Osmotic water permeability coefficient

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... 

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). 

In 1981, Helfrich [7] studied the effect of the external osmotic pressure on egg yolk phosphatidylcholine (EPC) giant vesicles by adding 15 mM of salt or glucose in the external medium of the vesicles. The vesicle radius appears to decrease linearly with time according to the law d /dt = -aPAc, where P is the membrane permeability coefficient to water, a, is the water molar volume, and Ac, the difference of molar concentrations. The water permeability coefficient for EPC bilayers was found to be 41 pms . ... 

Equation (20-80) requires a mass transfer coefficient k to calculate Cu, and a relation between protein concentration and osmotic pressure. Pure water flux obtained from a plot of flux versus pressure is used to calculate membrane resistance (t ically small). The LMH/psi slope is referred to as the NWP (normal water permeability). The membrane plus fouling resistances are determined after removing the reversible polarization layer through a buffer flush. To illustrate the components of the osmotic flux model. Fig. 20-63 shows flux versus TMP curves corresponding to just the membrane in buffer (Rfouimg = 0, = 0),... 

TABLE 1. Biophysical characteristics of human fetal liver CD34 CD38 cells. Legends Vo - cell volume in isoosmotic solutions, Vb - osmotically inactive volume, Lp - permeability coefficient of membranes for water, p - permeability coefficient of membranes for DMSO cryoprotectant, a - reflection coefficient. 

A reverse osmosis unit is to demineralize 750,000 L/day treated effluent. Pertinent data are permeability coefficient = 0.2 L/(m day kPa) at 25 °C, pressure difference between the feed and product water = 2500 kPa, osmotic pressure difference between the feed and product water = 300 kPa, lowest operating temperature = 10 °C. 

In many cases, the difference between Pf and P can be attributed to the presence of an unstirred layer. On the other hand, in the case of human red cell membrane the difference cannot be accounted for by the presence of an unstirred layer [14]. Additional support for this difference between Pf and Pdealing with the effect of antidiuretic hormone (ADH) on water movement across epithelia. It was found that in the presence of ADH, the osmotic permeability coefficient of this tissue to water is 120 times greater than the diffusional coefficient (see Table 9.5 in [23]). 

Permeability coefficients of representative membranes and tissues to water under both osmotic and diffusional flows ... 

In his early analysis of isotonic transport. Diamond [13] tried to use measured values of the whole epithelial water permeability, Lp, in place of the quantity Llb-The unacceptably large osmotic deviations from isotonicity that he computed caused him to reject the elementary compartment model of the lateral intercellular space. We should reconsider, therefore, the requirements imposed upon the elementary compartment model by the experimental data on rabbit gallbladder (Table 1). For N/Cq = 1.47-10 cm/s and C/Q = 0.27, Eqn. 84 requires = 5.5-10 cm/s. Eqn. 86 may be used to give a lower bound on the coupling coefficient. If mucosal equilibrium is within 2% of exact isotonicity then — C /Cq = 0.02 so that y = 0.95. Thus, if Lp = 1.7- lO"" cm/s.osm, Eqn. 85 implies L b is at least 34-10" cm/s.osm. It remains to consider these model predictions for and Llb i relation to the pertinent experimental data. 

According to Eq. 6.11, the DMFC determination of the methanol permeability requires the knowledge of the methanol drag factor, because the electro-osmotic flux could afford for a considerable fraction of the methanol flow, particularly at high methanol concentrations. An important drawback of this method is that the methanol drag coefficient is not well known, so Ren et al. [299] assumed that it was similar to the water drag coefficient ( =2.5). However, some recent NMR [300] and electro-osmosis [301] studies would indicate that this assumption is not valid, leading to considerable uncertainties in the methanol permeability coefficients determined by this method. 

A simple example of a use of homogeneous membranes involves reverse osmosis in the purification of seawater or brackish waters for drinking and agriculture. The transmembrane pressure must be greater than the osmotic pressure of the salt water so that the solvent flux is reversed. Some 50 to 80 bars are required. Cellulose membranes are used because of their high permeability coefficient to water see Table 4.5. Applications include potable water aboard ships and agricultural uses where arid lands border seas. 

A vesicle system prepared with purified soybean lecithin in 1 mM KCl has an inner radius of 15 nm. The system is then diluted with a large excess of distilled water. Estimate the time required for the encapsulated ions to transfer into the outer continuous phase given that the permeability coefficient for both ions is 10 cm/s and that the dimensions of the vesicles do not change despite the change in osmotic pressure. 

High-intensity electric field pulses accelerated osmotic dehydration of carrot [18], A Fickian diffusion coefficient for water and solute increased exponentially with electric field strength. This effect was attributed to increased cell wall permeability, which was also manifested by the softening of product. 

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