New hydraulic insights into rapid sand filter bed backwashing using the Carman–Kozeny model

Fluid flow through a bed of solid particles is an important process that occurs in full-scale water treatment operations. The Carman–Kozeny model remains highly popular for estimating the resistance across bed. It common practice to use particle shape factors fixed state match predicted drag coefficient with experimentally obtained coefficients. In fluidised state, however, where same are considered, this factor usually simply omitted from without providing appropriate reasoning. research, it shown not constant property but dependent on fluid properties as well. This dynamic irregularly shaped grains increases approximately 0.6 1.0 state. We found unstable packed beds moderate up-flow conditions pseudo-fixed and setting results decreasing voidage simultaneously coefficient, which seems quite contradictory. can be explained by collapse local channels bed, leading more uniform distribution improving available surface flow-through. Our experimental measurements show decreases considerably laminar transition regions. most likely caused orientation, realignment rearrangement particles’ packing position. A thorough hydraulic analysis shows filtration rapid sand filters under backwash causes almost imperceptibly. addition, improved expression demonstrated constant, however often assumed fact increasing rates. Furthermore, we propose new pseudo-3D image irregular shape. way, explain successful method using optimisation extended terminal sub-fluidisation wash (ETSW) filter backwashing procedure, turbidity peaks number reduced positive effect quality.