Simulations of flow through microchannels over nano particles are widely encountered in solid particle transportation. In these simulations, the rarefaction phenomenon will affect the microflow behavior and subsequently the aerodynamics coefficients such as the drag coefficient derived for the suspended particles in the flow stream. This is why we use the Lattice Boltzmann method LBM to study the flow past a confined cylinder placed in a microchannel. The LBM is a mesoscopic method capable of solving flow in macro and micro scales. Applying the Maxwellian scattering kernel, the slip velocity is modeled on the channel and cylinder walls appropriately. To validate our formulations, we firstly obtain the results for solving flow in a pressure driven microchannel and the macroflow past a square cylinder and compare our results with the other available numerical and analytical solutions. Next, we study the microflow over nano cylinder model describing nano suspended particles. The results show that the drag coefficient of the nano particle reduces in all ranges of blockage ratio due to the rarefaction domination. To appraise the effect of blockage ratio on the rarefaction effect, we define an effective parameter. The study indicates that the drag coefficient reduction due to rarefaction effect is higher for lower blockage ratios.

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