Frank Jordan

Dynamics of the aerosol particle photocharging process

In the photocharging process, aerosol particles become electrically charged through interaction with high-energy photons, e.g., ultraviolet (UV) irradiation. Photon adsorption by particles leads to electron emission and, as a result, particles become positively charged. While maximum achievable charges have been described in previous studies of dependency on particle and irradiation parameters, the influence of photoemitted charges on the charging process was not taken into account. In this work it is shown that such charges interact with the particles, which heavily influences the entire process. This complex process (the charging of particles positively by photons and simultaneously negatively by ions) is described in this work by a set of differential equations. These differential equations are solved numerically and, with simplifying assumptions, analytically. Multicomponent polydisperse aerosol is considered. As was found by comparing the analytical and numerical solutions, analytical results coincid...

On the effect of charge recombination on the aerosol charge distribution in photocharging systems

Abstract An experimental study has been carried out to determine the aerosol charge distribution through photocharging process. Particle charge distribution was studied in dependency on particle number concentration and irradiation intensity. While highly positively charged aerosols were obtained for particle number concentrations below 5×10 11 m −3 , approximately symmetrical bipolar charge distributions were measured for number concentrations of about 2×10 13 m −3 . The theoretical description was made on basis of the previously developed model, which was extended by a term accounting for ion diffusion losses. Theoretical results reflected experimental observations. The necessity of taking into account diffusion discharging of particles by gas ions is determined by a dimensionless factor depending on initial parameters. Since the charge distribution through photocharging becomes a known function of particle and irradiation parameters, a photocharger may be used instead of a neutralizer to produce a defined charge distribution.

A Study of Nanoparticle Aerosol Charging by Monte Carlo Simulations

A Direct Simulation Monte Carlo (DSMC) technique is applied for describing the dynamics of aerosol charging. The method is based on the transformation of known combination coefficients into charging probabilities. Changes in the particle charge distribution are computed as a stochastic game, calculating the time-step after each event. The simulations are validated by comparison with analytical solutions for unipolar aerosol diffusion charging and aerosol photocharging. The advantage of the DSMC method lies in the uncomplicated simulation of multi-dimensional systems that would result in very elaborate population balances. The DSMC method is used for simulation of the photocharging of moderately concentrated bicomponent polydisperse aerosols. By means of this method, the influence of the particle parameters (size, material) on the dynamics of the charge distribution in different size and material fractions has been studied. It is shown that charge separation between size or material fractions can be achieved for aerosol components with dissimilar work functions, while the total aerosol charge is zero.