Geometry static mixer

Fig. 12 CFD Images of the flow pattern as a function of the static mixer geometry for a periodic section of the reactor top double axe, bottom sieve plates...

Data for a Kenics twisted-ribbon static mixer geometry obtained by Baldyga et al. (1997) is shown in Figure 13-31. In this case only final yields for a complex reaction were measured. The static mixer used by Baldyga et al. (1997) was 0.04 m in diameter. The method developed above was used to simulate the reactions in the static mixer. Even though it is not true in individual elements of the static mixer, plug flow overall was assumed. Also, in contrast with the... 

Qualitative, numerical simulations were performed with the commercial tool FLUENT-5 to evaluate mixing efficiency [2], The simulations were oriented on concepts employed for conventional 3-D static mixing. The micro-mixer geometries were laid out using the GAMBIT predecessor as well as the meshing of surfaces and volumes and the specification of boundary conditions. Entrance and exit sections were also simulated. 

Bertsch, A., Heimgartner, S., Cousseau, P., Renaud, P., Static micromixers based on large-scale industrial mixer geometry, Lab Chip 2001, 1, 56-60. 

Endothermic reactions, such as steam reforming, are usually carried out in long narrow tubes filled with catalysts and externally heated by flames. The heat could be provided more uniformly and more accurately at the necessary level by a combustion catalyst coated on the outside of the tubes, and heat transfer rates could be further improved by coating the endothermic reaction catalyst on the inner wall of the tube. In this way, the heat of combustion is transferred to the heat sink (the endothermic reaction) through the solid wall, avoiding solid-gas heat transfer resistances. However, the tubular geometry is not most efficient for this application because of the difficulty to coat the inside of the tubes and the need to include static mixers to facilitate mass transfer to the catalytic surfaces. 

Class 1 equipment are also called column-type equipment. Under this category, there are the various multiphase contactors. Gas-liquid contactors include bubble columns, packed bubble columns, internal-loop and external-loop air-lift reactors, sectionalized bubble columns, plate columns, and others. Solid-fluid (liquid or gas) contactors include static mixers, fixed beds, expanded beds, fluidized beds, transport reactors or contactors, and so forth. For instance, fixed-bed geometry is used in unit operations such as ion exchange, adsorptive and chromatographic separations, and drying and in catalytic reactors. Liquid-liquid contactors include spray columns, packed extraction... 

The flow geometry in static mixers is complex and difficult to model. Velocity profiles, streamlines, and pressure drops can be computed using programs for... 

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. 

Numerous micromixers have been designed based on the prindple of laminar static mixers, where the fluid undergoes a periodic process of splitting, rotation and recombining. These mixers are inspired by chaotic mixing, where the geometry of the system imposes spatial periodicity. 

A. Bertsch, et al.. Static Micromixers Based on large-Scale Industrial Mixer Geometry. Lab Chip, 2001, 1. 

The left-hand side of Figure 6.10 shows the laminar static mixer model consisting of 3D geometry with three twisted blades of alternating rotations. The right-hand side of Figure 6.10 shows the computational mesh of the same laminar static mixer model. 

FIGURE 6.9 Geometry and computational mesh setup for the laminar static mixer. (Image made using COMSOL Multiphysics and is provided courtesy of COMSOL .)... 

Selecting Initial and Boundary Conditions Once the conservation equations are prescribed to the laminar static mixer computational model, the initial and boundary conditions must be applied to each geometry surface. Only appropriate boundary conditions completely describe the real-world physical system. 

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