Permeability typical values

The product flux obtained is determined by the applied pressure and the membrane resistance (or permeability). Typical values for applied pressures and fluxes are given in table 1.9. Present da industrial membrane processes involve microfiltration, ultrafiltration, nanofiltraiion and reverse osmosis. Other commercial membrane processes are elcctrodialysis. membrane electrolysis, diffusion dialysis, per aporation, vapour... 

Typical values for sedimentary rock permeability for the flow of hydrocarbons and other fluids are 100 millidarcies (md) or greater. Rocks exhibiting permeabilities of 50 md or less are considered tight, relative to the flow of most fluids. 

The changes of the C02 permeability and separation factor for C02/CH4, compared to the typical values of PPO standard are shown in Table II for PPO modified with different sulfonyl groups. The best enhancement was obtained for PPO containing phenyl sulfone groups. 

Four neutral lipid models were explored at pH 7.4 (1) 2% wt/vol DOPC in dode-cane, (2) olive oil, (3) octanol, and (4) dodecane. Table 7.5 lists the effective permeabilities Pe, standard deviations (SDs), and membrane retentions of the 32 probe molecules (Table 7.4). The units of Pe and SD are 10 6 cm/s. Retentions are expressed as mole percentages. Figure 7.22a is a plot of log Pe versus log Kd (octanol-water apparent partition coefficients, pH 7.4) for filters loaded with 2% wt/vol DOPC in dodecane (model 1.0, hlled-circle symbols) and with phospholipid-free dodecane (model 4.0, open-circle symbols). The dashed line in the plot was calculated assuming a UWL permeability (see Section 7.7.6) Pu, 16 x 10-6 cm/s (a typical value in an unstirred 96-well microtiter plate assay), and Pe of 0.8 x 10-6 cm/s... 

The effective diffusivity is obtained from D, but must also take into account the two features that (1) only a portion of the catalyst particle is permeable, and (2) the diffusion path through the particle is random and tortuous. These are allowed for by the particle voidage or porosity, p, and the tortuosity, rp, respectively. The former must also be measured, and is usually provided by the manufacturer for a commercial catalyst. For a straight cylinder, rp = 1, but for most catalysts, the value lies between 3 and 7 typical values are given by Satterfield. 

Equation 6 Calculation of optimum ratio of particle size and column length, with selectivity factor, a capacity factor of second component of critical pair under analytical chromatography conditions, fe 02 diffusion coefficient, (cm /s) (typical value for MW 1000 10 cm /s) viscosity, p (cP) specific permeability (1.2 X 10 for spherical particles), feo third term of the Knox equation, C and maximum safe operating pressure, Ap, (bar). 

The best way to use the Kozeny-Carman model and other permeability models (e.g. the anisotropic model by Gebart) [18], is to use them as interpolation formulas for intermediate volume fractions between known values. Extrapolation should be done with extreme caution because the models are developed for idealized reinforcements. Typical values for the permeability of different types of reinforcement are given in Table 12.1. 

The typical value of DM permeability varies from 1 to 10 Darcy (1 Darcy = 10-8 cm2) from Gurley measurement. 

Some typical values of permeability and porosity for a few materials are shown in Table 10.1. 

The specific surface area, like the PSD, is thus a quality whose value depends on how it is defined, and is liable to be affected by any pretreatment or conditions affecting the degree of flocculation. In practice, air permeability methods are widely used. Typical values are 300-350 m kg for modern ordinary Portland cements and 400-450 m kg " for rapidhardening Portland cements. 

Eq. (7.15) can be used to estimate the optimum particle size squared over the column length. Typical values for the column permeability factor, ko, is I x 10 the Knox parameter, C, is 0.1 and the molecular diffusion coefficient 1 x 10 cm-/s for small molecules and 1 x 10 cm /s for proteins. The SI units for solving these equations are AP (pascal or N/m-), p (Pas or N s/m ) and D, (m /s) to give dp and L in m. Thus, typical units for pressure are converted from psi to pascal, typical units for viscosity are converted from centipoise to poise and typical units for diffusion coefficient are converted from cm /s to m /s. 

