Sorption Cryogenic Refrigeration — Status and Future

Abstract

This paper describes sorption refrigeration development, which represents a relatively new breakthrough in cryogenic cooling. Sorption refrigerators have virtually no wear-related moving parts, have negligible vibration, and offer extremely long life (at least ten years). In sorption compressors, low pressure gas is physically adsorbed or chemically absorbed to cooled solids. When heated an additional 100°C to 200°C the gas becomes greatly pressurized and is desorbed, i.e., vented, from the solids. Precooling and expansion of the gas causes partial liquefaction, thus providing net cooling. Recent testing at JPL includes a 1000-hour life test of a hydrogen chemisorption refrigerator (14K–30K), a feasibility test of a nitrogen physisorption refrigerator (100K–200K) and a demonstration test of an oxygen chemisorption compressor (for 55K–90K). Although first stage sorption refrigeration systems require more power than mechanical systems, multiple-stage sorption systems are at least three times more efficient and at least ten times lighter than mechanical refrigerators for 7K–10K cooling (SH₂ vacuum sublimation onto hydrides). Due to the high reliability, long-life, light-weight, low vibration characteristics of sorption refrigeration, it is presently being considered for many spacecraft applications and may eventually have many ground applications as well.