Non-Equilibrium Phenomena near Vapor-Liquid Interfaces

Development of continuum mechanics (fluid dynamics) methods in last century has provided progress of transfer phenomena description and calculation in bulk of solid, liquid and gas (vapor). However, it is well known that for successful solution of fluid dynamics equations corresponding initial and boundary conditions should be formulated. These conditions should be prescribed for all fluid dynamics values.

One way to develop accurate boundary conditions is the application of molecular-kinetic theory to creation of these conditions. From point of this theory view intensity of evaporation and condensation processes (mass flux density j) can be defined. Brief history of study development about mass flux density j determination at evaporation and condensation of pure vapor is following.

It is well known that intensity of transfer processes at evaporation and condensation depends strongly on the presence of a non-condensable gas in vapor–gas mixture. This effect is confirmed by different calculations [1, 2] and experimental researches data [3, 4]. The presence even small gas quantity in the chamber strongly decreases the intensity of evaporation and condensation.

There are many researches that concentrated on the evaporation and dynamics of liquid—vapour interface during boiling. Among them as experimental results and as theoretical model with numerical simulation are presented. For example the transient film boiling in the vicinity of a stagnation point on the frontal surface of a very hot blunt body which moves with a constant velocity in an incompressible viscous fluid in the presence of a vapour layer near the body surface is studied in [1]. Within the unsteady two-phase boundary layer approximation, the equations of motion of the liquid and vapour phases are formulated with taking into account the conservation of mass, momentum, and energy on the a priori unknown phase interface. In the vicinity of the stagnation point on the body surface, the solution of the boundary layer equations is sought. At this a parabolic system of partial differential equations is obtained, which is solved numerically. The similarity parameters controlling the film boiling process are determined. On the basis of parametric numerical calculations, the dynamics of the vapour layer are investigated for the case of a plane hot body moving in water with the room pressure and temperature. In the space of governing parameters, the limits of the existence of steady and unsteady film boiling regimes are found.

This problem was investigated by Kryukov A. P. and Puzina Yu. Yu in [1, 2].

At study of heat and mass transfer problems on penetrable interface surfaces the corresponding non-equilibrium parameters should be calculated. If the order of these parameters values is one and more then influence of non-equilibrium effects should be taken into account at problems solutions. Quantitative values of this influence depend on the problem type. Among them can be the following parameters.