In this paper, the effects of microchannel aspect ratio on laminar friction factors are investigated for compressible gas flow. The compressible Nitrogen flow in a long microchannel was simulated numerically with a three-dimensional continuum model. The governing equations of the model were solved using a control volume method. The calculated mass flow rate and pressure distribution were compared with known analytical solution for a two-dimensional microchannel flow and experimental data. As the slip affects plays in important role in the friction characteristic of microchannel flows, slip boundary conditions were considered. It was found that a large increase in the normalized laminar friction constant was evident at both low and high aspect ratios, while the square microchannel had the minimum friction constant. Normalized friction constant was not only a function of aspect ratio but also of Knudsen number and compressibility (pressure ratio).
