Analyis and Optimization of Component Process Param- eter for Helium Refrigerator

Abstract

In nuclear fusion reactors liquid helium at 4.5 K is used for providing low temperature cooling for superconducting magnets. The existing system designed to generate 4.5 K liquid helium at 1.2 bar consists of the major components of screw compressor, eight heat exchanger, three turbo expander and J-T expansion valve. The effect of change in J-T inlet pressure on the refrigeration effect of the cycle is studied in the present work. The effect of various effectiveness of first level heat exchanger on the refrigeration effect is studied and the effect of change in effectiveness of the first level heat exchanger on the liquid nitrogen mass flow required for pre cooling of helium is studied. The effect of the effectiveness of the last level heat exchanger on the refrigeration effect is also studied. Turboexpander is the main device of the plant which produces the cooling effect by mass flow rate diverted to turboexpander. Mass flow rate is a critical parameter in deciding the capacity of the plant. The present study investigates the effect by comparing various mass flow ratio and fluid inlet temperature through turbo expander so as to obtain the best refrigeration effect of the system. The present work involves the validation and simulation of analytical result obtain with the help of Aspen Hysys simulation tool by understanding the process flow diagram and the operation sequence of different components. The large scale plant of helium liquefaction is required to select proper process parameter for being exergy intensive. The exergy analysis is the effective tool for the thermodynamic analysis of the cycle. The present study involves the effect of the various mass flow fraction of expander on the exergetic effciency of expander. The study computes the exergetic effciency of the plant components on optimum parameter of the cycle.