chemical reaction engineering laboratory characterization of flow patterns in stirred tank reactors...

CHEMICAL REACTION ENGINEERING LABORATORY

Characterization of Flow Patterns in Characterization of Flow Patterns in Stirred Tank Reactors (STR) Stirred Tank Reactors (STR)

Aravind R. RammohanAravind R. RammohanChemical Reaction Engineering Laboratory (CREL)

Advisor: Professor M. P. Dudukovic’ (CREL)Co-Advisor: Dr. V. V. Ranade (NCL, India)

CREL Annual MeetingNovember 15th, 2001


MotivationMotivation

1) For Single Phase Study

- Techniques like LDA, DPIV etc. : Eulerian measurements

- CARPT :Lagrangian information, complement the available information in stirred tanks

2) For Multiphase Study

- LDA, DPIV etc. limited to non-opaque multiphase systems with low holdup of dispersed phase

- Only ‘non’ optical techniques like CARPT & CT can probe into such flows


OutlineOutline

– Define Objectives

– Experimental Setup for Single Phase Study

– CARPT Technique

– Results and Discussions

– Identify the Issues that need to be Addressed


ObjectivesObjectives

– Verify mass balance

– Qualitative Validation• Compare Qualitative features captured by CARPT with

visualization studies (Kemoun, 1995)

– Quantitative Validation• Compare Radial Pumping numbers from CARPT with

Experimental data

• Compare Mean Velocities in Impeller Stream

• Compare Turbulent Kinetic Energy in impeller Stream

– Model Single Phase flows in stirred tanks

– Identify the issues that need to be addressed


Stirred Tank for Experimental StudyStirred Tank for Experimental Study

DI /4

DI/5

Blade

DI= DT /3

3DI /4

Rushton Turbine

• Fluid Used for Experiment - Water (density: 1 gm/c.c.)

• Reynolds Number range = 8000- 32000 (N=150 rpm, Reimp=12,345);

HT=

DT

DT=200mm

DT/3

DT/10

= DT/31.5


The Details of CARPTThe Details of CARPT

Z1

Z2

Z4

Z3

Octagonal Base Sc46, Radioactive strength (80Ci)

16 Na I detectors

Al Supports for detectors

Z1=2.86cms

Z2=7.72cms

Z3=12.59cms

Z4=17.45cms

Z1

Z3

Z1

Z3

Z1 Z3 Z1 Z3

Z2 Z4

Z2 Z4

Z2 Z4Z2 Z4

Details of SetupDetails of Setup• Data Processing of Radiation

Intensity Received by N detectors from a Single Radioactive Sc-46 Particle

• Intensity “I” for N detectors

(Photon Counts)

• Calibration Curves “I vs D(distance)”

• Distance “ D” from Particle to N Detectors

• Weighted Least Squares Regression

• Particle Position P(t)

• Filter Noise Due to Statistical Fluctuation

• Instantaneous Lagrangian Velocities

• Time Averaged Velocities• Turbulence Parameters


Calibration & ReconstructionCalibration & ReconstructionGrid for Calibration

R=0 , 1.9, 5.7 & 9.5 cms

(4 locations)

Z=0-20 cms

(11 locations)

=0-360o

(12 locations)

Ncalib=11+3x11x12=407

radioactiveparticle

Al rod for changingz location

Slots to calibrate atdifferent radial locations

Thetagraduations tocalibrate atdifferentangles


CARPT DetailsCARPT Details

Details of SetupDetails of Setup

Z1

Z2

Z4

Z3

Octagonal Base Sc46, Radioactive strength

(80Ci)

16 Na I detectors

Al Supports for detectors

Z1=2.86cms

Z2=7.72cms

Z3=12.59cms

Z4=17.45cms

• Data Processing of Radiation Intensity Received by N detectors from a Single Radioactive Sc-46 Particle

• Intensity “I” for N detectors

(Photon Counts)

• Calibration Curves “I vs D(distance)”

• Distance “ D” from Particle to N Detectors

• Weighted Least Squares Regression

• Particle Position P(t)• Filter Noise Due to Statistical

Fluctuation

• Instantaneous Lagrangian Velocities

• Time Averaged Velocities

• Turbulence Parameters


Lagrangian EulerianLagrangian Eulerian

Lagrangian Particle Trajectories & Lagrangian Velocities available

3-D grid in STR for CARPT3-D grid in STR for CARPT

ShaftBaffles

Disc

N= 72 cells , NR= 20 cells and NZ= 40 cells, total= 57600, =5o, r=5.0 mms, z=5.0 mms


Verification ofVerification of MassMass Balance Balance

DC

2b

Surface S1

Surface S2Blade

DI= DT /3

3DI /4

Surface S3

Control Volume for Mass Balance Calculations

• Compute Flow In and Flow Out Along Every Surface.

