Porous permeability

Filter aids as well as flocculants are employed to improve the filtration characteristics of hard-to-filter suspensions. A filter aid is a finely divided solid material, consisting of hard, strong particles that are, en masse, incompressible. The most common filter aids are applied as an admix to the suspension. These include diatomaceous earth, expanded perlite, Solkafloc, fly ash, or carbon. Filter aids build up a porous, permeable, and rigid lattice structure that retains solid particles and allows the liquid to pass through. These materials are applied in small quantities in clarification or in cases where compressible solids have the potential to foul the filter medium. 

Gu, W.Y., Lai, W.M. and Mow, V.C. (1993) Transport of fluid and ions through a porous-permeable charged-hydrated tissue, and streaming potential data on normal bovine articular cartilage. Journal of Biomechanics 26, 709-723... 

Pervasive fluid flow through a porous, permeable medium is described by Darcy s law, written here for three dimensions (cf. Bear, 1972) ... 

Reservoir Porous permeable rock, generally a sediment, capable of storing petroleum. 

Wood is a porous, permeable, hygroscopic, and orthotropic material of extreme chemical diversity and physical complexity. Because of this, its properties vary between species, between trees within a species, and even within a tree. This variability can result in an adhesive to produce bonded joints that will perform inconsistently and with different levels of performance among the several types of timber species. 

Filtration aids are employed to enhance filtration characteristics, particularly for hard-to-filter suspensions. These are normally applied as an admix to the suspensions. The role of the filter aid is to built up a porous, permeable and rigid lattice structure that assists in retaining solid particles while allowing liquid to flow through. 

Medical tapes are composed of a backing coated with adhesive (porous, permeable or occlusive). Some have a wound pad. 

Another important term is the "critical pigment volume concentration" or CPVC. CPVC is the minimum level of binder required to completely wet the pigment particles and fill the interparticle voids. At pigment volume concentrations above CPVC, there is not enough binder to completely fill the voids between the pigment particles. As a result, the film becomes more porous, permeable, and weak. CPVC usually occurs between 40 to 55% PVC. Figure 2 illustrates the changes in film properties as a function of PVC. 

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