Permeability values, range

The symbols Ko/K, Kg/K, and K /K are used to represent the relative permeabilities to oil, gas, and water, respectively. Obviously, relative permeability values range between 0 and 1. It has been found that, for a given porous medium, the relative permeability is a junction of saturation. Consider a system in which both oil and gas... 

Flow ratio index [kg/s], FRI = maximum solids flowrate expected after deaeara-tion of a powder in a bin. (Measures consistency small FRI for fine, highly compressible particles large FRI for particles > 400 gm, incompressible, very permeable.) Values range 0-90 kg/s. 

FIGURE 3.11 Range of hydraulic conductivity and permeability values. (After Freeze and Cherry, 1979.)... 

The applicability of an in vitro assay to classify drug substances is verified by demonstrating a rank-order relationship between the extent of human absorption and experimental permeability values with 20 model drugs. The model drugs should represent ranges of 0-50%, 50-89%, and 90-100% absorption (/a) and the results should clearly differentiate between HP and LP drugs. The model can also be characterized for the presence of functional active transporters (e.g., amino acids, di/tripeptides, monocarboxylic acids, nucleosides) and efflux mechanisms (e.g., P-gp, MRP). 

The Damkdhler-Peclet product also had an impact on performance the optimal value ranged from is 1.0 x 10 at 773K, to 1.0 x 10 at 873K. Little or no improvement was observed when the pressure in the tube was larger than the pressure in the shell, and no improvement was seen when the shell pressure exceeded the tube pressure. When the inert gas sweep rate was increased, the membrane reactor improved until the amount of sweep gas to reactant gas was approximately one hundred as seen in Figure 3. Once again there was an asymptotic limit to the amount of enhancement seen. There was no improvement when the permeabilities of any other component were increased over the permeability of methane. 

Fly ash is extensively used in civil engineering and is considered relatively impermeable with typical permeability values in the range 2 x 10 5 to 3 x 10 7m/s, but even at these... 

In calculating is is important to use the proper units those most commonly used by chromatographers are AP in bar (105 Pa), rM in seconds, dp in pm, t] in centipoise (mN s/m2), and L in centimeters. The most permeable columns are the most desirable, and they will have the smallest values of values ranging from about 500 for spherical microparticles to 1000 for irregular microparticles. 

Permeability is observed to vary enormously in what looks like homogeneous rock bodies, and it varies much more between the different rock types that constitute a studied system. Disregarding this large range of different prevailing permeabilities, mathematical models accommodate only single permeability values for entire case studies or for large sections of studied systems. Thus representative values are selected in the frame of a whole list of model simplifications. Such simplifications can lead to... 

Also the fact that only transcellular permeation is regarded in PAMPA experiments is valuable as it allows comparing PAMPA results to cellular permeation experiments that feature all possible permeation mechanism including paracellular or active transport and active efflux. Kerns (2004) recommended this comparison to get an insight into the permeation mechanism applied by a compound under investigation. The possibility to obtain permeability pH profiles is also really helpful to identify the relevant permeability value of a compound and cannot be determined by cellular assays due to the limited pH range usable with living cells. 

Scully et al. have reviewed the available data on H solubility and permeability in A1 and some of its alloys. Their review shows tremendous variability in the available data. However, H is very insoluble in A1 at 25°C and 1 atm pressure, with values ranging from 10 to 10 " atom fraction. They also concluded from data for A1 alloys that Li and Mg alloying additions increased the solubility of H in A1 because of their chemical affinity for H. A summary of the H diffusivity in A1 also revealed a wide range in values, but if it is assumed that the presence of aluminum oxide (AI2O3) on the surface is likely under all these tests, the fastest diffusivity is expected to be that closest to bulk diffusivity in Al, because this likely results from material with a defective or thinnest oxide film. There are several studies that resulted in diffusion coefficients at 25°C of about 10 cm /sec for Al. 

In the previous discussion of Darcy s Law only homogeneous fluid flow was considered. If the porous medium is only partially saturated with a fluid the permeability of the porous medium to the fluid will be less than the permeability obtained when the medium is 100% saturated. The permeability at less than 100% saturation is known as the effective permeability. Values of the effective penneability range between 0 and K where K represents the permeability at 100% saturation. The symbols Kg, Kg, and are used to represent the effective permeabilities to oil, gas, and water, respectively. 

Practitioners know from a description of soil based on grain size the range of permeability values to be expected. Table 2.4 shows the commonly accepted values. Classification systems may also show a range of values... 

Caco-2 cells are heterogeneous and their properties in final culture may differ based on the selection pressures of a particular laboratory. Direct comparison of compound permeability rates between laboratories is not possible unless the same Caco-2 cells and conditions are used. Therefore, transport rates and permeability classification ranges of specific drugs are expected to vary between reported studies. Most important is the ability to successfully classify compounds as low, medium, or high permeable drugs, and produce transport results that correlate to established human absorption values. 

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