.Vli i":•. t~iQ 1~

UNCLASSIHFED

AD423

DEFENSE DOCUMENTATION CENTERFOR,

SCIENTIFIC AND TECHNICAL INFORMATION

CAMERON STATION AlEXANDRIA. VIRGINIA

SF'

""LTD1AS 2HE

NOTICE: When government or other dravingi, speci-fications or other data are used for auy pwrpseother than in connection vith a definitely relatedgovernment procurement operation, the U. I.Government thereby incurs no responsibillty, nor anyobligation whatsoever; and the fact that the Govern.ment may have formulate4 tarnished, or inW an ysupplied the said draVngs, specifications. or otherdata is not to be regardef by implication or other-vise as in any manner lie-sin t-the bolder or. anyc.ther person or corpouti•r, or conveying aW rightsor permission to manufactua-e, use or sell anypatented inventiou that v, in avy eu be relatedthereto.

* ASD-TDR-63-506

FLUID MECHANICS AND TANKAGE DESIGNFOR LOW G.-AVITY ENVIRONMENT

Robert G. Clodfelter

TECHNICAL DOCUMENTARY REPORT NO. ASD-TDR-63-506

September 1963

AF Aero-Propulsion. LaboratoryResearch and Technology Division

Air Force Systems CommandWright-Patterson Air Force Base, Ohio

I... No. 2.4

S. .

.... . .. .

NOTICES

When Government drawings, specifications, or other data are used for anypurpose other than in connection with a definitely related Government procure-ment operation, the United States Government thereby incurs no responsibilitynor any obligation whatsoever; and the fact that the Government may haveformulated, furnished, or in any way supplied the said drawings, specifications,or other data. is not to be regarded by implication or otherwise as in anymanner licensing the holder or any other person or corporation, or conveyingany rights or permission to manufacture, use, or sell any patented inventionthat may in any way be related thereto.

Qualified requesters may obtain copies of this report fro.a the Defense

. Documentation Center (DDC), (formerly ASTIA), Cameron Station. Bldg. 5,

5010 Duke Street, Alexandria 4, Virginia

This report has been released to the Office of Technical Services. U.S

"Department of Commerce, Washington 25. D.C., in stock quantities for sulito the general public.

Copies of this r-tport sheuld tot be rm.tunvd to the AeronauticAt SysternDivision unttits ret~u ir ft re'16d by ~eacuit-y cun".idur*%tUotn, txonitratwobligations. or ao:4co oa tr. v*c;c.C % nc nt.

G ,..,I - ,.mIJ . ,m m. tI

S," .,. ,-. +P+ .. " ,+ + ,, •., B. S+ - U ,+'•.,-3- t.4•+,+•,+ • ,

"ASD-TDR-63-506S: FOREWORD

-i This report was prepared to present the results of an in-house study and test program

conducted by the AF Aero-Propulsion Laboratory. Aeronautical Systems Division. under

Project 3141, "Electric Propulsion Technology." Task 314105. "Space Environmental

Effects on Electric Propulsion." The report covers the effort between June 1961 and

April 1963.

The cooperation and assistance of the many persons who have contributed to the prograun

•" and specifically to the following Individuals of the AF Aero-Propulsion Laboratory arn

gratetully acknowledged: SM/Sgt C. W. Thompson for coordinating the experiments and

acting as aircraft test monitor for the program during the past 4 years: Elmer White for

developing the 7090 computer program to determine interface shapes; and P. J. Vore and

G. N. Nledisch for developing the drop tower into a useful zero-gravity test facility.

X

ASD-TDR-63-506

ABSTRACT

Electric propulsion systems for space vehicles must be able to restart and operatezero and low gravity. This operation can be achieved if the taokap delivers only single-phase propellants. The requirements for feed systems of electric engines are describedbriefly. Also, the 1. 85-secono drop-test facility is described and the testing tecbniques

4,' discussed.

The minimum energy principle is presented along with a method for determining thedirection of mass transfer in tapered tubes and liquid-vapor interfa shapes in an annulazspace between concentric cylinders. Possible feezd systems for electric engines are given.which utilize surface tenrion for fluid positioning and transfe

.2- ~.Zero-gravity and static-fluid configurations in cylindrical and spherical containers arediscussed along with experimental observations. The interface "ove••hoot" of the equilib-

''.4rium zeot-aravitv conlnravEn 40 *1*^~

?" i

PUBLIOAT1OU RPEVI•W

This technical oclwtry, rport hsbeen reviewe@d and is sqwad.

"FOR THE CO,•MANU

,*.. 4

Atro Sp"e Pow-r t~vigionAF MMo PtuOulg9os Lbaratoq~

I r

44ti

ASD-TDR-63-506

TABLE OF(X)KTENIS

N ~Pagp

Introduction . . . . . . ... . . 1

Electric Engines. . . . ... ...... . . .

Types of Engines. . . .. ..... ... .. .. .. ..... 1

Feed System Requiremems . a... ... . a.... .. a.... 2

Surface Tension Systems . . a . ..... . . a.. . 2

Annular Capillary Analysis ................ .... 10

Zero-Gravity Drop FacUiy ......... .. . ...... 16

Drop Test Procedures . ...... * ......... • • a - a 22

Static Fluid Configurations inCyliudrlkulCcntainors. .......... 26

Static FluidcoMdguratloain.sit Cemaitr5.. a • * , . . .. * . .C. 39

Itericlace Overshoot 4* * *. 0 * *** 48

Conclusis iand ReOCmomndflC o a * a. . a ...... 50

List of Rdferances a a a a 51

w.!

