Cold Compression of Helium for Refrigeration Below 4 K
In normal helium refrigeration cycles the refrigerant helium is compressed at or above room temperature. But under certain circumstances a partial compression at lower than ambient temperature is advantageous. The most common use of cold compression is in case of operation at temperatures below 4.4 K, where the vapor pressure of helium is below 1.2 bar. Here the influence of the cold compression on the cycle efficiency is discussed. A review of the available types of compressors is given and the prototype of a supersonic radial turbocompressor is shown with active magnetic bearings and direct electrical drive.
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