Coulombic force contribution to nano scale aerosol capture by a wire grid: Quantitative comparison of experiments and simulations

Abstract

Fibers of filter media and aerosol particles both typically have some distributions of electric charge. Attractive coulombic interactions between charged particles and fibers enhance aerosol filtration efficiency; however, these coulombic interactions are difficult to characterize due to the complex, nonuniform fiber charge, diameter and spacing of typical filter media. We develop an experimental filter assembly to control these coulombic interactions. The filter assembly consists of three sequential electrically isolated metallic grids—high voltage is applied to the middle grid and the adjacent outer grids are electrically grounded such that the electric potential distribution in the filter assembly is well-defined. We test this filter assembly with aerosols of controlled diameter (ranging between ∼70 and 500 nm) and electric charge (1e−), and systematically increase the applied voltage to the middle grid to enhance coulombic interactions and consequently the filter efficiency. We develop particle trajectory simulations to model our experimental filter assembly such that all parameters in the simulation have direct basis from the experimental system. We find excellent quantitative agreement between the filter efficiency measured in experiments and predicted from simulations without any fitting parameters. The precise control and accurate simulation of coulombic interactions demonstrated in this study indicate that the experimental and simulation methodologies developed here may be applied to uncover fundamental insights into the role of coulombic forces in more complex phenomena such as filter clogging.