AC electric fields and particle deposition on a sphere

Abstract

The National Radiological Protection Board's Independent Advisory Group on Non-ionising Radiation considered the possible effects on health of particle deposition in the vicinity of power lines and recommended, inter alia, that further studies were needed to reduce the uncertainties regarding the dependence of deposition on particle size and air flow. Empirical heat transfer data have been used to estimate the effects of thermophoresis on particle deposition on a sphere mimicking the human head. It is shown that these effects become significant for particle diameters >6 nm and skin temperature needs to be considered when modelling the deposition of larger particles. If one assumes that deposition takes place to smooth surfaces under isothermal conditions, the model predicts, in line with the calculations of Fews et al., that exposure to a power line electric field will enhance deposition (relative to that from diffusion) throughout the size range up to 10 mum. However, such models do not represent deposition on the skin because of the neglect of the effects of surface temperature and texture. Previous workers have measured the ratio of deposition with and without electric field exposure. It is suggested that this is a misleading parameter and data should be presented in terms of the collection efficiencies, which are proportional to the actual amount deposited.