Weber number static mixers

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). 

The predictive method for drop size is given in the Kenics Bulletin (May 1988, p. 28, Fig. 5-1) and in Figure 10.34. The ratio of Sauter mean drop size to the mixer ID (d/D) is a function of the Weber Number (V Dp/cr) and the ratio of dispersed phase to continuous phase viscosity (p-j/p.,). Now let s do two examples for static mixers. 

To define the iramiscible-liquid-segregation problem, the drop size range of the dispersed phase must be known or approximated. Weinstein and Middleman present drop correlations for pipeline contacting and static mixers while Coulaloglou and Tavlarides present correlations of liquid in liquid drop sizes for agitated vessels. All use the Sauter mean drop size definitions and involve use of the Weber number, a... 

Reynolds number for stirred vessel (impeller), p D /]I Reynolds number for spherical particle, PfVood/p,f Schmidt number, p,f/ppDab Suratman number for stirred vessel, PcaD/ Xj viscosity group for stirred vessel, (Pc/Pd) ttdND/0 for static mixer, (Pc/Pd) P-dV /0 Weber number for stirred vessel, PcN D /0 for static mixer, PcVg Dp/o... 

Literature data on dispersion in static mixers indicate that the Sauter mean diameter of dispersed drops can be correlated with Weber number and friction... 

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