Experiment to Determine Properties of Packed Particle Beds and Regenerators at Cryogenic Temperatures

The testing of the properties of packed-particle beds and regenerators at cryogenic temperatures as low as 4 K is an essential part of the magnetic refrigeration research and development program at the Los Alamos National Laboratory. We envision magnetic refrigeration and heat pump systems operating in various ranges from 4 K to ambient temperature and above. Only pressurized helium gas appears suitable as the heat exchange fluid for the low-temperature applications. Because published data on the properties of porous beds at low temperatures is sparse, we have found it necessary to develop an experimental test apparatus to study the properties of various configurations of beds and regenerators. Two of the well-known methods for such studies are the steady-enthalpy-flux method and the single-blow transient method. We have developed an experimental system in which gas flow can be suddenly switched to an alternate better (or colder) flow in step-function fashion at temperatures from 4 to 300 K. This apparatus will yield information on steady-state heat transfer and friction factors as well as on the transient behavior. Such information is very important to the design of high-efficiency magnetic refrigeration systems. This paper describes this experimental apparatus and presents the results and analysis of recent measurements on packed-particle beds in the liquid helium and liquid nitrogen temperature ranges