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On-orbit cryogenic fluid transfer research at NASA Lewis Research Center
On-orbit cryogenic fluid transfer research at NASA Lewis Research Center* W.J. Taylor, D.J. Chato, M.M. Moran and T.W. Nyland Lewis Research Center, Cleveland, OH, USA Cryogenic fluid transfer operations in the low-gravity environment of Earth orbit are necessary for many NASA mission concepts. Fluid transfer brings several benefits to the performance of space missions. Spacecraft already on orbit can be resupplied with cryogenic propellants, coolant fluids and other liquids. Lighter weight spacecraft can be built, since as they are launched dry and supplied on orbit they are not required to support the weight of cryogens during the 3 - 6 g launch environment. The filling of cryogenic tanks in low gravity poses an operational challenge. Among the difficulties encountered are vapour generation due to the energy stored in the tank walls and the uncertainty of liquid and vapour distributions in a tank in a low-gravity environment. Increased support for technological research in recent years has enabled NASA Lewis Research Center (LeRC) personnel to make significant advances in the state of the art of cryogenic fluid transfer operations via the no-vent fill method. This paper presents a summary of the results obtained to date in the ongoing programme at LeRC. The LeRC programme has two purposes, emphasizing an extensive ground test programme which is augmented by the development of analytical models for the no-vent fill transfer operation processes. Additionally, planning for the future development of this technology is continuing. This ongoing research effort should, in the near future, permit the design of space systems and spacecraft that benefit from the reusability and weight savings accrued through the use of cryogenic fluid transfer operations in a low-gravity environment.
Keywords: cryogenic liquids; fluid transfer; no-vent filling
Current concepts ~ for performing no-vent fills in space propose to use one or more pressure atomizing nozzles to inject liquid into the ullage volume of the receiver tank as a droplet spray. In the ullage, vapour will condense on the spray droplets. If the spray nozzles are submerged in the bulk liquid, it is assumed that the incoming liquid will form a jet. The jet will continue to promote condensation of the ullage vapour by inducing circulation in the bulk liquid, thereby bringing cooler liquid to the surface. Spraying the droplets through the ullage is expected to be much more efficient for condensing the ullage vapour than the submerged liquid jet, since a much larger liquid to vapour interface area will exist. Unfortunately, the location of the ullage in a lowgravity environment is uncertain, which makes the prediction of what the conditions in the receiver tank will be and the resultant heat and mass transfer at the liquid to vapour interface a difficult problem. In order to obtain data for the no-vent fill process, three liquid injection configurations were selected for testing in a *Paper presented at the 1991 Space Cryogenics Workshop, 1 8 - 2 0 June 1991, Cleveland, OH, USA This work is the property of the US Government, not subject to copyright in the USA for Government purposes.
normal gravity environment. The three configurations, illustrated in Figure 1, are intended to provide data that bound the results for a low-gravity environment. The top-spray configuration represents the best case. The liquid to vapour interface area is large and the residence time of the droplets in the ullage is at a maximum. Both of these conditions promote the condensation of the ullage vapour. The submerged, diffused inlet is designed to simulate the worst case conditions for heat and mass transfer at the liquid to vapour interface.
Top Spray
Upward Pipe Discharge
Bottom Diffuser
Figure 1 Fill configurations used for no-vent fills at CCL-7
0011 - 2 2 7 5 / 9 2 / 0 2 0 1 9 9 06 co) 1992 Butterworth - Heinemann Ltd
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On-orbit fluid transfer research: W.J. Taylor et al. The incoming flow is submerged in the bulk liquid and, owing to the incoming flow being diffused, no circulation is induced in the bulk liquid. The lack of circulation and mixing in the bulk liquid allows the liquid to become thermally stratified. The fiat liquid to vapour interface minimizes the area for heat and mass transfer between the bulk liquid and the vapour in the ullage. Both the thermal stratification of the bulk liquid and the small liquid to vapour interface area combine to minimize the heat and mass transfer at the liquid to vapour interface. The submerged jet nozzle and the upward pipe discharge represent the middle ground. The incoming flow induces circulation and mixing in the accumulated liquid, enhancing the condensation at the liquid to vapour interface owing to the cooler liquid temperature at the interface. The submerged jet nozzle may also cause the incoming liquid to geyser, thereby promoting condensation of the ullage similar to the top-spray configurations. Ground test programme
