[Calculation of the concentration Rayleigh number for isothermal transport processes across a polymeric membrane by a method for measuring diffusion flux in three component non-electrolytic solutions].

A method of determination critical value of concentration Rayleigh Number ((Rci)lim.) in isothermal membrane transport processes of three component non-electrolyte solutions was worked out. The method based on the derived in the paper equation, which include membrane transport coefficients (hydraulic permeability, reflection and diffusive permeability coefficients), solution parameters (viscosity coefficient, density and diffusion coefficient in solution). In order to experimental verification of these method the transport coefficients of symmetric flat polymeric membrane, parameters of solutions and diffusive flux for glucose solution in 0.2 mole/l aqueous ethanol solution were determined. Experiments were carried out by osmotic-diffusive single-membrane double-cell system. One cell in all experiments was filled with pure water while the other with the examined solutions. The experimental critical value of concentration Rayleigh Number (RCi)lim. = 1799 is comparable with theoretical critical value of thermal Rayleigh Number (TT)lim. = 1707.