S. Berliner, III's berliner-ultrasonics.org Ultrasonics Page 5 keywords = " ultrasonic ultrasound cavitat ultraschall sonde ultrasonique sonotrode acoustic sonic sound wave ultra liquid processing Ultrasonic Industry Association UIA bubble shock wave clean immersi vapor degreas weld join bond sew seal solder insert stak drill grind machin cut extru form spin sonochemi react accelerat pollut abat toxi waste treat beneficiat remediat particl dispers disrupt homogeniz emulsif dissol degas foam defoam sparg phaco phaeco lithotript liposuct prophyla history Narda microwave fusion propulsi fluid filtration home.att.net "
Updated:  29 Dec 2013; 13:15 ET
    [Created 23 Feb 2004;
original AT&T Worldnet Website begun 30 May 1996.]

Update info on the top on ALL pages for your convenience.
URL http://berliner-ultrasonics.org/uson-5.html
(formerly http://home.att.net/~Berliner-Ultrasonics/uson-5.html 
moved to this domain on 06 Mar 2010)

S. Berliner, III
Consultant in Ultrasonic Processing
"changing materials with high-intensity sound"

SONOCHEMISTRY * REACTION ACCELERATION * DISRUPTION
HOMOGENIZATION * EMULSIFICATION * POLLUTION ABATEMENT
DISSOLUTION * DEGASSING * FINE PARTICLE DISPERSION
BENEFICIATION OF ORES AND MINERALS
CLEANING OF SURFACES AND POROUS MATERIALS

also see
Keywords (Applications) Index

[consultation is on a fee basis]

Specializing in brainstorming and devil's disciplery for new products and
reverse engineering and product improvement for existing products.

{"Imagineering"}

Technical and Historical Writer, Oral Historian
Popularizer of Science and Technology  


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Ultrasonics Page 5



INDEX

PLEASE NOTE:  If some internal links refuse to work,
please click on Back and scroll down.

Ultrasonics Index

On the main Ultrasonics Page:

    Applications List.

    Probe-type Ultrasonic Processing Equipment.

    Quick Links to Major Ultrasonic Probe Manufacturers (moved to this page 10 Jul 2002).

    Brain Storming - bright ideas, pipe dreams, pie-in-the-sky?

On Ultrasonics Page A

    AL-1C - "CONDENSED GUIDE TO ULTRASONIC PROCESSING"
        (A Layperson's Explanation of a Complex Letterhead).

    AL-1P - "A POPULARIZED GUIDE TO ULTRASONIC PROCESSING".

On Ultrasonics Page 1:

    AL-1V - "A POPULARIZED GUIDE TO ULTRASONIC CAVITATION"
        (A Non-Technical Explanation of "Cold Boiling"
      moved from the preceding page 12 Feb 00).

    ULTRASONIC DEGASSING.

    TUBULAR HORNS (Radial Radiators).

    CARE of TIPS (Radiating Faces).

On Ultrasonics Page 1A:

    AL-4 - AMPLITUDE MEASUREMENT.

    Free Bubbling.

    Bubble Entrapment.

    Foaming and Aerosoling - moved 28 May 02 to this Page 4.   rev

    Extenders.

    Call for Contributions for Book.

On Ultrasonics Page 2 (the next page):

    More on Cavitation.

    AL-2 - "ULTRASONICS AND FINE PARTICLES -
        BENEFICIATION OF SLURRIES AND FINE-PARTICLE SUSPENSIONS
        [CERAMICS, COAL & ORES, COATINGS, COLUMN PACKINGS,
            SINTERING, SLIPS].

On Ultrasonics Page 3:

    AM-1 - "ULTRASONIC STERILIZATION and DISINFECTION".

    UM-1 - "ULTRASONICS, HEARING, and HEALTH"

    Keywords (Applications) Index.

    What's New?

On Ultrasonics Page 4:

    Dissolution.

    Foaming and Aerosoling - moved 28 May 02 from Page 1A.

    Ultrasonic Propulsion (Propulsive Force) - Moving Material.

    Ultrasonic Fountains - Atomization, Nebulization, Humidification,
        Misting, Particle Creation and Sizing.

    Ultrasonics and Nuclear Fusion.

    Boosters (Booster Horns).

    Quick Links to Major Ultrasonic Probe Manufacturers (moved to this page 10 Jul 2002).

