ine

Ads

orbe

d

(mm

oles

/g)

Figure 2-1Adsorption isotherms for dimethylamine, ammonia, ethanolamine, and morpholine ontomagnetite at 25 °C.

Results

2-2

The isotherms for adsorption of amine onto hematite, shown in Figure 2-2, are qualitativelysimilar to those measured for magnetite, but the adsorbed amounts are higher by a factor of ∼2for DMA, morpholine and ethanolamine, and higher by a factor of ∼4 for NH3 . As in the case ofmagnetite, the amount adsorbed at all amine concentrations decreases in the orderammonia > dimethylamine > ethanolamine ≈ morpholine.

The amounts of amine adsorbed onto magnetite and hematite at concentrations of 5 and 50 mM(deduced by linear interpolation of the isotherms in Figures 2-1 and 2-2) are listed in Table 2-1.The number of molecules adsorbed per unit area (BET specific surface area) at both amineconcentrations is higher than expected for monolayer adsorption, suggesting either multilayeradsorption or an underestimation of the specific surfaces areas of the oxides. To check on thereproducibility of the data, the amount of amine adsorbed at an amine concentration of 1000 mMwas re-measured for selected amine–oxide combinations. Higher oxide loadings were used forthese measurements in case the apparent multilayer adsorption was an artifact of the smallamount of oxide used for the previous measurements. In addition, measurements were madeafter 1-h and 24-h equilibration times. For each case, the amount of amine adsorbed was in goodagreement with the numbers listed in Table 2-1, thus showing that the measurements arereproducible, are not dependent upon oxide loading, and that the oxide surface has equilibratedwith the amine within 1 h.

0

10

20

30

40

50

60

0 200 400 600 800 1000

[D imethylam ine ] (mM)

Dim

ethy

lam

ine

Ads

orbe

d

(mm

oles

/g)

0

100

200

300

400

0 200 400 600 800 1000

[A mmonia ] (mM)

Am

mon

ia A

dsor

bed

(mm

oles

/g)

0

1 0

2 0

3 0

4 0

5 0

0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0

[E th a n o la m in e ] (m M )

Eth

anol

amin

e A

dsor

bed

(mm

oles

/g)

0

10

20

30

40

50

0 200 400 600 800 1000

[M orpho line ] (mM )

Mor

phol

ine

Ads

orbe

d

(mm

oles

/g)

Figure 2-2Adsorption isotherms for dimethylamine, ammonia, ethanolamine, and morpholine ontohematite at 25 °C.

Results

2-3

Table 2-1Amine adsorbed at concentrations of 5 and 50 mM

Adsorption onto Magnetitemolecules/nm 2

Adsorption onto Hematitemolecules/nm 2

Amine 5 mM 50 mM 5 mM 50 mM

Ethanolamine 70 200 100 820

Morpholine 50 310 200 580

Dimethylamine 120 520 250 2000

ammonia 200 2800 500 2100

The temperature dependence of DMA adsorption on magnetite is shown in Figure 2-3, expressedas the percentage adsorbed at temperature referenced to the amount adsorbed at 25°C. Theadsorbed amount is observed to decrease with increasing temperature, falling by about 13%between 25°C and 125°C. Considerable effort was expended trying to repeat thesemeasurements with other amine–oxide combinations but was unsuccessful because the quartzwindow in the cell invariably failed above 100°C. It was eventually determined throughdiscussions with the manufacturer that the high-temperature cell has a design flaw that causes thecell window to crack near the filling ports at temperatures not far in excess of 100°C. Recenttests with windows without filling ports were encouraging. Thus a combination of thickerwindows without filling ports and the substitution of stainless steel gaskets for the Teflon onesmay enable Raman spectra to be collected over the full temperature range.

80

85

90

95

100

0 50 100 150

Temperature ( oC)

DM

A A

dsor

bed

(%)

Figure 2-3Temperature dependence of the adsorption of dimethylamine onto the surface ofmagnetite

Results

2-4

2.2 Electrophoretic Mobility

Figure 2-4 shows the effect of 5 mM solutions of amine on the zeta potential of magnetite. In theabsence of amine, the zeta potential crosses zero near pH25 5.8, corresponding to an IEP of 5.8.Note that the zeta potential changes rapidly with pH in the vicinity of the IEP. The IEP in thepresence of 5 mM amine ranged from 5.8 to 6.3 for three of the amines, which is within theexpected range of variability of IEP from one sameple to another. Hence this variation cannot betaken as strong evidence for a shift in IEP, caused by the presence of amine. Ammonia appearedto shift the IEP to a lower value, but this was not reproducible and is likely the result ofcontamination of the sample.

Figure 2-5 shows the effect of 50 mM solutions of amine on the zeta potential and IEP ofmagnetite. For this set of measurements, the IEP of the reference sample is at pH25 6.7, which isin good agreement with the IEP of 6.5 for magnetite reported by Tewari and McLean (1972). Ineach case, the IEP of magnetite was higher in the presence of the 50 mM solution of amine, withthe shift in IEP ranging from +0.5 to +1.7 pH units. The shift in IEP to higher pH in thepresence of the 50 mM solutions of amine is strong evidence for the adsorption of a positivelycharged species onto the surface of the magnetite particles.

-50

-40

-30

-20

-10

0

10

20

30

40

50

0 1 2 3 4 5 6 7 8 9 10 11 12

Zet

a P

oten

tial (

mv)

Magnetite reference

morpholine + magnetite

dimethylamine + magneitite

ethanolamine + magnetite

ammonia + magnetite

pH

Figure 2-4Effect of 5 mM solutions of amine onthe surface potential of magnetite

-40

-30

-20

-10

0

10

20

30

40

4 5 6 7 8 9 10

pH

Sur

face

Pot

entia

l (m

V)

no amine, ethanolamine exptno amine, dimethylamine exptno amine, morpholine expt.zeta potential

Figure 2-5Effect of 50 mM solutions of amine on thesurface potential of magnetite

The effect of the addition of either morpholine or ammonia on the surface potential measured forhematite by electrophoresis is shown in Figure 2-6. In the absence of amine, the surfacepotential for hematite remains negative down to pH 4, with an estimated IEP of pH 3. This valueis much lower than the IEP reported for hematite synthesized by hydrolysis of a solution ofFe(III) (Fokkink et al., 1989; Matijevic and Schneiner (1978)) but is consistent with the IEPreported for reagent-grade hematite purchased from another commercial supplier (Jayaweera etal., 1992). The hematite used in the present investigation was washed thoroughly with acid andbase to remove adsorbed impurities from the surface. Hence the probability that the deviation inIEP from that reported in the literature cited above is the result of adsorbed impurities is low.The addition of 5 mM amine had a much greater effect on the surface potential of hematite thanon magnetite, shifting the IEP from an estimated pH 3 to approximately pH 6. Raising the amineconcentration to 50 mM increased the IEP a further + 0.5 pH units.

Results

2-5

-40

-30

-20

-10

0

10

20

30

40

0 1 2 3 4 5 6 7 8 9 10 11

Zet

a P

oten

tial (

mv)

No Amine

No Amine

50 mM ammonia

5 mM ammonia

50 mM morpholine

5 mM morpholine

pH

Figure 2-6The effect of additions of morpholine and ammonia on the surface potential of hematite,determined from the electrophoretic mobility

2.3 Atomic Force Microscopy

Several force curves measured at pH25 10 between a hematite particle and the surface of Inconel600 in a single experiment are shown in Figure 2-7, to illustrate the reproducibility of the data.For these measurements, a positive force signifies repulsion between the surfaces of Inconel 600and hematite, whereas a negative force signifies attraction. Figure 2-7 shows that the forcebetween the surfaces of hematite and Inconel 600 at pH25 10 is repulsive at all separations. Sincethe surface of Inconel 600 is negatively charged for pH25 >> 4, this result shows that the surfaceof hematite is negatively charged at pH25 10. Both the advancing (particle approaching surface)and the retracting (particle withdrawing from the surface) force curves are shown. The spread inthe force data is generally ±0.5 nN, and the location of the hard wall contact was reproducible towithin about 1 nm.

A check on reproducibility between experiments can be made by comparing the results ofmeasurements made in the absence of amine using different particle-tip combinations. When theforce data are scaled by F/2πr, the force curves should be the same under the same solutionconditions. This behaviour is indeed observed in Figure 2-8, where the reference data (i.e., zeroconcentration of amine) are shown for the morpholine, ethanolamine, and ammonia series ofmeasurements for the system magnetite–water–Inconel.

Results

2-6

-2

-1

0

1

2

3

4

5

6

7

8

-5 0 5 10 15 20 25 30 35 40

Separation (nm)

For

ce (

nN)

Figure 2-7Successive force curves measured using the same particle–tip combination under thesame s olution conditions. Filled circles are advancing measurements, open circles areretracting

0

1

2

3

4

5

6

0 10 20 30 40 50

Separation (nm)

For

ce (

nN)

Figure 2-8Force curves measured between a magnetite particle and an Inconel 600 surface using 3different particle–tip combinations. (Dimethylamine series: - diamonds; Morpholineseries: - open squares; Ethanolamine series; - filled triangles).

Several different behaviours of the advancing and retracting force curves were observed. Athigh pH, the force curves were often similar to those shown in Figure 2-8, where the advancingand retracting force curves were identical and no jump into an adhesive minimum was observed.In these force curves, a repulsive force was observed starting at separations of about 30 nm. Thisforce increased exponentially as the separation decreased. At small separations (<1 to 2 nm) theforce became more steeply repulsive. The steep repulsive part of the force curve seen at smallseparations is attributed to the interaction of surface asperities at small separations.

Results

2-7

Figure 2-9 shows 2 other types of behaviour of the advancing and retracting force curves. InFigure 2-9a (pH25 9, hematite particle, no amine added) the total force is repulsive uponadvancing to contact, and no jump into contact is observed. In spite of the absence of a jumpinto contact, upon separation of the surfaces the total force goes through an attractive minimum.

-40

-20

0

20

40

-50 50 150 250 350 450

Separation (nm)

For

ce (

nN)

-10

-5

0

5

10

15

-5 0 5 10 15 20 25 30 35

Separation (nm)

For

ce (

nN)

a

b

Figure 2-9Some representative force-distance curves, showing the behaviour of the advancing (f illedsymbols) and ret racting (open symbols) parts of the force curve: (a) pH25 9, hematiteparticle, no amine; and (b) pH25 8, hematite particle, no amine.

Jumps into contact were often observed when the electrostatic barrier was low, as illustrated inFigure 2-9b. The data suggest that when the electrostatic force is strongly repulsive, the jumpinto the primary minimum can be masked by contact of asperities on the 2 surfaces. In thesecases, a jump out of contact was sometimes observed and in other cases not, depending on theparticle–tip combination used. An abrupt increase in repulsion resulting from contact of surfaceasperities generally occurred at separations <2 nm. Thus force data from this region wasexcluded from the fit of Equation (1-6) to the force data.

Results

2-8

The IEP for magnetite and hematite can be determined from measurements of the force-distancecurves as a function of pH (in the absence of added amine). Since the surface potential ofInconel 600 is negative over the pH range of interest, the IEP of magnetite or of hematite or ofboth will be the pH at which the total force switches from repulsion (i.e., positive) to attraction(i.e., negative). Figures 2-10 and 2-11 show the best fits of Equation (1-6) to the force-curvedata for magnetite and hematite, respectively.

Figure 2-10 shows that the total interaction force is repulsive and increases in magnitude withdecreasing separation before going through a maximum for separations of ~4 to 6 nm. Thisresult shows that surface repulsion dominates for distances greater than 4 to 6 nm, and van derWaals attraction only becomes important at smaller separations. As the distance between thesurfaces is reduced from about 5 nm, the total force steadily decreases and eventually becomesattractive at a separation of ~2 to 4 nm. The magnitude of the repulsive force between magnetiteand Inconel 600 and the height of the energy barrier decreases steadily as the pH is reduced from10 towards 7. The total force, although very small, is still repulsive at pH25 7, indicating that theIEP for this magnetite sample is at a pH just below 7. This result is in good agreement with theelectrophoresis results for magnetite shown in Figures 2-4 and 2-5. Figure 2-11 shows that forhematite the repulsive force drops steadily with decreasing pH but is still strongly repulsive atpH 6. Thus the IEP of this sample of hematite appears to be at a pH well below 6, which is inagreement with the electrophoresis results shown in Figure 2-6.

-0.05

0

0.05

0.1

0.15

0.2

0 10 20 30

Separation (nm)

F/2

πR (

mN

/m)

10

9

8

6

7

Figure 2-10Best fit of Equation (1-6) to the force-distance data for magnetite approaching the surfaceof Inconel 600

Results

2-9

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0 5 10 15 20 25

Separation (nm)

F/2

πR

(m

N/m

)

10

6

7

8

9

Figure 2-11Best fit of Equation (1-6) to the force-distance data for hematite approaching the surface ofInconel 600

Figure 2-12 shows the effect of morpholine at concentrations of 5 and 50 mM on the force-distance curves measured between a magnetite particle and an Inconel 600 surface at theindicated pH. The force curves in the absence of added amine are also shown for comparison.In this figure, only the best fits of Equation (1-6) to the data are shown for clarity. Similar plotsfor ammonia, dimethylamine and ethanolamine are shown in Appendix B of this report.

In all cases, the addition of amine reduced the magnitude of the repulsive force between thesurfaces of magnetite and Inconel 600. The presence of a 5 mM solution of morpholine hadabout the same effect on the magnitude of the repulsive force across the pH25 range 6 to 10. The50 mM solution of morpholine had about the same effect on the repulsive force as did the 5 mMone for pH25 6 to 8. For pH25 9 and 10, however, the effect was much greater with the addition ofthe 50 mM solution. For pH25 ≥ 7, despite being reduced in magnitude with the addition ofmorpholine, the force between magnetite and Inconel 600 remains repulsive at large separations.At pH25 6, however, magnetite is close enough to its IEP that the total surface force is essentiallyzero for all separations greater than 10 nm in the presence of a 5 mM solution of morpholine.With the addition of a 50 mM solution of morpholine, the repulsive force has essentiallydisappeared, and the interaction force is attractive at all distances.

Similar results, with some minor exceptions, were measured for the addition of 5 and 50 mMsolutions of ammonia, ethanolamine, and ammonia, as shown in Figures B-1, B-2, and B-3. Likemorpholine, ethanolamine was much more effective at reducing the surface potential at aconcentration of 50 mM than at 5 mM.

Results

2-10

-0 .0 4

0

0 .0 4

0 .0 8

0 .1 2

0 2 0 4 0

S e p a ra ti o n (nm )

p H 9

-0 .0 4

0

0 .0 4

0 .0 8

0 .1 2

0 2 0 4 0


p H 1 0

-0 .0 4

0

0 .0 4

0 .0 8

0 .1 2

0 2 0 4 0


p H 8

-0 .0 4

0

0 .0 4

0 .0 8

0 .1 2

0 2 0 4 0


p H 7

-0 .0 4

0

0 .0 4

0 .0 8

0 .1 2

0 2 0 4 0


p H 6

Figure 2-12Plots of the best fit of the force curve versus separation for the system magnetite /Inconel600 as a function of morpholine concentration, at pH25 6 to 10. Units of the abscissa aremN/m. Upper, middle, and lower lines are for 0, 5, and 50 mM amine.

Figure 2-13 shows the effect of additions of morpholine to the total force acting between thesurfaces of hematite and Inconel 600 at selected pH25 between 6 and 10. The force curvesmeasured in the absence of amine are also shown for comparison. In this figure, only the bestfits of Equation (1-5) to the data are shown for clarity. Similar plots for additions of ammonia,dimethylamine, and ethanolamine are shown in Appendix B of this report.

Results

2-11

-0.15

0

0.15

0.3

0 20 40

Separation (nm)

0 mM

50 mM

5 mM

pH 9

-0.15

0

0.15

0.3

0 10 20 30 40

Separation (nm)

0 mM

5 mM

50 mM

pH 10

-0.15

0

0.15

0.3

0 20 40

Separation (nm)

pH 6

-0.15

0

0.15

0.3

0 10 20 30 40

Separation (nm)

pH 7

-0.15

0

0.15

0.3

0 20 40

Separation (nm)

0, 50 m M

5 mM

pH 8

Figure 2-13Plots of the best fit of the force curve versus separation for the system hematite–Inconel600 as a function of morpholine concentration at pH25 6 to 10. Units of the abscissa aremN/m. Upper, middle, and lower lines are for 0, 5, and 50 mM amine.

