Turbulence in stirred tanks: Anisotropic, approximate, and applied

Over the last ten years, many ways of characterizing the turbulence in stirred tanks have been proposed, and the importance of the local rate of dissipation of turbulent kinetic energy (epsilon) to various processes has been clarified. In this paper, our understanding of the role of epsilon is examined for the blend time of miscible fluids, for drop break-up, for reactor design, for cell damage in bioreactors, for gas dispersion, for crystallization, and for flocculation and coagulation. The conceptual difficulties inherent in approximate measurements of epsilon are discussed with examples and background theory. Particular attention is paid to the various length and time scales present in the tank, the anisotropic nature of the flow field, and the effect of organized structures on turbulence measurements. Progress in the area over the last ten years is reviewed in the context of these limitations.