Application of fluorescent PIV and digital image analysis to measure turbulence properties of solid–liquid stirred suspensions

This study describes an experimental technique which combines Fluorescent Particle Image Velocimetry (FPIV) and digital image analysis, to quantify the hydrodynamics of a solid–liquid suspension stirred by a 45° pitched-blade turbine impeller. Soda-lime glass spheres of 1000 μm diameter were employed for the dispersed phase, with up to volumetric concentrations of 0.5 vol% in water. The magnitude of the continuous phase mean velocity did not change significantly in the impeller jet or bulk flow, with the addition of up to 0.5 vol% dispersed phase. Turbulence levels of the continuous phase, in terms of rms velocities, turbulent kinetic energy and dissipation rate decreased above particle concentrations of 0.2 vol%, and the level of turbulence suppression remained constant up to 0.5 vol%. Continuous phase integral length scales remained unchanged in the presence of solids. The locally averaged particle concentration field showed high concentrations above and below the impeller and at the corner of the vessel base, extending up to the vessel wall. Particle turbulence levels measured at 0.5 vol% dispersed phase were lower than the corresponding continuous phase.