Study Of Pressure-Driven Liquid-Liquid Stratified Microchannel Flow

The interfacial effects are an important issue in microflows. Thorough study on itcan give guide to the research and application of microfluidic devices directly.Boundary slip and Electrical Double Layer (EDL) are two important properties andmainly discussed in this dissertation. In this dissertation, the analytical solution of twoimmiscibel liquid-liquid stratified flow under the combined effect of boundary slipand EDL is established and solved for the first time. The theory of the EDL at theinterface of two immiscible electrolytes (ITIES) is introduced to liquid-liquidstratified flow and the analytical solution is founded, and further, the analyticalsolution of liquid-liquid stratified flow under the combined effects of boundary slipand EDL at both liquid-liquid interface and liquid-solid interface is founded. Finally,the small disturbance method is adopted to study the stability of liquid-liquid stratifiedflow under the effects of boundary slip and EDL at liquid-solid interface inmicrochannels. The main conclusions are as the following:(i) The flow direction of slip velocity at channel walls is determined by the EDLeffect. The slip velocity at channel wall is in the flow direction once the effect of EDLis weak; on the contrary, the slip velocity at channel wall is in the opposite directiononce the effect of EDL is strong. The EDL effect increases with the decrease of thedimensionless electrokinetic separation distance. The back flow will be obvious andthe slip velocity in the opposite direction increases with the increase of EDL effect.The flow velocity under the model of IDM, SDM, and ZDM is related to zetapotential, boundary slip and dimensionless electrokinetic separation distance.(ii) With respect to the liquid-liquid stratified flow, the flow velocity decreaseswith the increase of viscosity ratio. With the increases of viscosity ratio, the EDLeffect at the channel wall in contact with the fluid with lower viscosity is decreasesand the slip velocity direct to the opposite direction decreases. With the holds of thefluids with higher viscosity decreases, the flow velocity increases, the EDL effect atthe channel wall in contact with the fluid with higher viscosity is increases and theslip velocity direct to the flow direction is decreases. With the increases ofconductivity ratio, the flow velocity increases, the EDL effect at channel walldecreases, and the slip velocity slide to flow direction increases. The Zeta potentialhave obvious effect on flow velocity if both boundary slip and EDL at the same sideof the channel wall and have inconspicuous effect if the boundary slip and EDL are not at the same side of the channel wall.(iii) With respect to the liquid-liquid stratified flow considering the EDL atITIES, the EDL at ITIES result in flow velocity distortion at liquid-liquid interface,reduce the flow rate, and increase the electroviscous effect. When the sign of Zetapotential at ITIES is in accordance with that at liquid-solid interface, the EDL atITIES enlarge the EDL effect at liquid-solid interface. When the sign of Zeta potentialat ITIES is opposite to that at liquid-solid interface, the EDL at ITIES weaken theEDL effect at liquid-solid interface and make the back flow near liquid-solid interfacedecreases or vanished. With the increases of dynamic viscosity ratio, the effect of theEDL at ITIES on the EDL effect at liquid-solid interface decreases. The EDL at ITIESenhance the augment effect of the conductivity ratio on the flow velocity. The smallerdistance between liquid-liquid interface and one side of channel wall is, the largereffect of EDL at ITIES on the EDL effect at this side of channel wall is. The effect ofboundary slip on flow velocity influenced by the EDL at ITIES, the potentialdifference at ITIES, the EDL at liquid-solid interface, dynamic viscosity ratio,interface position, and conductivity ratio.(iv) With respect to the liquid-liquid stratified flow, the effect of boundary slipon flow stability affected by the zeta potential, conductivity ratio, dynamic viscosityratio, interface position, and the channel height(dimensionless electrokineticseparation distance). The boundary slip enhances the flow stability once the EDLeffect is weak and weakens the flow stability once the EDL effect is strong.