The sintered agglomerate of hematite used to collect the data for the morpholine series had anIEP near pH25 8. This result is shown by the data in Figure 2-13, where the force betweenhematite and Inconel 600 at pH25 8 is attractive at all separations. This result is in contrast to theIEP determined from the electrophoresis measurements (see Figure 2-6), and is in contrast to theIEP determined for hematite from other AFM measurements; e.g., see Figure 2-11. For pH25 > 8,the force between hematite and Inconel 600 in Figure 2-13 is repulsive, indicating that thehematite is negatively charged. Additions of morpholine at 5 and 50 mM reduce the magnitudeof the repulsive force between the 2 surfaces. At pH25 8, where the force in the absence of amineis attractive, the addition of 5 mM morpholine results in the formation of a repulsive barrier,whereas at 50 mM morpholine the force again is attractive at all separations. This observationsuggests that the 2 surfaces do not behave identically and that close to the IEP small changes inamine adsorption can produce changes in both magnitude and sign of the total force. At pH25 6and 7, the total force is attractive at all amine concentrations, indicating that the surfaces were

Results

2-12

either uncharged or of opposite sign of charge. It was noted, however, that at pH25 6 and 7, theforce curves were not well described by the van der Waals attraction alone and that a better fitcould be achieved, by assuming that the Inconel 600 and hematite surfaces had opposite andunequal surface charges.

The hematite particle used in the morpholine experiments is unique in that the IEP is close to theliterature value of 8.5 (Fokkink et al., 1992). For the AFM measurements on the hematite–Inconel 600 system with the other amines, however, the IEP in the absence of amine is below 6and the force curves measured in the presence of amine are much like those measured formagnetite. For example, the addition of ethanolamine at a concentration of 5 mM has an almostnegligible effect on either the total force or the potential barrier over the range pH25 7 to 10 forthe hematite–Inconel system, whereas the addition of ethanolamine at a concentration of 50 mMlowers the repulsive barrier substantially, as shown in Figure B-6. A small energy barrier is stillpresent at pH25 6, however, even in the presence of 50 mM ethanolamine, showing that thesurface of hematite is still well above its IEP. Similar behaviour is observed for the addition ofdimethylamine, shown in Figure B-7, except that the energy barrier has completely disappearedat pH25 6 with the addition of a solution of dimethylamine at a concentration of 50 mM.

Potentials derived by fitting Equation (1-6) to the force-distance curves for magnetite andhematite are listed in Tables 2-2 and 2-3, respectively, for amine concentrations of 0, 5, and50 mM. The sign of the surface potential was inferred from the trends in the total force and fromcomparison with the electrophoresis data. The potentials become increasingly negative as the pHis increased and, with the exception of the data for morpholine, show quite clearly that the IEPfor this sample of magnetite is between pH25 6 and 7. Addition of amine for a given pH tends tomake the surface potentials less negative, and this observation is consistent with the reduction inthe total surface repulsive force measured by AFM.

Table 2-2Surface potential of magnetite in mV, determined by fitting Equation (1-6) to the AFMforce-distance data

pH ammonia dimethylamine ethanolamine morpholine

0 5 50 0 5 50 0 5 50 0 5 50

6 0 10.6 15.0 14.2 14.2 0 22.8 22.8 19.6 -15.4 -13.0 0

7 -15.0 -15.0 -15.0 -23.3 -17.9 0 -19.6 -20.7 -14.6 -17.3 -17.3 -15.4

8 -20.0 -34.6 -16.8 -25.6 -17.9 -12.6 -22.8 -24.6 -14.6 -21.1 -19.1 -18.5

9 -30.7 -30.7 -16.8 -29.8 -25.6 -20.8 -24.6 -24.6 -14.6 -22.9 -26.4 -18.5

10 -38.2 -34.6 -21.4 -33.5 -25.6 -20.8 -30.5 -30.5 -19.6 -28.9 -28.1 -18.5

With the exception of the results with morpholine, the surface potentials for hematite were allnegative over the pH range measured. As noted above, this observation is consistent with theelectrophoresis measurements and some literature reports of the IEP for hematite. The hematiteagglomerate used for the measurements with morpholine appeared to have an IEP closer to theexpected value of 8.

Results

2-13

Table 2-3Surface potential of hematite in mV determined by fitting Equation (1-6) to the AFM force-distance data


0 5 50 0 5 50 0 5 50 0 5 50

6 -13.0 22.7 9.2 -20.8 -a -10.3 -21.1 -28.3 -21.9 0 0 0

7 -24.6 -24.7 -24.7 -17.9 -a -14.6 -27.7 -27.0 -18.9 0 0 0

8 -24.6 -24.1 -24.2 -22.1 -22.5 -12.6 -29.1 -28.3 -18.9 0 -27.0 0

9 -31.2 -31.2 -29.7 -27.9 -24.5 -16.1 -33.1 -33.1 -24.6 -32.3 -31.4 -18.9

10 -34.1 -32.7 -32.7 -32.6 -32.6 -22.1 -36.3 -36.3 -28.6 -38.1 -27.0 -24.8

a - the force data for these pH values was unusable, possibly because of an air bubble in the cell

Surface charge densities for magnetite and hematite calculated from the surface potentials usingEquation (1-7) are listed in Tables 2-4 and 2-5, respectively, for amine concentrations of 0, 5,and 50 mM. As expected, the surface charge densities follow the same trends with pH andamine concentration as do the surface potentials.

Table 2-4Surface charge density (mC/m 2) calculated for magnetite from Equation (1-7).


0 5 50 0 5 50 0 5 50 0 5 50

6 0 2.43 3.46 3.27 3.27 0 5.36 5.36 4.57 3.56 2.99 0

7 -3.46 -3.46 -3.46 -5.49 -4.16 0 -4.57 -4.84 -4.01 -4.01 -4.01 -3.56

8 -4.67 -8.48 -3.89 -6.07 -4.16 -2.90 -5.36 -5.82 -3.37 -4.94 -4.45 -4.30

9 -7.41 -7.41 -3.89 -7.17 -6.07 -4.87 -5.82 -5.82 -3.37 -5.39 -6.28 -4.30

10 -9.52 -8.48 -5.01 -8.18 -6.07 -4.87 -7.36 -7.36 -4.57 -6.93 -6.72 -4.30

Results

2-14

Table 2-5Surface charge density (mC/m 2), calculated for hematite from Equation (1-7).


0 5 50 0 5 50 0 5 50 0 5 50

6 -3.0 5.4 2.1 -4.4 -a -2.4 -4.9 -6.8 -5.1 0 0 0

7 -5.8 -5.8 -5.8 -4.2 -a -3.4 -6.6 -6.4 -4.4 0 0 0

8 -5.8 -5.6 -5.7 -5.2 -5.3 -2.9 -7.0 -6.8 -4.4 0 -6.4 0

9 -6.3 -7.6 -7.1 -6.7 -5.8 -3.7 -8.1 -8.1 -5.8 -7.9 -7.6 -4.4

10 -8.3 -8.3 -8.0 -7.9 -7.9 -5.2 -9.0 -9.0 -6.9 -9.5 -6.4 -5.9

a - the force data for these pH values was unusable, possibly because of an air bubble in the cell

2.4 Surface Tension

Figure 2-14 shows a photograph of the cell at 25 °C. The magnetite surface is on the right andappears dark black, whereas the Inconel 600 surface is on the left and appears gray. Thephotograph has been digitally filtered to enhance the meniscus. It is clear from the picture thatthe contact angle on Inconel 600 is larger than that on magnetite.

Figure 2-14Photograph of the interior of the cell used to measure the contact a ngles ( θ) of amorpholine solution on Inconel 600 and magnetite, taken at 25 °C.

In the first trials with the apparatus, condensation on the windows resulted in poor images athigher temperatures. Therefore, the contact angles were measured by placing a magnifying lensin front of the cell and tracing the meniscus onto a piece of transparent plastic. The contactangles were then measured directly from the traced images.

The results of these measurements are shown in Figure 2-15. From Figure 2-15, it appears thatthe contact angle at the magnetite–solution interface increases linearly over the temperaturerange examined. In contrast, the contact angle at the Inconel 600–solution interface increases as

Results

2-15

the temperature is raised from 25°C to 50 °C, and then decreases linearly with increasingtemperature above 50°C. The 2 surfaces have the same contact angle at about a temperature of110°C.

The contact angles were less than 90° for both the water–Inconel 600 and water–magnetiteinterfaces over the temperature range examined, meaning that both Inconel 600 and magnetiteare hydrophilic. Magnetite appears to be less hydrophilic than Inconel 600 (magnetite has asmaller contact angle) and is becoming more hydrophobic with increasing temperature. If thetrend in Figure 2-15 continues, magnetite is predicted to be hydrophobic at steam generatoroperating temperatures. In contrast, the surface of Inconel 600 is becoming more hydrophilicwith increasing temperature above 50°C.

0

10

20

30

40

50

60

70

80

90

0 50 100 150

Temperature oC

Con

tact

Ang

le (

degr

ees)

magnetite

I-600

Figure 2-15The effect of temperature on the wetting angle of the Inconel-600–solution and themagnetite–solution interfaces

2.5 Loop Deposition Tests

Table 2-6 shows the matrix of loop deposition tests that were performed for this investigation.Some tests were performed to extend the database for ammonia, morpholine, ethanolamine,dimethylamine, and potassium hydroxide tests to 4 runs each. Other tests were done to examinethe effect of 3 additional amines (3-methoxypropylamine, pyrrolidine, and 4-aminobutanol) onthe particle deposition behaviour. Two extended deposition tests were done in which thecolloidal suspension of particles was injected for a period of 24 h instead of the usual 8 h. Thisanalysis was done to try to cover a greater fraction of the test section with particles and get someinsights into the longer-term deposition behaviour. Details of the operating and chemistryconditions for each of the 24 tests performed are listed in Table C-1of Appendix C of this report.

Results

2-16

Table 2-6Listing of loop deposition tests performed in this investigation

Tests with Magnetite Number of Tests

Morpholine 3

Ammonia 1

dimethylamine 2

potassium hydroxide 2

3-Methoxypropylamine 2

Pyrrolidine 2

4-Aminobutanol 2

Tests with Hematite Number of Tests

Ethanolamine 2

Dimethylamine 2

Potassium hydroxide 4

3-Methoxypropylamine 2

Figures 2-16 and 2-17 show representative plots of temperature and deposition rate as a functionof mixture quality for magnetite deposition using pyrrolidine and 3-methoxypropylamine,respectively for pH control. Additional figures showing similar plots for the other loop testsidentified in Table 2-6 are found in Appendix C of this report.

AECL Chalk River Laboratories, H3 Loop

0.10 1.50 4.102.10 2.70

0.0E+00

5.0E-04

1.0E-03

1.5E-03

2.0E-03

2.5E-03

3.0E-03

3.5E-03

-0.4 -0.2 0 0.2 0.4 0.6 0.8Mixture Quality [-]

Nor

mal

ized

Dep

ositi

on R

ate

K· [k

g/m

²·s]

150

200

250

300

Tem

pera

ture

[°C

]

Bulk Temp (Calc)

Inner Wall Temperature

K·rho, Diabatic Test Section

K·rho, Adiabatic Test Section

D099--Fe3O4 + Pyrrolidine

Axial Position on the Heated Sections [m]

Figure 2-16Normalized deposition rate as a function of steam quality. �� indicates locations along theheated (diabatic) test section. �� indicates locations on the unheated (adiabatic) testsection.

Results

2-17


0.10 1.50 4.102.10 2.70

0.0E+00

1.0E-04

2.0E-04

3.0E-04

4.0E-04

5.0E-04

6.0E-04

-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6

Mixture Quality [-]

Nor

mal

ized

Dep

ositi

on R

ate

K· [k

g/m

²·s]

150

200

250

300

Tem

pera

ture

[°C

]

Bulk Temp (Calc)




D102--Fe3O4 + MPA


Figure 2-17Normalized deposition rate vs. mixture quality. �� indicates locations along the heated(diabatic) test section. �� indicates locations on the unheated (adiabatic) test section.

The figures show deposition data for several different flow and heat-transfer regimes, as well asfor deposition on both heated (diabatic) and unheated (adiabatic) portions of the test section. Formixture qualities less than -0.22, the flow regime is single-phase forced convection. Depositiondata for this flow regime come from both unheated and heated regions of the test section. Theonset of sub-cooled nucleate boiling takes place at a mixture quality of approximately -0.22. Atthis point, the temperature at the wall–fluid interface is high enough to initiate bubble nucleationand growth at the wall, but the bulk temperature is still below the boiling point so that thebubbles collapse when they encounter sub-cooled fluid. This heat-transfer mode prevails, up to amixture quality of approximately zero. At this point, the fluid has reached saturationtemperature; the steam bubbles do not collapse when they leave the surface, and net steamquality is produced. This heat-transfer mode is called saturated nucleate boiling and prevails upto a steam quality of at least 0.20 (see Figure 2-21), where there is a transition to annular flowconditions. Deposition data in the saturated nucleate boiling regime come from both heated andunheated regions of the test section. The heat-transfer modes in the annular flow regime arecomplex, with nucleate boiling becoming less important at the expense of 2-phase forcedconvection, plus evaporation as the steam quality increases. Deposition data in the annular flowregime come from both heated and unheated portions of the test section.

Normalized deposition rates (measured deposition rates normalized to a magnetite concentrationof 10-6 kg/kg) for all deposition tests with magnetite are summarized in Table 2-7. Althoughfeatures may be found that are specific to just one test or another, the following generalobservations can be made based on the results in Table 2-7 and from Figures 2-17 and 2-18 andFigures C-1 to C-12 of Appendix C of this report.

Results

2-18

• The deposition rate for magnetite is lower on unheated than on heated regions of the testsection. This observation is consistent with the fact that the heated regions of the test sectionare primarily under flow-boiling conditions (either sub-cooled or saturated nucleate boiling),where bubble nucleation and growth provides a mechanism to enhance mass transfer of fluidto the surface. The unheated sections were in either single-phase (X < -0.22) or 2-phase(X > 0) forced convection, where the mass transfer mechanism for fluid to the surface is eddydiffusion, except for X ≥ 0.4, where deposition is enhanced by the deposition of dropletsentrained from the annular film (See Section 2.5). Thus the deposition rate is greater underflow-boiling conditions for 0 < X < 0.25 than for 2-phase forced convection at X = 0.03 and0.25. At X = 0.5, where the deposition rate is enhanced by droplet deposition (see Section2.5 for a discussion of the mechanism), the rate is also greater under flow-boiling conditionsthan for 2-phase forced convection.

Table 2-7Summary of loop deposition results for magnetite

Details from the loop deposition results for magnetite, Fe 3O4

Remarks Ex p.ID Kρ for Flow Boiling,kg/m²s

Kρ for Forced Convection, kg/m²s

0 < X < 0.25 X ~ 0.5 singlephase

X ~ 0.03 X ~ 0.25 X ~ 0.5

MORPHOLINE CHEMISTRY

Low A,O2

D097 4.68E-04 6.19E-03 3.37E-04 2.60E-04 3.13E-04 1.54E-03

D101 2.36E-04 7.89E-04 1.21E-04 8.93E-05 1.41E-04 8.85E-04

D119 3.41E-04 9.00E-04 6.13E-05 1.83E-04 1.57E-04 6.29E-04

AMMONIA CHEMISTRY

Low A D120 8.29E-05 1.33E-04 5.18E-05 6.73E-05 3.88E-05 3.22E-04

DIMETHYLAMINE CHEMISTRY

Low A D100 1.24E-04 9.40E-04 1.05E-04 3.97E-05 8.62E-05 1.01E-03

D105 1.21E-04 1.10E-04 3.94E-05 6.19E-05 7.80E-05 1.02E-04

POTASSIUM HYDROXIDE CHEMISTRY

? D098 9.99E-04 3.09E-04 5.15E-04 6.87E-04 9.58E-04 1.94E-02

D103 2.62E-04 6.60E-04 1.54E-04 2.58E-04 1.94E-04 3.47E-03

PYRROLIDINE CHEMISTRY

Low A D099 3.16E-04 8.01E-04 2.62E-04 4.08E-04 4.11E-04 2.30E-04

D117 8.12E-04 5.23E-04 1.81E-04 3.95E-04 2.18E-04 5.11E-04

3-METHOXYPROPYLAMINE CHEMISTRY

Low A D102 1.46E-04 5.22E-04 1.15E-04 9.84E-05 1.89E-04 2.57E-04

D104 6.19E-04 2.03E-04 7.56E-05 2.73E-04 4.10E-04 7.01E-04

4-AMINOBUTANOL CHEMISTRY

Low A D116 5.94E-04 5.20E-04 2.09E-04 4.78E-04 3.39E-04 1.03E-03

D118 3.04E-04 2.71E-04 1.91E-04 2.48E-04 1.70E-04 1.90E-04

Legend: "Low A"-low amine

Results

2-19

• The onset of sub-cooled nucleate boiling at about X = -0.22 results in a significant (up to10-fold) increase in deposition rate. The rate goes through a maximum, however, at Xgenerally between -0.15 and 0, and the rate for X > 0 is only 2 to 3 times greater than the ratefor single-phase forced convection. The maximum in the deposition rate near X = 0 wasobserved previously (Turner et al., 1997) but was not as pronounced as in this investigation.The difference can probably be attributed to the improved temperature control provided bythe newly installed flow control valve on the loop interchanger that helps maintain stablethermohydraulic conditions along the test section.

