Thread Content
It is generally determined based on the mixing range of the impeller; if the liquid layer is too deep, it is necessary to consider using multiple impellers. For low-viscosity liquids, such as those with a viscosity of less than 5000 mPa·s, the radial-flow impeller can stir the area within the tank over a range equal to 4 times the diameter of the impeller. Therefore, for the common case where the liquid layer depth H is equal to D, just one layer of impellers is sufficient. For progressive impellers, two layers are generally used only when the viscosity is very high, at 100 mPa·s, and the liquid layer height H is greater than 4d. For high-viscosity liquids, when the viscosity reaches 50,000 mPa·s, the range of liquid that can be stirred vertically is only half of the slurry diameter; therefore, it is necessary to increase the number of stirrer layers at this point. When the agitator is installed vertically at the center, the height C of the lower impellers of the paddle and turbine types from the bottom surface of the tank is generally 1 to 1.5 times the diameter of the paddle. To prevent sedimentation at the bottom, the impeller can also be placed lower, for example at a height from the bottom of C = D/100. The height of the top impeller from the liquid surface should be at least 1.5d; this is especially important when there are no baffles and the center of the liquid surface is sunken. If the stirrer is too close to the liquid surface, the impeller may become exposed due to the sinking of the surface. The C value for a forward-flow impeller is generally 1/3 of the liquid layer height.