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Some Fluid Dynamic Characteristics in the Scale-up of Rushton Turbine-Agitated Tanks

Ståhl Wernersson, Eva LU (1997)
Abstract (Swedish)
Popular Abstract in Swedish

Ett flertal produkter som framställs inom den kemiska och biotekniska industrin produceras i stora turbinomrörda tankar. Kvaliteten av produkten och utbytet av processen påverkas av blandningsförhållandena i dessa tankar.



Blandningsförhållandena i processen påverkas av vätskans hastighet och dess intensitet. I olika regioner av reaktorn, impeller regionen och bulk regionen, skiljer sig hastigheterna åt i riktning och styrka. Det är dessa hastigheter, som transporterar värme och massa i reaktorn vilket minskar diffusionsavståndet för molekylerna i processen. Turbulensen blir således det hastighetsavgörande steget. Därför är det intressant att studera hydrodynamiken för... (More)
Popular Abstract in Swedish

Ett flertal produkter som framställs inom den kemiska och biotekniska industrin produceras i stora turbinomrörda tankar. Kvaliteten av produkten och utbytet av processen påverkas av blandningsförhållandena i dessa tankar.



Blandningsförhållandena i processen påverkas av vätskans hastighet och dess intensitet. I olika regioner av reaktorn, impeller regionen och bulk regionen, skiljer sig hastigheterna åt i riktning och styrka. Det är dessa hastigheter, som transporterar värme och massa i reaktorn vilket minskar diffusionsavståndet för molekylerna i processen. Turbulensen blir således det hastighetsavgörande steget. Därför är det intressant att studera hydrodynamiken för turbinomrörda tankar.



Syftet med denna studie är att karaktärisera hydrodynamiken i turbinomrörda tankar med anemometri-mätningar i lokala mätpunkter för att finna skalningsparametrar relaterade till reaktorns geometri och processens driftsparametrar.



Ett mät- och data-insamlingssystem för turbulenta hastighetsmätningar konstruerades där mätmetoden var termisk anemometri. Två riktningar i flödet kunde mätas simultant med hjälp av en varmfilmsprob. Mätningarna gjordes i tre tankar med olika geometri och av olika storlekar (0.75 m3, 12 m3, 30 m3). Mätningarna utfördes under olika driftsförhållanden. Effekten per massenhet varierades för att kunna jämföra med energinivåerna i industriella fermenteringar och fermenteringar i bänkskala. Lokala turbulenta flödesparametrar, dvs den turbulenta kinetiska energin (q) och den lokala energi dissipationshasigheten (e) har relaterats till traditionella uppskalningsparametrar som impellerhastighet, impellerdiameter och effekt per massenhet, samt den lokala flödesparametern, den beräknade konvektiva hastigheten. Ett flertal hypoteser för beräkning av den lokala konvektiva hastigheten har prövats. Olika metoder för att beräkna den lokala energi dissipationshastigheten har jämförts både i impellerzonen och bulkzonen.



Studien visar att det föreligger en korrelation mellan den turbulenta kinetiska energin (q) och den lokala energi dissipationshastigheten (e) oberoende av tankens storlek, geometri och mätpunktens position, när de turbulenta parametrarna (q,e) normaliseras med den konvektiva hastigheten. Det bekräftar likformigheten i flödet vid höga turbulenta Reynolds tal. Samma likformighet visas också i skalning av vågtalsspektra för tankar av olika geometri, storlekar och i olika mätpositioner. Korrelationer ges för skalning av de turbulenta parametrarna (q,e) med hjälp av traditionella skalningsparametrar som impellerhastighet, impellerdiameter och effekt per massenhet, både i impellerzonen och bulkzonen. Karaktäristiska tidsvariationer har upptäckts både i medelflödet och i den turbulenta delen av flödet i impellerzonen och bulkzonen. Ökas effekten som tillförs processen påverkas impellerregionen mer än bulkregionen. Det visades i de högre lutningskoefficienterna för de turbulenta parametrarna jämfört med de globala parametrarna. (Less)
Abstract
Turbine-agitated tanks are used in chemical and biochemical applications to increase mixing which, in turn, affects the yield, productivity and product quality. The purpose of this work was to study the hydrodynamic influence on the scale-up of turbine-agitated tanks, commonly used in fermentation. Local turbulent flow parameters, the turbulent kinetic energy and the local energy dissipation rate, were related to the global scale-up parameters: the impeller tip speed, impeller diameter and power per unit mass, and to the local flow parameter, the calculated convective velocity.



A system for turbulent velocity measurements was designed using constant-temperature anemometry as the measuring method. A split-film probe was... (More)
Turbine-agitated tanks are used in chemical and biochemical applications to increase mixing which, in turn, affects the yield, productivity and product quality. The purpose of this work was to study the hydrodynamic influence on the scale-up of turbine-agitated tanks, commonly used in fermentation. Local turbulent flow parameters, the turbulent kinetic energy and the local energy dissipation rate, were related to the global scale-up parameters: the impeller tip speed, impeller diameter and power per unit mass, and to the local flow parameter, the calculated convective velocity.



