Microfilter Simulations and Scaling Laws

A series of direct simulation Monte Carlo calculations of flows through microfilters were performed to evaluate the range of validity of a previously derived scaling law. This scaling law, which describes how the pressure drop across a filter depends on the Reynolds number and filter geometry, is based on Navier-Stokes calculations and experiments in the continuum regime. The simulations show that this scaling law predicts the correct Reynolds number dependence for a fixed Knudsen number, but the magnitude of the pressure drop is overpredicted as effects due to collisional nonequilibrium become important. The results of the simulations were used to derive a correction term to the scaling law that includes the Knudsen number and, thus, accounts for nonequilibrium effects.