Chemical Engineering Science, Vol.62, No.13, 3429-3442, 2007
Effect of competition between particle-particle and gas-particle interactions on flow patterns in dense gas-fluidized beds
Particle-particle (P-P) and particle-fluid (P-F) interactions are two fundamental phenomena in dense particulate flows which interact mutually to compose a variety of flow structures. Using discrete particle simulation and energy budget analysis, we quantitatively explore the effect of competition between these interactions on flow patterns in dense gas-fluidized beds. A diagram, picturing flow pattern formation and its evolution, along with the altering roles of P-P collision and P-F interaction in their competition, is presented and detailed energy analysis is used to explore how P-P collision and P-F interaction drives flow pattern formation and transition. It is shown that the flow structures in various flow regimes, ranging from the fixed to the turbulent regime, can be reproduced from these simulations. Systems with strong collisional dissipation but weak gas-particle interaction display a distinct emulsion-bubble two-phase flow structure. On the contrary, systems with strong gas-particle interaction but less pronounced collisional dissipation produce uniform structures, as often observed in the uniform regime near the incipient fluidization point. If these two interactions are equally important, the system features complex flow patterns resembling those displayed in the turbulent fluidization regime. Energy analysis demonstrates that the competition between P-P collision and P-F interaction determines flow structure formation and its evolution. The flow regime transition is actually the macro-scale expression of the altering of degree of dominance of P-P and P-F interactions. (c) 2007 Elsevier Ltd. All rights reserved.