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Numerical Studies of Mixing in Pipes and Static Mixers

Regner, Mårten LU (2006)
Abstract (Swedish)
Popular Abstract in Swedish

Syftet med denna avhandling var att studera blandningsprocessen i statiska mixrar vid laminärt flöde och i rör vid förträngning av vätskor med olika fysikaliska egenskaper.



En numerisk metod och ett tillvägagångssätt för att karaktärisera statiska mixrar har utvecklats. Med hjälp av den utvecklade metoden och numerisk strömningsberäkning (CFD) har effekten på blandningsprocessen studerats med avseende på geometri, flödeshastighet, viskositetsskillnad och skillnad i volymsflöde mellan vätskorna.



Genom att använda den utvecklade metoden har det varit möjligt att studera hur virvlar i flödet i en statisk mixer påverkar blandningsprocessen och tryckfallet över... (More)
Popular Abstract in Swedish

Syftet med denna avhandling var att studera blandningsprocessen i statiska mixrar vid laminärt flöde och i rör vid förträngning av vätskor med olika fysikaliska egenskaper.



En numerisk metod och ett tillvägagångssätt för att karaktärisera statiska mixrar har utvecklats. Med hjälp av den utvecklade metoden och numerisk strömningsberäkning (CFD) har effekten på blandningsprocessen studerats med avseende på geometri, flödeshastighet, viskositetsskillnad och skillnad i volymsflöde mellan vätskorna.



Genom att använda den utvecklade metoden har det varit möjligt att studera hur virvlar i flödet i en statisk mixer påverkar blandningsprocessen och tryckfallet över mixern. Vid viker Reynoldstal som virvlar uppstår i flödet beror på vilket längddiameterförhållande som elementen i mixern har. De virvlar som uppstår i flödet bidrar till att strimmor som passerar genom mixern sträcks ut snabbare.



För förträngning av vätskor i rör har en numerisk metod utarbetats och beräknade resultat har utvärderats mot experimentellt uppmätta värden på hastighet- och koncentrationsfördelning vid förträngninga v yoghurt med hjälp av vatten. De beräknade värdena fångar den globala strukturen av hastighet- och koncentrationsfördelningen av de båda vätskorna som flödar i olika flödesregimer. Förträngningsförloppet har visat sig vara beroende på flödeshastigheten och yoghurtens reologi. (Less)
Abstract
The objective of the present work was to investigate the mixing process in static mixers under laminar flow conditions, and in pipes during the displacement of dissimilar liquids.



A numerical scheme and a method of characterizing static mixers were developed. The effects of changes in geometry, flow rate, viscosity ratio and volumetric flow rate ratio on the mixing process were investigated using computational fluid dynamics (CFD) and the methods developed. Eulerian and Lagrangian mixing analysis were used to evaluate the mixing process.



A rate of striation thinning method was developed to characterize the static mixer. Using elliptic Fourier descriptors it was possible to determine the uncertainty in... (More)
The objective of the present work was to investigate the mixing process in static mixers under laminar flow conditions, and in pipes during the displacement of dissimilar liquids.



A numerical scheme and a method of characterizing static mixers were developed. The effects of changes in geometry, flow rate, viscosity ratio and volumetric flow rate ratio on the mixing process were investigated using computational fluid dynamics (CFD) and the methods developed. Eulerian and Lagrangian mixing analysis were used to evaluate the mixing process.



A rate of striation thinning method was developed to characterize the static mixer. Using elliptic Fourier descriptors it was possible to determine the uncertainty in the particle tracking, and the number of particles and Fourier components needed to reproduce a desired level of detail.



With the method developed the formation of vortices could be observed in the flow using the Z factor, the magnitude of helicity and the rate of striation thinning as measures. The Reynolds number at which vortices were observed depended on the length-to-diameter ratio of the mixer elements. The vortices increased the stretching of the striations, but some striations passed the mixer elements almost unaffected regardless of the flow rate.



