Maximum permeability

Fig. 4.50. Influence of composition on the second permeability maximum in Co Fej- tOt, ferrites (Bickford, Pappis Stull, 1955).

Figure 2 illustrates the operation of a precoat filter with cake in place. Point A represents the entrance of the cake into the unfiltered suspension. Point B Fepresents the point of emergence and C is the point at which the cake, together with its accumulated suspension particles, reaches minimum permeability. Maximum filtration... 

With moving bed flows, solids loading ratios of well over 100 can be achieved if materials are conveyed with pressure gradients of about 20 mbar/m of horizontal pipeline. For plug-type flows the use of solids loading ratio is not as appropriate, for as the materials have to be very permeable, maximum values are only of the order of about 30. Despite the low value of solids loading ratio, materials can be reliably conveyed at velocities of 3 m/s and below in plug-type flow. 

Optimal conditions conespond to a magnetic excitation value such as permeability of the material is maximum. 

Vacuum Outgassing and Permeability. Under vacuum, modified ethylene—tetrafluoroethylene copolymers give off Htde gas at elevated temperatures. The loss rate is about one-tenth of the acceptable maximum rates for spacecraft uses. Exposing 750-pm specimens for 24 h at 149°C to a high vacuum results ia a maximum weight loss of 0.12% volatile condensible material is less than 0.02%. 

The backfill is either poured into the borehole, or the anodes are enclosed in sacks of permeable material filled with backfill. Such anodes are sunk into the borehole and backfilled with water and fine soil. Anodes installed in this way deliver their maximum current after only a few days. 

The use of 5 pm particles permits the use of much longer columns due to the increased permeability. This, in turn, permits the use of much larger sample volumes. In fact, for a column 20 cm long, eluting a solute at a (k ) of 5, the maximum sample volume that can be used without increasing the peak variance by more than 10% will... 

PDMS based siloxane polymers wet and spread easily on most surfaces as their surface tensions are less than the critical surface tensions of most substrates. This thermodynamically driven property ensures that surface irregularities and pores are filled with adhesive, giving an interfacial phase that is continuous and without voids. The gas permeability of the silicone will allow any gases trapped at the interface to be displaced. Thus, maximum van der Waals and London dispersion intermolecular interactions are obtained at the silicone-substrate interface. It must be noted that suitable liquids reaching the adhesive-substrate interface would immediately interfere with these intermolecular interactions and displace the adhesive from the surface. For example, a study that involved curing a one-part alkoxy terminated silicone adhesive against a wafer of alumina, has shown that water will theoretically displace the cured silicone from the surface of the wafer if physisorption was the sole interaction between the surfaces [38]. Moreover, all these low energy bonds would be thermally sensitive and reversible. 

Sephadex type Grade Dry bead diameter (/urn) Fractionation range peptides and proteins (g/mol) Fractionation range dextrans (g/mol) Swelling factor (ml/g dry Sephadex) Maximum operating pressure" (cm H,0) Permeability Ko Maximum linear velocity" (cm/hr) Swelling time (h) ... 

For illite (Figure 3B) the total amount of Cs adsorbed is two orders of magnitude larger (ca. 0.26 atoms/A2) due primarily to the permanent charge developed by substitution of Al for Si in the tetrahedral sites and to less efficient filtering of the solution caused by lower sample permeability. The maximum amount of hydrated Cs that can be accommodated on the illite surface is ca. 0.023 atoms/A, close to the amount... 

Dissolved Gas. Gas which enters the borehole when penetrating a high pressure zone may not dissolve immediately in the mud. The free gas considered here is the gas entering the borehole minus the dissolved gas. Table 4-128 indicates the maximum volume of dissolved gas at bottomhole conditions expressed in percent of annulus mud volume. Thus, when entering a high pressure permeable formation this much gas will dissolve first before free gas appears in the mud. 

