T E U N I V E R S I T Y OF MI C H I GAN COLLEGE OF ENGINEERING Department of Mechanical Engineering Heat Transfer and Thermodynamics Laboratory Progress Report No. 19 PRESSURIZATION OF LIQUID OXYGEN CONTAINERS.J. A. A.Clark D. F. Jankowski H. Merte, Jr..-W. O. Winer V.. S. Arpaci UMRI Project 2646 under contract with: DEPARTMENT OF THE ARMY DETROIT ORDNANCE DISTRICT CONTRACT NO. DA-220.18- 0ORD-15316 DETROIT, MICHIGAN administered: by: THE UNIVERSITY OF MICHIGAN RESEARCH INSTITUTE ANN ARBOR December 1959

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ABSTRACT Twenty-nine experimental runs have been made and the residual densities reduced and reported. For the twenty-nine runs the imposed heat flux was programmed at four levels, adiabatic, 1200, 2200, and 2800 Btu/hr-ft2. For each level of heat flux the inlet-gas temperature was varied from -275~ to 102~F. It is noted that the heat flux of 2800 Btu/hr-ft2 reduced the residual density based on the adiabatic runs by 14%. Installation of a new heat exchanger for low inlet-gas temperatures was made. Difficulties encountered in the correlation of theoretical analysis presented in Progress Report No. 18 with the experimental data are discussed. Methods for eliminating these difficulties are outlined. A summary of the final report on the influence of acceleration on boiling is given including significant figures. ii

I. EXPERIMENTAL PROGRAM During the last period further experimental runs were made. These runs included programmed heat-flux conditions at four levels of heat flux. The nominal values of heat flux at the four levels were; adiabatic, 1200, 2200, 2800 Btu/hr-ft2. -It was previously stated that with the 220-volt heaters a heat flux of 5000 Btu/hr-ft2 might be obtained, but due to the current limitations of the power supply, 3000 Btu/hr-ft2 is the maximum flux that can be obtained. At each level of heat flux the inlet-gas temperature was varied from approximately 185~R (-275~0F) to 562~R (+1020F). There were 29 runs made in the above categories. The difficulty mentioned in Progress Report No. 18 of erratic behavior of the inlet-gas thermocouple has been eliminated on all the above runs. This was done by installing a new heat exchanger used for the low inlet-gas temperature runs. The final mean density vs. inlet-gas temperature for these runs is plotted, along with the runs reported in Progress Report No. 18 -in Fig. 1. It can be seen from these results that, in the range of inlet-gas temperatures used, a heat flux of 2800 Btu/hr-ft2 will reducethe residual density by 14% based on the density obtained for the adiabatic runs. The insulation for the inside of the container has been fitted and ready to install. The programmed runs with inside insulation will be made when the work of correlating the theory presented in Progress Report No. 18 is completed. II. ANALYSIS OF GAS- AND WALL-TEMPERATURE RESPONSE DURING THE DISCHARGE OF A CRYOGENIC LIQUID FROM A CONTAINER Work on this phase has been directed toward the correlation of the experimental data to the theory presented in Progress Report No. 18. Thus far a good correlation has not been obtained. It is felt that the main difficulty in obtaining a good correlation is due to the uncertainty of the convection heat-transfer coefficient between wall and gas, and between wall and liquid. In the theory the convection coefficient was assumed constant to reduce the complexity of the analysis. It is now felt that the variation of the convection coefficient is too great to be ignored. The difficulty is especially pronounced in the heat flux case where the liquid-wall convection coefficient is known to be quite different from the gas-wall region convection coefficent. An added, and large, variation in the convection coefficient exists in I1

