Design of the Heat Exchanger for the Compressor After-Cooler of the Helium Plant

Abstract

Liquid Helium Plants (LHeP) are designed to produce liquid helium from any room temperature helium gas source with a minimum purity of 99%. The helium refrigerator/Liquefier (HRL) needs compression of helium gas, which is then, cooled and expanded to produce liquid helium at 4.5 K. To avoid high heating and to reduce the work requirement in the compression, oil of heavy molecule, which has a high specific heat, is mixed with helium before compression. Before using this helium gas for refrigeration, it is necessary to separate helium and oil from the mixture and cool it to about room temperature. For this cold water at 20˚C temperature is used to cool helium and oil in separate heat exchangers. This project is about the design and analysis of the oil/water heat exchanger. Oil absorbs about 80% heat load produced due to compression process. It is planned to have a similar design concept and configuration as that of the existing one at Institute for Plasma Research (IPR) for the Helium Refrigerator Liquefier compressor system of Steady State Superconducting Tokamak (SST-1) magnets. Heat duty requirement is about 900KW. The flow of helium in nominal case is at 14 bar pressure with temperature at 90˚C at inlet and it needs to be cooled down to 35˚C temperature. The cold water inlet is about 20˚C temperature and it exits at 25˚C temperature. To get the exact flow distribution, pressure drops and temperature distributions in the fluid, it is required to have a detailed analysis based on thermal design tools, and an optimized configuration of the heat exchanger to cool the oil. In the present study, the results obtained analytically are validated with the thermal design tool HTRI software. The thermal design optimization was carried out by varying parameters like inside diameter of tube and inside diameter of the shell subsequently, which results in change of length of the heat exchanger, and pressure drop on tube side and shell side.