• The deposition rate increases abruptly in the annular flow region—i.e., X > 0.20—but thesteam quality where this enhancement takes place is variable. Generally the rate starts toincrease by X = 0.4, but in some tests there was no increase up to X = 0.5. The increase indeposition rate is postulated to be associated with droplet entrainment and re-deposition fromthe liquid film that wets the heat-transfer surface in annular flow, and is discussed in detail inSection 2.5 and in Appendix D of this report. The annular film must develop before dropletre-entrainment becomes significant, however, and it may be that film development is affectedby subtle changes in surface roughness and loop operating conditions that affect, in turn, thesteam quality at which the enhanced deposition takes place.

• The deposition rates measured for pH controlled with dimethylamine are consistently lowerthan those measured for pH controlled with other bases, including potassium hydroxide.(The rate for ammonia in Table 2-7 appears anomalously low. (See discussion in Section 3.)Rates measured for the 3 additional amines included in this investigation—pyrrolidine,3-methoxypropylamine, and 4-aminobutanol—were closer to the rates measured formorpholine and ethanolamine. A full discussion of these results will be presented in Section3, where the discussion will include results of the previous investigation as well (see Turneret al., 1997).

Figures 2-18 and 2-19 show representative plots of normalized deposition rate and walltemperature as a function of mixture quality for hematite deposition with pH controlled usingdimethylamine and 3-methoxypropylamine, respectively. Additional figures showing similarplots for the other hematite tests listed in Table 2-6 are found in Figures C-13 to C-20 ofAppendix C of this report. Normalized deposition rates for all of the hematite tests are listed inTable 2-8. The main observations that follow from Figures 2-18, 2-19, C-13 to C-20 (ofAppendix C of this report), and Table 2-8 are as follows:

• Hematite showed the same trends in normalized deposition rate with mixture quality as didmagnetite.

• The deposition rate measured for hematite under flow-boiling conditions was significantlyhigher than the rate measured for magnetite, especially when oxygen was present in the loopduring the hematite test.

• The deposition rate of hematite in the flow-boiling regime is especially sensitive to theconcentration of dissolved oxygen. For the ethanolamine, dimethylamine, and potassiumhydroxide tests, the hematite deposition rate in the test done without oxygen in the loop was14.4%, 13.3%, and 10.2%, respectively, of the rate when oxygen was present.

• When dissolved oxygen was present, the deposition rate of hematite in the flow-boilingregime was an average of 18 times greater than the rate in single-phase forced convection.

Results

2-20

When oxygen was absent, the rate in flow-boiling conditions was only 26% higher than therate in single-phase forced convection.

• The deposition rate was lowest when 3-methoxypropylamine was used for pH control.


0.10 1.50 4.102.10 2.70

0.0E+00

2.0E-03

4.0E-03

6.0E-03

8.0E-03

1.0E-02

1.2E-02

1.4E-02

1.6E-02

-0.4 -0.2 0 0.2 0.4 0.6 0.8

Mixture Quality [-]

Nor

mal

ized

Dep

ositi

on R

ate

K· [k

g/m

²·s]

150

200

250

300

Tem

pera

ture

[°C

]

Bulk Temp (Calc)




D114--Fe2O3 + DMA




0.10 1.50 4.102.10 2.70

0.0E+00

1.0E-03

2.0E-03

3.0E-03

4.0E-03

5.0E-03

6.0E-03

7.0E-03

8.0E-03

-0.4 -0.2 0 0.2 0.4 0.6 0.8

Mixture Quality [-]

Nor

mal

ized

Dep

ositi

on R

ate

K· [k

g/m

²·s]

150

200

250

300

Tem

pera

ture

[°C

]

Bulk Temp (Calc)




D112--Fe2O3 + MPAA i l P i i h


Results

2-21

Table 2-8Summary of loop deposition results for hematite

Details from the loop deposition results for hematite, Fe 2O3

Remarks Ex p.ID Kρ for Flow Boiling,kg/m²s


0 < X < 0.25 X ~0.5 singlephase

X ~ 0.03 X ~ 0.25 X ~ 0.5

ETHANOLAMINE CHEMISTRY

O2 D111 8.60E-03 1.20E-03 9.81E-04 3.48E-04 4.38E-04 4.40E-04

No O2 D108 1.24E-03 1.59E-03 7.61E-04 2.55E-03 6.72E-04 3.63E-03


O2 D114 5.88E-03 1.35E-02 1.51E-04 1.87E-04 9.11E-04 3.14E-03

No O2 D106 7.81E-04 6.08E-04 7.44E-04 3.56E-04 3.43E-04 4.87E-04


O2 D109 3.08E-03 2.73E-04 1.83E-04 2.91E-04 6.48E-04 1.51E-04

D113 1.77E-03 4.25E-03 1.88E-04 7.54E-04 1.07E-03 2.79E-02

D115 4.26E-03 2.82E-03 1.17E-04 2.58E-04 7.97E-04 1.67E-03

No O2 D107 3.09E-04 5.09E-04 2.77E-04 1.57E-04 2.15E-04 7.22E-04


O2 D110 6.01E-04 1.57E-04 1.64E-04 2.17E-04 1.48E-04 8.74E-05

D112 1.07E-03 7.72E-04 1.20E-04 1.45E-04 9.64E-05 9.32E-05

Legend: "O2"-dissolved oxygen present in loop water, "No O2"-no oxygen present

Two of the deposition tests in this investigation, D-119 and D-120, were conducted with thedeposition phase extended by a factor of 5 to build up more deposit on the test section andinvestigate the effect of a tube deposit on the particle deposition rate. A plot showing the build-up of deposit on the test section as a function of time is shown in Figure 2-20.

For t< 0 h, the on-line γ-ray detector sees only residual activity on the loop surfaces fromprevious tests. Time 0 marks the beginning of the injection of magnetite into the loop; this eventis marked by an immediate increase in the level of radioactivity measured at the test section.Magnetite then deposits onto the test section at a constant rate over the next 48 h at which pointthe injection was switched off, as shown in Figure 2-20. Although enough magnetite haddeposited to cover the surface with a monolayer of deposit, SEM microscopy showed that thedeposit formed in discrete clumps and so had not entirely covered the surface. This test showsthat the injection time can be increased significantly (i.e., 5-fold) without difficulty and that thedeposition rate remains linear for significant coverage of the surface. It is reasonable to assumethat even higher degrees of surface coverage are possible by this method, and this assumptionwill be explored in subsequent work.

Results

2-22

0

50

100

150

200

250

300

-30 -10 10 30 50

Time [h]

Act

ivity

[Bq]

Figure 2-20Build-up of radioactivity resulting from the deposition of magnetite onto the surface ofInconel 600 under flow-boiling conditions. The suspension of magnetite particles wastraced using 59Fe so that the build-up could be followed using a γ-ray detector, asdescribed in Turner et al., 1997.

Morphology of the deposit from various locations along the test section was routinelydetermined using SEM. The implications of the morphological changes with steam quality arenot fully understood at this time, nor are they obviously related to differences in deposition ratefrom one amine to another or between magnetite and hematite. A sampling of typical depositmorphologies is included in Appendix E of this report, along with some descriptive notes forfuture reference.

2.6 Deposition Mechanism at High Steam Quality

In the previous investigation, it was observed that the rate of particle deposition increasessignificantly once the steam quality is raised to a value in excess of about 0.35 (Turner et al.,1997). A detailed analysis of heat- and mass-transfer phenomena at high steam qualities andtheir effect on particle-fluid interactions has been conducted, and a mechanism that couldaccount for the increase in deposition rate has been identified. Only the salient points will bediscussed in this section, and a full detailed analysis is presented in Appendix D of this report.

Figure 2-21 shows a schematic of the flow regimes that develop under flow-boiling conditions.Although the figure is drawn for fluid flow inside of a tube, the picture is applicable to flow onthe secondary side of the tube bundle in an operating steam generator as well. At a mixturequality of ~ 0, the liquid reaches saturation temperature and bubbles of steam produced byvaporization at the wall are distributed throughout the liquid phase. At higher mixture qualities,steam bubbles coalesce to form ‘slugs’ of vapour, and the flow regime is called churn flow. Ateven higher mixture qualities there is a transition to annular flow, where the steam travels in thecore of the tube while liquid travels in an annular film on the wall. In the loop tests and under

Results

2-23

typical steam generator operating conditions, the transition to annular flow takes place at amixture quality of approximately 0.2.

The liquid film thickness at the transition to annular flow is ~500 µm and decreases steadily withincreasing mixture quality, as shown in Figure 2-22. As a result of ‘slip’ between the steam andliquid phases, the steam travels at a progressively higher velocity than the liquid as the mixturequality increases. Whereas both phases have approximately the same velocity at a mixturequality of 0.02, Figure 2-22 shows that the steam velocity has increased to nearly 4 times theliquid velocity at a mixture quality of 0.7.

One conclusion that can be drawn from Figure 2-22 is that the liquid film velocity does notchange sufficiently with increasing mixture quality to account for the abrupt increase indeposition rate that is observed at high mixture qualities, i.e., mixture qualities in excess of 0.35(See, for example, Figure 2-17). Thus, the increase in deposition rate must be associated withthe onset of an additional particle transport mechanism. In the annular flow regime, fluidinstabilities cause droplets to be entrained from the surface of the liquid film. The entraineddroplets travel along a straight path and re-deposit on the opposite side of the tube. It ispostulated that re-deposition of entrained droplets carrying with them particles at the filmconcentration provides the additional transport mechanism that leads to the increased depositionrate at high mixture qualities.

The dashed line in Figure 2-23 shows the calculated droplet deposition rate as a function ofmixture quality. Not all droplets that re-deposit deliver particles to the wall of the tube. Thedroplets must also have sufficient momentum to coast through the liquid film to the wall. Thisconsideration gives rise to the solid line in Figure 2-23 for droplets with stopping distancegreater than the liquid film thickness, where the stopping distance is defined as the distance thata particle will travel in a fluid before its momentum is reduced to zero by the Stokes drag force(Friedlander and Johnson, 1957). For an estimated droplet diameter of 10 µm, and assuming thatthe droplet is rigid and is not miscible with the liquid film, the onset of increased deposition bythis mechanism is calculated to occur at a mixture quality of 0.4. Despite the assumptions madefor calculation of the stopping distance, this result is in good agreement with the results of thedeposition tests.

It is worth noting that the mechanism described above would not cause an increase in particledeposition at the wall if the droplets coalesced with the liquid in the film before they had time tocoast to the wall. One could presume that a reduction in either the surface tension or elasticity ofthe liquid droplets would tend to increase the rate of coalescence and consequently reduce therate of deposition in the annular flow regime. Dispersants are surface-active reagents that havethe property of reducing the surface tension of the air-water interface. High-temperature looptests with dispersants have shown both a reduction in wall superheat (related to surface tension atthe steam-water interface) and a reduction in deposition under flow-boiling conditions at lowsteam quality (Balakrishnan et al.,1998; Burgmayer et al., 1998), which suggests that they mightprove useful for reducing deposition at high steam quality as well.

Results

2-24

Figure 2-21Flow regimes under flow-boiling conditions

Results

2-25

Liquid Velocity

Steam Veloc ityAverage Liquid Fi lm Thickness, no Entrainment

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70

M ixtu re Quality [-]

Flu

id A

xial

Vel

ocity

[m/s

]

0

100

200

300

400

500

600

Ave

rage

Liq

uid

Film

Thi

ckne

ss [µ

m]

Figure 2-22Steam–liquid velocities and film thickness vs. mixture quality

Droplet Depositon Rate

Deposition Rate, only Droplets with

stopping distance > film thickness

0.0

0.1

0.1

0.2

0.2

0.3

0.3

0.4

0.4

0.5

0.5

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70Mixture Quality [-]

Liqu

id D

ropl

et D

epos

ition

Rat

e [k

g/m

²s]

Figure 2-23Calculated droplet deposition rate vs. mixture quality

3-1

3 DISCUSSION

The following observations were made in our previous investigation (Turner et al., 1997):

• The deposition rate for hematite was higher than the rate for magnetite.

• The deposition rate for magnetite increased with increasing amine concentration (at constantpH. Excess amine was neutralized by acidic contaminant in the cover gas),

• The deposition rate for magnetite decreased with increasing room temperature base strengthof the amine.

• The deposition rate for hematite decreased towards that of magnetite as the loop waterbecame less oxidizing.

These observations were taken as evidence for the importance of surface chemistry in governingthe deposition rate of corrosion products under steam generator operating conditions. Thedifference between the deposition rates of hematite and magnetite was attributed to thedifference in sign between their respective surface potentials at pHT = 6.2 and temperature =270°C. For example, magnetite—which is predicted to be negatively charged under steamgenerator operating conditions (Shoonen,1994)—will be repelled by the negatively chargedsurface of Inconel 600, whereas hematite—which is predicted to be positively charged under thesame conditions—will be attracted. This difference was proposed to account for the nearly 10-fold difference in the deposition rates between the 2 oxides. The effect of concentration and basestrength of the amine on the deposition rate of magnetite was hypothesized to be related toadsorption of amine onto the surface of the corrosion product. The reasoning was that the amineadded for pH control exists in solution in both the neutral and protonated form:

HA+ ⇔ A + H+ (3-1)

It was suggested that adsorption of the protonated amine onto the negatively charged surface ofmagnetite would reduce the repulsion between the surfaces of magnetite and Inconel 600 and,consequently, increase the rate of deposition. Thus greater adsorption of amine onto thecorrosion products is predicted to correlate with a higher rate of deposition.

Evaluation and testing of this hypothesis formed the basis for the present investigation. If,indeed, adsorption of amine onto the corrosion products and the effect this adsorption has onsurface potential has a marked effect on deposition behaviour, then this hypothesis provides astrong incentive to determine the properties of the amine that most affect its adsorption so thatthese properties can be optimized when selecting the amine for pH control in the feedwatercircuit.

Discussion

3-2

Each of the 4 amines tested showed a strong tendency to adsorb onto both magnetite andhematite at room temperature, as shown by the results in Section 2.1, with the amount adsorbedincreasing in proportion to the concentration of amine in solution. Since the concentration ofamine required to achieve a fixed pH increases with decreasing base strength, the amount ofamine adsorbed onto the corrosion products will increase as the base strength of the aminedecreases. A second factor that is expected to contribute to the amount adsorbed is the size ofthe amine molecule, or its “footprint” on the surface of the corrosion product. The results inSection 2.1 show that the amount of amine adsorbed per unit surface area of corrosion productincreases with decreasing molecular size for a given concentration of amine. Thus, if ourhypothesis is correct, a weaker base and smaller amine molecule should correlate with greateradsorption and a higher particle deposition rate.

Table 3-1 lists trends in the amount of amine absorbed, the base strength of the amine at 25°C,and the relative size of the amine molecule for the 4 amines included in this part of theinvestigation. The relative molecular sizes were estimated from 3-dimensional molecularmodels constructed for each amine. The ranking with respect to the amount adsorbed (in units ofmoles of amine per unit surface area) is consistent with the ranking with respect to molecularsize. Although ethanolamine and morpholine exchange places with respect to their rankingbetween 5 and 50 mM, the basic conclusion is that the surface adsorption of amine in moles perunit surface area of corrosion product varies inversely with molecular size for a givenconcentration of amine. The amount of amine required to achieve a particular pH, however,decreases with increasing base strength. Thus on the basis of base strength alone, one wouldexpect dimethylamine to be adsorbed the least for a given pH. This adsorption, however, will beoffset somewhat by its relatively small molecular size. Ammonia is expected to be adsorbed to agreater extent than dimethylamine for a given pH on 2 accounts: ammonia is a weaker base andit has a smaller molecular size. The large molecular size of morpholine reduces the amount ofadsorption for this molecule, but its relatively low base strength means that higher concentrationsare required in solution to control pH.

Table 3-1Comparison of trends in amine base strength, molecular size, and the relative amountadsorbed onto corrosion products for 5 and 50 mM concentrations of amine

Relative Ranking Base Strength Molecular Size Amount Adsorbed

5 mM 50 mM

Highest dimethylamine morpholine ammonia ammonia

ethanolamine ethanolamine dimethylamine dimethylamine

ammonia dimethylamine ethanolamine morpholine

Lowest morpholine ammonia morpholine ethanolamine

The effect of the adsorption of amine on the surface potential of the corrosion products is shownquite clearly by the results of both electrophoresis and AFM. The theory of electrophoresispredicts that adsorption of a cationic (positively charged) species will shift the IEP of an oxidetowards higher pH (Hunter, 1981). Thus the results of electrophoresis show that the addition ofamine to suspensions of both magnetite and hematite resulted in the adsorption of a cationic

Discussion

3-3

species, which is presumed to be the protonated amine. The shift in IEP towards higher pHmeans that the surface potential of the corrosion products has been reduced to less-negativevalues with the addition of amine. Hematite showed both a greater tendency to adsorb amineand a larger shift in IEP for a given amine concentration than did magnetite. It is not clear whythis should be the case, but the 2 trends are qualitatively consistent.

