NASA Reference Publication 1013

Triple Point Determinationsof Monomethylhydrazine andNitrogen Tetroxide (2.2 Percentby Weight Nitric Oxide)

Irwin D. Smith and Patrick M. Dhooge

NOVEMBER 1977

NASA

https://ntrs.nasa.gov/search.jsp?R=19780005291 2020-01-29T13:31:23+00:00Z

NASA Reference Publication, 1013

Triple Point Determinationsof Monomethylhydrazine andNitrogen Tetroxide (2.2 Percentby Weight Nitric Oxide)

Irwin D. Smith

Lyndon B. Johnson Space CenterHouston, Texas

and

Patrick M. Dhooge

Lockheed Electronics Gompatiy,:, Inc.Las Cruces, New Mexico ' ' ':

\'i ..V/:'.; i • ,--•-•,

• ; : "

NASANational Aeronauticsand Space Administration

Scientific and TechnicalInformation Office

1977

CONTENTS

Section Page

SUMMARY 1

INTRODUCTION ........ 2

TEST OBJECTIVES 2

TEST FLUIDS , 2

TEST DESCRIPTION 2

Laboratory System 2

Test Stand System ..... , 4

MMH TRIPLE POINT TEST RESULTS 5

Laboratory Results . . . . . . . .............. 5

Test Stand Results 6

MMH VAPOR PRESSURE TEST RESULTS 7

N204 TRIPLE POINT TEST RESULTS . Q

CONCLUDING REMARKS . n

REFERENCES . . n

111

TABLES

Table Page

I TRIPLE POINT OF MMH USING LABORATORY METHOD ..... i 6

II VAPOR PRESSURE OF MMH .............. . . 9

' I

FIGURES

Figure Page

1 Laboratory apparatus for measurement of triple 'point of fluids ......... ..... . .... : 4

2 Test stand apparatus for measurement of triple .. . ,point of fluids under spacelike conditions . . . :. 4

3 Test stand apparatus equipped with remotely !operated agitation arm ..... ......... . ' 5

4 Frozen MMH at conditions approaching the <triple point ......... ..'•. ........ 7

i

5 Calculated vapor pressure of MMH ........ :.'.'. .: 8

6 Photograph showing some dark liquid-statepresent in bottom of bag 15 seconds afterintroduction of the ̂ 04 ............. 1Q

7 Photograph taken a few seconds after that shown infigure 6, showing frozen N204 on sides of bag ... 10

iv

TRIPLE POINT DETERMINATIONS OF MONOMETHYLHYDRAZINE

AND NITROGEN TETROXIDE (2.2 PERCENT BY WEIGHT NITRIC OXIDE)

By Irwin D. Smith3 and Patrick M. DhoogebLyndon B. Johnson Space Center

SUMMARY

During the winter of 1975-76, aseries of tests was performed at theNASA Lyndon B. Johnson Space CenterUhite Sands Test Facility to ascertainthe triple point of monomethylhydrazineand nitrogen tetroxide. The triplepoint of a material is the set of tem-perature and pressure conditions atwhich that material will exist simul-taneously under equilibrium conditionsin the liquid, vapor, and solid phases.Two methods were used to establish thetriple point. The laboratory methodusing a closed system indicated thetriple point of monomethylhydrazine is219.5 K (-64.7° F) at 11.7 pascals(0.0017 psia). The laboratory methodis the technique normally used to meas-ure the triple point of fluids. In thesecond method, the fluid was exposed toa specific pressure in a very largechamber and allowed to cool by evapo-ration to the equilibrium temperaturefor the fluid at the pressure exerted.This method simulated a spacelikeenvironment to more properly evaluatethe behavior of monomethylhydrazinewhen exposed to the near vacuum ofspace. The results obtained using thesecond method indicate that a truetriple point situation was not achievedbecause of an observed pronouncedtendency of the monomethylhydrazine tosupercool. Once solid-phase materialis obtained in combination with liquid

material, the liquid material over aperiod of time converts to the solidphase. In recognition of these phenom-ena, the data obtained under spacelikeconditions should more appropriately becalled the effective freezing pointrather than the triple point of thematerial. Using this technique, theeffective freezing point under space-like conditions of monomethylhydrazine(with agitation) was found to be 211.5 K(-79.0° F) at 3.72 pascals (0.00054 psia).without agitation, supercooling was ob-served to temperatures as low as 207.6 K(-86.00'F).

