Experimental study on a small Brayton air refrigerator under -120 °C

A small Brayton air refrigerator with high-speed gas bearing turbo-expander and compact plate-fin heat exchanger was designed and fabricated. Performances of the two key components (turbo-expander and heat exchanger) and the refrigerator as a whole were investigated. The bearings used in the refrigerator were compliant foil journal bearings with elastic support, and stability inspection was conducted on them. The results indicate that the refrigerator had a high cooling capability, and that the gas bearings used here achieved good performance in a wide speed region up to 250,000 rpm. While the expander operated at its design speed (220,000 rpm), the refrigerator had a cooling capacity of 1500 W at -80 °C, and the lowest no-load refrigeration temperature of -124.5 °C was obtained. Moreover, the influence of nozzle number and velocity ratio on the turbo-expander and the effect of flow rate and cold inlet temperature on the heat exchanger are discussed in detail.