I,

•.1

IIv

SiIL

ASD-TDR-63-506LIST OF ILLUSTRATIONS

Figure Page

I Slghtly Tapered Tube . . . . . . . . . . . . . . . . . . . . . . . 3

2 Fluid Movementin Capillaries .... ..............

3 Low-Gravity Fluid Configurations Controlled by Surface Tension .... 6

4 Feed System of Ion Engine ..................... 7

5 Screen Capillaries . . ..... .... ......... .. 9

6 Capillary System . . *. ... .... ........... . . . 10

7 Systemn of Concentric C nder................... 12

8 Nondimensional Interface In Annular Capillary for 0Oa .0 . . .... 14

9 Nondimensional Interface in Annular Capillary for u a 120' , , , , 15

I "/, 10 Zero-Gravity Drop-Test Facility,. ... ......... -''" 18

S.... I1 Drag Shield and Honeycomb Paper ..... ....... ... • 19

112 RelaUve Position of Test Package and Drag Sheld. 0 .......

13 Drag Shkbld mdTanPaekage . ., . . .. , .. .. .. . .. 21

14 TestPackage ... , . . . • • . • . . . • . . • . • • • . . . • • 23I 15 Schernat of h8.S-Second Drop F lity . . , , o . o .. . 24

16 Find Positinidng of Drop Capsules. . .. .. ... .. . . . . . 25

17 Use of Wuting and Nonwenuin Fluid Configurations in Cylindrical Tanks . 26

' 18 nrogresuion at Wetting and Noowottlog Fluids for Drain Operation Udiers""Zeo-Gravity C9 9t99o99.4 4 26

19 Disoacement of WeulNg Fluid lertwace In a Cylindrical Tank...... 1

20 Displacement of Noetting Fluid interface In a Cylindrical Tank . .. 29

21 Coellguralon" a Ethyl AlceWI In Cylinders with Inside Dimeteamma t0,912, 0.825. o.7S9,0.0.0.57. 0.Sk 5and 0.418 Inces . . . . . . . . 30

22 Weting•Pluid Corflgur~tIons .t a CylndrcTal k TA 31

23 Noetting VluldCos figua*ton Ina Cyindrical Tank ........ . 32

4•

ASD-TDR-63-506

LIST OF ILLUSTR.ATIONS (Continued)

Figure Paip

24 Configurations of Ethyl Alcohol (50 Percent Fill) with Axis of Cylinder/L - L4) Vertical. . . . . . . . .. ... ... . 33

25 Configurations of Ethyl Alcohol (25 Percent Fill) with Axis of Cylinder*,(D/L = l.4) Horizontal and 45 Degrees. . . . . .. . . . . . . .. . U

26 Configurations of Ethyl Alcohol (75 Percent Fill) with Axis of CylinderW. (D/L L.4) Horizontal and 45 Degrees. . . . . . ..*. . . . . .. . 35

27 Two Low-Gravity Configurations of Ethyl Alcohol (50 Percnt Pill) in5-Centimeter Inside-Diameter Cylinder (Aircraft Test). ... .... 36

28 Low-Gravity Configurations of Carbon Tetrachloride and Mercury in 10-Centimeter Inside-Diameter Cylinder (Aircraft Test) ..... . . 37

29 Low-Gravity Configurations of H 0 (50 Percent Fill) in 15-CentinbterInside-Diameter and 5.5-Contij•zter Inside-Diameter Cylinders (AircraftTest) *. . * . . . .. . . . . . . . . . . . . . . . . . . . . . 38

30 Fluid Configurations In a Spherical Tank (Caur of Interfuce DisplacemeaO 40

31 Fluid Configurations in a Spherical Tank (Edge of tnterface Displacement) 41

32 Coiguratos o Mercury F1%100-MhIliter Sphere . . . . 42

33 Configurations of Mercury (25 Percent Fill) In 100-Mlllliter Sphere .. 43

34 Configuratkns of Mercury (25 Percent Fill) 4n 3004MilllUiter Sphere . 4

35 ClonfiguratIou ot Ethyl Alcohol (50 Percent Fill) In 500-MIlllIter Sphere 45

36 Configuratiomn of Carbon Tetrachloride (50 Percent Fill) in 100-MIBiUter

37 Configurations of Carbon Tetrachlorlde (50 Percent Fill) to 500-MilliliterSi•r . . .* . *.. * .... ..... ** .......... 4Sphere . 41

* 38 Surface EnergCondiUona.......... .... .. . o 4639 Inwteace Displacement History for Ethyl Alcohol (50 Percent Fill) in

2.16-Ceatmmer and 1.22-Ceatimeter hnside-Dianeter Cylinders.... 49

II

"ASD-TDR-63-S06S~INTRODUCTION

Electric propulsion systems for space vehicles must have both zero-gravity restert

"", - capability and low gravity (W0" G's to 10" Gs) operation capability. Smooth. reliable,and reproducible operation of the engine is essential and can be achieved only if single-phase propellants are delivered from the tankage.

In contrast to conditions on the surface of the earth, there can be rno assurance that thedesired propellant phase will be located at the outlet of the tank while the vehicle Isj.i freefall or under very low accelerations.

This technical report* presents Information on both the nature of fluids at low gravityand on tankage systems for electric enines, which control the propelant copfiguratioeby surface tension. This Information Is presented to assist designers in developing tank-"age systems that have many advantages over mru.mlcal methods (rotating tanka. bladderexpulsion, etc.) of fluid control at low gravity.

ELECTRIC ENGINES

TYPES OF ENGINES

The electric propulsion engines that are currently being considered for s$pe awpllca.-oten tre listed In ascending order of specific Impulse range: (1) resivtrice eagizea. (2)

arc-jet engines. (3) electromagnetic engines, and (4) electrostatic engises.

The electrothermal resistance engine showa pronime In the M)-second to 110-secondspecific-itnpui• range. In this erine, the propellant Is heated by a resitance hMaa ex-

chaniger of refractory metal; the maximum temperaturn of the propellanm Nd. tLrefore.S.W, sipelic impulse ti limited by the maxlmum temperature of the resstane entenwnt. The

clectrothermal arc-jet engine produces greater Wsefic Impulss because ft propeflanIs hemted by an electric arc without subjecting the structurAl elements o the maxlmwutemporature of the proeillant. 1te e!ccromag olt, engine prodwos thrust by the imwr-•Aerion of a neutrAl, but electrically ctwducting, plasmA propelhnt with electromagneticfields. Since the propellant Is Ac-eleratd by bxh aerodyndmic means Wnd electric bodyforces, a •.ater tpecitfi imliudw is amocated with the same inalmum allowable temper-ature of the propllant than with the arc-jet engine, IVe electroatatic engine (ion engine)operates in the UWOi-sccond to 20,OW-secoad sp•cific-impulse ramg. Thl# engine prodwos thrumxt almost tololy by accelerating charpeW particles by electrical mean3. tere,there, is Almomt comnplete d.couplhg of the maximum .attainable velocity of the exhaustand operrating temrperatute of the structural wi-pownnt. Since the arc-jet and clectro-st.itic egiwnes are closert to becoming priational. only thesw are i.jwuded in the diset"00oaon the roquret s for propellant fCed system.

