CFD Simulation And Experimental Verification Of Hydrodynamics In A Liquid-solid Fluidized Bed

Liquid-solid fluidized bed has two-phase mixing and excellent heat and mass transfer characteristics,which has been widely used in wastewater treatment,mineral separation,pharmaceutical synthesis and food processing.However,there is still no complete theory to explain the flow structure and characteristics of liquid-solid two-phase system within the bed.In this thesis,the flow characteristics of the homogeneous liquid-solid fluidized bed are investigated experimentally and numerically.A rectangular fluidized bed was designed and set up,and the flow characteristics of liquid-solid system in the bed were investigated by the combination of visual obversion and high-speed camera.Firstly,the profiles of solid holdup with superficial liquid velocity under three different initial bed heights was investigated in detail during the steady-state process.Experimental results were consistent with the predictions of Richardson-Zaki correlation,indicating the feasibility of the established experimental apparatus and measured method.For the dynamic process,the hydrodynamic characteristics of different expansion and contraction processes are obtained by changing the superficial liquid velocity instantaneously.Compared with the dynamic response theory by Gibilaro et al.,the results show that the bed dynamic height is nonlinear with time relationship and the gravity instability of the bed causes the actual duration of the expansion process to be significantly greater than the theoretical prediction,while the duration of the contraction process is basically consistent with this theoretical value.The Eulerian-Eulerian two-fluid model was used to describe the characteristics of two-phase flow in the liquid-solid fluidized bed.Based on the independent validations of grid and time step,the influence of the key model and parameters on the flow behavior was investigated.By comparing with the experimental results of solid holdup,it is found that Gidaspow model is selected for drag model and Gidaspow viscosity model for predicting solids viscosity.The particle to particle recovery coefficient,the particle to wall recovery coefficient and the mirror coefficient are 0.99,0.9 and 0.01.respectively.The above models and parameters are further employed to explore the influence of the superficial fluid velocity on the solid holdup distribution in the bed.