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The current trend in military avionics design is to physically move electronics closer to the components they control. This saves on weight, increases component maintainability, reduces aircraft manufacturing costs, and reduces the amount of electromagnetic shielding required. A disadvantage to this trend is the difficulty in achieving thermal control of these remotely located electronics. Accordingly, this thermal control issue is being addressed through the development of a loop heat pipe cold plate (LHPCP). The LHPCP is different than previous hardware of its kind by the fact that it operates in any orientation. The prototype LHPCP that was fabricated and tested was 30 inches long and weighed 1.2 pounds and was able to transport a minimum of 160 watts in any orientation. Future LHPCPs will be made flexible to allow relative motion between the package to be cooled and the heat sink.

This paper describes the transfer of Russian fine pore sintered powder metal wick structure fabrication technology to the United States for use in the construction of U.S. made loop heat pipes (LHPs), capillary pumped loops (CPLs) and heat pipes. Sintered powder metal wick structures have been used in U.S. made heat pipes for over twenty-five years. The typical pore radii for these wick structures range from 10 to 100 microns. Use of a wick material with a pore radius less than 10 microns was limited due to the high pressure drop encountered when used in a standard heat pipe. Conversely, the Russian loop heat pipe is able to get around this high pressure drop constraint due to its unique evaporator design. Prior to the work presented in this paper, the U.S. concentrated on the development of wick structure materials above 10 microns which created a technology void with the advent of the LHP.

The objective of this paper is to describe the results of a technical effort that demonstrated the feasibility of a heat pipe radiator for the M109 A6 Howitzer. The technical effort consisted of the following three parts: establishing full-scale M109 A6 radiator design requirements, designing a full scale heat pipe radiator, and fabricating and testing a representative segment of the full scale heat pipe radiator to demonstrate thermal and hydraulic performance. The design predictions of the heat pipe radiator showed good agreement with the measured test results. Experimental test results indicated that the representative segment heat pipe radiator met and exceeded the design heat load requirement under extreme environmental conditions.