High temperature superconducting magnetic refrigeration

Abstract

A near-room temperature active magnetic regenerative refrigerator (AMRR) was designed and built using a high-temperature superconducting (HTS) magnet in a charge-discharge cycle and a gadolinium-packed regenerative bed as the magnetocaloric component. Current to the HTS magnet was ramped periodically from zero to 100 amperes, which generated a ramp in field strength from zero to 1.7 tesla. Water was moved periodically through the bed and through hot and cold heat exchangers to accomplish a continuous refrigeration cycle. Cycle periods as short as 30 seconds were realized. Refrigerator performance was measured in terms of cooling capacity as a function of temperature span and in terms of efficiency expressed as a percentage of maximum obtainable (Carnot) efficiency. A three-watt cooling capacity was measured over a temperature span of 15 degrees C between hot and cold end temperatures of 25 degrees C and 10 degrees C. This experiment is directed to two possible applications for magnetic refrigeration: a no-moving part cryogenic refrigerator for space applications, and a compact permanent magnet refrigerator for commercial and consumer applications.