CHAPTER 1INTRODUCTION

Shell & tube heat exchangers are used extensively throughout the process industry and as such a basic understanding of their design, construction and performance is important to the practising engineer. The objective of this project is to provide a concise review of the key issues involved in their thermal design without having to refer to the extensive literature available on this topic.The design of a plate & frame heat exchanger involves the consideration of many interacting design parameters which can be summarised as follows:Process1. Process fluid assignments.2. Selection of stream temperature specifications.3. Setting plate side pressure drop design limits.4. Setting fluid velocity limits through plates.5. Selection of heat transfer models and fouling coefficients for.

Mechanical1. Selection of heat exchanger TEMA layout and number of passes.2. Specification of plate parameters - size, layout and material.3. Setting upper and lower design limits on plate length.

There are several software design and rating packages available, including Aspen BJAC, HTFS and CC-THERM, which enable the designer to study the effects of the many interacting design parameters and achieve an optimum thermal design. These packages are supported by extensive component physical property databases and thermodynamic models. It must be stressed that software convergence and optimisation routines will not necessarily achieve a practical and economic design without the designer forcing parameters in an intuitive way. It is recommended that the design be checked by running the model in the rating mode. It is the intention of this paper to provide the basic information and fundamentals in a concise format to achieve this objective. [4]

CHATER 2LITERATURE REVIEW

Shell and Tube-type heat exchanger have wide application in nuclear industry where they play an important role in the transfer of heat. Their cost minimization and pressure utilization are important targets for both designers and users. In this project a computer program for economical design of shell and tube heat exchanger using specified pressure drop is established. The design procedure depends on using the acceptable pressure drops in order to minimize the thermal surface area for a certain service, involving discrete decision variables. Also the proposed method takes into account several geometric and operational constraints typically recommended by design codes. The capability of the proposed model was verified through two design examples. The obtained results illustrate the capacity of the proposed approach through using of a given pressure drops to direct the optimization towards more effective designs, considering important limitations usually ignored in the literatures. In designing a shell & tube heat exchanger is designed many times by taking different variables. So in this project it designed by taking variable tube length. The optimization is taken on pressure drop which is 0.8 bar allowable. So in a computer programme MATLAB this exchanger is again designed and calculated.

CHAPTER 3SHELL & TUBE HEAT EXCHANGER

Heat exchangers (STHEs) are done by sophisticated computer software. However, a good understanding of the underlying principles of exchanger design is needed to use this software effectively.This article explains the basics of exchanger thermal design, covering such topics as: STHE components; classification of STHEs according to construction. And according to service; data needed for thermal design, tube side design, shell side design, including tube layout, baffling, shell side pressure drop, and mean temperature difference. The basic equations for tube side and shell side heat transfer and pressure drop are well known; here we focus on the application of these correlations for the optimum design of heat exchangers. [9]

3.1 Components of STHEsIt is essential for the designer to have a good working knowledge of the mechanical features of STHEs and how they influence thermal design. The principal components of an STHE are:1. Shell;2. shell cover;3. Tubes;4. Channel;5. Channel cover;6. Tube sheet;7. Baffles and8. Nozzles;

3.2 Classification based on construction

3.2.1 Fixed tube: Heat exchanger (Figure 1) has straight tubes that are secured at both ends to tube sheets welded to the shell. The construction may have removable channel covers (e.g., AEL), bonnet-type channel covers (e.g., BEM), or integral tube sheets (e.g., NEN). The principal advantage of the fixed tube sheet tube sheet construction is its low cost because of its simple construction. In fact, the fixed tube sheet is the least expensive construction type, as long as no expansion joint is required. A disadvantage of this type that the bundle is fixed to the shell and it cannot be removed. The outsides of the tubes cannot be cleaned mechanically. Thus, its application is limited to clean services on the shell-side. However, if a satisfactory chemical cleaning program can be employed; fixed-tube sheet construction may be selected for fouling services on the shell side.

