Lagrangian-Lagrangian simulation of unsteady gas-liquid flow in a bubble column

Abstract

In this study, the flow interactions between incompressible gas and liquid in the unsteady state in a bubble column were numerically analyzed. The corresponding analysis method could be implemented without a using mesh and adopted the Lagrangian–Lagrangian method, which is based on the particle system and, thus, reduces the numerical diffusion error. In previous studies, Eulerian methods have been generally used due to complex gas–liquid computations, and analyses were performed using a limited number of particles. By adopting the proposed method, a substantial number of particles can be rapidly calculated using a Graphics Processing Unit (GPU). Moreover, research involving the use of the Lagrangian–Lagrangian method for analyzing multi-phase flow is scarce. The Moving Particle Semi implicit method (MPS) and Discrete Bubble Method (DBM) methods were used for fluid implementation and gas implementation, respectively. Furthermore, results were obtained by coupling the results of these two methods. To verify the analysis method, three methods (MPS, DBM, MPS–DBM coupling) were verified. First, to verify the MPS method, the Dam break phenomenon was analyzed, and it was confirmed that the experimental results were well matched. Additionally, the analysis results of the pressure drop in a packed bed were consistent with the results obtained using the analytic Ergun equation. Second, to verify the DBM method, the terminal rising velocity of a single bubble was analyzed for each particle size, and it was consistent with the analytic results for each of the four different drag coefficients. Finally, to verify the MPS–DBM coupling method, the behavior between incompressible gas and liquid in the unsteady state inside the bubble column was implemented using numerical simulation, and the results were compared with the experimental results. Subsequently, based on the previous verifications, simulations on the influence of the flow of bubble columns with respect to bubble size and drag correlation on the constant bubble generation rate assumption was conducted. Moreover, the influence of the flow of bubble columns with respect to bubble size and drag correlation on different bubble generation rates was investigated. Lastly, to quantitatively describe the energy transferred from the flow of a bubble column to a liquid, the kinetic energy transferred from the gas to liquid was computed for each case.