Agitation. Mixing - Basic theoretical concepts

Agitation techniques, which were long considered an art, are now based on both theoretical and experimental considerations, enabling a scientific approach to the problems posed. Enormous progress has been made, thanks in part to the accumulation of data on the operation of industrial units, and in part to the major research effort made by a number of companies and university laboratories specializing in agitation and mixing.

In very general terms, determining a stirring unit involves either selecting the right device for a new process, or extrapolating (or interpolating) the results obtained with a given device in the context of existing production.

The potential of the new experimental and numerical resources enables us to develop a local approach that complements the classic global approach to the operation of stirred tanks.

Local analysis of the operation of a stirred tank (figure A) gives access to the spatial and temporal distributions of velocity and turbulence. This information can help to understand and control mixing in the agitated tank, and may lead to optimization of its operation under different conditions.

In all cases, a good knowledge of the process is essential to enable the most favorable choice to be made, particularly from an economic point of view.