Phase viscosity

Comparison of weighting methods for liquid phase viscosities. Mixture of n-hexane - n-hexadecane at 298 K. 

Static mixing of immiscible Hquids can provide exceUent enhancement of the interphase area for increasing mass-transfer rate. The drop size distribution is relatively narrow compared to agitated tanks. Three forces are known to influence the formation of drops in a static mixer shear stress, surface tension, and viscous stress in the dispersed phase. Dimensional analysis shows that the drop size of the dispersed phase is controUed by the Weber number. The average drop size, in a Kenics mixer is a function of Weber number We = df /a, and the ratio of dispersed to continuous-phase viscosities (Eig. 32). 

With regard to the liqiiid-phase mass-transfer coefficient, Whitney and Vivian found that the effect of temperature upon coiild be explained entirely by variations in the liquid-phase viscosity and diffusion coefficient with temperature. Similarly, the oxygen-desorption data of Sherwood and Holloway [Trans. Am. Jnst. Chem. Eng., 36, 39 (1940)] show that the influence of temperature upon Hl can be explained by the effects of temperature upon the liquid-phase viscosity and diffusion coefficients. 

The use of the nomograph is as follows Find the intersecting point of the curves of continuous phase and dispersed phase viscosities on the binary field (left side of nomograph). A line is drawn from this point to the common scale volume fraction of dispersed phase and continuous phase liquids. The intersection of this line with the Viscosity of Emulsion scale gives the result. 

Figure 4.21 demonstrates the effect of temperature on the resolution of PEOs on a TSK-GEL G6000PWxi. and G3000PWxl in series. Increased temperature will decrease mobile phase viscosity and improve diffusion, which will improve resolution. 

In the pneumatic pumping system, the pressure (and not the flow rate) is maintained constant as variations in chromatographic conditions occur. Thus, a change in mobile phase viscosity (e.g. gradient elution) or column back pressure will result in a change in flow rate for these types of pumps. The gas displacement pump in which a solvent is delivered to the column by gas pressure is an example of such a pneumatic pump. The gas displacement system is among the least expensive pumps available and is found in several low cost instruments. While the pump is nonpulsating and hence, produces low noise levels with the detectors in current use, its flow stability and reproducibility are only adequate. In addition, its upper pressure limit is only 2000 psi which may be too low in certain applications. 

Phase densities differ by a Phase densities differ by only about 10%. factor of 100-10,000 1. Viscosity in both phases is Liquid phase viscosity moderate, solid low. phase rigid. Phase separation is rapid Phase separation is slow surface-tension and complete. effects prevent completion. Countercurrent contacting is Countercurrent contacting is slow and quick and efficient. imperfect. ... 

Selection of columns and mobile phases is determined after consideration of the chemistry of the analytes. In HPLC, the mobile phase is a liquid, while the stationary phase can be a solid or a liquid immobilised on a solid. A stationary phase may have chemical functional groups or compounds physically or chemically bonded to its surface. Resolution and efficiency of HPLC are closely associated with the active surface area of the materials used as stationary phase. Generally, the efficiency of a column increases with decreasing particle size, but back-pressure and mobile phase viscosity increase simultaneously. Selection of the stationary phase material is generally not difficult when the retention mechanism of the intended separation is understood. The fundamental behaviour of stationary phase materials is related to their solubility-interaction... 

Hence it is the values of each viscosity, dispersed and continuous, and not just the viscosity ratio that is important in determining the average size. The average size increases with a decrease in either continuous or dispersed phase viscosity for fixed operating conditions. 

The average drop size increases with decrease in continuous or dispersed phase viscosity. 

Experimental observations show that the dense-phase viscosity for small Group A particles decreases significantly with pressure (King and Harrison et al., 1980 May and Russell, 1953) as shown in Fig. 11. However, the dense-phase viscosity of Group B and Group D particles... 

Andrews and Sundaresan (2005) have also extracted the filtered particle-phase viscosity from these simulations and found that at low particle volume fractions (0.0-0.25), the filtered viscosity varies nearly linearly with particle volume, and that it increases monotonically (and nearly linearly) with filter size. 

In dense systems such as encountered in solids suspension, particle-particle interaction may be important as well. Then, the closure of solid-phase stresses is an important issue for which kinetic theory models and solids phase viscosity may be instrumental (see, e.g., Curtis and Van Wachem, 2004). 

Efficiency the organic modifier can be used to adjust solvent selectivity as normally practiced in reversed-phase chromatography. Lowers mobile-phase viscosity and improves solute mass-transfer kinetics. 

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