As a result of the attempt todetermine the triple point of monomethyl-hydrazine under spacelike conditions, newexperimental values for the vapor pressureof the liquid phase were determined attemperatures between 275.2 K (35.60° F)and 207.6 K (-86.0° F). The new vaporpressure data were combined with existingliterature data to permit the generationof equations for the vapor pressure ofliquid monomethylhydrazine from the nor-mal boiling point to below the normalfreezing point and into the supercooledtemperature range for the fluid.

A laboratory determination of thetriple point of nitrogen tetroxide wasnot performed. Tentative values for theeffective freezing point under spacelikeconditions of nitrogen tetroxide contain-ing 2.2 percent by weight nitric oxidewere determined to be 259.4 K (7.2° F)at 15 444 pascals (2.24 psia).

aNASA Lyndon B. Johnson SpaceCenter White Sands Test Facility.

bLockheed Electronics Company, Inc.

INTRODUCTION

Personnel at the NASA Lyndon B.Johnson Space Center (JSC) White SandsTest Facility (WSTF) performed a seriesof Shuttle orbital maneuvering enginecold-flow tests during the winter of1975-76 to determine the amount ofresidual monomethylhydrazine (MMH) fuelremaining in the regeneratively cooledthrust chamber after various purge andvent sequences. These tests were per-formed at test chamber pressures of lessthan 6.89 pascals (0.001 psia) that werebelieved to be below the triple pointpressure of MMH. Freezing of the MMH wasnot observed in any of the tests as wouldhave been expected if the MMH had beensubjected to pressures below the MMHtriple point. An Atlantic Research Cor-poration report (ref. 1) indicated thatthe triple point of MMH was 13.79 pascals(0.002 psia) at 220.8 K (-62.3° F);however, the derived value was notbased on experimental data. A thoroughreview of the chemical literature alsoindicated that the triple point of MMHhad not been experimentally determined.Hence, WSTF personnel were requested todetermine the triple point of MMH toassist the Propulsion and PowerDivision at JSC in the interpretationof the data observed in the orbitalmaneuvering engine purge and vent, tests.

As an aid. to the reader, where nec-essary the original units of measure havebeen converted to the exact equivalentvalue (without regard for the number ofsignificant digits) in the Systeme Inter-national d1Unites (SI). The SI unitsare written first, and the original unitsare written parenthetically thereafter.

TEST OBJECTIVES

(0.25 psia). A third objective of thetests was the tentative determinationof the triple point of nitrogen tetrox-ide 0̂4) containing 2.2 percent byweight nitric oxide (NO) under aspace!ike environment.

The

TEST FLUIDS

and N~Q, used in the testsmet the applicable Space Shuttlerequirements. The compositions of thepropellents are provided in the tableon the opposite page.

TEST DESCRIPTION

Laboratory System

The laboratory method used for thedetermination of the triple point of MMHwas a modification of the system describedby Colarusso and Semon (ref. 2). Theprincipal modification consisted of theaddition to the test cell of a means formeasuring the pressure exerted by thefluid being tested. Figure 1 is a photo-graph of the test cell. The tube extend-ing into the center of the cell containedthe thermocouple (Chromel-Alumel). Thefluid being tested was placed in thelarge-diameter tube surrounding the tubein the center of the cell. The side tubewith the metal fitting was connected tothe transducer used to measure the pres-sure exerted by the fluid vapors. Thepressure was measured by a 0- to6895 pascals (0- to 1-psia full scale)Datametrics multiple-range Barocelltransducer. Adjustment of the trans-ducer range permitted accurate measure-ment of pressures as low as 0.69 pascal(1 x 10-* psia).

The primary objective of the testsdescribed in this report was the deter-mination of the observed triple pointof MMH under laboratory conditions andunder a spacelike environment. Thesecondary objective of the tests wasthe acquisition of MMH vapor pressuredata at pressures below 1724 pascals

Specifications, Space Shuttle FluidProcurement and Use Control. SE-S-0073, rev. B, Feb. 9, 1975. (Thesespecifications have since beensuperceded by SE-S-0073, rev. C, Feb.14, 1977.)

Composition parameter Requirement Actual

Monomethylhydrazine

Monomethylhydrazine assay,percent by weight

Water plus soluble impurities,percent by weight

98.0 (min.)

2.0 (max.)

