Study on the conjugate radiation heat transfer performance of radiator/condenser for heat pump thermal control system under lunar conditions

To ensure the thermal security for lunar landing, heat pump thermal control system (HPTCS) has potential to overcome the high lunar equivalent-temperature. Radiator/condenser is the core part to dissipate the heat from lunar lander to surrounding via radiation heat transfer. However, the conjugate heat transfer mechanism between condensation phase change and radiator radiation performance under the unique lunar gravity condition remains largely unexplored. This paper investigates the conjugate radiation heat transfer performance and liquid film development for the radiator/condenser considering the lunar micro-gravity and the thermal dynamic characteristics. A numerical model is established and verified by thermal vacuum test. The results suggest that in the HPTCS, under lunar micro-gravity, the liquid film is uniformly attached to the tube wall, forming a semi-annular flow pattern. Crucially, it is found that phase-change heat transfer can peak at 19.8 kW/(m²·K) but liquid film accumulation can significantly drop HTC to 4.69 kW/(m²·K). Increase in heat sink equivalent-temperature by 60 K can reduce the radiation heat by 51.98 W; increase in inlet temperature from 320 K to 350 K can significantly enhance the radiation heat by 37.26 W; while the influence of mass flow rate on radiation heat is mere. The findings provide a quantitative reference for the design of HPTCS radiators in extreme lunar environments.