<p>Large-scale helium refrigeration system in fusion devices employs cold-compressors at temperatures near 4.2 K or below for its stable operation as well as for mitigation of the effects of pulsed heat load during the operation of such fusion devices. In such systems, cold-compressor based vapor compression cycles have been proposed that produce refrigeration utilizing the excess low-pressure return stream in those helium refrigerators. The selection and design of appropriate cold compressors for such configurations are extremely critical towards the operability of such techniques. Centrifugal compressors are a preferable choice for such applications as it does not involve any valves and seals and hence require less mechanical maintenance. However, there are certain drawbacks that are associated with cold compressors such as heat in-leak and the narrow range of operation. Cold-compressors involve heat leakage from impeller hubs and the end of shafts into the flow passages reducing compressor aerodynamic performance and thereby having a significant effect on the compressor performance. Also for efficient operation, the cold compressor should operate in the stable region without entering the surge or stall region under both steady and transient modes. For the efficient design of cold compressors, the effect of heat in-leak and the compressor operation range should be identified. In this paper, a conceptual centrifugal compressor for such applications is designed based on the principles of Balje and Hasselgruber and is analysed for the determination of its operability under simulated pulsed load condition at helium refrigerators with fusion devices. CFD analysis was performed for analysing the effect of heat inleak on the compressor performance and for identification of the surge and stall line. Efforts were also made to identify the major geometric parameters that affect these impediments and design modifications were suggested for improvements.</p>

Conceptual Design of 4.2 K Cold-Compressors for Large-Scale Helium Refrigerators Used in Fusion Devices for Mitigation of Pulsed Heat Load

Paper Proceedings: https://asmedigitalcollection.asme.org/GTINDIA/GTINDIA2021/volume/85536

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