FLOW AND FILTRATION THROUGH GRANULAR MEDIA - THE EFFECT OF GRAIN AND PARTICLE-SIZE DISPERSION

A mathematical model of granular media filtration has been constructed based on an adaptation of the Carman-Kozeny equations for flow in por ous media to the cells of a non-homogeneous media, and a consideration of the capture probability when a particle passes close to a filter g rain. The model was based on a matrix of five size fractions and five pore voidages. The suspended solids also comprised five size fractions . The shear stress on the deposit was calculated at each time incremen t in each cell for each size fraction, and if this exceeded given limi ts either deposition was inhibited or the solids were Rushed out. All coefficients used have a physical significance. The resultant calculat ions produce a striking simulation of the behaviour found in real filt ers such as the formation of ''wormholes'' in the clogged layers, brea kthrough when the flow is increased on used filters, a linear increase in headless with time, etc. A new form of maturation resulting from t he redistribution of flow in the matrix has also been identified. The work was undertaken with the aim of producing a general model that mig ht be used by designers to predict all aspects of filter behaviour. Wh ile there may be much more that could be done some progress would appe ar to have been made. Copyright (C) 1996 Elsevier Science Ltd.