A system for turbulent velocity measurements was designed using constant-temperature anemometry as the measuring method. A split-film probe was used which enabled velocity measurements to be made in two directions simultaneously. Measurements were performed in three tanks of different geometries and sizes (0.75 m3, 12 m3 and 30 m3). Different operating conditions, in regard of power input per unit mass, were used, comparable both to commercial fermentation and bench-scale units.



Several estimates and hypothesis for the convective velocity were evaluated. Different methods for calculating the local energy dissipation rate were compared for measurements performed both in the impeller region and the bulk region of the tanks.



It was shown that there was a correlation between the local turbulent parameters, turbulent kinetic energy and energy dissipation rate, and the local flow parameter, the convective velocity Uconv, independent of the tank size, the tank geometry or position in the tank, which confirms the similarity of the flows at high turbulent Reynolds numbers. The similarity of the flow conditions at high turbulent Reynolds numbers was also evidenced by scaling of energy spectra in the space domain for tanks of different geometries, sizes and at different positions in the tanks. Correlations are given for the scaling of local flow parameters, the turbulent kinetic energy and the energy dissipation rate, in the impeller region of the tank, using global scale-up parameters. Long-term characteristics have been detected in the mean flow and in the turbulent flow in the impeller and bulk zones. Increasing the power supplied to a process affects the impeller region more than the bulk region, and therefore increases the turbulent mixing in the process. This was shown by the higher values of the slopes of turbulent parameters compared with global parameters. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Prof Nienow, Alvin, School of Chemical Engineering, University of Birgmingham, Edg baston, Birgmingham B15 2 TJ, UK
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Chemical technology and engineering, Livsmedelsteknik, Food and drink technology, Rushton turbine, turbulent kinetic energy, geometry, local energy dissipation rate, power input, scale-up, anemometry measurements, agitated tanks, turbulence, Kemiteknik och kemisk teknologi
pages
75 pages
publisher
Food Engineering, Lund Univeristy
defense location
Room A, Chemical Centre
defense date
1997-02-28 10:15
external identifiers
  • Other:ISRN: LUTTKDH/(TTKLT-1023)
language
English
LU publication?
yes
id
a4143249-d9ed-4f6a-9adf-2c3548e16f6f (old id 29051)
date added to LUP
2007-06-14 16:23:04
date last changed
2016-09-19 08:45:08
@misc{a4143249-d9ed-4f6a-9adf-2c3548e16f6f,
  abstract     = {Turbine-agitated tanks are used in chemical and biochemical applications to increase mixing which, in turn, affects the yield, productivity and product quality. The purpose of this work was to study the hydrodynamic influence on the scale-up of turbine-agitated tanks, commonly used in fermentation. Local turbulent flow parameters, the turbulent kinetic energy and the local energy dissipation rate, were related to the global scale-up parameters: the impeller tip speed, impeller diameter and power per unit mass, and to the local flow parameter, the calculated convective velocity.<br/><br>
<br/><br>
A system for turbulent velocity measurements was designed using constant-temperature anemometry as the measuring method. A split-film probe was used which enabled velocity measurements to be made in two directions simultaneously. Measurements were performed in three tanks of different geometries and sizes (0.75 m3, 12 m3 and 30 m3). Different operating conditions, in regard of power input per unit mass, were used, comparable both to commercial fermentation and bench-scale units.<br/><br>
<br/><br>
Several estimates and hypothesis for the convective velocity were evaluated. Different methods for calculating the local energy dissipation rate were compared for measurements performed both in the impeller region and the bulk region of the tanks.<br/><br>
<br/><br>
It was shown that there was a correlation between the local turbulent parameters, turbulent kinetic energy and energy dissipation rate, and the local flow parameter, the convective velocity Uconv, independent of the tank size, the tank geometry or position in the tank, which confirms the similarity of the flows at high turbulent Reynolds numbers. The similarity of the flow conditions at high turbulent Reynolds numbers was also evidenced by scaling of energy spectra in the space domain for tanks of different geometries, sizes and at different positions in the tanks. Correlations are given for the scaling of local flow parameters, the turbulent kinetic energy and the energy dissipation rate, in the impeller region of the tank, using global scale-up parameters. Long-term characteristics have been detected in the mean flow and in the turbulent flow in the impeller and bulk zones. Increasing the power supplied to a process affects the impeller region more than the bulk region, and therefore increases the turbulent mixing in the process. This was shown by the higher values of the slopes of turbulent parameters compared with global parameters.},
  author       = {Ståhl Wernersson, Eva},
  keyword      = {Chemical technology and engineering,Livsmedelsteknik,Food and drink technology,Rushton turbine,turbulent kinetic energy,geometry,local energy dissipation rate,power input,scale-up,anemometry measurements,agitated tanks,turbulence,Kemiteknik och kemisk teknologi},
  language     = {eng},
  pages        = {75},
  publisher    = {ARRAY(0xa810030)},
  title        = {Some Fluid Dynamic Characteristics in the Scale-up of Rushton Turbine-Agitated Tanks},
  year         = {1997},
}