The AFM results are remarkably consistent with those from electrophoresis, even to the extentthat the magnitude of the surface potentials for magnetite and hematite determined by bothmethods in the absence of amine are in good agreement. Atomic force microscopy not onlyshows that adsorption of amine reduces the magnitude of the surface potentials, it also provides aquantitative measure of how adsorption affects the total interaction potential between thecorrosion products and Inconel 600. When there is a strong force of repulsion between thecorrosion product and Inconel 600, the total interaction force between the 2 surfaces in questiongoes through a maximum. The energy required for a particle in a flowing suspension tosurmount this force barrier and deposit on the surface can be calculated by integrating the forcefrom infinite separation (in practice, the integration can start at a separation of about 40 nm,where the force is essentially zero) to the separation corresponding to the maximum force.

This calculation shows that a 0.25-µm magnetite particle would require an energy of 12 kT at25°C to surmount a force barrier of height 0.04 mN/m, where kT is the average thermal energyof the particle in a stagnant solution in thermal equilibrium with its surroundings. In the absenceof amine, the force barrier at pH 10 between the corrosion product and the surface of Inconel 600reached from 0.1 to 0.2 mN/m, corresponding to energy barriers for a 0.25-µm particle between30 and 60 kT. An energy barrier of this magnitude would be expected to significantly reduce therate of particle deposition from a flowing suspension. Both a reduction in pH and the addition ofamine effectively reduced the magnitude of this force barrier, in each case by reducing themagnitude of the surface potentials. For example, Figure 2-12 shows that a reduction in pH from10 to 7 and the addition of 50 mM morpholine at pH 10 are equally effective at reducing theheight of the force barrier to 0.01 mN/m, which corresponds to a barrier of 3kT at 25°C.

The results in Tables 2-3 and 2-5 show that the addition of amine generally made the surfaces ofhematite and magnetite less negative. This reduction in the magnitude of the surface potential isattributed to adsorption of the protonated amine, HA+. The corresponding reduction in themagnitude of the surface charge density was most pronounced with dimethylamine, presumablybecause it has the highest base strength of the amines tested and, therefore, produces the highestconcentration of HA+ in solution. The average change in surface charge density for all aminesevaluated at a concentration of 50 mM and pH 10 was about 3 mC/m2 (see Tables B-1 and B-2 ofAppendix B of this report). This change can be compared to the change in surface chargedensity predicted from the adsorption isotherms, but first we must consider what could happenwhen a charged species is adsorbed onto the surface of a metal oxide.

A metal oxide acquires a surface charge when exposed to water via reactions of the followingsort:

-M-OH + H+ ⇔ -MOH2

+ (3-2)

-M-OH + OH- ⇔ -MO- + H2O (3-3)

Discussion

3-4

The net surface charge density is given by the difference in the concentration of -MOH2

+ sitesand -MO- sites on the surface, and will be a function of both the pH and the magnitudes of theequilibrium constants for Reactions (3-2) and (3-3). The pH at which the net surface charge iszero is called the point of zero charge (PZC). For pH > PZC there is an excess of negativecharge on the surface of the metal oxide, and for pH < PZC, an excess of positive charge.

Two limiting cases will be considered for the adsorption of a cation (such as a protonated amine,HA+) onto the surface of a metal oxide at a pH > PZC, i.e., where the surface is negativelycharged. One limiting case is for the surface to respond to the adsorption of an HA+ by releasingan H+ cation into solution. In this case, the surface charge and surface potential will remainunaltered by the adsorption of a protonated amine; the adsorbed cation simply shifts theequilibrium in Reactions (3-2) and (3-3) so that one cation (HA+) is exchanged for another (H+) .

The second limiting case to be considered is that the adsorption of a protonated amine does notaffect the equilibrium between the surface species -MOH2

+ and -MO- . In this case adsorption ofeach protonated amine neutralizes 1 negative charge on the surface of the metal oxide.Calculations show that the reduction in the magnitude of the surface charge density with theadsorption of amine is significantly lower than that predicted by this second limiting case; that is,the reduction in the surface charge density appears to be significantly less than one chargeneutralized per adsorption of a protonated amine. The results are listed in Table 3-2 for an amineconcentration of 50 mM and pH 10.

Table 3-2Calculated change in surface charge density with adsorption of amine for the secondlimiting case

Amine Surface Charge Density (C/m 2)Magnetite

Surface Charge Density (C/m 2)Hematite

Morpholine 1.5 2.9

Ammonia 65 49

Ethanolamine 7.4 30

Dimethylamine 71 274

For this analysis, the concentration of protonated amine on the surface was calculated from thetotal amount of amine adsorbed with the assumption that the dissociation constant of the amineon the surface is the same as for the amine dissolved in solution. The changes in surface chargedensity predicted for the second limiting case are significantly greater than those determinedfrom the AFM results (see Tables 2-4 and 2-5), for which the surface charge density onmagnetite and hematite changed by only 3 mC/m2 with the adsorption of amine from a 50 mMsolution at pH 10. This value corresponds to a change of about 1 excess charge per 50 nm2.Thus the effect of the adsorption of amine on the surface charge density cannot be estimatedusing the simplifying assumption described for the second limiting case. In addition to thelikelihood that adsorption of a charged species does shift the equilibria in Reactions (3-2) and (3-3), the assumption that the dissociation constant remains the same for both dissolved andadsorbed amine molecules is likely flawed as well. Adsorption onto a surface (especiallymultilayer adsorption, as we appear to have in this case) will bring the amine molecules into

Discussion

3-5

much closer proximity to one another than is the case for molecules dissolved in solution.Protonation of the adsorbed amine molecule will, thus, be inhibited by the Coulomb repulsionbetween adjacent charged species, which will tend to reduce the magnitude of the dissociationconstant for adsorbed amine.

To compare the effect of adsorption of amine at 25°C with the deposition behaviour of thecorrosion products at 270°C, the discussion will also include results from the previousinvestigation (Turner et al., 1997). Tables 3-3 summarizes the deposition results for magnetitefrom both investigations, where the results of the current investigation are shown in bold type.Only average deposition rates are listed; rates for individual tests are listed in Table C-2 ofAppendix C of this report.

Table 3-3 shows clearly that under flow-boiling conditions the deposition rate of magnetiteincreases with increasing amine concentration at constant pH. (Recall that an acidic impurity inthe cover gas was acting to neutralize some of the amine so that higher concentrations wererequired to achieve the target pH, as discussed in Turner et al. (1997). Lower amineconcentrations were needed once a “scrubber” was installed on the cover gas line.) Thedependence of the deposition rate on amine concentration correlates well with the adsorption andAFM measurements, which show that the adsorption of amine and consequent reduction of thesurface charge on magnetite increases with increasing concentration of amine. Reduction of thesurface charge on magnetite lowers the force of repulsion between the surfaces of magnetite andInconel 600 which, in turn, results in an increase in deposition rate.

The effect of the adsorption of amine on the deposition rate of magnetite under flow-boilingconditions is further illustrated by the results listed in Table 3-4. The surface coverages of amineon the magnetite particles at 25°C for high and low amine concentrations were determined fromthe adsorption isotherms shown in Figure 2-1 using the average amine concentrations in theslurry addition tank (see Table C-1 and Table C-1 found in Turner et al. (1997)). For each of thefour amines, the results in Table 3-4 show a clear trend of deposition rate increasing withincreasing surface coverage of magnetite by the amine molecules. This trend correlates wellwith the reduction in surface repulsion between magnetite and Inconel 600 with increasingconcentration of amine as measured by AFM, and supports the hypothesis that adsorption ofamine onto the surface of the magnetite particles at 25°C is responsible for the increase indeposition rate under flow-boiling conditions at 270°C.

Discussion

3-6

Table 3-3Summary of deposition results for magnetite. Results of the current investigation areshown in bold, and the other results are from Turner et al. (1997)

Summary of all H3 loop deposition results for magnetite, Fe 3O4

Amine Remarks # of exp. Kρ for Flow Boiling,kg/m²s


for 0 < X < 0.25 at X ~ 0.5 at singlephase

at X ~0.03

at X ~ 0.25 at X ~0.5

Morph High A 2 1.64E-03

Low A 3 3.48E-04 2.63E-03 1.73E-04 1.77E-04 2.04E-04 1.02E-03

ETA High A 2 1.06E-03

Low A 3 5.52E-04 6.65E-03 5.46E-04

EtchedSurface

2 2.53E-03

Low A, SP 2 1.07E-04

NH3 High A 2 8.95E-04

Low A 1 8.29E-05 1.33E-04 5.18E-05 6.73E-05 3.88E-05 3.22E-04

DMA High A 4 6.17E-04

Low A 5 1.16E-04 6.96E-04 7.20E-05 5.08E-05 9.61E-05 5.58E-04

KOH ? 2 6.30E-04 4.85E-04 3.34E-04 4.73E-04 5.76E-04 1.14E-02

Low A 2 1.71E-04 2.23E-03 1.51E-04

Pyrr Low A 2 5.64E-04 6.62E-04 2.22E-04 4.02E-04 3.15E-04 3.70E-04

MPA Low A 2 3.83E-04 3.62E-04 9.54E-05 1.86E-04 2.99E-04 4.79E-04

4AB Low A 2 4.49E-04 3.95E-04 2.00E-04 3.63E-04 2.55E-04 6.11E-04

Legend: "Low A"-low amine, "High A"-high amine. The new results (of the currentprogram) are in bold type.

Discussion

3-7

Table 3-4Relationship between surface coverage of amine and the average magnetite depositionrate under flow-boiling conditions

Concentration ofAmine(mM)

Surface Coverage ofAmine at 25 °C

(molecules/nm 2)

Deposition Rate at270°C

(kg/m 2s)

Morpholine

Low Amine 1.24 12.4 0.35x10-3

High Amine 41 258 1.64x10-3

Ammonia

Low Amine 0.14 5.6 0.08x10-3*

High Amine 30 1640 0.90x10-3

Ethanolamine

Low Amine 0.70 9.8 0.55x10-3

High Amine 31 145 1.06x10-3

Dimethylamine

Low Amine 0.20 4.8 0.12x10-3

High Amine 22 271 0.62x10-3

*: Result from a single loop test.

The justification for using the low-temperature adsorption data to correlate the deposition ratesmeasured at 270°C is that the particles spend only a few seconds in the high-temperature regionof the loop during a run before entering the test section, whereas they spend several daysequilibrating with the amine at 25°C before the start of each test. The fact that theelectrophoresis data, which were obtained after a 24 h equilibration time, gave similar values forthe surface potential as those obtained by AFM after only 1 h equilibration suggests that thelatter time period is sufficient for both the adsorption of amine and the subsequent rearrangementof surface charge to have reached steady-state. Although Figure 2-3 shows that the aminedesorbs with increasing temperature, the time taken to heat the cell for these measurements waslong compared to the residence time of the particles in the high-temperature section of the loop.Thus the data in Figure 2-3 provide no information on the kinetics of desorption that can beapplied to the loop test.

Although the adsorption behaviour of pyrrolidine, 3-methoxypropylamine, and 4-aminobutanolwas not measured in this investigation, on the basis of base strength alone one would predict thefollowing trend in magnetite deposition rate with amine: 3-methoxypropylamine> 4-aminobutanol > pyrrolidine. Moreover, one would expect the rate with pyrrolidine to becomparable to the rate with dimethylamine since they have equivalent base strengths at 25°C.The rates measured for 3-methoxypropylamine and 4-aminobutanol are indeed greater than therate with dimethylamine, but the rate with pyrrolidine appears a little high. The adsorptionbehaviour for these amines needs to be measured, however, before drawing any conclusions.

Discussion

3-8

A summary of the deposition results for hematite particles is shown in Table 3-5 for both theprevious and current investigations, with the results of the current investigation shown in boldtype. Only average deposition rates are listed; rates for individual tests are listed in Table C-3 ofAppendix C of this report.

Table 3-5Summary of deposition results for hematite. Results of the current investigation areshown in bold, and the other results are from Turner et al., 1997

Summary of all H3 loop deposition results for hematite, Fe 2O3

Amine Remarks # ofexp.

Kρ for Flow Boiling,kg/m²s


for 0 < X <0.25

at X ~ 0.5 at singlephase

at X ~ 0.03 at X ~ 0.25 at X ~ 0.5

Morph O2 4 1.82E-02

ETA O2 3 1.08E-02 1.20E-03 9.81E-04 3.48E-04 4.38E-04 4.40E-04

No O2 3 8.53E-04 1.37E-02 6.24E-04

NH3 O2 4 1.99E-02

DMA O2 3 3.29E-03 3.01E-02 1.79E-03

No O2 1 7.81E-04 6.08E-04 7.44E-04 3.56E-04 3.43E-04 4.87E-04

KOH O2 3 3.04E-03 2.45E-03 1.63E-04 4.34E-04 8.38E-04 9.92E-03

No O2 1 3.09E-04 5.09E-04 2.77E-04 1.57E-04 2.15E-04 7.22E-04

MPA O2 2 8.36E-04 4.64E-04 1.42E-04 1.81E-04 1.22E-04 9.03E-05

Legend: "O2"-oxygen present, "No O2"-no oxygen present. The new results (of the currentprogram) are in bold type.

The deposition behaviour of hematite appears complex. There is a clear correlation between thedeposition rate of hematite and the amount of dissolved oxygen in the loop, with the depositionrate increasing with increasing concentration of dissolved oxygen. A commercially availablehematite was used for these tests which had an IEP near pH25 3. In contrast, hematite synthesizedby the hydrolysis of Fe(III) solutions (Matijevic and Schneiner, 1978; Fokkink et al., 1992) isreported to have an IEP near pH25 8.5. Shoonen (1994) predicted that the IEP of hematitesynthesized by the hydrolysis of Fe(III) solutions will drop from pH 8.5 to 7.5 when thetemperature is raised from 25°C to 270°C. Thus the latter hematite is predicted to be positivelycharged at pHT = 6.2 (since pHT < IEP). If positively charged, there will be no repulsive forcebetween the hematite and Inconel 600 to impede deposition, and the deposition rate would beexpected to be significantly higher than for magnetite.

Discussion

3-9

With decreasing concentration of dissolved oxygen, the deposition rate of the commerciallyavailable hematite decreased towards that of magnetite at 270°C. Thus the deposition behaviourof hematite tended towards that of a negatively-charged particle at lower oxygen concentrationand tended towards that of a positively-charged particle at higher oxygen concentration.Although the hematite had a lower IEP at 25°C than expected, it also showed a stronger tendencyto adsorb amine than did magnetite and the response in the IEP to the adsorption of amine wasalso much greater (see Figure 2-6). Additional work to determine the effect of amine adsorption,temperature, and oxygen concentration on the IEP of hematite is required before the observedhigh-temperature deposition behaviour of hematite can be fully understood.

Deposition rates measured as a function of steam quality show that the enhancement to thedeposition rate caused by boiling is most effective in sub-cooled nucleate boiling (where thesteam bubbles collapse before leaving the surface) and in annular flow at relatively high steamqualities, e.g., X typically > 0.35. The implications with respect to the mechanisms governingthe deposition and removal of particles at the heat-transfer surface is beyond the scope of thisinvestigation. It is instructive, however, to compare the deposition rate measured as a function ofsteam quality with the deposit distribution on tubes removed from once-through steamgenerators, as shown in Figure 3-1. The measured deposit loadings follow the same generaltrend as measured in the H3 loop tests up to steam quality of 0.55. There are no H3 loop data tocompare with the measured deposit loadings at Oconee-1 (Sykes and Sherburne, 1997) andOconee-3 (P.L. Frattini, EPRI, private communication, 1998) for higher steam qualities. It isworth noting, however, that the plateau between steam qualities of 0.5 and 0.7 followed by adecrease in deposit loading at higher steam quality is consistent with the trend predicted by thedeposition model for annular flow presented in Figure 2-23.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 0.2 0.4 0.6 0.8

Steam Quality

Dep

osit

Load

ing Oconee-1

Oconee-3

H-3 loop

Figure 3-1Comparison of typical deposition behaviour versus steam quality from the H-3 loop testswith deposit loadings measured on tubes pulled from Oconee-1 and Oconee-3

4-1

4 SUMMARY AND CONCLUSIONS

This work has demonstrated a clear link between the adsorption of amine onto the surface ofcorrosion products and a reduction in the force of repulsion between those corrosion productsand the surface of Inconel 600. Factors that lead to more adsorption of amine—e.g., higheramine concentration or a smaller amine molecule that covers less of the surface—result in alower force of repulsion between the corrosion product and the surface of Inconel 600. There isa good correlation between the adsorption behaviour measured at 25°C and the averagedeposition rate for magnetite particles measured at high temperature (flow-boiling conditions; 0< X < 0.25), as illustrated in Figure 4-1 (taken from Table 3-4; the result for high surfacecoverage by ammonia was not included in the figure for clarity). Low adsorption correlates withlow deposition rate and vice versa. Hematite deposition rates are sensitive to the level ofdissolved oxygen in the loop, suggesting that its surface composition and surface potential areboth functions of the oxidation potential of the water. As a general rule, the deposition rate ofhematite tends towards that of magnetite as the concentration of dissolved oxygen in the loopdecreases.

