variable conductance heat pipe for a variable thermal link c. j. peters, j. r. hartenstine, c....

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


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



Design Targets


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


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


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)


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



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



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



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



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


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


Adiabatic

Bimetallic Transition

NCG ReservoirNCG Tube

Evaporator

NCG Tube

Radiator

Condenser

Al

Al

SS


NCGReservoir

Con

dens

er(G

roov

es)

Evaporator(Screen)

VCHP Design – NCG Reservoir Adjacent to Evaporator


Adiabatic(Grooves)

WEB Enclosure

Radiator


ILN Anchor Node – NCG Reservoir Adjacent to Evaporator


Vertical Asymptotes1. Reservoir Near Evaporator: 0 K2. Reservoir Near Condenser: ≈29.78 K

Standard condenser location gives much higher mass


VCHP with Internal Reservoir


Evaporator

NCG Reservoir

Condenser

Adiabatic Section


VCHP with Internal Reservoir


Cooling Block

NCG Reservoir

Condenser

Adiabatic Section

Evaporator

Heating Block


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



VCHP Testing – Instrumentation

TC Locations



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



Task 3. VCHP Testing – Lunar Freeze/Thaw Results


Power

TC23 (Cond)

TC1 (Gas)

TC10 (Evap)TC30 (Cond)

TC27 (Cond)

TC26 (Cond)




VCHP Operation (25 °C, 95 W, -2.3°)




VCHP Cold Shutoff (-60 °C, 0.2 W, -2.3°)




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



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



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



Task 3. VCHP Testing – Lunar Performance Results


Temperature Profile (25 °C, 220 W, -2.3°)


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



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)


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



Task 3. VCHP Testing – Space Thermal Diode Results


Thermal Diode Temperatures (Evaporator at 25 °C, 0.1 Inch Adverse)


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)



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



Task 3. VCHP Testing – Space Performance Results


(25 °C, No NCG)

Zero-g power extrapolated


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




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




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



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.


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

variable conductance heat pipe for a variable thermal link c. j. peters, j. r. hartenstine, c....

Documents

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thermal management

w power

lunar night iso

as9100b certified slide

minimum night slide

web thermal control

heat losses