Ideal capillary porous membrane

On the other hand, when ideal capillary porous membranes are studied (that is, membranes with constant pore section and pore length equal to membrane thickness, Axp = Axj ), the membrane resistance can be considered as that corresponding to the parallel association of the electrolyte filling the pores (assuming the resistance of the solid membrane matrix is much higher than the solution) and Rm values might also give information on membrane porosity [46]. 

Mass Transport through a Porous Membrane Ifa membrane with thickness Lcon-sists of ideal parallel and cylindrical capillaries (pores) with uniform diameter dpore. the velocity of flow in the pores is given by Hc en-PoisemUe s law for laminar flow, see Eq. (3.4.6) in combination with Eq. (3.4.15) ... 

The pores in a porous membrane or paper and the channels in a porous bed may be idealized as capillaries of radius R. If we immerse a capillary of radius R made of a particular material into a liquid, we observe either of the following phenomena. If the material has a finite contact angle 6 < 90° (for example, for water and a glass capillary), the liquid rises into the capillary to a finite height ha (Figure 6.1.4), given by... 

If we consider the typical example of a catalytic porous asymmetric membrane constituted by a thin catalytic layer supported by a macroporous substrate and a wetting liquid phase on the support side and a gas phase on the small pore catalytic side, the liquid will easily fill the pores of both the support and the porous catalytic layer. In order to move the gas-liquid interface from the support towards the catalytic porous layer, a pressure difference of the gas phase has to overcome the capillary pressure of the support. For the same reason, the position of the interface between the two fluid phases inside the porous catalytic layer will depend on the quaUty of the catalytic layer and on the strict control of the pressure difference between the two membrane compartments. In membrane contactors, usually the condition of gas-phase filled pore is preferred in order to reduce the overall mass transfer resistance across the membrane. In a catalytic membrane, both reactants in the two fluid phases need to reach the catalytic sites in the pore and therefore an ideal situation wherein the interface between the phases is very close to the catalytic sites is to be preferred in order to achieve the maximum reactant concentration in the reaction zone. This situation can be approximated by using a wetting liquid, a thin catalytic layer and fluid-fluid... 

Dynamic methods such as gas relative permeability combined with aspects from percolation theory can be employed to obtain structural information on the porous network topology (dimensionality and connectivity) as well as on the pore shape. Model membranes with well defined structure formed by compaction of non-porous spherical particles, are ideal for testing the different characterization techniques. One should bear in mind though, that dynamic methods should be used as a complement of, rather than as an alternative to, the equilibrium methods. Furthermore, capillary network models are not always appropriate for the derivation of structural information, and for membranes made by compaction of spheres the use of advanced pore modeling tools based on random sphere packing geometry is required. 

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