Nonwetting liquid phase

Osmotic distillation (OD), sometimes called isothermal membrane distillation, is a membrane process in which a liquid phase (usually an aqueous solution) containing one or more volatile components flows across one surface of a microporous membrane whose pores are not wetted by the hquid, while the opposing surfece is in contact with a second nonwetting liquid phase (usually an aqueous solution) in which the volatile components are soluble or miscible [35]. The device is similar to the membrane contactor (MC) discussed in Chapter 1, which contains hollow fibre membranes that are hydrophobic (non-wetting. 

As demonstrated in Chapter 1, foam is a gas phase dispersed within a liquid phase and stabilized by surfactant adsorbed at the gas—liquid interfaces. In reservoir applications, foams are usually formed by nonwetting gases, such as steam or nitrogen, dispersed within a continuous, wetting aqueous phase containing surface-active agents. Foams formed with dense... 

Adhesion of gas bubbles to solid particles. In the hydrometallurgical process, flotation, gas bubbles are attached to ore particles and carry them to the surface of the liquid phase. The attraction force is adhesion of circular line elements at the contact of a nonwetted solid phase (ore), liquid phase (aqueous solutions of flotation agents), and gas phase (air or hydrogen bubble). This system is presented in Figure 1.17. 

The pore spaces in earthen materials may be occupied by gases, liquids, or both. For example, with respect to the liquid phase in a soil, a diy soil results when the pores are completely occupied by a gas, typically air (Fig. la), whereas a saturated soil results when the pores are completely filled with a liquid, typically water (Fig. lb). An unsaturated soil results when the pores comprise both a gas and a liquid (Fig. Ic). In the case of unsaturated soils containing both water and air (Fig. Ic), the water is the wetting fluid because the water is preferentially absorbed (i.e., relative to the air, the nonwetting fluid) to... 

If xis Xsv 180° and completely hydrophobic behavior occurs. Systems exhibiting 0 > 90° are considered non wetting. Thus, if the vapor phase likes the solid phase (i.e., has lower interfacial energy) more than the liquid phase likes the solid phase, nonwetting behavior will occur. 

Consider the P- P plot of a pure substance with a flat interface between the equilibrium gas and liquid phases (see Fig. 2.45). Sketch the P-T plot for the same system when the interface between the equilibrium gas and liquid phases has a constant curvature. Assume liquid is the wetting phase and gas is the nonwetting phase. What would be the results if gas were the wetting phase ... 

FIGURE 1.6 Young-Laplace representation of a three-phase contact line between solid, liquid, and gas phases. Cases of wetting and nonwetting liquids. 

The net adhesive force between the particles in a contact formed in a nonwetting liquid, p i, is given by the sum of the molecular adhesive force between the particles, p, acting in the gas phase and the capillary attractive force, Ap=p + ph... 

The problem of two-phase flow through noncircular ducts has received considerable attention in the last decades " and was studied specifically by Ransohoff and Radke. They addressed the problem of the low Reynolds number wetting liquid flow in a noncircular capillary occupied predominantly by a nonwetting gas phase by presenting a solution in terms of a dimensionless flow resistance, fi, depending on corner geometry and fluid parameters. 

The approximate overall effectiveness of Eq. 7.24 above can be used for reactor design for first-order reactions. For nonlinear kinetics, however, it is difficult to obtain an analytical expression for the overall effectiveness factor that is accurate for partially wetted pellets. Even when a relatively accurate effectiveness factor is available, the presence of different bulk and interfacial concentrations in both phases reduces the utility of the overall effectiveness factor except for limiting cases. Therefore, an internal effectiveness factor applicable to both wetted and nonwetted parts of the pellet is used here instead. For the low liquid velocities being considered, only dispersion in the liquid phase need be considered, and the gas phase may be treated as though it were in plug-flow (Levee and Smith 1976). 

The discussion presented above is valid whether absorption of a gas into a liquid or desorption of a gas from a liquid is carried out. If a vapor is absorbed into a liquid, the same considerations are valid. If stripping is implemented via vacuum in a nondispersive fashion, the pressure conditions for the two-phase system and the wetting criterion remain unchanged to ensure that the hydrophobic porous membrane remains nonwetted. If, however, the liquid phase exists inside the pores, then to achieve nondispersive operation, the gas-phase pressure should be equal to or greater than that of the liquid phase (Karoor and Sirkar, 1993). Vacuum stripping is not possible with liquid in the membrane pores, that is, wetted pores it is necessary to have a nonporous coating on the side of the membrane where the gas-liquid interface would have been loeated otherwise (Sirkar, 1992). 

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