Predicting the Onset of Aggregation of Aerosol ParticlesEPA Grant Number: U915237
Title: Predicting the Onset of Aggregation of Aerosol Particles
Investigators: Garabedian, Randy S.
Institution: University of Connecticut
EPA Project Officer: Lee, Sonja
Project Period: January 1, 1997 through January 1, 1999
Project Amount: $68,000
RFA: STAR Graduate Fellowships (1997) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Engineering and Environmental Chemistry , Fellowship - Chemical Engineering
The objective of this research project is to develop a model that predicts the onset of aggregation of submicron inorganic air pollutant aerosols formed by combustion processes.
Combustion-derived aerosol particles are typically amorphous, and therefore coalesce by viscous flow due to unbalanced stresses at the particle surface. Existing models for the complete coalescence of two particles require the use of finite-element methods to solve the Navier-Stokes equations, and they are computationally intensive. The computational requirements of the finite-element method inhibit its incorporation into aerosol models. To overcome this difficulty, a computationally efficient model for predicting the complete coalescence of two particles has been developed. The basis for the model is an analytical function, verified by experimental studies of viscous coalescence reported in literature, that closely describes the surface of the coalescing particles. The time dependence of the surface evolution is determined by approximately solving the boundary integral equations for the unknown surface velocities. This results in a computationally efficient model that can be incorporated into aerosol models. The coalescence model developed here compares favorably to the results of the more rigorous and computationally demanding finite -element method. The two-particle coalescence model will serve as a basis for the modeling of multiple particle coalescence within aggregates.
To predict the onset of aggregation of aerosol pollutants, the coalescence model was incorporated into an aerosol model that predicts the rate of particle collisions. The aerosol model is derived by modifying the coagulation kernels to include the effects of particle coalescence on the overall coagulation process. Consequently, the conditions under which the time for particle coalescence becomes comparable to the time for particle collisions can be determined. From this, the particle size and concentration corresponding to the onset of aggregation of aerosol pollutants can be determined from the initial mass loading of ash and combustion conditions.