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Variable Conductance Heat Pipe for a Variable Thermal Link
C. J. Peters, J. R. Hartenstine,C. Tarau, & W. G. Anderson
Advanced Cooling Technologies, [email protected]
Thermal & Fluids Analysis WorkshopTFAWS 2011August 15-19, 2011NASA Langley Research CenterNewport News, VA
TFAWS Paper Session
Presented By
Calin Tarau
2ADVANCED COOLING TECHNOLOGIES, INC.
ISO:9001-2000 / AS9100-B Certified
Presentation Outline
Design Targets
Variable Thermal Links
Variable Conductance Heat Pipe Design
Testing
Conclusions and Recommendations
3ADVANCED COOLING TECHNOLOGIES, INC.
International Lunar Network Trade Study
Objective: Develop Variable Thermal Link designs to be used for Thermal Management of the Warm Electronics Box (WEB) on the International Lunar Network (ILN) Anchor Node mission
Remove ~ 60 W during the lunar day Conserve heat to keep the electronics and battery warm during the
lunar night
ISO:9001-2000 / AS9100-B Certified
4ADVANCED COOLING TECHNOLOGIES, INC.
Design Targets
ISO:9001-2000 / AS9100-B Certified
Minimum Electronics Temperature -10°C (263 K)
Maximum Electronics Temperature 50°C (303 K)
Min. Radiator Load (Moon)73 W at lunar noon
(30 % margin: 94.9 W)
Max. Radiator Load (Moon)90 W during cruise
(30 % margin: 117 W) Power During Transit Assume Full Power
Trip Length 5 Days, or Several Months
Duration ~ 6 years
Warm Electronics Box GeometryWill be Larger for Solar Option
24” x 41” x 14” (height)
Radiator Dimensions 21” (tall) x 25” (wide)
Solar power controls, Maximum Day and Minimum Night
5ADVANCED COOLING TECHNOLOGIES, INC.
Design Targets
Minimizing power usage at night is extremely important 1 W power = 5 kg Batteries! 20° tilt means that conventional grooved aluminum/ammonia
CCHPs can not be used in the WEB to isothermalize the system– Maximum Adverse Elevation: 13.3 inch
ISO:9001-2000 / AS9100-B Certified
Maximum Tilt 20° (10° slope, 10° hole)
Maximum Radiator Sink Temperature (Landing)
263 K
Minimum Radiator Temperature 141 K
Minimum Soil Temperature -173°C (100 K)
Maximum Soil Temperature 116°C (390 K)
6ADVANCED COOLING TECHNOLOGIES, INC.
Variable Thermal Link
Three basic elements to the WEB thermal control system
1. A method to isothermalize the electronics and battery during the lunar night, and to remove heat to a second, variable conductance thermal link during the day (Constant Conductance Heat Pipes (CCHPs)).
2. A variable thermal link between the WEB and the Radiator
3. A radiator to reject heat Possible Thermal Links
– Variable Conductance Heat Pipes (VCHPs)– Loop Heat Pipes (LHPs)– LHPs with a Thermal Control Valve
ISO:9001-2000 / AS9100-B Certified
7ADVANCED COOLING TECHNOLOGIES, INC.
LHP Shut-Down
Need to shut down LHP during the Lunar night– Minimize Heat Losses from the WEB
Standard method uses a heater on the compensation chamber– During normal operation, the Compensation Chamber runs at a lower
temperature than the LHP evaporator
– Activate heater to shut down
– Increase saturation temperature and pressure of LHP
– Cancels the pressure difference required to circulate the sub-cooled liquid from the condenser to the evaporator
Standard method validated in spacecraft– 1 W = 5 kg
Develop variable thermal links with no power requirement– LHP with Thermal Control Valve – discussed in separate presentation
– VCHP
ISO:9001-2000 / AS9100-B Certified
8ADVANCED COOLING TECHNOLOGIES, INC.
VCHP Design Constraints
VCHP differs from normal VCHP in 5 different ways
1. Need to operate in space, and on the Lunar surface
2. Need to operate with fairly large tilts in the evaporator– Slope can vary from -20° to +20°
– ~13 inch adverse elevation across the WEB
– Grooved CCHPs operate with 0.1 inch adverse tilt
– Requires non-standard wick
3. Tight temperature control not required– Have a ~40°C range versus ±1°C for conventional VCHPs
4. No power available for reservoir temperature control– 1 W = 5 kg
– External reservoir will cool down to ~140 K
5. Need to minimize heat leak when shut down
ISO:9001-2000 / AS9100-B Certified
9ADVANCED COOLING TECHNOLOGIES, INC.
