Prediction of cloud height for solid suspensions in stirred tanks

For solids loadings greater than 10 weight percent in a stirred tank, a clear interface may form towards the top of the vessel at what is known as the cloud height. Under these conditions, mixing between the lower solids rich volume (the cloud) and the upper clear volume is very limited. This is of critical importance in slurry catalyst reactor design, as the poor mixing in the clear layer will lead to large amounts of unreacted fluid. This investigation concentrates on developing a model for the prediction of the solids cloud height. The model is based upon two essential features of the flow: the velocity decay in the three-dimensional wall jets which form along the baffles, and the impeller speed required to fully suspend the solids off the bottom of the tank (N-js).