the region of wall just above the liquid interface where a known condensation and re-evaporation phenomena is taking place. Because of this phenomenon the convection coefficient is large in this region, and this causes the wall temperature to experience a very rapid transient at any location corresponding to this band of condensation-evaporation. A further difficulty in the correlation arises from the gas-thermocouple arrangement presently installed in the tank. Under the present system the gas thermocouples are initially in the liquid, and as the run progresses they are successively exposed to the gas region. Because of this arrangement the thermocouple response is not representative of the gas temperature until the thermocouple is in equilibrium with the gas. This response period is further extended because the condensation-evaporation phenomenon discussed above takes place on the thermocouple wires as well as the wall. Because of these response difficulties, combined with a relatively short run (100 - 200 sec), the domain of correlation is small. In the hope of circumventing these response difficulties, a floating thermocouple column is now under consideration. This will keep the thermocouples in the gas region throughout the run and thus eliminate the response behavior due to the liquid-to-gas traverse of the thermocouples. Methods of revising the analytical model are presently under consideration to help eliminate some of the above-mentioned differences between the model and the physical system. III. POOL BOILING IN AN ACCELERATING SYSTEM* A study is made of the influence of system acceleration (1 to 21 g's) on pool boiling heat transfer in saturated distilled water at approximately atmospheric' pressure. This is the first study made of heat transfer by boiling in the presence of a force field greater than that due to standard gravity. A flat, electrically heated, chromium-plated copper disc served as the heat-transfer area,with a thin stainless-steel skirt attached to the periphery of the disc to provide a continuous surface. The water depth is maintained constant at 2-1/2 in., and a cooling coil on the underside of the cover condenses the vapor formed. Temperatures in the heating disc and water are measured with an uncertainty of + 0.10F by means of calibrated thermocouples. Figure 2 shows a cross section of the test vessel. Acceleration is attained by use of the centrifuge principle. The test vessel is pivoted from the cross arm on a vertical shaft so that the accelera*The final report on this phase was published in November, 1959, as A Study of Pool Boiling in an Accelerating System, H. Merte, Jr., and J. A. Clark, UMRI Report 2646-3-T.

tion is always normal to the heating surface, as indicated in Fig. 3. Thermocouple emf's on the rotating member are measured through mercury slip-rings. Figure 4 is an over-all view of the test apparatus. The magnitude of the acceleration is varied from that due to one standard gravity up to 21 times grativational acceleration. Heat-flux rate is varied from approximately 5,000 to 100,000 Btu/hr-ft2. Several tests were conducted with nonboiling convective heat transfer. The data agreed quite well with the correlation: Nu = 0.14 (Gr Pr)l/3 With boiling at heat-flux values up to 50,000 Btu/hr-ft2, it was found that a small degree of subcooling significantly influenced the results with the system under acceleration. Data are presented showing the influence of subcooling for heat flux of 10,000 and 25,000 Btu/hr-ft2 and for various accelerations. Figure 5 is a plot of the experimental data for boiling to saturated water in a standard gravity field.. Figure 6 shows the influence of acceleration on Tw - Tsat for the different levels of heat flux. The difference between the heating-surface temperature Tw and the water-saturation temperature Tsat at the heating surface decreases with an increase in acceleration at lower values of heat flux. As the heat-flux level increases, the decrease in Tw - Tsat becomes smaller, and at the higher values of heat flux, Tw - Tsat increases with an increase in acceleration. The decrease in Tw - Tsat at low values of heat flux is attributed to the increased contribution of natural convection with acceleration. At higher values of heat flux, the effect of natural convection is relatively smaller. It is believed that the action of acceleration results in smaller bubble sizes at departure, with an attendent decrease in agitation. For a given total heat flux, more nucleating sites are required, which in turn require the observed higher wall temperatures. Figure 7 is a plot of Tw - T5 versus acceleration for the different levels of heat flux, where T5 is the water temperature as measured 1/4 in. from the heating surface. The increase in Tw - T5 with acceleration at higher levels of heat flux occurs because of the increased subcooling of the water near the heating surface. Figure 8 illustrates the relation between the measured water temperature and the local saturation temperature for several accelerations. It appears that the water temperature approaches saturation only in the upper half of the liquid. The large force field tends to maintain the water at a uniform temperature corresponding to the saturation temperature near the surface. As a means for obtaining a theoretical understanding of the process of boiling under the influence of high acceleration including the simultaneous effect of natural convection, a concept of the "Area of Influence" of the bubbles is defined and values calculated for the various accelerations and heat-flux rates. The convection and boiling contributions to the total heat flux are considered separable, and are weighed using a natural convection correlation based on experimental data for the nonbo-iling contribution, and a correlation for the peak heat flux for the boiling contribution. This is equiv3

alent to taking the heat flux per unit bubble areaprojected on the heating surface equal to the peak heat flux. The change in Tw - Tsat with heat flux and acceleration is used to calculate the influence of heat flux on the number of active nucleating sites. IV. WORK DURING THE NEXT PERIOD During the next period efforts will be directed toward establishing a value for the convection coefficient in the system and how it varies within the system. Attempts will also be made to establish a closer resemblance between the analytical model and the physical system. Design and construction of the floating thermocouple column will begin.

