Turbo Brayton coolers for a range of loads and temperatures

Several reverse-Brayton cycle cryocoolers are being developed for long-life, vibration-free applications cooling spaceborne instruments. These coolers employ miniature high speed turbomachines with self-acting gas bearings and low mass shafts to provide the compression and expansion functions without vibration. Advanced, high performance recuperative heat exchangers result in high cycle efficiency at low pressure ratios. Recent advances in this technology permit the construction of smaller machines while preserving important geometric features. As a result, reasonable efficiencies are maintained in these components as sizes are reduced. This is critical for maintaining acceptable overall cycle efficiencies as refrigeration loads and temperatures are decreased. This paper summarizes the present status of developments with respect to turboBrayton crycoolers for a range of conditions between about 75 K and 6 K. The largest of the systems is capable of up to 15 W refrigeration at 70 K; the smallest is designed for less than 100 mW at less than 10 K. Important phsyical characteritics of severla systems and their components will be presented. System performance characteristics will be discussed.