Filtration of airborne particles by a trickle granular bed: a modelling approach

The removal of airborne particles was investigated using a trickle granular bed. This filtration process maintains a constant pressure drop during particles loading, which makes it an interesting alternative for aerosol filtration. In order to establish mathematical models for the design of the process, a modelling approach that takes into account the changes of the bed characteristics due to the liquid hold up is undertaken. This approach allows predicting the pressure drop and the filtration efficiency of the trickle granular bed, based on the assumption that the bed porosity decreases and the collectors diameter increases with increasing the liquid flow rate. The model predictions are in agreement with experimental data. For particles with diameters around 100 nm the collection efficiency presents a minimum. For smaller particles the collection efficiency increases as the dominating collection mechanism is Brownian diffusion. In the micronic range the collection is governed by inertial and interception mechanisms and consequently increases with increasing the particle size.