* A 16-mm film which t~ixplewnents the irformation proonted in t" report can be oltaledon loan by contacting the author.

hManscript releaaed by auitor on 21 May 1963 for pubictiuo .m ASD TechlucaI DOoU-menA~ry Report.

ASD-TDR-63-506"FEED SYSTEM REQUIREMENS

At the present time, the selection of the propellant for the arc-jet engine probably wlbe limited to ammocia, hydrogen, and the lithium seeded versions ot each. Ammonia Is

. easily stored in a no-loss system and as such offers weight advantages for long term: storage in space. Hydrogen while being superior to ammonia from the standpoint of engine

performance requires ciyogenic or supercritical storage techniques and no-loss systems"S.- are impractical for long term storage in space. On a mission where hydrogen boil-itf.-*. supplies the fuel required by the engine, hydrogen definitely appears to be the logical

choice between the rxo. Although the arc-jet engine will operate on either a liquid or gaspropellant, the feed control system. from a practical standpoint. requires the propellantto be in the gaseous state.

Cesium is easily stored as a liquid in a no-loss system and could be stored as a s"lidwith or without a refrigeration system.depending on the heat balance of the tank. With thecesium propellant, &,e critical requirements are the compatibility of the cesium with thetank materials and thae purity of the cesium delivered to the engine. Gaseous cesium must"be delivered to the emitter (ion generator) for prqer operation.

Before the high-performance potential oa electric engines can be fully realized. themeengines must have an efficient method of propellant storage. In addition to the environ-mental problems encountered in space that are common to other propulsion systems -3electric enginis will be required to perform in a low-gravity environment (less than 10G's) during their entire operational period, which may be as hWeh as 3 years This low-gravity enviromnent presents problems In liquid-vapor separation ind heat-tradserprocesoet. In recan: years much effort haot been devatcu to the analysib of these problems.

iMany different syrms have been Investigated (Refs. I through 16). The general conclusionwas that a bystem could be developed that offefed many dirsinct advantages in weliht, powcr,and simplicity over presnt state-of-the-art t"Inheqs of propellant storage If fluid poslton.Ing could be obtafwn. by natural nmanR (Van der Waals forces), The efforts described itReferences I throtlh 16 wero directed primarily toward the devdlopment Of propellantstorage techniqw-s for near future applications. Since there was a lack of design informainonon the behavlor of fluids In a low-gravity environimnt, loss destrable techniques wereselected for dcvelo-pwnL, 11we Intent of this report is to prownt. Mne information on ow.-gravity fluid bahtvor so that the full potantlal of advanced conepts of prIIPUat storapnmay be realized at som future date.

S.,. SURFACE TLNSION SYSMT.MS

From principlcs of thernodynamics. wo can chow that an bol".ed physical system willtend to assumn a tuxAe of milninium energy equilibrium. For a t.ym involving flulds,.tde energy mnay Ix dispipated by Irreversible action of viscosity, capillary friction, andSheat transfer. For fluid In a contatniwr untdor an a G's aceleratitn, the energy of theaystent that may b e tnnltoiai d In the enervgy as•octla".d with the liquid-enlid. liquid-wvator and vapor- i4d Interfaces plus the potential energy ascociated with acceleratedfluid. Us;Inj this prixiciple, the authors of iteferetNce 17 through 19 predict liquid-vaporInterface elinpeo in vAriotm tytpe of contatlner and accelerahion fields. The conitraintsfor a system in a zero-gravity anviromnent (a a 0) Is a liquid-vapor interfawo of conatancurvature Intrscting the container at the contat aogle.

2

ASD-TDR-63-S06

The Young and Laplace equation (Ref. 20). which deals with the pressure differenualacross a curved interface. Is a useful tool for Oredlczg the behavior of low-gravityfluid. This basic equation of capillarity Is

•'"Po p" .P pressure differential across quidvnr ieace

a surfaced wsion

R 1 and R2 a radii at cuxvature that describes the curved Interface.

The two radii of curvature of a curvnd surface may be obtlned by erecting a normalto the surface at the point In questlon and then pass a plae through the surface contal-n.gthe normaL. The radius ot curvature is that of a circle tapat to the Hoe of Intersectionat the point involved. The second radius 0 curvatur is kalncd in the same mardmr bypassng a second plane throuwW the surface containing th surface normal but perpendlcu-1#r to the first plaw. The AP aroes an haerfae cannot depend upon the manmr in whidcthe two radii of curvature are chosen therefore. R, and N need not necessarily be the

principal radii of cutvatu. %1 or are considred posive if they lie on the PO side adthe curved auxtame

The pressure drop across a liquid-vpr lnr(ac wiay be milli-d for mhss tranifit.

Conaider the sWu~ft exiaznple of slighty tapered tube (do" to Figure 1)6

*W L S.-To" t

I.•,

~ 4' whereA - 01 rdu sC

Cam" w' rI.tla

Cmbr hs woeu• is:•:

ASD-TDR-63-506

P, -Pp cosOp -- -- cos,rtt

* Now NO-P COS 92 a, Cos 6,

the fluid moms to the right, and if

"- cos op a, cos 6,( V3

the fluid moves to the left.

The relationship of the surface tensions, contact angles, and tube radii may be adjustedso that the fluid may be made to move in the desired direction. The surface tension andcontact angle may be varied by the use of additives, impurities, or temperature. Figure 2Illustrates fluid movement for various conditions. Here, the surface tension decreasedwithIncreasing temperature is assured in the figure. This fact is true for most liquids. As thegravity environment becomes smaller, capillary tubes may be increased to several inchesin diameter. Therefore, tht overaUl weight 6f a storage system is reduced when this principle

-for propellant control is used.

