OPTIMUM SELECTION OF REFRIGERANTS UNDER ENVIRONMENTAL CONSTRAINTS

摘要

In any thermal energy conversion systems such as refrigeration, air-conditioning and heat pumping systems, it is needless to emphasize that the optimum selection of working fluids is one of the most essential issues so as to achieve the designed performance of the specified system. The criteria for the optimum selection of working fluids for heat pump, or refrigerants in general for air-conditioning and refrigeration system, were used to be well-defined and comprehensive, but they have been forced to be modified significantly in the 1980s simply due to an increasing concern about global environmental issues. The stratospheric ozone depletion crisis followed by the current global warming (or more precisely, climate change) issue has definitely impacted the air-conditioning and refrigeration industry worldwide like no other event in history. In the present paper, the author attempts to provide an overview on the development of refrigerants over the last several decades in the light of various aspects recognized at each period in the past. The discussion will then cover the current state of the arts to select the optimum refrigerants among proposed candidates including HFC (hydrofluorocarbon) refrigerant mixtures and so-called natural working fluids. An emphasis, however, will be given to the current best knowledge on the thermophysical properties of proposed refrigerants and their blended mixtures of vital importance, since the present author has been involved in this field of science and engineering rather extensively for the last three decades. Concerning the future perspectives, some of the existing challenges in progress will also be covered to lead the concluding remarks.