Rapid Cooling Characteristics of Load with Large Heat Capacity in Joule-Thomson Refrigerator Using Helium

Helium throttling refrigeration technology is a key cooling method used in liquid helium temperature zones in space. Research on the rapid cooling of chillers coupled with large heat capacity loads is important for the efficient operation of large heat capacity loads. To clarify the cooling characteristics of helium throttling chillers under different rapid cooling schemes, cooling experiments with no additional measures scheme, room-temperature valve bypass scheme, and thermal switch scheme were conducted based on GM pre-cooled helium Joule-Thomson chillers under different heat capacity loads. The experimental results show that the load-free pull-down times of the three schemes were 39.8 h, 20.5 h, and 19 h, respectively. Based on thermodynamics and heat transfer theories, the changes in the radiation, convection, heat conduction, and throttling source terms during no-load cooling were quantitatively analyzed, and the reasons for the difference in cooling time of helium throttling chillers under different schemes were explained. With a simulated load of 0.136 kg of copper, schemes of the room-temperature valve bypass and hot switch were adopted, and the corresponding cooling times were 25.5 h and 20 h, respectively. The experimental results show that the cooling effects of the thermal switch and room-temperature valve bypass scheme are essentially the same for the cooling of a small heat capacity load. Therefore, thermal switch cooling has significant advantages for large-heat-capacity load cooling.