| Flow regimes of dense phase vertical pneumatic transport of solids, referred to in the literature as circulating fluidized beds, have been computed using a generalization of the Navier-Stokes' equations for two fluids.; In the less dense regime corresponding to volume fractions of solids of about one percent, the flow consists of centrally upward moving solids and downward moving clusters. The computations agree with experimental observations made by high speed movies and with measurements of radial solids concentrations and velocities. The model predicts reasonable dependence of the cluster formation on solids flux, gas velocity, particle size, bed height, pipe diameter and fine particle mixing. In general, with the decrease of the solids flow rate and the particle size the cluster population in the pipe decreases. With the increase of the fluidization gas velocity, fine particle mixing and pipe diameter the cluster population in the pipe decreases.; In the dense regime, corresponding to volume fractions of about ten percent, a core-annulus type of regime is obtained, with solids descending down at the wall. The inhomogeneous distribution of solid particles in the riser part of circulating fluidized beds is computed in this study. The computed voidage distributions and velocity profiles agree with measurements made at IGT and at City College of New York.; In a combination of the hydrodynamic model and a cluster mechanistic model, the bed-to-wall heat transfer coefficients are predicted for a circulating fluidized bed combustor. The predicted coefficients agree reasonably with measurements made at the University of British Columbia. |
