Ultrasonics: Applications and Processes
Ultrasonication is used in many applications, such as homogenizing, disintegration,
sonochemistry, degassing or cleaning. Below, you find a systematic overview over
the various ultrasonic applications and processes.
Ultrasonic Homogenizing
Ultrasonic processors are used as homogenizers, to reduce small
particles in a liquid to improve uniformity and stability. These particles (disperse phase)
can be either solids or liquids. Ultrasonic homogenizing is very efficient for the reduction
of soft and hard particles. Hielscher produces ultrasonic devices for the homogenization
of any liquid volume for batch or inline processing. Laboratory ultrasonic devices can be
used for volumes from 1.5mL to approx. 2L. Ultrasonic industrial devices are used for
the process development and production of batches from 0.5 to approx 2000L or flow
rates from 0.1L to 20m³ per hour
Ultrasonic Dispersing and Deagglomeration
The dispersing and deagglomeration of solids into liquids is an
important application of ultrasonic devices. Ultrasonic cavitation generates high shear
forces that break particle agglomerates into single dispersed particles. The mixing of
powders into liquids is a common step in the formulation of various products, such as
paint, ink, shampoo, beverages, or polishing media. The individual particles are held
together by attraction forces of various physical and chemical nature, including van der
Waals forces and liquid surface tension. The attraction forces must be overcome on order
to deagglomerate and disperse the particles into liquid media. For the dispersing and
deagglomeration of powders in liquids, high intensity ultrasonication is an interesting
alternative to high pressure homogenizers and rotor-stator-mixers.
Click here to read more about ultrasonic dispersing and deagglomeration!
Ultrasonic Emulsifying
A wide range of intermediate and consumer products, such as
cosmetics and skin lotions, pharmaceutical ointments, varnishes, paints and lubricants
and fuels are based wholly or in part of emulsions. Emulsions are dispersions of two or
more immiscible liquids. Highly intensive ultrasound supplies the power needed to
disperse a liquid phase (dispersed phase) in small droplets in a second phase (continuous
phase). In the dispersing zone, imploding cavitation bubbles cause intensive shock waves
in the surrounding liquid and result in the formation of liquid jets of high liquid velocity.
At appropriate energy density levels, ultrasound can well achieve a mean droplet sizes
below 1 micron (micro-emulsion).
Click here to read more about ultrasonic emulsifying!
Ultrasonic Wet-Milling and Grinding
Ultrasonication is an efficient means for the wet-milling
and micro-grinding of particles. In particular for the manufacturing of superfine-size
slurries, ultrasound has many advantages, when compared with common size reduction
equipment, such as: colloid mills (e.g. ball mills, bead mills), disc mills or jet mills.
Ultrasonication allows for the processing of high-concentration and high-viscosity
slurries – therefore reducing the volume to be processed. Ultrasonic milling is suitable for
processing micron-size and nano-size materials, such as ceramics, alumina trihydrate,
barium sulphate, calcium carbonate and metal oxides.
Click here to read more about ultrasonic wet milling and micro-grinding!
Ultrasonic Cell Disintegration
Ultrasonic treatment can disintegrate fibrous, cellulosic material into fine
particles and break the walls of the cell structure. This releases more of the intra-cellular
material, such as starch or sugar into the liquid. In addition to that the cell wall material is
being broken into small debris.
This effect can be used for fermentation, digestion and other conversion processes of
organic matter. After milling and grinding, ultrasonication makes more of the intracellular material e.g. starch as well as the cell wall debris available to the enzymes that
convert starch into sugars. It does also increase the surface area exposed to the enzymes
during liquefaction or saccharification. This does typically increase the speed and yield of
yeast fermentation and other conversion processes, e.g. to boost the ethanol production
from biomass.
Click here to read more about the ultrasonic disintegration of cell structures!
Ultrasonic Cell Extraction
The extraction of enzymes and proteins stored in cells and subcellular particles is an
effective application of high-intensity ultrasound, as the extraction of organic compounds
contained within the body of plants and seeds by a solvent can be significantly improved.
Ultrasound has a potential benefit in the extraction and isolation of novel potentially
bioactive components, e.g. from non-utilized by-product streams formed in current
processes.
Ultrasonic Degassing of Liquids
Degassing of liquids is an interesting application of ultrasonic devices. In this
case the ultrasound removes small suspended gas-bubbles from the liquid and reduces the
level of dissolved gas below the natural equilibrium level.
