Fluid permeation

Gel filtration chromatography (also known as size or molecular exclusion chromatography) separates molecules based on their ability to penetrate into the pores or channels in agarose or dextran beads. As a mixture of molecules in a fluid permeate through the beads of gel the volume available for diffusion is determined by their diameter and the size of the channels in the gel beads. The... 

The all or nothing feature of metal powder composites is very much a feature of conductive composite systems. In order to understand this behaviour, most theories borrow from percolation theory (Broadbent and Hamersley, 1957), which was originally developed as a model for predicting fluid permeation through porous media. The percolation model is based on having a medium... 

This analysis shows that permeability is a complex function of porosity and surface area, the latter being determined by the size distribution and shape of the particles. The appearance of specific surface in Eq. (20) offers a method for its measurement and provides the basis of fluid permeation methods of size analysis. This equation also applies in the studies of filtration. 

Vulcanization and curing processes Concentration changes in chemical reactions Thermal heating under load Fluid permeation, drying... 

Problem 5-12. Flow Through a Porous Tube. Let us consider flow through a cylindrical porous tube, which occurs in many membrane filtration processes. The tube is very long with radius R. At the inlet of the tube, the pressure is/ /. Fluid permeates or leaks out through the wall of the tube with a velocity k(P — Ps) ///, where P is the local pressure in the fluid, Ps is the pressure on the other side of the membrane, A is a permeation coefficient, and // is the viscosity of the fluid. We wish to determine how much fluid is filtered as a function of the length of the tube. 

D5886-95 Standard Guide for Selection of Test Methods to Determine Rate of Fluid Permeation Through Geomembranes for... 

Compounds with different lipid solubility have different fates in tissue. This is most clearly demonstrated in the brain using ventriculocisternal perfusion [88]. In these experiments, solutes delivered into the cerebrospinal fluid permeate through the ependyma into the extracellular space of the brain. Three classes of compounds, with different patterns of local distribution, have been identified (a) water-soluble compounds that remain in the extracellular space of the brain, occupying a volume fraction of 15-20% (e.g., sucrose and EDTA), (b) large, lipid-soluble compounds that have slow capillary transport, but quickly enter the cells of the brain, occupying a volume fraction of 50-200% (e.g., mannitol, creatinine, cytosine arabinoside), and (c) small, lipid-soluble compounds that are rapidly removed from the brain by capillary transport (e.g., H2O, ethanol, l,3-bis(2-chloroethyl)-l-nitrosourea (BCNU). Similar behavior probably occurs in extracranial tissues as well. 

We considered here a jointed rock, i.e. a formation of rock blocks separated by thin joints / fractures. Fluid flows through the fractures, while fluid permeation into the rock blocks is neglected. The rock formation is at high temperature initially, and is subjected to in-situ confining stresses. Under the conditions, low-temperature fluid is injected from a point into the fracture network. For such a case, we examined how the fluid injection changes the fracture network permeability assuming 2-dimensional cases for simplicity. 

Oxidizing substances, such as ozone, can cause peroxidation of cellular membranes, leading to membrane damage and increased permeability. The edematous fluid permeates through such membranes, accumulating and blocking the airway. This results in edema. Many other toxicants may produce cellular damage and edema, however. 

PT is the applied transmembrane pressure p is the viscosity of the fluid permeating the membrane Ax is the length of the channel (the membrane skin thickness)... 

ESC occurs, in general, in amorphous polymers such as PC, PMMA, PS, PVC, SAN, and ABS as well as in semicrystalline thermoplastics like PE, PP, PA, and PB (Wright 1996). Amorphous polymers exhibit a higher tendency for this type of failure because their loose structure facilitates fluid permeation into the polymer. Amorphous polymers show enhanced sensitivity to ESC at temperatures close to... 

There is increasing interest in hose forms of construction as a route to manufacturing reinforced thermoplastic pipes (RTP) on a continuous production basis. The most widely used high pressure hoses are composite structures intended to create a flexible, tubular connection within high-pressure fluid systems. The pressure containment is achieved by incorporating textile fibres or steel wires which can carry high stresses whilst the elastomeric or plastic components essentially protect the fibre or wire structures and act as a seal against fluid permeation. 

Macroscopic volume and mass Gas sorption SEM Static or d3mamic fluid permeation Sound velocity measurement Wetting EDX... 

Fluid permeation. Fluid permeation can be investigated by a classical stationary or a dynamic technique. It provides an effective pore diameter that is the result of the size distribution and the connectivity of the pores the latter can be expressed in term of the tortuosity t which is the ratio of the path that the fluid actually takes and the width over which the pressure gradient is applied (usually the sample thickness). If viscous flow rather than molecular diffusion is the dominant mechanism the weight of the pore size distribution with respect to its impact on the fluid permeation transport is shifted to the large pores. 

Figure 21.35. Scheme of a setup for a stationary measurement of fluid permeation. 

Blisters and internal cracks indicate that a seal is interacting with a fluid. Such failures, which are evident only upon close examination of the seal, are caused by fluid permeating into and expanding microscopic voids in the rubber. 

Bg is the pemeability [m ] measuring the capability of the porous media for fluid permeation. The use of Darcy s law as source terms allows the momentum equations to be applicable to both the gas channels and the porous media, as an infinitely large permeability can be used for the gas channel. 

Because of undesired ionic side products in the form of chlorides, sulfates, and anunonia which may disturb the transfer process, at least part of the aqueous carrier fluid has to be exchanged for purified water to reduce ion concentration in the suspension. Another reason for the reduction of ion concentration is that, at high concentrations, hardly any electrical repulsion between the particles can be achieved [16], The process of exchanging the water can be carried out by, for example, decantation or filtration of the suspension. Both methods have as their aim the retention of particles while the carrier fluid is changed. For decantation, the magnetic particles can be fixed at the bottom of the vessel by a permanent magnet. With the filtration process, selective membranes are needed which separate a particle-free fluid permeated by ionic components from a retentate in which the magnetic particles are suspended. 

Viramontes-Gamboa, G., Arauz-Lara, J. L., and Medina-Noyola, M. 1995. Tracer diffusion in a Brownian fluid permeating a porous medium. Phys. Rev. Lett. 75 759. 

In the previous equations, p and j] were the density and the viscosity of BSA solutions, respectively, n the velocity vector in the membrane module, and p the pressure within the module Pi and tji were, respectively, the viscosity and the density of the fluid (permeate) flowing within the membrane, Uj the velocity vector and the pressure in the membrane. 

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