Prediction of just suspended speed for mixed slurries at high solids loadings

Just‐suspended agitation of solid mixtures

“…The second was a mixture of two small, high‐density materials for which the just‐suspended speed was found to be constant (74‐ to 125‐μm glass with density of 2500 kg/m 3 and 61‐ to 104‐μm nickel with density of 8900 kg/m 3 and Archimedes numbers of 15 and 46, respectively). Stating that the sum of powers approach did not include particle interaction effects, Ayranci et al excluded the higher loading data for these mixtures from their analysis.…”

“…The details of the four mixed‐density solid mixtures, which combine a low‐density solid and a high‐density solid, are outlined in Table . In three of the four systems, the sum of individual powers estimates are in good agreement with the experimental mixture just‐suspended speeds, supporting the two mixed‐density data sets reported by Ayranci et al An example of this behaviour is shown in Figure for the glass ( ρ s = 2440 kg/m 3 and d p = 600 µm)–melamine ( ρ s = 1450 kg/m 3 and d p = 200 µm) system. This system approximates that studied by Etchells et al in terms of the densities and sizes of the solids.…”

“…This includes a mixture of two sizes of silicon carbide ( ρ s = 3130 kg/m 3 and d p = 400 and 1000 µm), although the sum of individual powers estimate is consistently higher than the experimental mixture just‐suspended speed (with the experimental just‐suspended speed averaging 4% lower than the estimate). The data obtained with these four mixtures of high‐density solids support the finding of Ayranci et al that the sum of powers approach provides a good estimate of the mixture just‐suspended speed from the just‐suspended speeds of the individual solids.…”

“…This is because small particles are immersed in the viscous sublayer near the vessel base and wall and are thus exposed to lower liquid velocities than larger particles that extend farther into the liquid. Similar to the results of the present study, Ayranci et al found that the sum of powers approach over‐predicted the just‐suspended speed of two binary mixtures. The first was the bronze–glass mixture that was discussed previously for which the just‐suspended speed decreased at high glass fractions.…”

“…They found that this heuristic was rarely valid, with the mixture just‐suspended speed generally being higher than the speed that suspends the most difficult solid. In a reexamination of the data of the Ayranci and Kresta study, Ayranci et al reported that the mixture just‐suspended speed of five mixtures and the sand‐urea formaldehyde mixture of Etchells et al could be predicted from the sum of powers to suspend the individual solids. In a primarily computational study, Scully and Frawley applied a drag coefficient model to simulate the cloud height of a mixture of granular and needle‐like L‐glutamic acid particles in an agitated vessel.…”