8.2.1 vessel geometry and liquid height
The shape of the base of stirred tanks affects the effects the efficiency of mixing. Several base shapes are shown in figure 8.2. If possible,the base should be rounded at the edges rather than flat;this eliminates sharp corners and pockets into which fluid currents may not penetrate,and discourages the formation of stagnant zones. The energy required to suspend solids in stirred tanks is sensitive to the shape of the vessel base:depending on the type of impeller and the flow pattern generated,the modified geometries shown in Figure 8.2 through (e) can be used to enhance paricle suspension compared with the flat-bottom tank of figure 8.2 in contrast,sloping sides or a conical base such as that shown in Figure 8.2 promotes settling of solids and should be avoided if solids suspension is required.