Turbulent Multi-Phase Flow Interactions Through Grid Turbulence Measured by Particle Image Velocimetry

Abstract

Industrial processes involving multi-phase flows such as flotation require an understanding of the relationships between bubbles, solid particles and the flow. For decades engineers and researchers based their calculations on algebraic formulas that model these interactions. These formulas were derived either from simple models, or from experimental data. Modern experimental tools are employed in this effort to measure with great accuracy the basic features of the motion of all three phases in turbulent flow. We employed a unique Digital Particle Image Velocimeter (DPIV) that can record with great accuracy and kHz temporal resolution, velocity vectors of all three phases, namely the fluid, the solid particles and the air bubbles. The interaction of these three phases was studied in grid turbulence. Flow was directed through a rectangular grid of circular rods and the resulting homogeneous isotropic turbulence was documented. Particles and bubbles were released and the motion of the three phases was monitored. The particle RMS was in good agreement with a model proposed by Shubert, having an average RMS velocity of about 13% of the free stream velocity in the fully developed region. A theoretical model, derived first by Levins and Glastonbury was found to underpredict the particle RMS. The bubble RMS was about 26% of the free stream in the homogeneous isotropic region, 100% greater than the particle RMS and not consistent with the model predictions.