EVALUATION OF CONCENTRATION EFFECTS IN THE CONCENTRATION BOUNDARY-LAYER OF SOLUTIONS IN VAPORIZATION AND CONDENSATION

Based on the equation of mass transfer in the concentration boundary l ayer forming around vapor bubbles in boiling solutions, an excess conc entration of a nonvolatile substance at the interface, as compared to its concentration in the bulk liquid, is evaluated. A simplified probl em of ''pure'' diffusion in the concentration boundary layer forming a round a flat bubble with a stationary boundary is considered. It is sh own that during a time comparable with the time of bubble growth, the concentration at the surface of the bubble may substantially differ fr om that in the original solution. In the condensation of steam on the film of an aqueous solution of a nonvolatile substance, the vectors of concentration gradient and mass-flux velocity of the solvent in the c oncentration boundary layer reverse their directions.