NASA Reference Publication 1013 Triple Point Determinations of Monomethylhydrazine and Nitrogen Tetroxide (2.2 Percent by Weight Nitric Oxide) Irwin D. Smith and Patrick M. Dhooge NOVEMBER 1977 NASA NASA Reference Publication, 1013 Triple Point Determinations of Monomethylhydrazine and Nitrogen Tetroxide (2.2 Percent by Weight Nitric Oxide) Irwin D. Smith Lyndon B. Johnson Space Center Houston, Texas and Patrick M. Dhooge Lockheed Electronics Gompatiy,:, Inc. Las Cruces, New Mexico ' ' ': \'i ..V/:'.; i • ,--•-•, • ; : " NASA National Aeronautics and Space Administration Scientific and Technical Information 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-state present in bottom of bag 15 seconds after introduction of the ^04 ............. 1Q 7 Photograph taken a few seconds after that shown in figure 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. Dhoogeb Lyndon B. Johnson Space Center SUMMARY material, the liquid material over a period of time converts to the solid phase. In recognition of these phenom- During the winter of 1975-76, a ena, the data obtained under spacelike series of tests was performed at the conditions should more appropriately be NASA Lyndon B. Johnson Space Center called the effective freezing point Uhite Sands Test Facility to ascertain rather than the triple point of the the triple point of monomethylhydrazine material. Using this technique, the and nitrogen tetroxide. The triple effective freezing point under space- point of a material is the set of tem- like conditions of monomethylhydrazine perature and pressure conditions at (with agitation) was found to be 211.5 K which that material will exist simul- (-79.0° F) at 3.72 pascals (0.00054 psia). taneously under equilibrium conditions without agitation, supercooling was ob- in the liquid, vapor, and solid phases. served to temperatures as low as 207.6 K Two methods were used to establish the (-86.00'F). triple point. The laboratory method using a closed system indicated the As a result of the attempt to triple point of monomethylhydrazine is determine the triple point of monomethyl- 219.5 K (-64.7° F) at 11.7 pascals hydrazine under spacelike conditions, new (0.0017 psia). The laboratory method experimental values for the vapor pressure is the technique normally used to meas- of the liquid phase were determined at ure the triple point of fluids. In the temperatures between 275.2 K (35.60° F) second method, the fluid was exposed to and 207.6 K (-86.0° F). The new vapor a specific pressure in a very large pressure data were combined with existing chamber and allowed to cool by evapo- literature data to permit the generation ration to the equilibrium temperature of equations for the vapor pressure of for the fluid at the pressure exerted. liquid monomethylhydrazine from the nor- This method simulated a spacelike mal boiling point to below the normal environment to more properly evaluate freezing point and into the supercooled the behavior of monomethylhydrazine temperature range for the fluid. when exposed to the near vacuum of space. The results obtained using the A laboratory determination of the second method indicate that a true triple point of nitrogen tetroxide was triple point situation was not achieved not performed. Tentative values for the because of an observed pronounced effective freezing point under spacelike tendency of the monomethylhydrazine to conditions of nitrogen tetroxide contain- supercool. Once solid-phase material ing 2.2 percent by weight nitric oxide is obtained in combination with liquid were determined to be 259.4 K (7.2° F) at 15 444 pascals (2.24 psia). aNASA Lyndon B. Johnson Space Center White Sands Test Facility. bLockheed Electronics Company, Inc. INTRODUCTION (0.25 psia). A third objective of the tests was the tentative determination of the triple point of nitrogen tetrox- Personnel at the NASA Lyndon B. ide ^04) containing 2.2 percent by Johnson Space Center (JSC) White Sands weight nitric oxide (NO) under a Test Facility (WSTF) performed a series space!ike environment. of Shuttle orbital maneuvering engine cold-flow tests during the winter of 1975-76 to determine the amount of TEST FLUIDS residual monomethylhydrazine (MMH) fuel remaining in the regeneratively cooled The and N~Q, used in the tests thrust chamber after various purge and met the applicable