Relating Water and Air Flow Characteristics in Coarse Granular Materials

This paper investigates the connection between the velocity (V)–pressure drop (ΔP) relationships for air and water flow in coarse porous filter media with the aim of linking the V–ΔP relationships for air and water. Investigations were carried out using a common biofilter medium, Leca® consisting of rounded porous particles of 2- to 18-mm diameter. V–∆P relations for water flow were measured for 14 different Leca® particle size fractions and compared with measurements of V–∆P relations for air flow in 36 different Leca® particle size fractions (including the 14 used for water flow). The measurements showed a strong relationship between the two types of relationships, and further that this relationship could be described using a single constant. An approach for predicting the water flow V–∆P relationship from the corresponding air flow relationship across different particle size fractions from the same material is suggested, tested, and found valid for Re numbers higher than that which is considered in the presently available studies of air/water V–∆P relationships.