Miniature Multiple Evaporator Multiple Condenser Loop Heat Pipe

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Miniature Multiple Evaporator Multiple. Condenser Loop Heat Pipe. Swales Aerospace. 5050 Powder Mill Rd. Beltsville, MD 20705. 19th Annual AIAA/USU.
Miniature Multiple Evaporator Multiple Condenser Loop Heat Pipe Swales Aerospace 5050 Powder Mill Rd Beltsville, MD 20705 19th Annual AIAA/USU Conference on Small Satellites

SSC05-XI-5

Acknowledgement  This study is a joint effort funded by NASA Goddard Space Flight Center and Swales Aerospace Inc.  Special thanks to Laura Ottenstein and Jentung Ku at NASA Goddard Space Flight Center for their valuable and constant support during this program.

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Objectives  Miniaturized dual-evaporator and dual-condenser LHP  Prototypical of a centralized thermal bus for a small satellite.  The focus of design and development was optimization of performance: ” Maximizing

heat transport ” Maximizing overall conductance ” Minimizing auxiliary power requirements ” Minimizing total system mass ” Reduce Integration constraints

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Classical LHP Advantages: 1. LHPs are capable of passively transporting large heat loads over long distances with small temperature gradients. 2. Small diameter, flexible transport lines, which can be used for deployable radiators or to simplify integration. 3. LHPs are reasonably insensitive to adverse elevation, which simplifies pre-launch system-level testing. 4. LHP is a natural thermal diode. Disadvantage:

Reservoir Reservoir

Evaporator Qin

Primary

Primary Wick Wick

In application to date, devices Limited to single evaporator.

Secondary Secondary Wick Wick

Liquid Line

Main Pump

Vapor Line d

Secondary Pump

Condenser Primary Flow Path

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Dual Evaporator Dual Condenser LHP Advantages:

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Primary Wick

Secondary Wick Compensation Chamber

Vapor Line

Evaporator

Liquid Line

1. Viable light-weight design alternative 2. Removing heat from multiple sources 3. Isothermalize the heat sources. 3. Heat from one source can be shared with unpowered heat sources, minimizing survival heater power. 4. If one radiator is warmed, it will be isolated automatically (dioding nature of LHP). The heat will be diverted to the radiator facing the colder sink. 5. Small diameter, flexible transport lines simplify integration.

Condensers

Flow Isolator

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Requirements  Evaporator operating range: -10 to 30oC  Condensers operating range: -60 to -10oC  Heat load: 5 to 100W  Adverse elevation: 10cm

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Design Summary  Evaporators: ” Heat

Flow Isolator

load acquisition interface

” Provide

Vapor Transport Line

heat load sharing

Radiator 1

 Compensation Chambers: ” Store

Liquid Transport Line

excess fluid

” Adequate

fluid inventory

” Control

operating temperature of mini-LHP

Compensation Chamber

Parameter Heat Load 5-100 W Evaporator Diameter 8mm (0.32in) Evaporator Length 50mm (2.0in) Liquid Transport line 1.5mm (0.06in) Vapor Transport Line 2.5mm (0.09in) o 340J/ C Thermal Mass Thermal Device Total Weight 316 grams SSC05-XI-5

Radiator 2 Evaporator 1 Thermal Mass

Vapor Manifold

Evaporator 2

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Design Summary  Transport Lines: ” Transport

21

vapor and liquid

11

” Flexible,

small diameter and

22

10

35

34

23

24 29

16

20

33

coiled  Condensers: 19

” Imbedded

17

28

15

into semi-circular

12

radiator

13

 Flow Isolator: operation with nonuniform sink conditions

32

25

26

18

” Allows

30

31 14

27

TC locations with respect to the condenser tubing

” Thermally

isolate warm condenser

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Test Setup and Instrumentation  Evaporators assembly leveled within +/- 1.5 mm and 10cm above condensers.  Each component was individually insulated to minimize heat exchange between the mini-LHP and ambient.  The condensers were not insulated  Tests performed in an environmental chamber to control sink conditions  50 type “T” thermocouples  Cartridge heaters for electrical heat input with an active length of 2 in  400 gram aluminum thermal masses

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Startup, Conductance and Maximum Power to Evaporator 20 15

120

Maximum Power

Startup

10 100

5

Evaporator 2

0 80

-10 -15

Saturation

-20

60

-25

Power (W)

o

Temperature ( C)

-5

-30 -35

Evaporator 1

40

-40 -45

20

-50 -55 -60 18:30 19:00 19:30 20:00 20:30 21:00 21:30 22:00 22:30 23:00 23:30

0 0:00

0:30

1:00

Time (hh:mm) Liq Line Ev 2

Chamber T

CC 1 SSC05-XI-5

CC 2

Ev 2 Power 9

Thermal Conductance 20

18

16

Conductance (W /K)

14

12

10

Power G= TEvap − TCC

8

6

4

Approaching Dryout

2

0 0

20

40

60

80

100

120

Evaporator Power (W) SSC05-XI-5

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Sink Transients Test 60

-5

Evaporator 1 -10 50

-15 -20

40

-25 -30 30

Liquid Return

-35

Power (W)

o

Temperature ( C)

Saturation

-40 20 -45

Condenser 1

Condenser 2

-50

10

-55 -60 19:30

0 20:18

21:06

21:55

Time (hh:mm) Evap 1

Cond 2

Condenser 1 SSC05-XI-5

CC 1

Liq Line Cond

Ev 1 Power 11

Power Switching, Condenser Cycling Test 60

15 10

E2

5

CC2

50

-10

E1

40

-15

CC1

0

-20 30 -25 -30

Power (W)

o

Temperature ( C)

-5

20

-35 -40 -45

10 -50 -55 -60 0 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 0:00 1:00

Time (hh:mm) Evap 1

Evap 2

Liq Line Ev 1

Liq Line Ev 2

CC 1

CC 2

Ev 1 Power

Ev 2 Power

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Chamber T

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Conclusions  Dual evaporator/dual compensation chamber system operated successfully under all test conditions ” ” ” ”

One or both evaporators powered One condenser superheated Evaporator power switching and sink cycling Non-uniform heat load

 Operating temperature depends on power applied to evaporator of controlling CC  Temperature oscillations observed with one evaporator powered at 50W and other evaporator unpowered. ”

Believed to be due to to bubbles expanding and collapsing in liquid-filled CC

 Flow isolator successfully permits operation with one condenser superheated

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