Micromixing phenomena

Each stage of particle formation is controlled variously by the type of reactor, i.e. gas-liquid contacting apparatus. Gas-liquid mass transfer phenomena determine the level of solute supersaturation and its spatial distribution in the liquid phase the counterpart role in liquid-liquid reaction systems may be played by micromixing phenomena. The agglomeration and subsequent ageing processes are likely to be affected by the flow dynamics such as motion of the suspension of solids and the fluid shear stress distribution. Thus, the choice of reactor is of substantial importance for the tailoring of product quality as well as for production efficiency. 

In turbulence theory, this is also known as the concentration macroscale, which plays an important role in the interpretation of micromixing phenomena. 

The case of reactors with two inlets was considered more than ten years ago by Treleaven and Tobgy (60). The BPT model allows an interesting representation of the flow in these reactors (56)(fi-gure 2). This will be useful when micromixing phenomena will be dealt with (next Section). 

Micromixing phenomena are the processes whereby different chemical species which are supposed to mix and react are coming into contact at the molecular scale. The result of imperfect micromixing is local unhomogeneity of the reacting mixture and this causes differences in the conversion and yield of chemical reactions, especially when portions of the fluid having reacted at different instants are mixed together. Fast reactions, combustions, precipitations, polymerizations may particularly be affected by these phenomena. 

Experimentally, many authors (see (J -6)) have tried to analyze micromixing phenomena using as an indicator the extent or yield of model reactions whose kinetics were known a priori. However to our knowledge, if one excepts the work of Bourne et al. O), the chemical method has not yet been systematically used to investigate the local state of micromixing at different points in a... 

By implication, therefore, processes which are particularly dependent on turbulent eddies and their associated forces are likely to be well correlated by energy dissipation rate. Bubble formation (Chapter IS) and micromixing phenomena (Chapter 10), for instance, fall into this category. However, processes which are dependent on the anisotropic ntain flows and for which the non-homogeneous nature of stirred tanks turbulence is significant, e.g. solid suspension and solid-liquid mass transfer (Chapters 16 and 17), are not well correlated that way. 

Villermaux, J. (1986) Micromixing phenomena in stirred reactors, in Encyclopedia of Fluid Mechanics... 

Villermaux, J. and R. David. Recent advances in the understanding of micromixing phenomena in stirred reactors. Chem. Eng. Comm. (1983), 105-122... 

Micromixing Phenomena in Continuous Stirred Reactors Using a Michaelis-Menten Reaction in the Liquid Phase... 

Villermaux, "Micromixing phenomena in stirred reactors". Encyclopedia of Fluid Mechanics Ch 27, Gulf Publishing Cy (1986)... 

Klein, J., R. David, and J. Villermaux (1980). Interpretation of experimental liquid phase micromixing phenomena in a continuous stirred tank reactor with short residence times, Ind. Eng. Chem. Fundam., 19, 373-379. 

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