Aerosol Filtration -- Agglomerate Particle Filtration and Particle Deposition Uniformity.

摘要

Particle control technologies are essential in many manufacturing industries (electronic and chemical industrial, mineral processing, and food and beverages) as well as in pollution abatement and environmental control (for example, post processing of power plant emissions and clean rooms). A variety of particle control technologies using various mechanisms have been developed. Among these technologies, filtration is known as the most economical for achieving high removal efficiency of fine aerosol particles. In numerous existing studies on the loading process of particle filtration, two assumptions are usually made: (1) particles are spherical or nearly spherical in shape and (2) particles are uniformly deposited on filter medium. However, in practical applications, these two assumptions are not always met. Agglomerate particles with non-spherical shape are ubiquitous in industrial processing and ambient environment, and non-uniform particle depositions are often met. The overall objective of this dissertation is to advance our current knowledge on these two specific areas of aerosol filtration: (1) agglomerate particle filtration and (2) particle deposition uniformity. For the first part, Agglomerate Particle Filtration, a system which is able to generate stable and controllable agglomerate particles was developed. Both branch-like and chain-like agglomerate particles were generated through the system, and their morphologies were characterized using both online and offline methods. Series of filter loading experiments were performed to study the filtration behavior of fibrous filters loaded with agglomerate particles over the entire filter lifetime, including the initial filtration, depth filtration, transition filtration and surface filtration. The filtration and loading of agglomerate particles exhibited different behaviors than those of spherical particles. Different effects, including filter media, fractal dimension of agglomerate particles, and the overall mobility size of agglomerate particles, on the loading behavior were explored. Moreover, for predicting the loading behavior of agglomerate particles, two semi-empirical models were proposed by modifying existing models. Good agreements were found for both of them. For the second part, Particle Deposition Uniformity, particle depositions under two scenarios were investigated. In the first scenario, particle deposition along pleated filter panels was studied using a COMSOL-Matlab based numerical model. The evolutions of particle deposition profile and pressure drop of pleated filter panels during dynamic particle loading process were investigated. The model was validated by experimental loading tests. In the second scenario, particle deposition uniformity on HVAC entrance filter panels installed in an aircraft was studied by a computational fluid dynamics model. The flow fields around entrance filter panels and particle depositions on them were investigated. Factors affecting particle deposition uniformity were identified and explored.