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Membrane permeability laminar

Flow Permeability Test. A rough estimate of an equivalent mean pore size may be made by measuring the porosity (6) and permeability (J) of the membrane. Assuming laminar flow, the Hagen Poiseuille relationship may be modified for a porous membrane ... [Pg.77]

Some other techniques involving membrane permeability have been developed that have not yet been extensively used. Concerning gas permeability, a method called permeametry has been developed [41], based on Adzumi equation. It consists of measuring the variation in membrane permeability when favoring either molecular (Knudsen) or laminar (Poiseuille) flow regime. A mean pore radius is obtained with this method. [Pg.526]

One method which is known under the name of permeametry [131] or Poiseuille-Knudsen method [124] is based on the law of gas permeability in a porous media in the two flow regimes molecular flow (Knudsen) and laminar or viscous flow (Poiseuille). According to Darcy s law, the gas flux through a membrane with a thickness / can be written as / = KAP/l, where K is the permeability coefficient and AP (AP = Pi - P2) the pressure difference across the membrane. If the membrane pore diameter is comparable to the mean free path of the permeating gas, K can be expressed as a stun of a viscous and a non-vis-cous term... [Pg.103]

Mass transfer rates attainable In menbrane separation devices, such as gas permeators or dlalyzers, can be limited by solute transport through the menbrane. The addition Into the menbrane of a mobile carrier species, which reacts rapidly and reversibly with the solute of Interest, can Increase the membrane s solute permeability and selectivity by carrier-facilitated transport. Mass separation is analyzed for the case of fully developed, one-dimensional, laminar flow of a Newtonian fluid in a parallel-plate separation device with reactive menbranes. The effect of the diffusion and reaction parameters on the separation is investigated. The advantage of using a carrier-facilitated membrane process is shown to depend on the wall Sherwood number, tfrien the wall Sherwood nunber Is below ten, the presence of a carrier-facilitated membrane system is desirable to Improve solute separation. [Pg.39]

In Eig. 5.13 profiles of axial and radial velocity are shown at three axial positions for the annulus, the membrane and the packed bed. The profiles correspond to an a-alumina membrane with a relatively low permeability (Bo = 9.5 x 10" m ) and a mean pore diameter of dp = 3pm (compare with Table 5.1). The Knudsen number is approximately 10 for this membrane at the given conditions, so that only viscous flow occurs. Because the annulus is empty and the flow within it is laminar, the resulting profile for the axial velocity component is parabolic. Compared to the annulus flow, the axial velocity component in the membrane is... [Pg.123]

Physical Methods. Physical methods are divided into two general approaches. The pesticide is entrapped within a physical structure either at a molecular or micro-domain level or the pesticide in the form of a reservoir is enclosed within a polymeric envelope (2). In the first approach, the pesticide is mixed with the polymer (or other material with high energy density) to form a monohthic structure or matrix. Release is normally through diffusion through the matrix or dissolution and erosion of the matrix. In the second approach, structures are based upon a reservoir of the pesticide enclosed by the polymer, from nano-scale up to centimeter-sized devices. The shapes of these devices are varied and include spherical, such as microcapsules, and laminar or layered structures with the reservoir bounded by permeable membranes. These membranes provide a permeable barrier which controls the release rate. Other mechanisms of release include capsule rupture and erosion of the membrane. [Pg.1838]

The chloroplasts in green algae and plants are the seat of photosynthessi and producers of glucose-l-P. They are disc-shaped partides 3 to 10 (x in diameter and 1 to 2 p in thickness. It is possible to isolate them from leaves and show that they are bounded by a definite membrane which is semi-permeable. The chloroplasts contain a number of gratia whose diameter varies, according to the type of cell, from 0 2 to 2 (x. A chloroplast contains from 10 to 100 gratia imbedded in a protein matrix. The electron microscope reveals that they have a laminar structure. They contain 33 to 50% protein and also contain lipides. The chloroplasts are auto-reproductive and can divide. [Pg.354]

Reverse osmosis hoUow fiber Gas separation hollow fiber Hemodialysis hollow fiber Turbulent (shell-side fed) Laminar Laminar (entry region) Shell-side fluid Membrane Core-side fluid k 10 to 10 m/s Permeabilities Sh = 1.86 ReSc- PDF ODF ODF... [Pg.421]


See other pages where Membrane permeability laminar is mentioned: [Pg.161]    [Pg.448]    [Pg.339]    [Pg.467]    [Pg.58]    [Pg.83]    [Pg.136]    [Pg.194]    [Pg.846]    [Pg.72]    [Pg.63]    [Pg.965]    [Pg.966]    [Pg.846]    [Pg.515]    [Pg.658]    [Pg.151]    [Pg.44]    [Pg.790]    [Pg.624]    [Pg.525]    [Pg.966]    [Pg.1001]    [Pg.787]    [Pg.111]    [Pg.966]   
See also in sourсe #XX -- [ Pg.526 ]




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