PERFORMANCE EVALUATION OF HEAT LEAK TO THE EVAPORATOR AND THE EFFECT OF LONGITUDINAL HEAT CONDUCTION FROM A COUNTER-FLOW CRYOGENIC HEAT EXCHANGER USING FINITE ELEMENT METHOD

摘要

The performance of heat exchangers working in the cryogenic temperature range is strongly affected by factors such as longitudinal wall conduction, heat in leak from the surroundings, flow maldistribution, fluid property variations etc. In most heat exchanger analyses the common assumption is that the ends are insulated. However, in case of small J-T refrigerators longitudinal wall conduction is significant. The cold end of the heat exchanger is almost directly connected to the evaporator. This leads to appreciable heat leak to the evaporator leading to significant drop in performance, to this paper the governing equations for a counteT-flow heat exchanger, with heat loss at the cold end, are solved by FEM and the methodology validated by comparing the results with numerical and experimental values published earlier. The analysis is further extended to understand the effects of variation of wall temperature at the cold end and the effect of NtuH not being the same as NtuC, on the performance of the heat exchanger.