Size Effects of Miniature Refrigeration and Liquefaction System

Abstract

This article examines the size effects on the performance of miniature refrigerators and liquefiers operated by the Linde cycle. The system sizes are cased into a function of the compressor characteristic length and the heat exchanger length while several cycle operation parameters are held constant. Simplified models of a Hampson-type counterflow heat exchanger and a reciprocating-type compressor were considered in the present analysis. For both the refrigerator and the liquefier, it was found that only for certain ranges of the compressor size is the system able to produce a heat exchanger effectiveness greater than the required minimum value. It was also found that there exists an optimal compressor size for obtaining maximum heat exchanger effectiveness, cooling effect, mass fraction of liquefied product, and coefficient of performance. For the refrigerator, the optimal compressor size for obtaining the maximum heat exchanger effectiveness is different from that for obtaining the maximum cooling effects because of the mass flow rate effect. For the liquefier, the optimal compressor sizes for obtaining the maximum heat exchanger effectiveness, mass fraction of liquefied gas product, and FOM are approximately the same. When the Claude cycle is employed, it is found that it theoretically offers a more satisfactory performance than the Linde cycle in the small size range. The FOM of a mesoscale system with the Claude cycle can reach the range of 20 to 23% with the liquid product temperature ranging from 65 to 90 K. This research was partially supported by the Andrew H. Hines, Jr./Florida Progress Endowment Fund.