Efficiency of Non-Azeotropic Refrigerant Cycle

Xin Liu Carlyle Compressor Division Carrier Corporation 6500 Chrysler Drive syracuse, NY 13221 Many researchers have believed and claimed that the application of non-azeotropic refrigerants would increase air conditioning or heat pump cycle efficiency. Some of them have carried out experiments in order to confirm their belief, and especially to provide an approach to air conditioner or heat pump design for improving cycle efficiency by using non-azeotropic refrigerants. However, even though there are some successful claims, the real benefits have not materialized in the air-cooled commercial products. The question is why? Air conditioning and refrigeration machines can be divided into two types. One is watercooled machines and the other is air-cooled machines. The literature and some commercial products have shown that the efficiency of a water-cooled machine is improved by a nonazeotropic refrigerant cycle as compared to a pure or azeotropic refrigerant cycle. However, the results for the air-cooled machines are mixed. A close examination of the claims of success for the air-cooled machines suggests some problems with their results. The most common problem is defining the base line for comparison. Therefore, those claims may not do fair comparisons. The basic question goes back to the fundamental cycle analysis. The water source and indoor air are normally limited and thus it represents a finite heat source or sink. The out-door air is unlimited and it represents an infinite heat source or sink. For an infinite heat source or sink theoretically the temperature of the source or sink does not have to increase or decrease. Practically, the temperature change can be very small. For an infinite heat source or sink, the temperature glide associated with non-azeotropic refrigerants does not represent a benefit but a deterioration of cycle efficiency. Therefore, a non-azeotropic refrigerant provides benefits for water-cooled machine which have a finite heat source or sink. Those benefits would be reduced or even disappear for air-cooled machines due the outdoor air as an infinite heat source or sink. INTRODUCTION The concept of using a non-azeotropic refrigerant mixture can be traced back to the U.S. patent issued to Ashley et al. (I 949). The patent claimed that a refrigerant mixture with temperature glide would offer a process that "involves no irreversible loss of thermal head since the vapor and the corresponding liquid phase are at each point in contact. There is a progressive interchange of the two components between the vapor and liquid phase which proceeds apace with the condensing action to maintain the vapor and liquid in equilibrium." After the patent, many researchers have tried to prove the claim of energy efficiency associated with nonazeotropic refrigerant mixtures and practitioners have tried to put it in work.