VCHP Design
Develop a VCHP design with three novel features
1. Hybrid-Wick– Screen wick in evaporator, grooved wick in condenser– Allows operation on the Lunar surface, and during transit
2. Reservoir Near Evaporator– Keeps the reservoir warm at night– Minimizes the reservoir size
3. Bimetallic Adiabatic Section– Grooved stainless steel section in the adiabatic section acts as
a thermal dam to minimize heat leak during shutdown
ISO:9001-2000 / AS9100-B Certified
10ADVANCED COOLING TECHNOLOGIES, INC.
Standard VCHPs use grooved wick - not suitable for Moon– 0.1 inch against gravity
Tilt range for lunar surface: ±14° VCHP evaporator needs to operate against gravity
– Maximum adverse elevation: (9 inch) × sin(14°) = 2.2 inch
Screen wick in evaporator; Grooved wick in condenser– Grooves and screen pump in space
– Screen pumps on lunar surface
ILN Anchor Node – Hybrid Wick
ISO9001-2008 & AS9100-B Certified
moong
-14°, Evaporator Works Against Gravity
0°, Puddle Flow in Evaporator
+14°, Evaporator Gravity Aided
11ADVANCED COOLING TECHNOLOGIES, INC.
NCG Reservoir
Con
dens
er
Evaporator
Overall Design – NCG Reservoir Adjacent to Evaporator
Reservoir is located near evaporator instead of condenser– Placing near condenser is standard for most
spacecraft VCHPs with electric heaters– Condenser is too cold– Would require oversized reservoir
Location of reservoir inside WEB ensures that its temperature will be regulated
NCG tube connects reservoir to condenser
ISO9001-2008 & AS9100-B Certified
Adiabatic
Bimetallic Transition
NCG ReservoirNCG Tube
Evaporator
NCG Tube
Radiator
Condenser
Al
Al
SS
12ADVANCED COOLING TECHNOLOGIES, INC.
NCGReservoir
Con
dens
er(G
roov
es)
Evaporator(Screen)
VCHP Design – NCG Reservoir Adjacent to Evaporator
ISO9001-2008 & AS9100-B Certified
Adiabatic(Grooves)
WEB Enclosure
Radiator
13ADVANCED COOLING TECHNOLOGIES, INC.
ILN Anchor Node – NCG Reservoir Adjacent to Evaporator
ISO9001-2008 & AS9100-B Certified
Vertical Asymptotes1. Reservoir Near Evaporator: 0 K2. Reservoir Near Condenser: ≈29.78 K
Standard condenser location gives much higher mass
14ADVANCED COOLING TECHNOLOGIES, INC.
VCHP with Internal Reservoir
ISO:9001-2000 / AS9100-B Certified
Evaporator
NCG Reservoir
Condenser
Adiabatic Section
15ADVANCED COOLING TECHNOLOGIES, INC.
VCHP with Internal Reservoir
ISO:9001-2000 / AS9100-B Certified
Cooling Block
NCG Reservoir
Condenser
Adiabatic Section
Evaporator
Heating Block
16ADVANCED COOLING TECHNOLOGIES, INC.
VCHP Testing – Objectives
Lunar Surface Operations (1/6 g)– Freeze tolerance; conductance of “on” versus “off” states
– Performance in adverse gravity orientations
Space Operations– Thermal diode behavior
– Thermal Performance
ISO9001-2008 & AS9100-B Certified
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VCHP Testing – Instrumentation
TC Locations
ISO9001-2008 & AS9100-B Certified
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Task 3. VCHP Testing – Lunar Freeze/Thaw
Purpose– Demonstrate ability to shut down– Demonstrate ability to startup and operate for brief periods of time when
cold– Determine overall thermal conductance
Procedure– Vary sink conditions to simulate lunar cycle
-60ºC (liquid) and -177ºC (frozen)– Several orientations
-2.3º & +2.3º Condenser nearly vertical Adiabatic and condenser sections gravity aided
– 25ºC initial evaporator temperature– Measure performance
Evaluate temperature gradients across heat pipe; conductances; input power
ISO9001-2008 & AS9100-B Certified
19ADVANCED COOLING TECHNOLOGIES, INC.
