chato lox tank helium removal for propellant scavenging presentation 2009

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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LOX Tank Helium Removal for PropellantScavenging Test

Dr. David J. Chato

Presented January 8th 2008 at AIAAAerospace Sciences Meeting, Orlando, FL

2

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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


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

5


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


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


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Test 12 Start

Test 12 End

Test 27 Start

- Test 27 End

0d6

50E


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


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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


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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