On Ultrasonics Page 5 (this page):

    Ultrasonic Whistles (Nozzles, Atomizers, Nebulizers). rev.gif (06 Mar 10)

    Ultrasonic Probe Atomizers   new.gif (14 Feb 2012) and   rev.gif (26 Feb 2012)

    AM-9 - The Use of Ultrasonic Probes in Fuel Research.

On Ultrasonics Page 6:

    Flow Through Horns.

    Explosion Resistance.

On the Ultrasonic Cleaning Page:

    Ultrasonic Cleaning {in process}.

Immersible Transducers.

What's New?

On the ULTRASONICS GLOSSARY page:

    ULTRASONICS GLOSSARY {in process}.

ULTRASONICS BIBLIOGRAPHY
    Ultrasonic Bibliography Page 1 - Reference Books on Acoustics,
        Vibration, and Sound.
    Ultrasonic Bibliography Page 2 - Sonochemistry.
    Ultrasonic Bibliography Page 3 - Selected Articles.


You are invited to visit the ULTRASONIC INDUSTRY ASSOCIATION home page.



CALL FOR CONTRIBUTIONS:  I am writing a book on "High-Intensity Ultrasonic Technology and Applications", on the practical application of power (high intensity) ultrasonics, the use of ultrasonic energy to change materials.  Contributions are welcome (see below).


THE CAVITATION BUBBLE

Larry Crum's Cavitation Bubble

[image from University of Washington, Applied Physics Laboratory (Lawrence Crum, Ph.D.)
- bubble diameter approximately 1mm]


ULTRASONICS


Ultrasonic Whistles
(Nozzles, Atomizers, Nebulizers)

Ultrasonic whistles are perhaps best known as dog whistles; whistles that sound at frequencies well above human hearing (~>18KHz).  However, such whistles can be used to perform useful work, primarily as ultrasonic nozzles, also known as ultrasonic atomizers or ultrasonic nebulizers.

An ultrasonic whistle is basically little more than an ordinary whistle with air (or other gas, even steam) forced through under higher pressure such that the jet going over the orifice or reed is moving fast enough to generate ultrasonic vibrations.  Englishman Francis Galton, author of the acclaimed seminal treatise on modern scientific psychology: "Inquiries into Human Faculty and Its Development" (1883), also invented many devices used in psychological investigation.  One of these was the Galton Whistle (1876) which was a clever combination of a micrometer and a whistle, whereby he was able to precisely vary the length, and thus the frequency, of the resonant chamber of a whistle:

Galton Whistle ca. 1900
(23 Feb 04 drawing by and © 2004 S. Berliner, III - all rights reserved)

This whistle was used to generate sounds to measure the upper limits of human hearing.

Ultrasonic whistles have been used to levitate powders and also to stratify and sort them.   rev (06 Mar 10)

Further research developed whistles with resonant cavities into the orifices of which liquids could be injected; the ultrasonically-induced cavitation in the liquid caused it to atomize and the gas flowing out of the nozzle delivered the resultant fine droplets to a volume or surface where they could be measured or used.

A typical ultrasonic nozzle might look like this:

Ultrasonic Whistle
(16 May 07 drawing by and © 2007 S. Berliner, III - all rights reserved)

Introducing a liquid into the intense acoustic field, through a hollow stem in this instance, allows the liquid to be atomized and sprayed outward:   added.gif (06 Mar 10)

Ultrasonic Atomizer
(06 Mar 2010 drawing by and © 2010 S. Berliner, III - all rights reserved)

One of the first uses for such nozzles was in humidification of Belgian lace works, where fine airborne lints caused disastrous explosions.  Another use is in spray drying, whereby dissolved solids can be precipitated out and formed as microscopic spheres in the nozzle effluent stream.  Such nozzles have been used to form ultrathin laydowns, such as in coating magnetic media.

Any dry gas can be use to drive ultrasonic nozzles.  Steam can also be used but has the drawback that condensate can sputter off the end of the nozzle.

Ultrasonic transducers and probes can also be used to generate a mist, as described earlier in these pages under the "ultrasonic fountain", but some propulsive means must be furnished.  The popular ultrasonic humidifiers sold publicly work in this manner.


