Diffusers open channel

Solids-liquid-gas mixing 275 Solids-liquid mixing 275 Solids—solids mixing 275 Sonic velocity 150, 156,158, 189 Sorel effect, thermal diffusion 589 Spalding, D. B, 393,562 Sparrow, E. M. 465, 564 Specific energy, open channel flow 98... 

Facilitated diffusion within organisms takes place when carriers or proteins residing within membranes—ion channels, for instance—organize the movement of ions from one location to another. This diffusion type is a kinetic, not thermodynamic, effect in which a for the transfer is lowered and the rate of diffusion is accelerated. Facilitated diffusion channels organize ion movements in both directions, and the process can be inhibited both competitively and noncompetitively. It is known that most cells maintain open channels for K+ most of the time and closed channels for other ions. Potassium-ion-dependent enzymes include NaVK+ ATPases (to be discussed in Section 5.4.1), pyruvate kinases, and dioldehydratases (not to be discussed further). 

PP bead foams of a range of densities were compressed using impact and creep loading in an Instron test machine. The stress-strain curves were analysed to determine the effective cell gas pressure as a function of time under load. Creep was controlled by the polymer linear viscoelastic response if the applied stress was low but, at stresses above the foam yield stress, the creep was more rapid until compressed cell gas took the majority of the load. Air was lost from the cells by diffusion through the cell faces, this creep mechanism being more rapid than in extruded foams, because of the small bead size and the open channels at the bead bonndaries. The foam permeability to air conld be related to the PP permeability and the foam density. 15 refs. 

Taylor (T4, T6), in two other articles, used the dispersed plug-flow model for turbulent flow, and Aris s treatment also included this case. Taylor and Aris both conclude that an effective axial-dispersion coefficient Dzf can again be used and that this coefficient is now a function of the well known Fanning friction factor. Tichacek et al. (T8) also considered turbulent flow, and found that Dl was quite sensitive to variations in the velocity profile. Aris further used the method for dispersion in a two-phase system with transfer between phases (All), for dispersion in flow through a tube with stagnant pockets (AlO), and for flow with a pulsating velocity (A12). Hawthorn (H7) considered the temperature effect of viscosity on dispersion coefficients he found that they can be altered by a factor of two in laminar flow, but that there is little effect for fully developed turbulent flow. Elder (E4) has considered open-channel flow and diffusion of discrete particles. Bischoff and Levenspiel (B14) extended Aris s theory to include a linear rate process, and used the results to construct comprehensive correlations of dispersion coefficients. 

Since the number of ion-conducting channels is small, the rate of sodium passage through the open channels must be extremely rapid and has been estimated as -108 ions / s.433 This is within an order of magnitude of the diffusion-limited rate (Eq. 9-30). 

Experimental investigations of turbulence diffusion. A factor in transportation of sediment in open channel flow. J Applied Mechanics, 12 A91-A100. 

Like diffusion, ionic conduction is a thermally activated process. Low activation barriers are, therefore, achieved in the same manner. Geometric features, such as open channels, result in larger diffusivities (easier ion movement) because this lowers the magnitude of the AH terms in Eqs. 6.38 and 6.39. For example, in /3 alumina, the sodium ions are located in sparsely populated layers positioned between spinel blocks. Accordingly, they diffuse through these channels easily owing to the large number of vacancies present. 

Figure 17.11a shows a mixing induced by the turbulence produced by a submerged baffle. The arrangement in Figure 17.1 lb produces turbulence over and under the baffles. The arrangement shown in 17.11c is similar to the one shown in Figure 17.10c, except that in the former, the diffuser is installed in a closed conduit the latter is in an open channel. The arrangement in Figure 17.1 Id is also in an open channel and is equipped with a hanging-nozzle type diffuser.

Such processes as mechanical surface aeration, diffused aeration, spray fountains, spray or tray towers, open-channel cascades, and countercurrent packed towers are encompassed by the term air stripping. These procedures produce a condition in which a large surface area of the water to be treated is exposed to air, which promotes transfer of the contaminant from the liquid phase to the gaseous phase. This occurs because under normal conditions the concentration of the contaminant in ambient air is much lower than the concentration in contaminated water. 

Repair of the calcium gate/block due to diffusion occurs equally simply because of ionic depletion and competitive association. In particular, relaxation of the sodium or potassium ionic gradient in the vicinity of the open channel mouth quickly brings the levels of these ions locally to that of calcium. At that point, calcium competes effectively to bind to the phosphate. The system repairs to its resting state. The monovalent cations then can build up the concentration gradients observed through diffusion. 

Compared to the film model or the penetration model, the surface renewal approach seems closer to reality in such a case where the surface of liquid in an agitated tank is in contact with the gas phase above, or with the surface of a liquid flowing through an open channel. The values of s are usually unknown, although they could be estimated from the data acquired from carefully planned experiments. As with the penetration model, kL values should vary with diffusivity Do s. 

At one time calcium ions seemed to be the logical internal messenger between rhodopsin and the plasma membrane. If light absorption opened channels from the internal space of the rod discs, calcium ions could be released and diffuse quickly to the plasma membrane and block the entrance of sodium ions. However, light does not increase the free [Ca " "] in the cytoplasm but may decrease it from 500 nM to as low as 50 Stryer suggested that the essential... 

Mitochondria and cell death Although oxidative phosphorylation is a mitochondrial process, most ATP utilization occurs outside of the mitochondrion. ATP synthesized from oxidative phosphorylation is actively transported from the matrix to the intermembrane space by adenine nucleotide translocase (ANT). Porins form voltage-dependent anion channels (VDAC) through the outer mitochondrial membrane for the diffusion of H2O, ATP metabolites, and other ions. Under certain types of stress, ANT, VDAC, and other proteins form a nonspecific open channel known as the mitochondrial permeability transition pore. This pore is associated with events that lead rapidly to necrotic cell death. 

The upper diagram in Fig. 6.6 shows a simple device with a membrane on a porous support with a solid, porous body filling the sandwich. The central diagram is similar in concept except that there are distinct multiple layers of porous bodies. In both cases, however, there are no open channels, and the gas must diffuse along the length of the solid porous support to an exit chaimel. The lower diagram shows a membrane with multiple porous supports with the center piece containing channels to enable gas to diffuse out of the device to a collection manifold. This decreases the resistance to gas phase mass transfer of the device. 

---