Simulation and Experimental Study on the Pre-cooling Performance of the Condenser in Helium Sorption Cooler

Helium sorption coolers are widely used for achieving sub-kelvin temperatures due to their advantages of no moving parts, simple structure, and high reliability. While research has primarily focused on system design and sorption characteristics, studies on the condensation process of helium gas in these coolers remain limited. In this study, a three-dimensional simulation model is developed based on a laboratory helium sorption cooler prototype using helium-4 (4He) as the working fluid. The cooler reaches a minimum temperature of 827 mK with a holding time of 20 h. Experimental validation confirms the high accuracy of the model. The study analyzes the flow dynamics of liquid helium during condensation. Liquid helium flows along the narrow walls of the condenser heat exchanger, enters the evaporator through the pump tube, and evaporates, lowering the evaporator temperature. The evaporated helium gas then rises through the center of the pump tube. The study also examines the effect of pre-cooling temperature and operating pressure on the cooling rate. A decrease in pre-cooling temperature from 3.3 to 3.2 K leads to a sharp increase in the cooling rate, with cooling time dropping from 167 to 123 s. As the pre-cooling temperature further drops, the cooling time continues to decrease, but the impact on the cooling rate diminishes. Similarly, increasing the operating pressure from 37 to 41 kPa accelerates the cooling process initially, but the impact lessens as pressure continues to rise.