A study of the dynamics of unsteady-state evaporation of pure liquids into chemically inert gases revealed regions of two different evaporation modes controlled by either diffusion or convection. If the molecular weight M_A of the evaporating component is higher than the molecular weight M_B of the chemically inert gas, then the mass transfer is controlled by diffusion and described by expressions (1) and (2) (see below). If the molecular weight of the evaporating liquid is lower than that of the inert gas (M_A < M_B), the density of the forming vapor is lower than the inert gas density. According to Archimedes' principle, the lighter vapor rises up and the heavier inert gas moves down. The rate of pressure equalization in the cell, which is determined by the elastic properties of the medium, considerably exceeds the convective transfer rate; therefore, the pressure in the cell can be assumed to be constant.
展开▼