0.0E+00

2.0E-04

4.0E-04

6.0E-04

8.0E-04

1.0E-03

1.2E-03

1.4E-03

1.6E-03

1.8E-03

0 100 200 300

Surface Coverage (molecules/nm 2)

Nor

mal

ized

Dep

ositi

on R

ate

(kg/

m2 s)

Figure 4-1Effect of surface coverage of amine on the average deposition rate of magnetite underflow-boiling conditions

A simple method for measuring the wetting angle at solid–liquid interfaces as a function oftemperature has been identified and tested up to 140°C. The results indicate that the magnetite–solution interface is becoming increasingly hydrophobic (i.e., increasingly non-wetting) and theInconel 600–solution interface increasingly hydrophilic (i.e., more easily wetted) as the

Summary and Conclusions

4-2

temperature is raised. This apparatus could be used to probe the relationship between wettingangle (itself a function of surface tension) and the deposition behaviour of corrosion products.

This investigation has established a test protocol that can be used to evaluate the deposit-controlproperties of amines or other chemicals added to adjust water chemistry. The test protocolincludes three, and possibly four, components:

• Screen the amines for adsorption onto magnetite and select one that adsorbs the least.

• Qualify the choice of amine by measuring the effect of adsorption on the magnetite–Inconel600 interaction using AFM.

• Perform final validation with loop tests to quantify the effect of adsorption on the depositionrate.

A new particle deposition mechanism has been identified that is operable at high mixturequalities and appears to account for the enhanced deposition rate reported for mixture qualitiesgreater than 0.35. The enhanced deposition rate is associated with the transport of liquid dropletscarrying corrosion product through the liquid film that wets the tube surface in the annular flowregime. Only those droplets that strike the liquid film with sufficient inertia are able to penetrateit and contribute to deposition at the tube surface. Modification of some property of the liquid–steam interface, such as surface tension or elasticity, may act to reduce the deposition rate atthese high mixture qualities.

This mechanism leads to a fourth component that, if valid, could be added to the test protocol.

• Measure the effect of the amine (modified perhaps with a dispersant) on the surface tensionof the steam-water interface.

The effect of the modified amine on surface tension could be assessed by a measurement of thewetting angle (i.e., hydrophobicity) of the solid/solution interface, or by measuring the effect ofthe modified amine on the wall superheat under flow-boiling conditions.

5-1

5 IMPLICATIONS FOR CONTROLLING TUBE-BUNDLEFOULING

This work has identified 2 trends in the deposition rate of corrosion products with waterchemistry. These trends are illustrated in the bar graph shown in Figure 5-1.

• Magnetite deposition rate decreases with decreasing adsorption of amine.

• Hematite deposition rate decreases with decreasing dissolved oxygen concentration in thepresence of a reducing agent.

These trends result in 2 criteria to ensure the lowest possible deposition rate of corrosionproducts onto the tube bundle. They are:

• Minimize the concentration of dissolved oxygen in the feedwater

• Select an amine for pH control that shows the least adsorption onto magnetite

The criterion to select an amine for pH control that will result in the lowest deposition rate formagnetite on the tube bundle become:

• Select an amine for pH control that has high base strength (to reduce the concentration ofamine required to achieve the target pHT)

• Select an amine with a large “footprint” on the surface of magnetite (to reduce the amount ofadsorption for a given concentration of amine)

One final criteria for controlling tube-bundle deposition that comes from the high-steam qualitydeposition results is as follows:

• The amine should reduce the surface tension or elasticity of the steam–water interface (toprevent enhanced deposition at high mixture qualities).

The last criterion needs to be evaluated further but it is supported by deposition results withdispersants that show a reduction in deposition rate with some dispersants that also show areduction in wall superheat, which is a function of surface tension (Balakrishnan et al., 1998).

Implications for Controlling Tube-Bundle Fouling

5-2

Mor

ph

ET

A

NH

3

DM

A

KO

H

Pyr

r

MP

A

4AP

magnetite, low amine

magnetite, high aminehematite, no O2

hematite, O2

1E-04

1E-03

1E-02

1E-01

Nor

mal

ized

Dep

ositi

on R

ate,

K· ρ

, kg/

m²·

s

Amine

magnetite, low amine

magnetite, high amine

hematite, no O2

hematite, O2

Figure 5-1Trends in magnetite and hematite deposition rate with water chemistry under flow-boilingconditions

6-1

6 REFERENCES

Balakrishnan, P.V., S.J. Klimas, L. Lépine, and C.W. Turner (1998). “Polymeric Dispersants forControl of Steam Generator Fouling”, 3rd International Steam Generator and Heat ExchangerConference, June 21-24, 1998, Toronto, Canada.

Burgmayer, P.R., R. Crovetto, S.J. Klimas, and C.W. Turner (1998). “ Effectiveness of SelectedDispersants on Magnetite Particle Deposition on Simulated PWR Heat Transfer Surfaces”, 3rd

International Steam Generator and Heat Exchanger Conference, June 21-24, 1998, Toronto,Canada.

Brunauer, S., L.S. Emmett, and E. Teller (1938), J. Am. Chem. Soc. 60, 309.

Ducker, W.A., J.T. Senden, and R.M. Pashley (1991). "Direct Measurements of ColloidalForces Using an Atomic Force Microscope", Nature 353, 238.

Fokkink, L.G.J., A. De Keizer, and J. Lyklema (1989). “Temperature Dependence of theElectrical Double Layer on Oxides: Rutile and Hematite”, J. Colloid and Interface Sci. 127, 116.

Friedlander, S.K., and H.F. Johnstone (1957). “Deposition of Suspended Particles fromTurbulent Gas Streams”, Ind. and Eng. Chem. 49, 1151.

Hiemenz, P.C. (1977) Principles of Colloid and Interface Science, Marcel Dekker, Inc., NewYork.

Hunter, R.J. (1981). Zeta Potential in Colloid Science, Academic Press, New York.

Jayaweera P., S. Hettiarachchi, and B.G. Pound (1992). “Identifying Prospective Antifoulingcoatings for Venturis”, Electric Power Research Institute Report EPRI TR-101256.

Matijevic, E. and P.Schneiner (1978). “Ferric Hydrous Oxide Sols 3. Preparation of UniformParticles by Hydrolysis of Fe (III)”, J. Colloid. Interface Sci. 63, 509-524.

Schoonen, M.A.A.(1994). “Calculation of the Point of Zero Charge of Metal Oxides between 0and 350oC”, Geochimica et Cosmochimica Acta, 58, 2845.

Sugimoto, T. and E. Matijevic (1980). “Formation of Uniform Magnetite Particles byCrystallization from Ferrous Hydroxide Gels”, J. Colloid and Interface Sci. 74, 227.

References

6-2

Sykes, L.J. and P.A. Sherburne (1997). “Analysis of Steam Generator Tubing from Oconee Unit1 Nuclear Station”. Electric Power Research Institute EPRI TR-106484.

Tewari, P.H. and McLean, A.W. (1972). “Temperature Dependence of Point of Zero Charge ofAlumina and Magnetite, J. of Colloid and Interface Sci. 40, 267.

Turner, C.W., S.J. Klimas, and M.G. Brideau (1997). “The Effect of Alternative Amines on theRate of Boiler Tube Fouling”. Electric Power Research Institute Report EPRI TR 108004 .Atomic Energy of Canada Ltd. Report, AECL-11848 (1997).

Vold R.D. and M.J. Vold (1983). Colloid and Interface Chemistry, Addison and WesleyPublishing Company, Inc., London.

7-1

7 NOMENCLATURE

D = dielectric constant

H = Hamaker constant (J)

T = temperature (K)

W = energy (J m-2)

X = quality of 2-phase mixture

e = unit of electric charge (C

h = separation between charged surfaces in AFM measurements (m)

k = Bolztmann constant (J molecule-1 K-1)

n0 = number density of ions in solution (m-3)

u = electrophoretic mobility (m2 V-1 s-1)

z = ionic valence

ε0 = permittivity of free space (8.854 x 10-12 F m-1)

κ = diffuse layer decay constant (m-1)

µ = dynamic viscosity (kg m-1 s-1)

σ = surface charge density (C m-2)

ξ = zeta potential (V)

ψ0 = surface potential (V)

θ = contact angle (°)

A-1

A AMINE ADSORPTION ISOTHERMS ON MAGNETITEAND HEMATITE

y = 116.77xR2 = 0.9981

0.0E+00

2.0E+04

4.0E+04

6.0E+04

8.0E+04

1.0E+05

1.2E+05

0 200 400 600 800 1000

[D imethylamine] (mM)

Ram

an In

tens

ity

y = 18.556xR2 = 1

0.0E+00

5.0E+03

1.0E+04

1.5E+04

2.0E+04

0 200 400 600 800 1000

[Ammonia] (mM)

Ram

an In

tens

ity

y = 22.523xR 2 = 0.9998

0 .0E+00

5 .0E+03

1 .0E+04

1 .5E+04

2 .0E+04

2 .5E+04

0 200 400 600 800 1000

[Ethanolamine] (mM)

Ram

an in

tens

ity

y = 37.857xR2 = 1

0.0E+00

1.0E+04

2.0E+04

3.0E+04

4.0E+04

0 200 400 600 800 1000

[Morpholine] (mM)

Ram

an In

tens

ity

Figure A-1Raman intensity versus amine concentration for dimethylamine, ammonia, ethanolamine,and morpholine. Linear fits to the data constrained to go through the origin are shown.

The intensity of the Raman scattering increased in linear proportion to the concentration ofamine, as shown in Figure A-1. Thus:

I = JC, (A-1)

where J is the molar scattering coefficient, and C is the molar concentration. To normalize thespectra at different amine concentrations, the water band at 1640 cm-1 was used as an internalstandard. The intensity of the band at 1640 cm-1 was measured for each amine concentration anda scaling factor FB was calculated using

Amine Adsorption Isotherms on Magnetite and Hematite

A-2

FI

IB

w

Cw= 1000 , (A-2)

where Iw1000 is the intensity of the water band in the spectrum containing 1000 mM amine and Iw

C

is the intensity of the water band in the spectrum for concentrations of 1, 10 or 100 mM amine.The intensities of the selected CH stretching mode were then scaled by FB:

ICH

C,s = FB⋅ICH

C . (A-3)

A plot of ICH

C,s versus concentration gives the value of J for that amine.

To normalize the spectra in the presence and absence of oxide, the water band near 1640 cm-1

was again used. The spectrum of the water region of the sample in the presence of oxide, Sw

oC,was subtracted from the spectrum of the water region of the sample in the absence of oxide, Sw

ref:

Sw

dif = Fs⋅ Sw

ref - Sw

oC . (A-4)

The subtraction factor, Fs, was adjusted until the difference spectrum Sw

dif was zero over thespectral region of the water band. Fs was then used to scale the spectrum of the CH stretchingregion of the sample without magnetite, and then the spectrum of the CH stretching region withmagnetite was subtracted:

SCH

dif = Fs⋅ SCH

ref - SCH

ox . (A-5)

The intensity of the CH stretching bands in the difference spectrum, ICH

dif , was then measured,and the concentration of amine removed from solution calculated using

Crem = J⋅ICH

dif. (A-6)

The adsorbed amount ca, as g amine adsorbed/g oxide, is calculated from

cC V MW

marem= ⋅ ⋅

, (A-7)

where V is the volume of solution used, MW is the molecular weight of the amine, and m is themass of oxide particles used. The number of adsorbed molecules per nm2, Cm, is related to cα by

Cc N x

MW Ama A

s

= ⋅ ⋅⋅

−1 10 18

, (A-8)

where NA is Avogadro’s number and As is the surface area of the oxide, as measured by theBrunauer–Emmett–Teller (BET) method (Brunauer et al., 1938).

REFERENCES

Brunauer, S., L.S. Emmett, and E. Teller (1938). J. Am. Chem. Soc. 60, 309.

B-1

B CALCULATION OF FORCE-DISTANCE CURVES FROMNANOSCOPE II RAW FORCE DATA

A typical raw force curve measured by the Nanoscope II used in this work is shown in Figure B-1.

Figure B-1Typical raw data output from atomic force microscopy (AFM). Regions of zero force andof constant compliance are indicated

The Nanoscope II used in this work contained no software function to store the force datameasured by the machine in a form such as an ASCII x-y pair, which could be directly importedinto a spreadsheet or plotting program. The steps used to convert the Nanoscope II force outputinto a useable form are described below.

The data were captured as a screen dump into a file labelled filename.scr.3 Using the programNano2pst.exe, supplied with the Nanoscope II, this screen file was converted to a TIF filelabelled filename.tif. This TIF file was then cropped to remove unnecessary white space andlabels using Corel PhotoPaint 7 and stored as a PCX format file called filename.pcx. The file“filename.pcx” was loaded into Un-Scan-it Version 3 (Silk Scientific Corporation), wasdigitized, and was stored as a text file named filename.prn.

The text file was imported into Microsoft Excel Version 7.0a, and the raw force data wereconverted into a force-distance curve. The text file consists of X-Y pairs, where the X values are

3 File names were always of the form yymmddxx, e.g., 98jl2901. The numbers xx were incremented by one for eachforce curve stored, starting with 01.

Calculation of Force-Distance Curves from Nanoscope II Raw Force Data

B-2

the position of the piezoelectric crystal on which the Inconel 600 surface is mounted, and the Yvalues are the cantilever deflection signal. By plotting the X-Y values and taking the slope of thelinear part of the force curve (labelled region of constant compliance in Figure B-1) thesensitivity SENS is obtained. The cantilever deflection, DEFLEC, is obtained from the rawcantilever data, Y, by

DEFLEC = Y/SENS . (B-1)

The separation, h, is then calculated from the raw piezoelectric position data, X, by

h = X + DEFLEC + OFFSET . (B-2)

Since the AFM does not directly give the zero of separation, the location of zero separation wastaken to be the intersection of the best straight line through the constant compliance part of theforce curve and the best straight line through zero force part of the curve. The term OFFSET inthe above equation corrects the separation to this calculated zero separation.

The force F at each value of separation was then calculated by

F = DEFLEC * k, (B-3)

where k is the spring constant of the cantilever.


B-3

Best Fits of Equation (1-6) to Force-Distance Data for the Magnetite–Water–Inconel 600and Hematite–Water–Inconel 600 Systems

-0.05

0

0.05

0.1

0.15

0.2

0 20 40

Separation (nm)

pH 9

0, 5

50

-0.05

0

0.05

0.1

0.15

0.2

0 20 40

Separation (nm)

pH 100

50

5

-0.05

0

0.05

0.1

0.15

0.2

0 20 40

Separation (nm)

pH 8

0

5

50-0.05

0

0.05

0.1

0.15

0.2

0 20 40

Separation (nm)

pH 7

0, 5, 50

-0.05

0

0.05

0.1

0.15

0.2

0 20 40

Separation (nm)

pH 6

50

0

5

Figure B-2Fits of F/r versus separation for the system magnetite–Inconel 600 as a function ofammonia concentration for pH = 6 to 10. The concentration of added amine is indicated inunits of mM. Units for F/r are mN/m. Energy required by a 1- µm particle to surmount aforce barrier of 0.04 mN/m is 49kT.


B-4

-0.04

0

0.04

0.08

0.12

0 20 40

Separation (nm)

pH 9

0, 5

50

-0.04

0

0.04

0.08

0.12

0 20 40

Separation (nm)

pH 8

0, 5

50

-0.04

0

0.04

0.08

0.12

0 20 40

Separation (nm)

pH 7

0, 5

50

-0.04

0

0.04

0.08

0.12

0 20 40

Separation (nm)

pH 6

50

0, 5

-0.04

0

0.04

0.08

0.12

0 20 40

Separation (nm)

pH 100, 5

50

Figure B-3Fits of F/r versus separation for the system magnetite/–nconel 600 as a function ofethanolamine concentration for pH = 6 to 10. The concentration of added amine isindicated in units of mM. Units for F/r are mN/m. Energy required by a 1- µm particle tosurmount a force barrier of 0.04 mN/m is 49kT.


