Project Cirrus Progress Report No. 6

8/9/2019 Project Cirrus Progress Report No. 6

1/15
http://www.blackvault.com/


2/15

ADB9673UNCLASSIFIED I LIMITED

Project Cirrus. Occasional Report Number 6

GENERAL ELECTRIC CO SCHENECTADY NY

15 OCT 1948

Distribution authorized to U.S. Gov't. agencies and theircontractors; Administrative/Operational Use; 15 OCT 1948. Otherrequests shall be referred to Signal Corps Engineering Labs.,

Evans Signal Lab., Belmar, NJ.


3/15

UNCLASSIFIED I LIMITED

Redistribution Of OTIC-Supplied Information NoticeAll information received from OTIC, not clearly marked "for public release" maybe used only to bid on or to perform work under a U.S. Government contract orgrant fo r purposes specifically authorized by the U.S. Government agency thatis sponsoring access OR by U.S. Government employees in the performance oftheir duties.Information not clearly marked "for public release" may not be distributed on thepublic/open Internet in any form, published for profit or offered fo r sale in anymanner.Non-compliance could result in termination of access.

Reproduction Quality NoticeOTIC's Technical Reports collection spans documents from 1900 to the present. We employ 100 percent quality control at each stage of the scanning and reproduction process to ensure that our document reproduction is as true to the original as current scanning and reproduction technology allows. However, occasionally the original quality does not allow a better copy. If you are dissatisfied with the reproduction quality of any document that we provide, please free to contact our Directorate of User Services at (703) 767-9066/9068 or OSN 427-9066/9068 fo r refund or replacement.

Do Not Return This Document To DTIC


4/15

,

"1I

-

.0 )0

> ' \ : ) :1 /1-- - - - - - - - -

Variation with Temperature of Nucleation Rate - ' - - ,---.- ----, I ;"";11 .J: d I Oo ~ \ l p e r c o o l e d Liquid Tin W a ~ e r Drops -Oist I--


7/15

VARIATION WITH TEMPERATURE OF THE NUCLEATION RATE OF SUPERCOOLED LIQUID TIN AND WATER DROPS A. rnTRODUCTION

In investigations of the kinetics of the formationof a new _phase, it is Important to learn at what ratenuclei, or centers oC Cormation Cor -the new phase,make their appearance. It i s possible to investigatethe rate of nucleation by observing single massesof material during and after a phase transformation.However, in many cases it is difficult to separatethe kinetics of nucleation from the kinetics of thegrowth of the new phase after nuclei have madetheir appearance. The nucleation of a substancecan often be more easily studied by dividing It Intoa l arge number of small, mutually independentpar-ticles and observing as afunction of time the number of partic les which have undergone transCormation. The time required for a particle to change from one phase to another once a nucleus has formedwill, -In general, be proportional to the first powerof the particle radius. The chance that a nucleuswill form _will generally be proportional to the sec-oild or third power of it s radiUS. Therefore, bymaking particle sufficiently small, the timerequired -for the occurrence of a_nucleus can bemade-large In relation to the timej'equlred for theparticle to transform once a nucleus-has appeared.It Is advantageous to make nucleation-measurementson systems containing a sufficiently large number ofparticlesJo be easily treated statistically.

Preliminary investigations have been made onthe nucleation of supercooled tin _nd supercooledwater. Observations were made at constant temperatures on the freezing rate of systems composedof large_numbers of supercooled drops.B. EXPERIMENTAL METHODS AND RESULTS1 .Nucleation of Supercooled Liquid Tin

In the experiments on tin, the samples wereprepared from a fine tin powder Jobtalned fromEimer and Amend) conSisting of small spheres oftin ranging in diameter from approximately 1 to 10microns. (The fact that the particles were far fromuniform:in diameter complicated the interpretationof experimental results. In future -work, it will bedesirable to perform the experiments on samplescontaining drops as nearly identical as possible.)In-the first experiments, the sample of tin powderwas mixed with a bakelite varnish-and spread as afilm on a glass slide. The slide was mounted in


