Three-dimensional laminar and turbulent water flows in smooth and rough micro channels with rectangular cross-section were numerically simulated. The hydraulic diameter of the smooth micro channel is 190 μm and 191 μm for the rough one. The roughness inducing surfaces, which were modelled by three rectangular elements placed on the sidewall of the micro channel, are 50 μm high and 50 μm wide. The simulations were conducted for Reynolds numbers between 100 and 4000. The effects on the friction factor and flow characteristics due to the roughness elements, varying Reynolds numbers and low-Reynolds number turbulence models were investigated and compared with the experimental values reported by Hao et al. [1]. Furthermore, the velocity profiles in various Reynolds number and flow regimes have been compared with μPIV measurements. At Reynolds numbers less than 2100 the computed friction factors in the smooth micro channel agree well with the measurements and the values of the conventional theory. For the micro channel with roughness elements, the friction factor approaches the value of measurements and conventional theory, when Re < 900. Transition from laminar to turbulent flow occurs at about Reynolds numbers of 2100 and 900 in smooth and rough micro channel, respectively. Comparison of simulated results using the Spalart-Allmaras and SST K-ω turbulence models with experimental values show good agreement. By contrast, the K-ε model overestimates the pressure loss in micro channels.

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