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As a first step to study the mechanism of filtration of deformable
particles, the compression and deformation behaviors of calcium-alginate
gel particles bed under mechanical loading and hydraulic drag in a
particles bed were conducted in the first part of this study. Experimental
results show that progressive decreases in the bed height, volume, and
porosity of the bed took place gradually as the pressure on the bed was
increased, with the particles being deformed into flattened dodecahedrons.
Cake filtration and crossflow filtration experiments of Saccharomyces
cerevisiae and PMMA were conducted to examine the structure of flux
limiting layer formed by deformable particles. Effect of particle
deformation due to friction drag and mass of cake on the reduction of
porosity was studied to examine how this variation led to the increase in
filtration resistance. Results showed that as the cake formed by deformable
gel particles exhibits a rapid increase in flow resistance or decrease in
porosity due to area contact between particles, a flux limiting layer,
resistant material is formed next to the filter medium during filtration.
A dynamic analysis proposed by Lu and Hwang (1993) was modified to
investigate cake formation in both cake filtration and crossflow filtration
of deformable particles by taking the transient effect of cake compression
and the effect of area contact between particles into consideration.
The simulated results agreed well with the experimental data.
In the second part of this study, three-dimensional particles
deposition on four basic woven structures was studied numerically by
analyzing forces acting on the depositing particles and was applied to
estimate the change of clarity of filtrate at the initial stage of
filtration. The effects of woven structures, feed concentration and
particle/pore size ratio on the transient behavior of cake filtration and
the variation of medium resistances at the beginning stage of cake
filtration were analyzed quantitatively. The simulated results showed that
the filtration period at the initial stage can be divided into the three
modes of standard pore blocking, intermediate blocking and cake formation
in accordance with the law of blocking for all types of pores. Furthermore,
the critical concentration proposed by previous investigators is also
confirmed quantitatively in this study.
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