CFD Simulations of an Air-Water Bubble Column: Effect of Luo Coalescence Parameter and Breakup Kernels
نویسندگان
چکیده
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.
منابع مشابه
CFD Hydrodynamics Analysis of Syngas Flow in Slurry Bubble Column
In this paper, a CFD model of syngas flow in slurry bubble column was developed. The model is based on an Eulerian-Eulerian approach and includes three phases: slurry of solid particles suspended in paraffin oil and syngas bubbles. Numerical calculations carried out for catalyst particles, bubble coalescence and breakup included bubble-fluid drag force and interfacial area effects. Also, the ef...
متن کاملA study of hydrodynamics and interfacial momentum exchange terms in cylindrical bubble column by CFD
Flow fields and bubble size distribution are two critical issues in the determination of mass transfer and reaction rate in bubble columns. In this work the hydrodynamics of bubble driven flow was investigated in a laboratory scale cylindrical bubble column. The column was a semi batch reactor which was initially filled with tap water and only gas was evenly fed to the column from the bottom wi...
متن کاملNew Approaches for Theoretical Estimation of Mass Transfer Parameters in Both Gas-Liquid and Slurry Bubble Columns
Bubble columns (with and without suspended solids) have been used widely as chemical reactors, bioreactors and equipment for waste water treatment. The key design parameters in bubble columns are: • gas holdup; • gas-liquid interfacial area; • volumetric liquid-phase mass transfer coefficient; • gas and liquid axial dispersion coefficients; Despite the large amount of studies devoted to hydrody...
متن کاملCFD Modeling of Three-phase Bubble Column: 2. Effect of Design Parameters
The effect of design parameters on the flow pattern in a three-phase bubble column by means of Computational Fluid Dynamics (CFD) has been studied. The simulations were performed for air-water-glass beads in a bubble column of H = 0.6 m, D = 0.1 m and ds = 0.05 m to study the flow pattern. Eulerian–Eulerian three-phase simulations with kturbulence for liquid phase were carried out using the com...
متن کاملInvestigation of Heat Transfer Parameters of a Bundle of Heaters in a Simple Bubble Column Reactor Using CFD Method
Bubble columns are gas- liquid contactors that are widely used in chemical and bio- chemical industries. High mixing that result in high heat and mass transfer rates are amongst their advantages. Heat transfer in a bubble column having a bundle of heaters investigated and the variation of heat transfer coefficient with variation in heaters pitch to diameter ratios in a bundle of heaters reporte...
متن کامل