Description and Performance of a Near-Room Temperature Magnetic Refrigerator

Abstract

Magnetic refrigeration has been viewed as primarily a cryogenic technologybecause the necessary high magnetic fields are most easily providedby superconducting magnets. However, some of the largest magnetocaloriceffects are exhibited by gadolinium-based alloys near room temperature.Ames Laboratory and Astronautics Corporation of America have beencollaborating to apply such materials to large-scale commercial andindustrial cooling near room temperature. Astronautics has designedand operated a reciprocating magnetic refrigerator that uses wateras a heat transfer fluid. The device uses the active magnetic regenerationconcept of recent cryogenic devices, but in contrast to the cryogeniccase, the heat capacity of the fluid in the pores of the regeneratorbed is comparable to that of the solid matrix. Using a 5 T field,the refrigerator reliably produces cooling powers exceeding 500 wattsat coefficients of performance of 6 or more. This record performanceputs magnetic refrigeration in a class with the best of current technology,vapor cycle refrigeration, without having to use volatile, environmentallyhazardous fluids.