Computational Fluid Dynamics (CFD)-Discrete Element Method (DEM) Simulation of Gas-Solid Turbulent Flow in a Cylindrical Spouted Bed with a Conical Base

摘要

Three dimensionally coupled computational fluid dynamics (CFD) and discrete element method (DEM) were studied for modeling the turbulent gas-solid flow in a cylindrical spouted bed with a conical base. The particle motion was modeled by the DEM, and the gas motion was modeled by the k-e two-equation turbulent model. Drag force, contact force, Saffman lift force, Magnus lift force, and gravitational force acting on an individual particle were considered in establishing the mathematical models. Calculations on the cylindrical spouted bed with an inside diameter of 152 mm, a height of 700 mm, and a conical base of 60° were carried out. Experimental results from the University of British Columbia [He, Y. L.; Qin, S. Z,; Lim, C. J.; Grace, J. R. Particle velocity profiles and solid flow patterns in spouted beds. Can.J. Chem. Eng. 1994, 72 (8), 561 -568] were used as a numerical benchmark to quantitatively assess the simulations. Despite the somewhat larger simulated spout diameter found, the present simulated results were in well-agreement with the experiments. The average error of particle velocity was less than 15%. On the basis of the simulations, the development of spout with time and distributions of particle velocity, particle concentration, and spout diameters at various spouting gas velocities were obtained. Besides, detailed information on particle collision and drag forces adding on particles at different bed regions was discussed. The results showed that particle velocity gradually decreases along the radial direction, with speeds of particles moving upward decreasing with an increasing bed height, while in the annulus region, particles decelerate downward in the cylindrical section and then accelerate in the conical base. The particle concentration increases in the spout region, is kept nearly constant in the annulus region, but decreases in the fountain region along the radial axis. An increasing bed height leads to an increasing particle concentration in the spout region but a decreasing particle concentration in the annulus and fountain regions. Particle collision number, particle turbulent intensity, and the transient collision force and drag force are significantly larger in the spout region than in the annulus and fountain regions. Besides, an increasing spouting gas velocity leads to a remarkable increased speed of particles moving upward or downward, spout diameter, particle collision, drag force, and particle turbulent intensity but decreased particle concentrations.