Modified scaba 6SRGT impellers for process intensification: Cavern size and energy saving when stirring viscoplastic fluids

Mixing of a viscoplastic fluid using Scaba 6SRGT impellers in a cylindrical vessel has been studied. Cuts have been introduced in each blade of the impeller in order to reduce the power requirements. Effects of the cut-height (h(2)/D = 0, 0.015, 0.04, 0.065 and 0.09, respectively), cut-length (l/D = 0, 0.06, 0.12 and 0.18, respectively), and of the number of cuts (n(b) = 1, 2, 3, 4, and 5) on the hydrodynamics and power consumption were explored. The suggested designs, compared to the classical Scaba 6SRGT impeller, display a reduction in power number by about 20%, 19.9% and 66.6% when the cut-height, cut-length and number of cuts are changed from h(2)/D = 0 to 0.09, l/D = 0 to 0.18 and n(b) = 1-5, respectively. However, the increased surface area of cuts is accompanied by a reduction in the size of radial jet of fluid, resulting thus in a weakened axial flow and a decrease in cavern size. As a result, the best trade-off between the reduced power consumption and enlarged cavern size correspond to the case n(b) = 3, l/D = 0.12. The reduction in power number for this case is estimated to be as about 15%.