Non-azeotropic refrigerant mixture (NARM) vapor compression cycles

Scope and method of study. The objectives of this study were: (1) To examine and evaluate alternative cycles designed to take advantage of unique non-azeotropic refrigerant mixture properties. (2) To develop a simulation model to predict the performance of various vapor compression cycles using safe NARM's as working fluids. (3) To identify the most promising combination of NARM and cycle configuration for air-conditioning and chiller applications.;Four NARM cycles considered include one basic cycle with dry-evaporator and single-stage compressor and three advanced cycles: one with dry-evaporator and multi-stage compressor; two with flooded-evaporators, with and without liquid pump. For comparison, two pure refrigerant cycles were considered.;Findings and conclusions. Two operating conditions were evaluated to compare the performance of NARM systems to pure refrigerant systems. (1) For systems with high temperature drop across the evaporator: (a) The coefficients of performance (COP) of the advanced NARM cycles were approximately 7-8% higher than those of the basic NARM cycles and approximately 27-31% higher than those of the basic pure refrigerant cycles. (b) The COP of advanced NARM dry-evaporator systems were the highest of the cycles studied. They required heat exchanger sizes approximately twice as large as the pure refrigerant systems. The compression ratios were lower than the pure refrigerant systems. (c) The COP of the flooded-evaporator systems were nearly as high as the advanced NARM dry-evaporator systems, though they required heat exchangers approximately 50% larger than the dry-evaporator systems. They had the lowest operating compression ratios. (2) For systems with low temperature drop across the evaporator, the advantages of the NARM cycles were not as pronounced. The COP of advanced NARM cycles were approximately 3-4% higher than those of the basic NARM cycles and approximately 15-17% higher than those of the basic pure refrigerant cycles. (3) For both cases, R-123 was frequently a component of the optimum NARM's.