Electroosmotic water transfer

Figure 22.32a. The accumulation of chloride ions in the occluded solution reaches a stationary level, at which the rate of inward ion migration equals the rate of outward diffusion of the ions. Furthermore, the anodic chloride ion migration is accompanied by an electroosmotic flow of water molecules into the occluded solution. The final chloride concentration thus established in the steady state is determined by the ratio of the chloride ion migration rate to the electroosmotic water flow rate. It is therefore the transference numbers, Ter an(J tH2o, of chloride ions and water molecules that determine the chloride ion concentration in the occluded solution.

Some water will be transferred out of the depleting compartments by electroosmosis. The rate of electroosmotic transfer is determined by the nature of the membranes. E mates of the decrease in the amount of demineralized product because of this water transfer can be obtained from the supplier of the... 

Soil has long been considered as a chemical system due to its semipermeability to chemicals, bioactivity, interactions with chemicals, and so on. As a result, soil has been idealized as a leaky semipermeable membrane in chemical osmosis to explain various abnormal transport phenomena of water and chemicals in soil (Hanshaw, 1972 Marine and Fritz, 1981 Fritz and Marine, 1983 Yeung, 1990 Keijzer, Kleingeld, and Loch, 1999) as a Donnan membrane (Donnan, 1924) to examine the influences of soil type, water content, electrolyte concentration, and the cation and anion distribution in pore fluid on electroosmotic flow of fluid in soil (Gray and Mitchell, 1967) as a bioreactor to evaluate the impact of oxygen transfer on efficiency of bioremediation (Woo and Park, 1997) and so on. 

The last assumption means that local electroosmotic flux of water in membrane is exactly counterbalanced by back diffusion. Recent studies [14,27] have shown that in a wide range of operating conditions total transfer coefficient of water from the anode to the cathode does not exceed 0.2. Since electroosmotic drag coefficient in Nafion is 1.5 [28], we conclude that the average over the cell surface electroosmotic flux in the membrane is almost fully compensated for by back diffusion. Note that the local value of total water flux in the membrane may significantly deviate from the surface-averaged value, e.g. close to the outlet of the oxygen channel [27]. Nevertheless, assumption 5 seems to be a reasonable approximation. 

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