0.9 0.84 0.7i 0.6 0.4 /2- /200 A A'P._? — 2200 lTU/ER- l. 0.3 AD/ABA TIC 0NO HEATFLUX GAS REGION 0.2 00 APPROX /200 BTU/HR-FT' A APPROX 2200 BTU/HR-FT2 v APPROX 2800 BTU/HR-FT2 0.1 0o 50 l00 150 200 250 300 350 400 450 500 550 600 650 INLET GAS TEMPERATURE T, ~OR Fig. 1. Final mean density pf of pressurizing gas as a function of inlet gas temperature Ti.

PIVOT ARM TGO -6, WATER TC-5, WATER CONDENSER COIL OUTER CGONTAINER DRIP PLATE,' ~~~ ~ ~ ~/ o FLOW GUIDE "J- 31' I / r F k INNER CONTAINER 0,- - __-| | _ __ TO-I, HEATER HEATER BLOCK HEATER COVER ],;e (' 2 S.S.SPAER RING' D~~~~~~~~~'', +~INSUHEATER GUARD DcI- HEATER. " CHROMEL RESISTANC THERMOCATER COUPLE Figure 2. Test Vessel. Figure 2. Test Vessel.

~T~AC~HOMETER ~COOLING WATER INLET TACHOMETER GENERATOR (TO ELECTRONIC COUNTER) BELT DRIVE KEROSENE THERMOCOUPLE COMPENSATION BATH_ MERCURY THERMOCOUPLE SLIP-RING ASS'Y ~~~~~~~~~~~~~~~~~10 CHANNEL'S ~VARIABLE - SPEED HYDRAULIC TRANSMISSION GOUNTERWEIGHT MAI N SHAFT CGOOLING \ CELECTRIC WATER OUTLET DRIVE MOTOR TEST VESSEL POWER SLIP-RING ASS Y FTr DRAIN Figure 3. Centrifuge Assembly.

i~~~~~~~g} fl | |, i | E X _ _ w _ - i - -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~::...:.::-:jii::::: F B l e 4. Ovrl iie of Tes Appi a s

q/A -BTU/HR- FT2 x 104 ot I I' -I W I0 0~ ~ I I-J'31 HD I4 cf v 1- 00 i eo oL!

31 30- A 29 q/A 99,50o BTU/HR- FT2{ ORUN NO.B-21 l A of go -20 28 27 q/A 73,000 BTU/HR-FT RUN NO. B-22 26 25 23 IZ 4/A =1,870 BTU/HR-FT{ 0 RUN NO. 8-12 - 2 A,, -14 0 A RUN NO. B-8 2 1 Aq/A= 24450 BTU/HR-FT t0,, s 8-9 0 0~3 uI B-Il 20 19 18TOTAL ACCELERATI m 7 8Pool~ Boiling to Sat RUN NO. B-15 A -,, B- 7 6 6 14 Figure 6. Influence of Acceleration on Tw-Tsa t with Pool Boiling to Saturated WFater.

38 36 q/A 99,500 BTU/HR-FT2 34 RUN NO 8-21 32 30 =q/A 73,000 BTU/HR-FT2| 28 0 26 26 /48,800 BTU/HR-FT2'~ 24 -'''' -'~RUN NO B-14 24 22 - V -- q/A =24,450 BTU/HR - FT2 RUN NO 8-9 20 18 q/A -10,870 BTU/HR-FTl RUN NO B- 1 16 14 12 0 2 4 6 8 10 12 14 16 18 20 22 TOTAL ACCELERATION - a/g Figure 7. Plot of Tw-T5 vs. Acceleration with Pool Boiling to Saturated Water.

244 q/A' 48,800 BTU/HR.FT2 242 240 238.l =W190 RPM W = 220 RPM o/g = 15.73 a/g = 21.15 218 216 SAT SAT 214 210 240 wi 110 RPM 8. 155 RPM I238 /9 5.29 a/g =10.47 236 216 TsATTs 212 210 208 HEAT ER SURFAC E p-HEATER SURFACE WATER SURFACE.. WATER SURFACE Figure 8. Run No. B-14. Temperature Profile between Heater and Water Surface for Various Accelerations.

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