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Publisher Summary The Large Helical Device (LHD) has been being under construction at National Institute for Fusion Science (NIFS) at the Toki site in Gifu prefecture. Due to its size superconducting magnets of LHD need large refrigeration system. As the magnets and the large cryostat for the magnets are still under design or construction, heat load and heat load distribution might be changed from the figures. In order to estimate the plant condition in such cases, the plant performance at off-design condition has to be simulated. Performance at off-design conditions of a large scale helium refrigerator is estimated by the simulation model that has been developed for a study of a standard helium liquefier. The process simulation model is based on characteristics of hardware such as heat exchangers and expansion turbines. Required input data to the simulation model are process variables that can be fixed or controlled. Simulation results of the large refrigerator for LHD, which has 7 expansion turbines and 15 heat exchangers, agree with the data observed at the commissioning. As an extreme off-design condition, performance without 3 upper expansion turbines is studied. |
