Master of Engineering Science
Mechanical and Materials Engineering
The inverse three-phase fluidized bed has excellent potentials to be used in chemical, biochemical, petrochemical and food industries because of its high contact efficiency among each phase which leads to a good mass and heat transfer. The understanding of the hydrodynamics and flow structures in inverse three-phase fluidized beds is important for the design and scale up purposes.
A CFD model based on the Eulerian-Eulerian (E-E) approach coupled with the kinetic theory of the granular flow is successfully developed to simulate an inverse three-phase fluidization system. The proposed CFD model for the inverse three-phase fluidization system is validated by comparing the numerical results with the experimental data. Investigations on the hydrodynamics and flow structures in the inverse three-phase fluidized bed under a batch liquid mode are conducted by numerical studies. The development of the fluidization processes and the general gas-liquid-solids flow structures under different operating conditions are further studied by the proposed three-phase E-E CFD model. Parametric studies including different inlet superficial gas velocities, particle densities, and solids loadings are investigated numerically. The numerical results show a general non-uniform radial flow structure in the inverse three-phase fluidized bed. It is also found that the particle distribution profiles in the axial direction relate to the solids loading, particle density and inlet superficial gas velocity. The existences of the liquid and solids recirculation inside the inverse three-phase fluidized bed are also noticed under the batch liquid mode.
Moreover, the proposed CFD model for the inverse three-phase fluidized bed is further modified by adjusting the bubble size. The modified CFD model takes the bubble size effects into account and performs better on estimating the average gas holdup. In addition, a correlation between the bubble size and the superficial gas velocity, gas holdup and physical properties of the liquid and solid phases is proposed based on the numerical results. The predicted bubble size and the gas holdup in the inverse three-phase fluidized beds under a batch mode using the proposed correlation agree well with the experimental data. Therefore, the proposed three-phase E-E CFD model incorporated with the bubble size adjustment can be used to predict the performance of the inverse three-phase fluidization system more accurately.
Liu, Yunfeng, "Numerical Simulation of Three-Phase Flows in the Inverse Fluidized bed" (2018). Electronic Thesis and Dissertation Repository. 5730.