Development of a magnetic refirgerator for hydrogen liquefaction

Abstract

This paper describes recent progress on a hydrogen magnetic refrigerator. Magnetic refrigeration makes use of the magnetocaloric effect, and is well known as an efficient method in principal because its cooling cycle can most closely follow the Carnot cycle with appropriate heat switches. A liquefaction principal of our magnetic refrigerator is based on the thermo-siphon method, in which liquid hydrogen is condensed directly on the surface of magnetic refrigerants and drops downward. In liquefaction experiments, we have successfully liquefied hydrogen gas preliminarily cooled to a temperature slightly above the boiling point. To improve liquefaction efficiency, the filling factor and spherical form of the magnetic material have been considered. Increasing the filling factor from 0.34 to 0.45 resulted in increasing %Carnot and cooling power by ∼50%. Spherical magnetic material DGAG with a 0.4 mm diameter was successfully developed. The thermal efficiency during the liquefaction process was increased largely by using the sphere DGAG, but it was observed that the condensed liquid hydrogen was trapped inside the spheres. This disadvantage will not be serious when we use a hybrid cycle consisting of Carnot and AMR. © 2008 American Institute of Physics.