98.9

1.1

Nitrogen tetroxide

Nitrogen tetroxide assay,percent by weight . . .

Nitric oxide assay,percent by weight . . .

N204 plus NO,percent by weight

Water equivalent,percent by weight

Chloride content,percent by weight

97.0 (min.)

1.5 (min.)to 3.0 (max.)

99.5 (min.)

.20 (max.)

.040 (max.)

97.6

2.2

99.8

.06

<.04

A line at the top of the test cellconnected a liquid nitrogen trap andvacuum pump to the system; the linecould be isolated from the test cell atappropriate times in the test^procedureby a glass vacuum stopcock.

The method used in the laboratoryclosely followed that described byColarusso and Semon. The procedureconsisted of the following sequence ofactions after the MMH had been placedin the test cell.

1. Through use of a monochloro-trifluoromethane/dry ice bath surround-ing the test cell, the MMH was frozen,and the space above the MMH was evacu-ated to remove dissolved gases.

2. The MMH was then allowed tomelt.

3. The process of freezing andevacuation was repeated several times

(as many as six times) to thoroughlyremove the gases dissolved in thefluid.

4. After the dissolved gases hadbeen removed, the temperature and pres-sure in the cell were monitored as thetemperature of the frozen material wasslowly increased.

5. The triple point was noted bythe presence of liquid around thecenter core of frozen fluid and by thechange in the slope of the pressurecurve as a portion of the frozen fluidtransformed to the liquid state.

This method is very similar tothat used by the National Bureau ofStandards to determine the triple pointof fluids, characteristically in aclosed system that limits the amountof material that may become vapor.Reproducible results are obtained only,when the dissolved gas content of the

Figure 1.- Laboratory apparatus formeasurement of triple point offluids.

Figure 2.- Test stand apparatus formeasurement of triple point fluidsunder spacelike conditions.

fluid has been removed or reduced toa minimum.

Test Stand System

A very large test stand (401) atthe WSTF was used to acquire triplepoint data under spacelike conditions.This test stand has an internal volumeof approximately 935 cubic meters(33 000 cubic feet), which may be main-tained at a desired vacuum through theuse of mechanical vacuum pumps. Fig-ure 2 shows two identical test setupsused to ascertain the triple point ofMMH under spacelike conditions. Approx-imately 40 cubic centimeters of MMH wereloaded into the 1.27-centimeter-diameter(0.5 inch) tubing assembly mounted abovethe 6.35-millimeter (0.25 inch) solenoidvalves before closing of the test chamber.As shown in the photograph, a5.08-centimeter-long (2 inch) sectionof 6.35-minimeter (0.25 inch) tubingextended below the valve into the

10.16-centimeter-square (4 inch),10.16-centimeter-high (4 inch), 0.13-millimeter-thick (5 mil) polytetra-fluoroethylene bag. The bag wassupported by a wire frame to minimizethe conduction of heat into the MMHcontained in the bag. A bare-tipChromel-Alumel thermocouple was mountedwith the tip on the bottom of the bag.The pressure in the test stand wasmeasured by a Barocell transduceridentical to that used in thelaboratory tests described in thepreceding section.

For each test, the pressure in thetest chamber was reduced to the desiredvalue by the mechanical vacuum pumps,and then the MMH was introduced intothe bag by opening the solenoid valve.The MMH in the bag was monitored (bytelevision) for the presence of a solidphase while the temperature and pressurewere continuously recorded. The triplepoint in these tests was defined as theset of temperature and pressure conditions

at which the MMH was present in the bagin both the liquid and solid phases.

A similar test setup was placedadjacent to a window in the test standas shown in figure 3. This view of thesetup taken from inside the test standshows the placement of a solenoid-actuated "arm" covered with foaminsulation; the arm was used to softlystrike the bottom of the bag to providesome agitation to the MMH in the bag.This setup permitted visual observationof the MMH in the bag during severaltests.

The test results obtained by thismethod provide data that more realis-tically relate to the behavior of thefluid in a vacuum of unlimited volume,because of the large ratio of test-stand volume to test-liquid volume.This spacelike condition requires thatthe fluid being tested cool itself(while in the open) by evaporation of

0.13-mm (5 mil],; polytetrafluoro-i ethylene bag

a portion of the fluid. These triplepoint test conditions more closelyresemble those that might occur inspace and differ significantly from thelaboratory test conditions for theclosely controlled measurement of thetriple point.

