Evolution Dynamics of Fractal Aggregates in Continuously Stirred Tank Aerosol Reactors using Generalized Condensation Exponents

Understanding the evolution of aerosol metrics in Continuously Stirred Aerosol Reactors (CSTAR) is of considerable importance for the generation and synthesis of aerosol particles with controlled size and morphological properties. Generally, the dynamic equations governing the depletion of precursor monomer species as well as the evolution of aerosol metrics are solved by method of moments. These provide a simpler, alternative system of ordinary differential equations in place of the complicated integro-partial differential system of general dynamics equation for the entire size distribution function. A fundamental question pertains to the existence of closure of the moment equations, consistent with aerosol processes. In this article, we derive constraints on the values of condensation exponent in the pre-coagulation regime of CSTAR, which lead to a system of closed moment equations. The relevant condensation processes on fractal aggregates corresponding to some of these exponents are also identified. Stability analysis for these systems is carried out by formulating and solving their characteristic equations. The solutions are examined by numerically integrating the moment equations, which show interesting non-monotonic behavior with respect to ventilation rate (reciprocal of residence time). The study not only highlights the general features of the aerosol evolution equation, but also demonstrates its usefulness for optimizing the yield of particles across a range of growth exponents. Copyright (c) 2020 American Association for Aerosol Research