HYDRODYNAMICS GENERATED BY A PITCHED-BLADE TURBINE IN A STIRRED SUSPENSION

摘要

The hydrodynamic conditions in a suspension of solid particles, agitated by a pitched-blade turbine pumping down-wards in an agitated tank, are investigated experimentally. A three-dimensional phase-Doppler anemometer is used to measure local, instantaneous, three-dimensional velocities of the fluid and of the suspended particles. A shaft encoding technique is used to resolve the turbulent velocity fluctuations from the periodic velocity fluctuations due to the impeller blade passage. Spatial distributions of periodicity of the flow, the turbulent levels, the energy dissipation rates and Reynolds stresses are evaluated. The results show that the flow is three-dimensional, highly fluctuating and anisotropic below the impeller. Also the energy dissipation rate and the Reynolds stresses, including both normal and shear stresses, are high in that region. In addition, the mean velocity difference between the liquid and solid phase is found in the same region. The particle concentration is low below the impeller but is high above the impeller tip. An energy balance around the impeller shows that there is a good agreement between the estimated power input and the measured net outgoing kinetic energy.