When the Idea of mass transfer by surface tension is used, several possible tank systemsmay be postulated. For exnmple see Figure 3. Figure 3a shows a tapered tank with a trans-,fer line connecting the two tank ends. A wetting fluid will tend to collect at the small end ofthe tank regardless of the initial fluid configuration. Another type of tank is shown in Figure3b. Thic tank consists of several concentric cylinders. When these cylinders are sizedco-rectly, the liquid can be collected in the center portion of the tank with the ullage in theouter-most annular space. This effect could be used to reduce the heat leak of the tank.This method will be discussed In more detail later on. Other tank concepts utLUzing surfaceforces axe given in Reference 21

For very low feed-rate systems such as those associated with the electric engines, thecapillary forces alone are sufficient to provide the fluid to the engin-e. In other words, n•pump or pressure transfer system is requIred to maintain the proper feed rate. This factoris particularly attractive for the ion angine where the liquid ceslium may he transferredfrom the tank to the vaporizer by surface tension only.

Figure 4 gives a possible tank configuration of the Ion engine. Basically this feed systemconslss of a storage rank that has the inner walls coated with a poru sponge material(nickel. stalratess steel, etc.). The outlet tube is filled with a fine porous sponge ratteriaLThe outlet tubt terminates in thet vaporizer. Ieat Is radiated from an electric heater to"the liquid-vapor Interfaw located at the end ot the outlet tube; therefore vapor is providedto the enim. The flow raw can be controlled by adjuring the power to the heswer. Sincethe pores of the tank sponge are larger than those ot the outiet.tube sponge, the proellaxtts treantertied to the end of the outlet tube if the propellant in the tank is io contact with thetank sponge. Analyisa of surface energies. and verified by many ewpertments condumed byASD, NASA. and athers, lusures catsct at the propelant with the tank sponge. to otherworde all luids that have coatact a&ales od•r then 180 degrees will be wall bonded.

.5.'

.......

ASD-TDR463-506

Cal 6~Ga< 900•0

TAPER AS SHOWN

b> 90'

TAPER AS" SHOWN

O'O COL i.- HOT o,.. O, < 90"

•"-•--11 [21NO TAPER

COLD HOT > go-

-- d)', 0*1 >. Wid,) NO TAPER

._•.,• , > 0,> go"". ((I (21•e

•;•€ '•NO TAPER'

" ' NO TAPERI) (2)

a. )k) ( W O TAPr

1.. ..•'• ,

ASD-TDR463-506

UNSTABLE

STABLE

UNSTABLE(al)

Figme 3. Low-Oravity IbMl Cenftguraimm CoofivtWe by Su~ace T~m.In

........ .S . ..' .- ' .

ASD-TDR63-SO6

I

N - TANK

VAPORIZER

OUTLET LINE

TO. ENGINEFINE • -

POROUSMATERIAL

" HEATER

POROUS "-

MATERIAL

Fiure 4. Feed BSyWdM Of bni= e

is'.

-=6,

ASD-TDR-63-506

Note that the characteristic dimension of the vaporizer Is less than the characteristicdimension of the tank. This means that the propellant would fill the vaporizer and vaporline in the absolute minimum surface-energy configuration. This problem may be over-come by either (1) lowering the characteristic dimension of the tank below that of thevaporizer or (2) by designing the vaporizer so that the propellant surface energy increasesas the propellant leaves the outlet tube. In other words, the vaporizer presents an energybarrier to liquid that leaves the outlet aub.

For the arc-jet engine. it Is desirable to use the beat leaks of the cryogenic storagetank to provide the vapor for the engine. Here the method is positioning the fluid andlocating the feed line in the vapor region.

The control surfaces utilized for fluid positioning need not necessarily be of solid ma-terial. Screen may be used to reduce weight. When screen is used as a control surface, thestability of the fluid on the surface of the screen must be considered in the design. Thisproblem is discussed in detail In Reference 22.

Two drop tests were conducted to illustrate the use of screens. Results of the tests areshown in Figure 5. Both tests utilized two Pyrex cylinders each with an inside diameter of2.5 centimeters. Ethyl alcohol was used as the test fluid. One cylinder contained a 35-meshscreen and the other a 25-mesh screen standpipe. In Figure 5a, the standpipe diameter wasI centimeter. F6r this arrangement, the motion of the liquid into the standpipe was predictedby the minimum energy principle. In Figure 5b, the standpipe diameter was 2 centimeters.Here the motion of the fluid was.out of the standpipe. The variation of the interface in theannular space was the result of slight misalignment of the standpipe. A method of determiningthe direction of fluid motion and Interface shape for. an annular space is given In the sectionon Annular Capillary Analysis. These tests showed that in a capillary system the screensurface acted as a solid sdrface

11.

NS

ASD-TDR-63-506

ripin~~~I S.Sre Cphre

A ' 9

I . . . .. . . .

ASD-TDR-63-506

ANNULAR CAPILLARY ANALYSIS

A sketch of a capillary system that will now be considered Is shown in Figure 6.

VI

' 8 " CONTACT ANGLE

.0 J TA N #AT

A •%TAN 0 AT a,

-O0 AT.o

For igurs rvolulon Figure 6. Capillary SystemFor figures or revolution, explicit expressions can be written for R1I and R 2.

',': From analytical geometry

and * o

From the Young and Laplace equation

IR R2".o-P •0' (Let

S* aw let

dPd

NovPd!•II• k + , = ,ds

•I f, f(+ ,÷lv (I pa

10

S. . . . • . - . . . . + .., • , ... :- , • • + i + . . +. . + : i ' , . ,, + / + ++ . . _ • . . . , • , • " . . . .

.. ASD-TDR-63-506The integrand turns out to be the exact differential ot.

* uP

* so thatli +

(I +p(I+ va

From the boundary conditions

2 P a ton 4iat Kg

p a- ton # oftoa

and since!,,• • 4'=so-.

we find

2 cot 8k -

and

C . - I cot'9.2.

These equations may be nondimensionalized by the substitutlon at

r x-

It1

•, These equations now. maybewitna

and

* - - I

-a-osh361t

In'.

- c .

ASD-TDR-63-506

Now t pressure drop across the interface may be determined as follows-

V1 i • - u• 2com8

x2 - l

Consider the system of concentric cylinders (Figure 7) if it Is desired to drain fluid firstfrom the outer annular space (3) then from anaular space (2) and finally from afe (1).

