Effective Liquid Permeability

Water-filled pores in the ionomer (radius corresponding water volume fraction Sei), and primary and secondary pores contribute to the liquid permeability, which is written in the following form 

In this expression, a percolation dependence is assumed in the mesopore space 5 is a constrictivity factor and t is a tortuosity factor (Dullien, 1979). 

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Effective liquid permeability in CCL COad + OHad recombination rate constant... 

Sites suitable for conventional SVE have certain typical characteristics. The contaminating chemicals are volatile or semivolatile (vapor pressure of 0.5 mm Hg or greater). Removal of metals, most pesticides, and PCBs by vacuum is not possible because their vapor pressures are too low. The chemicals must be slightly soluble in water, or the soil moisture content must be relatively low. Soluble chemicals such as acetone or alcohols are not readily strippable because their vapor pressure in moist soils is too low. Chemicals to be removed must be sorbed on the soils above the water table or floating on it (LNAPL). Volatile dense nonaqueous liquids (DNAPLs) trapped between the soil grains can also be readily removed. The soil must also have sufficiendy high effective porosity (permeability) to allow free flow of air through the impacted zone. 

The challenge for modeling the water balance in CCL is to link the composite, porous morphology properly with liquid water accumulation, transport phenomena, electrochemical kinetics, and performance. At the materials level, this task requires relations between composihon, porous structure, liquid water accumulation, and effective properhes. Relevant properties include proton conductivity, gas diffusivihes, liquid permeability, electrochemical source term, and vaporizahon source term. Discussions of functional relationships between effective properties and structure can be found in fhe liferafure. Because fhe liquid wafer saturation, 5,(2)/ is a spatially varying function at/o > 0, these effective properties also vary spatially in an operating cell, warranting a self-consistent solution for effective properties and performance. 

Liquid permeability Hagen- Poiseuille Kozeny- Carman Cylindrical Voids between spheres 0.1-10 p Pore hydraulic radius Experimental simplicity. Assumptions laminar flow in HP equation, zero wetting angle, no pre-existing agent on the surface. Great influence of pore geometry and tortuosity on the interpretation of results. Network effects. 

E. Systemic Effects. Liquid arsenical vesicants on the skin, as well as inhaled vapor, are absorbed and may cause systemic poisoning. A manifestation of this is a change in capillary permeability, which permits loss of sufficient fluid from the bloodstream to cause hemoconcentration, shock, and death. 

Effective Permeability. Bernard and co-workers (31, 32) pursued pioneering studies to quantify gas and liquid permeabilities in the presence of foam. They either coinjected surfactant solution and nitrogen, or used alternating slugs of each. For consolidated porous media with absolute permeabilities that range from 0.1 to 0.25 /zm2, they found several... 

At low gas pressures and for small pore size, the mean free path of the gas molecules may be on the order of the pore size and therefore velocity slip occurs (Knudsen effect), resulting in higher permeabilities. However, an increase in the permeability due to an increase in gas pressure has been found in some experiments. Scheidegger [24] discusses the effect of the Knudsen slip, the internal surface roughness, surface absorption, capillary condensation, and molecular diffusion on the measured permeability. By examining these effects at the pore level, it becomes clear that the measured gas and liquid permeabilities can be noticeably different. 

J. Bixler and A.S. Michaels Effect of Uniaxial Orientation on the Liquid Permeability and Peremselectivities of Polyolefins" 53 rd National Meeting American Institute of Chem. Eng. Pittsburgh, (1964), Preprint 32d. 

The nature of the bottlenecks for proton conductance in the dry membrane state or on the way to it is, however, still the subject of debates. This wiU only be resolved after more detailed experimental studies (of macroscopic transport parameters such as proton conductance and electro-osmotic coefficients as a function of water content, or gas and liquid permeability before and after operation, and of microscopic structural probes such as small-angle neutron and X-ray scattering) will have discriminated between competing models. By and large, the direction of effects that go with dehydration is obvious enough to be introduced into phenomenological models of overall cell performance. 

Transient effects in permeability measurements. Liquid water flux of PFSA membrane as a function of time. Membrane thickness 4 mils and temperature 29 C. 

