Water permeability measurement

RETORT CALCULATION During the retort process we assume that no oxygen is present so that only water transport is considered. At retort temperatures the diffusion coefficient of water in materials of interest is sufficiently high so that a pseudo-steady-state model, in which linear profiles are assumed across all structural layers, can be used. The EvOH layer is assumed to be at a uniform water activity at a given time which is good assumption based on water permeability measurements in EvOH at humidities found in package applications (13 ). 

An important part of the retort simulation for LEP and PEP structures is the temperature dependence of the polypropylene and polycarbonate water permeabilities. Measurements of polypropylene and polycarbonate water permeabilities were made using a MOCON Permatran-W and it was found that polycarbonate has a water permeability which decreases slightly with temperature whereas polypropylene increases with temperature. Near retort temperature the water permeabilities of both materials are similar at storage polycarbonate has a water permeability about ten times greater than polypropylene. Measurements shown in Figure 4 are in good agreement with previously reported results for polycarbonate (2,14-18) and polypropylene (5,19-11). ... 

Verkman, AS., Water permeability measurement in living cells and complex tissues, /. Membr. 

Rejection for BSA at 90%, Water permeability measured at 20°C. Salt concentration =1000 mg trans-membrane pressure = 0.5 MPa, MWCO molecular weight cutoff... 

Among these factors flic most difficult to quantify and thus to control are adsorption and fouling. In order to determine as much as possible about the actual structural character of the membrane, low interacting solutions should be used under conditions giving low fouling levels. However, since it is impossible in practice to avoid fouling completely, its influence on the porous stracture should always be evaluated. This can be accomplished by measuring the decline of flow rate with time and the pine water permeability measured before and after operation [130]. 

The pores between the rock components, e.g. the sand grains in a sandstone reservoir, will initially be filled with the pore water. The migrating hydrocarbons will displace the water and thus gradually fill the reservoir. For a reservoir to be effective, the pores need to be in communication to allow migration, and also need to allow flow towards the borehole once a well is drilled into the structure. The pore space is referred to as porosity in oil field terms. Permeability measures the ability of a rock to allow fluid flow through its pore system. A reservoir rock which has some porosity but too low a permeability to allow fluid flow is termed tight . 

Membrane Limitations Chemical attack, fouling, and compaction are prominent problems with RO and NF membranes. Compaction is the most straightforward. It is the result of creep, slow cold flow of the polymer resulting in a loss of water permeability. It is measured by the slope of log flux versus log time in seconds. It is independent of the flux units used and is reported as a slope, sometimes with the minus sign omitted. A slope of—0.001, typical for noncelhilosic membranes, means that for every threefold increase in log(time), 10 seconds, a membrane looses 10 percent of its flux. Since membranes are rated assuming that the dramatic early decline in permeability has already occurred, the further decline after the first few weeks is veiy slow. Compaction is specific to pressure, temperature, and envi-... 

Water Permeation of Nitrile Copolymers. While the AN content bears a direct relationship to the gas barrier, the water permeability presents quite an anomaly. If the water permeation of the commercial SAN films (25% AN) is measured, the rate is higher than that of polystyrene. Thus it appears that films with greater AN content have even higher water permeation rates. It was discovered, however, (I, 7) that as the AN content increases there is a shift in permeation, and the higher AN/S materials show water barriers of excellent quality. Table VIII... 

Water Permeation and Solute Separation through the Membrane. The measurements of water permeability of the 67 membranes prepared under different conditions were carried out by using an Amicon Diaflo Cell (effective membrane area, 13.9 cm2) under a pressure of 3 kg/cm2 at 25 °C. Some results are listed in Table 1067. It is apparent that much higher water absorption and permeability than the cellulosic membrane are characteristic of the 67 membranes prepared by both the casting polymerization and conventional casting. 

Ghosh [548] used cellulose nitrate microporous filters (500 pm thick) as scaffold material to deposit octanol into the pores and then under controlled pressure conditions, displace some of the oil in the pores with water, creating a membrane with parallel oil and water pathways. This was thought to serve as a possible model for some of the properties of the outermost layer of skin, the stratum comeum. The relative proportions of the two types of channel could be controlled, and the properties of 5-10% water pore content were studied. Ibuprofen (lipophilic) and antipyr-ine (hydrophilic) were model drugs used. When the filter was filled entirely with water, the measured permeability of antipyrine was 69 (in 10 6 cm/s) when 90% of the pores were filled with octanol, the permeability decreased to 33 95% octanol content further decreased permeability to 23, and fully octanol-filled filters indicated 0.9 as the permeability. 

It is obvious from Equation 14.14 that the most important parameter determining the volumetric air flow rate <2W is the intrinsic permeability K of soil. At this point it is important to stress the difference between water permeability (or hydraulic conductivity) k , air permeability ka, and intrinsic permeability K. In most cases, when permeability data are provided for a type of soil or geological formation, these data are based on hydraulic conductivity measurements and describe how easily the water can flow through this formation. However, the flow characteristic of a fluid depends greatly on its properties, e.g., density p and viscosity p. Equation 14.16 describes the relationship between permeability coefficient k and fluid properties p and p ... 

This condition has been recently used in a vaporization-exchange model for water sorption and flux in phase-separated ionomer membranes. The model allows determining interfacial water exchange rates and water permeabilities from measurements involving membranes in contact with flowing gases. It affords a definition of an effective resistance to water flux through the membrane that is proportional to... 

All symbols are defined at the end of the paper. Equation 10 defines the pure water permeability constant A for the membrane which is a measure of its overall porosity eq 12 defines the solute transport parameter D /K6 for the membrane, which is also a measure of the average pore size on the membrane surface on a relative scale. The Important feature of the above set of equations is that neither any one equation in the set of equations 10 to 13, nor any part of this set of equations is adequate representation of reverse osmosis transport the latter is governed simultaneously by the entire set of eq 10 to 13. Further, under steady state operating conditions, a single set of experimental data on (PWP), (PR), and f enables one to calculate the quantities A, Xy 2> point... 

In the same way, o-nitrophenyl octyl ether (o-NPOE) was immobilized on polycarbonate (PC) filters and the apparent permeability measured after 5 h incubation time was correlated to log Pnpoe for a series of reference compounds (log Pnpoe ranging from —1 to 3.6) [90]. Lipophilicity values in the alkane/water system were also determined using PAMPA with hexadecane-PC coated filters [89]. In this case, a correlation was found between intrinsic permeability (log Pq, permeability corrected for ionization and for unstirred water layer contribution, which particularly affects permeability of lipophilic compounds) and log P ik. However, log Pq is obtained from the knowledge of the pJC, value(s) and the permeability pH profile and therefore requires the full permeability pH profile to be measured for each compound, which negatively impacts the assay throughput. 

Fig. 3 Aquaporin deletion reduces osmotic water permeability in lung, but does not impair active fluid absorption, a AQP expression in epithelia and endothelia in nasopharyngeal cavity, upper and lower airways, and alveoli, b Osmotically driven water transport across the airspace/capillary barrier in perfused lungs from wildtype and indicated AQP null mice. Note the remarkable slowing of osmotic equilibration in mice lacking AQPl or AQP5. c Alveolar fluid clearance measured from the increased concentration of a volume marker 15 min after instillation of isosmolar fluid at 37°C. Where indicated, fluid absorption was inhibited by amiloride or stimulated by isoproterenol. From Bat et al. (1999) and Ma et al. (2000a)...

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