The effects of interfacial convection were quantitatively investigated at high Rayleigh numbers （5×10⁷ < Ra < 1.5×10¹¹）, when a solute was transferred through membrane. A theoretical model for mass transfer was suggested on the basis of the flow patterns which had been observed by shadowgraph. It was assumed that turbulent mass transfer in the present system was controlled by two mechanisms:(1) steady state molecular diffusion in a thin layer and (2) unsteady convection of buoyant elements in its adjacent layer. The generation periods of buoyant eddies were correlated by the Rayleigh number. By relating these results with the model, a correlation for the Sherwood number was obtained as a function of the Rayleigh number, the thickness of a whole fluid layer and the thickness of a diffusion layer. The thickness of a diffusion layer was found to be almost constant. The present experimental results were well represented by the following correlation.
Sh=0.29Ra^0.25-0.0671（δ_s/L） Ra^0.51-exp[3.86(L/δ_s)Ra^-0.25]² erfc[3.86(L/δ_s)Ra^-0.25]