NASA Lewis Research Center (LeRC) personnel are conducting no-vent fill experiments at two facilities: the Cryogenic Components Laboratory (CCL) located at LeRC in Cleveland and the K-Site at LeRC's Plumbrook Station located in Sandusky, OH, USA. At the CCL, moderate-size testing is underway using small dewars to study the effects of several test parameters, including tank size, inlet mass flow rate, inlet temperature and liquid injection configuration, with a minimum of set-up. Completed work at the CCL includes the no-vent filling of a 141.6 dm 3 (5 ft 3) dewar using a top spray and the no-vent filling of a 34 dm 3 (1.2 ft 3) dewar by a top spray, an upward directed pipe discharge located near the bottom of the tank and a diffuser discharging downward also mounted near the bottom of the tank. K-Site's hazardous cryogens vacuum chamber is large enough to allow large-scale testing with lightweight, flight-qualified tankage. The tests conducted at K-site are designed to demonstrate the ability to apply the novent fill technologies to actual flight-scale systems and components. The test tank currently being used at K-Site
Figure 2
200
has a volume of 4955 dm 3 (175 ft3). The testing conducted at K-Site used two liquid injection configurations as shown in Figure 2, a top-spray ball and a bottom jet spraying upward. Large receiver tests The large receiver tank tested at CCL is a 141.6 d m 3 (5 ft 3) stainless-steel dewar. The bottom of the tank is an elliptical dome section. The top lid assembly bolts to a flange at the top of the cylindrical section of the tank and forms an inverted spherical dome section at the top of the test volume. Results with this receiver tank indicate that no-vent fills with nitrogen above 90% full by volume are achievable using a top-spray liquid injection configuration, in a lg environment, with inlet liquid temperatures as high as 79.4 K (143 R), and an initial average tank wall temperature of more than 166.7 K (300 R)2. This inlet temperature corresponds to a saturation pressure of 0.131 MPa (19 psia) for nitrogen. Hydrogen proved considerably more difficult to transfer between tanks without venting. The highest temperature conditions resulting in a fill percentage greater than 90% using the 141.6 dm 3 (5 ft') receiver tank were with an inlet liquid temperature of 18.9 K (34 R) and an estimated tank wall temperature of slightly more than 72.2 K (130 R) 2. The saturation pressure for hydrogen at this inlet temperature is 0.069 MPa (10 psia). All of these receiver tank no-vent fill tests were performed with a top-mounted full cone nozzle for liquid injection. The nozzle produces a 120 ° conical droplet spray at a differential pressure of 0.069 MPa (10 psi). The pressure in the receiver tank was restricted to less than 0.207 MPa (30 psia) for all tests. The shape of the pressure versus time curve for novent fill tests using the top-spray technique is characterized by three distinct regions. These regions, illustrated in Figure 3, are delineated by (1) an initial steep pressure rise as the incoming liquid flashes as it enters the low-pressure tank and is vaporized as it impinges on the warm tank walls, (2) a decrease in slope of the transient pressure response as the effect of ullage vapour condensation on the incoming liquid droplets
K-Site bottom-jet nozzle and 13-nozzle top-spray ball
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pressure rise for no-vent fills with both nitrogen and hydrogen.
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3 Typical tank pressure as a function of time for a hydrogen no-vent fill test using the top-spray fill configuration. (1) Flashing of inlet liquid, chilldown of the tank wall; (2) ullage vapour condensation on incoming liquid droplets, continued vaporization; (3) ullage compression, spray nozzle becomes submerged Figure
becomes more evident and (3) a sudden pressure rise as the liquid interface begins to submerge the inlet nozzle and enters the top dome region of the tank. Region 3 develops only in those tests which exceed the 90% fill level by volume for the test configuration employed. The liquid inlet temperature was found to be the primary parameter affecting the magnitude of the receiver tank
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A total of 42 tests were performed with different liquid inlet temperatures, inlet mass flow rates, initial tank wall temperatures and injection techniques with liquid hydrogen in a 34 dm 3 (1.2 ft 3) stainless-steel Dewar 3. The tank geometry is similar to that of the large receiver tank, with an elliptical bottom dome, a cylindrical midsection and hemispherical top dome. The injection techniques employed included a droplet spray directed downward from the top of the tank, a diffused inlet at the bottom and upward pipe discharge from the bottom. The effects of each of the parameters on the tank pressure history and final fill level were evaluated. Approximately 40% of the hydrogen no-vent fill tests performed resulted in final fill levels _ 90 % by volume. The unsuccessful tests were terminated owing to excessive pressure [ > 0.207 MPa (30 psia)] in the receiver tank. Each of the three liquid injection techniques employed displayed significantly different transient pressure reponses in the receiver tank during the no-vent fill process. The top-spray configuration cools the tank wall rapidly early in the test, owing to the impingement of the droplets on the wall. The vapour generated, as the wall is cooled, causes a rapid initial pressure rise in the receiver tank. As the transfer continues, the ullage is condensed on the spray droplets and the pressure remains nearly constant. The transient pressure response
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Figure 4 Tank pressure as a function of time for hydrogen no-vent fill tests with (a) top-spray, (b) upward pipe discharge and (c) bottomdiffuser fill configurations.
