Dispersion

For dispersing, three different cases have to be distinguished: when dispersing gas in a liquid phase a high mass transfer rate is the aim. Typical examples for this are hydrogenations or gassing operations in fermenters.

An example for dispersing of solid particles in a liquid is the incorporation of pigments in paints and lacquers. The incorporation of solid particles in liquids is the more difficult the finer the particles become and the bigger the surface tension of the liquid is.

Dispersion of two immiscible liquids is required for example for polymerization reactions or to make emulsions.

The droplet sizes of 0.5 to 500 mm that can be achieved in liquid-liquid dispersion can only be explained with the physics of micro-turbulence. In theory, the structure of micro-turbulence does not depend on the type of turbulence producer. There is, however, a zone of increased energy dissipation in the vicinity of the impeller whose intensity does in fact depend on the action of that impeller.

The dispersing effect occurs when the turbulent shear stresses induced in the droplets by the micro-turbulence cause a sufficient deformation of the droplet to counteract the stabilizing effect of surface tension resulting in the droplet being broken up.