3.2.2 U-tube: The tubes of a U-tube heat exchanger (Figure 1) are bent in the shape of a U. There is only one tube sheet in a U-tube heat exchanger. However, the lower cost for the single tube sheet is offset by the additional costs incurred for the bending of the tubes and the somewhat larger shell diameter (due to the minimum U-bend radius), making the cost of a U-tube heat exchanger comparable to that of a fixed-tube sheet exchanger. The disadvantage of a U-tube heat construction is that the insides of the tubes cannot be cleaned effectively, since the U-bends would require flexible-end drill shafts for cleaning. Thus, U-tube heat exchangers should not be used for services with a dirty fluid inside tubes. 3.2.3 Floating head:The floating type heat exchanger is the most versatile type of STHE, and also the costliest. In this design, one tube sheet is fixed relative to the shell, and the other is free to float within the shell. This permits free expansion of the tube bundle, as well as cleaning of both the insides and outsides of the tubes. Thus, floating-head SHTEs can be used for services where both the shell side and the tube side fluids are dirty making this the standard construction type used in dirty services, such as in petroleum refineries. There is various type of floating-head heating-head construction. The two most common are the pull-through with backing device (TEMA S) and pull-through (TEMA T) designs.

3.3 Classification based on service Heat exchanger: both sides single phase and process streams (that is, not a utility). Cooler: one stream a process liquid and the other cooling water or air Condenser: one stream a condensing vapor and the other cooling water or air. Chiller: one stream a process fluid being condensed at sub-atmospheric temperatures and the other a boiling refrigerant or process stream. Reboiler: one stream a bottoms stream from a distillation column and the other a hot utility (steam or hot oil) or a process stream. [9]

VARIOUS TYPES OF SHELL-AND-TUBE HEAT EXCHANGER

Fig 1.different type of heat exchanger [2]

CHAPTER 4 DESIGN OF HEAT EXCHANGER

4.1 Procedure of heat exchanger design For design of heat exchanger following steps are applied.1. Assume tube diameter and BWG, Assume tube length, L2. Assume fouling factor based on inside and outside tubes, hdi and hdo3. Assume material of construction for the tubes thermal conductivity?

Table no. 1 thermal conductivity of various materials [1]MetalTemperature (oC)kw (W/moC)

Aluminium0202

100206

Brass097

(70 Cu, 30 Zn)100104

400116

Copper0388

100378

Nickel062

21259

Cupro-nickel (10% Ni)0-10045

Monel0-10030

Stainless steel (18/8)0-10016

Steel045

10045

60036

Titanium0-10016

4. You have the option to assume three known temperature and find the fourth one or four temperature values and find one of the shell or tube side flow rate. Use the heat duty equation (mCP T)h AND (m CP T)C where subscripts c and h refer to cold and hot streams. Then obtain the heat duty, q.5. Based on the type of flow, calculate Log Mean Temperature Difference, LMTD. For counter current.

6. Based on the exchanger configuration obtain the Temperature correction factor. For 1- shell-2-tube pass exchanger.

Figure no. 2 Temperature correction factor: one shell pass; two or more even tube 'passes [1]

7. Calculate the mean temperature difference using DTm= Ft LMTD m 8. Assume overall heat transfer coefficient as initial guess from the table no. 02 given below.

Table no. 2 overall heat transfer coefficient [1]Shell and tube exchanger

Hot fluidCold fluidU (W/m2 oC)

Heat exchanger

WaterWater800-1500

Organic solventOrganic solvent100-300

Light oilsLight oils100-400

Heavy oilsHeavy oils50-300

Gases Gases10-50

coolers

Organic solventswater250-750

Light oilsWater350-900

Heavy oilsWater60-300

GasesWater20-300

Organic solventBrine150-500

WaterBrine600-1200

GasesBrine15-250

Heater

SteamWater1500-4000

SteamOrganic solvent500-1000

SteamLight oil300-900

SteamHeavy oils60-450

SteamGases30-300

Condensers

Aqueous vapoursWater 1000-1500

Organic vapoursWater700-1000

Organics (some non-condensable)Water500-700

Vacuum condensers Water200-500

vaporisers

Steam Aqueous solution1000-1500

SteamLight organics900-1200

SteamHeavy organics600-900

9. Calculate the provisional area A= q/UT

10. Based on the assumed tube diameter (ID and OD at a given BWG) and tube Length, L, calculate number of tubes: Nt = A/dL11. Calculate tube pitch and the bundle diameter pt = 1.25 do Db = do (Nt/K1)1/n1

Where Nt = no. of tubes, Db = bundle diameter, mm do = tube outside diameter, mm K1 and n1 are obtained on the type of tube arrangement of triangular or square pitch.