LIQIOUTLET

Flpyae 7. Syiam of Cowentide Cylindmr

11e necessary conditions are:

or% . &

'4 P8 20 P

Substituting for'

we find

Finally It Is necess'y that

''Surprisingly, the same results may be obtained simply by defining

vertical force at the solid-liquid-vapor interfaceA, annular are&

,va$coos I €S!> €o

12

ASD-TDR-63-5M

271•71 Cos + 2W 12 • Cos 2 w cot

A2 V12, - Val 1 -I

and

t?'•wr2 cot* + 2w%3 o'cos 8 2osAP3 2s -W 3 -P ' , 2 . . . . . .2

i "lThe fact that the two techniques give the same results for this particular problem su stsSthe possibility that the pressure drop may be determ ined by the latter method for cm VI x

Caplllary systems, which cannot easily be found by rigid analysis. This concept is pmandywider. investigation in the drop tower.

Now refer to the eqtion

2 if + pa "I

by nondiml onariz and rearrat•ut gSIeS

ell

S'3

The shge of de tnterface may bie detertmined by solving the preceding equwto. N• ieri-.. l solutions were calculated on a 7090 comp•wr for vurlous condtloas.

Flguife 8 gives the nordlmensloml Ite•rfact ah" for a wet flud (0 - A FOg9 deals witb a nnwueni fluld e -I3 .

413

"s i

______ ______ ASD-TDR-63-506

* I*

I*I

Mpt L_______bdftI AW~ CU~qb

H1

ASD-TDR-63-S06

\0

-21~ ~ i ..... 2---

3 4 36

Fir~t 9 No~m~w"l ateue 1 Aa~i~ C*VL~r W IW

ASD-TDR-63-506

ZERO-GRAVITY DROP FACILITY

The experimental methods used to Investigate the effects of zero gravity must all applythe underlying principle that the apparatus experiencing zero gravity must be allowed toaccelerate uniformly because of r:-)- influence of only the external force of gravity. Possibleways to apply this principle are given in Table 1. No one method can be used to provide allthe information necessary. However. the drop method provides the most reliable and repeti-tive test conditions for the least a.mount of investment In manpower and money. Experienceat ASO) and other operational droý>-test facilities substantiate the validity of results obtainedfrom this method.

Past effort at ASD has centered around the aircraft method of producing the low-gravitytest environment. The aircraft trae.ctory in many cases causes a fluid sloshing condition,which often distorts the phenomena under investigation. References 23 through 25 give thedetails of aircraft testing. Much qualitative information has been obtained from past air-craft testing. However. a drop facility was developed at ASD to enhance future aircraft"testing, to provide quantitative d..:a. and to investigate phenomena that could not success-fully be determined from aircraft tests. The results presented in this report were obtainedin this facility.

The drop facility has a usable drop height of 5S feet and yields free-fall time of 1.85seconds. This drop facility is loc.-ed in ASD Building 718 and is shown in Figure 10. Theeffect of air drag on the test pack ize is kept to a minimum by allowing the test package to"fall within a protective drag shi..-l Guide cables are used to facilitate positioning of thecapsule assembly at the top of the shaft and to ensure that the capsules do not tip over aftercoming to rest at the bottom of the shaft.

A honeycomb paper material. Laveloped by the Army for parachute drops and procuredunder Military Specification !t96$4. is used to absorb the kinetic energy of the capsule$ COimpact. This paper is available In three strengths expressed in the force required to crw&I square foot of the material. Th 2800-pound per square foot paper In presently being tredwith the 300-pound capsule in the 1.8-second drop facility. The paIpr sack is shown inFigure 11.

lBy varying the cross sectional area of the honcyct-mb paper and leittcng the correct"strength of paper. one can control thw C forces encountered at the bottm of the drop to,- ".prevent any damage to the exprlnmont or instrumomtlc~On.

Various other methods of catct-lng the capsule were tud•ed, obbuved, and investigate&.•,. The preceding method has prov•, very satisfactory.

During the free-fall period, the air resistance on the test package is kept below 10-3 G*6of deceleration by allowing the test package to (all within the 3W.oixuid drag shield. Bathdrug shield and test package fAl ttwerher during the drop. The relOtve positions of thetent package and drag shield ar, shown in Figure 12. The ratio of welot-to-aMr-drag to

* kept high so that the deviation L-fo a true free tal will be kopt to a mlainnum. The dragshield is shown in Figure 13.

At Impact of the drag shield 's Ith the honeyconb paper, air resistatce tas doewed thedrag shield to the point where t!e test package is ipprexitnately 1/2 ifoh from the bottWlof the drag soleld. This conditiei predents no pro•lem sia-ce a 3-inch layr of honeycombpater forms the drag shield floor and gives addllnoal prtmo*.W to the UO package.16

J ASD.TDR-63-506

Whii the above technique is used, maximum utilization of available shaft height is obxained.* The total shaft height is 62.5 feet and produces 1.85 seconds of weightlessnesa.

TABLE 1

LOW-GRAVITY SIMULATION MfLqUO[S

"Method Zero-Gravity Size and Dynamics RemarksDuration

'Drop test I to 6 seconds Size limited by tower available; Comparatively In-ideAd steady transfenr conditions expensive, highfrom 1 G to zero gravity. Im- usage rate, lowpact sbock must be cotrolled. manpower require-

meats.

Helicopter 1 to 7 seconds Wumbte conditions prior to true Expensive. Highdrop ton zero gravity. Size limited. Coon- manpower. ScWtd.

.pletely self-coatained casule uling difficult be-

SereV1red. Technique hac t cause of aircraft.,boa demonstrated. weather and avall-

ability of recovery* are a. Only one drop

per mnsslom,

Aircraft C-13111 And KO- Froe fUolari capsule Welgt* Expensive. th~gparJlt1ic 135. 15 and 80 limited to aprox. 200 Ibs. m4woer re4uire-

traectry SeConds trajectory Htfly unstAble condtions ftwnte. Sche&dltngtin**, 4 to 8 oct- prwr to true zet to ravky. difficult becaue ofe.ds a• stibaliazd Tte period walUthi from aircraft and wstberzaro-gravity umime 00wualizons ot aiircrft prebtcM1.CnL a4

LarWr tie down experiwmets ttily l•w "P ra".possimwe. Situ luuubd only by"a"ircash dor.

