ABSTRACT
The methods of modeling of gas ows in microuidics depend on the regime. In the hydrodynamic limit, when the molecular mean free path is signi‰cantly smaller compared with a characteristic size of gas ow, the continuous medium mechanics [1] is successfully used. If the mean free path is just slightly smaller than the characteristic size, the hydrodynamic solution should be corrected by applying the velocity slip and temperature jump boundary conditions [2-6]. The opposite limit, when the mean free path is signi‰cantly larger than the ow characteristic size, is called the free-molecular regime. Under such a condition, all molecules move independently on each other, and the modeling requires another approach. Anyway, this regime is relatively easy for analytical and numerical calculations (see, e.g., [7,8]). However, the transitional regime, when the mean free path has the same order of magnitude as the characteristic size, represents signi‰cant dif‰culties for numerical and analytical calculations of rare‰ed gas ows. In this regime, the continuous medium mechanics is not valid any more, but the intermolecular collisions cannot be neglected. Then, gas ows are modeled on the molecular level. The ‰eld of uid mechanics dealing with the freemolecular and transitional regimes is called as rare‰ed gas dynamics (RGD).