Table no. 3 bundle diameter calculation [1]Triangular pitch pt = 1.25 do

No. passes12468

K10.3190.2490.1750.07430.0365

n12.1422.2072.2852.4992.675

Squre pitch

K10.1250.1560.1580.04020.0331

n12.2072.2912.2632.6172.643

Figure no. 3 calculating shell diameter [1]

12. Calculate the shell diameter from figure 313. Calculate the baffle spacing. Bs 0.4Ds 14. Calculate the equivalent diameter For square pitch arrangement [3] de = 1.27(pt2-0.785 do 2)/do for triangular pitch arrangement [3] de = 1.10(pt2-0.917 do 2)/do 15. Calculate the shell-side Reynolds number16. Obtain the shell-side heat transfer coefficient Nu= jh( Re) (Pr)1/3 (/ w)0.14 Where jh is obtained from the chart bellow

Figure no. 4 jh and Re [1]

17. Calculate the pressure drop in the shell Ps = 8jf (Ds/ de) (L/ lB) ( / w ) -0.14 (ut2/2) Where L = tube length lB = baffle spacing jf may be obtained from the chart bellow

Figure no. 5 j f & Re [1]

18. Calculate pressure drop in tube side

Pt = Np[8jf (L/di) ( / w ) -0.14 +2.5] (ut2)/2

19. Calculate overall heat transfer coefficient (based upon inside tube flow)

Based upon outside tube flow

20. Compare the calculated overall heat transfer coefficient you obtained from the previous step with that you assumed in step 8. If it is close to what you assumed, then you had a valid assumption, and then tabulate your results such as total surface area of tubes, number of tubes, exchanger length and diameter, heat duty and other design specification. Otherwise, use the calculated value in step 8 and do loop until the difference between the calculated U between two consecutive iterations is small.

4.2 DESIGN OF SHELL & TUBE HEAT EXCHANGERObject: Design a heat exchanger for the following duty.Fluid 1.

Hot fluid Kerosene

Mass flow rate (G)20000 Kg/hr.

Inlet temperature2000C

Outlet temperature900C

Inlet pressure5 bar

Fouling0 .0003 m2 0C/W

Fluid 2.

(Cold fluid)Crude oil

Mass flow rate (G)70000 Kg/hr

Inlet temperature400C

Inlet pressure6.5 bar

Fouling0.0002 m2 0C/W

SolutionSpecification Calculate duty Duty = mCpdTDuty= 200002.47(200-90)/3600 = 1509.4 kWCrude oil outlet temperature700002.01(t2-40) = 1509.4t2= 77.90C

Table no. 4 physical properties of kerosene and crude oilKeroseneInletMeanOutlet

Temperature200145900C

Specific heat2.722.472.26KJ/Kg0C

Thermal conduct..130.132.135W/m0C

Density690730770Kg/m3

Viscosity.22.43.08mNsm-2

Crude oilOutletMeanInlet

Temperature7859400C

Specific heat2.092.052.01KJ/Kg0C

Thermal conduct..1330.1340.135W/m0C

Density800820840Kg/m3

Viscosity2.43.24.3mNsm-2

LMTDTln = [(200-78) (90-40)]/Ln (122/50) = 80.7 oCCorrection factor (Ft) = 0.88Actual LMTD = 0.8880.7 = 71.0 Layout and tube sizeCrude oil is viscous so taking purpose of cleaning of heat exchanger so take floating heat exchanger. Fluid is non-corrosive and operating pressure is also not too high, so plain carbon steel is used. Crude oil is taken in tube side. Tubes are taken in standard size of 19.05mm outer diameter and 14.83mm inner diameter. Taking standard i.e. 5m long and triangular pitch of 23.81mm.

