Linking gas and liquid pressure loss to particle size distribution and particle shape in granular filter materials

The cost efficiency of filtration is often associated with the filter flow velocity (V) and pressure loss (?P). Knowledge of the VP relationship for a given filter medium-fluid combination is therefore necessary when assessing operation costs. Liquid VP measurements are generally much more time-consuming than for gases, thus predicting liquid VP relationships from corresponding gas data is advantageous. The objective of this work was to identify the relationship between air and water pressure gradients during air and water flow in granular filter media. Three materials: crushed granite, gravel, and Leca (an insulation material) with very different particle shapes were used. Twenty-one media with different particle size distributions were produced from each material (63 in total) and VP measurements carried out using air and water. The results showed that it is indeed possible to predict liquid VP relationships fromcorresponding gas VP measurements together with medium physical characteristics. A simple model concept for prediction was proposed. The results also indicated that it is possible to predict both gas and liquid VP relationships in coarse granular filter media based simply on knowledge about the particle size distribution and particle shape for the medium in question.