The permeability of liposomes to other cations also seems to depend on the size of the vesicle In small vesicles, sodium permeability ranges around 10 14 cm/s, whereas in large vesicles, sodium permeability is about 100-fold greater. The permeability of lipid bilayers to monovalent anions like chloride is consistently higher typical values are in the range of 10 10 cm/s. The question of greater anion permeability has been addressed by Flewelling and Hubbell (22), who concluded that permeability is in part a function of a dipole potential at the bilayer surface that favors permeation of anions. 

Values of k for natural porous materials vary widely. Typical permeability values for soils are clean gravel 10 9 10 7 m2, clean sand 10-11 10 10 m2, peat 10 13 10-11 m2, stratified clay 10-16 10-13 m2, and unweathered clay 10-2° 10-16 m2. Table I shows typical values of permeability. In some literature, especially in the early studies, the unit of Darcy (cm2cP/atms = 0.987 X 10 12 m2) is also used. 

In the second case, the fault model, the same matrix mesh is employed, but with the addition of a single 2-D embedded planar fault. The orientation and dip of the fault have been estimated from the seismic location data for cluster a. The matrix permeability is held constant at a typical value for intact crystalline rock and the fault diffusivity is calibrated to match the observed 4.5 month time delay of the pressure wave to 2 km depth. 

This group of soft-ferrite applications is based on their ability to transform ac signals of small amplitude into substantially large variations of magnetic flux. The fact that at low fields the initial permeability is a linear function of the field explains the name these devices are also known as small-signal applications. There are other materials, such as metallic alloys (see Chapter 6), which possess permeability values considerably higher than the typical values of ferrites however, as frequency increases, conductivity losses prevent efficient use of metallic materials. 

The critical current densities of the samples in Table I were calculated from the local magnetic inductions measured by means of an ac method (/=llHz), as described by Rollins et al Tc and Bc2 were taken from common permeability measurements. These data and typical values for at T = 4.2 K, Bdc = 2.5 T, and a distance of 2 /im from the surface are given in Table II. The values of Tc and Bc2—measured up to 6 T—represent the middle of the transition. For the sample reacted at 1850°C, the onset of Bc is used. The transition width of this sample was approximately 10 times larger than those of the others, which were typically 0.1 K. 

A porous material is said to have a permeability of 1 darcy if a pressure gradient of 1 atm/cm results in a flow of 1 cm /s of a fluid having viscosity of 1 cP through an area of 1 cm. In S.I. units, it is expressed as m and 1 darcy i lO m. Evidently, the lower the permeability, the greater is the resistance to flow. Typical values of permeability range from 10 m for fibre glass to for silica powder and limestone. 

Permeability constants for membranes must be determined experimentally for the particular type of membrane to be used. For cellulose acetate membranes, typical water permeability constants A , range from about 1 x 10to 5 X 10" kg solvents/s m -atm (Al, M3, Wl). Values for other types of membranes can differ widely. Generally, the water permeability constant for a particular membrane does not depend upon the solute present. For the solute permeability constants of cellulose acetate membranes, some relative typical values are as follows, assuming a value of = 4 X 10 m/s for NaCl 1.6 x 10 m/s (BaClz), 2.2 X 10" (MgClz), 2.4 x 10 (CaClj), 4.0 X 10 (Na2S04>, 6.0 x 10 (KCl), 6.0 x 10 (NH4CI) (Al). 

Paint coated materials are exposed primarily to the natural atmosphere. Consequently, paint adhesion is influenced by atmospheric factors, particularly moisture and water. All organic polymers and organic coatings are permeable to water. They differ only in the degree of permeability. Table 12.1 provides typical values for the permeability and the diffusion coefficient for water in a number of different polymers. 

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