MMH TRIPLE POINT TEST RESULTS

Laboratory Results

Before the MMH triple point test,the test system and procedure wereperformance-checked using reagent-gradecarbon tetrachloride (CC1.) as the testfluid. The literature values for thetriple point of CC14 calculated fromdata cited by Moelwyn-Hughes (ref. 3)are 250.2 K (-9.4° F) at 1082 pascals(0.157 psia). Two laboratory testsyielded identical values of 250.2 K(-9.4° F) at 1069 pascals (0.155 psia).The nearly perfect agreement with theliterature data confirmed that the testsystem and procedure were satisfactoryfor measuring the triple point of MMH.

The triple point pressure andtemperature data obtained using thelaboratory test system and procedureare provided in table I. The data,obtained on two samples of MMH, indi-cate that the average values for thelaboratory (closed system) triple pointare 219.4 K (-64.7° F) at 11.72 pascals(0.0017 psia). Some variation in theobserved pressure may be due to leakageof air into the test system. In anyevent, the variation is not consideredsignificant because of the limited ac-curacy in measuring the relatively lowpressures involved.

The observed laboratory values forthe triple point of MMH are reasonablyclose to the values of 13.79 pascals(0.002 psia) at 220.8 K (-62.3° F)indicated in the literature (but notexperimentally determined) by AtlanticResearch Corporation personnel.

Figure 3.- Test stand apparatusequipped with remotely operatedagitation arm.

TABLE I.- TRIPLE POINT OF MMH USING LABORATORY METHOD

Sampleno.

11111

111222

Temperature,K (OF)

219219219219219

219218219220220220

.7

.2

.2

.2

.2

.2

.2

.7

.2

.2

.2

(-64(-65(-65(-65(-65

(-65(-67(-64(-63(-63(-63

.3)

.2)

.2)

.2)• 2)

.2)

.0)

.3)

.4)

.4)• 4)

121091315

1381010119

Pressure,Pa (psia)

.41

.34

.65

.79

.17

.79

.96

.34

.34

.72

.65

(0.0018)(.0015)(.0014)(.0020)(.0022)

(.0020)(.0013)(.0015)(..0015)(.0017)(.0014)

Average 219.4 (-64.7)

0.6 1.1

11.47 (0.00171.73 + 0.0003)

1.96 0.0003

Test Stand Results

The test system and procedure usedin the test stand triple point testsconducted under spacelike conditionswere also evaluated using CC14 as areference material. Two tests yieldedthe following results.

Observed temperature, Observed pressure,K (0 F) Pa (psia)

248.8 (-11.9)248.4 (-12.6)

1048 (0.152)1000 (.145)

In both tests, the CC14 began to freezeless than 2 minutes after being releasedinto the polytetrafluoroethylene bag.

It should be noted that, in thismethod, cooling of the fluid to thetriple point is accomplished by removal

of heat from the fluid by evaporation in-to the very large volume of the test stand,The amount of fluid evaporated does notsignificantly affect the pressure in thetest stand. The amount evaporated wassufficient to approach true vapor pressureequilibrium conditions as indicated by theconstant temperature of the fluid afterthe initial vaporization and subsequentfluid cooling. The fluid temperaturewas observed to remain constant as longas the test stand pressure remainedconstant. Because of the nature of thecooling process, it is possible for thefluid to become supercooled below thetriple point. The temperature and pres-sure values in the preceding paragraphare lower than the literature and labora-tory test values of 250.2 K (-9.4° F) at1082 pascals (0.157 psia). However, thedifferences were considered minor, leadingthe experimenters to believe that theprocedure would effectively ascertain thetriple point of MMH under spacelikeconditions.

Before the MMH triple point testswere conducted using the test stand,

the literature value for the meltingpoint of MMH was checked in the labora-tory and found to be approximately220.6 K (-62.60 F). Because the melt-ing point of a material is near thetriple point, this temperature datumwas used to guide the triple pointtests conducted under space!ike condi-tions through comparison of observedtemperatures with the melting point.

Numerous attempts to observe thetriple point of MMH were made. Mosttrials failed to produce solid MMH incombination with liquid MMH but didyield values of temperature and pres-sure, which are used in a later sectionof this report to construct a new curvefor the vapor pressure of liquid-phaseMMH. On the basis of these tests, itwas concluded that liquid MMH willsupercool rather than freeze whenexposed to a pressure below the vaporpressure (12.4 pascals (0.0018 psia))at the normal freezing point (220.7 K(-62.5° F)). In an attempt to counterthis tendency to supercool, some testswere performed using the test setup(fig. 3) in which the liquid MMH in thebag could be agitated during thecooling process.

