Experiments in Fluids

, Volume 50, Issue 2, pp 259–269 | Cite as

Experimental comparison of measurement techniques for drop size distributions in liquid/liquid dispersions

Research Article

Abstract

An online measurement technique for drop size distribution in stirred tank reactors is needed but has not yet been developed. Different approaches and different techniques have been published as the new standard during the last decade. Three of them (focus beam reflectance measurement, two-dimensional optical reflectance measurement techniques and a fiber optical FBR sensor) are tested, and their results are compared with trustful image analysis results from an in situ microscope. The measurement of drop sizes in liquid/liquid distribution is a major challenge for all tested measurement probes, and none provides exact results for the tested system of pure toluene/water compared to an endoscope. Not only the size analysis but also the change of the size over time gives unreasonable results. The influence of the power input on the drop size distribution was the only reasonable observation in this study. The FBR sensor was not applicable at all to the used system. While all three probes are based on laser back scattering, the general question of the usability of this principle for measuring evolving drop size distributions in liquid/liquid system is asked. The exterior smooth surface of droplets in such systems is leading to strong errors in the measurement of the size of the drops. That leads to widely divergent results. A different measurement principle should be used for online measurements of drop size distributions than laser back scattering.

Abbreviations

CLD

Chord length distribution

DSD

Drop size distribution

FBR

Forward–backward ratio

FBRM

Focus beam reflectance measurement

fps

Frames per second

ORM

Optical reflectance measurement

PSD

Particle size distribution

List of symbols

D

Stirrer diameter (m)

d32

Sauter mean diameter (m)

dl,B

Immersion depth of baffles (m)

dP

Particle diameter (m)

dMax

Maximum measurable particle diameter (m)

H

Liquid level of the tank (m)

h

Distance between stirrer and tank bottom (m)

lC

Chord length (m)

N

Stirrer speed (rpm)

n

Refractive index (−)

P/V

Power input (W/m³)

Po

Power number

Q0

Cumulative number distribution (−)

q0

Number density distribution (1/m)

q3

Volume density distribution (1/m)

T

Tank diameter (m)

t

Temperature (°C)

tS

Scanning time of one particle (s)

vS

Scanning velocity of the laser focal point (m/s)

wB

Width of baffles (m)

wTip

Tip velocity of the stirrer (m/s)

γ

Interfacial tension (mN/m)

η

Dynamic viscosity (mPa s)

ρ

Density (kg/m³)

σ

Standard deviation (%)

φ

Dispersed-phase fraction (−)

Notes

Acknowledgments

We gratefully acknowledge the financial support from the Bayer Technology Services GmbH and especially Dr. Joachim Ritter, who gave the basic ideas for this research.

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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  1. 1.Department of Chemical and Process EngineeringTU BerlinBerlinGermany
  2. 2.Department of Fluid MechanicsAnhalt University of Applied SciencesKöthenGermany
  3. 3.Department of Chemical EngineeringUniversity “Otto-von-Guericke” MagdeburgMagdeburgGermany

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