B-5

-0.04

0

0.04

0.08

0.12

0.16

0 20 40

Separation (nm)

pH 90

50

5

-0.04

0

0.04

0.08

0.12

0.16

0 20 40

Separation (nm)

pH 100

50

5

-0.04

0

0.04

0.08

0.12

0.16

0 20 40

Separation (nm)

pH 8

0

5

50-0.04

0

0.04

0.08

0.12

0.16

0 20 40

Separation (nm)

pH 7

0

5

50

-0.04

0

0.04

0.08

0.12

0.16

0 20 40

Separation (nm)

pH 6

50

0, 5

Figure B-4Fits of F/r versus separation for the system magnetite–Inconel 600 as a function ofdimethylamine concentration for pH = 6 to 10. The concentration of added amine isindicated in units of mM. Units for F/r are mN/m. Energy required by a 1- µm particle tosurmount a force barrier of 0.04 mN/m is 49kT.


B-6

-0.15

0

0.15

0.3

0 20 40

Separation (nm)

0, 5 mM

50 mM

pH 9

-0.15

0

0.15

0.3

0 10 20 30 40

Separation (nm)

0 mM

5, 50

pH 10

-0.15

0

0.15

0.3

0 20 40

Separation (nm)

pH 6

5 mM0 mM

50 mM

-0.15

0

0.15

0.3

0 10 20 30 40

Separation (nm)

pH 7

0, 5, 50 mM

-0.15

0

0.15

0.3

0 20 40

Separation (nm)

0, 5, 50 mM

pH 8

Figure B-5Fits of F/r versus separation for the system hematite–Inconel 600 as a function ofammonia concentration for pH = 6 to 10. The concentration of added amine is indicated inunits of mM. Units for F/r are mN/m. Energy required by a 1- µm particle to surmount aforce barrier of 0.04 mN/m is 49kT.


B-7

-0.15

0

0.15

0.3

0 10 20 30 40

Separation (nm)

0, 5 mM

50 mM

pH 10

-0.15

0

0.15

0.3

0 20 40

Separation (nm)

pH 6

5 mM

0, 50 mM

-0.15

0

0.15

0.3

0 20 40

Separation (nm)

50 mM

0, 5 mM

pH 8

-0.15

0

0.15

0.3

0 20 40

Separation (nm)

0, 5 mM

50 mM

pH 9

-0.15

0

0.15

0.3

0 10 20 30 40

Separation (nm)

pH 7

0,5 mM

50 mM

Figure B-6Fits of F/r versus separation for the system hematite–/Inconel 600 as a function ofethanolamine concentration for pH = 6 to 10. The concentration of added amine isindicated in units of mM. Units for F/r are mN/m. Energy required by a 1- µm particle tosurmount a force barrier of 0.04 mN/m is 49kT.


B-8

-0.05

0

0.05

0.1

0.15

0.2

0 10 20 30 40

Separation (nm)

pH 7

0 mM

50 mM

-0.05

0

0.05

0.1

0.15

0.2

0 10 20 30 40

Separation (nm)

0, 5 mM

50 mM

pH 10

-0.05

0

0.05

0.1

0.15

0.2

0 20 40

Separation (nm)

pH 6

5 mM

50 mM

-0.05

0

0.05

0.1

0.15

0.2

0 20 40

Separation (nm)

50 mM

0, 5 mM

pH 8

-0.05

0

0.05

0.1

0.15

0.2

0 20 40

Separation (nm)

0 mM

50 mM

pH 9

5 mM

Figure B-7Fits of F/r versus separation for the system hematite–Inconel 600 as a function ofdimethylamine concentration for pH = 6 to 10. The concentration of added amine isindicated in units of mM. Units for F/r are mN/m. Energy required by a 1- µm particle tosurmount a force barrier of 0.04 mN/m is 49kT.


B-9

Table B-1Change in the surface charge density (mC/m 2) on magnetite after the adsorption of amine.A positive change corresponds to a surface that is less negative. A surface chargedensity of 1 mC/m 2 corresponds to approximately 1 electronic charge per 200 nm 2.


5 mM 50 mM 5 mM 50 mM 5 mM 50 mM 5 mM 50 mM

7 0 0 1.3 5.5 -0.27 0.56 0 0.45

8 -3.8 0.78 1.9 3.2 -0.46 2.0 0.49 0.64

9 0 3.5 1.6 2.3 0 2.5 -0.89 1.1

10 1.0 4.5 2.1 3.3 0 2.8 0.21 2.6

Table B-2Change in the surface charge density (mC/m 2) on hematite following the adsorption ofamine. A positive change corresponds to a surface that is less negative. A surfacecharge density of 1 mC/m 2 corresponds to approximately 1 electronic charge per 200 nm 2.


5 mM 50 mM 5 mM 50 mM 5 mM 50 mM 5 mM 50 mM

7 0 0 - 0.8 0.2 2.2 0 0

8 0.2 0.1 - 2.3 0.2 2.6 -6.4 0

9 -1.3 -0.8 0.9 4.0 0 2.3 0.3 3.5

10 0 0.3 2.7 2.7 0 2.1 3.1 3.6

C-1

C CHEMISTRY, OPERATING CONDITIONS, ANDRESULTS FOR LOOP TEST

Chemistry, Operating Conditions, and Results for Loop Tests

C-2

Table C-1Loop chemistry and operat ing conditions for each test

Experimental Con ditions

Exp.ID P q" m" C Tank C Loop [A] Tank [A] Loop pH Tank pH loop O2 N2H2

MPa kW/m² kg/m²s mg/kg mg/kg mmol/kg mmol/kg pH unit pH unit µg/kg µg/kg

EXPERIMENTS WITH MAGNETITEMORPHOLINE CHEMISTRYD097 5.7 222 295 238 1.0 0.861 0.178 9.21 9.31 153 40D101 5.7 223 298 66 0.76 2.169 0.249 9.21 9.18 3 45

D119 5.5 225 316 950 1.12 0.683 0.142 9.24 9.29 0 25

AMMONIA CHEMISTRY

D120 5.7 239 318 882 2.90 0.143 0.071 9.74 9.58 0 2DIMETHYLAMINE CHEMISTRYD100 5.7 225 287 70 0.52 0.004 0.027 9.17 9.12 0 75D105 5.6 223 304 62 0.88 0.377 0.046 9.19 9.17 0 100POTASSIUM HYDROXIDE CHEMISTRYD098 5.6 223 294 122 0.78 0.068 0.036 9.02 8.85 0 53D103 5.7 224 317 72 0.54 0.048 0.043 8.98 9.03 10 43PYRROLIDINE CHEMISTRYD099 5.6 227 299 134 1.48 0.035 0.024 9.19 9.04 0 75D117 5.6 227 284 46 0.80 0.063 0.031 9.05 9.01 0 403-METHOXYPROPYLAMINE CHEMISTRYD102 5.6 221 304 88 1.06 0.355 0.077 9.73 9.63 0 60

D104 5.8 219 319 62 0.76 0.976 0.087 9.68 9.62 3 554-AMINOBUTANOL CHEMISTRY

D116 5.6 225 271 16 0.36 0.157 0.054 9.39 9.52 3 60

D118 5.7 222 304 74 0.66 0.146 0.040 9.47 9.51 0 43

EXPERIMENTS WITH HEMATITEETHANOLAMINE CHEMISTRYD108 5.6 228 296 58 0.36 0.188 0.075 9.55 9.47 0 0

D111 5.7 232 298 38 0.68 1.146 0.095 9.57 9.46 169 0


D106 5.7 211 299 66 1.38 0.195 0.095 9.30 9.22 0 55

D114 5.5 225 288 128 1.92 0.089 0.050 9.20 9.02 405 0


D107 5.5 227 318 24 1.56 0.135 0.027 8.97 8.95 23 38D109 5.6 229 292 104 9.60 0.143 0.037 8.92 8.94 125 0

D113 5.5 226 287 16 0.22 0.089 0.032 8.95 8.94 8 0

D115 5.6 231 278 150 1.82 0.205 0.022 8.99 9.01 213 0


D110 5.7 230 300 40 0.54 0.510 0.012 9.65 9.61 265 0

D112 5.5 233 285 40 0.48 0.222 0.080 9.77 9.70 74 0


C-3

Table C-2Database of all the H3 loop deposition res ults for magnetite, Fe3O4.

Remarks Exp.ID K• for Flow Boiling, kg/m²s K• for Forced Convection, kg/m²sfor 0 < X < 0.25 at X ~ 0.5 at single

phaseat X ~ 0.03 at X ~ 0.25 at X ~

0.5MORPHOLINE CHEMISTRYHigh A D034 1.70E-03High A D035 1.58E-03Low A D097 4.68E-04 6.19E-03 3.37E-04 2.60E-04 3.13E-04 1.54E-03Low A D101 2.36E-04 7.89E-04 1.21E-04 8.93E-05 1.41E-04 8.85E-04Low A D119 3.41E-04 9.00E-04 6.13E-05 1.83E-04 1.57E-04 6.29E-04 ETHANOLAMINE CHEMISTRYHigh A D036 8.91E-04High A D037 1.22E-03"Etched"surf

D052 2.19E-03

"Etched"surf

D053 2.86E-03

Low A D068 5.44E-04 1.80E-03Low A D071 6.57E-04 1.01E-02Low A D083 4.54E-04 8.06E-03 5.46E-04Low A, SP D081 1.56E-04Low A, SP D082 5.89E-05AMMONIACHEMISTRYHigh A D038 1.17E-03High A D039 6.20E-04Low A D120 8.29E-05 1.33E-04 5.18E-05 6.73E-05 3.88E-05 3.22E-04DIMETHYLAMINE CHEMISTRYHigh A D042 5.69E-04High A D043 5.38E-04High A D050 6.51E-04High A D051 7.11E-04Low A D069 1.27E-04 1.75E-03Low A D072 8.96E-05 3.67E-04Low A D084 1.19E-04 3.14E-04 1.24E-04Low A D100 1.24E-04 9.40E-04 1.05E-04 3.97E-05 8.62E-05 1.01E-03Low A D105 1.21E-04 1.10E-04 3.94E-05 6.19E-05 7.80E-05 1.02E-04POTASSIUM HYDROXIDE CHEMISTRYLow D070 1.29E-04 1.87E-03

Low D073 2.13E-04 2.58E-03 1.51E-04

Low D098 9.99E-04 3.09E-04 5.15E-04 6.87E-04 9.58E-04 1.94E-02

Low D103 2.62E-04 6.60E-04 1.54E-04 2.58E-04 1.94E-04 3.47E-03PYRROLIDINE CHEMISTRYLow A D099 3.16E-04 8.01E-04 2.62E-04 4.08E-04 4.11E-04 2.30E-04Low A D117 8.12E-04 5.23E-04 1.81E-04 3.95E-04 2.18E-04 5.11E-043-METHOXYPROPYLAMINE CHEMISTRYLow A D102 1.46E-04 5.22E-04 1.15E-04 9.84E-05 1.89E-04 2.57E-04Low A D104 6.19E-04 2.03E-04 7.56E-05 2.73E-04 4.10E-04 7.01E-044-AMINOBUTANOL CHEMISTRYLow A D116 5.94E-04 5.20E-04 2.09E-04 4.78E-04 3.39E-04 1.03E-03Low A D118 3.04E-04 2.71E-04 1.91E-04 2.48E-04 1.70E-04 1.90E-04Legend: "Low A"-low amine, "High A"-high amine. The new results (from the current program) are in bold type.


C-4

Table C-3Database of all the H3 loop deposition res ults for hemat ite, Fe2O3

Remarks Exp.ID K• for Flow Boiling,kg/m²s

K• for Forced Convection, kg/m²s

for 0 < X <0.25

at X ~0.5

at singlephase

at X ~ 0.03 at X ~ 0.25 at X ~ 0.5

MORPHOLINE CHEMISTRYO2 D046 2.74E-02O2 D047 2.70E-02O2 D056 1.33E-02O2 D057 5.14E-03ETHANOLAMINE CHEMISTRYO2 D060 2.10E-03O2 D061 2.17E-02no O2 D079 2.34E-04 1.27E-02 6.91E-04no O2 D080 1.09E-03 2.69E-02 5.10E-04no O2 D108 1.24E-03 1.59E-03 7.61E-04 2.55E-03 6.72E-04 3.63E-03O2 D111 8.60E-03 1.20E-03 9.81E-04 3.48E-04 4.38E-04 4.40E-04AMMONIA CHEMISTRYO2 D048 8.84E-03O2 D049 2.69E-03O2 D058 4.28E-02O2 D059 2.52E-02DIMETHYLAMINE CHEMISTRYO2 D077 3.46E-03 2.68E-02 3.30E-03O2 D078 5.32E-04 5.00E-02 1.16E-03no O2 D106 7.81E-04 6.08E-04 7.44E-04 3.56E-04 3.43E-04 4.87E-04O2 D114 5.88E-03 1.35E-02 1.51E-04 1.87E-04 9.11E-04 3.14E-03POTASSIUM HYDROXIDE CHEMISTRYno O2 D107 3.09E-04 5.09E-04 2.77E-04 1.57E-04 2.15E-04 7.22E-04O2 D109 3.08E-03 2.73E-04 1.83E-04 2.91E-04 6.48E-04 1.51E-04O2 D113 1.77E-03 4.25E-03 1.88E-04 7.54E-04 1.07E-03 2.79E-02O2 D115 4.26E-03 2.82E-03 1.17E-04 2.58E-04 7.97E-04 1.67E-033-METHOXYPROPYLAMINE CHEMISTRYO2 D110 6.01E-04 1.57E-04 1.64E-04 2.17E-04 1.48E-04 8.74E-05O2 D112 1.07E-03 7.72E-04 1.20E-04 1.45E-04 9.64E-05 9.32E-05

Legend: "O2"-dissolved oxygen present in loop water, "no O2"-no oxygen present. The newresults (of the current program) are in bold type.


C-5

Figure C-1Normalized deposition rate as a function of stea m quality. �� indi cates locations along theheated (diabatic) test sect ion. �� indicates l ocati ons on the unheated (adiabatic) testsect ion.



C-6

Figure C-3Normalized deposition rate as a function of stea m quality. �� indicates locatio ns along theheated (diabatic) test sect ion. �� indicates l ocati ons on the unheated (adiabatic) testsect ion.



C-7




C-8




C-9




C-10




C-11




C-12


Figure C-16Normalized deposition rate as a function of stea m quality. �� indi cates locations along theheated (diabatic) test sect ion. �� indicates l ocati ons on the unheated (adiabatic) testsect ion


C-13




C-14




C-15




C-16




C-17

Magnetic Field In side I-600 Test Section

The magnetic flux density was measured inside a I-600 test section on the B250 H3 loop using aGauss/Tesla meter with two types of Hall-effect probes: axial and transverse. The magnetic fieldis of interest because it could affect the movement of ferromagnetic magnetite particlesapproaching the tube wall during the deposition experiments and thus possibly alter the results.The test section is electrically heated using AC current. The electrical current is 600 A during atypical deposition experiment. Considering the Ampère’s Law and the test section symmetry, nomagnetic field is expected inside the test section in an ideal case. However some magnetic fieldis expected to be present in a real system.

The test set up was prepared as follows: the probe was inserted into a 5/16” ( 7.94 mm) ODTeflon tubing plugged at one end with a cork stopper. This Teflon tubing was then inserted intothe I-600 test section and a ½” (12.7 mm) tee was installed to allow a 1 L flow throughout thetest section. The heated test section was 1.6 m. The probe tip was located 25 cm from the testsection inlet.

The conditions during the measurements were as follows: flow 1 L/min, pressure < 0.25 MPa,inlet temperature 22°C - 63°C and outlet temperature up to 100°C. The current was varied from0 to 300 A. Three series of measurements were made using: (1) axial probe, (2) transverseprobe and (3) transverse probe rotated 90 degrees in respect to test 2.

The results of these measurements are shown in Figure 1. The values of the magnetic fluxdensity extrapolated to the conditions expected during the deposition experiments are:

0.1399 mT - in the tube axial direction,

2.0488 mT - in the tube transverse direction,

1.5585 mT - in the tube transverse direction, perpendicular to the previous direction.


C-18

Magnetic field inside I-600 test section

y = 0.0035x - 0.026

R2 = 0.9981

y = 0.00024x - 0.00304

R2 = 0.97365

y = 0.0026x - 0.0292

R2 = 0.9936

0

0.5

1

1.5

2

2.5

3

0 100 200 300 400 500 600 700 800

Current (A)

Mag

netic

Flu

x D

ensi

ty (

mT

)

Axial direction

Transverse direction

Transverse rotated 90°

Linear (Transverse direction)

Linear (Axial direction)

Linear (Transverse rotated 90°)

Forcast for I=600 AMFD=0.1399 mT

Forcast for I =600 AMFD=1.5585 mT

Forcast for I=600 AMFD=2.0488 mT

Figure C-25Magnetic fl ux density fr om axial and tra nsverse di rect ion

D-1

D THERMOHYDRAULIC PARAMETERS UNDER TWO-PHASE FLOW WITH FOCUS ON STEAM GENERATORFOULING

STEAM QUALITY

The mass quality is defined as the mass fraction of the vapour phase in the total mass flow of the2-phase mixture:

Xm

mG

TP

= (D-1)

The thermodynamic quality is defined as

XH H

HTP L SAT

L G

=−

−

, (D-2)

The mass quality and the thermodynamic quality are equal if the system is under thermodynamicequilibrium. Real diabatic systems cannot be in thermodynamic equilibrium, and the massquality and thermodynamic quality are, in general, different. Hsu and Graham (1986) give anexample of non-equilibrium quality distribution. Their sketch is reproduced in Figure D-1. Itdemonstrates that the true quality exceeds the equilibrium quality at subcooled boiling and atflow-boiling with low steam quality. The opposite is true for high steam qualities.

