Beyond Navier-Stokes: hydrodynamic models for rarefaction phenomena in micro scale gas flows

Gas microsystems present a unique engineering challenge in that, even when operating at atmospheric pressures, they display important physical phenomena attributable to rarefaction of the flow. The physical effects of gas rarefaction can be particularly significant close to solid surfaces, and so they have important implications for system performance at the microscale in that they can directly affect quantities of interest, such as drag force and mass flowrate (Gad-el-Hak, 1999). Numerical simulations of such flows, therefore, need to be able to capture observed non-equilibrium characteristics