Cavitation in Sonolators
David
1
2
Ryan ,
1University
Mark
1
Simmons ,
Mike
2
Baker
– June 2012
of Birmingham, UK; 2Unilever Research and Development, Port Sunlight, UK
Acoustic results and frequency spectra
Aims and Objectives
Overall EngD project aim: to determine how the Sonolator makes
emulsions and disperses fluids, and apply the findings to industry.
Objective of this poster: to present recent results showing evidence
of cavitation in the Sonolator.
Figure 7: Audio file for cavitating flow
What is a Sonolator?
The microphone output (Figure 7) is not particularly useful by itself,
however the frequency spectrum (Figure 8) reveals dB peaks at
frequencies between 3kHz and 11kHz when the flow cavitates.
Figure 1 shows a schematic diagram
of a Sonolator. A mixture of water and
oil droplets passes through a narrow
orifice (Figure 2). This subjects the Figure 1: Sonolator sketch
droplets to intense forces, and breaks
them. An emulsion of very small oil
droplets in water forms. This
technique can be used to make many
industrially useful fluids, such as, Figure 2: Sonolator orifice
foods and personal care products.
Figure 8: Frequency spectrum
Cavitation Measurement
Figure 9 shows audio spectra recorded for (top to
bottom): no flow, non-cavitating low speed flow,
cavitating high speed flow. Extra high frequency
sounds only appear between 3-11kHz when the flow
cavitates. Cavitation measurement is defined as
“average dB measurement in 3-11kHz band”.
Figure 9: Spectra
Plot of cavitation measurement vs flow rate
Experimental equipment
Figure 3 shows the Sonolator rig used
for experiments. It has a large clear
section made from Perspex. This allows
the flow inside to be seen. It was
designed to allow small particles in the
flow to be photographed, helping
determine local flow speeds using a
technique called Particle Imaging
Velocimetry (PIV).
Figure 10: Cavitation vs flow rate
Figure 11: Cavitation for 3 orifices sizes
Cavitation shows a sharp onset at a specific flow rate (Figure 10). The
onset varies according to the orifice (Figure 11).
Figure 3: Perspex rig
Summary
Cavitation observations
Figure 4 shows a white jet after the orifice,
observed for higher flow rates. Hissing
noises were heard at the same time. The
close up, Figure 5, shows that the jet is
split into upper and lower sections. This is
cavitation coming off the sharp upper and
lower edges of the orifice. (When fluids
travel fast, their pressure reduces. When
fast enough, pressure goes below vapour
pressure. Gas bubbles form and collapse,
which is cavitation, and can be heard.)
Figure 4: Cavitation jet
Figure 12: Results Table
Conclusions
Figure 5: Close-up of jet
Acoustic measurement
Figure 6: Microphone
Figure 6 shows a microphone placed on the
rig. A soft putty seal reduces external noises.
Sound damping is especially good at higher
frequencies. So high frequency sound is only
picked up if it comes from within the Perspex,
e.g. cavitation noises. A computer records the
audio output for analysis.
For additional information contact:
David Ryan, Chemical Engineering,
University of Birmingham, B15 2TT
(davidryan1998@hotmail.com)
Theory predicts a fixed
pressure drop for onset
of cavitation (Figure
12). This disagrees with
experiment. Literature
values fall in the middle
of experimental values.
• A Perspex Sonolator section has been made, allowing the flow in the
Sonolator to be seen clearly
• Cavitation was observed visually and aurally
• Measurement of cavitation onset is possible using audio spectra
• Smaller orifices cavitate at higher pressures, disagreeing with theory
Future Developments
• Explaining why smaller orifices cavitate at higher pressures
• Checking whether the blade affects cavitation
• Comparing experimental data to computational models (CFD)
• Understand how cavitation affects mixing and emulsification
References: •Håkansson, A., et al (2010) “Visual observations and acoustic
measurement of cavitation in an experimental model of a high-pressure homogenizer”
Journal of Food Engineering 100 (3), 504–513
•Quan, K. M., Avvaru, B., Pandit, A. B. (2011) "Measurement and Interpretation of
Cavitation Noise in a Hybrid Hydrodynamic Cavitating Device" AIChE Journal 57 (4),
861-871
Acknowledgements:
• Duncan Court, Unilever R&D
Port Sunlight, UK
• Bob Sharpe, Bill; Chem
Eng, Univ. of Birmingham