Numerical investigation of heterogeneous nucleation of water vapour on PM10 for particulate abatement

A heterogeneous nucleation model with inclusions of the line tension effect, the particle roughness effect, and the surface diffusion mechanism was presented. Effects of the particle roughness and the wetting agent on the heterogeneous nucleation behaviour were examined. The scaled nucleation barrier was analyzed and subsequently implications of the nucleation behaviour in the particulate abatement by vapour condensation were discussed. It was found that the effect of particle roughness on the nucleation behaviour was greatly affected by the line tension. There existed an optimal concentration of wetting agent at which the lowest nucleation barrier and critical saturation ratio could be obtained. The surface diffusion mechanism played an overwhelmingly important role in governing the embryo growth for hydrophilic particles with a diameter D-p > 0.1 mu m and an embryo size smaller than the critical size, otherwise the contribution of direct vapour deposition mechanism could be significant. Based on the scaled nucleation barrier, three distinct nucleation regimes, i.e. athermal heterogeneous nucleation, thermal heterogeneous-dominant nucleation, and homogeneous-dominant nucleation, have been identified. When the contact angle was large, the wetting agent might need to be added to reduce the contact angle so as to reach the athermal heterogeneous and thermal heterogeneous-dominant nucleation regimes, thus achieving efficient particulate abatement at low cost. The prediction results matched reasonably with the experimental data.