CFD Analysis of Hydrodynamics and Mass Transfer of a Gas-Liquid Bubble Column

Abstract

Bubble columns are widely used as gas–liquid contactors and as reactors in chemical, petrochemical and biochemical industries. Effective mixing as well as high interfacial area between the phases, leading to improved heat and mass transfer characteristics, relatively cheap to install and the lack of moving parts, are the factors that render under bubble columns an attractive choice as reactors for the described processes.
Gas-liquid flow in bubble column reactors is characterized by a combination of inherently unsteady complex processes with widely varying spatial and temporal scales. Understanding the complexity of the fluid dynamics and mass transfer in bubble column and is important due to its application in the chemical and bioprocess industries. The potential of Computational Fluid Dynamics (CFD) for describing the hydrodynamics and heat and mass transfer of bubble columns has been established by several publications in the past. CFD predicts what happens quantitatively, when fluids flow, often with the complications of simultaneous flow of heat, mass transfer (eg perspiration, dissolution), phase change (eg melting, freezing, boiling), chemical reaction (eg combustion, rusting), mechanical movement (eg of pistons, fans, rudders), stresses in and displacement of immersed or surrounding solids. Thus CFD can successfully be used to study the gas-liquid mass transfer in bubble column reactor.
In the present work an attempt has been made to understand the hydrodynamic behavior and gas-liquid mass transfer (transfer of oxygen from air to de-aerated water) of a concurrent gas(air)-liquid(water) up-flow bubble column by CFD analysis. The system used in the study is a cylindrical column of 10 cm ID and 1.88 m height. GAMBIT 2.3.16 has been used to generate a 2D coarse grid of 0.01m by 0.01m mesh size. The eulerian-eulerian approach has been used for modeling the multiphase flow and the oxygen mass transfer from air to de-aerated water and the column hydrodynamics. The standard k-ε mixture turbulence model has been used to account the effect of turbulence. FLUENT 6.3.26 has been used to simulate the system for various hydrodynamics parameters such as phase dynamics, phase velocity profile, pressure drop and the gas-liquid mass transfer. The simulated results have been compared with the experimental results found in the literature.