Determination of the just-suspended speed, N_js, in stirred tanks using electrical resistance tomography (ERT)

N_js, the minimum agitation speed to just-suspend dispersed solids in liquids in stirred tanks, is a critical parameter to operate industrial processes. The focus of this work was to develop a novel observer-independent method to experimentally obtain N_js in tanks that cannot be visually inspected internally using electrical resistance tomography (ERT). The mean bulk resistivity was measured across electrodes mounted on an ERT linear sensing probe placed inside a stirred tank containing water and glass beads. 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 that could be analyzed to determine N_js. The N_js values obtained with this novel approach compared very favorably with those obtained using other methods requiring transparent tanks. It is expected that the ERT method proposed here could find applications in many industrial solid–liquid mixing processes.