In the experiments conducted at Purdue, the air flow in rectangular cross-section microchannels was investigated using the pressure sensitive paints. The high resolution pressure measurements were obtained for inlet-to-outlet pressure ratios from 1.76 to 20 with the outlet Knudsen numbers in the range from 0.002 to 0.06 based on hydraulic diameter of 157.9 micron and the length-to-height ratio of about 50. In the slip flow regime, air flow was simulated by the 2D and 3D Navier-Stokes equations with no-slip and slip boundary conditions. For various pressure ratios, the entrance flow development, compressibility and rarefaction effects were observed in both experiments and numerical simulations. It was found that accurate modeling of gas flows infinite-length channels requires that inlet and outlet reservoirs to be included in computations. Effects of entrance geometry on the friction factor were studied for 3D cases. In both experiments and numerical modelings, significant pressure drop was found starting at the inlet chamber. The numerical modeling also predicted an apparent temperature drop especially at the channel exit.

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