Theoretical Study of Electroosmotic Flow With Replacement Solutions Available to Purchase

Electroosmotic flow with solution displacement in microchannels is often encountered in many lab-on-a-chip devices where washing procedures are designed. In order to investigate the detailed flow structures for a displacement process between two different electrolyte solutions, a three-dimensional numerical model is developed in this paper. KCl solution and LaCl₃ solution are mainly used as sample solutions. A 2cm long straight microchannl with a rectangle cross sectional area (height of 100μm and width of 200 μm) was employed in this study. The governing equations of applied electrical field, flow field and concentration field were numerical solved with SIMPLE algorithm, which are based on a finite control volume scheme. The observed flow structures such as back flow in the center of the channel and distortion of plug-like electroosmotic velocity profile are discussed in detail. It is found that the distortion in flow field is due to the induced pressure gradient, which is resulted from the nonuniformity of electroosmotic mobilities and electrical conductivities of two solutions. Finally, the displacement between DIUF water and LaCl₃ solution is briefly studied.