Turbulent micromixing in chemical reactors - a review *

Abstract The idea of micromixing, its definition and measures are outlined. The concepts of mixing environments and mixing earliness are presented. The paper concentrates on the effects of turbulent mixing of incompressible fluids in single-phase systems on the course of chemical reactions. The processes of turbulent micromixing are discussed in detail: the fluid mechanical interpretation of turbulent micromixing (effect of fluid element deformation on the acceleration of molecular diffusion, engulfing of environment, inertial—convective disintegration of large eddies and local intermittency) is presented. It is concluded that stretching of material elements and vortices, accompanied by molecular diffusion results in the growth of the mixing zones. The groth of the zone mixed on the molecular scale is a characteristic feature of micromixing and should be included in micromixing modelling. The characteristic time constants for the consecutive stages of mixing are presented and compared with the characteristic time for chemical reaction — the numerical criteria are outlined. The two approaches, i.e. eulerian and lagrangian, are described; it is shown that each requires different methods of description and generates specific problems (closure problem, problem of environment). The applications of the micromixing theory to the most important fields of industrial practice, such as complex reactions, precipitations and polymerizations, are outlined.