Design consideration for piping and equipment layout within the cold box of helium refrigerator/ liquefier

The indigenous Helium Refrigeration/Liquefier (HRL), being developed at IPR, is planned to have cooling capacity and different component layout/configuration, nearly same as that of the existing HRL of the magnet system of Steady State Superconducting Tokamak (SST-1) of IPR. The existing HRL has equivalent refrigeration capacity of about 1.3kW at 4.5 K. The indigenous HRL will have option of upgrading the cooling capacity in modular way up to approximately 2kW. The vacuum chamber of the cold box will contain all the cold equipments/elements necessary to produce liquid helium at 4.5 K. Similar to the existing one, it is planned to have horizontal long cylindrical vacuum chamber with two removable cover plates at both ends for maintenance access to the components inside the chamber. There will be provisions for penetration of process pipes, instrumentation tubes, cable feedthroughs and valve penetrations. Turbo expanders will be placed such that without opening the end plates of the chamber these can be removed and replaced. At the low temperature end of the cold box, heat load to the cold components could reduce cooling capacity of the HRL. Appropriate thermal shield, cooled by LN₂ (liquid nitrogen) at about 80 K, need to be designed to reduce this external heat load. This will need planned layout of different cold components/elements inside the vacuum chamber of the cold box considering thermal, hydraulic, mechanical, maintenance and repair requirements. During operation, at low temperature, these components will shrink and can lead to severe thermal stress. To avoid this it will need a proper piping layout and flexibility analysis to check whether stresses are within limit. (author)