Measurement and Computation of Turbulence in Risers Using Kinetic Theory

Abstract

Detailed experimental velocity, particle concentration and stresses for flow of particles in a vertical pipe, riser are needed for verification of various CFD models for multiphase flow in the industrially important circulating fluidized bed (fast fluidization) regime. This study provides such information for flow of 530 μm glass beads in the fully developed flow region of a 7 m symmetric riser with a splash plate. Instantaneous particle velocity distributions were obtained using a particle velocity imaging technique and a probe inserted into the riser, while the particle concentrations were measured with a gammaray densitometer. Time averaged particle velocity distributions can be well represented by a parabolic velocity distribution, with the mean velocity obtained from flux divided by the measured bulk density. The radial granular temperature profiles agree with an analytical expression similar to the thermal temperature distribution in Poiseuille flow with viscous heat generation. A solution to the complete CFD model shows that the assumptions made in the analytical solution are valid. Our measurements of stresses in the risers and bubbling beds show the existence of two types of random kinetic energies or granular temperatures. The true granular temperature is due to oscillations of particles, while the second is the average of the normal Reynolds stresses. In the core of the riser, the true granular temperature is much larger than the Reynolds type granular temperature. The reverse is true in the bubbling bed.