Ultrasonic Probe Atomizers

Another way to create a mist or fog ultrasonically is to employ a variation of the Flow Through Horn.  As with the Ultrasonic Fountain, some propulsive means must be furnished.  Basically, all this method entails is fitting a sealed collar around the nodal point of a Flow-Through Horn so that liquid can be injected into the central channel in the horn and inverting the horn and convertor.  As liquid exits the horn at the tip (through the sonication annulus, it pools on the radiating face in a thin film which cavitates, thus generating cavitation bubbles.  The bubbles then rise through the film and burst at the surface, creating a mist which can then be blown onto a collector plate or otherwise trapped and processed.   new.gif (14 Feb 2012)

Ultrasonic Probe Atomizer
(14 Feb 2012 drawing by and © 2012 S. Berliner, III - all rights reserved)

This is an especially convenient method for quick tests or short runs if an ultrasonic probe machine is available.  In the method's simplest form, a low-viscosity liquid can be fed into the collar by gravity.  Angling the probe slightly can even avoid the need for an air/gas stream to move the mist particles, utilizing the ballistic effect of Ultrasonic Propulsive Force.

Actually, there is an even simpler alternate for "quick and dirty" tests - simply invert a standard (undrilled) horn and drip-feed liquid onto the radiating face from a pipette or syringe:   rev.gif (26 Feb 2012)

Alternate Ultrasonic Probe Atomizer
(26 Feb 2012 drawing by and © 2012 S. Berliner, III - all rights reserved)
added.gif (26 Feb 2012)

[Now, you simply can NOT claim that I'm not trying to be helpful!]


AM-9 APPLICATIONS MONOGRAPH 27 April 2004

THE USE OF ULTRASONIC PROBES
IN FUEL RESEARCH

[based on an undated paper written prior to 1976 by
Howard Alliger, then President,
HEAT SYSTEMS-ULTRASONICS INCORPORATED
(now MISONIX INCORPORATED)
1938 NEW HIGHWAY, FARMINGDALE, NEW YORK  11735
telephone 516-694-9555]

Revised and updated by
S. Berliner, III
27 April 2004 and 29 Dec 2013

The potential of ultrasonic energy has often not been appreciated in such diverse applications as emulsifying, extracting, and dispersing.

Instruments that perform these functions, like the SONICATOR® Disruptor (Ultrasonic Processor) from Misonix, have long been used in biological research and have found wider application in physics, chemistry, and industry.  The availability of much larger power outputs and the use of continuous flow attachments have made this transition possible.  Better understanding of ultrasonic theory has helped, as well.

When applied to fuel research, the SONICATOR probe has several interesting applications: emulsifying fuel and water, breaking long chain polymers in fuel as anti-mist agents, dispersing coal particles in oil, dissolving coal in solvents, extracting oil from shale, and aiding the determination of chitin in contaminated fuels.

 

Some Theory

When an A.C. voltage is applied to a crystal, it changes shape in phase with the electric field.  This is the piezoelectric effect.  These continuous changes in shape are the pulsations or sound waves which travel through the probe into the liquid.  Alternate compressions and rarefactions of this wave produce a phenomenon known as cavitation --- the creation and collapse of microscopic bubbles.  These bubbles or cavities take many cycles to grow to "resonant" size.  At this point, they collapse violently in one compression cycle, producing on the order of 20,000 atmospheres of pressure.  This mechanical shock is felt at a distance of a few microns from the cavitation bubble collapse.

Although the SONICATOR is an interesting instrument and, also, relatively simple to use, knowledge of ultrasonic theory as well as techniques developed since its introduction is important for best possible results.

Almost any variable that tends to suppress cavitation --- such as higher ambient pressure, higher surface tension or tensile strength, degassing, lower temperature --- will increase intensity if there is enough power to produce cavitation.

A rise in temperature may allow more bubbles to nucleate and grow, enhancing the scrubbing action of a tank-type ultrasonic cleaner.  But the increased vapor pressure within a cavitation bubble reduces the violence of collapse; a violence which is necessary for the probe SONICATOR's more difficult work.  As fuels are reduced in temperature, they can then more easily be emulsified with water.  Similarly, applying static pressure during treatment compresses and dissolves air bubbles in the fluid.  This increases intensity by removing the air which will cushion bubble collapse.  It is possible to completely eliminate cavitation in organic solvents by saturating with certain gases.  These gases fill the cavitation bubble and prevent collapse.

Raising the frequency also lowers the intensity by reducing the size of the cavitation bubble, which then collapses with less force.  Cavitation is more difficult to produce as the frequency is raised and cavitation can not be initiated at any power level at frequencies over about 2.5 MHz.

