Abstract Summary (Max 250 words)
Solids suspensions must be processed using mixing tanks in many industrial operations and some knowledge of the just-suspended speed (Njs) is required for tank design and operation. In this study, experiments were conducted using three geometrically similar mixing tanks (T = 0.4 m, 1 m, 2.5 m) to measure Njs for concentrated, coarse particle suspensions in steel mixing tanks. A range of sand particle diameters, mixture concentrations and suspending fluid properties was tested. Measurements of Njs measurements were obtained using a number of methods, i.e. (i) each of these tanks was custom-built to include a clear viewing window that extended from the bottom of the tank almost to the top so visual indication of the presence of a settled bed could be obtained; (ii) using a traversing gamma ray densitometer positioned just above the tank bottom; side-wall pressure taps (located at 0.2T, 0.4T, 0.6T, 0.8T and T off the tank bottom) so that the pressure gauge measurement (PGM) for Njs could be tested; and (iii) a novel “bed detector” placed on the external (outer) side of the tank bottom. This device, which was developed at SRC, is sensitive to the reduction in the rate heat transfer that would occur once a stationary bed of solids formed. We will compare the different Njs measurement methods tested during this study, and evaluate their performance over a wide range of test conditions. We also will compare the Njs results with predictions obtained using existing Njs correlations.
