(406b) Power, Flow and Efficiency: Effect of Adding Tiplets on Impeller Efficiency

Impellers in stirred tanks can be considered as pumps and their performance can be assessed in terms of their power drawn, flow generated, and efficiency. The hydraulic efficiency is defined as the kinetic energy of the flowing fluid divided by the mechanical energy input by the impeller, or the mass flow efficiency is the mass of fluid pumped per unit of energy input by the impeller. Both definitions show that hydrofoils are the most efficient impellers and Rushton turbines, the least (Grenville et al., Chem. Engg., 2017).

Impellers also generate a trailing vortex at their tip where the high-pressure region on the front of the blade meets the low pressure on the back. This is the location of the highest energy dissipation rate within the vessel where break-up processes, such as and the dispersion of immiscible liquids, are controlled. But the energy dissipated in the trailing vortex is not available to generate flow, and there is evidence that suppressing the vortices with tiplets at the end of the impeller blades does increase their efficiencies. This result has been found for the Lightnin A6000 (with tips) and A6100 and the Philadelphia Mixing Solutions MHE and MHET (with tips) hydrofoils.

It is not clear that the increased efficiency results in, for example, an increase in the rate of blending, reducing the blend time, or a reduction in the power required to suspend particles in a slurry. Blending and solids suspension performance for impellers with and without tiplets will be compared and analyzed in terms of their power input and flow generation.