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Intermediate Temperature Fluids Life Tests - Experiments

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There are a number of different applications that could use heat pipes or loop heat pipes LHPs in the intermediate temperature range of 450 to 725 K 170 to 450 deg C, including space nuclear power system radiators, fuel cells, and high temperature electronics cooling. Historically, water has been used in heat pipes at temperatures up to about 425 K 150 deg C. Recent life tests, updated below, demonstrate that titaniumwater and Monelwater heat pipes can be used at temperatures up to 550 K 277 deg C, due to waters favorable transport properties. At temperatures above roughly 570 K 300 deg C, water is no longer a suitable fluid, due to high vapor pressure and low surface tension as the critical point is approached. At higher temperatures, another working fluidenvelope combination is required, either an organic or halide working fluid. An electromotive force method was used to predict the compatibility of halide working fluids with envelope materials. This procedure was used to reject aluminum and aluminum alloys as envelope materials, due to their high decomposition potential. Titanium and three corrosion resistant superalloys were chosen as envelope materials. Life tests were conducted with these envelopes and six different working fluids AlBr3, GaCl3, SnCl4, TiCl4, TiBr4, and eutectic diphenyldiphenyl oxide Therminol VP-1Dowtherm A. All of the life tests except for the GaCl3 are ongoing the GaCl3 was incompatible. As the temperature approaches 725 K 450 deg C, cesium is a potential heat pipe working fluid. Life tests results are also presented for cesiumMonel 400 and cesium70-30 coppernickel heat pipes operating near 750 K 477 deg C. These materials are not suitable for long term operation, due to copper transport from the condenser to the evaporator.

Subject Categories:

  • Non-electrical Energy Conversion
  • Properties of Metals and Alloys

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