Continuous Disinfection of Hot Water Systems
To fight the dangerous Legionella bacteria in hot water systems and
secure a safer showering environment the Gruenbeck company has developed the GENObreak® system. This system uses Hielscher ultrasonic technology in combination with
UV-C light
CHEMICAL EFFECTS OF ULTRASONICS
A large number of experiments have been conducted on the effect of intense sound
waves upon chemical reactions. Certain types of chemical reactions have been
speeded
by the application of intense waves. However, in some cases it is difficult to isolate
the
thermal effects due to the sound and the effects due to the sound alone. Another
chemical effect is the breaking down of molecules. For example, a chain molecule of
starch has been broken into six fragments. The application of intense sound waves
to
speed up the aging of whiskey has been suggested. the explanation is that in the
aging
process there is a gradual change in the structure of complex molecules which could
be accomplished in a relatively short time with the application of sound.
BIOLOGICAL EFFECTS OF ULTRASONICS
Ultrasonics have a very destructive effect upon small living organisms. Small fish
have
been killed by high-power echo ranging and sounding devices.
Ultrasonics have been used in the extraction of antigens secreted in the cells of
pathogenic bacteria. These antigens are used in serums for immunization against
typhoid and other diseases. The bacterial cell walls are broken down by the
application
of ultrasonic waves and the antigens are set free. The cell walls of the bacteria are
separated from the antigens by centrifuging.
It appears that bacteria can be destroyed by ultrasonics. The bacteria in milk have
been
reduced by the application of ultrasonics. This indicates that milk can be sterilized
by
ultrasonics.
Another application in medicine is the use of sound to produce stimulation within
the
body. Therapeutic effects of a different nature but similar to those produced by heat
and radio-frequency diathermy may be obtained.
As in the case of chemical effects the biological effects are somewhat obscure but
very
interesting.
MEDICAL APPLICATIONS OF ULTRASONICS
The applications of ultrasonics in the medical field have involved analysis and
treatment. The developments in the medical field appear to be very promising.
The effect of ultrasonics on tissues has been investigated. The heating and
mechanical
effects have been isolated. The conclusion is that there is an effect outside of the
heating effect.
The effects of the changes produced by high intensity sound upon the central
nervous
system has been investigated. The results show that nerve cells are particularly
sensitive to ultrasonics, while blood vessels and nerve fibers are much more
resistant.
A study of the therapeutic effect of ultrasonics shows that the heat which is
produced
plays the major role. However, ultrasonics also produces a mechanical effect.
Ultrasonics has been used to produce deep-seated heating in the treatment of
arthritis.
The cerebral ventricular geometry has been portrayed by means of ultrasonic
techniques. The head is immersed in water. An underwater projector sends an
ultrasonic wave through the head. A hydrophone picks up the transmitted sound. A
frequency of 2.5 megacycles was used. A scanning system together with a facsimiletype recorder presents the ultrasonogram in the form of a picture showing the
cerebral ventricular geometry. This method provides a means for the detection of
brain tumors similar to that of the X-ray.
Recent work on tumor detection employs ultrasonic waves and echo-ranging
techniques with cathode-ray presentation. the pulses are sent into the body and the
echos return in different intensities depending upon the difference in acoustical
impedance of the malignant and nonmalignant tissues and in different times
depending upon the depths of the reflecting boundaries.
A small version of the ultrasonic drill has been developed for use by dentists in
drilling
teeth. the advantages of the ultrasonic drill is reduction in pain and improved
definition of the drilled area.
Destructive ultrasonic probes have been developed for medical use. These probes
typically operate between 20 and 60 kilohertz, usually of the piezoelectric type and
have
high strokes at their distal ends.
One such probe is tubular in shape with a small frontal surface area. This surface
area
produces little or no cavitation when placed in water, however, due to high
mechanical
vibration this probe can cut through tissue and aspirate the emulsified particles
through the center without damage to connective tissue.
Another tubular probe widely used for medical applications is the phacoemulsifier.
The
phacoemulsifier is used in ophthalmology for removing cataract lenses from ones
eye.
The same principal of mechanical action with little or no cavitation is present at the
probes tip that actually cores the lens and aspirates it through the center.
Still another medical use of ultrasonics is cutting through tissue with a knife edge.
Advantages of this technique for the patient is reduced bleeding from coagulation of
blood vessels and the ease at which the knife blade cuts from reduced friction and
increased sharpness.