Hydrodynamic dispersion in long microchannels under conditions of electroosmotic circulation. I. Non-electrolytes

摘要

This study deals with the description of stationary transport of non-electrolyte molecules or electroneutral particles in straight long channels occurring due to hydrodynamic dispersion under conditions of electroosmotic flow compensated by pressure-driven counterflow (electroosmotic circulation). The electroosmotic flow is assumed to be induced due to electroosmotic slip at the charged channel walls in the presence of a buffer electrolyte with a constant concentration. It is demonstrated that for such systems, the celebrated Taylor-Aris (TA) theory is applicable locally within an inner part of the channel in a wide range of P,clet numbers (Pe). Simple analytical expressions are derived for the flux and concentration profiles inside the channel. Numerical simulations show minor deviations from analytical solutions. The breakdown of TA theory is related to the distortion of transversal concentration profiles within transition regions at the channel ends whose length increases linearly with the Pe number. Taking into account the dependence of the transition regions on Pe number, it is possible to derive simple analytical approximation for the inner concentration gradient in terms of only few parameters, determined numerically. This approximation can be used in future experimental studies.