Development of Cold Box for Upgradable Helium Refrigerator Plant of 200 W at 4.5 K

Abstract The cold box for helium refrigerator plant of cooling power ~200 W at 4.5 K has been developed at IPR, Gandhinagar, India. Helium compressor system, which gives helium flow ~60 g/s at 14 bar, has been used for this plant. The cold box of the plant is made using a vertical vacuum chamber, within which all cold components are assembled. The thermodynamic process used is a modified Claude Cycle. This cold box has 7 plate-fin heat exchangers, 3 turbo-expanders, an 80 K helium purifier and a JT valve. LN2 pre-cooling is used in the cold box to ensure 80 K before the helium purifier. Turbine-1 and 2 are warmer ones and are connected hydraulically in series. The 3 rd turbine is colder one and is in series with JT valve. This plant, due to certain reasons, has been developed using components made for other purposes. Later, based on the detailed process analysis and optimization, it was found that if only 7 th heat exchanger, the coldest one, is replaced by a higher capacity, cooling power of the plant can be improved significantly. Similarly, there are other possibilities to upgrade it up to cooling power ~1 kW at 4.5 K. Hence, provision was kept for up-gradation to a plant of higher capacity with different modes of cooling. The architecture of this layout has been developed and implemented indigenously. Details of the design concept of the cold box and experiences of initial operations will be discussed in this paper.