Abstract
This paper is an introduction to the cycle proposed by the authors related to research directions concerning the problems of condensation of zeotropic refrigerant mixtures. For over a hundred years, research has been conducted on the search for new working fluids in the cycles for cooling devices and heat pumps. Initially, the natural refrigerants used were replaced with homogeneous synthetic refrigerants, followed by mixtures of two or more refrigerants. Among the mixtures, there are azeotropic and zeotropic mixtures. In the case of an azeotrope mixture, a liquid solution of two or more chemical compounds is in thermodynamic equilibrium with the saturated vapor resulting from this mixture. The chemical composition of the liquid and vapor is identical. A zeotropic mixture is a liquid-vapor system in which the composition of a liquid mixture (solution) of two or more chemical compounds is always different from that of the saturated vapor generated from this liquid. This is due to the different boiling and condensation temperatures of the individual components of the mixture at the same pressure. There is a so-called temperature glide. The phase transformations of individual components do not run simultaneously, which means that the boiling or condensation phase transition temperature changes during the process being carried out. This raises a number of computational, design, and operational problems for power equipment. Today, however, zeotropic mixtures find an alternative to refrigerants with a high GWP potential. Despite the disadvantage of temperature glide, they also have advantages. These include ecological, energy, and economic indicators. As a result, they are increasingly used in the energy economy. This prompts researchers to conduct further research in the field of a detailed description of the phenomenon of boiling and condensation phase transformations of zeotropic mixtures under temperature glide, searching for new computational relationships, new design solutions, and applications. It is still an insufficiently recognized research problem. Bearing the above in mind, the authors made an attempt to review the state of knowledge in this area. Particular attention was paid to the progress in modeling the condensation phenomenon of zeotropic mixtures for application in compact heat exchangers. Miniaturization of cooling devices creates great application possibilities in this area.