Coefficient of permeability

Coefficient of permeability (cm/s) 1 0 1 o AASHTO T215/ASTM D2434... 

Figure 26.9 illustrates Darcy s law, the basic equation used to describe the flow of fluids through porous materials. In Darcy s law, the coefficient k, hydraulic conductivity, is often called the coefficient of permeability by civil engineers. 

Transmissivity is simply the coefficient of permeability, or the hydraulic conductivity (k), within the plane of the material multiplied by the thickness (T) of the material. Because the compressibility of some polymeric materials is very high, the thickness of the material needs to be taken into account. Darcy s law, expressed by the equation Q = kiA, is used to calculate the rate of flow, with transmissivity equal to kT and i equal to the hydraulic gradient (see Figure 26.22) ... 

Under conditions of internal restraint, the expansion produced is proportional to the ratio of steel to concrete and the dosage of the admixture. Special care should be taken to ensure that reinforcement is located in its proper position during placement and consolidation so that adequate restraint and good bond to steel is obtained. Restrained expansion increases the density of the matrix and produces concrete or mortar with a lower coefficient of permeability than that of corresponding Portland cement concretes and mortar. 

Figure 4. Comparison of coefficient of permeability as a function of air-voids content in sand-asphalt-sulfur and asphaltic concrete mixes (15,). Sand-asphalt-sulfur mixes were prepared with medium-coarse sand and 150/180 pen. asphalt. Key --------------, sand-asphalt-sulfur mixes andXKW. asphalt concrete.

SEA-OGFC mixes over conventional mixtures is reflected in their higher coefficients of permeability, Ky, and flooding rainfall intensity, If shown in Table 3 [50]. 

I AM column chromatography has also been used to predict the transdermal transport of drugs [42], The retention time, log kw (capacity factor extrapolated to 100% aqueous phase at pH 5.5, IAM column) and log Poet. were compared for the studied drugs (Tables 4.11 and 4.12). The coefficients of permeability through human skin, Kp, were not correlated with either log fcw or log Poet.. The authors had, however, pre-... 

There are two ferrite material properties which were not discussed in Section 9.3.1 but which are important in the inductor context they are the temperature and time stabilities of the permeability which, of course, determine the stability of the inductance. The temperature coefficient of permeability must be low, and this has been achieved for certain MnZn ferrite formulations as indicated in Fig. 9.18. A small residual temperature coefficient of inductance can be compensated by a suitable coefficient of opposite sign in the capacitance of the resonant combination. 

A convenient way to define the coefficient of permeability, in order to compare its value for different types of rocks, is to determine its empirical value for hydraulic gradients of 45°, that is, for Ah/Al=l. In such cases k=V. 

Fig. 2.9 Darcy s law applied to a groundwater system the velocity (V) at which water flows in the aquifer rocks is proportional to the coefficient of permeability (k) and the gradient (Ah/Al). This is a greatly simplified approach, and a number of assumptions have to be checked with hydrochemical methods (see text).

As stated in section 2.10, the velocity by which groundwater flows is commonly calculated from the water table gradient and the coefficient of permeability (k, or the related parameter of transmissivity). The k value is determined by a pumping test. During such a test a studied well is intensively pumped and the water table is monitored in it as well as in available adjacent observation wells. The change in water table level as a function of the pumping rate serves to compute the aquifer permeability. 

These membranes are used for the ultrafiltration of biological liquids (blood and urine), for hemodialysis in an artificial kidneys and for hemooxygenation in an artifidal lung The extraordinarily hi water permeability allows us to use the polyionic complexes as the additives to usual film-forming resins for preparing materials with a high coefficient of permeability to water vapor ... 

The coefficient of permeability of the wick F is related with porosity of the wick H, diameter of the particles and the coefficient of the tortuosity of the wick channels P... 

COEFFICIENT OF PERMEABILITY The gross velocity of flow of water under laminar flow conditions through a porous medium under a unit hydraulic gradient and standard temperature conditions (usually 20° C). Laboratory test results are usually expressed in centimeters per second. 

PERMEABILITY A property of a porous solid which is an index of the rate at which a liquid can flow through the pores. See COEFFICIENT OF PERMEABILITY. 

Table 23. Effect of the acetyl content on the coefficients of permeability PC, diffusion D and solubility S of CA membranes [143] ...

Velocity profiles across the capillary have a Poisseuille shaped flow and the expression predicts that the electroosmotic coefficient of permeability should vary with the square of the radius. In practice, it is found generally that this law is not as satisfactory as the Helmholtz-Smoluchowski approach for predicting electroosmotic behavior in soils. The failure of small pore theory may be because most clays have an aggregate structure with the flow determined by the larger pores [6], Another theoretical approach is referred to as the Spiegler Friction theory [25,6]. Its assumption, that the medium for electroosmosis is a perfect permselective membrane, is obviously not valid for soils, where the pore fluid comprises dilute electrol d e. An expression is derived for the net electroosmotic flow, Q, in moles/Faraday,... 

Therefore, the coefficient of permeability of the crack homogenization model, k, is defined by... 

The relation between coefficient of permeability k and crack length a/w is shown in Figure 8 for four cases of unit cell intervals h/w=0.125, 0.25, 0.5 and 1. The difference of coefficient of permeability becomes larger when the crack length become larger. 

The relation between effective compliance AJAf, and coefficient of permeability k is shown in Figure 10. As this figure shows, almost all results are also plotted on the almost same curve, and the characteristic point of the result is that the value of k is almost proportional to the value of AJka on the log-log plots in the range of AJXq > 2. 

Figure 8. Relation between coefficient of permeability and crack length.

Even if the permeation tests may be carried out with any Hquid, in general the coefficient of permeability is measured with water. One side of a sample of concrete is placed in contact with water (with pressure up to 10 bar) and either the depth of penetration by water in a given time, the time necessary for water to penetrate the entire thickness of the sample or the flow through the sample are measured. 

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