Modeling of aerosol formation in a turbulent jet with the transported population balance equation-probability density function approach

摘要

Processes involving particle formation in turbulent flows feature complex interactions between turbulence and the various physicochemical processes involved. An example of such a process is aerosol formation in a turbulent jet, a process investigated experimentally by Lesniewski and Friedlander [Proc. R. Soc. London, Ser. A454, 2477 (1998)]. Polydispersed particle formation can be described mathematically by a population balance (also called general dynamic) equation, but its formulation and use within a turbulent flow are riddled with problems, as straightforward averaging results in unknown correlations. In this paper we employ a probability density function formalism in conjunction with the population balance equation (the PBE-PDF method) to simulate and study the experiments of Lesniewski and Friedlander. The approach allows studying the effects of turbulence-particle formation interaction, as well as the prediction of the particle size distribution and the incorporation of kinetics of arbitrary complexity in the population balance equation. It is found that turbulence critically affects the first stages of the process, while it seems to have a secondary effect downstream. While Lesniewski and Friedlander argued that the bulk of the nucleation arises in the initial mixing layer, our results indicate that most of the particles nucleate downstream. The full particle size distributions are obtained via our method and can be compared to the experimental results showing good agreement. The sources of uncertainties in the experiments and the kinetic expressions are analyzed, and the underlying mechanisms that affect the evolution of particle size distribution are discussed.