EVALUATION OF METAL HYDRIDE COMPRESSORS FOR APPLICATIONS IN JOULE-THOMSON CRYOCOOLERS

The Joule-Thomson expansion of hydrogen gas offers potential for efficient and reliable cryocoolers to produce temperatures between 10 and 50 K. A critical component to the development of these devices is the metal hydride storage bed that provides a nonmechanical method to compress the hydrogen gas via the reversible absorption by the appropriate metals or alloys. The influences of the thermophysical properties of these metal hydrides as well as compressor design constraints on the performance potentials of hydrogen sorption refrigerators have been examined. A thermodynamic model has been used to calculate the impact of operational parameters such as input/output pressure ratios and bed temperature on system efficiency. Detailed comparisons are reported for a compressor which utilizes vanadium metal as the sorbent for either hydrogen or deuterium where the unusually large isotope differences between VH(x) and VD(x) have been considered.