• Mass Balance Check ? Qtotin=Qtotout


Verification of Mass Balance

Researcher TechniqueUsed

RegionConsidered

Accuracy

Gunkel &Weber(1975)

HFA 0<z/D<.16,0<r/D<1

~ 4%

Yianneskis,Popilek &Whitelaw(1987)

LDA C.V. aroundimpeller

~ 1%

Wu &Patterson(1989)

LDA -.22<z/D<.22,0<r/D<0.55

~ 1%

Ranade &Joshi (1990)


~ 5%

Yianneskis &Whitelaw(1993)


~ 1%

Zhou &Kresta (1996)

LDA -.15<z/D<.23,0<r/D<.525

~ 5-10%

Current work CARPT C.V. aroundthe impeller

~ 7%


Qualitative ValidationQualitative Validation- Location of Eye of Recirculation Loops -- Location of Eye of Recirculation Loops -

Azimuthally Averaged Velocity vector plot

Vtip=0.53 m/s

Eye of Loop


Location of Eye of Recirculation LoopsLocation of Eye of Recirculation LoopsLocation of Eye of Circulation Loops

(T = tank diameter)Researcher Lowe

r r/TLower z/T

Upperr/T

Upperz/T

Clearance Hc/T

Yianneskis,Popilek &Whitelaw(1987)

0.3 0.20 0.30 0.48 0.33

Costes &Couderc(1988)

0.4 0.25 0.4 0.75 0.50

Schaefer,Hofken &Durst (1997)

0.4 0.20 0.4 0.5 0.33

Kemoun,Lusseyran,Mallet &Mahoust(1998)

0.4 0.20 0.4 0.5 0.33

Current work 0.4 0.20 0.4 0.5 0.33


Qualitative Validation - Shape and Location of Dead ZonesQualitative Validation - Shape and Location of Dead Zones

Dead zones

Star Fish Pattern

R cm

R cm

VV

r .

Disc

Blades

Baffles

Plane at the bottom of the tank

StarFishPattern

Deadzones

Reproduced from Kemoun(1995) with permission

CARPTVisualization


Grid Independence of CARPT measurementsGrid Independence of CARPT measurements

Table 1 Details of the grids examined in this study.Grid Parameters Grid I (GI) Grid II (GII) Grid III (GIII)

NI 36 72 72NJ 10 40 20NK 20 80 40

r (cms) 1.0 0.25 0.5z (cms) 1.0 0.25 0.5

(degrees) 10O 5O 5O


Grid Independence of CARPT measurementsGrid Independence of CARPT measurements

(b) Radial Profile of Radial Velocity at Z2=D/3

0

0.1

0.2

0.3

0.4

0.5

-0.4 -0.2 0 0.2 0.4 0.6 0.8 1Radial Co-ordinate (r-RI)/(R-RI)

Ra

dia

l Ve

loc

ity

Vr

Vr(Z2=D/3, GI)

Vr(Z2=D/3, GII)

Vr(Z2=D/3, GIII)


Comparison of Radial Pumping Numbers from CARPTComparison of Radial Pumping Numbers from CARPT with Data from the literaturewith Data from the literature

DQ

NNQ

P

P3

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 0.1 0.2 0.3 0.4 0.5 0.6

Radial Co-ordinate (r-RI)/(R-RI)

Pu

mp

ing

Nu

mb

er

Qp/(

ND

3 )

CARPT

Wu and Patterson (1989)

Ranade and Joshi (1990)

Drobolov et al. (1978)

Cooper and Wolf (1968)

Stoots and Calabrese (1995)

2

0

2

2

,,

b

brP dzrdzrVrQ


Axial Profile of Radial Velocity in the Impeller StreamAxial Profile of Radial Velocity in the Impeller Stream

0.2

0.25

0.3

0.35

0.4

0 0.2 0.4 0.6 0.8 1

Dimensionless Radial Velocities Vr/Vtip

Dim

en

sio

nle

ss

Ax

ial

Co

-ord

ina

te Z

/T


Rutherford et al. (1996) t/D=0.0337, e.a.

