CFD-DEM Simulation Of Complex Dense Gas-solid Flow

The dense gas-solid two-phase flows are frequently encountered in the apparatus of fluidization engineering. With the increasingly widely utilization of the gas-solid fluidization technology, the dense gas-solid two-phase flows have been hot spots issues focused by both the academic researchers and the engineering workers, for which the fully understanding on the mysterious essence has been obtained only in some aspects due to the complexity and the multivariate lying in its latent mechanism. As a result of the development of the computational technology, numerical simulation has become a powerful tool in the scientific research and the application of engineering. Since the direct numerical simulation (DNS) has not been applied in the simulation research on the practical issue encountered in the industry and many assumptions have to be made to close the governing equations in the Euler-Euler approach, a mediate approach called CFD-DEM (Computational fluid dynamics-Discrete element method) has been increasingly favored by numerical researchers.The current work conducted a series of numerical study on the gas-solid two phase flow in the bubbling fluidized bed and spouted bed based on the coupling of CFD-DEM approach under the platform of a large scale computational hardware. The main content of the current work can be divided into the following four parts:The first part of this research is carried out in a pseudo3D bubbling fluidized bed with the methods of CFD-DEM and Two fluid model method (TFM), respectively. Firstly, the investigation concentrates on the comparison between the simulation results obtained with these two methods in the2D computational model, followed with the researches on the effects of two turbulence models and several drag force models on the simulation results with the3D coupling framework of CFD-DEM. Moreover, the mixing and dispersion properties of the solid phase in the bubbling fluidized bed have been analyzed based on the post-processing of the simulation results.The second part of the research is focused on the investigation of the gas-solid flow property in a conical-based cylindrical spouted bed in the framework of CFD-DEM coupling method. First of all, the simulation has been compared with the experimental results, followed with the discussion on the gas-solid behavior, the distribution properties of the velocity and the flux both for the gas and solid phases, the voidage distribution property of fluid phase, and the the influence of the superficial gas velocity on the related parameters of the system. Then, the systematic research and comparison have been conducted on the effect of the entrainment distance and the length of the draft tube in the3D spouted bed on the gas-solid behaviors. At last, the erosion property of the draft tube and the systematic dispersion characteristic of the solid phase were studied.The third part of the work lies in the3D slot rectangular spouted bed to capture the gas solid flow properties. And the flow property, the velocity distribution behavior of both the fluid and solid phases, the distribution property of solid flux, the voidage and the influence of the superficial gas velocity on the gas-solid flow behaviors in the system were systematically investigated. Moreover, the difference on the gas solid flow behavior were observed based on the comparison of the simulation results carried out in the3D and the2D spouted bed, respectively. The results show that the3D computation method is required in the numerical study of the gas solid flow in the spouted bed.The final part of the current work is concentrated on the discussion of the scale-up of the geometry parameters of the spouted bed using the CFD-DEM method, for which the numerical simulation is carried out in a3D rectangular spouted bed with two diverging bases and two slots. The gas solid flow behaviors, the information of the velocity, the flux and the voidage both of the fluid and solid phases were investigated. Then, the mutual effect between the two spouted beds in the system is discussed, which is useful for the mechanism understanding and the scale-up designing of the spouted bed.