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TFAWS Paper Session Variable Conductance Heat Pipe for a Variable Thermal Link C. J. TFAWS Paper Session Variable Conductance Heat Pipe for a Variable Thermal Link C. J. Peters, J. R. Hartenstine, C. Tarau, & W. G. Anderson Advanced Cooling Technologies, Inc. Bill. Anderson@1 -act. com Presented By Calin Tarau Thermal & Fluids Analysis Workshop TFAWS 2011 August 15 -19, 2011 NASA Langley Research Center Newport News, VA

Presentation Outline ® Design Targets ® Variable Thermal Links ® Variable Conductance Heat Pipe Presentation Outline ® Design Targets ® Variable Thermal Links ® Variable Conductance Heat Pipe Design ® Testing ® Conclusions and Recommendations ADVANCED COOLING TECHNOLOGIES, INC. ISO: 9001 -2000 / AS 9100 -B Certified 2

International Lunar Network Trade Study ® Objective: Develop Variable Thermal Link designs to be 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 ADVANCED COOLING TECHNOLOGIES, INC. ISO: 9001 -2000 / AS 9100 -B Certified 3

Design Targets Minimum Electronics Temperature -10°C (263 K) Maximum Electronics Temperature 50°C (303 K) Design Targets Minimum Electronics Temperature -10°C (263 K) Maximum Electronics Temperature 50°C (303 K) 73 W at lunar noon (30 % margin: 94. 9 W) 90 W during cruise (30 % margin: 117 W) Assume Full Power Min. Radiator Load (Moon) Max. Radiator Load (Moon) Power During Transit Trip Length 5 Days, or Several Months Duration ~ 6 years Warm Electronics Box Geometry Will be Larger for Solar Option Radiator Dimensions 24” x 41” x 14” (height) 21” (tall) x 25” (wide) Solar power controls, Maximum Day and Minimum Night ADVANCED COOLING TECHNOLOGIES, INC. ISO: 9001 -2000 / AS 9100 -B Certified 4

Design Targets Maximum Tilt 20° (10° slope, 10° hole) Maximum Radiator Sink Temperature (Landing) Design Targets Maximum Tilt 20° (10° slope, 10° hole) Maximum Radiator Sink Temperature (Landing) Minimum Radiator Temperature 263 K 141 K Minimum Soil Temperature -173°C (100 K) Maximum Soil Temperature 116°C (390 K) ® 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 ADVANCED COOLING TECHNOLOGIES, INC. ISO: 9001 -2000 / AS 9100 -B Certified 5

Variable Thermal Link ® Three basic elements to the WEB thermal control system 1. 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 ADVANCED COOLING TECHNOLOGIES, INC. ISO: 9001 -2000 / AS 9100 -B Certified 6

LHP Shut-Down ® Need to shut down LHP during the Lunar night – Minimize 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 ADVANCED COOLING TECHNOLOGIES, INC. ISO: 9001 -2000 / AS 9100 -B Certified 7

VCHP Design Constraints ® VCHP differs from normal VCHP in 5 different ways 1. 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 ADVANCED COOLING TECHNOLOGIES, INC. ISO: 9001 -2000 / AS 9100 -B Certified 8

VCHP Design ® Develop a VCHP design with three novel features 1. Hybrid-Wick – 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 ADVANCED COOLING TECHNOLOGIES, INC. ISO: 9001 -2000 / AS 9100 -B Certified 9

ILN Anchor Node – Hybrid Wick ® Standard VCHPs use grooved wick - not ILN Anchor Node – Hybrid Wick ® 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 -14°, Evaporator Works Against Gravity 0°, Puddle Flow in Evaporator +14°, Evaporator Gravity Aided ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 10

Overall Design – NCG Reservoir Adjacent to Evaporator ® Reservoir is located near evaporator Overall Design – NCG Reservoir Adjacent to Evaporator ® Reservoir is located near evaporator instead of condenser NCG Tube – Placing near condenser is standard for most spacecraft VCHPs with electric heaters – Condenser is too cold – Would require oversized reservoir Condenser NCG Tube NCG Reservoir Al Evaporator Condenser ® Location of reservoir inside WEB ensures that its temperature will be regulated ® NCG tube connects reservoir to condenser Radiator SS Bimetallic Transition Adiabatic Evaporator ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 11

VCHP Design – NCG Reservoir Adjacent to Evaporator Condenser (Grooves) Radiator WEB Enclosure NCG VCHP Design – NCG Reservoir Adjacent to Evaporator Condenser (Grooves) Radiator WEB Enclosure NCG Reservoir Evaporator (Screen) Adiabatic (Grooves) ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 12

ILN Anchor Node – NCG Reservoir Adjacent to Evaporator ® Standard condenser location gives ILN Anchor Node – NCG Reservoir Adjacent to Evaporator ® Standard condenser location gives much higher mass Vertical Asymptotes 1. Reservoir Near Evaporator: 0 K 2. Reservoir Near Condenser: ≈29. 78 K ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 13

VCHP with Internal Reservoir Adiabatic Section Condenser NCG Reservoir Evaporator ADVANCED COOLING TECHNOLOGIES, INC. VCHP with Internal Reservoir Adiabatic Section Condenser NCG Reservoir Evaporator ADVANCED COOLING TECHNOLOGIES, INC. ISO: 9001 -2000 / AS 9100 -B Certified 14

VCHP with Internal Reservoir Evaporator NCG Reservoir Condenser Adiabatic Section Cooling Block Heating Block VCHP with Internal Reservoir Evaporator NCG Reservoir Condenser Adiabatic Section Cooling Block Heating Block ADVANCED COOLING TECHNOLOGIES, INC. ISO: 9001 -2000 / AS 9100 -B Certified 15

