A three-dimensional numerical simulation of flow through serpentine microchannels with designed roughness in form of obstructions placed along the channels walls is conducted here. CFD-ACE+ is used for the numerical simulations. The effect of the roughness height (surface roughness), geometry, Reynolds number on the friction factor is investigated. It is found that the friction factor increases in a nonlinear fashion with the increase in obstruction height. The friction factor is more for rectangular and triangular obstructions and it decreases as the obstruction geometry is changed to trapezoidal. It is observed that the obstruction geometry, i.e., aspect ratio plays an important role in prediction of friction factor in rough channels. It is also found that the pressure drop decreases with the increase in the roughness pitch. Hence, the roughness pitch is an important design parameter for microchannels.

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Numerical simulation of flow through a threedimensional serpentine microchannel, subjected to a voltage perpendicular to the flow direction is presented here. Commercial CFD software CFD-ACE+ is used for the numerical analysis. A parametric study is conducted to investigate the effect of radius of curvature, Reynolds number, zeta potential and Debye length on the pressure drop and friction factor. Each case is compared with flow without electroosmotic effect. It is found that electroosmosis induces secondary flow patterns in the straight portion of the channel in addition to secondary vortices at bends. This electroosmosis-induced secondary flow causes additional pressure drop as compared to flow without electroosmosis. For flow with and without electroosmosis, the pressure drop increases with Reynolds number and the nature of variation is qualitatively similar in both the cases. It is also found that the pressure drop increases as the Debye length is reduced.

In this paper, the flow through a serpentine microchannel with obstructions on wall is studied. Various obstruction geometries ranging from rectangular to triangular are considered. For each geometry pressure drop across single obstruction is studied at various Reynolds numbers. Also the effect of obstruction height on the pressure drop is investigated. A parametric study is conducted for different obstruction heights, geometries and Reynolds numbers. NOMENCLATURE µ Viscosity of liquid ρ Density of liquid u Velocity component in x-direction * Corresponding Author v Velocity component in y-direction P Pressure H obs Height of obstruction l 1 Streamwise length of obstruction at top l 2 Streamwise length of obstruction at bottom L 1 Length of longer section of channel L 2 Length of shorter section of channel Re Reynolds number

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