Newly modified curved-bladed impellers for process intensification: Energy saving in the agitation of Hershel-Bulkley fluids

The power consumption in stirred tanks is a key parameter to determine the efficiency of a rotating impeller. This parameter is highly related to the viscous forces of the working fluid, especially when a complex non-Newtonian behavior exhibits. From this basis, an attempt is made in this paper to reduce the power requirements of Scaba 6SRGT impellers for stirring viscoplastic fluids in cylindrical unbaffled vessels. For this purpose, perforations are created in each blade of the impeller. Effects of the perforation diameter (d(p)/h = 0, 0.04, 0.07, 0.10 and 0.13), perforation shape (circular, lozenge, rectangular and triangular shapes) and number of perforation (n(b) = 0, 2, 4, 6, and 9) on the hydrodynamics induced and power consumption are investigated. The obtained results revealed an interesting decrease in power numbers by using the perforation technique. When changing the perforation diameter from 0 to 0.13 and the number of perforations from 0 to 9, Np is reduced by about 3.7 %-21.6 % and 2.6-6.7 %, respectively. In a comparison between the different shapes of perforation, the circular shape has allowed a reduction by about 3.8 % less than that for the other cases, which had almost the same power requirements.