On Thermodynamics of Evaporation Processes in Nonequilibrium Systems

Thermodynamic theory of phase equilibrium is the main base for the development of the methods of fluid mixtures separation. Thermodynamic approach has a lot of advantages in the practical application when conditions of separation processes are close to the equilibrium. For nonequilibrium processes these advantages fail and one should use another methods including empirical relationships and models. The nonequilibrium thermodynamic seems to be a good approach but the practical applications meet many difficulties. On the other hand there are a number opportunities to use equilibrium thermodynamic relationships for the treatment of systems or processes that are nonequilibrium as a whole but some parts and stages of them could be considered as equilibrium. For example it could be the case of equilibrium phase transitions in the system with nonequilibrium chemical reaction. In this paper we consider some thermodynamic regularities and singularities of the structure of diagrams of phase transitions in nonequilibrium multicomponent systems vapour – condensed phases. The lack of equilibrium in the evaporation could be caused by a numerous reasons. In a general case the gradients of intensive variables are driving forces for phase processes, and the affinity is the driving force for the chemical reactions in nonequilibrium system. Gradients of the temperature, of the pressure and of the chemical potentials also effect on the rate of the processes in a nonequilibrium system. The topology of diagrams in the case of the absence of vapour–liquid equilibrium was considered in the work [1]. The mass balance in both equilibrium and nonequilibrium evaporation can be described by the Rayleigh equations: