Thermal Systems Modeling of Chemical Heat Integrated Power Source (CHIPS) to Survive Lunar Night Environments
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Herein we present the thermal systems modeling of Chemical Heat Integrated Power Systems (CHIPS) to survive lunar night environments. The objective is to deliver at least 100 thermal Watts and 30~40 electric Watts for 336 hours (14 lunar nights) in a 50 kg payload. The chemical reaction is based on Lithium, Li(s) and Sulfur Hexafluoride, SF6(g) yielding a specific energy of 4049 W-hr/kg using a reactant mass of 11 kg. The overall thermal system architecture is comprised of an oxidizer tank, a Li-SF6 reactor tank, a Stirling power generation unit, sodium heat pipes and a heat exchanger which interfaces with a lunar lander. Typical hot and cold side Stirling power generation device temperatures are 650 C and 20 C, respectively. Stirling conversion efficiencies are approximately 30%. The primary thermal design challenge is to match the reactor and Stirling hot side temperatures and thermal flows. This is accomplished using sodium heat pipes. The reactor tank is modeled as a volumetric heat source, and internal tank fins enhance the heat transfer from the reactant vapor volume to the reactor walls. Stirling device performance data was implemented as a look up function using SINDA logic. The SINDA logic developed herein iterates to compute automatically the correct internal conductance values and power output/efficiency of the Stirling device, thus providing a robust model which can be implemented parametrically in support of design trade studies. Key thermal interfaces include the heat pipe evaporator to tank wall, heat pipe condenser to Stirling hot side. Details of the design of these interfaces using metal foams and high thermal conductivity alloys are discussed. The results of the thermal model are being used to design a CHIPS payload test-bed. The paper will present results of thermal model predictions and include a review of the thermal testing work performed to date.