Simulation of Mixing and Chemical Reaction

If reaction time is found to be critical, in-line mixers can be considered for liquid-liquid reactions because of their effectiveness in creating scalable drop size distributions and mass transfer rates (see Chapter 7 and Example 13-8a). 

Models that couple the local reaction and mixing processes allow simulation of the spatial variations of concentrations due to mixing and diffusion, and thus the rates of chentical reaction. These conpled models usually use some type of computational fluid dynantics (CFD) computer program as a basis for the calculations, as discussed in Chapter 5. Simulation methods may be divided into those 

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Paired-interaction closure [eqs. (13-29) and (13-30)] may be used in three dimensional simulations of turbulent mixed reactors with multiple simultaneous chemical reactions. The assumptions of the closure are that (1) only one concentration probability need be used to capture the most important aspects of the interaction of mixing and chemical reaction, and (2) that the reactants need only be considered in pairs and that higher-order interactions of the reactants are not important. These assumptions give a closure that is very fast to compute and results very close to experimental results (see Zipp and Patterson, 1998 Randick, 2000). 

Mixing and chemical reaction. We must now discuss the coupling between the mixing processes and chemical reactions. Simulations via the IEM model or the C-D model have already been presented in the preceding section. The key parameter is the ratio of... 

M3TD Groundwater MT3D is a transport model that simulates advection, dispersion, source/sink mixing, and chemical reactions of contaminants in groundwater flow systems in either two or three dimensions. 

The systems to be studied in some detail here involve various aspects of a continuous-flow, well-agitated vessel, with interacting variables such as flow, pressure, mixing, and chemical reaction. The study of stirred tanks is important for two reasons. First, stirred tank vessels are an important and frequent piece of process equipment, and engineers must be capable of modeling this kind of system. Second, the stirred tank concept is an important idealized lumped unit which can be used effectively by an experienced engineer to simulate the behavior of more complicated process equipment. 

D.L. Marchisio, Large eddy simulation of mixing and reaction in a confined impinging jets reactor. Computers Chemical Engineering, 33 (2), 408-420,2009. 

Simulation of mrbnlent flnid mechanics, mass transfer, mixing, and chemical reaction reqnires the nse of one (typically differential) balance equation for each... 

The earliest attempts to simulate mixing and chemical reaction in stirred vessels were based on the use of connected zones within which mixing and reaction took place. In some of these simulations, the flow in and out, Ls and e, were based on experimental data (Patterson, 1975 Mann and Knysh, 1984). It is now possible using standard CFD codes to numerically compute spatial distributions of Reynolds-averaged variables of the turbulent flow and mixing of miscible fluids with similar viscosities and densities in almost any geometry (see Hutchings... 

As the problem of the interrelation of turbulent mixing and chemical transformation is complicated and ambiguous, these processes are simulated together, as shown above in the diffusion model. However, separate analysis of these processes is also interesting in the estimation of their contributions to fast liquid-phase chemical reactions in real conditions. 

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