Rutherford et al. (1996) t/D=0.0337, p.a.

Mahoust (1987)

Kemoun (1991)

CARPT


Axial Profile of Radial Velocity in the Impeller StreamAxial Profile of Radial Velocity in the Impeller StreamComparison of recent reports of Radial Velocities at

the Impeller tip from LDA measurements with CARPT

Researcher Vrmax/Vtip % Deviationfrom CARPT

Mahoust (1987) 0.50 4%Wu & Patterson(1989, e.a.)

0.73 34%

Wu & Patterson(1989, p.a.)

0.51 6%

Kemoun (1991) 0.525 8.6%Rutherford et al.(1996)t/D= 0.008 (e.a.)

0.98 51%

Rutherford et al.(1996)t/D= 0.008 (p.a.)

0.72 33%

Rutherford et al.(1996)t/D= 0.0337 (e.a.)

0.81 41%

Rutherford et al.(1996)t/D= 0.0337 (p.a.)

0.59 11%

CARPT (2000)t/D= 0.045

0.48 ______


Turbulent Kinetic Energy Profile in the Impeller StreamTurbulent Kinetic Energy Profile in the Impeller Stream

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 0.2 0.4 0.6 0.8 1Dimensionless Radial Co-ordinate (r-RI)/(R-RI)

Dim

en

sio

nle

ss T

KE

K.E

./U

tip

2

Costes and Couderc (1988)

Ranade and Joshi (1990)


CARPT(2000)


FindingsFindings

• CARPT measured Mean Velocities compare well (within 4-8%) with Mahoust (1987) and Kemoun (1991) whose tank dimensions are exactly same as current setup. However, CARPT measurements are lower (10-20%) than the other reported data.

• CARPT measured rms velocities are lower than those obtained from other techniques.

• CARPT measured turbulent kinetic energy lower (30-50%) than that obtained from other techniques.


Where are we losing this information ?Where are we losing this information ?

• Flow considerations

– Sampling frequency (50 Hz) too low ? – Is the tracer too big to follow the fluid closely ?

• Nature of the experimental technique

– Statistical nature of photon emission

– Reconstruction based on calibration map where solid angle effects are not accounted for (Roy et al., 1999)

– Wavelet-based filtering - Are we filtering off fluctuations of the fluid in addition to noise ?


Current WorkCurrent Work

• Evaluated flow followability of tracers of different size and density ratio

• Probed two phase flows (gas -liquid) in STR using CARPT and CT (Computed Tomography)

• Obtained extensive local gas holdup and liquid velocity information


Single Phase CFD ApproachesSingle Phase CFD Approaches

• Black Box Approach (Needs experimental input)

• Unsteady Approaches (Computationally very intensive)

Deforming mesh

Sliding mesh

• Quasi steady approaches

Multiple reference frames

Snapshot approach

• Grids used for current work N=94, NR=57 & Nz=78 (Ntot~410000)


Predictions of Radial Profile of Tangential VelocityPredictions of Radial Profile of Tangential Velocity

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 0.2 0.4 0.6 0.8 1

Dimensionless Radial Co-ordinate (r-RI)/(R-RI)

Dim

en

sio

nle

ss

Ta

ng

en

tia

l Ve

loc

ity

V /

Vti

pChen et al. (1988)


CARPT (2000)

MRF

SNAP

Single phase CFD simulations predictions are comparable to LDA values but over predict the CARPT data


Current CFD WorkCurrent CFD Work

• Lagrangian particle tracking simulations

• 2 phase simulations in STR using two fluid model + snapshot approach


Acknowledgements Acknowledgements

- CREL Sponsors

- Colleagues at CREL

chemical reaction engineering laboratory characterization of flow patterns in stirred tank reactors...

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