Hydrodynamics of solid and liquid phases in a mixing tank containing high solid loading slurry of large particles via tomography and computational fluid dynamics

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

“…Therefore, we speculate that even in more concentrated solid suspensions our ERT approach to evaluate N js using a linear sensing probe would still work. In fact, ERT was recently, and successfully, used in a study where high solid concentrations (30–50 wt%) were tested with multiple circular sensing geometries in order to assess the turbulent and hydrodynamics of the mixing of solid slurries of large particles (~700 μm) 44 . However, further studies are required to confirm that the ERT method proposed here would work also in such cases.…”

“…In this study, unlike other ERT studies focused on solid suspension in higher solids concentration ranges, 43,44 we have examined only very low solids concentration (0.2 wt%). Even in this case, the ERT method yielded quite satisfactory results, indicating that the ERT method is sensitive enough even at very low solids concentrations.…”

“…When the sensor rod was inserted vertically inside the tank, the image reconstruction algorithms embedded in the software generated 2D images of the conductivity distribution inside the tank on a vertical plane through the rod, extending about 1/3 of the length of the rod in the direction perpendicular to the electrodes, that is, radially toward the impeller shaft. This ERT apparatus was used to quantify the change in conductivity in the solid–liquid systems 44,61–63 examined in this work as the agitation speed was increased and more solids became suspended, as described below in greater detail.…”

“…More recently, electrical resistance tomography (ERT) has been used to characterize solid suspension in stirred tanks 43,44 . ERT is an experimental methodology through which the distribution of the local conductivities, and hence resistivities, of individual volume elements in a liquid mass inside a vessel, pipe, or another processing unit can be obtained by inserting a series of electrodes directly in the liquid or, nonintrusively, around the periphery of the container.…”

“…ERT investigations in the mixing area have often been focused on the determination of the degree of homogeneity and the experimental measurement of mixing time in stirred vessels, 46–52 which, in turn, are affected by different operating and geometric parameters, such as agitation speed, impeller shape and size, baffles, and impeller clearance off the vessel bottom 52–55 . Several authors have investigated solid suspension and distribution in tanks by using ERT for a wide range of solids concentration (1–50 wt%), 43,44 and for low impeller clearances 43 . Nevertheless, and to the best of our knowledge, a simple observer‐independent approach to extract N js from ERT data has not been fully developed.…”