Small Business Innovation Research/Small Business Tech Transfer
Low Cost Variable Conductance Heat Pipe for Balloon Payload
Project Description
While continuously increasing in complexity, the payloads of terrestrial high altitude balloons need a thermal management system to reject their waste heat and to maintain a stable temperature as the air (sink) temperature swings from as cold as -90oC to as hot as +40oC. Currently, constant conductance, copper-methanol heat pipes are utilized on balloon payloads to remove the waste heat. It would be desirable to use a Variable Conductance Heat Pipe (VCHP) instead, to allow the thermal resistance to increase under cold operating or cold survival environment conditions, keeping the instrument section warm. In spacecraft, thermal management is achieved using axially-grooved aluminum-ammonia heat pipes and VCHPs, which are relatively expensive to manufacture and validate. Advanced Cooling Technologies, Inc. (ACT) is proposing a low-cost VCHP based on smooth-bore, thin-wall stainless steel tubing, with either methanol or pentane as working fluids, that is capable of passively maintaining a relatively constant evaporator (payload) temperature while the sink temperature varies between -90oC and +40oC. The thin wall will be much lighter and will provide much better temperature control due to its higher thermal resistance, while the combination of working fluid and envelope material result in a heat pipe that is much less expensive to manufacture than standard grooved aluminum heat pipes. Spacecraft VCHPs normally have the gas reservoir at the end of the condenser, and maintain its temperature with electrical heaters. The proposed VCHP moves the reservoir near the evaporator, eliminating the need for electrical power to control the temperature. Preliminary calculations show that either system, methanol based or pentane based, is capable of meeting the thermal performance requirements. For both the pentane and methanol systems, the evaporator (payload) temperature varies less than 6oC while the heat sink temperature varies from 90oC to +40oC.
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Anticipated Benefits
One commercial application is VCHP heat exchangers in fuel cell reformers. In a fuel cell reformer, diesel fuel and air pass through a series of high temperature reactors to generate hydrogen. The operating temperature of the reactors must be closely controlled to maintain their chemical equilibrium. The current scheme uses a bypass valve, which has several drawbacks: it requires active control, requires power, and has a large pressure drop. ACT believes that VCHP heat exchangers can replace the current heat exchanger and control system with a passive system that automatically maintains the output stream from the heat exchanger at a constant temperature. The second application is adding feedback temperature control to ACT's current line of commercial isothermal furnace liners, which are annular alkali metal heat pipes that provide nearly isothermal temperature uniformity. Adding feedback control will allow the temperature to be controlled within millikelvins, adding in isothermal processing of materials, thermophysical properties characterization, and calibration of temperature references.
The immediate application for this technology is thermal management for balloon-borne instrumentation systems. It is expected that the technology developed will provide temperature stabilization of the instrumentation system without the need for power-consuming control or trim heat and without the need for heavy and expensive louvers or heat switches. The technology will be based on low-cost stainless steel/methanol heat pipes, which use inexpensive smooth-bore tubing and whose charging and fabrication processes are much less costly and time consuming than the industry-standard axially-grooved aluminum/ammonia heat pipes currently used on spacecraft. Other applications would be the variable conductance thermal link between the Warm Electronics Box (WEB) from lunar anchor nodes and the radiator. During the long lunar night, the radiator temperature drops considerably increasing the waste heat flow from the WEB. The VCHP regulates the waste heat flow to the cold radiator to maintain the WEB at warm temperatures. More »
The immediate application for this technology is thermal management for balloon-borne instrumentation systems. It is expected that the technology developed will provide temperature stabilization of the instrumentation system without the need for power-consuming control or trim heat and without the need for heavy and expensive louvers or heat switches. The technology will be based on low-cost stainless steel/methanol heat pipes, which use inexpensive smooth-bore tubing and whose charging and fabrication processes are much less costly and time consuming than the industry-standard axially-grooved aluminum/ammonia heat pipes currently used on spacecraft. Other applications would be the variable conductance thermal link between the Warm Electronics Box (WEB) from lunar anchor nodes and the radiator. During the long lunar night, the radiator temperature drops considerably increasing the waste heat flow from the WEB. The VCHP regulates the waste heat flow to the cold radiator to maintain the WEB at warm temperatures. More »
Primary U.S. Work Locations and Key Partners
| Organizations Performing Work | Role | Type | Location |
|---|---|---|---|
| Advanced Cooling Technologies, Inc. | Lead Organization | Industry | Lancaster, Pennsylvania |
Goddard Space Flight Center
(GSFC)
|
Supporting Organization | NASA Center | Greenbelt, Maryland |
Primary U.S. Work Locations
-
Maryland
-
Pennsylvania
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