Computational study of 3D rarefied gas flow in microchannel with 90 bend

The pressure driven compressible gas flow through three-dimensional microchannel with 90° bend is numerically investigated using compressible viscous Navier–Stokes equations coupled with the first-order slip and Smoluchowski temperature jump boundary conditions. The results are compared to those from equivalent straight channel geometry in terms of mass flow rate and Poiseuille number. The competition between geometry, rarefaction and compressibility effects is discussed. The effect of slip boundary condition by comparison with no-slip results is estimated. The flow structure shows that 90° bend has in general a local effect and global performances are quite similar to those of a straight channel, allowing a certain freedom in the design of microdevices. However, it is found that the inclusion of a bend in a micro-channel produces a mass flow rate enhancement. Moreover, the pressure in bend is independent on an aspect ratio and behaves somewhat similar to two-dimensional microchannels, even for the square cross section. The velocity profile near the centerline is relatively similar along the width and depth for an aspect ratio of more than four, suggesting that the bent microduct can be modeled as a two-dimensional one, although, the velocity component along the depth is never identically zero, implying that the flow is not truly two dimensional.