A flow model has been proposed of a mixing vessel with a screw impeller and a draught tube. The volume of the mixed batch has been divided into a non-ideally mixed part, a so-called laminar distributor, and a stagnating volume. Convective exchange of mass takes place by recirculation of liquid between the non-ideal mixer and the laminar distributor. By the Laplace transform of the frequency functions for both regions and their summation, the time dependence has been determined of the local change of concentration in an arbitrary position within the system. Using results of measured pumping capacities and mixing times, relationships have been obtained between the model parameters and simplexes of geometrical similarity of the mixing system.
