Space-charge effects in nanoparticle processing using the differential mobility analyzer

A sectional method to solve the evolution of polydisperse non-spherical particles undergoing coagulation and coalescence is proposed. Two sets of sectional equations that describe the evolution of particle volume and surface area, respectively, based on one-dimensional aerosol dynamics are simultaneously solved considering the effect of morphological change of aggregate particles. From the correlation between volume and surface area concentration of particles at each volume section, the evolution of the morphology of aggregate particles can be determined. Results obtained by the present method have been compared with those obtained by both a model assuming monodisperse distribution and a more rigorous two-dimensional sectional model in which particle volume and surface area are independent variables. Number concentration, surface area equivalent diameter, primary particle size and number obtained by the present method are in good agreement with those obtained by the twodimensional sectional model without costing very heavy computation load and memory needed for the analysis of two-dimensional aerosol dynamics. The present method also successfully predicts the bi-modal polydisperse size distributions of non-spherical particles and morphological evolutions even in the presence of particle generation due to chemical reactions. Computation time for the present method was approximately 1/1000 of that needed for the two-dimensional sectional model.