,MitUe or 20 tula 0 Sil limited. Bigh IlUnch acoel- Recovery or als-

,Mgmettc or Steady state. Zero Limod ,dze wA lim-ted to 1oub itialelectric gri.q provdmed oaly params#getic mattiale. Mor eoqipmnett. to-field or only In %ery ava La heat trimdor atudlec arurtatutoo n4

_ vibristion VohMe. TA~qwe bas UM beens demo reordio g of dausloglato rami&n difficult becAuse at

the tdgb mapaki

17

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ASD-TDR-63-506

LIFTING GR, "WiRE RELEASE MECHANISM

4-

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FLOOR ONDRAG SHIELD

-N A. BEFORE DROP--V SUPPORT WIRE

S. DURING DROP

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HONEYCOMBPAPER

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Figure •- . Relative Position of Test Package and Drag MIeM

"20

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ASD-TDR-63-506

DROP TEST PROCEDURES

The test fluids were contained in Pyrex flasks of various sizes and shapes. These con-tainers were suitably mounted in the test package and illuminated to allow a high-speed- motion picture camera to photograph the entire container during free fall. The test package

is shown in Figure 1 % A 16-millimeter, high-speed, Bell and Howell camera with a 200-foot film capacity was used to obtain the photographic data. The average film speed was 200frames per second. Illumination of the containers wag provided by four 75-watt, 24-voltlight bulbs. The containers were mounted inside a light box having a dull white. interiorfinish to keep highlights and glare to a minimum. The light bulbs were arranged to provideindirect lighting. Electrical power for the lights and camera was carried by trailing wires

* .first to the drag shield and then from the drag shield to the test package. These were verylight and flexible wires and had no effect on the experiments. Several drops were made withthe electrical power supplied from a battery pack mounted in the test package to check the

, effect the wires had on the experiments. No detectable effect was indicated for Identicalexperiments using the two methods of supplying electrical power.

The liquids used in this investigation were 190-proof ethyl alcohol, triple distilled mer-cury, distilled water, and chemically pure. carbon tetrachloride. The bulk of the experi-mental data was obtained with wetting fluids, that is, etbyl alcohol and carbon tetrachloride.

, Mercury represented a nonwetting liquid. We found that distilled water did not give repeti-tive results and, therefore, was discarded. The properties of these, liquids are given InTable 2. Air in every case was In the ullage space above the liquid. The experimental in-vestigations were conducted at essentially ambient pressure and temperature. The contactangle of fluid against Pyrex glass was determihed by both the tilLing plate and the capillary-rise surface-tensiox methods. The ring method was used to determine surface xenslon. Thetilting plate apparatus is described In detail in Reference 26.

Before each drop test, the containers were carefully cleaned with a detergent solutionin an ultra sonic cleaner and then with chromic acid solution; then rinsed in tap water.then in distilled water, and finally dried with hot air. After Cleaning, the containers werefilled to the proper amount with the test liquid.

During the initial checkout of the drop facility, an accelerometer was mounted on thedrag shield. Using the data obtained on 10 of these initial drops, we determined the free-fall time to be 1.85 seconds. Using this time and counting the film frames from releaseto Impact, we determined an average camera speed for each drop test. On some of thedrops, a timing trace using 60-cycle-per-second line current was made by the cameraon the film as a check on the preceding method. Any time interval after release of thetest package was known to an accuracy of 1.3 percent of that interval.

After the experiment was mounted in the test package, the capsule was balanced andcamera operation and alignment were checked. The support wire was attached to thetest package and guided through a hole In the top of the drag shield. The wire was thenattached to the lifting bar to form a rigid assembly of test package, drag shield, and liftingxbar as shown in Figures 11 and 13. The wire was 316 stainless steel and 0.06 inch in

diameter. The release mechanism was permanently mounted on the lifting bar and consistedof a double-acting solenoid with a hard steel-knife edge. Actuation of the solenoid forced"the knife edge to cut the wire against an anvil, thereby ensuring a smooth release. Afterthe test package was mounted, the hoist at the top of the shaft was energized to lift theentire assembly approximately 3 feet. The honeycomb paper was then placed In position.The paper was a glued assembly of 13 layers of honeycomb 19 inches by 26 Inches Incross section and 39 inches in height.22

ASD-TDR-63-506

"Fromi this point on, the drop operation was conducted from the control room. Thecapsule assembly was then hoisted to within 2 ificbes of the I-beam supports at the topof the shaft. Final positioning of the lifting bar against the I-beam supports was accomplishedby a motor-driven actuator that deflected the hoisting cable. See Figures 15 and 16. Thispositioning made a completely rigid assembly at the top of the shaft. After about 10 minutes.the camera and lights were energized; then after 10 seconds. the wire release mechanismwas energized cutting the support wire and releasing simultaneously both the týst packageand drag shield.

.. ... . ..

.~I

Figure 14. Test Package

TABLE 2

TEST FLUID PROPERTIES

Density Viscosity Surface Tensik § Surface Tension Contact Angle(grams (centipoises in Air at 20*C Density with Pyrex

3 at 201)dnsc (degFluids per cm 'c_at 20C• "C -

Mercury 13.55 1.554 476 35.1 .120-125

Alcohol 0.7893 L200 22.3 28.3 20-26

CarbonTetra-chloride L595 0.969 26.95 16.9 16-19

DWtied dWater 0.9982 L00S 7Me 73 le"s than 12

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STATIC FLUID CONFIGURATIONS IN CYLNDRICAL CONTAINERS

Since the contact angle (0) is kiown to be preserved at ero gravity and since the mini-mum energy principle .requires a liquid-vapor interface of constant curvature, which for anunrestricted cylinder would be a section of a sphere, the zero-gravity configuration may bedetermined. Figures 19 and 20 give the displacement of the Interface for the entire rangeof contact angles. These figures assume no end effects or restriction in the container. Alsoa gradual translation from positive to zero gravity is assumed. These predictions wereverified in the drop tower for fluids of zero contact angle. Figure 21 Illustrates both theI-G and zero-G configuration for ethyl alcohol Identical results were obtained with carbontetrachloride and distilled water. A point was also verified for the nonwetting fluid config-uration using mercury. In all cases in these experiments, there was an overshoot of theequilibrium position during the formation process. This condition will be discussed indetail later on. The percent of liquid and diameter-to-length ratio (D/L) of the cylindercontainer also has m effect on the static interface configuration. Figure 22 gives thiseffect for wetting fI aids and Figure 23 deals with nonwetting fluids. Figure 17 illustratesthe use of Figures 22 and 23.