The steps involved in modeling performance and water balance in CCLs are indicated in Figure 8.2 [50, 51]. At the materials level, it requires constitutive relations between random composition, dual porous morphology, liquid water accumulation, and effective physico-chemical properties, including proton conductivity, gas diffusivities, liquid permeabilities, electrochemical source term, and vaporization source term. The set of relationships between structure and physico-chemical properties has been discussed in [3, 47, 50-51]. Since the liquid water saturation S (z) is a spatially var5dng function at jf,>0, these physicochemical properties become spatially varying functions in an operating cell. This demands a self-consistent solution for non-linearly coupled properties and performance. 

Membrane Pervaporation Since 1987, membrane pei vapora-tion has become widely accepted in the CPI as an effective means of separation and recovery of liquid-phase process streams. It is most commonly used to dehydrate hquid hydrocarbons to yield a high-purity ethanol, isopropanol, and ethylene glycol product. The method basically consists of a selec tively-permeable membrane layer separating a liquid feed stream and a gas phase permeate stream as shown in Fig. 25-19. The permeation rate and selectivity is governed bv the physicochemical composition of the membrane. Pei vaporation differs From reverse osmosis systems in that the permeate rate is not a function of osmotic pressure, since the permeate is maintained at saturation pressure (Ref. 24). 

Insoluble corrosion prodiic ts may be completely impeivious to the corroding liquid and, therefore, completely protective or they may be quite permeable and allow local or general corrosion to proceed unhindered. Films that are nonuniform or discontinuous may tend to localize corrosion in particular areas or to induce accelerated corrosion at certain points by initiating electrolytic effects of the concentration-cell type. Films may tend to retain or absorb moisture and thus, by delaying the time of drying, increase the extent of corrosion resulting from exposure to the atmosphere or to corrosive vapors. 

Wells, S. A. and Dick, R. I. (1993) "Permeability, Solid and Liquid Velocity, and Effective Stress Variations in Compressible Cake Filtration," Proceedings, American Filtration Society Conference on System Approach to Separation and Filtration Process Equipment, Chicago, Illinois, May 3-6, pp. 9-12... 

Ionic liquids have already been demonstrated to be effective membrane materials for gas separation when supported within a porous polymer support. However, supported ionic liquid membranes offer another versatile approach by which to perform two-phase catalysis. This technology combines some of the advantages of the ionic liquid as a catalyst solvent with the ruggedness of the ionic liquid-polymer gels. Transition metal complexes based on palladium or rhodium have been incorporated into gas-permeable polymer gels composed of [BMIM][PFg] and poly(vinyli-dene fluoride)-hexafluoropropylene copolymer and have been used to investigate the hydrogenation of propene [21]. 

Technical procedures to determine production rate, reservoir pressure, temperature, permeability, and skin effect, and to sample gas and liquids for analysis. 

Buoyancy in some form is employed in nearly all categories of underwater and surface systems to support them above the ocean bottom or to minimize their submerged weight. The buoyant material can assume many different structural forms utilizing a wide variety of densities. The choice of materials is severely restricted by operational requirements, since different environmental conditions exist. For example, lighter, buoyant liquids can be more volatile than heavier liquids. This factor can have a deleterious effect on a steel structure by accelerating stress corrosion or increasing permeability in reinforced plastics. 

These tests show that CC -foam is not equally effective in all porous media, and that the relative reduction of mobility caused by foam is much greater in the higher permeability rock. It seems that in more permeable sections of a heterogeneous rock, C02-foam acts like a more viscous liquid than it does in the less permeable sections. Also, we presume that the reduction of relative mobility is caused by an increased population of lamellae in the porous medium. The exact mechanism of the foam flow cannot be discussed further at this point due to the limitation of the current experimental set-up. Although the quantitative exploration of this effect cannot be considered complete on the basis of these tests alone, they are sufficient to raise two important, practical points. One is the hope that by this mechanism, displacement in heterogeneous rocks can be rendered even more uniform than could be expected by the decrease in mobility ratio alone. The second point is that because the effect is very non-linear, the magnitude of the ratio of relative mobility in different rocks cannot be expected to remain the same at all conditions. Further experiments of this type are therefore especially important in order to define the numerical bounds of the effect. 

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