All calculations presented in this report were performed under the assumption that the massquality equals the thermodynamic quality.

Thermohydraulic Parameters Under Two-Phase Flow with Focus on Steam Generator Fouling

D-2

Figure D-1Schematics of the steam quality change during a non-equilibrium 2-phase flow. Re-printedfrom Tong and Tang (1997) should the reference be Hsu and Graham (1986)?.

SUPERFICIAL MASS FLUX, VELOCITY, AND REYNOLDS NUMBER

The superficial mass flux of liquid, m'L, is calculated as if only liquid flowed in the channel. Theliquid superficial velocity is obtained by dividing the superficial mass flux by liquid density.

The liquid-only Reynolds number is defined as

Re'

LL

L

m D=

µ . (D-3)

This value is identical to the Reynolds number of the liquid film

Re ,L f

f L

L

u=

ρ δµ

4 , (D-4)

which justifies the usage of the Reynolds number based on the liquid superficial mass flux.

Analogous quantities can be obtained for the gas phase. The justification for their usage is thatthe gas phase typically occupies most of the channel cross-sectional area; therefore, thesuperficial values are close to the real values for gas.


D-3

FLOW PATTERNS

The Hewitt and Roberts flow pattern map (Whalley, 1987) can be used for approximateevaluation of the flow patterns for vertical upwards flow of water–steam mixture over a range ofpressures in small diameter tubes (10 to 30 mm).

Figure D-2 shows a flow map from Whalley (1987). It is overlapped with a graph obtained forwater-steam mixture at 5.6 MPa at different steam qualities and mass fluxes. The underlyingflow map is based on Whalley (1987). For the experimental conditions of m" = 300 kg/m²s, thegraph predicts that slug flow occurs below 5% quality, followed by the churn flow regime (up toX ≈ 18%), followed by annular flow. The values on the axes may be interpreted as the liquid-and gas-phase momentum fluxes.

Figure D-2Hewitt and Roberts flow pattern map (Whalley, 1987) for vertical upwards flow inside atube.

An analytical criterion for the transition from churn to annular flow is that of Taitel and Dukler(L. K.H. Leung and D.C. Groeneveld, Chalk River Laboratories, personal communication,1998). According to this criterion, annular flow occurs if

( )( )3112

1

4.

'm Xg G L Gσ ρ ρ ρ− < . (D-5)

This criterion predicts that, under the experimental conditions, the transition to annular flowregime would occur at X ≈ 0.20. Another simple, analytical criterion for the transition fromchurn to annular flow is given by Wadekar and Kenning (1997):


D-4

jG* <1 for slug/churn flow, and jG

* >1 for annular flow, where,

( )( )j

m X

gDG

L G G

*.

'=−ρ ρ ρ 0 5 . (D-6)

According to this criterion, under the experimental conditions the transition from churn toannular flow would occur at quality X ≈ 0.16.

Annular flow is defined as "a flow regime of 2-phase gas-liquid flow characterized by thepresence of a liquid film flowing on the channel wall and with the gas flowing in the gas core"(Hewitt et al., 1997). The numbers given above should be treated as approximate only since theflow maps are not exact. Thus the boundaries for the transitions between the flow patterns arenot sharp.

It should also be borne in mind that these flow maps were created mostly for adiabaticconditions. There are several reasons for the presence of heat transfer to affect the transitions.At the experimental conditions with heat flux, the true quality is expected to exceed thethermodynamic quality for low qualities, and lag behind the thermodynamic quality at highqualities. Another important aspect of annular flow is its developing nature. Up to 400 tubediameters may be required to achieve "equilibrium" (Whalley, 1987). Examples of phenomenathat require significant length for developing are the entrained fraction of the liquid, whichincreases steadily along the tube, and the film thickness, which decreases. A true equilibriummay never be achieved, even under adiabatic conditions because of the pressure drop andflushing off the liquid. Under diabatic conditions, annular flow is by definition developingbecause of constant increase in steam quality. Therefore, diabatic and adiabatic flow patterns aregenerally different, and adiabatic flow maps are used for diabatic conditions for lack of betterdata.

Hosler (cited in Tong and Tang, 1997) conducted measurements of flow pattern transition forflow boiling under diabatic conditions in rectangular channels. According to his data, thetransition to annular flow would occur at X ≈ 0.20 at the conditions of our experimental program.Plug, churn, and annular flow patterns have their equivalents in 2-phase flow in rod bundles.The transitions between the patterns occur, however, at different conditions. According toVankateswarara (cited in Tong and Tang, 1997), the transition to annular flow in rod bundlestakes place at a gas phase superficial velocity of 7 to 11 m/s for the liquid flow rates of interest.This velocity s equivalent to 0.65 < X < 1.0 under our experimental conditions. The quality atwhich the transition takes place will decrease linearly with increasing mass flux.

The flow patterns are important for system characterization because the geometry of the flow isdifferent for different flow patterns. The heat-transfer characteristics of annular flow are verydifferent from those of slug–churn flow. There is almost no difference between the slug and thechurn flow regions; from the point of view of heat transfer, churn flow may be treated as aspecial case of slug flow (Wadekar and Kenning, 1997).


D-5

VOID FRACTION

Void fraction is defined as the volume fraction of the gas phase in the gas-liquid mixture over alength of the flow channel:

α =+

V

V VG

L G

. (D-7)

It can be presented in terms of quality and the slip ratio (Hewitt et al.,1994):

α ρρ

=+ −

X

X S X G

L

( )1 . (D-8)

For low values of the reduced pressure (ratio of the pressure to the critical pressure,approximately 4 under the experimental conditions), the empirical correlation of Armand isrecommended for prediction of void fraction in the annular flow regime (Hewitt et al., 1997):

αβ

β

= −+

+−

+

14

8

7

51

8

7

b

b

, (D-9)

where,

β ρ

ρ ρ

=+

m

m m

G

G

G

G

L

L

'

' ', (D-10)

b a LL

G

=

4 0 125

0 5

(Re ) .

.ρρ

, (D-11)

a FrL= + − +0 69 1 4 219. ( )( . )β . (D-12)

The constants a, b and β are introduced for convenience of notation only, and do not have specialdefinitions.

The liquid-only Froude number is

Frm

gDL

L

L

=' 2

2ρ . (D-13)


D-6

Another way to estimate the void fraction is to use Equation (D-8) with the slip ratio calculatedaccording to an existing empirical correlation, e.g., Premoli correlation, which is discussed later.Estimation of the void fraction can also be made by using the homogeneous model (Equation(D-8) with S = 1). This tends to overestimate the true void fraction. Under the experimentalconditions, the void fraction is expected to reach over 90% for X ~ 0.5.

SLIP RATIO

The slip ratio is the ratio of the velocity of the gas phase to the velocity of the liquid phase:

Su

uG

L

= . (D-14)

The void fraction and slip ratio are closely related. The slip ratio can be calculated from the voidfraction (e.g., the Armand correlation) and from Equation (D-8).

The Premoli correlation (also known as the CISE correlation) can be used to calculate the slipratio directly:

S Ey

yEyE= +

+

−

1

112

2 , (D-15)

y =−β

β1 , (D-16)

β ρρ ρ

=+ −

X

X XL

L G( )1 , (D-17)

E L

G1

0 19

0 22

1578=

−. Re .

.ρρ

, (D-18)

E We L

G2

0 51

0 08

0 0273=

−

−

. Re .

.ρρ

, and, (D-19)

Wem DL

L

= ' 2

σρ . (D-20)

The constants E1, E2, y, and β are introduced for convenience of notation and do not have specialdefinitions.


D-7

Another particularly simple method of calculating the slip ratio is the Chisholm correlation(Whalley, 1987):

S X L

G

= − −

1 1

1

2ρρ

. (D-21)

An even simpler, but less accurate, correlation is the Zivi correlation (Whalley, 1987):

S L

G

=

ρρ

1

3

. (D-22)

The accuracy of the various correlations has been observed to decrease in the following order:Premoli > Chisholm, > Zivi (Whalley, 1987). The standard deviation of the mean densitycalculated on the basis of the Premoli correlation is approximately 40%.

TWO-PHASE DENSITY

The 2-phase density is defined as (Hewitt et al.,1994)

ρ α ρ αρTP L G= − +( )1 , (D-23)

which, for homogenous flow, is equivalent to

ρρ ρTP

G L

X X= + −

−1

1

. (D-24)

VELOCITY OF THE PHASES

When the thermodynamic quality and the void fraction (or the slip ratio) are known, the velocityof the liquid and gas phases are simply

um

um

LL

LG

G

G

=−

='

( ),

'

1 α ρ αρ . (D-25)

The gas velocity calculated using this equation is a very good approximation of the value in realsystems. For liquid, however, the radial velocity exhibits a considerable profile as the tube wallis approached and, therefore, the calculated value represents only a mean.


D-8

SINGLE-PHASE SHEAR STRESS, FRICTION VELOCITY, FRICTIONFACTOR, AND PRESSURE DROP

The Fanning equation represents the force balance for flow inside a channel:

A P Aflow fric wall∆ = τ . (D-26)

The shear stress is

τρ

=f uFanning

2

2 . (D-27)

The frictional velocity is defined as

u* = τρ

. (D-28)

From Equations (D-27) and (D-28), the frictional velocity is

uf

uFanning* =2 . (D-29)

Two different friction factors are found in the literature: the Moody friction factor and Fanningfriction factor. The relationship between them is

f fMoody Fanning= 4 . (D-30)

For laminar flow, the Hagen-Poiseuille equation is used for prediction of the single-phasefriction factor:

f Fanning = 64

Re . (D-31)

For turbulent flow in smooth pipes, the Blasius equation may be used:

fFanning = < <0 0793000 100000

1 4

.

Re, Re

/ . (D-32)

The implicit Colebrook-White formula (Hewitt et al., 1997) is recommended for prediction ofthe Moody friction factor for transitional and fully developed single-phase turbulent flow (gas orliquid) in fully rough or smooth tubes:


D-9

10 86

37

2 510 5 0 5f

D

fMoody Moody. .. log

/

.

.

Re= − +

ε . (D-33)

The single-phase frictional pressure drop is predicted from the D'Arcy-Weisbach equation:

∆PL

Df uSP fric Moody L, = 1

22ρ . (D-34)

TWO-PHASE PRESSURE DROP

The 2-phase pressure drop consists of 3 parts: the acceleration pressure drop, the gravitationalpressure drop, and the frictional pressure drop:

∆ ∆ ∆ ∆P P P PTP TP acc TP grav TP fric= + +, , , . (D-35)

The 2-phase acceleration pressure drop is calculated from the momentum balance (Collier andThome, 1994):

∆ ∆P mX X

TP accG L

, '( )

( )= + −

−

2

2 21

1αρ α ρ . (D-36)

The 2-phase gravitational pressure drop is calculated from (Collier and Thome, 1994):

( )∆ ∆P g zTP grav G L, sin( ) ( )= + −θ αρ α ρ1 , (D-37)

where α is the mean void fraction over the tube length ∆z:

α α=+

∫1

∆

∆

zz dz

z

z z

( ) . (D-38)

the integral should be larger in displayed equations, around 18 pt.

The 2-phase frictional pressure drop is calculated from the single-phase frictional pressure drop(as if the flow was liquid-only) and the 2-phase multiplier (Collier and Thome, 1994):

∆ ∆P PTP fric LO L fric, ,= φ2 .(D-39)

When µµ

L

G

< 1000(it is approximately 5.5 for the experimental condition), the recommended

correlation for evaluation of the single-phase multiplier is that of Friedel (Collier and Thome,1994):


D-10

φLO AA A

Fr We2

12 3

0 045 0 035

324= +

.. .

, (D-40)

where:

A X Xf

fL GO

G LO1

2 21= − +

( )

ρρ

, (D-41)

A X X20 78 0 2241= −. .( ) , (D-42)

A L

G

G

L

G

L3

0 91 0 19 0 7

1=

−

ρρ

µµ

µµ

. . .

, (D-43)

Frm

gDTP

TP

= '2

2ρ , (D-44)

Wem D

TP

TP

= ' 2

ρ σ , (D-45)

and ρTP is the homogenous mixture density defined by Equation (D-24). The constants A1, A2

and A3 are introduced for convenience of notation only and do not have special definitions. Thestandard deviation of the Friedler correlation is 40% to 50%, an accuracy considered very goodfor 2-phase flow conditions.

INCEPTION OF DROPLET ENTRAINMENT

As the velocity of a gas increases, the initially stable wall film becomes wavy (incipience ofripples), then the waves become irregular (onset of 2-dimensional ripples), and, with furtherincreased velocity, large-amplitude concentration (density) waves appear (inception of rollwaves); finally, the tops of some of the waves can break and liquid droplets becomes suspendedin the gas core (onset of entrainment).

For entrainment to occur, both liquid and gas flow rates must exceed critical values. The criticalliquid film Reynolds number is predicted by (Collier and Thome, 1994):

Re exp . .,

/

L critG

L

L

G

= +

58504 0 42491 2

µµ

ρρ

. (D-46)

When the above condition is met, the onset of entrainment occurs if the gas volumetric flux islarger than


D-11

j AGG

L

G

=

σµ

ρρ

1 2/

, (D-47)

where the constant A is given different values by different authors: either 1.5 x 10-4 or 2.42 x 10-4

(Collier and Thome, 1994).

For 200 < ReL< 3000, the amount of entrainment is a function of both the vapour and liquid flowrates, and for ReL > 3000, the entrainment depends mainly on the velocity of the vapour (Collierand Thome, 1994).

Another practical entrainment-inception model is presented by Hewitt (1982). The inception ofentrainment occurs when the gas volumetric flux is greater than

j

N for N1

15, Re 1635

0.115m

for N1

15, Re 1635

11.78N Rem

for N1

15, Re 1635

1.35Rem

for N1

15, Re 1635

G

0.8

L

L

GL

L

L

GL

0.8L

1

3

L

L

GL

L

1

3

L

L

GL

=

< >

> >

< <

> <

−

−

µ µ

µ

µ µ

µ

σµ

ρρ

σ ρρσ ρ

ρσ ρ

ρ

, (D-48)

where the viscosity number, Nµ, is defined as

N

g

L

LL G

µµ

ρ σ σρ ρ

=

−

( )

/1 2 . (D-49)

DROPLET ENTRAINMENT RATE

The droplets appear in the gas core when the interfacial shear stress is capable of overcoming theforces of cohesion of the liquid. The droplet entrainment rate can be evaluated from (Collier andThome, 1994)

( )J m m mD

E G L f L critL

G

= ⋅ −

−575 10 5 2

2

0 316

. ' ' ', ,

.

ρσρ

, (D-50)

where m'L,crit is the liquid mass flux corresponding to the critical Reynolds number of the liquiddefined by Equation (D-46). Under diabatic conditions, the boiling process can additionallyenhance entrainment.


D-12

DROPLET DEPOSITION RATE

The droplets entrained in the gas core may be re-deposited onto the liquid film at the tube wall.The droplet deposition rate can be presented as (Hewitt and Govan, 1990a, b)

J K Cd d= , (D-51)

where C, the mean homogenous droplet concentration in the vapour core, is given by

Cm

m mL E

L E

L

G

G

=+

,

,

ρ ρ

, (D-52)

The Govan correlation (Collier and Thome, 1994) can be used for predicting the dropletdeposition coefficient

KD

forC

C

Dfor

Cdep

G G

G G G

=

<

>

−

018 03

0 083 03

1

2

0 651

2

. .

. ..

σρ ρ

ρσ

ρ ρ

. (D-53)

ENTRAINED FRACTION

The fraction of entrained liquid is defined as a ratio of the flow rate of the liquid as droplets tothe total liquid flow rate:

Em

mL drop

L total

= ,

,

. (D-54)

Droplet entrainment is a dynamic process, and the entrained fraction is a result of a steady statewhen the deposition rate equals the entrainment rate.

Annular flow develops slowly (hundreds of tube diameters), and a steady state may never bereached in practical systems because of the pressure drop. Under diabatic condition, the systemis additionally removed from steady state because the quality increases along the tube andtherefore the flow conditions constantly change. Attempts, however, were made to establish thesteady-state value of the entrained fraction.

