DIODE HEAT PIPES FOR LONG-LIVED VENUS LANDERS

Abstract

Cooling during normal operation of the Long-lived Venus Lander can be provided with a radioisotope Stirling power converter that energizes Stirling coolers. High temperature heat from roughly 10 General Purpose Heat Source (GPHS) modules must be delivered to the Stirling convertor with minimal ΔT. In addition, the cooling system must be shut off during transit to Venus without overheating the GPHS modules. This heat is managed by a High Temperature Thermal Management System (HTTMS). During normal operation, waste heat is produced at both the cold end of the main Stirling converter and the hot end of the highest rank Stirling cooler. It is critical for this waste heat to be rejected into the environment also with a minimal ΔT to maintain a high efficiency for the cooling system. A passive Intermediate Temperature (~520ºC) Thermal Management System (ITTMS) that will reject this waste heat is under development. During transit, the cooling system rests and no waste heat is generated. In turn, the HTTMS will reject high temperature heat bypassing the Stirling converter’s heater head and heating the ITTMS. Diode heat pipes are required so that heat will not be transmitted in the reverse direction, from the radiator heat pipes to the cold end of the Stirling converter and hot end of the highest rank cooler. A gas charged alkali metal Diode Heat Pipe (DHP) is under development for this purpose. Two proof of concept potassium DHPs that differ in the size of their reservoir connecting tube were tested at 525ºC transporting a power of 500W. The pipes worked in both Heat Pipe Mode and Diode Mode intermittently as the power was applied at the evaporator and condenser, demonstrating the concept. The DHP with a larger diameter reservoir connecting tube showed faster transients during the returning from the Diode Mode to the Heat Pipe Mode.