The dynamics of filtration efficiency and pressure drop during the simultaneous filtration of soot and oil aerosols on single-and multi-layer filters were investigated, and the determined filtration efficiency was compared with the theoretical efficiency obtained via the classical filtration theory. Additionally, the influence of liquid-phase aerosols on the morphology of the formed deposits was investigated. It was concluded that the addition of oil aerosols decreased the filtration efficiency and lowered the pressure drop increase rate for multi-layer filters.Additionally, for the filtration of aerosols containing soot and high oil concentrations, once maximum filtration efficiency was reached, an efficiency decrease occurred. The system imperfection factor was proposed as a mean to predict the efficiency of multi-layer filters. The modified version of the single fibre efficiency method was used to calculate filter mass change with reasonable accuracy.
A methodology for calculating aerosol filtration efficiency using non-woven filters with polydispersity distribution of fibre diameters was formulated. In order to verify the results of the calculations experimentally, filters made of polypropylene non-woven fabric were used to filter solid (soot) and liquid (oil) aerosols and their mixtures with different concentrations. In order to increase the accuracy of the calculations, the division of the diameter distribution into several (1-100) ranges of values was considered. The influence of the number of these intervals for theoretical and empirical equations available in the literature was investigated. This effect was found to be significant, and replacing one diameter value representing all the fibres in the filter with twenty diameter ranges, each representing only a fraction of the total fibres, is sufficient to minimize the error due to the underrepresentation of the actual fibre distribution in the filter. Calculation of the mean particle size after the filter was performed using a set of theoretical and empirical equations. The calculations take into account the change in packing density, flow velocity and fibre diameter over time as a result of filling the filter with particles deposited on it. The obtained results were compared with the measurement results. It has been found that such changes in the monofilament performance model are insufficient to properly describe the effects inside the filter.
The pressure drop dynamics during the filtration of three-component mixture aerosols are investigated and compared with two and single-component aerosols. The main area of interest is the effect of the addition of a small quantity of liquid (oil) and solid (soot) particles during the filtration of aerosol containing water mist. In addition, calculations of the change in filter mass during oil aerosol filtration have been carried out and compared with the experimental results. The new, improved filtration efficiency model takes into account a better coefficient fitting in the filtration mechanism equations. The limitations in the change in fibre diameter and packing density resulting from the filter loading have been implemented in the model. Additionally, the calculation model employs the fibre size distribution representation via multiple average fibre diameters. The changes in fibre diameter are dependent on each fibre’s calculated filtration efficiency. The improved filtration model has been utilised to predict the mass change of the filters during the filtration of pure and mixture aerosols. The pressure drop calculation model based on changes in filter mass has been formulated. The model is then utilised to calculate pressure drop changes resulting from the filtration of the oil aerosol and water and oil mixture aerosol.
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