The replacement of CFCS in refrigeration equipment by environmentally benign alternatives

Abstract

The replacement of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) is of prime importance since these refrigerants make up the vast majority of the working fluids used by the refrigeration industry and suitable alternatives must be found. A number of suitable pure fluids were considered to establish their properties and, in the case of flammable fluids, a risk analysis was carried out in order to assess their safety. The properties of their mixtures were calculated and suitable equations and p-h charts presented. Compressor lubricants have had to be changed since the majority of the CFC and HCFC replacements are hydrofluorocarbons (HFCs). Typically, HFCs are immiscible in the traditional mineral oils and thus a new generation of synthetic oils (usually polyol ester based) have been produced. The properties of these oils have been investigated and various models, including a modified Flory-Huggins equation, have been used to describe their solubility in refrigerants. The effects of refrigerant/oil solubility of the pure refrigerants and their mixtures on system performance have also been analysed and, in the case of refrigerant mixtures, there is a possibility of a composition change due to the differential solubility which influences performance. Finally, compact plate heat exchangers were found to be excellent heat exchangers for the refrigeration industry, provided that it is remembered that there are control and capacity variation limitations associated with their use. The falling film evaporator is studied in detail and there is a possibility that it will fulfill its potential. Compressors tested with alternative refrigerants have shown (in the case of R407c, a replacement for R22) a deterioration in performance with decreasing evaporator temperature when compared to that of R22, while some of the flammable refrigerants may require larger compressors than the CFC and HCFC counterparts, due to their smaller mass flow rates.