Comparison of growth of laminar flows in capillary: Poiseuille flow, electroosmotic flow and electroosmotic circulation

Growth of electroosmotic circulation (EOC) of a liquid in a closed capillary, which is generated after the application of an electric field between the two electrodes which cover the ends of the silica capillary, is examined numerically. The applied electric field accelerates the excess cations in the electric double layer on the inner surface of the capillary. The occurrence of collisions between the accelerated cations and the neutral molecules induces electroosmotic flow (EOF). A forward flow, caused by the EOF, initiates the EOC. The EOC generates a uniform cross-sectional force to create a return flow for conserving zero total flux, and approaches a steady parabolic flow profile, which is similar to the flow profile of the Poiseuille flow. Flow spectra reveal that the forward and return flows enhance each other under zero total flux and accelerate the growth of the EOC, which is more rapid than that of the EOF and the Poiseuille flow.