mixing suspensions in slender tanks

Industrial suspension mixing processes are carried out both in standard tanks (H/D =1) and in the tanks with height H/D > 1. When only one impeller is used in such slender tanks, it may be difficult to produce a suspension of desired homogeneity. Hence it may be necessary to install a larger number of impellers on the shaft.The aim of this study was to explain the mechanism of suspension formation in slender tanks (H/D = 2) with an increased number of impellers. On the basis of the solid bed height on the tank bottom, the position of the suspension - water interface and the concentration profile of solid particles in the suspension (standard deviation of solid body concentration) the operation of the impellers was estimated and conclusions were drawn on how and at what distance from each other to install them were presented.The location of the upper, highest impeller appeared to be specially significant. On the basis of this study it is recommended to locate the upper impeller so that its distance from the free liquid surface is less than 0.8 D. It was found that such a position of the highest impeller was also advantageous from the energy point of view.