The simple, but not highly recommended, Ishii-Mishima correlations are presented by Whalley,(1987):


D-13

E u dG L= ⋅ − + +tanh( . Re ). . .7 25 107 2 5 1 25 0 25 , (D-55)

where

( )u u

gG G

G

L G

+ =−

ρ

σ ρ ρ

4

3

1

3

1

4

, (D-56)

d dg L G+ = −

( )ρ ρσ

1

2 . (D-57)

Because the deposition rate, the entrainment rate, and the entrained fraction are interrelated, theequations describing these phenomena must be solved simultaneously.

TURBULENCE INTENSITY IN THE GAS CORE

To describe the turbulence, the fluid velocity may be represented as a sum of 2 components, themean velocity and a fluctuation from the mean (White, 1994):

u u u= + ' . (D-58)

The turbulence intensity is defined as a time-average mean square of the fluctuation:

uT

u dtT

' '2 2

0

1= ∫ . (D-59)

The distribution of the axial velocity of the gas phase was found experimentally to beapproximately normal, as expected for a truly random phenomenon (Azzopardi and Teixeira,1994a). The normality of the circumferential and radial velocity distribution was not tested, butthere is no reason to believe that they are not normal. In the same investigation, the radial andcircumferential turbulence intensity were found to be approximately equal. The axial turbulenceintensity, which is of no interest in this investigation, was found to be higher. The radialturbulence intensity was in the range of 8% to 15% of the axial gas velocity.

For pure gas flow (only gas in the core, no entrainment), the turbulence intensity was shown toexhibit a characteristic profile in the radial direction when made nondimensional with the frictionvelocity (Azzopardi and Teixeira, 1994a), with extrapolated ratios of approximately 0.8 at thetube axis and 2 at the gas-core periphery. Therefore, utilizing Equations (D-26) and (D-28), thegas-core turbulence intensity at the core periphery can be approximated by


D-14

u uD

PG G fric' *,= =2

ρ∆ . (D-60)

The presence of the entrained droplets additionally enhanced turbulence.

The variance of the radial velocity distribution of the liquid droplets entrained in the gas core ispostulated to be proportional to the gas-core turbulence intensity:

u C u CD

Pdrop x RMS f G f G fric' , ,*

,= =2ρ

∆ . (D-61)

Turbulence is scale-dependent, and only turbulence at the particle-size scale and above isrelevant. It is recommended that a better relationship be developed for the velocity distribution ofparticles in turbulent flow, or the value of the correlation factor, Cf be determined.

DROPLET SIZE, VELOCITY AND DISTRIBUTION

Azzopardi and Teixeira (1994b) investigated drop sizes and velocities in vertical annular flow ofan air-water mixture at relatively low mass fluxes of 16 to 48 kg/m²·s for the liquid and 25 to 56kg/m²·s for the gas phase using the phase Doppler anemometry technique. The mean dropletsvelocity was approximately equal to the gas superficial velocity, or 20% lower than thecorresponding local velocities of the gas. Its standard deviation was 9% to 15 %, depending onthe mean velocity (the higher the velocity, the lower the standard deviation). The velocity of thedrops was relatively size-insensitive down to 100 µm, after which there was a tendency for thesmallest investigated droplets (30 µm) to travel up to 25% faster than the largest ones (500 µm),the velocity of the former approaching the velocity of the gas. The radial profile of the dropaxial velocity was relatively flat, with the droplets in the centre travelling 10% to 20% faster.The mean drop size also showed a radial distribution with the droplets closer to the interfacehaving a 12% smaller Sauter diameter:

d

d

d

p

ii

ii

,32

3

2

=∑

∑ . (D-62)

The maximum droplet size is (Hewitt and Hall-Taylor, 1970):

dWe

uC

G G pmax =

−

σρ

, (D-63)

where the critical Weber number, Wec , is approximately 22. The parameter, uG-p, is the relativegas-particle velocity.


D-15

FILM THICKNESS

From the definition of the void fraction and neglecting the volume of the entrained droplets, thefilm thickness can be calculated from

δ α α= − ≈ −D D

21

41( ) ( ) . (D-64)

It has to be emphasized that the film thickness is typically non-uniform because of disturbancewaves of amplitude that are 5- to 6-fold larger than the film thickness (Hewitt et al., 1997), andEquation (D-64) computes the mean value. If the entrainment rate is significant the calculationof the film thickness is less straightforward. One method is to calculate the 2-phase pressuredrop and, through the interfacial shear stress, utilize the correlation for the interfacial frictionfactor to calculate the film thickness.

The interfacial friction factor is calculated by

fu

Fanning ii

G G

, =τ

ρ1

22

. (D-65)

The calculations are conducted for the gas phase because the velocity of the gas is easier toestimate than the velocity of the liquid.

According to Whalley (1987), the interfacial friction factor may be given by either

f fDFanning i Fanning G, ,= +

1 360δ

, (D-66)

or

f fD

Fanning i Fanning GL

G, ,= +

1 24

1

3ρρ

δ

, (D-67)

where fFanning,G is is calculated using Equation (D-32).

These correlations, although probably not very accurate, permit estimation of the liquid filmthickness. A more complicated method is to employ the triangular relationship. The triangularrelationship is a set of dependencies bounding 3 variables: liquid film flow rate (kg/s), film shearstress, and the average film thickness. The triangular relationship permits the calculation of anyone of these variables to be calculated if the values of the two remaining variables are known.


D-16

NOMENCLATURE

D = pipe diameter (m)C = concentration (kg m-3)H = enthalpy (kJ kg-1)J = flux (kg m-2 s-1)K = rate constant (kg m-2 s-1)P = pressure (Pa)Re = Reynolds numberS = slip ratioV = volume (m3)X = mass or thermodynamic quality

d = droplet diameter (m)g = gravitational acceleration (m s-2)j = volumetric fluxm = mass flow (kg s-1)m’ = mass flux (kg m-2 s-1)

t = time (s)u = velocity (m s-1)u* = friction velocity (m s-1)z = length (m)

α = void fractionδ = film thickness (m)µ = dynamic viscosity (kg m-1 s-1)ρ = density (kg m-3)σ = surface tension (N m-1)τ = shear stress (N m-2)

Subscripts

d = depositionE = entrainmentf = filmG = gas or vapourG-p = relative gas-particleL = liquidL-G = vaporizationSAT = saturation temperatureTP = two-phase


D-17

REFERENCES

Azzopardi, B.J. and J.C.F. Teixeira (1994a), "Detailed Measurements of Vertical Annular Two-Phase Flow—Part II: Gas Core Turbulence", J. Fluids Eng. 116, 796-800.

Azzopardi, B.J. and J.C.F. Teixeira (1999b). "Detailed Measurements of Vertical Annular Two-Phase Flow—Part I: Drop Velocities and Sizes", J. Fluids Eng. 116, 792-792.

Collier J.G. and J.R. Thome (1994). Convective Boiling and Condensation, Third Edition,Carendon Press, Oxford.

Hewitt G.F. and N.S. Hall-Taylor (1970). Annular Two-Phase Flow, Pergamon Press, Oxford.

Hewitt G. F. (1982). “Flow Regimes" in Handbook of Multiphase Systems G. Hetsroni ed.,Hemisphere Publishing Corporation / McGraw-Hill Book Company, Washington, New York.

Hewitt G.F. and A.H. Govan (1990a). "Phenomenological Modelling of Non-equilibrium Flowwith Phase change", Int. J. Heat Mass Transfer 33, 229-242.

Hewitt G. F. and A.H. Govan (1990b). "Phenomena and Prediction in Annular Two-phase Flow.Invited Lecture", Advances in Gas-Liquid Flows-1990. Presented at the winter annual meetingof the American Society of Mechanical Engineers, Dallas, Texas, November 25-30, InternationalSymposium on Gas-Liquid Two-Phase Flows (1990: Dallas, Texas).

Hewitt G.F, G.L. Shires, and T.R. Bott (1994). Process Heat Transfer, CRC Press, Boca Raton,New York.

Hewitt G. F., G.L. Shires, and Y.V. Polezhaev (1997). International Encyclopedia of Heat andMass Transfer, CRC Press, Boca Raton, New York.

Hsu, Y.Y., R.W. Graham (1986). Transport Processes in Boiling and Two-Phase Systems,American Nuclear Society, Inc. La Grange Park, Illinois.

Tong L.S. and Y.S. Tang (1997). Boiling Heat Transfer and Two-Phase Flow, Taylor andFrancis, Bristol.

Wadekar, V.V. and D.B.R. Kenning (1990), “Flow Boiling Heat Transfer in Vertical Slug andChurn Flow Region”. Presented at International Heat Transfer Conference, Jerusalem, Israel,1990 August 19-24, Hemisphere Publishing, New York.

Whalley P.B. (1987). Boiling, Condensation, and Gas–Liquid Flow, Clarendon Press, OxfordUniversity Press.

White F.M. (1994). Fluid Mechanics, McGraw-Hill Inc., New York, NY.

E-1

E SEM MICROGRAPHS OF TUBE DEPOSITS

SEM Micrographs of Tube Deposits

E-2

(a) (b)

(c) (d)

(e)

Figure E-1Morphology of surface deposits created under magnetite/morpholine chemistry,Experiment D097

(a) Tube G, flow boiling at X ≈ -0.05 (15°C of subcooling). Relatively few single particles and some clusters present;(b) Tube K, flow boiling at X ≈ 0.10. Numerous single particles possible with some recrystalization; (c) Tube 0, flowboiling at X ≈ 0.25. Some particles and clusters present, possible with recrystalization. Some needle-shaped crystals;(d) Tube U, flow boiling at X ≈ 0.50. Surface completely covered with needle-shaped crystals, individual particlesvisible on the top of the crystals. This is the region in which the deposition rate increases rapidly. This depositionmorphology is observed only occasionally--the frequency of its observation may indicate that a coincidence of factorsis necessary for it to occur, or it may be a reflection of the transitory nature of the crystals. The identity of the phasewas not established, goethite is suspected. (e) Tube AD, two-phase forced convection (unheated test section) at X ≈0.03. The particles deposited as dispersed single particles. This is a typical morphology for deposits formed undernon-boiling conditions (either single- or two-phase conditions at low X).


E-3

(a) (b)

(c) (d)

(e)

Figure E-2Morphology of surface deposits created under magnetite/morpholine chemistry, run D119

This experiment aimed to achieve high surface coverage. In reality, only moderate surfacecoverage was obtained, but the deposit consolidation was among the highest ever observed. (a),(b), and (c) Tube B, forced convection/subcooled flow-boiling at X ≈ -0.2 (~70°C subcooling).Well consolidated aggregates of particles, approximately 10 µm in size. (d) and (e), tube G, flowboiling at X ≈ -0.05 (~15°C of subcooling). Significant deposit clustering/re-crystalization leadsto crystals exceeding 10 µm in size. In contrast with the previous sample, the aggregates are notdistributed uniformly over the surface.


E-4

(a) (b)

Figure E-3Morphology of surface deposits created under magnetite/ammonia chemistry, run D120

This experiment aimed to achieve high surface coverage. Only moderate coverage was obtained,but the deposit consolidation was among the highest ever observed. (a) Tube B, forcedconvection/flow boiling at X ≈ -0.2 (~70°C subcooling). (b) Tube G, flow boiling X ≈ -0.05(~15°C subcooling). In both cases, significant deposit clustering and re-crystalization leads tostructures exceeding 10 µm in size.


E-5

(a) (b)

(c) (d)

(e) (f)

Figure E-4Morphology of surface deposits created under magnetite/dimethylamine chemistry (D100and D105)

(a) and (b) Tube B, flow boiling at X ≈ -0.2 (~70°C subcooling). Clusters of particles.(c) Tube G, flow boiling X ≈ -0.05 (~15°C subcooling). Undeveloped structures and someparticles in the region of approximately zero steam quality (nucleate boiling). (d) Tube K, flowboiling X ≈ 0.1. Undeveloped structures. (e) Tube O, flow boiling at X≈ 0.3, just upstream ofthe region of rapidly increasing deposition rate. Undeveloped structures. (f) Tube U, X ≈ 0.5,the region of rapidly increasing deposition rate. Single particles and small clusters.


E-6

(a) (b)

Figure E-5Morphology of deposits created under magnetite/potassium hydroxide chemistry

(a) D098, Tube G, X ≈ -0.05 (~15°C subcooling). “Undeveloped” structures characteristic for thenucleate boiling region, which appear to reduces the sharpness of the surface details. (b) D103,Tube AH, two-phase force convection (no heat transfer) at X in the area of the very rapidincrease of the deposition rate).


E-7

(a) (b)

(c) (d)

(e) (f)

Figure E-6Morphology of surface deposits created under magnetite/pyrrolidine chemistry control

(a) D099, Tube B, forced convection / subcooled flow boiling, X ≈ -0.2 (~70°C subcooling).Clustered particles. (b) D099, tube G, X ≈ -0.05 (~15°C subcooling). Undeveloped structures.(c) D117, Tube B, flow-boiling X ≈ -0.2 (~70°C subcooling). Needles of crystals approximately1 µm long. (d) D117, tube G, X ≈ -0.05 (~15°C subcooling). Needles of crystals 0.3 µm longand less. (e) D117, Tube K, X ≈ 0.10 (as well as further downstream). Isolated particles.


E-8

(a) (b)

(c) (d)

Figure E-7Morphology of surface deposits created under magnetite/3-methoxypropylaminechemistry (experiment D102)

(a) and (b) Tube B, forced convection/subcooled flow boiling, X ≈ -0.2 (~70°C subcooling).Particle clustering. (c) Tube G, flow boiling, X ≈ -0.05 (~15°C subcooling). Undevelopedstructures. (d) Tube K, X ≈ 0.10. Individual particles (little clustering).


E-9

(a) (b)

(c) (d)

Figure E-8Morphology of surface deposits created under magnetite/4-aminobutanol chemistry

(a) D116, Tube B, forced convection/subcooled flow boiling, X ≈ -0.20 (70°C of subcooling).Particle clustering. (b) D118, Tube G, flow boiling, X ≈ -0.05 (15°C of subcooling).Undeveloped structures often associated with nucleate boiling region. (c) D116, Tube K flowboiling, X ≈ 0.10. Small crystals/isolated particles. (d) D116, Tube AH two-phase forceconvection mass transfer (unheated area) X ≈ 0.50, (region of the rapid deposition rate increase).The particles are preferentially captured on the asperity protruding into the flow, particularly onits outermost surface. This is a direct illustration that the transport and attachment are governingthe observed deposition, not re-entrainment (in which case, the cavities would be expected to fillup first).


E-10

(a) (b)

(c) (d)

Figure E-9Morphology of surface deposits created under hematite/ethanolamine chemistry, D108 andD111

(a) Tube B forced convection/subcooled flow boiling, X ≈ -0.20 (~70°C of subcooling). Largeparticle clusters, up to 10 µm. (b) and (c) Tube G, nucleate flow boling, X ≈ -0.05 (~15°C ofsubcooling). “Amorphous” features typically associated with nucleate boiling region. (d) D111,Tube O, flow boiling, X ≈ 0.30. Single particles/crystals.


E-11

(a) (b)

Figure E-10Morphology of surface deposits created under hematite/dimethylamine chemistry,hydrazine present, no oxygen, experiment D106

Magnetite particles can be detected only on some micrographs. (a) Tube B, forcedconvection/subcooled flow boiling, X≈-0.2 (70°C subcooling), small clusters. (b) Tube K, flowboiling, X ≈ 0.1, single particles.


E-12

(a) (b)

(c) (d)

Figure E-11Morphology of surface deposits created under hematite/potassium hydroxide chemistryD113 and D115

(a) and (b) Tube B, forced convection/subcooled flow boiling, X ≈ -0.2 (70°C subcooling).Typical clusters, approximately 10 µm in size. (c) D115, Tube G subcooled flow boiling, X ≈ -0.05 (15°C subcooling). (d) D113, Tube U, subcooled flow boiling, X ≈ 0.5. No particlesdetactable.


E-13

(a) (b)

(c) (d)

(e)

Figure E-12Morphology of surface deposits created under hematite/3-methoxypropylamine chemistry,experiment D110

(a) and (b) Tube B, forced convection/subcooled flow boiling, X ≈ -0.2 (70°C subcooling).Typical clusters. (c) and (d) Tube G subcooled flow boiling, X ≈ -0.05 (15°C subcooling).Undeveloped “amorphous” features in the region of nucleate boiling, with ~ 1 µm needle-likecrystals appearing. (e) Tube U, flow boiling, X ≈ 0.50. In the higher steam quality region, thesurface features are sharp again, no amorphous material.


E-14

(a) (b)

(c) (d)

Figure E-13Morphology of surface deposits created under hematite/3-methoxypropylamine chemistry,experiment D112

(a) and (b) Tube B, subcooled flow boiling, X ≈ -0.2 (70°C subcooling). Heavy deposit,clustering typical for these conditions. (c) Tube G, subcooled flow boiling X ≈ -0.05 (15°Csubcooling). “Amorphous” material on the surface. (d). Tube O, flow boiling X ≈ 0.3. Needle-shaped crystals.

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