Analysis and Optimization of a Dual-Load Vapor Compression Cycle Using Non-Azeotropic Refrigerant Mixtures

摘要

Some Non-Azeotropic Refrigerant Mixtures (NARMs) have been identified as potentialreplacements for R12 because of their low ozone depletion potential, low global warmingpotential and promising thermodynamic characteristics which could improve cycle efficiency. ANARM experiences a variable temperature glide during a constant-pressure phase changeprocess, making it a logical candidate for the two-temperature level cooling found inrefrigerators. There are two fundamental thermodynamic benefits to using a NARM over a purerefrigerant: 1) mixture and air-temperature glides can be better matched to improve the systemperformance, and 2) lower refrigerant temperatures can be achieved through the use ofintercooling with no decrease in evaporating pressure. The objective of this research was toinvestigate optimal pure refrigerant (R12 and R134a) and NARM (65% R22135% R123 and 80%R22120% R 141 b) refrigerator system configurations that minimized life-cycle cost.A two-evaporator flow loop was constructed to help develop an evaporator heat transfermodel and take NARM heat transfer data. For the mass flux range of 25-45 kglm2-s, the mixtureheat transfer coefficients were on the order of 50% less than those of R12. For higher massfluxes, the mixture coefficients rose rapidly, and approached the R12 values.A steady-state optimization model was used to minimize the life-cycle cost of eachsystem configuration studied. The optimized system configuration with the lowest life-cycle costwas a R221R123 system with both high and low-temperature intercoolers. This system used5.7% less energy, 23% more evaporator area, and its life-cycle cost was 2.1 % less than that of anoptimized R134a single-evaporator system. Furthermore, this system used 10.5% less energy,46% more evaporator area, and its life-cycle cost was 4.5% less than that of a modeled R12 basecasesystem. The optimized R221R123 systems performed better than the equivalent R221R141bsystems. The high-temperature intercooler mixture systems performed as well as the twointercooler systems. Mixture heat transfer coefficient enhancement had a limited impact on lifecyclecost.