Film Mass Transfer Coefficient Expressions for Electroosmotic Flows

Expressions are developed and presented that could be used to determine the film mass transfer coefficient of a solute in electroosmotic flows. In contrast to pressure-driven flows at low Reynolds numbers where the film mass transfer coefficient is independent of the linear characteristic dimension of the channel for flow, in electroosmotically driven flows at low Reynolds numbers the film mass transfer coefficient is shown to be a function of the ratio R/lambda, where R is the channel radius and lambda is the Debye length. This result implies that for electroosmotically driven flows in a packed bed or porous monolith with channels for flow having similar geometry but different sizes, the film mass transfer coefficient would vary with the size of the interstitial channels for bulk flow while in pressure-driven flows the film mass transfer coefficient would be the same for all interstitial channels. From the expressions presented in this work, one can show that for the same volumetric flow rate the film mass transfer coefficient of electroosmotically driven flows is proportional to that for pressure-driven flows. Copyright 2000 Academic Press.