VCHP Testing – Objectives ® Lunar Surface Operations (1/6 g) – Freeze tolerance; conductance 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 ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 16

VCHP Testing – Instrumentation TC Locations ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & VCHP Testing – Instrumentation TC Locations ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 17

Task 3. VCHP Testing – Lunar Freeze/Thaw ® Purpose – Demonstrate ability to shut 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 Ú -60ºC (liquid) and -177ºC (frozen) – Several orientations Ú -2. 3º & +2. 3º Ú Condenser nearly vertical Ú Adiabatic and condenser sections gravity aided – 25ºC initial evaporator temperature – Measure performance Ú Evaluate temperature gradients across heat pipe; conductances; input power ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 18

Task 3. VCHP Testing – Lunar Freeze/Thaw Results TC 27 (Cond) TC 1 (Gas) Task 3. VCHP Testing – Lunar Freeze/Thaw Results TC 27 (Cond) TC 1 (Gas) TC 26 (Cond) TC 10 (Evap) TC 30 (Cond) TC 23 (Cond) Power ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 19

Task 3. VCHP Testing – Lunar Freeze/Thaw Results VCHP Operation (25 °C, 95 W, Task 3. VCHP Testing – Lunar Freeze/Thaw Results VCHP Operation (25 °C, 95 W, -2. 3°) ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 20

Task 3. VCHP Testing – Lunar Freeze/Thaw Results VCHP Cold Shutoff (-60 °C, 0. Task 3. VCHP Testing – Lunar Freeze/Thaw Results VCHP Cold Shutoff (-60 °C, 0. 2 W, -2. 3°) ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 21

Task 3. VCHP Testing – Lunar Freeze/Thaw Results VCHP Very Cold Shutoff (-177 °C, Task 3. VCHP Testing – Lunar Freeze/Thaw Results VCHP Very Cold Shutoff (-177 °C, 0. 1 W, -2. 3°) Heat Pipe Overall Conductances for Freeze/Thaw (-2. 3° Inclination) Testing Condition Overall Conductance (W/°C) 25 °C Operation 4. 7 -60 °C Shutdown 0. 00310 -177 °C Shutdown 0. 00057 9 Inch Evaporator; 12 Inch Condenser ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 22

Task 3. VCHP Testing – Lunar Freeze/Thaw Results ® VCHP can undergo freeze/thaw cycles 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 ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 23

Task 3. VCHP Testing – Lunar Performance ® Purpose: Demonstrate thermal performance in a 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 Ú Condenser nearly vertical Ú Adiabatic and condenser sections gravity aided – 25ºC evaporator temperature ® Test Results Summary – 220 W @ -2. 3º – 212 W @ 0º – 220 W @ +2. 3º ® Dryout was not demonstrated, test was terminated based on elevated temperature on TC 9 – Possible gap between evaporator wall and screen wick resulting in a “hot spot” – 2 × target power ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 24

Task 3. VCHP Testing – Lunar Performance Results Temperature Profile (25 °C, 220 W, Task 3. VCHP Testing – Lunar Performance Results Temperature Profile (25 °C, 220 W, -2. 3°) ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 25

Task 3. VCHP Testing – Lunar Performance Results ® Powers demonstrated are twice maximum 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 ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 26

Task 3. VCHP Testing – Space ® Thermal diode – Backward operation (reverse heat 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 ® For All Space Tests – Near horizontal – Vary adverse elevation of evaporator (0. 1 in, 0. 2 in, 0. 3 in) ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 27

Task 3. VCHP Testing – Space Thermal Diode ® The purpose of this test 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 ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 28

Task 3. VCHP Testing – Space Thermal Diode Results Thermal Diode Temperatures (Evaporator at Task 3. VCHP Testing – Space Thermal Diode Results Thermal Diode Temperatures (Evaporator at 25 °C, 0. 1 Inch Adverse) ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 29

Task 3. VCHP Testing – Space Thermal Diode Results ® Pipe is an effective 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) ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 30

Task 3. VCHP Testing – Space ® Purpose: Demonstrate thermal performance in a simulated 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 ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 31

Task 3. VCHP Testing – Space Performance Results (25 °C, No NCG) Zero-g power Task 3. VCHP Testing – Space Performance Results (25 °C, No NCG) Zero-g power extrapolated ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 32

Task 3. VCHP Testing – Space Performance Results ® Pipe carries approximately 72 % 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 ADVANCED COOLING TECHNOLOGIES, INC. ISO 9001 -2008 & AS 9100 -B Certified 33

Conclusions and Recommendations ® Variable Thermal Link can be provided by – Loop Heat 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 ADVANCED COOLING TECHNOLOGIES, INC. ISO: 9001 -2000 / AS 9100 -B Certified 34

Conclusions and Recommendations ® Simulated Lunar performance testing demonstrated – Shuts off at cold 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 ADVANCED COOLING TECHNOLOGIES, INC. ISO: 9001 -2000 / AS 9100 -B Certified 35

Acknowledgements ® The trade study was sponsored by NASA Marshall Space Flight Center under 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. NAS 802060. 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. ADVANCED COOLING TECHNOLOGIES, INC. ISO: 9001 -2000 / AS 9100 -B Certified 36

TFAWS Paper Session Variable Conductance Heat Pipe for a Variable Thermal Link C. J. TFAWS Paper Session Variable Conductance Heat Pipe for a Variable Thermal Link C. J. Peters, J. R. Hartenstine, C. Tarau, & W. G. Anderson Advanced Cooling Technologies, Inc. Bill. Anderson@1 -act. com Presented By Calin Tarau Thermal & Fluids Analysis Workshop TFAWS 2011 August 15 -19, 2011 NASA Langley Research Center Newport News, VA