Numerical analysis of gas flow in microchannels

The present work studies numerically gas flow in microchannels. The working fluids are nitrogen and helium, and their Knudsen numbers at the channel outlet are 0.055 and 0.165, respectively. The proposed model assumes the fluid is a continuum but employs a slip boundary condition on the channel wall. The results of the present study reveal some interesting features of microchannel flows. First, because of the extraordinarily small dimensions, a large pressure gradient is required to drive the flow. Although the pressure gradient is large, the velocity remains very small in the cases studied owing to the high shear stress at the wall. In the nitrogen flows studied, the maximum u velocity is only 1.16 m/s for a pressure ratio of 2.701. Second, since the Reynolds numbers are small, of the order of 10(-3)-10(-2) for the flows simulated they can be safely assumed to be laminar. Third, gas flow in microchannels is typically classified into one of four flow regions: continuum flow, slip flow, transition flow, and free molecular flow. The present study covers the slip flow. The differences between numerical results and experimental data are within 1.15% for pressure and 3.13% for mass flow rate. This indicates that the proposed model is able to predict microchannel flows operating in the slip flow region.