Computational fluid dynamics applied to bubble columns

Other Title(s)

نمذجة CFD في الأعمدة الفقاعية

Dissertant

Ahmad, Shakir Mahmud

University

University of Technology

Faculty

-

Department

Department of Chemical Engineering

University Country

Iraq

Degree

Ph.D.

Degree Date

2006

English Abstract

Computational fluid dynamics (CFD) is increasingly used in the design, scale up, optimization and trouble-shooting analysis in today's chemical process industry.

In this work, 2D and 3D models capable of predicting the hydrodynamics for any type of two phase flows in bubble columns with rectangular and cylindrical geometry, were developed using Mixture-Model and Euler-Euler approaches.

The k-£ model extended for two phase flows was used for turbulence modeling of the continuous phase.

A simulation code was further developed to predict any flow variable including local holdup, velocities, and turbulence properties ; turbulent kinetic energy, rate of dissipation and eddy viscosity or diffusivity.

Liquid circulation is the most effective means of transportation for momentum, heat and mass in buoyancy driven gas-liquid flow in bubble column reactors.

Drag force was found the most dominant contribution among interfacial forces acting at the interface between the phases.

Drag force estimated on the basis of buoyancy provides the driving force needed to maintain liquid circulation inside bubble columns.

2 D Mixtures-Model showed a reasonable prediction compared to literature, whereas 2D Euler-Euler models were more capable in predicting flow patterns, as the dominant drag force has been accounted for properly.

Moreover, with inclusion of the bubble induced viscosity to account for the turbulence induced due to the movement of the rising bubbles, 3D Euler-Euler model was most capable one, as it is close to reality, where the effective viscosity becomes more realistic and less numerical diffusion can be found.

For code verification, a comprehensive comparison was made to investigate the effect of interfacial forces using different closures, aspect ratios, grid resolution, and superficial gas velocity and sparing location on the hydrodynamics of 2D and 3D rectangular and cylindrical bubble columns.

Comparison to results obtained from a series of experiments using a Computerized Conductivity Probe Interface System for three different bubble columns (7.5, 15 and 30 cm diameters), showed the ability to employ CFD for better design and scaling up considerations.

Simulation of rectangular airlift bubble column with riser confirms that the code can further be extended to capture the hydrodynamics of more complex system and geometries.

Main Subjects

Chemistry

Topics

• Fluid dynamics
• Dynamics
• Bubble wrap

• APA
• MLA
• AMA

Language

English

Data Type

Arab Theses

Record ID

BIM-305801