Permeability coefficient water

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. 

If the penetration involves the entire thickness of the sample, so that it is possible to measure the flow, Eq. (7) is written as  

For concrete of low porosity, high pressures may be required to obtain flow through the sample within reasonable time. In these cases, a permeability coefficient may be estimated (k m/s) by measuring the average depth of the wet front in time t (s), using Valenta s equation ky = Vj / (2 H t) where H is 

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Nodes, E.E., Mazur, P., Watson, P.F., Kleinhans, F.W., Critser, J.K. (1993). Determination of water permeability coefficient for human spermatozoa and its activation energy. Biol, of Reprod. 48,... 

Radiation Crossllnked PVA Meinbranes. The water and salt permeability coefficients of the radiation crossllnked PVA membranes, obtained by using equations 1 and 2 were found to decrease with increasing the applied pressure. A linear correlation was found between the reciprocal of the water permeability coefficient and the pressure, as shown in Figures 1 and 2, at various temperatures. This linear correlation can be expressed by the following equation ... 

Figure I. Dependence of the water permeability coefficient on pressure (radiation cross-linked, 86,000 mol wt, 100% hydrolyzed PVA )...

Figure 9. Effect of the duration of heat treatment at I75°C on salt and water permeabilities of PVA at 30°C (A) salt permeability coefficients (O) water permeability coefficients. Open symbols refer to 100% hydrolyzed, 86,000 mol wt PVA solid symbols refer to ]00%> hydrolyzed, 115,000 mol wt PVA.

A = water permeability coefficient (a function of the diffusivity of water through the membrane)... 

LP (hydraulic conductivity coefficient) K (water permeability coefficient) Minor both indicate water permeability... 

Table VI gives salt water permeability coefficients obtained at 60°C for the control samples and the stretched samples, and at an unknown, but higher temperature (probably about 75°C) for those samples idilch were ultrasonlcally stressed (en-sonlfled and thereby heated) during permeation. It is apparent that the presence of silica caused no difference in permeability, nor did the static stress of lOZ stretch (when corrected for the 10% decrease in thickness dilch occurred). However, a very striking result was that ensonlfIcatlon yielded a 370% Increase in permeability coefficient, tdilch could have been due to the excess heating.

Change in cell water = Permeability Coefficient x Driving Force. One version was reported in 1931, but the details are not appropriate for our purposes. However, it is evident that the higher the value of the permeability coefficient, i.e., the more permeable the cell membrane is to water, the more rapidly the cell will shrink to its equilibrium volume of 60. 

One of the earliest theoretical objections to the calculation of the water permeability coefficients of biological membranes was advanced by Dainty [22] in his excellent review on water relations in plant cells. He argues—and correctly so—that all the equations used in calculating permeability coefficients are based on the implicit assumption that the aqueous solutions on both sides of the membrane are so well stirred that the concentrations at the membrane faces are the same as the bulk concentrations. It is well recognized that such a situation is impossible to achieve... 

Table A3 tabulates and Figure 15.3 shows 17 permeability coefficient values for 11 compoimds (14 fully validated and 3 excluded data points 10 fully validated compoimds) measured in rat skin. This database is small and consists mainly of phenols, alcohols, and water. Because all chemicals in this database are of relatively low MW and many are structurally related (meaning that MW and log are correlated), log is more clearly linear with log than in Figure 15.1 and Figure 15.2. Water permeability coefficients are similar to human skin (i.e., 1.47 x 10" cm h" in rats compared to 1.18 x 10" cm h in humans). However, the permeability coefficient for paraquat in the rat is significantly higher than in humans (i.e., 3.07 X 10" cm h in rats compared to 8.70 x lO- cm h" in humans, a ratio of about 35). Paraquat permeability was similar in the haired and hairless rat.

L is the water permeability coefficient Ap is the transmembrane pressure difference Ax is the difference in osmotic pressure between the upstream and downstream sides of the membrane... 

Membrane performance is a trade-offbetween membrane selectivity and membrane productivity. Membrane selectivity, a (=A/B), is defined by the ratio of permeability of components through the membrane where A is the water permeability coefficient and B is the solute permeability coefficient. In the case of RO and NF membranes, water/NaCl selectivity for seawater RO membranes is about 10,000. The higher the selectivity, the lower the permeate flux or productivity. This relationship for various RO membranes used with dilute NaCl solution is shown in Figure 1.6. The shaded regions refer to different feed concentrations and to different types of membranes. The data is fairly independent of the feed concentration but is a function of the physical and chemical properties of the membrane. 

