Effects of Liquid Slip and Wall Sliding on Transport Phenomena in Microchannels

The objective of the present study is to explore the influences of the slippage phenomena at solid-liquid interface on the hydrodynamic and heat transfer characteristics in a microchannel flow with the presence of electrokinetic (Ek) effects. With the decrease in the scale of the microchannel liquid flow, the Ek effects become significant and cannot be ignored. Whereas the slippage of aqueous flow due to Ek effect at the solid-fluid interface becomes increasingly remarkable as the channel scale reduced. Besides this electrokinetic slip (Ek-slip) mentioned above, in some applications, microfluidic systems consist of hydrophobic solid surfaces, on which hydrodynamic slippage (Hydro-slip) may occur. Both the Ek-slip and the Hydro-slip are influential to the flow field. As one of the solid boundaries is sliding, e.g. in application of hydrodynamic lubrication, the situation becomes more complicated due to the presence of the complicated electrohydrodynamic interactions stemmed from the motion of the ions in the Stern layer and, in turn, the resultant changes in streaming current and streaming potential. In the present study, the slippage effects are first studied theoretically with a simplified constant-property Ek flow model. In the analysis, flow channel of the order of magnitude of 10μm with significant effects of electric double layer (EDL) are considered. Furthermore, with consideration of non-isothermal flow, a numerical analysis is developed for the Ek flow with temperature gradient, variable electric conductivity, fluid viscosity and permittivity of the liquid. Effects of fluid slippage at the solid-liquid interface on the transport phenomena are investigated. The results are valuable to the microfluidic applications with the interfacial phenomena dominated, especially to the systems with requirement of precisely controlled micro/nano flowrate.