Laminar mixing static mixers

In laminar flow, static mixers are typically required. The energy for mixing mnst be made available as pressnre that will be dissipated in the process. Line pressnre drop will be a design criterion. 

When it is deleterious, laminar flow can be avoided by mixing over the cross section. For this purpose static mixers in line can be provided. For very viscous materi s and pastes, screws of the type used for pumping and extrusion are used as reactors. 

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 7.29 shows a Sulzer type SMX static mixer where the mixing element consists of a lattice of intermeshing and interconnecting bars contained in a pipe 80 mm diameter. It is recommended for viscous materials in laminar flow. The mixer shown is used in food processing, for example mixing fresh cheese with whipped cream. 

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. 

Mixing in static mixers considered as chemical reactors was essentially studied by Nauman (165, 166). This author proposed a model which consists of a tubular reactor comprising N zones in laminar flow (parabolic velocity profile). Mixing between each zone is achieved accross a plane by a permutation of the radial position of fluid particles (r — , in this way the flowrate... 

Solvent Mixing. During gradient operation, the HPLC solvents that comprise the mobile phase must be mixed adequately, most commonly with either a static or dynamic mixer. Static mixers rely on laminar-flow dynamics, whereas dynamic mixers use magnetic stirrers. Solvent viscosity affects mixing characteristics inadequate mixing is detected by many UV detectors and may be expressed as an unstable baseline. 

Static mixers are widely used in situations where continuous in-line or pipeline mixing is required. Table 9.17 shows that applications span the entire spectrum from laminar to turbulent flow regimes, and they cover a wide variety of mixing processes involving the blending of gas-gas... 

FIGURE 9.43 Comparative mixing performance of various static mixers in laminar flow. 

Measured Laminar Mixing Efficiency for Selected Static Mixers... 

These interesting devices consist of a tube or duct within which static elements are installed to promote cross-channel flow. See Figure 8.5 and Section 8.7.2. Static mixers are quite effective in promoting radial mixing in laminar flow, but their geometry is too complex to allow solution of the convective diffusion equation on a routine basis. A review article by Thakur et al. (2003) provides some empirical correlations. The lack of published data prevents a priori designs that utilize static mixers, but the axial dispersion model is a reasonable way to correlate pilot plant data. Chapter 15 shows how Pe can be measured using inert tracers. 

The static mixers (SM) operate on the principle of repetitive dividing of a flow channel into at least two new channels, reorienting them by 90°, and dividing again. The flow is a pressure driven, laminar shear. Mixing by SM is related to the numbers of striations (N ) generated by a number of SM elements (n ) and the number of divisions (new channels) engendered by each element (n ) ... 

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