Transition regime collisions in aerosols

Abstract

In most natural and engineered aerosol systems, particles fall in the "transition regime", intermediate to the free molecular and continuum ranges. Furthermore, while theories for transport properties of spherical particles in the free molecular and continuum ranges have been available for decades, theories that are applicable to particles of arbitrary shape are lacking. This thesis addresses the transport of neutral and charged molecules (ions) as well as coagulation with particles of arbitrary shape and size. Computational and experimental studies are performed to develop and validate models of collisional mass transfer onto aerosol particles. A broad overview of the thesis is presented in Chapter 1. Using dimensional analysis and Brownian Dynamics trajectory calculations, the collisions between spherical and nonspherical particles are analyzed in Chapters 2 & 3. This approach is extended to include the effect of Coulombic potential interactions in Chapter 4, along with a critical assessment of existing theories. Further, the unipolar charging of arbirary shaped aerosol particles is studied in Chapter 5. Different from previous chapters, an approach to directly calculate the steady state charge distribution of particles exposed to arbitrary bipolar ion populations is developed in Chapter 6. Experiments are conducted with spherical and cylindrical particles to better understand momentum transfer (Chapter 7) and bipolar charging (Chapter 8) in the transition regime. Finally, conclusions derived from this research and future directions are discussed in Chapter 9.