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The problem of filtration of liquid aerosols by both wettable and nonwettable filters has been extensively studied and the results of the theoretical calculations together with the experimental results are presented. More realistic models of filtration by both wettable and nonwettable filters have been developed and verified experimentally. A new instrument has been developed, and used in the experiments, for the measurement of the absolute concentration of aerosols in the gas stream. This instrument is based on the measurement of the initial vapour content of the gas stream simultaneously with the measurement of the vapour content after the total evaporation of aerosol. The concentration of the aerosol is calculated as the difference between these two values. The instrument was developed to provide fast and accurate measurements of aerosol concentration. The main advantages of the instrument are: high accuracy, simplicity of measurement, possibility of use for a wide range of substances, perfect suitability of operation for automatic monitoring technologies, etc. All rights for this instrument have been reserved and the fully automatic version will be available in the near future. It was found that the efficiency of filtration of aerosol on the wettable filter depends on the thickness of the liquid film on the fibre. This parameter was taken into account in the development of a theoretical model of filtration on wettable fibrous filters. The particle breakthrough problem has been solved by the optimisation of the aspect ratio (the ratio of the height by width) of the wettable filter. On this basis, industrial devices have been developed, patented, and implemented in industry. These devices provide a stable operating efficiency of higher than 99%. It was found experimentally that the efficiency of filtration of aerosol on the nonwettable filter depends on the diameter of the drop suspended on the filter, and on the area of the filter blocked by drops: this influences the velocity of filtration. All these parameters were taken into account in the development of a theoretical model of filtration on nonwettable fibrous filters. On the basis of this model, satisfactorily verified by the experiments, an industrial device has been developed. The harnessing of atomisers makes it possible to maintain the efficiency of filtration higher than 99%, even with a relatively high velocity of filtration of 2.7m/s. The new technology is tackling the problem of handling huge amounts of exhaust gases and this is particularly important for cramped installations when the space available for the air pollution control technology is quite limited. A highly efficient gas cleaning technology has been developed. This technology is based on combining two stages (wet scrubber and filter) of currently utilised air pollution control devices by submerging the fibrous filter into the liquid on the plate. The new device provides an effective division of the main gas stream into ultra-small bubbles which increase the contact area between the gas and liquid phases. It was estimated theoretically and verified experimentally that the efficiency of the proposed 'combined' technology, is 45% higher than the efficiency of the two stages technology. The technology has been patented and will be offered for industrial implementation in the near future.

This thesis examines the particle capture, fibre wetting and droplet flow processes within wet filters collecting solid and liquid aerosols and within filters collecting only liquid aerosols. The processes involved in this type of filtration were examined through a series of experiments and models developed to describe the behaviour of fibre/liquid systems. This work can be summarized in 4 categories: (1) The bounce and immediate re-entrainment of liquid and solid monodisperse aerosols under a stable filtration regime (pre cake formation) by wet and dry fibrous filters. In this work it was found that the solid particles generally exhibited a lower fractional filtration efficiency than liquid particles (of the same size), although this difference decreased in the smaller size fractions. However, for the wet filtration regime (each fibre of the filter was coated by a film of water), no significant difference in filtration efficiency was detectable between solid and liquid aerosols. Either the bounce effect of the particles is inhibited by the liquid film, or the filtration conditions in the wet filter are so different that the aerosol properties are less significant with respect to capture. (2) A microscopic study of the effect of fibre orientation on the fibre wetting process and flow of liquid droplets along filter fibres when subjected to airflow and gravity forces was conducted. The flow of the liquid collected by the fibres was observed and measured using a specially developed micro-cell, detailed in the thesis. The experimental results were compared to a theoretical model developed to describe the flow of droplets on fibres. The theory and experimental results showed a good agreement. A sensitivity analysis of the model was performed which showed the droplet radius to be the most significant parameter. The model has the potential to improve filter self-cleaning and minimise water use. (3) An experimental study of the capture of solid and liquid (oil) aerosols on fibrous filters wetted with water. Variable quantities of liquid irrigation were used, and the possibility for subsequent fibre regeneration after clogging or drying was also studied. It was found that self-cleaning (removal of solid aerosols by water) occurred even under heavily dust-laden conditions, and post evaporation of water. With the collection of oil aerosols on fibres wetted with water, a predominance of the barrel shaped droplet on the fibre was observed, with oil droplets displacing water droplets (if the oil and fibre combination created a barrel shaped droplet), creating various compound droplets of oil and water not previously reported in literature. (4) An extensive experimental investigation of the wetting processes of fibre/liquid systems during air filtration (when drag and gravitational forces are acting) has shown many important features, including droplet extension, oscillatory motion, and detachment from fibres as airflow velocity increases. The droplet oscillation is believed to be induced by the onset of the transition from laminar to turbulent flow as droplet size increases. To model such oscillation it was necessary to create a new conceptual model to account for the forces both inducing and preventing such oscillation. The agreement between the model and experimental results is satisfactory for both the radial and transverse oscillations.