Task 3. VCHP Testing – Lunar Freeze/Thaw Results
ISO9001-2008 & AS9100-B Certified
Power
TC23 (Cond)
TC1 (Gas)
TC10 (Evap)TC30 (Cond)
TC27 (Cond)
TC26 (Cond)
20ADVANCED COOLING TECHNOLOGIES, INC.
Task 3. VCHP Testing – Lunar Freeze/Thaw Results
ISO9001-2008 & AS9100-B Certified
VCHP Operation (25 °C, 95 W, -2.3°)
21ADVANCED COOLING TECHNOLOGIES, INC.
Task 3. VCHP Testing – Lunar Freeze/Thaw Results
ISO9001-2008 & AS9100-B Certified
VCHP Cold Shutoff (-60 °C, 0.2 W, -2.3°)
22ADVANCED COOLING TECHNOLOGIES, INC.
Task 3. VCHP Testing – Lunar Freeze/Thaw Results
ISO9001-2008 & AS9100-B Certified
VCHP Very Cold Shutoff (-177 °C, 0.1 W, -2.3°)
Heat Pipe Overall Conductances for Freeze/Thaw(-2.3° Inclination)
Testing ConditionOverall Conductance
(W/°C)
25 °C Operation 4.7
-60 °C Shutdown 0.00310
-177 °C Shutdown 0.00057
9 Inch Evaporator; 12 Inch Condenser
23ADVANCED COOLING TECHNOLOGIES, INC.
Task 3. VCHP Testing – Lunar Freeze/Thaw Results
VCHP can undergo freeze/thaw cycles without performance degradation
Effectively shuts off at cold temperatures and reduces heat transfer VCHP can experience short-duration full-power bursts during -60 °C
and -177 °C cold shutdown Evaporator stays within -10 °C to +50 °C temperature range with no
power except heat in-leak
ISO9001-2008 & AS9100-B Certified
24ADVANCED COOLING TECHNOLOGIES, INC.
Task 3. VCHP Testing – Lunar Performance
Purpose: Demonstrate thermal performance in a simulated lunar environment
Test Procedure – 1 temperature, 3 elevations– -2.3º, 0º and +2.3º inclinations
Condenser nearly vertical Adiabatic and condenser sections gravity aided
– 25ºC evaporator temperature Test Results Summary
– 220W @ -2.3º– 212W @ 0º– 220W @ +2.3º
Dryout was not demonstrated, test was terminated based on elevated temperature on TC9– Possible gap between evaporator wall and screen wick resulting
in a “hot spot”– 2 × target power
ISO9001-2008 & AS9100-B Certified
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Task 3. VCHP Testing – Lunar Performance Results
ISO9001-2008 & AS9100-B Certified
Temperature Profile (25 °C, 220 W, -2.3°)
26ADVANCED COOLING TECHNOLOGIES, INC.
Task 3. VCHP Testing – Lunar Performance Results
Powers demonstrated are twice maximum target power Pipe can operate against lunar gravity Evaporator stays within -10 °C to 50 °C target temperature
range
ISO9001-2008 & AS9100-B Certified
27ADVANCED COOLING TECHNOLOGIES, INC.
Task 3. VCHP Testing – Space
Thermal diode– Backward operation (reverse heat input/output & elevation)
– Measure heat transport in reverse direction
Thermal Performance– Determine dryout
– Extrapolate dryout power to 0-g
ISO9001-2008 & AS9100-B Certified
For All Space Tests– Near horizontal
– Vary adverse elevation of evaporator (0.1 in, 0.2 in, 0.3 in)
28ADVANCED COOLING TECHNOLOGIES, INC.
Task 3. VCHP Testing – Space Thermal Diode
The purpose of this test is to demonstrate that the pipe can behave as a diode in space
Test Procedure – 3 elevations, 1 evaporator temperature– 0.1”, 0.2” and 0.3” adverse elevation
– 25ºC evaporator temperature
– 20ºC ΔT between evaporator and condenser
– Determine reverse heat transfer rate required to meet 20ºC ΔT requirement
– Conservative NCG charge
Test Results– 0.1 inch, 4.3 watts, -0.0195 W/°C
– 0.2 inch, 3.2 watts, -0.0157 W/°C
– 0.3 inch, 3.2 watts, -0.0160 W/°C
ISO9001-2008 & AS9100-B Certified
29ADVANCED COOLING TECHNOLOGIES, INC.
