Simulation of aerosol filters at intermediate Knudsen numbers

Gas flow and the deposition of submicron particles on a model filter (in a system of fibers perpendicular to the flow) were studied at low Reynolds nu mbers and intermediate Knudsen (Kn) numbers, The cell model and the BGK mod el of the kinetic theory of gases were employed to determine the flow field . The instantaneous picture of the gas velocity and density distributions d uring the movement of a fiber placed into the cell center is assumed to be stationary; the surfaces of cell and fiber are considered to be impenetrabl e for gas molecules. The Maxwell boundary conditions on a fiber and the Kuw abara conditions at the cell boundary are employed. The fields of gas veloc ity and pressure are determined from the solution of the kinetic equation f or the distribution function of gas molecule velocities. It was shown that the dependence of the reciprocal dimensionless force acting upon a unit fib er length on the Knudsen number is approximated by a line coinciding with t he extrapolation solution for a viscous regime with slip (Kn much less than 1). The dependence obtained corresponds to the experimental data for model fibrous filters at Kn similar to 1. Accounting for the incomplete accommod ation of molecules does not affect the linear pattern of this dependence. I t was also demonstrated that accounting for the profile of gas flow velocit y in the Knudsen layer results in a noticeable decrease in the collection e fficiency of single fibers under the diffusion mechanism of deposition as c ompared to the efficiency calculated by the known formulas for the regime o f viscous flow including the gas slip and slightly affects the efficiency d ue to interception.