Effect of Heat Exchanger Configuration on the Performance of Joule-Thomson Refrigerators
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A typical Joule-Thomson (J-T) refrigerator consists of a recuperative heat exchanger, a gas expansion nozzle, a mandrel, and a compressed gas storage bottle. The thermodynamic performance of a J-T refrigerator depends highly on the hydraulic and heat transfer characteristics of the recuperative heat exchanger. The typical recuperative heat exchanger of a J-T refrigerator has a double helical tube and fin configuration, but other heat exchanger configurations may be used, including the two-flow type helical tube and fins configuration, the twostage heat exchanger configuration, a double helically wound tube circuit arranged in a spiral channel, etc. In this study, the performance of J-T refrigerators with single and two-flow type recuperative heat exchangers was investigated. The effectiveness-NTU approach was adopted to predict the thermodynamic behaviors of the heat exchangers for the J-T refrigerators. The results show the effect of the operating conditions on the performance of the heat exchanger and refrigerator for three types of heat exchangers. The influences of mass flow rate and supply pressure on the effectiveness of the heat exchanger and the refrigeration power are discussed in detail.