Apparent pore size

Spunbonded fabrics are effective filters in that they are layered stmctures of relatively fine fibers, the three-dimensional stmcture of which creates a torturous path. Even relatively thin spunbonded fabrics (eg, 0.2—0.25 mm) present a significant challenge to the passage of soil fines and are suitable for use in some filtration appHcations. The porosity of geotextile fabrics is classified by means of several procedures such as flux (volume flow/area per time) and equivalent opening size (EOS), which is a measure of the apparent pore size of the openings in the fabric. The flux measures the porosity to Hquid water, and the EOS measures the porosity to soHd particles of a known diameter. Literature is available on limitations of particular styles of fabrics within an apphcation (63). 

This deposit is composed of suspended particles similar to conventional filter cakes, and more importantly, a slime that forms as retained solutes exceed their solubility. The gel concentration 6 is a function of the feed composition and the membrane-pore size. The gel usually has a much lower hydrauHc permeabihty and smaller apparent pore size than the underlying membrane (27). The gel layer and the concentration gradient between the gel layer and the bulk concentration are called the gel-polarization layer. 

A microscopic description characterizes the structure of the pores. The objective of a pore-structure analysis is to provide a description that relates to the macroscopic or bulk flow properties. The major bulk properties that need to be correlated with pore description or characterization are the four basic parameters porosity, permeability, tortuosity and connectivity. In studying different samples of the same medium, it becomes apparent that the number of pore sizes, shapes, orientations and interconnections are enormous. Due to this complexity, pore-structure description is most often a statistical distribution of apparent pore sizes. This distribution is apparent because to convert measurements to pore sizes one must resort to models that provide average or model pore sizes. A common approach to defining a characteristic pore size distribution is to model the porous medium as a bundle of straight cylindrical or rectangular capillaries (refer to Figure 2). The diameters of the model capillaries are defined on the basis of a convenient distribution function. 

In the case of polyacrylamide gels, Stellwagen [367] found that buffer type (TAE vs TBE) did not affect the apparent pore size (21 mn for 10.5% T 5% C to 200 mn for 4.6% r/2% C), although more extreme variations in salt content and buffer physical properties may very likely strongly affect pore structure in polyacrylamide gels. 

Stellwagen, NC, Apparent Pore Size of Polyacrylamide Gels Comparison of Gels Cast and Run in Tris-acetate-EDTA and Tris-borate-EDTA Buffers, Electrophoresis 19, 1542, 1998. Stellwagen, NC Gelfi, C Righetti, PG, The Free Solution Mobility of DNA, Biopolymers 42, 687, 1997. 

The gel usually has a much lower hydraulic permeability and smaller apparent pore size than the underlying membrane. (The gel layer and the concentradon gradient between the gel layer and die bulk concentration are called the gel-polarization layer.)... 

Figure 3. Apparent Pore Size Distribution of Desulco by Mercury Porosimetry.

Figure 1. Apparent pore size distributions obtained for (a) whole and (b) fragmented samples from batch E2. ( , mercury intrusion and Kloubek correlation o, mercury extrusion and Kloubek correlation , mercury extrusion and new correlation , nitrogen adsorption , nitrogen desorption).

Hagel, L., Ostberg, M., and Andersson, T. Apparent pore size distributions of chromatography media, /. Chromatogr., 743, 33,1996. 

The substitution of phosphorus in the framework structure of Type L zeolite results in reduced adsorption capacity (—50% ) and a reduction in apparent pore size from about 10 to 6-7 A. Na+-exchange of P-L zeolite results in a further reduction in adsorption capacity except for water. Ca2+-exchange of P-L results in an increased adsorption capacity for KUO and 02 to about 90% of that of phosphorus-free L zeolite, but reduces... 

Clinoptilolite has a monoclinic symmetry and its typical formula is (Na2,K2)0.Al203.10SiO2.8H2O. Its porous structure may resemble mordenite.The dimensions of its channels are 0.75 x 0.30, 0.43 X 0.33 and 0.31 x 0.33 nm. However, the apparent pore size of the nondecationized clinoptilolite is close to that of small-pore zeolites. Its pore size can be enlarged by decationization and dealumination. 

BS 6906-2 1989. Methods of test for geotextiles. Determination of the apparent pore size... 

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