National Aeronautics and Space Administration
LOX Tank Helium Removal for PropellantScavenging
Dr. David J. ChatoAbstract:System studies have shown a significant advantage to reusing the hydrogen and oxygen left inthese tanks after landing on the Moon in fuel cells to generate power and water for surfacesystems. However in the current lander concepts, the helium used to pressurize the oxygen tankcan substantially degrade fuel cell power and water output by covering the reacting surface withinert gas. This presentation documents an experimental investigation of methods to remove thehelium pressurant while minimizing the amount of the oxygen lost. This investigationdemonstrated that significant quantities of Helium (>90% mole fraction) remain in the tank afterdraining. Although a single vent cycle reduced the helium quantity, large amounts of heliumremained. Cyclic venting appeared to be more effective. Three vent cycles were sufficient toreduce the helium to small (<0.2%) quantities. Two vent cycles may be sufficient since once thetank has been brought up to pressure after the second vent cycle the helium concentration hasbeen reduced to the less than 0.2% level. The re-pressurization process seemed to contribute todiluting helium. This is as expected since in order to raise the pressure liquid oxygen must beevaporated. Estimated liquid oxygen loss is on the order of 82 pounds (assuming the third ventcycle is not required).
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National Aeronautics and Space Administration
LOX Tank Helium Removal for PropellantScavenging Test
Dr. David J. Chato
Presented January 8th 2008 at AIAAAerospace Sciences Meeting, Orlando, FL
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National Aeronautics and Space Administration
Introduction:
• Helium used to pressurize the oxygen tank since thisproduces significantly lighter gas residuals at stageburn-out.
• Helium substantially degrade fuel cell power andwater output
• This experiment investigates methods to removemaximum amount of helium pressurant whileretaining the maximum amount of the oxygenresiduals.
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Objectives
• Understand the amount of residual helium in LOXtanks after landing
• Demonstrate the ability to remove the majority of thehelium via venting without losing significant quantitiesof oxygen
• Measure the oxygen/helium content of the remaininggases as they would be sent over time to the fuel cellsystem
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Approach
• Thermodynamic analysis of the system processeswill be performed to predict expected heliumconcentrations before and after various ventingscenarios.
• Ground testing will be conducted to validate theanalysis predictions and correct the analysis. Testswill be conducted at SMiRF at GRC.
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Test Tank in Handling Fixture
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Table 2 Close Rang Diode Rake
Mean distance Height from TankRelative from datum BottomFill (in) (in)Volume oftotalTank)
30% 46.5 21.5625
21.3125
21.0625
20.8125
20.5625
20.3125
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Temperature Diode Location
Table 1 Broad Range Diode Rake
Relative Fill Volumeof Total Tank*
Height frombottom of tank(in)
Distance fromdatum* (in)
5% 6.35 61.21
10% 9.57 57.99
20% 15.32 52.24
30% 21.03 46.53
40% 26.75 40.81
50% 32.47 35.09
60% 38.19 29.37
70% 43.91 23.65
80% 49.63 17.93
90% 55.51 12.05
95% 59.41 8.15
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to vacuum pum p3
e from tank
bottom
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Gas Sample System
5
5
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Tests CompletedTest IDNumber
StartingPressure (psia)
EndingPressure (psia)
Notes
8 50 20 Liquid NitrogenCheckout
12 50 20
18 100 20 Gas sample data notavailable
21 150 20
24 50 20 Cyclic vent Threevents total
27 50 20
29 50 20 Direct vent, No gassample holds
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Test 12 Start
Test 12 End
Test 27 Start
- Test 27 End
0d6
50E
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Test Results for Vents from 50 psia
100
- Test 29 Start
- f - Test 29 End
G Test 24 Cycle 1 Start
- -0- - Test 24 Cycle 1 End
00
30
60
Height from tank bottom
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Test Comparison for Vents from 50 psia and 150psia
100
A Test 27 Startd0
Test 27 EndE 50 Test 21 StartE
— t — Test 21 End
x
00
30
60
Height from tank bottom
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Test 12 Start
Test 12 End
Test 27 Start
- Test 27 End
0d6
50E
National Aeronautics and Space Administration
Test Results for Vents from 50 psia
100
- Test 29 Start
- f - Test 29 End
G Test 24 Cycle 1 Start
- -0- - Test 24 Cycle 1 End
00
30
60
Height from tank bottom
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Test Results for Three Cycle Vent Test
100
0as0
c0
50
c0UE0
0
0 30 60
Height from Tank Bottom (in)
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L
200L
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Temperature Profiles During Three Cycle Vent
400
0—Start of Cycle 1
— —*— — End of Cycle 1
Start of Cycle 2
— ^— — End of Cycle 2
e Start of Cycle 3
— ^— —End of Cycle 3
0
0 30
60
Height from Tank Bottom (in)
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100
as02
50E7
Time History of Three Cycle Vent
60
.y
C.
30 LHHLa
n He MiddleHe Bottom
o Gas Analyzer
0 _!L_ Pressure history __^ 0
6:00 AM
12:00 PM
6:00 PM
12:00 AM
Time (hours:minutes)
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Preliminary Results
• Significant (>90%) Helium is found in the tank afterdraining
• Although a single vent cycle reduces the helium largequantities remain
• Three vent cycles are sufficient to reduce the heliumto small (<0.2%) quantities
• Repressurization seems to contribute to dilutinghelium
• Propellant loss estimated at 82 lbm assuming thirdvent cycle is not required
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