Using that test setup, frozen MMHwas observed in combination with liquidmaterial approximately 3 minutes afterthe MMH was released into the bag.During this period, the liquid MMH wasagitated several times. When thefrozen MMH appeared, the fluid temper-ature was 211.5 K (-79.0° F) and thepressure in the test stand was3.72 pascals (0.00054 psia). Thequantity of frozen MMH increased withtest time, indicating a nonequilibriumcondition; the frozen MMH was presentin conjunction with liquid MMH forseveral minutes. After 10 minutes,all the MMH remaining in the bag hadfrozen, as shown in figure 4.

As previously noted, once solid-phase material had been obtained incombination with liquid-phase material,the liquid-phase material over a periodof time converted to the solid phase.In recognition of this phenomenon, thedata obtained under spacelike conditions

Figure 4.- Frozen MMH at conditionsapproaching the triple point.

should more appropriately be called theeffective freezing point rather than thetriple point of the material. Therefore,the test stand tests indicated that theeffective freezing point of MMH underspacelike conditions was 211.5 K (-79.0° F)at 3.72 pascals (0.00054 psia).

MMH VAPOR PRESSURE TEST RESULTS

The numerous tests conducted inthe attempt to find the triple point ofMMH under spacelike conditions resultedin the derivation of data on the tempera-ture of liquid-phase MMH at the teststand pressure under near-equilibriumconditions. These results, therefore,represent the vapor pressure data of theMMH under stable temperature conditions.The 15 vapor pressure data points givenin the literature and the 31 pointsobserved during the test stand triplepoint tests are listed in table II. Itshould be noted that the vapor pressure

values at several of the 31 temperaturepoints represent the average of two ormore actual observations.

The data in table II were smoothedby the least-squares technique to anequation of the form normally used torelate vapor pressure as a function oftemperature.

log vapor \pressure^ = a + (absolute temp.)

c(absolute temp.)

where a, b, and c are derived co-efficients.

During the least-squares process,the data were slightly weighted asindicated in table II at the high-temperature end to compensate for thelarge number of low-temperature points.All the data points were found to fitthe following equations within lessthan 3c variation.

689(0.1)

68.9. (.01)

6.89(.001)

.689•(.00011

Log (Pa) • 9.181 621 065. 025 088

K

158 905. 544 5 -

Log Haiti • 5.476 093 - 2E8.727760 .477730.2677

°R °R2

where °R -°F + 459.59

689 400(100.0)

68940(10.0)

6894(1.0)

199.8 222.0 244.3 266.5 288.7 310.9 333.2(-100) (-60) (-201 (20) (60) (100) (1401

Temperature, K (°F)

(.1)355.4(180)

Figure 5.- Calculated vapor pressureof MMH. (The Systeme Internationalunits correspond closely but notexactly to this line because ofvariation in significant figures.The original measurements weretaken in customary units.)

log (Pa) =9.181 621 - 1065f5 °88r\

158 905.5445

K2

log (psia) = 5.476 093 -

; a = 170

2058.727 760o

477 730.2677

R

; a = 0.0779

The derived equations were usedto provide the smooth calculated valuesof vapor pressure at each temperaturelisted in table II.

The existing literature valuesranged from 360.1 K (188.52° F) - thenormal MMH boiling point - to 275.2 K(35.600 F). The new data extend thevapor pressure data to 207.6 K

(-86.0° F), which is below the normalfreezing point of 220.7 K (-62.5° F);therefore, these data include somevapor pressure data for supercooledMMH. The smoothed data listed in thetables are graphed in figure 5.

N204 TRIPLE POINT TEST RESULTS

The test setup described earlierwas used to evaluate the behavior ofN204 containing 2.2 percent by weightNO under spacelike conditions. Forthese tests, the small reservoir pre-viously used for MMH was replaced witha 1-liter bottle containing N204. Thetest procedure was similar to that usedfor the MMH test, except the solenoidvalve was opened for 2 seconds todeliver approximately 40 cubic centi-meters of oxidizer from the N204 reser-voir bottle under its own vapor

8

TABLE II.- VAPOR PRESSURE OF »IH

ObservedKtemperature,3 Observed vapor pressure. Calculated vapor(OF) Pa (psla) pressure, "

Pa (psla)

Deviation, observed vs.calculated,Pa (psia)

Literature data0

360.11354.67351.07343.34337.81

331.68325.77319.72313.07309.47

298.36293.73290.33284.93284.26

(188.52) 99 154 (14.(178.74) 81 551 (11.(172.25) 71 423 (10.(158.35) 53 331 (7.(148.38) 42 582 (6.

