Numerical study of flows related to aerated stirred tanks
(2007) Abstract
 The overall purpose with this work is to investigate the bubbly flow in a aerated stirred tank using numerical simulations. Aerated stirred tanks are commonly used in chemical processes for producing for example insulin and antibiotics. The main requirement of these tanks, is to provide an optimal environment for the microorganisms found inside, with homogeneous mixing of air. The flow in a aerated stirred tank is complex and turbulent with stagnation points, swirling motion and recirculation zones. Introducing bubbles in this environment creates a wide range of bubble sizes. For the aerated stirred tank, Large Eddy Simulation (LES) is used for the continuous phase and the twoway coupled EulerianLagrangian model for the dispersed phase.... (More)
 The overall purpose with this work is to investigate the bubbly flow in a aerated stirred tank using numerical simulations. Aerated stirred tanks are commonly used in chemical processes for producing for example insulin and antibiotics. The main requirement of these tanks, is to provide an optimal environment for the microorganisms found inside, with homogeneous mixing of air. The flow in a aerated stirred tank is complex and turbulent with stagnation points, swirling motion and recirculation zones. Introducing bubbles in this environment creates a wide range of bubble sizes. For the aerated stirred tank, Large Eddy Simulation (LES) is used for the continuous phase and the twoway coupled EulerianLagrangian model for the dispersed phase. A breakup and coalescence model has been incorporated. Since the bubbles inside a bioreactors are many and with a wide range of sizes as well as largely varying interdroplet distance, the underlying assumptions of the model can have significant error. However, the approach offers computational efficiency and allows one to include bubble breakup and coalescence models. The moving blades, representing the rotating impeller, is modeled by using the Volume of Solid (VOS) model. The averaged radial and tangential liquid velocities decreased with increasing gas volume fraction. Additionally, for the axial velocities the gas redirected the radial jet upwards and the symmetry of the ring vortices vanished. Although, low gas flow rate, the periodicity from the impeller is decreased and interfere with the creation of the trailing vortex pair behind the impeller. Including bubble breakup and coalescence model in the aerated stirred tank, induces small spherical bubbles. For large bubbles, shapes become important and can be modeled using the Volume of Fluid (VOF) model. Numerical simulations has been performed for deformable airbubbles in a straight channel. Bubble features such as aspect ratio, equivalent diameter, velocity and path are compared against experimental data obtained by using shadowgraph technique. The VOF model is capable to predict the different bubble features and shows a promising future for studying the detailed interaction between the different phases inside a bioreactor. The limitations of the EulerianLagrangian model arises when the interparticle distance is small. From the simulations of Lattice Boltzmann Method (LBM), both drag and liftcoefficients were obtained for cases with strong particleparticle (so called fourway) interaction. A novel approach of handling large spherical bubbles combined with the EulerianLagrangian model in the Large Eddy Simulation (LES) framework, has been developed and utilized. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/record/599197
 author
 Arlov, Dragana ^{LU}
 supervisor

 Johan Revstedt ^{LU}
 Laszlo Fuchs ^{LU}
 opponent

 Professor, Dr. Ing. Hjertager, Bjorn, Aalborg University Esbjerg, Denmark
 organization
 publishing date
 2007
 type
 Thesis
 publication status
 published
 subject
 keywords
 plasma, fluiddynamik, Gaser, plasmas, fluid dynamics, Gases, Lattice Boltzmann method, Volume of Fluid, Aerated stirred tank, Large Eddy Simulation, EulerianLagrangian model, Energy research, Energiforskning, Mechanical engineering, hydraulics, vacuum technology, vibration and acoustic engineering, Maskinteknik, hydraulik, vakuumteknik, vibrationer, akustik
 pages
 98 pages
 publisher
 Fluid Mechanics
 defense location
 Lecture hall M:B, Mbuilding, Ole Römers väg 1, Lund University Faculty of Engineering.
 defense date
 20071123 10:15
 external identifiers

 other:ISRN: LUTMDN/TMHP07/1055SE
 ISSN
 02821990
 ISBN
 9789173240
 language
 English
 LU publication?
 yes
 id
 d544604ebe0244b98f2b8f385c984dff (old id 599197)
 date added to LUP
 20071112 20:47:16
 date last changed
 20180529 11:12:25
@phdthesis{d544604ebe0244b98f2b8f385c984dff, abstract = {The overall purpose with this work is to investigate the bubbly flow in a aerated stirred tank using numerical simulations. Aerated stirred tanks are commonly used in chemical processes for producing for example insulin and antibiotics. The main requirement of these tanks, is to provide an optimal environment for the microorganisms found inside, with homogeneous mixing of air. The flow in a aerated stirred tank is complex and turbulent with stagnation points, swirling motion and recirculation zones. Introducing bubbles in this environment creates a wide range of bubble sizes. For the aerated stirred tank, Large Eddy Simulation (LES) is used for the continuous phase and the twoway coupled EulerianLagrangian model for the dispersed phase. A breakup and coalescence model has been incorporated. Since the bubbles inside a bioreactors are many and with a wide range of sizes as well as largely varying interdroplet distance, the underlying assumptions of the model can have significant error. However, the approach offers computational efficiency and allows one to include bubble breakup and coalescence models. The moving blades, representing the rotating impeller, is modeled by using the Volume of Solid (VOS) model. The averaged radial and tangential liquid velocities decreased with increasing gas volume fraction. Additionally, for the axial velocities the gas redirected the radial jet upwards and the symmetry of the ring vortices vanished. Although, low gas flow rate, the periodicity from the impeller is decreased and interfere with the creation of the trailing vortex pair behind the impeller. Including bubble breakup and coalescence model in the aerated stirred tank, induces small spherical bubbles. For large bubbles, shapes become important and can be modeled using the Volume of Fluid (VOF) model. Numerical simulations has been performed for deformable airbubbles in a straight channel. Bubble features such as aspect ratio, equivalent diameter, velocity and path are compared against experimental data obtained by using shadowgraph technique. The VOF model is capable to predict the different bubble features and shows a promising future for studying the detailed interaction between the different phases inside a bioreactor. The limitations of the EulerianLagrangian model arises when the interparticle distance is small. From the simulations of Lattice Boltzmann Method (LBM), both drag and liftcoefficients were obtained for cases with strong particleparticle (so called fourway) interaction. A novel approach of handling large spherical bubbles combined with the EulerianLagrangian model in the Large Eddy Simulation (LES) framework, has been developed and utilized.}, author = {Arlov, Dragana}, isbn = {9789173240}, issn = {02821990}, keyword = {plasma,fluiddynamik,Gaser,plasmas,fluid dynamics,Gases,Lattice Boltzmann method,Volume of Fluid,Aerated stirred tank,Large Eddy Simulation,EulerianLagrangian model,Energy research,Energiforskning,Mechanical engineering,hydraulics,vacuum technology,vibration and acoustic engineering,Maskinteknik,hydraulik,vakuumteknik,vibrationer,akustik}, language = {eng}, pages = {98}, publisher = {Fluid Mechanics}, school = {Lund University}, title = {Numerical study of flows related to aerated stirred tanks}, year = {2007}, }