Geometric scaling of a 4.2 K Gifford-McMahon refrigerator

An approach is presented to increase the cooling power of small regenerative cycle cryogenic refrigerators (cryocoolers). While several researchers have demonstrated Gifford-McMahon refrigerators capable of producing 0.5W of cooling at 4.2K, the U. S. Navy is interested in several applications, including mine countermeasures and electric ship propulsion, that have cryogenic refrigeration requirements of several times that amount. These applications are the impetus for scaling the existing 0.5W, 4.2K Gifford-McMahon refrigerators to a size where they can produce more cooling power. The approach is to properly increase the size of the various components based on the basic thermodynamic processes involved and the known performance of the present systems. This scaling method allows the estimation of increased compressor requirements as well as other important parameters. A new larger refrigerator, 1.5W at 4.2K, has been designed and operated. Test results of that refrigerator are presented.