PowerPoint-Pr

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Numerical simulation of the flow in an
experimental device for emulsification
Mag. Renate Teppner Ass.-Prof. Dr. Helfried
Steiner Univ.-Prof. Dr. Günter Brenn
Part of the CONEX project
Emulsions with Nanoparticles for New Materials
Conex mid-term meeting, Oct. 28th to 30th 2004,
Warsaw
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Numerical simulation flow configuration
Cylindrical-gap emulsifier
Z
Cross section A-A
Detail Z Processing element
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Boundary conditions
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Parameters for the numerical simulation

• Volumetric flow rate Q 0.13 l/s
• Properties of the fluid (emulsion of water and
  soybean oil)
• r 977.6 kg/m3 , m 2.5 x 10-3 Pas
• -gt Reynolds number at circular inlet (diameter D
  0.013 m)
• Re ?5000
• CFD-Code FLUENT 6.1.22
• Turbulence models - standard k-e
• - realizable k-e
• - RNG
• near wall treatment using low Reynolds number
  model
• Grid 780.000 cells, structured unstructured
  subdomains

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Results of the numerical simulation
gap 1
Contours of axial velocity component in m/s
upstream from gap1
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Results of the numerical simulation
Velocity vector field near gap1
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Results of the numerical simulation
Contours of turbulent kinetic energy k in m2/s2
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Results of the numerical simulation
A,B,C,D
C
A
B
B
D
Contours of turbulent dissipation rate e in
m2/s3
Contours of dissipation rate e in m2/s3
Contours of axial velocity component in m/s
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Results of the numerical simulation
inside gap 1
A
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Results of the numerical simulation
inside gap 1
A
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Turbulent kinetic energy k in m2/s2
inside gaps
C
A
after gaps
D
B
gap
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Turbulence intensity
inside gaps
C
A
gt v-prof
gap
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Axial velocity, inner wall region in
y-coordinates
inside gap2
C
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Axial velocity, inner wall region in
y/hgap-coordinates
inside gap2
C
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Dissipation rate e in m2/s3
C
A
after gaps
D
B
inside gaps
gap
maximum of e condition
inside 2nd gap relevant for final dropsize

distribution
C
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Estimation of maximum drop size dmax based on
numerical results
Kolmogorov-Hinze (1955)
Turbulent kinetic energy spectrum
inertial forces surface tension forces
maximum drop size
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Estimation of maximum drop size dmax based on
numerical results
(Karabelas, 1978)
with
dmax according to Kolmogorov-Hinze (1955)
Consideration of viscous forces in dispersed
phase (Davis,1985)
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Estimation of maximum drop size dmax based on
numerical results
Dissipation rate e volumetric average of
numerical solution over annular gap volume
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Estimation of maximum drop size dmax based on
numerical results
Comparison with experimental data
Exptl. dropsize data provided by Slavka
Tcholakova at the LCPE, Sofia from measurements
with cylindrical emulsifyer

Case 1 Case 2 Case 3
surface tension s N/m 10 x 10-3 7 x 10-3 3.8 x 10-3
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Estimation of maximum drop size dmax based on
numerical results
Experimental drop size pdf d95
Case 1
Case 1 d95 9.05 mm
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Estimation of maximum drop size dmax based on
numerical results
Experimental dropsize pdf d95
Case 2
Case 2 d95 6.33 mm
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Estimation of maximum drop size dmax based on
numerical results
Experimental dropsize pdf d95
Case 3
Case 3 d95 5.17 mm
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Estimation of maximum drop size dmax based on
numerical results
Comparison with experimental data
Exptl. drop size data provided by Slavka
Cholakova at LCPE Sofia from measurements with
cylindrical emulsifier
Case 1 Case 2 Case 3
Experiments d95 mm 9.05 6.33 5.17
Kolmogorov -Hinze (1955) dmax mm 8.68 7.01 4.86
Davis (1985) dmax mm 16.24 15.01 13.6
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Conclusions further work
Conclusions

• strong contraction of the flow in the first gap
  enforces homogeneity in the circumferential
  direction
• flow around the processing element axisymmetric
  (2D)
• flow is insensitive to up-stream conditions
• strong enhancement of turbulent motion in the
  wake downstream from every gap
• gap-to-gap increase of the mean dissipation rate
  inside the gap
• design criterion for the processing
  element
• strong spatial variation of the dissipation rate
  e inside each gap
• identification of the relevant
  input value into break-up models ?
• how assess the predictive
  capability of the break-up models ?

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Further work
Simulation of the flow in the plane emulsifier
flow
gap
obstacles
gap
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Further work
Simulation of the flow in the plane emulsifier

• Main issues
• Two cylindrical obstacles upstream from the gap
  is the gap flow still
• practically homogeneous in spanwise direction?
• Variation of the geometry of the processing
  element 1,2,3 gaps
• effect on achievable turbulence intensity and
  dissipation rate?