Tensile strength is not a term normally applied to liquids.  However, the forces necessary to separate water molecules (probably van DerWaal's), like those of metals, are quite high.  In fact if water were absolutely pure, it would take about 15,000 psi to cause fracture or cavitation.  Since water is never pure --- distilled water has many thousands of impurities per cc, air and particles , far less pull, or negative pressure, is necessary to produce cavitation.  The greatest strength achieved in a liquid is -277 atmospheres; this was produced in a highly purified water which was "fractured" in a spinning tube by centrifugal force.

Solvents or fuel oil have lower tensile strengths than water and cavitation bubbles produced in them collapse with less force.  Ordinary degassed kerosene requires about one atmosphere of negative pressure for cavitation, water seven atmospheres.  When comparing most organic fluids, higher viscosity and lower vapor pressure may be used as a rough indicator of tensile strength --- or expected cavitation intensity.  Although other liquid properties such as density, surface tension, and speed of sound are also involved, the former two are the most useful or practical predictors.  Adding a polymer to a particular fluid increases viscosity, but this will not increase intensity of bubble collapse.  The added viscosity is due to friction, not greater molecular attraction, and the bubble would simply collapse more sluggishly.

The addition of wetting agents also reduces tensile strength, or its close cousin, surface tension.  The use of solid combustible powders like lampblack as emulsifying agents, rather than the soap-type, might be preferable since this will not affect surface tension and intensity as drastically.  One reason oil-in-water emulsions are easier to form ultrasonically than water-in-oil is possibly due to the "stronger" disperse phase.  Cavitation in a continuous water phase is more intense for a given generator setting than for a continuous oil phase.

As a matter of interest, the height of Redwood trees is limited by the tensile strength of the water rising to the top branches by capillary action.  If the trees grew higher, the liquid would "fracture" and the uppermost leaves would not be fed.

[As an aside here, the resultant steam explosion would blow the top off the tree! - SBIII]

 

Making Emulsions

The use of water/oil emulsions is recognized as having several advantages in combustion processes and engine fuel:

    reduction of emissions -- CO, NOx, smoke

    utilization of heavier or less expensive fuel

    small improvement in efficiency

  The challenge facing us now:

    find the optimum emulsion --- size, distribution, concentration

    produce it without emulsifiers or wetting agents

    produce it in fairly stable form

    measure it
Here, ultrasonic techniques hold great promise.  The SONICATOR will produce an oil and water emulsion of 1 micron size in a few seconds; and in a minute, 1/10 micron.  The distribution curve is sharp compared to that of mechanical homogenizers.

As sonication proceeds, the particle size gets smaller and the size distribution narrows.  For any particular intensity there is a size and disperse phase concentration limit.  At some point in the sonication process, the particle size will start growing rather than reducing, because flocculation or coagulation have become more predominant than ultrasonic dispersing.

It takes less intensity to initiate an oil-in-water emulsion than its reverse and the particle size is smaller.  Oil droplets in and oil/water emulsion are electrically charged which tends to stabilize the mixture.

As might be expected, the addition of stabilizers increases the concentration of the emulsion as well as the rate of formation.  Highly dispersed emulsions of 35% concentration can be obtained without surface active agents, however.  Conceivably, if the disperse phase is broken down fine enough, say, approaching 1/100 micron, the dispersion might be stable without emulsifiers, like a colloid.  Certainly, there is less tendency to "cream out" due to sedimentation.  A water/oil ratio of up to 45% (water/water + fuel) can be burned.  With just natural surfactants in fuel, the ultrasonic emulsifying capacity may approach this higher ratio.  Oil/water/oil or multiple emulsions might be an interesting addition to fuel research.  These are frequently formed when inverting the emulsion.  Possibly the phases go on, ad infinitum, although this phenomenon is not easily seen in a microscope or otherwise detected.

In the usual case, lower temperature produces better emulsions.  Oil/water is more stable under the effects of temperature than water/oil, and probably more stable with time in general.  If there is a change in the relative temperature of the two phases, emulsification will be reduced.  A little water, or a little oil, is easier to emulsify.

The process becomes more difficult as the starting ratios of oil and water approach 50/50.  It is also more difficult if one phase is, or becomes, more viscous than the other.

Research on emulsions and their practical use in fuel oil has been hampered by a lack of good means for measuring water droplet size, the disperse phase.  Indication of size distribution by an in-line detecting system would be especially valuable.

