Speaker
Description
The cold box for helium refrigerator plant of cooling power ~200 W at 4.5 K is being developed at IPR, Gandhinagar, India. Helium compressor system, which gives helium flow ~60 g/s at 14 bar will be 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. All 3 turbines are of aerodynamic bearing with eddy-current brake type and these are fitted vertically at the top dish end of the vacuum chamber. All seven plate-fin heat exchangers are made using serrated fins of Al-alloy and are vacuum-brazed. LN2 pre-cooling is used to ensure 80 K before the helium purifier. Turbine-1 and 2 are warmer ones and are connected hydraulically in series and helium outlet from turbine-2 is connected to the low pressure line of the cycle. The 3rd turbine is colder one and is in series with JT valve. Later, based on the detailed process analysis and optimization, it is found that if only 7th heat exchanger, the coldest one, is replaced by a higher capacity, cooling power of the plant can be improved significantly. Hence, provision has been kept for future up-gradation to a plant of higher capacity. Appropriate provisions to upgrade the plant from only-refrigerator to refrigerator-cum-liquefier and for LHe extraction have been included. This refrigerator plant has been designed to handle high air impurity up to ~500 PPM. The component and piping layout within the cold box has been done considering thermal, structural and hydraulic aspects for different operations and future up-gradations. The architecture of this layout has been developed and implemented indigenously. Sufficient instruments and data acquisition have been included to diagnose troubles easily, as, such helium plant is being made at IPR 1st time. Details of the design concept of the cold box and experiences of initial operations will be discussed in this paper.
| Submitters Country | India |
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