New Type Lubricant for Ammonia Refrigerating Systems

New lubricant which can dissolve with ammonia refrigerant was developed. PAG based oil was found to be dissolved with ammonia and to have fine stability. It contributes to realize maintenancefree refrigerating system because oil returning are possible. It also helps to reduce refrigerant amount because of improvement of thermal conductivity. Ammonia refrigerant will be focused more as an alternative for HCFCs. INTRODUCTION Ammonia is known as high efficient refrigerant,' and now, it is focused again because of its environmental safety properties, ODP-free and GWP-free. But, ammonia has several unfavorable properties, such as smell, toxicity, flammability, corrosivity, and so on. The most unfavorable property on the view of operating ammonia refrigeration systems is immiscibility with mineral oil. Immiscible oil has possibility to be left inside a evaporator and reduces the efficiency. Once oil is discharged with refrigerant, It could hardly return to a compressor, then the compressor with few oil will result in failure. To prevent these troubles, refrigeration equipment needs an oil separator, interval oil removal from the evaporator inside and oil replenishment into the compressor. For the spread of wide applications including alternation of HCFCs with ammonia refrigerant, it is indispensable to realize a compact, maintenance-free and direct evaporation system. And development of new oil which has miscibility with ammonia refrigerant will realize a such new easy-operation refrigerating system with environmental-friendly refrigerant. INVESTIGATION OF MISCIBLE LUBRICANT Search for Miscible Base Oil The first step to develop new miscible refrigerating oil was finding out miscible base oil. In this investigation, It was very useful that know-hows which were found out in the investigation to develop new refrigerating oil for HFC refrigerants. HFCs also do not dissolve with mineral oil. This phenomenon