8/15

'...._.m e ~ e m e n t o f the rate 'ofnucleation was made byfirst beating the bulb to II. temperature above themeltiDg point c[ & (265OC),and thcn. placing i t in asilicone oU, c O l i . ~ t a n t - t e m p e r a t u r e b,aih. The'rateof nucleation,wasnatermined by observing the rate.of volume decrease as melLSlll'ed by-the motion ofthe "Octoll S" along a graduated capillary tube. Along capUlarytube was used in the first experim(lnts,but it-was found that appreciable error was ClUl8edby the,slow dratugeof the llquid from the walls ofthe time. ThiSod1ffleulty' was m1nim1zed by uSingthe r e s e r v o ~ s h o w n in:Fig. 2. Duiingthe meltingof the sample, tbe tube was held ,at an angle s6thatt h e o U c o v e r e d ~ e n d o f l b e s m a l l f u S e d q u a r t z t u h e sealed into the P11'8x capUlary. (The 'small tube W8.3made offusedquartz 80Uiat i t would'not melt-whilei t was being sealed i n ~ o the pyrex cap1ll,ary).Vihen the sample had been cooled to 'almost tile desired temperature, the tube was tipped so that theexcess liquid ran away.fro,in the end Of the capWarytube, thus f o r ~ the ,meniscus in ' a convenientp O s l ~ o n . T}le results' of the' experiments, are shawn lJ,Flg:,3. The t i ~ e has been plotted on a log scale tocondense the c\irves for rims made over a long,timeinterval. If the chances -of a nucleus , occurrilig ineacli:ttn particle were euctl , the -same and,wereindependentof 'the length-of time i t ,had been super cooled, one w o ~ d expect the rate of nucleation todecrease e x p o n e ~ t i a l l y w i t h time. The curves;shawclearly that inothese exPeriments "this is not thecase. The fraction of the sample c1jstallizmg peruniUime steadily decreaSes with ume. Some dropsnucleate more readily t.haIl others, probably b ~ c a u s e they,are either larger tliin the others or becausethey' c'ontain certain impurities whl,ch increase theprobability of nucleus forination. The data obtainedshoUld be interpreted as the behavior of super'cooled tin w i t h ; - w h ~ t e v e r .. i m p u r i t i e ~ were p r ( ! ~ e n t .

I t is 'probable'that tin, free of impurities, i f i t couldbe obWned, might behave very differently.One of :the most striking features of the data Is

t h ~ very great-:effect of temperature on the rate of

nucleation. A dc!crease in temperllture of sevendegrees causes a sixtyfold increase in the nucleation rate. In observations on the rate of nucleationof supercooled water clouds in the presence oC silveriodide smoke, the author has observed a 'simUarlarge negative temperature coefficlent{l); For agiven smoke, the rate of ice crystal formation wasapprOximately thirty times greater at . laoe thanat -lOOC.An approximate value for the activation energyof the nucleation reaction can be c o m ~ t e d fromthe data in'Flg. 3. The log of the reciprocal of thetime required for one third of the sample to freezewas plotted against the reciproCal of the ,absolutetemperature to give the curve in Fig. 4. This cor-responds to an activation energyof -2 x105calorie!:.The.data takenat 116.7OC has not been used becausenucleation at that tenlperature proceeds so rapidly

~ a t most of the sample is frozen by the time it s,temperature has come to equilibrium with the constant tempe,rature bath. .Nucleation of Supercooled WaterThe author first attempted to measure the nucleat!on of supercooled water w h U e c o n d u c ~ e x p e r i mentsat theDe-icing Research Laboratoryat M.I.T.'Anemulsionofwaterdl-ops suspended in lub'ricating011 was c'ooled to -29OC with ' the expectation ofmeasuring the nucleation rate by the rate of volumeincrease. This methocfwas noLSuccessfui,becausethe solubility of water ill the oil was sufficientlylarge so that diffusion rapidly took place:-from theullfrozen to,the frozen dr0pH.Some preliminary ,studies -on water ha.ve been

~ a d l ! in cl:ds laboratory using -a variation-of the

z...1010

N ' 7I eoZ 60jII! 40Z;:15 30IE 20

10

TIME IN MIMlTE!o ,FIC. , FucUon oll)n drop" r c n u l : ' I I n ~ uniro.t''f .l!l: luncllntl 01 IImr Irom dJlllomtftr d . a 1 ~ .

1. VOMegut, B. To be published CHE MI CAL REVIEWS.


9/15

method descr.l.bed above. In these experiments, 64drops of distilled water weighing approximatelythree milligrams each were placed in a square pattern on a polished c h r o m l u m - p ~ a t e d metal plate.On the recommendation of Dr. V. J. Schaefer ofthis laboratory, the chromium surtace of the metal

plate was covered with a thin-film of _polystyrene bydipping it into a solution; This-had been. found bySchaefer to lower the temperature to which thewater could be supercooled. The plate with thedrops on it s surface was tlien placed on a thE'rmostated copper block at some temperature belowfreezing. To prevent impurities in the ai r fromsettling on the water drops, -the plate was coveredwHh a piece of plate glass which rested on a raisedrim on the copper block. The heat t ransfer betweenthe block and plate was sufficient to bring the dropson the plate to the temperature 'of the block in lessthan one minute. The number of unfrozen waterdrops was measured as a function of time by visualobservation. Figure 5 is a curve showing the nucleation of the drops at v a r i o u s t ~ m p e r a t u r e s .