Shell & tube specificationTube outer diameter do = 19.05mmTube inner diameter di = 14.83mmNumber of tubes Nt = 360 Number of pass Np = 4 (always take even no. of pass)Tube cross-sectional area = (14.8310-3)/4 = 0.0001727m2Area per pass = 0.0001727360/4 = 0.01555 m2Volumetric flow = 70000/(3600820) = 0.0237 m3/sTube side velocity ut = 0.0237/0.01555 = 1.524 m/sBundle diameter Db = do (Nt/K1)1/ n1K1 = 0.175 & n1 = 2.285 (by table 3)So Db = 537mmShell diameter Ds = 537+59 = 596mm (fig. 3)Baffle spacing = Ds/5 = 119.2

Shell side areaAs = [(pt-do) Ds lB]/ptpt = tube pitch = 23.81mmdo = tube outer diameter = 19.05mmDs = shell diameter = 596mmlB = baffle spacing = 100mmso As = 0.167 m2

Heat transfer coefficient

Tube sideNu= jh( Re) (Pr)1/3 (/ w)0.14Re= (.u.dh)/ = (8201.52414.8310-3)/3.210-2 = 5792L/d = 5000/14.83 = 337jh = 3.510-3 (by figure 4)Nu = h dh / kSo h = 680 W/m2 0C

Shell side Volumetric flow rate on shell side = 20000/(3600730)=0.0076m2us = 0.0076/ As = 0.455 m/s de = 13.52mmRe= (u dh)/ = (730 0.45513.5210-3)/0.4310-3 = 14644Pr = Cp /k = 8.05jh = 4.810-3 (by figure 4)Nu = h dh / kSo h = 1177 W/m2 0C

Overall heat transfer coefficientU = 288 W/m2 0C.It is in range of allowable limit so we can take this specification.

Pressure drop calculation

Tube sidePt = Np[8jf (L/di) ( / w ) -0.14 +2.5] (ut2)/2jf = 5.510-3 (figure 5)Pt = 66029 N/m2 = 0.66 bar

Shell sidePs = 8jf (Ds/ de) (L/ lB) ( / w ) -0.14 (ut2/2)jf = 4.610-2Ps = 0.47 barIt is in allowable limit so we can take this specification.

CHAPTER 5ECONOMIC OPTIMIZATION OF SHELL & TUBE HEAT EXCHANGER

Shell and Tube-type heat exchanger have wide application in various industries where they play an important role in the transfer of heat from core to the heat sink; their cost minimization is an important target for both designers and users. In this project a computer program for economical design of shell and tube heat exchanger using specified pressure drop is established to minimize the cost of the equipment. The design procedure depends on using the acceptable pressure drops in order to minimize the thermal surface area for a certain service, involving discrete decision variables. Also the proposed method takes into account several geometric and operational constraints typically recommended by design codes, and may provide global optimum solutions as opposed to local optimum solutions that are typically obtained with many other optimization methods. While fulfilling heat transfer requirements, it has anticipated to estimate the minimum heat transfer area and resultant minimum cost for a heat exchanger for given pressure drops. The capability of the proposed model was verified through two design examples. The obtained results illustrate the capacity of the proposed approach through using of a given pressure drops to direct the optimization towards more effective designs, considering important limitations usually ignored in the literatures.Cost minimization of Shell-and-tube heat exchangers is a key objective. Traditional design approaches besides being time consuming, do not guarantee the reach of an economically optimal solution. So, in this project, a new shell and tube heat exchanger optimization design approach is developed based on a computer programme MATLAB. The MATLAB algorithm has some good features in reaching to the global minimum in comparison to other evolutionary algorithms. In this study technique has been applied to minimize the total cost of the equipment shell and tube heat exchanger by varying various design variables such as tube length, tube outer diameter, pitch size, baffle spacing, etc. Based on proposed method, a full computer code was developed for optimal design of shell and tube heat exchangers For our key objective economic cost optimization of shell and tube heat exchanger for a given pressure constant for both tube and shell side. We are going to develop a computer program for different designs of shell and tube heat exchangers.From this program we get a design of heat exchanger for the same condition and varying tube length and the new design is given below

