Sectional Modeling of Aerosol Dynamics in Multi-Dimensional Flows

Abstract

The integration of computational fluid dynamics (CFD) with computer modeling of aerosol dynamics is needed in several practical applications. The use of a sectional size distribution is desirable because it offers generality and flexibility in describing the evolution of the aerosol. However, in the presence of condensational growth the sectional method is computationally expensive in multidimensional flows, because a large number of size sections is required to cope with numerical diffusion and achieve accuracy in the delicate coupling between the competing processes of nucleation and condensation. The present work proposes a methodology that enables the implementation of the sectional method in Eulerian multidimensional CFD calculations. For the solution of condensational growth a number conservative numerical scheme is proposed. The scheme is based on a combination of moving and fixed particle size grids and a re-mapping process for the cumulative size distribution, carried out with cubic spline interpolation. The coupling of the aerosol dynamics with the multidimensional CFD calculations is performed with an operator splitting technique, permitting to deal efficiently with the largely different time scales of the aerosol dynamics and transport processes. The developed methodology is validated against available analytical solutions of the general dynamic equation. The appropriateness of the methodology is evaluated by reproducing the numerically demanding case of nucleation-condensation in an experimental aerosol reactor. The method is found free of numerical diffusion and robust. Good accuracy is obtained with a modest number of size sections, whereas the computational time on a common personal computer remained always reasonable.