Separation Technologies
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Surface filtration
In surface filtration the medium is used to support the captured solids which deposit onto the medium (called septum, membranes, cloth etc.) during operation.
Removal of solids is effected by the previously deposited solids or cake. As the cake builds so does the resistance to flow. Depending on the force driving the fluid through the medium (i.e. displacement pump, centrifugal pump, or just a constant liquid head above the filter) the filtrate rate can decrease and/or the pressure across the filter will increase until the filtering process is terminated.
The cake resistance is a function of the porosity and thickness of the deposit which can change with time. Filter aids are often added as a layer on the medium for additional support (called precoat) to reduce compression of the cake and impart high permeability.