Trends in Refrigeration Lubricants for Natural Refrigerants and Their Applications

摘要

Concern over depletion of the ozone layer and global warming are two environmental problems that have been heightened because of refrigerants used in air conditioners and refrigerators, among other uses. Refrigerants are a necessary and indispensable substance used to efficiently convert electrical and mechanical energy into thermal energy. Around the time mankind began to use refrigerants for the purpose of using evaporative latent heat, carbon dioxide and ammonia that existed in the natural world were used as refrigerants. After that, due to the progress of chemistry, chlorofluorocarbon (CFC) was developed around the middle of the twentieth century and was widely used in place of carbon dioxide and ammonia because of cooling efficiency and safety concerns. However, as Professor F.S. Rowland of the U.S. pointed out in 1974, the possibility of a problem for mankind and the ecosystem with ozone layer depletion when chemically stable CFCs have been discharged into the air [1], concern for environmental problems on a global scale heightened. On the other hand, except for the movement of ozone layer depletion, at the end of the nineteenth century Arrhenius was already pointing out the consequences of carbon dioxide and global warming [2]. From the second half of the 1970s, 100 years after that, global warming on a world scale began to be discussed. Particularly, in 1992 the Framework Convention on Climate Change was adopted and the principle that "the advanced countries that entered into the treaty will take the initiative and deal with climate change and the harmful effects thereof was provided for. The Kyoto Protocol prescribing specific numerical standards of the various advanced countries that are legally binding was adopted [3] at the "Conference of the Parties to the United Nations Framework Convention on Climate Change" held in Kyoto in 1997. For Japan, a 6% decrease compared to the carbon dioxide discharge amount of 1990 was decided on, and it was decided that a decrease close to 8% in the actual performance of 2002 was necessary. In this kind of situation, although refrigerants are not directly related to carbon dioxide emissions, hydrofluorocarbon (HFC) that is used as a substitute for CFC refrigerant is regarded as a greenhouse effect gas target gas. Consequently, decreasing and converting refrigerants are regardedas inevitable because of both the global environmental problem due to ozone layer depletion and global warming due to the greenhouse effect. In this article we briefly discuss natural refrigerants that are subsitutes for HFC refrigerants pursuant to the prevention of global warming of recent years and comment on the various refrigerating machine oils for natural refrigerant use.