Despite precautions _o keep-the water drops f reefrom impurities, it is c e r t a l n t J t h e drops werecontaminated by foreign material from the atmosphere and from the s u r f a c e plate, which increased the rate of nucleatio!1. -Here again the datawould probably be fa r differeI:\rfor completely purewater. The striking feature of -the -data 1s againthe large negative temperature coefficient whichcharacterized the results of the- experiments on

V"-/ / ,//

// VV

3 .0

2.5

2.0~ - - ' ~ II 1.5

1.0

0.5

0.00247 0.00250 0 .00253T

Fig. 4 Nuclullon . .tt 0/ tin drops as alunctlon 01temperat"re.

2. Schaefer, V. J. SCIENCE, 104, pp. 457-4593. Schaefer, V. J. BULLETIN- OF AMERICANpp. 1'75-182 (April, 1948).

ffi!lO..

20o~ . , oJIL010II:ill 7

6z S4

-_ _ ......,........._ _ _ _ _ _ -14.2C-16.O'c

3 0 ~ ~ 2 ~ - 4 ~ - 6 ~ ~ - = ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ - J TIME

Fig. 5 rucllon.olw:tcr drops remaining unlro:c n as a lonetlon 01 time.

supercooled tin and ona supercooled cloud seededwith silver iodide.The data for the freezing of water drops givenin Fig. 5 can be interpreted :in terms of the rate ofnucleus formation per gram of water. Figure 68 r - - - - - - - - - ~ - - - - - - - - - - - - - - - - ~ /I7 I6 I/ I IIa: 5 /Ie /

i

/I

4a: /IAI ICL 3 /I&ig 2 /Iz2 /

/

0

- I TEMP cI./-2 0 -25 -30 -3 5

.00385

Fie. e NlIeleaUDG rale at "ater drope .. a hlDcUOII til t.mp ,Abu'e.(November 15,1946). METEOROLOGICAL SOCIETY, 29, No.4,
http:///reader/full/rucllon.olhttp:///reader/full/rucllon.ol


10/15

r--- - - -- - - - - - - - - -- - - - --- -

'relates the rate of nucleus formation per gram tothe reciprocal of the absolute temperatures. Therate of nucleation was calculated from the timesrequired for the fir!lf 22 drops !ofreeze at the Tarious temperatures. The -energy of activation computedfrom the slope of the curve in Fig. 6i s - 1 . 6 x 1 ~ cal. It is interesting to extrapolate this data forcomparison with observations made by Dr. V. J.Schaefer(2)(3) in his experiments on supercooledclouds. If i t is assumed that the liquid water content in the cloud in the cold box is of the order of1 gm/m3, at a temperature of -25OC, according tothis data ice crystals should be appearing at therate of about 104 per second. Actually, with cleanai r at this temperature, _no crystals are observed.It is not until the temperature falls below -39.0+0.1 0C that many crys tals begin to form. The rateof nucleation in the water drops on the metal plateis much larger than that in the water drops in acloud, probably because of the nucleating effect ofthe surface of the plate and_chance impurit ies.

The sudden appearance of-large numbers of ice

crystals when the temperature is _3g0C or lowerindicates thafinSchaefer's experiments the increaseIn nucleation rate with decreasing temperature mustbe even greater than that found in this work.C. SUMMARY

X-ray diffraction, dilatometric, and visual techniques are described for measuring the extent ofcrystallization of systems composed of many smal lmutually Independent volumes of supercooled liquid.Preliminary -measurements on supercooled liquidtin and sllpercooledwater show their rate of nucleation has a vc"y large negative temperature co-eff icient corresponding to an activation energy of theorder of -2 -x 105 calories.ACKNOWLEDGEMENTS

The author wishes to thank Dr. D. Harker for.his helpful advice and the use of his x-ray facilitiesin thlswork, a n ~ Drs. I. Langmuir and V. J. Schaeferfor their Interest and many valuable suggestions.


