Simulation Of Bubble Behaviors In The Fluidized Bed With Binary Particles

Due to its desirable characteristics such as high heat and mass transfer rates,temperature homogeneity,and rapid mixing of particulate materials,the bubbling fluidized bed has been widely used in many industries.However,many kinds of particles are usually used in industrial processes.Bubble is a key factor that affects heat and mass transfer of gas and solids in the fluidized bed,and then reactor efficiency.Although the extensive literature has been published on the bubble behavior and the studies have been carried out,few studies have paid attention to the bubble behavior in the bi-dispersed particles fluidized bed,especially the effect of particle properties on the bubble behavior.Therefore,it is a great significance to study the effects of particle properties on the bubbles in the bubbling fluidized bed with binary particles..Two-fluid model with Eulerian approach has been employed to simulating bubble behavior in the bubbling fluidized bed with binary particles.The finite volume method is used to discrete control equations,studying the effect of the time step,the choice of relaxation factor and the grid size.The appropriate restitution for the binary particle system was set and the effect of particle coefficient of restitution on the particle velocity,solid phase volume fraction and bed pressure drop were investigated.Matlab software was employ to process the images of solid concentration contour,which come from the simulation of gas solid flow in the bubbling fluidized bed.The program was developed with Matlab language to get the bubble information,such as bubble diameter and bubble velocity.The simulation results show that the bubble diameter and bubble velocity increase linearly along the bed height with increasing the gas velocity,and they are in reasonable agreement with the experimental data.The more bubbles accumulate near the wall of the bed and the maximal bubble density lies at the radial location of 25 mm and 175 mm,which decreases with increasing the superficial gas velocity.However,the bubble density increases with increasing gas velocity in the central region of the bed.The axial distribution of number of bubbles shows the parabolic shape,that is the bubble density decrease firstly and then increases along the bed column.The bubble diameter and velocity decrease with the increase of the heavy mass fraction.The bubble diameter decreases with increasing particle density of the second component in silica gel fluidized bed,which contributes to the higher bed pressure drop.The bubble aspect ratio decreases with increasing particle density of the second component,which means that the more bubbles become irregular.The bubble diameter decrease with the increase of the diameter difference of two kinds of silica gel particles,while the diameter difference has a slight influence on bubble velocity.The bubble diameter decreases and bubble volume fraction increases with increasing particle density of the second component in silica gel/dolomite fluidized bed.