Investigation of the Mass Transfer through Turbulent Boundary Layers in Liquid‐Liquid Emulsions

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Abstract
Mass transfer through turbulent hydrodynamic boundary layers of liquid‐liquid emulsions (i.e. mass transport conditions for two phase electrolysis) has been investigated by measuring diffusion limited currents in quadratic tubes with large electrodes as well as with micro‐electrodes inserted into the macro electrode. As model systems 30 vol. % emulsions of CCl4 (p = 1.6 g/cm3) and n‐hexene (p = 0.6 g/cm3) with well defined drop diameters were used. The probe system was Fe(CN)3–4‐6 dissolved in the aqueous phase. Weakly enhanced (20–30%) mass transfer—as compared with one phase flow of identical streaming velocity—was observed in the CCl4 emulsion whereas for the emulsion of the n‐hexane which possesses a remarkably lower density than the aqueous phase the same mass transfer coefficients were measured as for one phase (aqueous) flow.—The micro‐electrode measurements showed that with CCl4 the quasi‐stationary laminar sublayer is compressed somewhat but is stabilized additionally. Under the applied conditions neither droplets of a lighter phase (n‐hexane) nor of a denser phase (CCl4) are able to penetrate down to the wall. Thus in the boundary layer some sort of demixing of the emulsions is observed which is shown to be due to friction damping of the droplet movement or differences in momentum of the supporting aqueous and the dispersed organic phase resp.