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Experiment Title: Transverse Flat-Plate Heat Pipe Experiment

Original Principal Investigator(s): Shular, Mr. Dave - Invest. Role: Present, Owen, Mr. James - Invest. Role: Present, Owen, Mr. James - Invest. Role: Original, Edelstein, Fred - Invest. Role: Original,

The use of heat pipes as a thermal control system in industrial, military, and space applications has increased in recent decades. Applications cover a wide range of temperatures from cryogenic and ambient to high temperature systems, and employ working fluids such as methanol and ammonia to liquid metals. Heat pipes are employed in everyday uses such as circuit board cooling and pipeline de-icing systems, as well as tactical missiles, battlefield communications systems, and spacecraft electronics.

The operational performance of heat pipes has also increased with expanded applications. Early generation heat pipes could transport 50-100 watts of power only a few feet at ambient temperatures. Currently, artery wick heat pipes can transport 1000 watts of power up to distances of 10 feet or more with temperature drops in the range of a few degrees. Heat pipes are also incorporating variable conductance features and diode functions to maintain heat source temperatures at a constant level while the heat input increases up to 200 percent or more.

The application of heat pipes as a thermal control system offers many advantages over a conventional pumped fluid loop or cold plate. Due to the nature of their design, heat pipes have an inherent reliability since they possess no moving parts. Since the enthalpy of vaporization for a fluid is generally quite large, heat pipes have the capability of transporting heat energy over relatively large distances with very little temperature drop. Also, since heat pipes are driven by the pressure differences between the fluid and the vapor, no external power is required. These features, along with the variable conductance capability to provide temperature control over wide variations in source heat loads, make heat pipes a high attractive option for waste heat management of on-orbit systems and spacecraft.

For a number of years, NASA Marshall Space Flight Center has actively pursued the practical application of heat pipe technology to actual thermal control hardware. A number of heat pipe concepts have been developed into breadboard hardware and extensively tested under thermal vacuum condition to verify performance. For example, programs have been successfully completed which demonstrated a deployable heat pipe radiator, transverse heat pipes, an isothermal heat pipe plate, and a total heat pipe thermal control system. In addition to these hardware programs, thermal investigations of future vehicles, such as the space station, strongly indicate the advantages of heat pipe thermal control systems. With this overwhelming support favoring heat pipe thermal control systems, future payload currently in the early design phase still revert to flight-proven thermal control techniques. This experiment offers a unique opportunity to provide flight demonstration of currently available heat pipe thermal control technology to remove the stigma from its general acceptance for space applications.

A transverse heat pipe is a variable-conductance heat pipe (VCHP) which can handle relatively large thermal loads. It was developed to circumvent the gas bubble artery blockage problem associated with conventional artery wick designs which limited their capacity to small loads in the VCHP mode. In the basic design of a transverse heat pipe, liquid flows in a direction transverse or perpendicular to the vapor flow. Temperature control is achieved by using conventional noncondensible-gas techniques.

The concept of this investigation was to utilize current basic heat pipe technology to design and fabricate a heat pipe thermal control module experiment, demonstrate the hardware capability and performance in the Shuttle flight environment, and verify the ground verses flight data correlation. It was anticipated that the self-regulated transverse flat-plate heat pipe would maintain the temperature control areas of the experiment within the tolerance specified with varying heat inputs independent of LDEF orientation.

Photograph Classification: Postflight

Associated Photograph(s):
LaRC - L92-17793
KSC - KSC-390C-612.02
JSC - None
LaRC - L90-10444
KSC - None
JSC - S32-78-076
LaRC - None
KSC - None
JSC - None

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