Simulation of bubbly flow in a flat bubble column
(2014) KET920 20141Department of Chemistry
Chemical Engineering (M.Sc.Eng.)
- Abstract
- Numerical, transient simulations of a meandering bubble plume in a rectangular flat bubble column was carried out, using the commercial CFD package ANSYS Fluent 15 within the framework of a Eulerian-Eulerian description. A Sensitivity analysis of turbulence closure was performed using four turbulence models: standard, RNG, Realizable k − epsilon and the Reynolds stress model. The effect of dispersed phase turbulence on the continuous phase was also investigate. The interaction force term included drag, virtual mass and turbulent dispersion. Some simulations were also made using lift and wall lubrication forces. The available drag and dispersion models available in Fluent were evaluated. Lastly, the impact of numerical methods was... (More)
- Numerical, transient simulations of a meandering bubble plume in a rectangular flat bubble column was carried out, using the commercial CFD package ANSYS Fluent 15 within the framework of a Eulerian-Eulerian description. A Sensitivity analysis of turbulence closure was performed using four turbulence models: standard, RNG, Realizable k − epsilon and the Reynolds stress model. The effect of dispersed phase turbulence on the continuous phase was also investigate. The interaction force term included drag, virtual mass and turbulent dispersion. Some simulations were also made using lift and wall lubrication forces. The available drag and dispersion models available in Fluent were evaluated. Lastly, the impact of numerical methods was investigated where the model was tested for discretization scheme, gradient limiter, time step and grid size.
The standard and Realizable k − epsilon models resultsed in a meandering bubble plume that oscillated with a period of 32.5 seconds. The Reynolds stress model did not reach a quasi-steady state, as the period kept increasing during the flow-time. The RNG k − epsilon model produced an oscillating plume, but the recorded time series show that the velocity fluctuated in a more chaotic way. The analysis of the dispersed phase turbulence modelling showed that the chaotic oscillations predicted by the RNG k − ² was a results of under predicting the turbulent viscosity. Comparing drag models showed that the drag coefficient influenced the amplitude of the velocity measurements, and that higher drag coefficient yield a higher amplitude. It was also found that including the turbulent dispersion force is imperative to capture the dispersion of the bubble plume. The lift force did not influence the oscillation frequency of the plume, but only the dispersion. Including the lift force caused the non-physical effect of pushing the bubbles towards the back and forth wall. It was also shown that this effect could be counteracted by including wall lubrication, and keeping the dispersive effect of the lift force. The choice of time step had the largest impact on the oscillation frequency. Decreasing the time step below 4 ms caused the oscillation frequency to decrease rapidly. If a time step of 2.5 ms was used, the time between peaks doubled. (Less) - Popular Abstract (Swedish)
- En bubbelkolonn är en väldigt vanlig operation i modern kemisk industri, då den utgör en billig och effektiv lösning för kemiska reaktioner mellan gas- och vätska. Detta då gasen, som kommer in från botten står för själva omrörningen, vilket gör att man inte behöver använda någon omrörare. I detta arbete så studerades möjligheten att simulera flödet i en bubbelkolonn, och hur resultatet påverkades av olika fysikaliska- och matematiska modeller. Arbetet utfördes i en kommersiell simuleringsmjukvara genom att variera de matematiska- och fysikaliska modeller som fanns tillgängliga. För att utvärdera hur väl simuleringarna stämde överens med verkligheten så jämfördes de med experimentell data från vetenskaplig litteratur.
Arbetet visade... (More) - En bubbelkolonn är en väldigt vanlig operation i modern kemisk industri, då den utgör en billig och effektiv lösning för kemiska reaktioner mellan gas- och vätska. Detta då gasen, som kommer in från botten står för själva omrörningen, vilket gör att man inte behöver använda någon omrörare. I detta arbete så studerades möjligheten att simulera flödet i en bubbelkolonn, och hur resultatet påverkades av olika fysikaliska- och matematiska modeller. Arbetet utfördes i en kommersiell simuleringsmjukvara genom att variera de matematiska- och fysikaliska modeller som fanns tillgängliga. För att utvärdera hur väl simuleringarna stämde överens med verkligheten så jämfördes de med experimentell data från vetenskaplig litteratur.
Arbetet visade att simuleringarna stämde bra överens med experiment. Dock så visade det sig att resultatet var känsligt när det gällde val av fysikaliska modeller. Det visade sig att systemet var väldigt känsligt för modelleringen av turbulens, men även för hur interaktionen mellan gas och vätska beskrevs. Dock visade det sig att om fysikaliska modeller väljs på ett intelligent vis, så kan en bubbelkolonn beskrivas med matematiska medel på ett sätt som stämmer väl överens med verkligheten. Simulering av bubbelkolonner kan användas som underlag för att dimensionera verkliga kolonner till som skall användas i industrin. Detta kan vara ett mycket kostnads- och tidseffektivt alternativ till att utföra experiment. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/4730957
- author
- Nygren, Andreas LU
- supervisor
- organization
- alternative title
- CFD Simulering av bubbelkolonn
- course
- KET920 20141
- year
- 2014
- type
- H2 - Master's Degree (Two Years)
- subject
- keywords
- Computational Fluid Dynamics, Bubble Column, Turbulence Modelling, Eulerian-Eulerian framework
- language
- English
- id
- 4730957
- date added to LUP
- 2014-10-28 13:57:08
- date last changed
- 2014-10-28 13:57:08
@misc{4730957,
abstract = {{Numerical, transient simulations of a meandering bubble plume in a rectangular flat bubble column was carried out, using the commercial CFD package ANSYS Fluent 15 within the framework of a Eulerian-Eulerian description. A Sensitivity analysis of turbulence closure was performed using four turbulence models: standard, RNG, Realizable k − epsilon and the Reynolds stress model. The effect of dispersed phase turbulence on the continuous phase was also investigate. The interaction force term included drag, virtual mass and turbulent dispersion. Some simulations were also made using lift and wall lubrication forces. The available drag and dispersion models available in Fluent were evaluated. Lastly, the impact of numerical methods was investigated where the model was tested for discretization scheme, gradient limiter, time step and grid size.
The standard and Realizable k − epsilon models resultsed in a meandering bubble plume that oscillated with a period of 32.5 seconds. The Reynolds stress model did not reach a quasi-steady state, as the period kept increasing during the flow-time. The RNG k − epsilon model produced an oscillating plume, but the recorded time series show that the velocity fluctuated in a more chaotic way. The analysis of the dispersed phase turbulence modelling showed that the chaotic oscillations predicted by the RNG k − ² was a results of under predicting the turbulent viscosity. Comparing drag models showed that the drag coefficient influenced the amplitude of the velocity measurements, and that higher drag coefficient yield a higher amplitude. It was also found that including the turbulent dispersion force is imperative to capture the dispersion of the bubble plume. The lift force did not influence the oscillation frequency of the plume, but only the dispersion. Including the lift force caused the non-physical effect of pushing the bubbles towards the back and forth wall. It was also shown that this effect could be counteracted by including wall lubrication, and keeping the dispersive effect of the lift force. The choice of time step had the largest impact on the oscillation frequency. Decreasing the time step below 4 ms caused the oscillation frequency to decrease rapidly. If a time step of 2.5 ms was used, the time between peaks doubled.}},
author = {{Nygren, Andreas}},
language = {{eng}},
note = {{Student Paper}},
title = {{Simulation of bubbly flow in a flat bubble column}},
year = {{2014}},
}