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On-orbit fluid transfer research: W,J. Taylor et al. Table 1 CCL no-vent fill test Initial wall temperature (K)
Liquid inlet temperature (K)
Top spray Upward pipe
71.1
19.5
discharge
44.4 48.3
19.1 21.1
Fill configuration
Bottom
Inlet mass flow rate (kg h - 1)
Final pressure (MPa)
Final fill percentage
54.5
0.103
98
122.7 40.9
0.096 0.200
96 76
diffuser
for a no-vent fill with a top-spray liquid inlet is shown in Figure 4a. The upward pipe discharge configuration initially cools most of the tank wall owing to the geysering of the incoming liquid, which results in a rapid pressure rise, similar to that observed during the top-spray tests, during the early portion of the fill process. As the outlet of the discharge pipe becomes submerged by the rising liquid, condensation of the ullage vapour is limited to the liquid free surface. The bulk fluid motion induced by the upward pipe discharge arrangement enhances condensation at the interface as the cooler incoming liquid is circulated upward toward the liquid-vapour interface. Figure 4b shows the receiver tank pressure versus time for a test using the upward pipe discharge liquid injection configuration. The bottom diffuser injection technique cools only the lower portion of the tank wall during the initial phase of a no-vent fill, resulting in a more gradual pressure rise at the start of the fill process. As the fill progresses, the submerged diffuser does not produce much liquid motion, resulting in less condensation at the liquidvapour interface than for the other two inlet configurations. The receiver tank pressure as a function of time for a test run with the bottom diffuser inlet is shown in
Figure 4c. The test conditions and process variables corresponding to the test results shown are summarized in Table 1. The initial wall temperature shown are mass-weighted averages based on the temperatures measured axially along the tank wall. The final pressures are the pressures recorded at the termination of the respective tests.
pressure drop of 0.069 MPa (10 psi). Figure 2 shows the two spray systems employed. Figure 5 illustrates the installed position of these systems in the tank. The K-Site test tank is ellipsoidal with a 2.21 m (87in) major diameter and a 1.2:1 major-to-minor axis ratio. The two end dome sections are joined by a short 3.81 cm (1.5in) cylindrical section. The tank is fabricated of 2219 aluminium chemically milled to a nominal thickness of 0.22 cm (0.087in). Thicker sections exist where they were required for manufacturing (mainly weld lands). There is a 0.72 m (28.35in) access flange on the top. The tank has a mass of 149.8 kg (329.25 lb) and a volume of 4955 dm 3 (175 ft3). It was originally designed for a maximum operating pressure of 0.551 MPa (80 psia). Prior to the start of testing the tank was requalified by a pneumatic test for a maximum operating pressure of 0.345 MPa (50 psia). The insulation system consists of a blanket of 34 layers of multilayer insulation (MLI) made with double aluminized Mylar and silk net spacers. Twelve fibre-glass epoxy struts support the tank in the test stand. No-vent fills with liquid hyrogen in excess of 90 % by volume were achieved using both fill configurations with initial wall temperatures exceeding 111 K (200 R). The lowest tank pressure for a test exceeding 90% full by volume (see Figure 6, Test 18) was 0.177 MPa (25.6 psia). Pressure histories for three tests with the bottom-jet liquid injection configuration and for three tests with the top-spray liquid injection configuration are
K-Site tests
Recently completed efforts include the no-vent fill of the 4955 dm 3 (175 ft 3) research with both top- and bottomjet systems 4. The bottom-mounted liquid injection system has a single jet nozzle directed upward. The nozzle will submerge soon after liquid begins to accumulate in the tank (at ---7% full by volume), and therefore heat and mass transfer between the accumulating liquid and the ullage vapour will only occur at the liquid surface. The top-mounted spray system uses a cluster of 13 nozzles. The cluster size was dictated by the availability of a commercial manifold. These nozzles are not submerged until the tank is 92 % full of liquid. The flow capacities of each inlet spray system are sized, within the constraints of commercially available nozzle sizes, to have the same inflow rate for a given inlet pressure. The nozzles were sized to provide =454 kg h -1 (1000 Ibm h -l) of liquid hydrogen at a
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Figure 5
Spray nozzle locations in K-Site test tank
On-orbit fluid transfer research: W.J. Taylor et al. Table 2
K-Site no-vent fill test parameters
Test No.
Fill configuration
Initial wall temperature (K)
Test Test Test Test Test Test
Bottom jet Top spray Top spray Bottom jet Bottom jet Top spray
21.7 104.4 126.1 101.7 66.7 70.0
18 19 20 21 22 23
Liquid inlet temperature (K)
Inlet mass flow rate (kg h - 1)
Final pressure (MPa)
Final fill percentage
22.2 23.0 22.4 22.2 21.7 22.8
500.0 421.8 337.7 448.6 504.9 419.5
0.176 0.227 0.257 0.233 0.188 0.210
94 94 94 94 94 94
presented in Figures 6 and 7, respectively. Table 2 presents a summary of the test parameters for each of the sets of test results presented in Figures 6 and 7. Since the fill systems were selected as boundary cases for the low-gravity fill, the fact that both systems were capable of filling the tank shows promise for the feasibility of the no-vent fill technique in the desired on-orbit applications. Direct comparison between the performances of the two fill systems is difficult owing the variations in the test conditions between the tests.
