Abstract
In this work, CFD simulations of an air-water bubbling column were performed and validated with experimental data. The superficial gas velocities used for the experiments were 0.019 and 0.038 m/s and were considered as an homogeneous regime. The former involves simpler physics when compared to a heterogeneous regime where the superficial velocities are higher. In order to simulate the system, a population balance model (PBM) was solved numerically using a discrete method and a closure kernels involving the Luo coalescence model as well as two different breakup models: Luo's and Lehr's. For the multi-phase calculations, an eulerian framework was selected and the interphase momentum transfer included drag, lift, wall lubrication, and turbulent dispersion terms. A sensitivity analysis was performed on a Luo coalescence kernel by changing the coalescence parameter (c0) from 1.1 to 0.1 and results showed that the radial profiles of gas holdup and axial liquid velocity were significantly affected by such parameter. From the simulation results, the main conclusions were: (a) A combination of the Luo coalescence and Luo breakup kernels (Luo-Luo) combined with a decreasing value of c0 improves the gas holdup profiles as compared to empirical values. However, at the lowest value of c0 investigated in this work, the axial liquid velocity deteriorates with regards to experimental data when using a superficial gas velocity of 0.019 m/s. (b) A combination of the Luo coalescence and Lehr breakup models (Luo-Lehr) was shown to improve the gas holdup values with experimental data when compared to the Luo-Luo kernels. However, as c0 decreases, the Luo-Lehr models underestimate the axial liquid velocity profiles with regards to empirical values. (c) A first and second order numerical schemes allowed predicting similar radial profiles of gas holdup and axial liquid velocity. (d) The mesh sensitivity results show that a 3 mm mesh size can be considered as reasonable for simulating experimental data. (e) The inclusion of wall lubrication parameter was found to be significant, although only when using finer meshing. In addition, it allows an improvement of the axial liquid velocity at the core of the bubble column.
Highlights
Bubble columns have reportedly been used in the chemical, petrochemical, bioprocesses, and pharmaceutical industries
Many researchers have used computational fluid dynamics (CFD) techniques to simulate biphasic bubble columns. The latter are in most cases simulated by the Euler-Euler approach due to a lesser computational cost when compared to the EulerLagrange or volume of fluid (VOF) approaches
Results show so far that there is no significant difference in the predicted radial profiles
Summary
Bubble columns have reportedly been used in the chemical, petrochemical, bioprocesses, and pharmaceutical industries. Depending on superficial velocities and column diameter, the regime inside the bubble column is either homogeneous, transitional, or heterogeneous (Deckwer, 1992). The former involves simpler physics as compared to the latter and most of the models (interphase, coalescence and breakup) were developed in that regime before being later implemented in the heterogeneous regime. Many researchers have used computational fluid dynamics (CFD) techniques to simulate biphasic bubble columns. The latter are in most cases simulated by the Euler-Euler approach (two-fluid) due to a lesser computational cost when compared to the EulerLagrange or volume of fluid (VOF) approaches. In gas-liquid flow, the interface involves both drag and non-drag forces
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
