Pressure Controlled Heat Pipe Applications

In a Variable Conductance Heat Pipe (VCHP), a Non-Condensable Gas (NCG) is added to the heat pipe to vary the condenser length, and hence the conductance. A Pressure Controlled Heat Pipes (PCHP) is a modified VCHP, where the heat pipe operation is controlled by varying either the gas quantity or the volume of the gas reservoir. This paper will discuss two applications for PCHPs: 1. Precise temperature control, and (2) Switching thermal power between multiple sinks. A prototype aluminum/ammonia PCHP was built and tested to demonstrate the capability of controlling the temperature of the evaporator section of an aluminum/ammonia pressure controlled heat pipe to milli-Kelvin levels over an extended period of time, while the heat sink temperature and evaporator power were varied. In a second program, a heat pipe solar receiver was designed to accept, isothermalize and transfer the solar thermal energy to reactors for oxygen production from lunar regolith. The receiver has two PCHPs and two Constant Conductance Heat Pipes (CCHPs) to supply heat to two reactors. During operation, one reactor is producing hydrogen at low solar power, while the other reactor is warming up a fresh batch of regolith. The PCHPs are used to switch power between the two reactors as required.