Development of solid—liquid mixing models using tomographic techniques

Abstract

The need for tomographic technology to assist in the development of reliable correlations for scale-up of slurry mixing processes is described. In situ measurements of the axial and radial solid concentration profiles and vector velocities of particulates are required which indicate the effect of mixing impeller geometry, mixing speed, solid concentration and size distribution of solids on mixing performance. The current status of tomographic techniques that could be suited for the applications is assessed. Recent results obtained using the two methods of electrical resistance tomography (ERT) and positron emission tomography (PET) are described together with complementary measurements performed using an invasive single point conductivity probe. The effect of particle size on the “just suspension speed” N js, as determined from conductivity measurements, was compared with the Zweitering correlation (Th. N. Zweitering, Chem. Eng. Sci., 8 (1958) 244-253). Good agreement was obtained. The principle of using data derived from conventional probes and three-dimensional tomograms to yield mixing indices for control decision making is described.