Critical suspension conditions in stirred crystallizers

Experimental data are provided for the critical rotational speed, often referred to as the just-suspension speed N_js, necessary to maintain particles in suspension in a 15 1 draft-tube-magma (DTM) crystallizer with a profiled base. The results are compared with previously published data obtained for a flat-bottom tank. The combination of a draft-tube and profiled base improves significantly the suspension capability of the crystallizer. This is shown by a reduction in the value of N_js. The data obtained in the DTM crystallizer and previously published results from the flat-bottom tank are analysed using a simple model of suspension based on a balance between the gravitational force and the dynamic force acting on the particles at the critical point when they are lifted into suspension. Agreement between theory and experiment is satisfactory.