381) 100 181 (14.530)828) 82 599 (11.980)359) 72 388 (10.499)735) 53 938 (7.823)176) 43 244 (6.272)

(137.36) 33 157 (4.809) 33 515 (4.861)(126.71) 25 959 (3.(115.82) 19 650 (2.(103.86) 14 052 (2.(97.38) 11 942 (1.

(77.38) 6 666 (.(69.04) 5 162(62.92) 4 234 (.(53.21) 3 046 (.(52.00) 3 551

765) 25 910 (3.758)850) 19 671 (2.853)038) 14 320 (2.077)732) 11 976 (1.737)

-1027 (-0.149)-1048 (-.152)-965 (-.140)-607 (-.088)-662 (-.096)

-359 (-.052)48 (.007)-21 (-.003)-269 (-.039)-34 (-.005)

9668) 6 665 (.9667) .7 (.0001)7487) 5 136 (.7449) 26 (.0038)6141) 4 214 (.6112) 20 (.0029)4418) 3 043 (.4413) 3.4 (.0005)515) 2 916 (.423) 634 (.092)

Test stand data1*

282.04275.15274.26269.26267.59

267.04263.71263.15255.37254.82

247.59246.48245.93244.82243.15

238.71238.15234.82234.26230.37

229.26226.48225.37223.15221.48

218.71217.59214.82210.93208.71207.59

(48.00) 3 489 (0.(35.60) 1 615(34.00) 1 717 (.(25.00) 1 027(22.0) 1 014

(21.00) 1 014

506) 2 537 (0.368) 951 (0.138)2342) 1 618 (.2346) -2.8 (-.0004)249) 1 524 (.221)149) 1 076 (.156)147) 951 (.138)

147) 917 (.133)

193 (.028)-48 (-.007)62 (.009)

96 (.014)(15.00) 682 (.0989) 717 (.1040) -35 (-.0051)(14.0) 696 (.(.0) 352

(-1.0) 347

(-14.0) 177 (.(-16.0) 177(-17.0) 152(-19.0) V34(-22.0) 125

(-30.0) 84.8 (.-31.0) 81.4 .(-37.0 60.0 .(-38.0) 55.2 .(-45.0) 36.5 .

(-47.0) 34.5 .(-52.0) 27.6 .(-54.0) 17.9 (.(-58.0) 13.8 (.

101) 688 (.0998) 8.3 (.0012)0511) 374 (.0543) -22 (-.0032)0504) 358 (.0519) -10.3 (-.0015)

0256) 194 (.0282) -17.9 (-.0026)0256) 176 (.0255) .7 (.0001)0221) 168 (.0243) -15 (-.0022)0194) 152 (.0220) -18 (-.0026)0182) 130 (.0189) -4.8 (-.0007)

0123) 85.5 (.0124) -.69 (-.0001)0118 81.4 (.0118) .0 (.0000)0087 58.6 .0085 1.38 .00020080 55.2 (.0080) .0 (.0000)0053 37.2 (.0054) -.69 (-.0001)

0050) 33.1 (.0048) 1.38 (.0002)0040) 24.1 (.0035) 3.4 (.0005)0026) 21.4 (.0031) -3.4 (-.0005)0020) 16.5 (.0024) -2.8 (-.0004)

(-61.0) 11.0 (.0016) 13.8 (.0020) -2.8 (-.0004)

(-66.0) 11.0 (.(-68.0) 7.58 (.(-73.0) 6.21 (.(-80.0) 4.14 (.(-84.0) 3.45 (.(-86.0) 2.76 (.

0016) 10.3 (.0015) .69 (.0001)0011) 8.96 (.00130009) 6.21 (.00090006) 3.45 (.0005

-1.38 (-.0002).0 (.0000).69 (.0001)

0005) 2.76 (.0004) .69 (.0001)0004) 2.07 (.0003) .69 (.0001)

"To compensate for the large number of low-temperature data points, the three high-temperature points were weighted in the least-squares process by the following factors.