NONWETTING FLUID WETTING FLUID

S" I- 4 42

U .5-6 I• 6C 0.0

0 o/L 0 D/L

Figure 17. Use of Wetting and Nonwetting Fhd Cosalpratn s in Cylindrical Tanks

For a given container (D/L constant) and fluid (9 conr:iM). the configuration is as showain Figure I&, NONWETTING FLUID

M AM -M;;] -. -0i 0.,,o.1 2 3 4 5 6 7

. ~ J VAPOR

SLIQUIDWETTING FL.UID

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ASD-TDR-63-506

In Figures 22 and 23. the common point of the four-configuration regions is an unstableconfiguration. For a fill operation under zero-gravity condition with nonwetting fluids,the progression of fluid configurations can be determined from the appropriate figure.However, in going from configuration region 3 to 4, a vapor volume may be trapped atthe fill end of the container.

Note that for a drain operation Involving wetting fluids under zero-gravity conditions,which proceeds from configuration region I to region 4, some liquid may be trapped atthe vapor end of the container. For 0 = 0". the vapor bubble of configuration region I isnot restricted to the position shown and may be found any place in the bulk liquid. If a 0of 180* is possible, the liquid bubble of configuration region 3 may "float" off the wallsof the container.

From this discussion, we may conclude that Figures 20 and 21 on interface displacementapply only f6r D/L and percent of liquid combination lying in configuration region 4 ofFigures 22 and 23.

Several drop tests were performed using ethyl alcohol in a Pyrex cylinder (D/L - 1.4)to determine the effect of Initial fluid position on final Interface configuration. Figure 24gives both the 1-G and zero-G configuration with the axis of the cylinder vertical. Referringto Figure 22 with 8 - 0. D/L - 1.4, and 50 percent liquid, we determined that both configur•.-tion regions 1 and 4 were possible and the zero-G configuration, therefore, verified. Fig-ure 25 gives configurations for ethyl alcohol (25 percent) with the cylinder axis horizontaland at a 45-degree angle. By checking Figure 22 for these conditions, one can predictboth configuration regions 4 and 3. The test results check with the predictions; however&when the axis of the cylindei was horizontal, the fluid was located at both ends of thecontainers or a "double" conflguration 3. This condition resulted because the Initialprobability for locating at either end of the cylinder was the same. The experiment wasrepeated with the 75-percent fill. Prediction of configuration region I is shown IA Figure

.22. The results were as predicted as shown in Figure 26.

Experiments were also conducted In the KC-135 and C-131 aircraft. The procedures foraircraft testing are given in Reference 25. Since the aircraft provides long periods of zerogravity, larger containers could be Investigated. The fluids considered were H20, carbon

tetrachloride, ethyl alcohol, and mercury. The cylinders were approximately 5, 10. and IScentimeters In diameter. The configuration obtained was similar to the drop-tower resultsas illustrated In Figures 27 through 29. Since in aircraft testing, the positive to zero-gravity

_g• translation does vary from run to run, this condition was found to produce two differentstable configurations as shown In Figure 27. This fact points out that if a designer is toutilize the minimum energy principle to control fluid orientation, an accurate knowledgeof the effect of the G translation is necessary. As the size of the cylinder was increased,obtaining the stable zero-gravity configuration became Increasingly difficult The 15-centimeter container Illustrated in Figure 29 was the largest cylinder investigated.

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ASD-TDR-63-506

INTERFACE OVERSHOOT

The displacement of the edge and center of the liquid-vapor interface in a cylindericalcontainer was determined by a frame-by-frame analysis of several drop tests with ethylalcohol. The results are displayed in Figure 39. Note that there is an "overshot' by the

.. * interface of the equilibrium zero-gravity configuration. This overshoot phenomenon mayin special cases present problems for the designer of propellant tanks utilizing surfacetension for fluid orientation. An example might be the following. Note Figure 22, if the

W tank was des!gned so that the translation from positive to zero gravity occurred at a fillratio only slightly below the line separating configuration regions 1 and 4. the overshootcould cause a translation from region 1 to region 4. Once in region 4, for fluids with contactangles other than zero, the overshoot may cause the vapor bubble that would normally bewall bounded to break free of the wall and "float" internal to the liquid. In most cases theproblem of overshoot can be circumvented by proper design. Acceleration perturbationsduring the translation to low gravity has a more important effect on the low-gravity liquid-vapor configuration. This effect has been noted many times in comparing the results ofaircraft tests with results of drop tests. This situation brings out a point that is oftenomitted when determining low gravity configurations using the minimum energy principle.Depending on the initial condition of the fluid as the low-gravity environment is reached,

there are many relative minimum energy states for the fluid. That is, the fluid may stabi-lize in a relative minimum energy configuration, and the surface energy must be increasedto drive the fluid from this "energy well" to the absolute minimum energy configuration.

'-K This condition is illustrated in Figure 38.

)v. a b) M(c

TWO VAPOR COALESCENCE SINGLE VAPORBUBBLES BUB84E

Figure 38. Surface Energy Condtions

Figure 38a shows a condition of relative minimum energy. This condition has been noedmany times in aircraft tests at ASD. Figure 38b shows that the condition at coalescenmrequires a higher energy state because of the increase in liquid-vapor Interface area.Coalescence has not been noted in aircraft tests for times ks high as 15 seconds. Figure38c shows a condition that would be predicted by the minimum energy principle.

Using liquid-liquid models (two equal density Insoluble fluids), we found that aftergenerating several bubbles (condition 1) approximately 15 minutes were required to obtalnconditton 3. The Coalescence could possibly be explained by the presence of small velocityand/or thermal gradients that could support the coalescence. The rate at which coalsemeoccurs at low gravity is of extreme importance in some heat-transfer proceswa.

