Numerical Study On Particle Characteristics In A Bubbling Fluidized Bed

A fluidized bed is a system using the solid fluidized technology, making theparticles suspended in the fluid medium, thereby changing the contact form ofparticles and giving the particles fluid-like properties. Fluidized bed was firstused in the chemical industry, followed by the energy industry and sparked ahuge technological change. Bubbling fluidized bed is kind of fluidized beds, andhas a wide application in energy, chemical, metallurgical, pharmaceutical andbio-engineering and other industries. The research on the bubbling fluidized bedhas also been one of the hot research fields.For decades of development, some basic rules of bubbling fluidized bedwere found including the flow structures and particle characteristics. Withfurther researches, however, there had also been some more problems, includingtranslational motion and rotational motion characteristics and the characteristicsof the model parameters related to its specific impacts. Therefore, this work isfocused on the microscopic dynamics of particles, and trying to solve theproblems mentioned above.The simulation in this work is based on the Eulerian-Lagrangian model, andthe basic principles of the gas-solid two-phase flow were formed. A continuousmodel was used for the gas phase, which solved the volume-averagedNavier-Stokes equations directly and added large eddy simulation method withthe mutative Smagorinsky constant in Smagorinsky sub-grid model. The discreteparticles hard sphere model and the one-component and binary solid phase wereused for the solid phase. Particle dynamic characteristics, including thetranslation and rotation movement were investigated, and focused on themicroscopic scale of particle translational and rotational speed pulsations. Thecharacteristics of the model parameters such as inlet air velocity, bed height,different component of solid phase and the coefficient of restitution wereinvestigated.For the one-component solid phase bubbling fluidized bed, the approach ofDPM model with the Beetstra drag model and normal restitution coefficient of0.97can simulate the experiment of Müller et al. Drag model mainly affects the macroscopic particle motion characteristics, the superficial gas velocity has aninfluence on all of the particle motions, while the normal coefficient ofrestitution has a greater impact on particle characteristics, but there is no obviouspattern.For the binary solid phase bubbling fluidized bed, the approach of DPMmodel with large eddy simulation method with the mutative Smagorinskyconstant in Smagorinsky sub-grid model can simulate the experiment of Lu et al.Because of the presence of big and small particles, the mechanism of particlecollision is more complex. Particle translational velocity, bubble granular andparticle translational granular temperature will increase as the bed heightincreases, but for the particle rotation characteristics there is no law. Thedistribution of the particle dynamic characteristics will not be changed by thedifferent component of solid phase, but the magnitude will be changed. Normalrestitution coefficient can affect the small-scale velocity fluctuations such asparticle rotational granular temperature and particle translational granulartemperature, while there is little effect on the particle translational and rotationalvelocity.