0.2 0.16 0.12 0.08 0.04//
400 Fill 18
4
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Figure 8 Comparison of analytical model results (dashed line) and test data (solid line) for CCL small receiver tank test 9072B. Fluid, hydrogen; inlet mass flow rate, 0.32 kg rain-l; inlet temperature, 19.7 K; wall temperature, 53.6 K; final fill percentage, 98%
Fill 22
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Wall Inlet Flow T e m p . T e m p . Rate
0-
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(K)
(K) (kgh -1)
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100
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I
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K-Site bottom-jet no-vent fill test results
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300
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(K) (kgh -1)
Fill 19 104.4 23.0 421.8 Fill 20 126,1 22.4 337.7 Fill 23 70.0 22.8 419,5
K-Site top-spray no-vent fill test results
Analytical modelling In addition to the ground-test programme, an effort to develop an analytical model to predict the pretest performance and to aid in understanding the experimental data is in progress 1,5,6. Recently completed work includes the development of a simple thermodynamic model of the no-vent fill process and the comparison of the model results with the results from the no-vent fill tests conducted with both the 34 dm 3 (1.2 ft 3) and the 141.6 dm 3 (5.0 ft 3) receiver tanks at CCL-77. The model is based on conservation of mass and a first-law energy balance for a control volume. The ullage, the bulk liquid and the tank wall are each represented by a single node. At present the model is limited to analysing the top-spray configurations. The details of the model structure and the basic equations are presented elsewhere ''5"7. Figure 8 presents a comparison of the test data and the analytical results for a no-vent fill test conducted at CCL-7 with the small receiver tank.
Concluding remarks Variable test parameters and liquid injection configurations have provided some insight into the conditions necessary for a successful transfer of liquid hydrogen by
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On-orbit fluid transfer research: W.J. Taylor et al. the no-vent fill method. The magnitude of the maximum receiver tank pressure was found to be dependent on the liquid inlet temperature, the inlet mass flow rate and the initial temperature. Future experimentation at the CCL will retest the 141.6 dm 3 (5 ft 3) dewar with both top-spray and axial spray-bar configurations. The spray-bar configuration is representative of design concepts proposed for operational systems, since the axial system and its ability to promote condensation of the ullage vapour should be insensitive to the liquid position inside the tank. The CCL test facilities will remain available for additional testing of other concepts. Results of the first K-Site tests also indicated several areas for further work. Test results are currently being compared with the previous analytical work and plans for follow-on testing are in progress. Near-term followon tests will repeat some of the previous tests with more stable liquid inlet thermodynamic conditions and improved instrumentation, and will include some new higher inlet flow rate testing. Test plans include the addition of a 2010 dm 3 (71 fC) tank for demonstrations of tank-to-tank transfers from the 4955 dm 3 (175 ft 3) tank. Spray-bar and bottom-jet systems also will be incorporated in this smaller tank for the tank-to-tank liquid transfer tests. Testing is also planned at different degrees of subcooling of the incoming liquid. Future work in the analytical modelling area will include completing a comparison of the model with results from the K-Site tests and modifying the present
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model so as to be able to analyse other liquid injection configurations and to be able to model the process in low- to zero-gravity environments. Additionally a thermodynamic equilibrium model is being developed. The equilibrium model will provide a baseline for comparing the performance of the different liquid injection systems as the model results depend only on the initial conditions, the incoming liquid mass flow rate and thermodynamic state of the incoming liquid.