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CONCLUWONS AND RECOMMENDATOI

The following conclusions and recommendatiow are made:

1. Th drop test facility is a useful tool for providing bosic informwamon on fluids

of low gravity.

2. The aibsolute minimum energy configuration of fluid at zero gralty In simple

container may be readily determined.

3. Lx-cuindilng on the condition of fluids during the transfer from positive to zerogravity and tile type container, the fluid may stabdlize in a relative minimum energy

configuration.

4. All real fluid will eventually form into low-gravity configuratiom with the

liquid phatiu wall bounded.

5. In tho capillary system, screens can be made to act as solid sudaces. Thiu

appears to Ieu one method of controlling fluid orientation with low-weight penalty,

6. Tbh' momentum associated with the fluid during the transfer frmn poottbe o

low gravity will cause an overshoot of the absolute minimum energy c- guratinm and

may result In the fluid stabilizing In a relative minimum energy configuration.

7. TJnkage system that utilizes surface tension for propellant poetioning and/or

mass tranatfLr appears particularly attractive for the electric engines.. Systems at thistype should le developed for this application.

so

ASD-TDR-63-5ffi

LIST OF REFERENCES

1. Electrothetmal Engine Propellant Storase and Feed System Study. Phase III ýporr. Enpneering Report No. 13558. Contract NAS-8-2574, Be-ch AircrafCorporation. September 1962.

2. l:uv, Feed Systems for Arc Jet Engiq.n Report No. ER-4821, Final Report amContract NAS-8-2526, Thompson Ramo Wooldridge, Inc. March 1962.

3. Analysis of Cryogenic Propellant Feed Systems for Electrothermal EngJlE.•Sumnmary Report, Contract NAS-8-1962, Air Products and Chemicals, Inc.October 1961.

4. Rcsea.rch and Development of Lithium and Lithium Hyride Propellants FeedSystems for Electric Propulsion Systems Summary Report, Contract NAS4--2529, MSA Research Corporation. 27 June 1962.

5. Investigations of Propellant Feed Systems for Electrothermal Eegine_., FinalReport, Contract NAS-8-1695, Arthur D. Little, Inc. October 1961.

6. Cryogenic Propellant Feed Systems for Electrcthermal Engines Report No.AE-1952-R° Contract NAS-8-1694, Mresearch Manufacturing Diviion. 3November 1961.

7. Cesium Ion Engine Propellant Feed System. Summary Report, Contract NAS-8-1621, Dresser Industries, Inc. 20 November 1961.

8. Research and Development of Propellant Feed System for Ion Engine. SummaryReport, Contract NAS-8-1620, Rocketdyne. November 1961.

9. Propellant Feed Systems for Ion EngInes: Tle Cesium Hydride S ,SummazyReport, Contract NAS-8-1616, Kelsey-Hayes Company. 15 February 1962.

10. Research and Development of Propellant Feed Systems for Ion Enes. SummaryReport, Contract NAS-8-1617, MSA Research Corporation. 6 Se•tember 196L

11. Research and Development of Propellant Feed Sysemms for on nes SummaryReport. Contract NAS-8-1619, National Research Corporation. 30 September 1961.

12. Study of Feed System for Cesium Ion Eng e..s Summary Report Contract NAS-8-1614, Aerojet-General Nucleonics. October 1961.

13. Research and Development of ProIpelant Feed Systems for Ion Engije. FinalReport, Contract NAS-8-1615, General Electric Company. 16 September 1961.

14. Cesium Ion Propellant Feed System. Report No. ER-4619, Cottract NAS-8-1618*Thompson Ramo Wooldrldge, Inc. September 1961.

15. Cesium Ion Propellant Sym ASD-TN-61-662, Prepared by Thompson RamoWooldridge, Inc., on Contract AF33(616)-7219. for Aeronautical System DIvisie,Wright-Patterson Air Force Base, Ohio. 29 December 1961.

S$1

ASD-TDRt-463-S0

LIST OF REFERENCES (4Coeutbud)

16. _Applied Research an CoqMa Ionizjrion Thrustor Cotract AP33(657)4137.Hlectro-f.r)Opcal Systems, Inc. March 1963.

17. Reynolds. W. C.. Ly ._.my C Consideratloni for the Dosq ofVeryy Low GrviW Environments, Technical Report LG-lo Stanford Uudiverlty.

1 September 196L

18. LI, Ta, Dr., IIydrostatics in Various Gravitational Fields General DynaIndcsAstronautics.

19. Benedikt. Elliot T., Eplhydrostartcs of a Liquid in a Rectangular Taask WithVertical Walls. ASL-TM-60-38, Northrop Corporation, Norair Divison.November 1960.

20. Adamson, Arthur W., Physical Chemiscry of Surfaces Intersclence PublisherszInc. 1960.

21. Petrash. D. A.. and Otto. E. W.. Studies of the Liquld-Vapor Interface Corfgp-ration in Weightlessness Prepared by Lewis Research Center, NASA lotAmerican Rocket Society Space Power Systems Conference. 25-28 September1962.

22. DeveloPment of Expulsion and Orientation Systems for Advanced LtquoldPropulsion Sysm Contract AF-(611)-;;200. Bell Aero6~stems Company.

October 1962.

23. Niener, J. J., The Effect of Zero Gravity on Fluid Behavior and System Des.1n,WADD-TN-59-149, ASTIA Document AD-215428, Propulsion Laboratory, Aero-nautical Systems Division, Wright-Patterson Air Force Base, Ohlot April 1959.

24. Truselo, R. A., Captain. and Clodfelter. R. G.. Heaot Transfer Problems of SpaeVehicles Power Systems, SAE Aeronautical Meeting. New York, New York.5-8 April 1960.

25. Clodfelter. R. G., and Lewis, R. C. I/Lt. Fluid Studies In a Zero GravityEnvironment ASD-TN-61-84, Propulsion Laboratory, Aeronautical SystemsDivision, Wright-Patterson Air Force Base. Ohio. June 1961.

26. Hobrocko Lowell M.. Liquid Contact Angle Measurement ASD Flight andEngineering Test Report, ASTEP 62-50R. Dlirectorate of Engineering Tent.Aeronautical Symsms Division. Wright-Patterson Air Force Base. Ohio.29 August 1962.

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