Osmotic flux

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),... 

The physical mechanism of membrane water balance and the formal structure of modeling approaches are straightforward. Under stationary operation, the inevitable electro-osmotic flux has to be compensated by a back flux of water from cathode to anode, driven by gradients in concentration, activity, or liquid pressure of water. The water distribution in PEMs that is generated in response to these driving forces decreases from cathode to anode. With increasing/o, the water distribution becomes more nonuniform. the water content near the anode falls below the percolation threshold of proton conduction, X < X. This leaves only a small conductivity due to surface transport of water. As a consequence, increases dramatically this can lead to failure of the complete cell. 

B - Breton B - Breton tion solute con- Osmotic, flux. (Note 2) thickness ... 

If a small molecule not carrying a charge has a migration time /m = 5 min, deduce the value of the electro-osmotic flux //ros. 

If the internal lining is rendered neutral there would be no more electro-osmotic flux and as a result the compound will no longer migrate towards the cathode but will reappear in the anode compartment. 

In brain research, microdialysis sampling employing a miniaturized dialysis unit (probe) containing a dialysis membrane of a few millimeters length has become popular. The probe is implanted into the tissue or organ of the test animal and is infused with an isotonic solution (typically at 0.5-25 L/min). A steady-state osmotic flux across the membrane removes molecules with a mass below the cutoff of the membrane from the extracellular matrix. Microdialysis yields relatively clean samples of volumes in the range 20-100 jU-L. However, the recovery of neuropeptides can be as low as 0.5-15%, leading to a low neuropeptide concentration in the samples [5,6]. 

Osmotic flux of water to and from the internal droplets, possibly associated with inverse micellar species in the oil phase... 

P Pohl, SM Saparov, YN Antonenko. The effect of a transmembrane osmotic flux on the ion concentration distribution in the immediate membrane vicinity measured by microelectrodes. Biophys J 72 1711-1718, 1997. 

Figure 5.52 Change in reduced osmotic flux through anion exchange membranes with temperature. ( ) anion exchange membrane with N-isopropylacrylamide component ( ) commercial anion exchange membrane (ion exchange groups benzyl trimethylammonium groups without N-isopropylacrylamide component). Reduced osmotic flux through the anion exchange membranes was measured between 4.0 N sodium chloride solution and pure water at different temperatures.

Heister K, Kleingeld PJ, Keijzer TJS, Loch JPG. (2005). A new laboratory set-up for mea-sinement of electrical, hydraulic, and osmotic fluxes in clays. Engineering Geology 77(3-4) 295-303. 

There are three main fluxes through the membrane. A proton flux that goes from anode to cathode, a water electro-osmotic flux that develops along with the proton flux, and a water-gradient flux. This last flux is sometimes known as the water-back flux or back-diffusion flux it is due to a difference in the chemical potential of water at the two sides of the membrane and may be in either direction although the direction is typically from cathode to anode due to water production at the cathode. In addition to the above three fluxes, there are also fluxes due to crossover of oxygen and hydrogen, which are described in Section 5.9. 

The basic mechanisms of membrane operation in an operating fuel cell are shown in Fig. 8. Proton flow, as the primary membrane process, induces water transport from anode to cathode by electro-osmosis. Stationary operation implies that the electro-osmotic water flux has to be balanced by an internal backflux. This requires an appropriate gradient in water content across the membrane as a driving force. The stationary balance between electro-osmotic flux and backflux, thus, establishes to a profile of water across the membrane. 

The initial mass increase in 4.0 M HCIO4 most likely reflects the presence of a threshold level of charge density within the polymer that can be tolerated before the osmotic flux of solvent becomes thermodynamically favored, which leads to a... 

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. 

Another problem is the flooding of the cathode CL due to the high electro-osmotic flux of water through the PEM, largely studied in the context of hydrogen-feed PEMFCs [22],... 

Using Eq. (3.78), thermo-osmotic flux in a one-component system may be written as. 

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