References 1 Chato,D.J. Thermodynamicmodelingof the no-ventfillmethodology for transferringcryogensin low gravityNASA Technical Memorandum 100932, July 1988 2 Moran, M.E., Nyland, T.W. and Papeil, S.S. Liquid transfer cryogenictest facility--initialhydrogenand nitrogen no-ventfill data NASA Technical Memorandum 102572, March 1990 3 Moran, M.E., Nyland, T.W. and Driscoll, S.L. Hydrogenno-vent fill testing in a 34 liter (1.2 cubic foot) tank, paper presented at Cryogenic EngineeringConference,June 1991 4 Chato,D.J. Groundtestingof the nonventedfill methodof orbital propellant transfer: results of initial test seriesA1AA Paper No. 91-2326, June 1991 5 Chato, D.J. Analysis of the nonvented fill of a 4.96-cubic-meter lightweight liquid hydrogen tank NASA Technical Memorandum 102039, August 1989 6 Chato, D.J., Moran, M.E. and Nyland, T.W. Initial experimentation on the nonventedfill of a 0.14 m3 (5 ft3) dewar with nitrogenand hydrogen NASA Technical Memorandum 103155, June 1990 7 Taylor, W.J. and Chato, D.J. Improvedthermodynamicmodelingof the no-vent fill process and correlationwith experimentaldata AIAA Paper No. 91-1379, June 1991
Keywords: cryogenic liquids; fluid transfer; no-vent filling
Current concepts ~ for performing no-vent fills in space propose to use one or more pressure atomizing nozzles to inject liquid into the ullage volume of the receiver tank as a droplet spray. In the ullage, vapour will condense on the spray droplets. If the spray nozzles are submerged in the bulk liquid, it is assumed that the incoming liquid will form a jet. The jet will continue to promote condensation of the ullage vapour by inducing circulation in the bulk liquid, thereby bringing cooler liquid to the surface. Spraying the droplets through the ullage is expected to be much more efficient for condensing the ullage vapour than the submerged liquid jet, since a much larger liquid to vapour interface area will exist. Unfortunately, the location of the ullage in a lowgravity environment is uncertain, which makes the prediction of what the conditions in the receiver tank will be and the resultant heat and mass transfer at the liquid to vapour interface a difficult problem. In order to obtain data for the no-vent fill process, three liquid injection configurations were selected for testing in a *Paper presented at the 1991 Space Cryogenics Workshop, 1 8 - 2 0 June 1991, Cleveland, OH, USA This work is the property of the US Government, not subject to copyright in the USA for Government purposes.
normal gravity environment. The three configurations, illustrated in Figure 1, are intended to provide data that bound the results for a low-gravity environment. The top-spray configuration represents the best case. The liquid to vapour interface area is large and the residence time of the droplets in the ullage is at a maximum. Both of these conditions promote the condensation of the ullage vapour. The submerged, diffused inlet is designed to simulate the worst case conditions for heat and mass transfer at the liquid to vapour interface.
Top Spray
Upward Pipe Discharge
Bottom Diffuser
Figure 1 Fill configurations used for no-vent fills at CCL-7
0011 - 2 2 7 5 / 9 2 / 0 2 0 1 9 9 06 co) 1992 Butterworth - Heinemann Ltd
Cryogenics 1992 Vol 32, No 2
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On-orbit fluid transfer research: W.J. Taylor et al. The incoming flow is submerged in the bulk liquid and, owing to the incoming flow being diffused, no circulation is induced in the bulk liquid. The lack of circulation and mixing in the bulk liquid allows the liquid to become thermally stratified. The fiat liquid to vapour interface minimizes the area for heat and mass transfer between the bulk liquid and the vapour in the ullage. Both the thermal stratification of the bulk liquid and the small liquid to vapour interface area combine to minimize the heat and mass transfer at the liquid to vapour interface. The submerged jet nozzle and the upward pipe discharge represent the middle ground. The incoming flow induces circulation and mixing in the accumulated liquid, enhancing the condensation at the liquid to vapour interface owing to the cooler liquid temperature at the interface. The submerged jet nozzle may also cause the incoming liquid to geyser, thereby promoting condensation of the ullage similar to the top-spray configurations. Ground test programme
NASA Lewis Research Center (LeRC) personnel are conducting no-vent fill experiments at two facilities: the Cryogenic Components Laboratory (CCL) located at LeRC in Cleveland and the K-Site at LeRC's Plumbrook Station located in Sandusky, OH, USA. At the CCL, moderate-size testing is underway using small dewars to study the effects of several test parameters, including tank size, inlet mass flow rate, inlet temperature and liquid injection configuration, with a minimum of set-up. Completed work at the CCL includes the no-vent filling of a 141.6 dm 3 (5 ft 3) dewar using a top spray and the no-vent filling of a 34 dm 3 (1.2 ft 3) dewar by a top spray, an upward directed pipe discharge located near the bottom of the tank and a diffuser discharging downward also mounted near the bottom of the tank. K-Site's hazardous cryogens vacuum chamber is large enough to allow large-scale testing with lightweight, flight-qualified tankage. The tests conducted at K-site are designed to demonstrate the ability to apply the novent fill technologies to actual flight-scale systems and components. The test tank currently being used at K-Site
Figure 2
200
