Distributive static mixer

A number of approaches have been proposed for a continuous emulsification and improved control of product size distribution static mixers, membrane emulsification, and microchannel emulsification. For the last two, emulsions are produced by extruding a liquid through many individual pores or microchannels. 

A relatively recent development in static mixers is the Dispersive/Distributive Static Mixer (DDSM) [308]. This mixer is specifically designed to generate strong elonga-tional flow for improved dispersive mixing. The DDSM is an extension of the CRD... 

Two repeating units of the Dispersive/Distributive Static Mixer... 

Figure 12.55 Computed particle tracking in one module of the Dispersive/ Distributive Static Mixer using BEM...

Gramann, P.J., Davls, B.A., Osswald, T.A., Rauwendaal, C.J., A New Dispersive and Distributive Static Mixer for the Compounding of Highly Viscous Materials, SPEAN-TEC (1999)... 

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). 

A practical method of predicting the molecular behavior within the flow system involves the RTD. A common experiment to test nonuniformities is the stimulus response experiment. A typical stimulus is a step-change in the concentration of some tracer material. The step-response is an instantaneous jump of a concentration to some new value, which is then maintained for an indefinite period. The tracer should be detectable and must not change or decompose as it passes through the mixer. Studies have shown that the flow characteristics of static mixers approach those of an ideal plug flow system. Figures 8-41 and 8-42, respectively, indicate the exit residence time distributions of the Kenics static mixer in comparison with other flow systems. 

Figure 7.27. Twisted-blade type of static mixer operating in the laminar flow regime (a) Distributive mixing mechanism showing, in principle, the reduction in striation thickness produced (f>) Radial mixing contribution...

Figure 6. Experimental distributions from static mixer at 200°C A = Feed, B = Product ([I] =0.9 wt %).

The mixing sensitivity of (fast) polymerizations is known and frequently described in literature. This is due to the fact that radical polymerizations typically take 1 s until chain termination [125]. However, typical mixing times of large-scale mixers, including conventional static mixers, are longer. Accordingly, the course of mixing has an effect on the product quality, i.e. the polymer-chain distribution. 

Figure 4.74 Radical polymerization of acrylates in a iaboratory-scaie experimentai set-up with a Sulzer-type pre-mixer. Fouling at the feeding point of the static mixer (top) and molecular weight distribution (bottom) [125],...

OS 61] ]R 20] ]P 44] The polymer molecular-weight distribution of a static mixer-based processing, which was determined both by UV and refractive index analysis. 

Fig. 23. Screw sections for enhancing distributive mixing in single-screw extruders (a) Dul-madge mixer, (b) Saxton mixer, (c) pin mixer, (d) pineapple mixer, (e) cavity transfer mixer, (f) slotted screw flight, (g) Kenics and Ross ISG static mixers [148]...

S. Middleman, Drop size distribution produced by turbulent pipe flow of immiscible liquids through a static mixer, bid. Eng. Chem., Process. Des. Dev. 13(1), 78-83 (1974). 

Acid is normally added to the low-pressure RO feed-water supply line, which requires a static mixer to ensure rapid and even distribution of the acid. Problems can occur at this point if the mixing is not complete before the resultant lower pH water reaches the high/low pH controller, as the controller will shut off the feed-water supply to the RO (to avoid... 

Distributive Mixing with Traditional Static Mixer Designs... 

Fig. 7.43 The evolution of concentration distribution after 4, 10, and 20 elements with alternately left and right twisting plates at 140°. [Reprinted by permission from O. S. Galaktionov, P. D. Anderson, G. W. M. Peters, and H. E. H. Meijer, Morphology Development in Kenics Static Mixers (Application of the Extended Mapping Method), Can. J. Chem. Eng., 80, 604-613 (2002).]...

Static mixers, as reviewed in Chapter 7, contain mixing elements enclosed in a tubular housing through which radial mixing is achieved. They redistribute fluid across the flow channel and consequently rearrange temperature and composition distributions. They are often used to promote mixing in laminar flow systems thus having a pronounced effect on the RTD. 

Computational fluid dynamics (CFD) is an effective tool in analyzing the velocity distribution and other pertinent parameters in a static mixer. CFD is also being recognized as an effective tool in enhancing the performance of mixers and reactors, which is reviewed in Chapter 10. 

---