Mass Transfer in Dilute Solid–Liquid Stirred Tanks

This work deals with solid–liquid mass transfer in dilute solids suspension. The dissolution dynamics of salt particles in water are determined in two baffled tanks of similar geometry and different dimensions stirred by Rushton turbines, Pitched Blade Turbines and Lightnin A310 impellers. The liquid conductivity variation during the salt dissolution is measured locally by electrical resistance tomography. The mass transfer coefficient, k L, that ranges from 2.7 × 10–5 to 1.5 × 10–4 m/s, is obtained from the conductivity time traces as a function of the operating conditions and the stirred tank geometry. Stirring conditions aimed at energy savings are also considered. A dimensionless correlation for the mass transfer coefficient in dilute solid–liquid systems is proposed. It matches fairly well the experimental data collected in this and previous investigations, being the overall estimated error equal to 19% for tanks stirred by Rushton turbines, and its applicability can be easily extended to other impellers.