360.11 K (188.520 F) - 5354.67 K 178.74° F) - 4351.07 K (172.250 F) - 3

Additional weighting of the data was restricted by the least-squares program.

bLog (Pa) - 9.181 621 - 1 065f5 08* - 158 9^544 5; 1700

(Log (psia) = 5.476 093 -

cRef. 4.dRef. 5.

2 058.727 760 477 730.267 7.OR (°R)Z

0 = 0.0779.)

pressure (approximately 137 895 pascals(20 psia)). As discussed earlier, inthis technique, the effective freezingpoint of the fluid under spacelike con-ditions is actually determined ratherthan the triple point. Accordingly,the effective freezing point of ^04containing 2 percent by weight NO wasdetermined to be approximately 259.4 K(7.2° F) at 15 444 pascals (2.24 psia).Figures 6 and 7 show the ̂ 64 in thebag when the temperature was near thetriple point. Figure 6 was takenapproximately 15 seconds after theoxidizer was introduced into the bag.The dark (green) liquid-phase oxidizercan be seen on the bottom of the bag,and some light-colored (light blue-green) frozen oxidizer can be seen onthe sides of the bag. Figure 7, taken

Figure 6.- Photograph showing somedark liquid-state ̂ 0* present inbottom of bag 15 seconds after in-troduction of the NoO*.

Figure 7.- Photograph taken a fewseconds after that shown in figure6, showing frozen N~0, on sides ofbag. Some dark liquid-state N^O,is still present on bottom of bag.

shortly after figure 6, shows that thefreezing process had progressed further,but some dark (green) liquid-phase oxi-dizer was still present on the bottomof the bag.

Because of limited test time, thisexperiment was not repeated at aslightly higher test stand pressure toverify the values reported in the pre-ceding paragraph. In several testsconducted at lower pressures, the oxi-dizer froze immediately when releasedinto the bag. The literature value forthe triple point of pure N?04 contain-ing little or no NO was determined in1938 by Giauque and Kemp (ref. 6) to be261.9 K (11.730 F) at 18 637 pascals(2.703 psia).

10

CONCLUDING REMARKS

The tests conducted at the WhiteSands Test Facility indicate that thelaboratory (closed system) value forthe triple point of monomethylhydrazine(MMH) is 219.4 K (-64.7° F) at11.74 pascals (0.0017 psia). Thesevalues were found to be reasonablyclose to the derived values reportedin the literature. It was concludedthat a true triple point determinationcould not be made under space!ikeconditions, in which the fluid ispermitted to self-cool by evaporation.It was observed in tests conductedunder spacelike conditions that, oncesolid-phase material was obtained incombination with liquid-phase material,the liquid-phase material over a periodof time converted to the solid phase.In recognition of this phenomenon, thedata obtained under spacelike condi-tions should more appropriately becalled the effective freezing pointrather than the triple point.

Accordingly, the effective freez-ing point of MMH with agitation underspacelike conditions was experimentallydetermined to be approximately 211.5 K(-79° F) at 3.72 pascals (0.00054 psia).It should be noted (1) that the effec-tive freezing point of MMH underspacelike conditions was very difficultto observe because of the tendency ofMMH to supercool below the normal freez-ing point as a result of the evaporationof the liquid phase, and (2) that theeffective freezing point may indeed beeven lower than 207.6 K (-86.00 p) inthe absense of agitation.

A side benefit of the various MMHtriple point tests was the acquisitionof new vapor pressure data attemperatures below 275.2 K (35.60° F).Literature data for vapor pressure ofMMH did not exist below thistemperature.

The new data were combined withthe previously published data for thegeneration of equations yielding thevapor pressure of MMH in both Inter-national System and conventional units.

The temperature range of the data isfrom the normal boiling point to 207.6 K(-86.0° F). This temperature is belowthe normal freezing point of 220.7 K(-62.5° F); therefore, some of the datarepresent information obtained on super-cooled MMH. All the data were foundto fit the equation satisfactorily.

An approximate value for theeffective freezing point of nitrogentetroxide containing 2.2 percent byweight nitric oxide was also determinedunder spacelike conditions. The valuewas found to be approximately 259.4 K(7.2° F) at 15 444 pascals (2.24 psia).This value differs considerably fromthe triple point values of 261.9 K(11.73° F) at 18 637 pascals (2.703 psia)determined using the 1938 laboratorytriple point technique on nitrogentetroxide containing little or no nitricoxide.

