THE CHARACTERISTICS OF AERATED 12-BLADE AND 18-BLADE RUSHTON TURBINESAT TRANSITIONAL REYNOLDS-NUMBERS

Rushton turbines with 6, 12 and 18 blades have been studied under unae rated and aerated conditions in water and 0.8% CMC solutions giving fu lly turbulent and transitional flow regimes, respectively. In water, a s reported earlier, enhanced blade numbers give both a higher ratio of gassed to ungassed power, P-g/P, and a greater air handling capacity at an equal specific power input. However, in the transitional regime, it is found that these advantages no longer exist. This is because, a t these Reynolds numbers, the size of the gas-filled cavities is great er and independent of air flow rate. Thus, P-g/P falls to values as lo w as 0.4, regardless of the number of blades. Comparison with radial f low Scaba 6SRGT impellers in which the flat blade of the Rushton is re placed with one parabolic in cross-section shows that changing the sha pe is always a superior way of improving impeller performance, compare d to increasing the number of flat blades, especially if retrofitting is required.