Porous solids permeability distribution

The Coulter Porometer II provides complete pore size flow and number distributions and permeability data in the overall size range 0.05pm to 300pm. Applications include paper, sintered products, porous solids such as core samples, and woven and non-woven fabrics including Alter cloths. The instrument operates on the principle that the (gas) pressure required to displace a liquid which freely wets the material is related to the pore radius. 

A model study of the combined effect of macroscopic heterogeneity and heteroporosity on the relative gas permeability of a porous solid, as a function of the fraction of pore volume occupied by a foreign sorbate, is reported. The heteroporous solid was modelled as a regular capillary network with randomly varying capillary radius, characterized by the radius distribution and the structure of the network, notably network connectivity. Macroscopic heterogeneity was introduced by allowing the local porosity of the solid to vary along or across the axis of permeation. Model calculations were performed for various macroscopic and microscopic parameter nalues, in order to obtain a realistic assessment of the relative importance of the respective effects and the way in which they combine to produce the final observable result. 

In previous work [1-4] it was shown that the relative permeability of porous solids is an important source of information about their pore structure. For the simulation of the pore structure, a network model has been employed, consisting of a regular array of nodes joined together by cylindrical capillaries of randomly varying radius r. The model is completely characterized by the capillary radius probability distribution f(r) and the connectivity of the network, nrji, given by the number of capillaries meeting at each node. 

A porous medium is simply a solid containing void spaces. Several properties of porous media that affect the flow of suspensions in these media are as follows porosity, permeability, and pore size distribution of the rock. In the following sections, a brief description of these properties is given. 

The solid line (a = 0) represents a uniformly distributed porous structure the dashed line (a = 1) corresponds to a randomly generated (Poisson distributed) system with a large total number of cylinders. The area between these two lines gives the most probable values of permeability for randomly distributed systems. Note that the permeability of disordered layers can be higher than that of ordered layers by a factor of more than 3, at identical sohd volume fraction and cylinder... 

There are a variety of designs [23] of vacuum filter, the selection of which depend strongly on the particle size distribution and density of the suspended solids in the feed slurry. The main types are drum, disc or horizontal belt filters. In each case the filter medium is usually a porous cloth, the permeability of which is chosen to suit the feed particle size. 

The general theoretical picture described above relating pore size distribution and relaxation time spectra works satisfactorily for solid materials of reasonably uniform surface chemistry, such as many model porous systems (glass bead or particle packs), and most sandstones. A number of laboratory studies have used it to deduce pore size distributions from longitudinal or transverse decay curves in saturated porous systems. The fact that NMR and mercury porosimetry, which measure respectively the accessible surface and the throat dimensions, give comparable pore size distributions can be explained by the regular geometry of these systems. One should also mention that an empirical correlation between hydraulic permeability and some representative relaxation time value have been observed to be... 

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