Lyndon B. Johnson Space CenterNational Aeronautics and Space

AdministrationHouston, Texas, August 5, 1977

986-15-00-00-72

REFERENCES

1. Gift, Ralph D.; Simmons, John A.;et al.: Study of Propel 1 antValve Leakage in a Vacuum:Final Report, June 7, 1965, toAug. 15, 1966. NAS9-4494,Atlantic Research Corporation,Alexandria, Virginia, Oct. 28,1966.

2. Colarusso, Vincent G.; and Semon,Michael A.: Measurement ofCalibration Standards for Ther-mometry. Analytical Chemistry,vol. 40, no. 10, Aug. 1968,pp. 1521-1524.

3. Moelwyn-Hughes, E. A.: PhysicalChemistry. Pergammon Press,2nd ed. 1961, reprinted withcorrections 1964.

•11

4. Handbook of the Properties ofUnsymmetrical Dimethylhydrazineand Monomethylhydrazine.Aerojet General Corp., Rep. 1292,May 1958.

5. Aston, J. 6.; Fink H. L.; Janz,G. J.; and Russel, K. E.: TheHeat Capacity, Heats of Fusionand Vaporization, Vapor Pres-sures, Entropy and ThermodynamicFunctions of Methylhydrazine.J. American Chem. Soc., vol. 73,no. 5, May 1951, pp. 1939-1943.

Giauque, W. F.; and Kemp, J. D.:The Entropies of Nitrogen Tetrox-ide and Nitrogen Dioxide. TheHeat Capacity from 15°K to theBoiling Point. The Heat ofVaporization.and Vapor Pressure.The Equilibria N204 = 2N02= 2ND +62- J. Chem. Phys.,vol. 6, Jan. 1938, pp. 40-52.

12

. 1. Report No. 2. Government' Accession No.NASA RP- 1013

4. Title and SubtitleTRIPLE POINT DETERMINATIONS OF MONOMETHYLHY-DRAZINE AND NITROGEN TETROXIDE (2. 2 PERCENT BYWEIGHT NITRIC OXIDE)

7. Author(s)Irwin D. Smith, Johnson Space Center, and PatrLockheed Electronics Company, Inc.

ick M. Dhooge,

9. Performing Organization Name and Address

Lyndon B. Johnson Space CenterHouston, Texas 77058

12. Sponsoring Agency Name and Address

National Aeronautics and Space AdministrationWashington, D.C. 20546

3. Recipient's Catalog No.

5. Report DateNovember 1977

6. Performing Organization Code

JSC- 128768. Performing Organization Report No.

S-475

10. Work Unit No.

986-15-00-00-7211. Contract or Grant No.

13. Type of Report and Period Covered

Reference Publication

14. Sponsoring Agency Code

15. Supplementary Notes

16. AbstractA series of tests was performed to ascertain the triple points of monomethylhydrazine andnitrogen tetroxide. A laboratory method indicated a triple point for monomethylhydrazine,but tests in a large vacuum chamber indicated that a triple point does not occur in spacelikeconditions because the monomethylhydrazine tends to supercool. Instead, an effective freezingpoint (with agitation) was obtained. New experimental values for liquid monomethylhydrazinevapor pressure were determined for temperatures from 275.2 to 207.6 K. The values wereused to derive vapor pressure equations. Tentative values were obtained for the effectivefreezing point of nitrogen tetroxide under spacelike conditions. :

17. Key Words (Suggested by Author(s))Chemical fuels Vacuum testsMonomethylhydrazineMelting pointsVapor pressureNitrogen tetroxide

18. Distribution Statement

STAR Subject Category:28 (Propellants and Fuels)

19. Security Qassif. (of this report) 20. Security Classif. (of this page)Unclassified Unclassified

21 . No. of Pages 22. Price*

15 $3.50

'For sale by the National Technical Information Service, Springfield, Virginia 22161NASA-Langley, 1977

National Aeronautics andSpace Administration

Washington, D.C.20546

Official Business

Penalty for Private Use, $300

SPECIAL FOURTH CLASS MAILBOOK

Postage and Fees PaidNational Aeronautics andSpace AdministrationNASA-451

NASA POSTMASTER: If Undeliverable (Section 158Postal Manual) Do Not Return