High sorption capacities with respect to protein macromolecules are observed when highly permeable macro- and heteroreticular polyelectrolytes (biosorbents) are used. In buffer solutions a typical picture of interaction between ions with opposite charges fixed on CP and counterions in solution is observed. As shown in Fig. 13, in the acid range proteins are not bonded by carboxylic CP because the ionization of their ionogenic groups is suppressed. The amount of bound protein decreases at high pH values of the solution because dipolar ions proteins are transformed into polyanions and electrostatic repulsion is operative. The sorption maximum is either near the isoelectric point of the protein or depends on the ratio of the pi of the protein to the pKa=0 5 of the carboxylic polyelectrolyte [63]. It should be noted that this picture may be profoundly affected by the mechanism of interaction between CP and dipolar ions similar to that describedby Eq. (3.7). 

The physical characterisation of membrane structure is important if the correct membrane is to be selected for a given application. The pore structure of microfiltration membranes is relatively easy to characterise, SEM and AFM being the most convenient method and allowing three-dimensional structure of the membrane to be determined. Other techniques such as the bubble point, mercury intrusion or permeability methods use measurements of the permeability of membranes to fluids. Both the maximum pore size and the pore size distribution may be determined.1315 A parameter often quoted in manufacturer s literature is the nominal... 

The expansion index [51,102,103], defined as the ratio of cell fresh weight to dry weight evaluated at the time of maximum fresh weight, is a more qualitative indicator of changes in cell/aggregate size, under various cultivation conditions. Wongsamuth and Doran [58] identified the filtration characteristics of suspensions of Atropa belladonna, specifically cake permeability, which is at least partially related to morphology, as a useful indicator of shear effects. 

Classical commercial ceramic porous materials, as those obtained via sol-gel processes, generally have adequate permeabilities but could present some drawbacks They indeed have a limited thermal stability and are generally not permselective enough their pores are in the mesoporous range and maximum separation factors correspond to Knudsen diffusion mechanisms. 

For ionizable molecules, the membrane permeability, P (Pc in cellular models), depends on pH of the bulk aqueous solution. The maximum possible Pm is designated Pq, the intrinsic permeabiUty of the uncharged species. For monoprotic weak acids and bases, the relationship between P and Pq may be stated in terms of the fraction of the uncharged species,, as Pm= Pofo, i-e. ... 

In a binary separation, the highest purity of integrated permeate occurs at 0 = 0. Purity decreases monotonically until it reaches the feed purity at 0 = 1. In a ternary system, the residue concentration of the gas with the intermediate permeability will reach a maximum at some intermediate stage cut. 

The maximum value for the tortousity was 30 and the value for the tortusity of each sample was estimated from the formation factor. The formation factor was taken either from resistivity measurents or estimated from NMR measurements and the Myers pore-combination model [37]. A comparison of the estimated permeability correlations is given in Figure 3.6.9. The SDR model overestimates the permeability of low permeability samples and the Chang model underestimates the permeability of high permeability samples. The modified Chang model, Eq. (3.6.9), improves the estimate of permeability for both low and high permeability samples. 

Permeability is also as reported in Barrier, one Barrier being equal to 1X10 1°P. It can be seen from Table I that no change either in permeability for C02 or C02/CH4 selectivity was obtained when the degree of bromination for PPO is low (6.5 mole%). However, at higher levels of bromination, there were increases in both permeability for C02 and C02/CH4 selectivity. The maximum effects (an increase of 2.47 times for C02 permeability and 1.45 times for C02/CH4 selectivity to that of PPO) were reached at 100% substitution degree of the aromatic ring. 

The shapes of permeability-pH profiles mirror those of solubility-pH (see, Figs. 6.1a, 6.2a, and 6.3a), with slopes of opposite signs. In solutions saturated with an insoluble compound, the product of solubility and permeability ( flux, as described in Chapter 2) is pH-independent This is indicated in Fig. 2.2 as the maximum flux portions of the curves. 

Figure 7.35 shows the characteristic log Pe-pH curve for a weak base, phenazo-pyridine (pKa 5.15). With bases, the maximum permeability is realized at high pH values. As in Fig. 7.34, the PAMPA assays were performed under iso-pH conditions (same pH in donor and acceptor wells), using the 2% DOPC in dodecane lipid... 

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