has a volume of 4955 dm 3 (175 ft3). The testing conducted at K-Site used two liquid injection configurations as shown in Figure 2, a top-spray ball and a bottom jet spraying upward. Large receiver tests The large receiver tank tested at CCL is a 141.6 d m 3 (5 ft 3) stainless-steel dewar. The bottom of the tank is an elliptical dome section. The top lid assembly bolts to a flange at the top of the cylindrical section of the tank and forms an inverted spherical dome section at the top of the test volume. Results with this receiver tank indicate that no-vent fills with nitrogen above 90% full by volume are achievable using a top-spray liquid injection configuration, in a lg environment, with inlet liquid temperatures as high as 79.4 K (143 R), and an initial average tank wall temperature of more than 166.7 K (300 R)2. This inlet temperature corresponds to a saturation pressure of 0.131 MPa (19 psia) for nitrogen. Hydrogen proved considerably more difficult to transfer between tanks without venting. The highest temperature conditions resulting in a fill percentage greater than 90% using the 141.6 dm 3 (5 ft') receiver tank were with an inlet liquid temperature of 18.9 K (34 R) and an estimated tank wall temperature of slightly more than 72.2 K (130 R) 2. The saturation pressure for hydrogen at this inlet temperature is 0.069 MPa (10 psia). All of these receiver tank no-vent fill tests were performed with a top-mounted full cone nozzle for liquid injection. The nozzle produces a 120 ° conical droplet spray at a differential pressure of 0.069 MPa (10 psi). The pressure in the receiver tank was restricted to less than 0.207 MPa (30 psia) for all tests. The shape of the pressure versus time curve for novent fill tests using the top-spray technique is characterized by three distinct regions. These regions, illustrated in Figure 3, are delineated by (1) an initial steep pressure rise as the incoming liquid flashes as it enters the low-pressure tank and is vaporized as it impinges on the warm tank walls, (2) a decrease in slope of the transient pressure response as the effect of ullage vapour condensation on the incoming liquid droplets
K-Site bottom-jet nozzle and 13-nozzle top-spray ball
Cryogenics 1992 Vol 32, No 2
On-orbit fluid transfer research: W.J. Taylor et al.
pressure rise for no-vent fills with both nitrogen and hydrogen.
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3 Typical tank pressure as a function of time for a hydrogen no-vent fill test using the top-spray fill configuration. (1) Flashing of inlet liquid, chilldown of the tank wall; (2) ullage vapour condensation on incoming liquid droplets, continued vaporization; (3) ullage compression, spray nozzle becomes submerged Figure
becomes more evident and (3) a sudden pressure rise as the liquid interface begins to submerge the inlet nozzle and enters the top dome region of the tank. Region 3 develops only in those tests which exceed the 90% fill level by volume for the test configuration employed. The liquid inlet temperature was found to be the primary parameter affecting the magnitude of the receiver tank
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A total of 42 tests were performed with different liquid inlet temperatures, inlet mass flow rates, initial tank wall temperatures and injection techniques with liquid hydrogen in a 34 dm 3 (1.2 ft 3) stainless-steel Dewar 3. The tank geometry is similar to that of the large receiver tank, with an elliptical bottom dome, a cylindrical midsection and hemispherical top dome. The injection techniques employed included a droplet spray directed downward from the top of the tank, a diffused inlet at the bottom and upward pipe discharge from the bottom. The effects of each of the parameters on the tank pressure history and final fill level were evaluated. Approximately 40% of the hydrogen no-vent fill tests performed resulted in final fill levels _ 90 % by volume. The unsuccessful tests were terminated owing to excessive pressure [ > 0.207 MPa (30 psia)] in the receiver tank. Each of the three liquid injection techniques employed displayed significantly different transient pressure reponses in the receiver tank during the no-vent fill process. The top-spray configuration cools the tank wall rapidly early in the test, owing to the impingement of the droplets on the wall. The vapour generated, as the wall is cooled, causes a rapid initial pressure rise in the receiver tank. As the transfer continues, the ullage is condensed on the spray droplets and the pressure remains nearly constant. The transient pressure response
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Figure 4 Tank pressure as a function of time for hydrogen no-vent fill tests with (a) top-spray, (b) upward pipe discharge and (c) bottomdiffuser fill configurations.
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On-orbit fluid transfer research: W,J. Taylor et al. Table 1 CCL no-vent fill test Initial wall temperature (K)
Liquid inlet temperature (K)
Top spray Upward pipe
71.1
19.5
discharge
44.4 48.3
19.1 21.1
Fill configuration
Bottom
Inlet mass flow rate (kg h - 1)
Final pressure (MPa)
Final fill percentage
54.5
0.103
98
122.7 40.9
0.096 0.200
96 76
diffuser
for a no-vent fill with a top-spray liquid inlet is shown in Figure 4a. The upward pipe discharge configuration initially cools most of the tank wall owing to the geysering of the incoming liquid, which results in a rapid pressure rise, similar to that observed during the top-spray tests, during the early portion of the fill process. As the outlet of the discharge pipe becomes submerged by the rising liquid, condensation of the ullage vapour is limited to the liquid free surface. The bulk fluid motion induced by the upward pipe discharge arrangement enhances condensation at the interface as the cooler incoming liquid is circulated upward toward the liquid-vapour interface. Figure 4b shows the receiver tank pressure versus time for a test using the upward pipe discharge liquid injection configuration. The bottom diffuser injection technique cools only the lower portion of the tank wall during the initial phase of a no-vent fill, resulting in a more gradual pressure rise at the start of the fill process. As the fill progresses, the submerged diffuser does not produce much liquid motion, resulting in less condensation at the liquidvapour interface than for the other two inlet configurations. The receiver tank pressure as a function of time for a test run with the bottom diffuser inlet is shown in
Figure 4c. The test conditions and process variables corresponding to the test results shown are summarized in Table 1. The initial wall temperature shown are mass-weighted averages based on the temperatures measured axially along the tank wall. The final pressures are the pressures recorded at the termination of the respective tests.