Table 1. Parameters that control the rates of moisture cure at 25°C volume of sealant that reacts with 1 mol of water (V), water permeability coefficient (P)...

The cured adhesive acts as a barrier for the permeation of water to the uncured material. Any water that passes through this barrier quickly reacts with uncured material, and thus the barrier is thickened. The rate (dn/dr) at which moles of water permeate unit cross section of the cured layer is given by Eqn. 1. Here p is the vapour pressure of water in the surroundings and P is the water permeability coefficient of cured adhesive. 

Figure 16. Arrhenius plot of water permeability coefficient for PVC/DOAB and PVC/SDHP composite membranes (PVC/arti-ficial amphiphile = 85/15 by weight).

The water permeability coefficient can be obtained via eq. V - 43 using experiments with pure water. Because the osmotic pressure difference is zero, there is a linear relationship between the hydrodynamic pressure AP and the volume (water) flux Jy (eq. V - 43), and from the slope of the corresponding flux-pressure curve the water permeability coefficient Lp can be obtained. Figure V - 3 is a schematic representation of the volume flux plotted as a function of the applied pressure for a more open membrane (high Lp) and a more dense membrane (low Lp). 

The water permeability coefficient A (also defined as the hydrodynamic permeability coefficient) is a constant for a given membrane and contains the following parameters (see also chapter V - 6.1). 

Eq. VI - 127 can be used to calculate the conversion rate when the water permeability coefficient of the pervaporation membrane is known. Figure VI - 77 shows a conversion curve for a value of B = 0 (traditional equilibrium batch process) and a value of B > 10. 

The hydraulic or water permeability coefficient (L ) can be determined from a simple permeation experiment Assume for a given membrane a Lp value of 5 lO m/hr. bar. The membrane has a rejection coefficient of 95% for NaCl and of 99.8% for NajSO< at 40 bar and 10000 ppm salt Calculate the solute permeability coefficient for both salts. 

A cellulose acetate membrane has a water permeability coefficient Lp = 2.105 g/cm=.s.bar and a solute (NaCl) permeability coefficient B = 4.10 cm/s. This membrane is used for a desalination experiment The feed concentration is 35 g/l of NaCl and the applied pressure is 60 bar. Calculate the water flux, salt flux, rejection coefficient and the concentration of NaCl in the permeate. The density of the solution is 103gfl. 

A homogeneous cellulosic ester membrane with a thickness of 20 im is placed in a pervaporation cell with a diameter of 10 cm. The permeate side is kept at a vacuum of I mbar.. In a steady state permeation experiment at 20°C 12.0 g of water is collected in 1 hours. Calculate the water permeability coefficient in moljn/m. s.Pa en in cm (STP).cm/cm7.s.cmHg. 

A porous polypropylene membrane with a water permeability coefficient of 4.2 m/s.bar is used in membrane distillation. Calculate the pure water flux for a feed temperature of 50 C and 90°C, respectively. The temperature at the permeate (distillate) side is 20°C. Neglect temperature polarization. 

Surface water with 5000 ppm NaCl must be desalted to a product quality of less than 300 ppm salt at a rate of 25 m /h. The membranes have a rejection of 97% (at 5000 ppm and AP = 15 bar) and a water permeability coefficient of 3.0 l/m2.h.bar. Calculate for a single pass system the required membrane area and the power consunqition for an applied pressure of 15 bar and 30 bar, respectively. 

Nitric acid is recovered from a 316 steel etching bath with diffusion dialysis. The inlet stream contains 1(X) g/1 nitric acid and 25 g/1 iron(II)nitrate. The outlet feed concentration is 19.4 g/1 of nitric acid and 22.6 g/1 of iron(U)nitrate. The inlet feed and dialysate flow rates are both 2501/h, and the inlet diaJysate is pure water and the dialysate contains no iron (II)nirrate.The average nitric acid concentration at the diluate side is 44 g/1 (dialysate inlet is pure water and outlet is 88 g/1). The membrane has a water permeability coefficient L = 240 l/m. dav.bar. 

The flux i.s given at 15 bar. 16 C and I5(X) ppm NaCl so that the water permeability coefficient A must be calculated under these conditions. The volume flux is given by... 

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