Characteristics Of Flow Behavior In A Liquid-Solid Fluidized Bed Based On Subgrid Scale Model

Research of liquid-solid two-phase fluidization is an important direction. Liquid-solid fluidized bed has an advantage of good mixture, heat transfer and mass transfer. However, the theoretical research is relatively less and characteristics of liquid-solid system in the fluidized bed with nonlinear and non-uniformity of the structure is inadequate. Therefore, it is urgent to discuss the nature and mechanism of two-phase flow in the liquid-solid fluidized bed.The numerical simulation method has been adopted in the dissertation. According to the subgrid scale two-fluid model with wall corrections of considering the effect of wall,introducing the two-fluid model(TFM) and the kinectic theory of granular flow, the two-dimentional flow model of circulating fluidized bed riser and spouted bed were set up.The dissertation disscusses the characteristics of the particles under different conditions,analyzes the distributions of average concentration and average axial velocity of particles in order to conduct in-depth research on liquid-solid two-phase flow property. By the numerical simulation method, liquid-solid two-phase flow behavior in the circulating fluidized bed riser was analyzed. The results shows that subgrid scale model of adding wall amended corrections has a strong grid adaptability so that ccurately reflect the microscopic flow behavior in the coarse grid computing. It was shown core-annulus structure as well as the phenomenon of back-mixing near the wall in the development of the riser section. The results obtained from subgrid scale model of adding wall corrections are better than those of the other drag force models, compared with experimental results. It is used for the subgrid scale model to carry on the reasonable model validation.By the numerical simulation of liquid-solid flow behavior in the spouted bed, there are three regions containing the spouted area, annular area and fountain area. The results show that with the increasing of inlet velocity and the viscosity of liquid, the bed expansion height increase gradually, the concentration of particles decreases and the axial velocity of particles and liquid increases obviously. The inverted cone angle of spouted bed is mainly influence on the annular area.With the decreasing of the cone angle, the particles of the annular area flow to the spouted area gradually gathers and the concentration and the axial velocity of particles decrease. Compared with subgrid scale model of adding wall corrections and the other drag force models, we can capture low particles concentration in the spouted area, high particles concentration in the annular area and circulatory movement of solid particles from annular area to spouted area. It effectively confirms the applicability of this model in the liquid-solidtwo-phase spouted bed.