Space Shuttle vent sequences. These tests were per- requirements. The compositions of the formed at test chamber pressures of less propellents are provided in the table than 6.89 pascals (0.001 psia) that were on the opposite page. believed to be below the triple point pressure of MMH. Freezing of the MMH was not observed in any of the tests as would TEST DESCRIPTION have been expected if the MMH had been subjected to pressures below the MMH triple point. An Atlantic Research Cor- Laboratory System poration report (ref. 1) indicated that the triple point of MMH was 13.79 pascals The laboratory method used for the (0.002 psia) at 220.8 K (-62.3° F); determination of the triple point of MMH however, the derived value was not was a modification of the system described based on experimental data. A thorough by Colarusso and Semon (ref. 2). The review of the chemical literature also principal modification consisted of the indicated that the triple point of MMH addition to the test cell of a means for had not been experimentally determined. measuring the pressure exerted by the Hence, WSTF personnel were requested to fluid being tested. Figure 1 is a photo- determine the triple point of MMH to graph of the test cell. The tube extend- assist the Propulsion and Power ing into the center of the cell contained Division at JSC in the interpretation the thermocouple (Chromel-Alumel). The of the data observed in the orbital fluid being tested was placed in the maneuvering engine purge and vent, tests. large-diameter tube surrounding the tube in the center of the cell. The side tube As an aid. to the reader, where nec- with the metal fitting was connected to essary the original units of measure have the transducer used to measure the pres- been converted to the exact equivalent sure exerted by the fluid vapors. The value (without regard for the number of pressure was measured by a 0- to significant digits) in the Systeme Inter- 6895 pascals (0- to 1-psia full scale) national d1Unites (SI). The SI units Datametrics multiple-range Barocell are written first, and the original units transducer. Adjustment of the trans- are written parenthetically thereafter. ducer range permitted accurate measure- ment of pressures as low as 0.69 pascal (1 x 10-* psia). TEST OBJECTIVES The primary objective of the tests described in this report was the deter- mination of the observed triple point Specifications, Space Shuttle Fluid of MMH under laboratory conditions and Procurement and Use Control. SE-S- under a spacelike environment. The 0073, rev. B, Feb. 9, 1975. (These secondary objective of the tests was specifications have since been the acquisition of MMH vapor pressure superceded by SE-S-0073, rev. C, Feb. data at pressures below 1724 pascals 14, 1977.) Composition parameter Requirement Actual Monomethylhydrazine Monomethylhydrazine assay, percent by weight 98.0 (min.) 98.9 Water plus soluble impurities, percent by weight 2.0 (max.) 1.1 Nitrogen tetroxide Nitrogen tetroxide assay, percent by weight . 97.0 (min.) 97.6 Nitric oxide assay, percent by weight . 1.5 (min.) to 3.0 (max.) 2.2 N204 plus NO, percent by weight 99.5 (min.) 99.8 Water equivalent, percent by weight .20 (max.) .06 Chloride content, percent by weight .040 (max.) <.04 A line at the top of the test cell (as many as six times) to thoroughly connected a liquid nitrogen trap and remove the gases dissolved in the vacuum pump to the system; the line fluid. could be isolated from the test cell at appropriate times in the test^procedure 4. After the dissolved gases had by a glass vacuum stopcock. been removed, the temperature and pres- sure in the cell were monitored as the The method used in the laboratory temperature of the frozen material was closely followed that described by slowly increased. Colarusso and Semon. The procedure consisted of the following sequence of 5. The triple point was noted by actions after the MMH had been placed the presence of liquid around the in the test cell. center core of frozen fluid and by the change in the slope of the pressure 1. Through use of a monochloro- curve as a portion of the frozen fluid trifluoromethane/dry ice bath surround- transformed to the liquid state. ing the test cell, the MMH was frozen, and the space above the MMH was evacu- This method is very similar to ated to remove dissolved gases.