The Characterization of Several High Specific Heat Regenerator Materials in a Gifford McMahon Refrigerator
Recent developments in the use of low-temperature, high specific heat materials in Gifford McMahon (GM) refrigerators has produced remarkable demonstrations of ultra-low temperatures. These materials, consisting of heavy rare earth and ceramics, exhibit a magnetic phase transition leading to a sharp rise in specific heat at the transition temperature. From recently published data, it is clear that these materials improve refrigerator performance, but the key material and operating parameters affecting the reported performance improvements are not clearly defined. Therefore, with this goal in mind, the General Electric Research and Development Center has manufactured a number of high specific heat materials and tested them in two GM refrigerators.
Spheres from 5 materials were fabricated and tested in both pneumatic and mechanical drive refrigerators. The materials consisted of 4 rare earth materials with transition temperatures ranging from 7.5 to 14 K, and one ceramic material with a sharp specific heat spike at 6.0 K. Spherical particles in the size range from 150 to 500 μm were produced by a spark erosion and gas atomizing manufacturing process. The test results identified several critical performance parameters important to the commercial use of these materials, and demonstrated a capacity increase of 150% at 10 K. Disappointingly, the ultra-low temperatures reported by other researchers were not achieved in these studies. We present the results of this testing, along with a discussion of the difficulties encountered in the manufacture and use of these materials.
KeywordsPorosity Enthalpy Helium Brittle Rhodium
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- 1. T. Kuriyama, Hakamada, Nakagome et al., High Efficiency Two Stage GM Refrigerator with Magnetic Material in the Liquid Helium Temperature Region, in: “Advances in Cryogenic Engineering,” Vol. 35B, Plenum Press, New York, (1990), p. 1261.Google Scholar
- 2.J. L. Walter, “On the Preparation of Powder by Spark Erosion”, General Electric Corporate R&D Center Technical Information Series, 88CRD202, (1988).Google Scholar