Cycle performance testing of nonazeotropic mixtures of HFC-142a/HCFC-124 and HFC-32/HCFC-124 with enhanced surface heat exchangers.

摘要

In an effort to improve the efficiency of residential heat pumps using altemative refrigerants, two nonazeotropic refrigerant mixtures (NARMs) were tested over a range of heat exchanger capacities to determine their cooling mode performance at US Department of Energy (DOE) heat pump rating conditions of 82(degrees)F (27.8(degrees)C). The two mixtures, 30% HFC-32/70% HCFC-124 and 75% HFC-143a/25% HCFC-124, were selected on the basis of a previous study that screened refrigerant pairs using such factors as boiling point, stability, ozone depletion potential (ODP), and coefficient of performance (COP) to determine suitable candidates for residential heat pump performance. Three refigerant-side heat transfer enhancements were tested to determine improvements to overall system performance. Comparisons were made on the basis of the COP as a function of capacity. The results for one of the heat exchanger combinations, a segmented evaporator and finned condenser, were quite promising. Improvements in COP, relative to that for HCFC-22, were from 9 to 17% for the 30% HFC-32/70% HCFC-124 mixture and from 5 to 9% for the 75% HFC-143a/25% HCFC-124 NARM. Another combination, a smooth tube evaporator with a perforated foil insert and finned condenser, had similar gains at low capacities but experienced decreased performance at the higher capacities. The final combination, a smooth tube evaporator with a perforated foil insert and smooth tube condenser with a benttab insert resulted in poor performance.