Flow Resistance of Used Media

Hatschek [1926] pubUdied a study of the throttling of the free area in a medhuu, following the depo on of sofids. The effect is most pronounced in the deposition of the first layer of particles and this early work demonstrated that the structure of subseqent deposits will be influenced by the initial throttling process. The resistance of a cloth phis a thin lay of cake is nmch greater than would be expected from the sum of the resistance of the dean cloth and the resistance of the layer. 

Later studies [Rushton Hassan,1980] involved repeated fihrations of dilute suspensions of fine particles on cloths of various types. Between each filtration, the cloths were back-washed thoroughly, then checked for permeability to pure water. It was demonstrated that the ratio appeared to influence the change in permeability with use. The results below refer to the change in permeability after fifteen filtration-cleaning cycles. 

Quantitative and reproducible measurements are made difficult by the fact that the degree of pore plugging is related to the shape of the particle the latter tends to orientate itself in the flowing fluid so that it represents minimum resistance to fluid drag force. 

Grace [1958] described the filtrate flow-time relationsJiip in standard law conditions in terms of the filter medium properties for constant pessure and constant filtrate rate  

Dmitrieva and Paki ver [1951] relate the tendency to blind to the sedimentation velocity of the suspension. A parameter = 18 AP/i (n-p) g was suggested for classification of the blinding tendency of particles of size rin a medium of resistance R . Pore phig g occurs for values greater than 1000 cake filtration msues for 100. Between these limits 100 1000 an intermediate t)pe of dqiosition takes place. 

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