For the investigation of mixing of dissimilar liquids in a pipe a numerical scheme was developed and verified against experimental data for the velocity and concentration distribution during the displacement of yoghurt by water. The scheme reproduces the global velocity and concentration distribution of the two liquids flowing in different flow regimes. Using the scheme developed, the displacement process was found to be affected by the flow rate and the rheological properties of the yoghurt.



When studying the mixing of two dissimilar liquids in a static mixer it was found that the viscosity ratio between the two liquids influences the mixing process: the greater the difference in viscosity, the lower the rate of striation thinning, i.e. the slower the mixing. This is due to a difference in elongation rate between the liquids, which exists until equilibrium in shear stress has been reached at the interface between the liquids. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Tanguy, Philippe, École Polytechnique, Département de génie chimique, Montréal, Canada
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Turbulent mixing, Secondary flow, Viscosity ratio, Computational fluid dynamics, Food and drink technology, Livsmedelsteknik, Rate of striation thinning, Static mixer, Laminar mixing
pages
146 pages
publisher
Department of Food Technology, Engineering and Nutrition, Lund University
defense location
Lecture hall A, Centre for Chemistry and Chemical Engineering, Faculty of Engineering, Lund University
defense date
2006-05-31 13:00
ISBN
91-628-6812-8
language
English
LU publication?
yes
id
89deaa85-3577-4975-99aa-173302f086b4 (old id 546782)
date added to LUP
2007-10-13 11:31:11
date last changed
2016-09-19 08:45:05
@misc{89deaa85-3577-4975-99aa-173302f086b4,
  abstract     = {The objective of the present work was to investigate the mixing process in static mixers under laminar flow conditions, and in pipes during the displacement of dissimilar liquids.<br/><br>
<br/><br>
A numerical scheme and a method of characterizing static mixers were developed. The effects of changes in geometry, flow rate, viscosity ratio and volumetric flow rate ratio on the mixing process were investigated using computational fluid dynamics (CFD) and the methods developed. Eulerian and Lagrangian mixing analysis were used to evaluate the mixing process.<br/><br>
<br/><br>
A rate of striation thinning method was developed to characterize the static mixer. Using elliptic Fourier descriptors it was possible to determine the uncertainty in the particle tracking, and the number of particles and Fourier components needed to reproduce a desired level of detail.<br/><br>
<br/><br>
With the method developed the formation of vortices could be observed in the flow using the Z factor, the magnitude of helicity and the rate of striation thinning as measures. The Reynolds number at which vortices were observed depended on the length-to-diameter ratio of the mixer elements. The vortices increased the stretching of the striations, but some striations passed the mixer elements almost unaffected regardless of the flow rate.<br/><br>
<br/><br>
For the investigation of mixing of dissimilar liquids in a pipe a numerical scheme was developed and verified against experimental data for the velocity and concentration distribution during the displacement of yoghurt by water. The scheme reproduces the global velocity and concentration distribution of the two liquids flowing in different flow regimes. Using the scheme developed, the displacement process was found to be affected by the flow rate and the rheological properties of the yoghurt.<br/><br>
<br/><br>
When studying the mixing of two dissimilar liquids in a static mixer it was found that the viscosity ratio between the two liquids influences the mixing process: the greater the difference in viscosity, the lower the rate of striation thinning, i.e. the slower the mixing. This is due to a difference in elongation rate between the liquids, which exists until equilibrium in shear stress has been reached at the interface between the liquids.},
  author       = {Regner, Mårten},
  isbn         = {91-628-6812-8},
  keyword      = {Turbulent mixing,Secondary flow,Viscosity ratio,Computational fluid dynamics,Food and drink technology,Livsmedelsteknik,Rate of striation thinning,Static mixer,Laminar mixing},
  language     = {eng},
  pages        = {146},
  publisher    = {ARRAY(0x98b9110)},
  title        = {Numerical Studies of Mixing in Pipes and Static Mixers},
  year         = {2006},
}