CHARACTERIZATION OF 3 DIFFERENT IMPELLERS USING THE LDV-TECHNIQUE

A characterisation of three commonly used impellers was made in this s tudy by measuring local mean velocities and the fluctuations of these velocities with the LDV technique. The data was used to estimate volum etric flow, velocity fluctuations and turbulent intensity in the impel ler region of the tank. The impellers investigated were a high flow im peller, a pitched blade turbine and a Rushton turbine. The cylindrical vessel used was made of Perspex, had a dished bottom (DIN 28013), was equipped with four baffles and had an inner diameter of 0.45 m. It wa s found that the bulk velocities could be scaled with the tip-speed of the impeller (ND). The flow rate at constant impeller speed increased in the order high flow impeller - Rushton turbine - pitched blade tur bine. The corresponding order for the turbulence fluctuation is: high flow impeller - pitched blade turbine - Rushton turbine. The velocity profile of the flow out from the high flow impeller was furthermore, n ot as smooth as could be expected.