pressure drop of 0.069 MPa (10 psi). Figure 2 shows the two spray systems employed. Figure 5 illustrates the installed position of these systems in the tank. The K-Site test tank is ellipsoidal with a 2.21 m (87in) major diameter and a 1.2:1 major-to-minor axis ratio. The two end dome sections are joined by a short 3.81 cm (1.5in) cylindrical section. The tank is fabricated of 2219 aluminium chemically milled to a nominal thickness of 0.22 cm (0.087in). Thicker sections exist where they were required for manufacturing (mainly weld lands). There is a 0.72 m (28.35in) access flange on the top. The tank has a mass of 149.8 kg (329.25 lb) and a volume of 4955 dm 3 (175 ft3). It was originally designed for a maximum operating pressure of 0.551 MPa (80 psia). Prior to the start of testing the tank was requalified by a pneumatic test for a maximum operating pressure of 0.345 MPa (50 psia). The insulation system consists of a blanket of 34 layers of multilayer insulation (MLI) made with double aluminized Mylar and silk net spacers. Twelve fibre-glass epoxy struts support the tank in the test stand. No-vent fills with liquid hyrogen in excess of 90 % by volume were achieved using both fill configurations with initial wall temperatures exceeding 111 K (200 R). The lowest tank pressure for a test exceeding 90% full by volume (see Figure 6, Test 18) was 0.177 MPa (25.6 psia). Pressure histories for three tests with the bottom-jet liquid injection configuration and for three tests with the top-spray liquid injection configuration are
K-Site tests
Recently completed efforts include the no-vent fill of the 4955 dm 3 (175 ft 3) research with both top- and bottomjet systems 4. The bottom-mounted liquid injection system has a single jet nozzle directed upward. The nozzle will submerge soon after liquid begins to accumulate in the tank (at ---7% full by volume), and therefore heat and mass transfer between the accumulating liquid and the ullage vapour will only occur at the liquid surface. The top-mounted spray system uses a cluster of 13 nozzles. The cluster size was dictated by the availability of a commercial manifold. These nozzles are not submerged until the tank is 92 % full of liquid. The flow capacities of each inlet spray system are sized, within the constraints of commercially available nozzle sizes, to have the same inflow rate for a given inlet pressure. The nozzles were sized to provide =454 kg h -1 (1000 Ibm h -l) of liquid hydrogen at a
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Figure 5
Spray nozzle locations in K-Site test tank
On-orbit fluid transfer research: W.J. Taylor et al. Table 2
K-Site no-vent fill test parameters
Test No.
Fill configuration
Initial wall temperature (K)
Test Test Test Test Test Test
Bottom jet Top spray Top spray Bottom jet Bottom jet Top spray
21.7 104.4 126.1 101.7 66.7 70.0
18 19 20 21 22 23
Liquid inlet temperature (K)
Inlet mass flow rate (kg h - 1)
Final pressure (MPa)
Final fill percentage
22.2 23.0 22.4 22.2 21.7 22.8
500.0 421.8 337.7 448.6 504.9 419.5
0.176 0.227 0.257 0.233 0.188 0.210
94 94 94 94 94 94
presented in Figures 6 and 7, respectively. Table 2 presents a summary of the test parameters for each of the sets of test results presented in Figures 6 and 7. Since the fill systems were selected as boundary cases for the low-gravity fill, the fact that both systems were capable of filling the tank shows promise for the feasibility of the no-vent fill technique in the desired on-orbit applications. Direct comparison between the performances of the two fill systems is difficult owing the variations in the test conditions between the tests.
0.2 0.16 0.12 0.08 0.04//
400 Fill 18
4
10
'PLme(~)
Fill21 3OO
Figure 8 Comparison of analytical model results (dashed line) and test data (solid line) for CCL small receiver tank test 9072B. Fluid, hydrogen; inlet mass flow rate, 0.32 kg rain-l; inlet temperature, 19.7 K; wall temperature, 53.6 K; final fill percentage, 98%
Fill 22
• - , ° , . ~ , , s " , , / l ' - . ta'S ..
200
Wall Inlet Flow T e m p . T e m p . Rate
0-
•
(K)
(K) (kgh -1)
Fill 18 21.7 22.2 500.
