(97d) Benchmark Data and Analysis of Dilute Turbulent Fluid-Particle Flow in Viscous and Transitional Regimes
The effects of flow rate and solids concentration of a liquid-solid flow consisting of water and glass spheres 0.5, 1.0, or 1.5 mm in diameter are varied to investigate the viscous, transitional, and collisional flow regimes in a vertical three inch pipe. The flow is highly turbulent, with single-phase Re from 2.0x105 to 5.0x105 and solids concentration from 0.7% to 3% by volume. These conditions span a wide range of Stokes and Bagnold numbers. Laser Doppler velocimetry is used to measure the mean and fluctuating velocities of the two phases simultaneously, while the phase Doppler method is used to measure particle size and thus discriminate between the phases. The detailed, non-intrusive velocity measurements under the conditions investigated provide a unique data set by which multiphase computational fluid dynamics (CFD) models can be validated.
For all particle sizes, Re, and solids concentrations the mean fluid velocity profile is very similar in shape to that of the single-phase fluid. The slip between the fluid and 0.5 mm particles is very small. The 1.0 mm particles exhibit an increase in slip as solids concentration increases. The fluctuating velocity measurements show trends characteristic of both collision-dominated and viscous-dominated flow, clearly showing the flow is in a transitional regime. In all cases, the effects of changing the Re are greater than the effects of changing the concentration of solids. There is a reduction in turbulence of both phases across the pipe with increasing Re. However, at the highest Re there is an increase in both fluid and solid turbulence, which can be explained by an increase in vortex shedding at Rep > 300.
The solid fluctuating velocity of the 1.0 mm particles is significantly greater than that of the 0.5 mm particles for all conditions. At each respective Re, the solids fluctuations for the 1.0 mm particles are greater than those of the fluid in their presence, except very near the wall where they become similar. Conversely, the solids fluctuations for the 0.5 mm particles are less than those of the fluid in their presence. The difference in turbulence between the two phases decreases with increasing Re. The turbulence of both phases becomes increasingly flat near the center of the pipe with increasing Re and solids concentration. This is in agreement with the flat profiles of both fluid and solid turbulence in inertia-dominated gas-solid flows. In general, the 0.5 mm particles damp the fluid turbulence while the 1.0 mm and 1.5 mm particles are either neutral or enhance the turbulence. These data give insight into the fluid-particle interactions over a wide range of flow conditions.