(671e) Application of Electrical Resistance Tomography (ERT) to Solid-Liquid Mixtures in Stirred Vessels for the Determination of the Just-Suspended Speed, Njs

The minimum agitation speed to just-suspend finely dispersed solids in liquids in stirred vessels, often referred to as N_js, is a critical parameter to operate industrial mixing processes. A novel observer-independent method was developed using Electrical Resistance Tomography (ERT) in order to experimentally obtain N_js in vessels that cannot be visually inspected internally. Accordingly, the mean bulk resistivity was measured across electrodes mounted on a single ERT linear sensing probe placed vertically inside a stirred tank containing water and glass beads as the dispersed phase. As the agitation speed increased, more solids became suspended and the resistivity measured by the probe changed. Plots of resistivity variation vs. agitation speed resulted in an S-shaped curve, which was then mathematically analyzed by using several methods to extract the value of N_js. The N_js values obtained with this novel approach compared very favorably with those obtained using other methods requiring transparent tanks, namely the visual observation method originally developed by Zwietering (Zwietering TN. 1958. Chem. Eng. Sci. 8:244-253), and the imaging method recently developed by our research group (Teoman B, Shastry S, Abdelhamid S, Armenante PM. 2021. Chem. Eng. Sci. 231, 116263). It is expected that the novel ERT method proposed here could find wide applications in many industrial solid-liquid mixing processes.