Permeability polarisation

Barth, C. F., Steigerwaid, E. A. and Troiano, A. R., Hydrogen Permeability and Delayed Failure of Polarised Martensitic Steels , Corrosion, 25, 353 (1969)... 

Permeabilities measured for pure gases can serve as a rough guide for selection of membrane materials. For design, data must be obtained on gas mixtures, where selectivities are often found to be much lower than those calculated from pure-component measurements. This effect is often due to plasticisation of the membrane by sorption of the most soluble component of the gas. This allows easier penetration by the less-permeable components. The problem of concentration polarisation, which is often encountered in small-scale flow tests, may also be responsible. Concentration polarisation results when the retention time of the gas in contact with the membrane is long. This allows substantial depletion of the most permeable component on the feed side of the membrane. The membrane-surface concentration of that component, and therefore its flux through the membrane, decreases. 

In ultrafiltration and reverse osmosis, in which solutions are concentrated by allowing the solvent to permeate a semi-permeable membrane, the permeate flux (i.e. the flow of permeate or solvent per unit time, per unit membrane area) declines continuously during operation, although not at a constant rate. Probably the most important contribution to flux decline is the formation of a concentration polarisation layer. As solvent passes through the membrane, the solute molecules which are unable to pass through become concentrated next to the membrane surface. Consequently, the efficiency of separafion decreases as fhis layer of concentrated solution accumulates. The layer is established within the first few seconds of operation and is an inevitable consequence of the separation of solvent and solute. 

Parallel plates, 527 Parallel polarised light, 299 Paramagnetic, 355 Pardox of Kauzmann, 151 Partially immobilising sorption, 682 Partly oriented yams, 483 Peclet number, 56,59 P-electron conjugation, 140,161,183 Penetrant, 655 Performance properties, 52 Permachor, 676 Permeability, 656, 673, 676 coefficient, 656 magnetic, 287 of polymers, 675 Permeation coefficient, 673... 

This may be of importance in membrane filtration, where significant changes in concentration may take place in the boundary layer, where molecular conformation may influence gel layer permeability. However it may only be relevant for feeds of high NOM, high recovery and significant concentration polarisation. 

Where n is the refractive index, e the permittivity and p the permeability of the dielectric media. The incident, reflected and refracted rays are coplanar (located in the x-z plane, the plane of incidence, in Fig. 14.36). Transverse electric (TE), perpendicular (-L) or s-polarised light has its electric vector perpendicular to the plane of incidence (x-z plane) in Fig. 14.36, while transverse magnetic (TM), parallel ( ) or p-polarised light has its magnetic vector perpendicular to the plane of incidence. 

Kakiuchi, T., M. Kotani, J. Noguchi, M. Nakanishi, and M. Senda, Phase transition and ion permeability of phosphatidylchohne monolayers at the polarised oil-water interface, J Colloid InterfSci, Vol. 149, (1992) p. 279. 

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