Electroosmosis and Forced Convection

When a liquid is forced through a microchannel under hydrostatic pressure, the ions in the mobile region of the electrodischarge layer (EDL) are carried toward one end. The motion of the ions in the diffuse mobile layer affects the bulk of the liquid flow via momentum transfer due to viscosity. In macroscale flows, the interfacial electrokinetic effects are negligible since the thickness of EDL is very small compared to the hydraulic diameter of the duct. However, in microscale flow, the EDL thickness is comparable to the hydraulic diameter, and the EDL effects must be considered during the analysis of fluid flow and heat transfer. The EDL effect on the flow depends on the Debye number defined as De = =. When De 1, EDL 

Substituting the above boundary condition in equation (6.160), we get Q = 0. Integrating equation (6.160) again, we get 

Equation (6.163) gives the velocity distribution assuming constant potential inside the Debye layer. Let us derive the velocity profile assuming the Debye-Htickel linear approximation as 

EDL results in a reduced fiow velocity (higher apparent viscosity), thus affecting the temperature distribution and leading to smaller heat transfer rate. 

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