Computer modeling of electrical enhancement in fibrous filters

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This work is a continuation of our recently published study (Rao and Faghri (1988). Aerosol Sci. Technol. 8:133–156) in which an in-line array of parallel circular cylinders, placed transverse to the flow, was proposed as a model for fibrous filters. In the previous study, the pressure drop and particle collection efficiency due to the mechanisms of interception and Brownian diffusion were theoretically predicted. In this work particle collection due to interception, inertia effects, and electrostatic forces is considered. As in the previous study, the flow within the in-line array is obtained by solving the full Navier-Stokes equations with the assumption of fully developed flow. A control volume differencing scheme is used for this purpose. The enhancement in particle collection is considered for the case when an electric field is applied across the filter. The increase in collection efficiency due to electrostatic effects is modeled using the method of images. Here, the electric field around a fiber is obtained by including the interference effects of the eight closest neighboring fibers. Predictions of particle collection due to interception, inertial impaction, and electrostatic effects have been obtained. Particle collection is studied for the case of charged particles (electrophoresis) and for the case of uncharged, polarized particles (dielectrophoresis). The collection of charged inertialess particles is predicted by defining a streamfunction for the electrophoretic force, in the manner of Henry and Ariman ((1983). Paniculate Sci. Technol. 1:139–154). This stream function is superimposed onto the flow stream function so that the lines of constant value of the resulting total stream function coincide with particle trajectories. In the case of particles with inertia, deposition is studied by numerically integrating the particle equations of motion, to obtain individual particle trajectories. The results for the single fiber efficiency have been compared with the data from previous studies, whenever possible. It is shown that electrostatic effects can lead to great increases in particle collection, especially for the case of particles with low inertia. © 1990 Elsevier Science Publishing Co., Inc.

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Aerosol Science and Technology