Improved heat pump processes using new refrigerants

Other conference contribution, 1981

During recent years the use of nonazeotropic refrigerant mixtures has been much discussed as a possibility to improve the COP in various types of heat pumps to small or moderate additional investment costs. Due to the fact that nonazeotropic mixtures have gliding temperatures during the condensation and the evaporation a heat pump using such a mixture can often be thermodynamically more fitted to meet the temperature gradients of the heat sink and the heat source than if a pure refrigerant is used. Earlier research in this field, at least before the seventies, has been emphasized on .refrigeration and air conditioning systems. During recent years, with the growing interest in heat pumps in general, a few experimental investigations concerning the use of nonazeotropic mixtures ~n various types of heat pumps have been carried out. Jakobs (1) gives a good literature survey of both theoretical and experimental work in this field made up to 1980 for all types of refrigeration and heat pump applications. In this paper the thermodynamical consequences of using a mixture instead of a pure refrigerant will be discussed and some experimental results from investigations at Chaimers and by others will be presented and compared with each other. It will in particular be.'pointed out that the thermodynamical gain with a mixture compared to a pure refrigerant is to a high extent depending on how the comparison is made, i.e. on the assumption of constant outer conditions or constant inner ones in the heat pump itself. In the reference list some papers of interest in this contxt are listed.