Experimental Investigation And CFD Simulation On Fluid Dynamics Of Gas-Liquid-Solid Three-Phase Bubble Column Systems

The gas-liquid-solid three-phase flow occurs in the energy, chemical and environmental processes. One operation bed is the gas-liquid-solid three-phase bubble column, which has an important application in the fields of the energy and environment. The gas-liquid-solid three-phase flow behaviors in the bubble columns are much more complicated compared to the gas-liquid or gas-solid two-phase flow, and the knowledge of the three-phase flow is limited. Therefore, it is important to investigate the hydrodynamics of the three-phase flow and gain a deep insight. All the knowledge can help us to reveal the influence mechanism of the particles in the gas-liquid flow and to design the bed and optimize the bed operations more reasonably. It can also provide fundamental data for the industry applications. The present work is devoted to revealing the complex fluid dynamics of the gas-liquid-solid three-phase bubble column by experiments and CFD approaches.The experimental system of the three-phase bubble column was set-up. Experimental studies on the flow pattern and transitions were carried out. The high-resolution digital image acquisition and processing system was used. The three-phase flow patterns under different operation conditions were studied. Four distinct flow patterns were identified in the experimental system, and they were discrete bubble regime (DBR), transition regime (TR), bubble coalescence regime (BCR) and strong turbulent regime (STR). Typical flow patterns by certain criteria as well as schematic diagrams and flow pattern images were presented. The effects of the particle properties, liquid properties and bed sizes on the flow pattern transitions were investigated and revealed.The high-precision multi-channel pressure/differential pressure signal acquisition and processing system was adopted. The time domain analysis, time-frequency domain analysis and state space analysis were combined to identify the transition points of the three-phase bubble columns. The statistical, Hurst, Hilbert-Huang transform and Shannon entropy analysis were used to analyze the differential pressure fluctuation time series of the three-phase system. The quantities obtained from the four analysis methods are linked to the hydrodynamic characteristics of the three-phase bubble column system. The Hilbert-Huang transform and Shannon entropy analysis methods offer very high resolution in identifying the different flow regimes, and they performed better than the statistical and Hurst analysis. Therefore, it revealed the good and useful methods for identifying flow regimes in the three-phase bubble column systems.The experimental investigations on the important hydrodynamic parameters of the gas-liquid-solid three-phase bubble columns were carried out. The total gas holdup, local gas holdup, bed pressure drop, the minimum gas velocity for the solid complete suspension, bed expansion ratio and fluctuation ratio are correlated with the operation parameters under four different flow regimes. The new correlation of the average gas holdup was developed considering the effects of the particle properties.A mathematical model of a gas-liquid-solid three-phase flow was built in this study based on the three-Euler multiphase models. The numerical schemes were tested and the better approaches were selected for the momentum discretization, wall conditions of the three phases and the time step for calculation. Interphase drag forces of the three phases were tested. The appropriate interphase drag forces to describe the three phase flow were revealed in this study. Based on the numerical modelling platform, the effects of superficial gas velocity, particle properties (solid volume fraction, particle size and density) on the hydrodynamics of a three-phase bubble column were discussed. The radial and axial distributions of the gas holdup and solid holdup, and the profiles of the liquid axial velocity, liquid turbulence parameters and solid axial velocity under distinguished operation conditions were obtained. The CFD results were compared with the experimental flow structures for the first time. It revealed the simulation abilities on different flow regimes and different regions in the bed, such as the sparger region, bulk region and foaming region.The effects of the bed dimensions and shapes and the operation condition of the elevated pressure on the fluid dynamics of the three-phase bubble columns were obtained by the CFD simulation. Based on the simulation platform, the four-Euler model was built to investigate the mix effects of two types of particles. It revealed the effects of two types of particle mixture (with different particle size and the same density; or with different particle density and the same size) on the profiles of the gas holdup and solid holdup in the bubble column.