Thermal Vacuum Testing of a Miniature Loop Heat Pipe With Multiple Evaporators and Multiple Condensers

This paper describes thermal vacuum testing of a miniature loop heat pipe (MLHP) with two evaporators and two condensers designed for future small systems applications requiring low mass, low power and compactness. Each evaporator contains a wick with an outer diameter of 6.4 mm, and each has its own integral compensation chamber (CC). Multiple evaporators provide flexibility for placement of instruments that need to be maintained at the same temperature, and facilitate heat load sharing among instruments, resulting in a reduced auxiliary heater power requirement. A flow regulator is used to regulate heat dissipations among all condensers, thus providing flexibility for placement of radiators on the spacecraft. A thermoelectric converter (TEC) is attached to each CC for operating temperature control and enhancement of start-up success. Tests performed include start-up, power cycle, sink temperature cycle, high power and low power operation, heat load sharing, and operating temperature control. The MLHP demonstrated excellent performance in the thermal vacuum environment. The loop started successfully and operated stably under various evaporator heat loads and condenser sink temperatures. The TECs were able to maintain the loop operating temperature within ±0.5K of the desired set point temperature at all power levels and all sink temperatures. The un-powered evaporator would automatically share heat from the other powered evaporator. The CC control heater power was reduced by more than 50 percent when a TEC was used instead of conventional electrical heaters. The flow regulator was able to regulate the heat dissipation among the radiators and prevent vapor from flowing into the liquid line.