Flow through compressible porous media: short-time filtration, wall friction in compression-permeability cells, and rheological models



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Both theoretical and. experimental studies were made to elicit a better understanding of the process of filtration. Flow equations were established for rotary drum filtration. Rotary .drum filtration is characterized by short filtration times, low pressure differentials and generally by high slurry concentrations. In the development of the flow equations cognizance was taken of two effects; (1) the variation of flow rates throughout the cake due to the changes in cake porosity; and (2) the simultaneous flow of liquid and solids towards the medium. Operating and feed parameters were studied-using the equations. A modified compression-permeability cell was used to determine the degree of friction which exists between the filter cake and the side-wall of the cell. A simplified equation was derived and tested which described the frictional effect. Using this equation, factors were derived which correct the measured porosity and specific resistance for side-wall friction. Although the correction factor for porosity is not usually large, a measurable error would . result if this effect were to be neglected. The correction for specific resistance is considerably larger and normally should not be neglected. Further experimental studies were made to determine the effect of primary compression on filter cakes. Several rheological models were compared with the experimental results. A Kelvin model was found to adequately describe the primary compression.