100
Fill21 101.7 22.2 448.6 Fill 22 66.7 21.7 504.9 I
I
I
I
I
0.2
0.4
0.6
0.8
1
1.2
Time (h)
Figure 6
K-Site bottom-jet no-vent fill test results
400
300
.
,.. ......,........-....,......-'..-'..."...""%'".'".."""......:
-.r. fi :~-:~" "..." . . . . .
200
.....
7
Wall Inlet F l o w Temp.Temp.Rate
/ 1O0
/
(K)
"///
J 0.2
t 0.4
J 0.6
J - - - J - . ~ 0.8 1
T i m e (h)
Figure 7
(K) (kgh -1)
Fill 19 104.4 23.0 421.8 Fill 20 126,1 22.4 337.7 Fill 23 70.0 22.8 419,5
K-Site top-spray no-vent fill test results
Analytical modelling In addition to the ground-test programme, an effort to develop an analytical model to predict the pretest performance and to aid in understanding the experimental data is in progress 1,5,6. Recently completed work includes the development of a simple thermodynamic model of the no-vent fill process and the comparison of the model results with the results from the no-vent fill tests conducted with both the 34 dm 3 (1.2 ft 3) and the 141.6 dm 3 (5.0 ft 3) receiver tanks at CCL-77. The model is based on conservation of mass and a first-law energy balance for a control volume. The ullage, the bulk liquid and the tank wall are each represented by a single node. At present the model is limited to analysing the top-spray configurations. The details of the model structure and the basic equations are presented elsewhere ''5"7. Figure 8 presents a comparison of the test data and the analytical results for a no-vent fill test conducted at CCL-7 with the small receiver tank.
Concluding remarks Variable test parameters and liquid injection configurations have provided some insight into the conditions necessary for a successful transfer of liquid hydrogen by
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On-orbit fluid transfer research: W.J. Taylor et al. the no-vent fill method. The magnitude of the maximum receiver tank pressure was found to be dependent on the liquid inlet temperature, the inlet mass flow rate and the initial temperature. Future experimentation at the CCL will retest the 141.6 dm 3 (5 ft 3) dewar with both top-spray and axial spray-bar configurations. The spray-bar configuration is representative of design concepts proposed for operational systems, since the axial system and its ability to promote condensation of the ullage vapour should be insensitive to the liquid position inside the tank. The CCL test facilities will remain available for additional testing of other concepts. Results of the first K-Site tests also indicated several areas for further work. Test results are currently being compared with the previous analytical work and plans for follow-on testing are in progress. Near-term followon tests will repeat some of the previous tests with more stable liquid inlet thermodynamic conditions and improved instrumentation, and will include some new higher inlet flow rate testing. Test plans include the addition of a 2010 dm 3 (71 fC) tank for demonstrations of tank-to-tank transfers from the 4955 dm 3 (175 ft 3) tank. Spray-bar and bottom-jet systems also will be incorporated in this smaller tank for the tank-to-tank liquid transfer tests. Testing is also planned at different degrees of subcooling of the incoming liquid. Future work in the analytical modelling area will include completing a comparison of the model with results from the K-Site tests and modifying the present
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model so as to be able to analyse other liquid injection configurations and to be able to model the process in low- to zero-gravity environments. Additionally a thermodynamic equilibrium model is being developed. The equilibrium model will provide a baseline for comparing the performance of the different liquid injection systems as the model results depend only on the initial conditions, the incoming liquid mass flow rate and thermodynamic state of the incoming liquid.
References 1 Chato,D.J. Thermodynamicmodelingof the no-ventfillmethodology for transferringcryogensin low gravityNASA Technical Memorandum 100932, July 1988 2 Moran, M.E., Nyland, T.W. and Papeil, S.S. Liquid transfer cryogenictest facility--initialhydrogenand nitrogen no-ventfill data NASA Technical Memorandum 102572, March 1990 3 Moran, M.E., Nyland, T.W. and Driscoll, S.L. Hydrogenno-vent fill testing in a 34 liter (1.2 cubic foot) tank, paper presented at Cryogenic EngineeringConference,June 1991 4 Chato,D.J. Groundtestingof the nonventedfill methodof orbital propellant transfer: results of initial test seriesA1AA Paper No. 91-2326, June 1991 5 Chato, D.J. Analysis of the nonvented fill of a 4.96-cubic-meter lightweight liquid hydrogen tank NASA Technical Memorandum 102039, August 1989 6 Chato, D.J., Moran, M.E. and Nyland, T.W. Initial experimentation on the nonventedfill of a 0.14 m3 (5 ft3) dewar with nitrogenand hydrogen NASA Technical Memorandum 103155, June 1990 7 Taylor, W.J. and Chato, D.J. Improvedthermodynamicmodelingof the no-vent fill process and correlationwith experimentaldata AIAA Paper No. 91-1379, June 1991