CHARGING-INDUCED DRIFT AND DIFFUSION OF AEROSOL-PARTICLES IN OSCILLATING ELECTRIC-FIELDS

We investigate the recently predicted bipolar charging-induced drift and diffusion phenomena of aerosol particles in rectangular oscillating electric fields. A model system consisting of surface ionization sources is considered. A detailed analysis is made in the continuum regime, but the results are approximately extended to non-continuum regimes. It is found that the induced drift decreases to zero as the oscillation frequency (OMEGA) is increased to a characteristic value, OMEGA(c) = pi(thetabeta/6)1/2, where theta and beta are the relaxation constants for the ion concentration field and the particle charge. For OMEGA > OMEGA(c), a small negative drift persists which vanishes for all OMEGA > 2pitheta. The induced diffusivity, D(c)(OMEGA), also decreases monotonically with OMEGA, attaining much smaller values at OMEGA(c) as compared to static field diffusivities. The reduced values of D(c) can still be rendered orders of magnitude larger than the Brownian diffusivities of particles. The paper discusses the design and operational aspects of the model system, its ideal mass transfer characteristics and a novel application. The phenomena may be more easily observed for small particles (radius < 0.05 mum), at high ion concentrations ( > 10(6) cm-3), at moderate fields (0.5-2 kV cm-1) and allow frequencies (0-500 Hz).