Mixture Aerosols Filtration on Filters with Wide Fibre Diameter Distribution - Comparison with Theoretical and Empirical Models

Abstract

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.

Pressure Drop Dynamics during Filtration of Mixture Aerosol Containing Water, Oil, and Soot Particles on Nonwoven Filters

“…The electrostatic mechanism was omitted due to the filtration material not being charged with static charges (samples were neither intentionally charged nor discharged; however, the existence of some charges related to the manufacturing process may still be possible). The filtration efficiency calculations and its changes over time were based on the following empirical equations which were discussed in detail in our previous papers [ 36 , 42 ]: where η dif —diffusion mechanism efficiency (-), Pe—Peclet number (-), η int —interception mechanism efficiency (-), α—packing density (-), Ku—hydrodynamic factor of Kuwabara flow (-), R—interception parameter (-), η imp —impaction mechanism efficiency (-), and Stk—Stokes number (-).…”

“…The measured distribution was reduced to ten average values, each representing one-tenth of all fibre diameters. This allowed the simplification of the model without significantly affecting the accuracy [ 42 ]. The calculations of efficiency change over time were performed for each of the fibre diameters independently, and their contribution to the total filter efficiency was weighed based on their share.…”

“…The calculations of efficiency change over time were performed for each of the fibre diameters independently, and their contribution to the total filter efficiency was weighed based on their share. The details of this method were described in our previous work [ 42 ].…”