INTERPOLATIVE DETERMINATION OF THE HEAT CAPACITY OF ALLOYS OF RARE-EARTH METALS FOR REGENERATORS OF COOLING SYSTEMS

摘要

Cooling systems that operate on Stirling, Gifford-MacMahon, pulsation-tube, and other cycles, where such materials as copper, lead, bronze, and stainless steel are used as packing in regenerative heat exchangers, are now widely used in micro-cryogenic equipment. A drawback of these materials stems from their low heat capacity at temperatures below 60―80 K; this lowers the effectiveness of cryogenic systems at low cryostatting temperatures. One means of improving the effectiveness of Stirling and Gifford―MacMahon coolers is to create multilayer regenerators in which the material of the low-temperature packing in each layer is selected such that its heat capacity is maximum at the operating temperature of the layer. In rare-earth metals (REM) and also in their compounds, alloys, and composites, an anomalous increase in heat capacity, which exceeds the heat capacity per unit volume by several times within a certain range, is observed in the vicinity of the temperatures of the magnetic phase transitions (Fig. 1). Use of REM in regenerators will therefore improve the effectiveness and lower energy consumption, and make it possible to achieve helium temperatures in two-stage microcryogenic systems with no throttling circuit.