Three dimensional numerical simulations of the laminar fluid flow and heat transfer of water in silicon microchannels with non-circular cross-sections were performed. Two kinds of non-circular microchannel were investigated: trapezoidal and triangular. The continuum medium assumption was adopted and the corresponding governing equations and boundary conditions were used. The finite volume method was used to discretize the differential equations. The QUICK scheme was used for the discretization of convective term and the CLEAR algorithm was adopted to deal with the coupling between velocity and pressure. The water thermal physical properties were assumed to be constants except the viscosity. For both microchannels the grid system of 82 × 42 × 142 was used. Numerical results were compared with experimental data available in the literature, and good agreements were achieved. The effects of the geometric parameters of the microchannels were investigated, and the variations of Nusselt number with Reynolds number were discussed from the field synergy principle. The simulation results reveal the effects of the geometric parameters of the microchannels, and indicate that when the Reynolds numbers are less than 100, the synergy between velocity and temperature gradient is much better than the case with Reynolds number larger than 100. There is an abrupt change in the intersection angle between velocity and temperature gradient around Re = 100. In the low Reynolds number region the Nusselt number is almost proportional to the Reynolds number, while in the high Reynolds number region, the increase trend of Nusselt number with Reynolds number is much more mildly, which showed the applicability of the field synergy principle. In addition, the fully developed Nusselt number for the microchannels simulated increases with the increasing of on Reynolds number, rather than a constant. The present study shows that for liquid such as water the heat transfer and fluid flow in microchannels with geometric dimension in the order of 10–100 micrometer without the effect of external electro-field, the continuum assumption is still valid and numerical simulation can be conducted with conventional model and approach.

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