11/15

, ----- .. . . , . - - - - - - - - - - - - : - - - . . . , . . . . - - - - - - - - - . . . , , - : : : - - ~ - - - - - - - - - -

DISTRIBUTION LIST FOR REPORTS ON PROJECT CIRRUSNo. ofCopies50 Transportation Officer, SCEL, Evans Signal Laboratory, Bldg. 42,

Belmar, N . ~ w Jersey. Marked: "For Signal Property Officer. H50 Chl,$f of Naval Research, Navy Department, Washington 25, D. C.Attn: Code N42850 Chief of Staff, U. S. Air Force, Washington 25, D. C.Attn: Dir. of R&D, DCS/M'1 Director, Mt. Washington Observatory2 Divinity Avenue, Cambridge 38, Massachusetts1 Committee on Geophysical.:_Sciences, Research and-pcvelopmentBoard, Washington 25, D. C1 Panel on Meteorology, Research and DevelopmentJ30ard, Washington25; D. C. '1 U. S. Weather Bureau, 2 4 t h , ~ Streets, N.W., Washington 25, D. C.Attri: Dr. H. Wexler1 U. So Weather Bureau, 2 4 t ~ a n d M Streets,N.W., W a s h ~ g t o n 25, D. C.Attn: Dr. Ross Gunn .1 D i r ~ c t o r , National Bureau ofStandards, WashingtoiJ.::25, D. C.Attn: Mr. Hugh Odishaw1 D$p,rtment of Agriculture,-Washington, D. C.2 C O I l 1 m i s s i o n e r ~ Bureau oLReclarnation, Was4ingtQn 25, D. c.Attn: 'Section 7241 Chief Hydraulic Engineer,_J-. SoGeological Survey" W ~ s h i n g t o n 25, D. e.Attn: Div. of Water Utilization3 Dire_ to r of Aeronautical Research, N A.C IA., 1724 F -Street; N. W.;Washington, D. C.1 N ' A : ~ C . A . Laboratories, C ~ e v e l a n d Airport, Cleveland, OhioAttn: Mr. L. A. Rodert1 M ~ $ s a c h u s e t t s Institutl? of Technology, Department 9f :Meteorology,Cambridge 39, MassachusettsAttn: Dr. H. G. Houghton


12/15

No. ofCopies1 New York U n i v e r s i t y ~ Department. of Meteorology, New-York, New York Attn: Dr. B. Haurwitz 1 New York University, College of Engineering, New York, New York Attn: Dr. A. F. Spilha.us 1 University of -Chicago, Department ,of Meteorology, Chicago, Illinois. Attn: Dr. Horace Byors 1 . University of Californb. at Los Angeles, Department of -Meteorology, Los Angeles, California, Attn: Dr. M. Neiburger 1 Pennsylva..'1ia state -College, Division of Meteorolog"'y, State College)

1 ? ~ ) n n s y l v a n i a , Attn: Dr. H. Neiburger 1 Director, Blue Hill Observatory, Milton 86, Massachusetts1 Institute for A d v ~ n c e . d Study, Princeton, New Jersey, Attn: Dr. J. Von NEilunlann 1 Woods Hole Oceangraphic Institution, Woods ~ o l e , MassachusettsAttn: Dr. C. O ' D ~ -Iselin1 St. Louis University, 3621 Olive Street, st. Louis 8, MissouriAttn: Dr. J. -B. Macelwane, S. J.-1 University of T e ~ a s , Austin, Texas, Attn: W. E. Gordon1 New Mexico Scho_ol of Mines, Box 6000, Station A, Albuqueque, NewMexico, Attn: Dr. -E. J. Workman1 University of New Mexico, Albuquerque, New M ~ x i c o , : : A : t t ~ : Dr. V. H. Reg1 Scripps Institution-of -Oceanography, La Jolla, California, Attn: D. Leippe1 Stanford University, palo Alto, California, Attn: Dr. S. -Chapman1 University of Alaska; College, Alaska, Attn: Dr. E. F. George1 Chief, State Water Survey Division, Urbana, Illinois1 Landing Aids Expe!ir.nent Station, Transocean Air Lines, Inc., Arcata,California, Attn:R. L. Champion3 Project Cirrus, General Electric Flight Test Hangar, SchenectadyCounty Airport, S c h ~ n e c t a d y , New York, Attn: Comdr. 'E. B. Faust

10 Commercial Service-Section, Syracuse, New York, Attn: -c. P. Reynolds65 Reserve-

260 TOTAL
http:///reader/full/Spilha.ushttp:///reader/full/Spilha.ushttp:///reader/full/Spilha.ushttp:///reader/full/Spilha.us


13/15


[ This page is intentionally left blank. ]


14/15


[ This page is intentionally left blank. ]


15/15


Distributed ByD TiCInformation For The Defense Community

Documents

Project Cirrus Progress Report No. 6