GB1324402A - Superconducting coils - Google Patents

Abstract

1324402 Heat exchangers; liquefying gases INTERNATIONAL RESEARCH & DEVELOPMENT CO Ltd 19 April 1971 [9 Feb 1970] 6134/70 Headings F4P and F4S [Also in Division H1] A superconducting coil assembly comprises a cryostat having an inner vessel housing the coil to be cooled and surrounded by an outer vessel enclosing a vacuum space; a refrigerator plant circulates cryogenic fluid (e.g. helium) through the inner vessel and incorporates a heat exchanger system comprising one or more exchanger units having electrically isolated fluid conducting members also serving as electric current connections to the coil. A compressor supplies gaseous helium to a cryostat containing the coil through a heat exchanger for cooling a helium counterflow returning to the compressor. The emergent helium stream divides to operate an expansion turbine and to enter another heat exchanger for further cooling by the return stream, after which it again divides to operate an expansion turbine and to enter a second similar heat exchanger system after which it passes to the superconductor coil cryostat over a liquefying expansion valve and subsequently returns (Fig. 1). The heat exchanger may be placed in the vacuum between the inner and outer vessels of the cryostat, and the coil therein is current energized through electrically conductive members of the exchanger. Parallel-connected heat exchangers may be used, electrically insulating sections being inserted in the helium inflow and outflow lines which divide into parallel paths through each exchanger; thus providing isolated current paths (Fig. 2, not shown). A typical exchanger may comprise a stack of rectangular electrically insulating plates 20 (e.g. of epoxy resin) and a pair of metal foils 21, 22 of zig-zag form, interleaved with the plates and with each other. Perforations through the pates an d foils define respective passages 24, 25 for the heat exchanging fluids (e.g. gaseous helium streams at differing temperatures). Connections X 1 convey one fluid stream to and from passages 24 and connections Y 1 convey the other fluid stream to and from passages 25. Heat transfer is mainly through the foils 21, 22 which serve also to convey the electric current supply to the equipment in the vessel. Electrically insu ating sections 23 may be included in the fluid lines external to the heat exchanger.