Stirred-Flow Cell

The rates of ion exchange for heterogeneous mixtures of ion exchanger may also be investigated in a stirred-flow cell. For a better understanding of the characteristics of the stirred-flow method, however, the results obtained for homogeneous systems are discussed briefly first [28]. This... 

The kinetic behavior of a well-defined heterogeneous mixture of ion exchangers in a stirred-flow cell has obviously not yet been investigated, neither theoretically nor experimentally. To remedy this situation an attempt is made to extend the theory for homogeneous ion exchangers to... 

Figure 13 Fractional attainment of equilibrium, U(t), for five size fractions of a polydisperse cation exchanger, simultaneously in a stirred flow cell (bottom) during their conversion from the pure A form to the pure B form. For the e Bu-ent solution, the concentrations, Ca/Ca, , for the ions A take up by the ion exchanger, and for the ions B released, Cb/c, , o, as a function of time are given (top). Because the total conversion of the ion exchanger is considered c,, = Flow rate 1.5 mk/s. Solid lines calculated with Eqs. (50), (51), and (52). Dotted lines calculated for a monodisperse system which assumes the panicle radius to be represented by the median radius of the polydisperse mixture.

Cd) from nonpolluted soils has also been investigated thoroughly, and pH-DOC synergic effects have been identified for some elements under certain scenarios (Strobel et al., 2001). Stirred-flow cells have also been presented as a promising vehicle to assess the metal readsorption phenomenon in the various steps of SEPs, the extent of which was found to be influenced by the element itself, the organic matter content of the sample, the extracting flow rate, and the metal concentration level (Chomchoei et al., 2002). 

In the serum replacement technique (2, 3), the dispersion is confined in a stirred flow cell. The confinement of the... 

Figure 8.5 Dispersion coefficient versus injected volume inflow injection analysis using a stirred-flow cell.

Convection occurs when a mechanical means is used to carry reactants toward the electrode and to remove products from the electrode. The most common means of convection is to stir the solution using a stir bar. Other methods include rotating the electrode and incorporating the electrode into a flow cell. 

Peter and Wang [266] invented a channel flow cell for rapid growth of CdTe films they showed that 2 p,m Aims can be deposited in less than 20 min, as opposed to the 2-3 h normally required in the conventional stirred single batch cells. The as-deposited films were structurally more disordered than the conventional ones, but after annealing and type conversion they became suitable for fabrication of efficient solar cells. A test cell with an AMI.5 efficiency approaching 6% was fabricated using a film prepared in the channel cell. 

Table 13 Influence of Stirring Flow Rate on the Permeability of [14C] Testosterone Across Caco-2 Cell Monolayer/Filter Support in 02/C02 Gas Lift Side-by-Side Diffusion at 37°C...

Figure 7. (a) Flow diagram of the optical fibre continuous-flow system for bioluminescence and chemiluminescence measurements S, sample C, carrier stream PP, peristaltic pump IV, injection valve W, waste FO, optical fibre FC, flow-cell, (b) Details of the optical fibre biosensor/flow-cell interface a, optical fibre b, sensing layer c, light-tight flow-cell d, stirring bar. 

Figure 8. Flow cell for electrochemilumiiiescence measurements (a) glassy carbon electrode (b) sensing layer (c) reagent solution outlet (d) Plexiglas window (e) liquid core single optical fiber (f) stirring bar (g) reagent solution inlet (h) platinum electrode.

Figure 10 Schematic diagrams of flow cells (a) flow cell using air bubbles for better stirring (reprinted with permission from Ref. 9), (b) flow cell using counterbalancing inlet flows, (c) flow cell with changeable volume (reprinted with permission from Ref. 10), (d) coiled flow cell (reprinted with permission from Ref. 11), and (e) fountain cell (reprinted with permission from Ref. 12). The arrows show the direction of the flow.

Figure 2 shows the essential parts of such an arrangement. There is a (smaller) cell with provisions for measurement of pH, titration, stirring with an inert stirrer, and gas bubbling through the solution. When the solution in this cell has been titrated to the selected pH value, a peristaltic pump takes the solution to the inlet of the flow cell. Before the solution comes to the metal electrode, it passes two thin holes in the bottom of the... 

Fig. 5.10 Computer-assisted extraction kinetics-measuring apparatus for highly stirred phases (A) high-speed stirrer (B) stirrer shaft (C) sample inlet (D) Teflon stirring har (E) Teflon phase separator (F) water hath (G) flow-cell (H) spectrophotometer (I) peristaltic pump (J) chart recorder (K) A/D converter (L) clock (M) minicomputer (N) dual-floppy disk drive (O) printer, (P) plotter. (From Ref. 16.)...

A dissolution testing apparams consists of a set of six or eight thermostatted, stirred vessels of an established geometry and volume from the USP guidelines. The dissolution apparatus provides a means to dissolve each sample, but does not provide a means to determine the concentration of the aetive ingredient in the bath. In the most well-established scheme, sipper tubes withdraw samples from each dissolution vessel and send them through a multiport valve to a flow cell sitting in the sample chamber of a UV-vis spectrophotometer. In recent years, moves have been made to make in situ measurements in the dissolution baths by means of fiber-optic probes. There are three possible probe implementations in situ, down shaft, and removable in situ (see Table 4.2). 

For fast or moderately fast liquid phase reactions, the stirred-tank reactor can be very useful for establishing kinetic data in the laboratory. When a steady state has been reached, the composition of the reaction mixture may be determined by a physical method using a flow cell attached to the reactor outlet, as in the case of a tubular reactor. The stirred-tank reactor, however, has a number of further advantages in comparison with a tubular reactor. With an appropriate ratio of... 

The most important effect of concentration polarization is to reduce the membrane flux, but it also affects the retention of macromolecules. Retention data obtained with dextran polysaccharides at various pressures are shown in Figure 6.12 [17]. Because these are stirred batch cell data, the effect of increased concentration polarization with increased applied pressure is particularly marked. A similar drop of retention with pressure is observed with flow-through cells, but the effect is less because concentration polarization is better controlled in such cells. With macromolecular solutions, the concentration of retained macromolecules at the membrane surface increases with increased pressure, so permeation of the macromolecules also increases, lowering rejection. The effect is particularly noticeable at low pressures, under which conditions increasing the applied pressure produces the largest increase in flux, and hence concentration polarization, at the membrane surface. At high pressure, the change in flux with... 

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