| Abstract
| - For a pseudofluid consisting of a particle assembly, particle stress is transmitted through mutualcontact between particles. When the particles are densely agglomerated, contacts are usually oflong duration and frictional, and this part of the stress is the frictional stress. When the particlesare sparsely spaced, on the other hand, contacts are temporary and collisional, and this part ofthe stress consists of kinetic and collisional stresses. In many cases the particle contact liesbetween these two extremes in a gas−solid fluidized bed, and all of these three parts of thestresskinetic, collisional, and frictional stressesplay important roles in particle-phasetransport. However, the existing kinetic theory for granular flow (KTGF) only involves the kineticand collisional parts of transport. In this paper, a frictional particle pressure was introducedfor correction of KTGF in the case of highly dense flow, and the solid shear stress was correctedto be consistent with Einstein's effective viscosity equation for dilute suspensions. This modifiedKTGF model may account for the stress over the entire range between two extremes of a denselypacked state and a sparsely spaced state. As verification in the dense gas−solid flow, the time-averaged total pressure drop and the particle pressure predicted by this modified KTGF modelwere found to be in agreement with the measurements in a cylindrical fluidized bed. Theinflection point on the particle pressure curve, implying competition among the three transportmechanisms, was also predicted. Moreover, instantaneous formation of slugs starting from ahomogeneous inflow condition was reproduced through simulation and the quantitativecomparison of the slug velocity with empirical correlation was approving. For dilute gas−solidflow in a circulating fluidized-bed riser, the model predictions agree with the time-averagedsolid viscosity in order of magnitude. Further modeling may require a better understanding ofthe drag force and turbulence.
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