5.1 New design

KEROSENEflow rate Kg/h20000inlet temp 0C200outlet temp0C90inlet pressure5allowable pr. Drop (bar)0.8fouling factor0.0002CRUDE OILflow rate Kg/h70000inlet temp 0C40outlet temp0Cinlet pressure (bar)6.5allowable pr. Drop (bar)0.8fouling factor0.0003mean temp of kerosene 145duty1509.444444crude outlet temp0C78.62117982mean temp 0C59.31058991heat transfer area70.86layout and tube sizetube outer diameter mm19.05tube inner diameter mm14.83tube length meter (change parameter) 7triangular pitch mm23.81pitch/dia1.249868766area of one tube0.41885235no of tubes280no of passes2tube side cross sectional area0.000172644tube per pass140area per pass0.024170186volumertic flow rate0.023712737tube side velocity0.981073833bundle and shell diameter2 tube passk10.249n12.207bundle diameter (mm)459.510917clearence from diagram56shell diameter515.510917heat transfer coefficient tube sidereynold no.3729prendtl no.48.96L/di472jh from figure0.027nussult no.363.5832041hi3285.242707heat transfer coefficient shell sidebaffle spacing mm160area0.016489421equivalent diameter13.51957786shell side volumetric flow rate0.00761035shell side velocity0.461529248reynold no.10592.94613prendtl no.8.05baffle cut25%jh from figure0.0021Nussult no.44.5828696hs435.2901288overall heat transfer coefficient1/U0.00338129U295.7451384pressure dropTube sideRe3729Jf from figure0.021pt64560.03225p in bar0.645600323Shell sidejf from figure0.066Re10592.94613ps68482.25238p in bar0.684822524

CHAPTER 6CONCLUSION

Table no. 5 comparisons between present and previous workCalculated results

Previous workPresent work

AREA (m2)70.86

70.86

Heat transfer coefficient (W/m2 oc)268

302

Number of tubes280

360

Number of tube passes24

Inside tube diameter (mm)14.8314.83

Outside tube diameter (mm)19.0519.05

Number of baffles 3242

shell diameter (mm)515.51596

tube length (m)75

Baffle spacing (mm)160119.2

Pressure (tube side) (bar)0.6450.66

Pressure (shell side) (bar)0.6850.47

In this work, an optimization model for the design of a shell and tube heat exchanger has been proposed. The optimization strategy based upon the presented analytical optimization analysis is developed as a computer aided design package. Important additional constraints, usually ignored in previous optimization schemes, are included in order to approximate the solution to the design practice. Two cases for optimal design of shell and tubes heat exchanger based upon the devised computer program were presented. In case study one the obtained results in the present work are consistent with the corresponding values. In case two the comparison showed that the proposed model is more efficient in terms of providing excellent optimum solutions than standard optimization method. Also the result of the study cases ends up with the final conclusion that the use of the model provides the best solutions with higher quality together with short duration of real time.

CHAPTER 7REFERENCES

1. Sinnott, R.K. (1993) Coulson & Richardsons Chemical Engineering Vol. 6, 3rd edition. Page No. 634-7792. HEAT EXCHANGER selection, rating, and thermal design by Sadik kaka, hongtan Liu (department of mechanical engineering university of miami). Page 249-278, 323-348.3. Roy G. K. Fundamental of Heat and mass transfer operation Page No. 37-82.

4. Hewitt, G.F. et al (1994) Process Heat Transfer, (CRC Press)5. Perry ,R.H. and Green, D. (1984) Perrys Chemical Engineers Handbook, 6th edition (McGraw Hill)6. Kern, D.Q. (1950) Process Heat Transfer (McGraw Hill)7. Chemstations, Inc. CHEMCAD THERM Version 5.1 User Guide8. Schlunder, E.U. (1993) VDI Heat Atlas (Woodhead Publishing)9. Seider, D.S., Seader, J.D.Seader and Lewin, R.L. Process Design Principles, (John Wiley & Sons, Inc.)10. Lee, Jin-Jong and others, Reduce revamp costs by optimizing design and operations, Hydrocarbon Processing, April 2007.20