Theoretical optimization of a regenerated air refrigerator

Abstract

The performance analysis and optimization of a regenerated air refrigerator is carried out by taking the cooling load density, i.e. the ratio of cooling load to the maximum specific volume in the cycle, as the optimization objective using finite-time thermodynamics or entropy generation minimization in this paper. Analytical relationships between cooling load density and pressure ratio, as well as between coefficient of performance (COP) and pressure ratio are derived. The irreversibilities considered in the analysis include the heat transfer losses in the hot- and cold-side heat exchangers and the regenerator, the non-isentropic compression and expansion losses in the compressor and expander, and the pressure drop losses in the piping. The comparison of the cycle performances under maximum cooling load density and maximum cooling load conditions is performed. The optimal performance characteristics of the cycle are obtained by optimizing the pressure ratio of the compressor, and searching the optimum distribution of heat conductances of the hot- and cold-side heat exchangers and regenerator for the fixed total heat exchanger inventory. The influences of the effectivenesses of the regenerator as well as the hot- and cold-side heat exchangers, the efficiencies of the expander and the compressor, the pressure recovery coefficient, and the temperature ratio of the heat reservoirs on the cooling load density and COP are examined and shown by numerical examples.