Task 3. VCHP Testing – Space Thermal Diode Results
ISO9001-2008 & AS9100-B Certified
Thermal Diode Temperatures (Evaporator at 25 °C, 0.1 Inch Adverse)
30ADVANCED COOLING TECHNOLOGIES, INC.
Task 3. VCHP Testing – Space Thermal Diode Results
Pipe is an effective thermal diode Pipe has very low thermal conductance Pipe reduces reverse heat transfer (transports only 4 % of
maximum power)
ISO9001-2008 & AS9100-B Certified
31ADVANCED COOLING TECHNOLOGIES, INC.
Task 3. VCHP Testing – Space
Purpose: Demonstrate thermal performance in a simulated space environment
Test Procedure – 3 elevations, 1 temperature– 0.1”, 0.2” and 0.3” adverse elevation– 25ºC evaporator temperature
Pipe operation with NCG and without NCG– Possible asymmetry – Flipped pipe 180º– Marked improvement in performance
ISO9001-2008 & AS9100-B Certified
32ADVANCED COOLING TECHNOLOGIES, INC.
Task 3. VCHP Testing – Space Performance Results
ISO9001-2008 & AS9100-B Certified
(25 °C, No NCG)
Zero-g power extrapolated
33ADVANCED COOLING TECHNOLOGIES, INC.
Task 3. VCHP Testing – Space Performance Results
Pipe carries approximately 72 % of the zero-gravity target power
Possible contributing factors causing asymmetry and lower than expected thermal performance– Screen attachment resulting in a gap between the wall and wick– Interface between screen and grooves resulting in a larger than
designed hydraulic joint
ISO9001-2008 & AS9100-B Certified
34ADVANCED COOLING TECHNOLOGIES, INC.
Conclusions and Recommendations
Variable Thermal Link can be provided by – Loop Heat Pipe– LHP with Thermal Control Valve– Variable Conductance Heat Pipe
VCHP has the following benefits– No power to shutdown– Least expensive– However, lowest TRL level
VCHP was developed with the following– Hybrid-Wick, to allow the VCHP to operate with a tilt– Reservoir Near Evaporator, to minimize the reservoir size– Bimetallic Adiabatic Section, to minimize axial heat leak to the
cold radiator during shutdown
ISO:9001-2000 / AS9100-B Certified
35ADVANCED COOLING TECHNOLOGIES, INC.
Conclusions and Recommendations
Simulated Lunar performance testing demonstrated– Shuts off at cold temperatures and reduces heat transfer
– Freeze/thaw cycles without performance degradation and accommodated short-duration full-power bursts during -60 °C and -177 °C cold shutdown
– Design can meet target power at adverse elevations
– Demonstrated start up with frozen condenser and can operate briefly at low condenser temperatures
Simulated 0-g testing demonstrated– Effective thermal diode operation
– Performance shortfalls encountered in testing indicated potential hybrid wick design and fabrication issues
Currently examining sintered wick insert– Eliminate hot spots
– Better wick/groove interface
ISO:9001-2000 / AS9100-B Certified
36ADVANCED COOLING TECHNOLOGIES, INC.
Acknowledgements
The trade study was sponsored by NASA Marshall Space Flight Center under Purchase Order No. 00072443. The VCHP was sponsored by NASA Marshall Space Flight Center under Purchase Order No. NAS802060. Jeffery Farmer was the Technical Monitor
Kara Walker was the engineer on the Variable Thermal Link trade study. Tim Wagner as the technician at ACT. We would like to thank Kyle Van Riper for technical discussions about the VCHP.
Any opinions, findings, and conclusions or recommendations expressed in this presentation are those of the authors and do not necessarily reflect the views of the National Aeronautics and Space Administration.
ISO:9001-2000 / AS9100-B Certified
Variable Conductance Heat Pipe for a Variable Thermal Link
C. J. Peters, J. R. Hartenstine,C. Tarau, & W. G. Anderson
Advanced Cooling Technologies, [email protected]
Thermal & Fluids Analysis WorkshopTFAWS 2011August 15-19, 2011NASA Langley Research CenterNewport News, VA
TFAWS Paper Session
Presented By
Calin Tarau