Although conventional light microscopes are not too useful for size estimations much below a micron, new "interference" methods might be applicable.  There are also several other possibilities.  For example, since the viscosity of a given phase ratio is influenced by mean droplet size as well as size distribution, measurement of this parameter might provide a continuous flow measurement system.

Electrical conductance has been used as a qualitative test for phase type, and high voltage AC is known to break emulsions.  Instinct would suggest that there is an electrical approach to this problem.  High and low voltages or currents, AC superimposed on DC, or capacitance of a thin emulsion film, might be tried.

Still another possibility is the coherent light source of a laser.  By monitoring both the absorption and scattered radiation from a laser beam, the particle size and distribution may be determined.  The highest frequency available, 25MHz, produces a wavelength in fuel oil of 70 microns.  Only a small amount of sound energy will therefore be scattered by one micron water droplets.  However, if the sound receiver is positioned to pick up scattered radiation only, and the source is a multi-frequency transmitter, a suitable emulsion detecting device is possible.

[It is not the provenance of this monograph to examine droplet measurement systems].

 

Making Anti-Mist Agents

Polymers are now being added to fuel oil as anti-mist agents.  If the polymers can be broken sufficiently when needed, for example, ... to start an engine, their use becomes a practical solution to the fire hazard problem.  Researchers have used ultrasonics to break long-chain polymers since the early thirties.  These polymers are usually dissolved in organic solvents.  Ultrasonic degradation or depolymerizing of many molecules have been studied, including polystyrene, methyl methacrylate, nitrocellulose, proteins, rubber, and starch.

The larger the molecule and more intense the ultrasonics, the faster the degradation.  An increase of intensity also reduces the ultimate particle size.  The molecule is usually broken in half at the C-C bond, and its fragments are in turn broken in half, producing finally a narrow dispersion of molecular weights.  As a contrast, depolymerization due to heat or oxidation produces fragments of varying molecular weights.

Polystyrene can be reduced to 1/6 its original molecular weight.  The disruption of these molecules is not due to frictional forces produced by the sound wave or by heat.  Neither is it due to a resonant effect in the long chain --- although the largest polymers may reach a length of 1 micron, the sound wavelength in liquid even at 1MHz is far longer.  Cavitation produces this breaking effect; and suppression of cavitation by degassing or high static pressures usually prevents it.  There is evidence that vibrating bubbles without collapse can cause breakage.  This phenomenon produces large local pressure changes also and is the probable cause of cavitation erosion damage to ship propellers rather than actual bubble collapse.

Dissolved gases within the organic solvent may have a significant effect.  Highly soluble gases such as sulfur dioxide, ammonia, or carbon dioxide dissolved in benzene can suppress cavitation activity by penetrating into the cavitation bubbles in great amount, cushioning or preventing collapse.

Depolymerization may produce free radicals or ions concomitant with the splitting of the C-C bond.  These radicals can be detected by their ability to oxidize iodide to iodine.

 

THE SONICATOR

As a research tool or production device the SONICATOR ultrasonic processor (as a disruptor/emulsifier) is ideal in many respects.  Periodic maintenance is obviated since there are no "moving" parts and nothing to be cleaned.  Smoothly variable output intensities provide much needed flexibility for pilot development.  The Continuous Flow Cell permits adjustment of static pressure as well as fuel flow rate.  This cell is made of polycarbonate resin (such as LEXAN®) so that emulsification or other process can be viewed; and the outlet may be placed directly in series with the combustion nozzle or measuring device (cells of other materials are also available).

The standard 600 {now 700} watt, 20KHz, SONICATOR will emulsify about ½ gal/min down to 1 micron droplet size.  Lower frequency 10KHz devices, which once were available in the 8,000 watt range, were more effective emulsifiers because of the larger cavitation bubble, and were more efficient for a given wattage input.  10KHz SONICATORS were, however, quite noisy and physically much larger than the equivalent 20KHz device and are no longer in production.



You may wish to visit the main ULTRASONICS page, et seq., with more on ultrasonics, as well as the Ultrasonics Cleaning page {in process} and the Ultrasonics Glossary page {also in process}.


Those persons interested in SONOCHEMISTRY might wish to look at the sonochemistry pages of:

    Prof. Kenneth S. Suslick of the University of Illinois at Urbana-Champaign, and

    Dr. Takahide Kimura at Shiga University in Japan.


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To tour the Ultrasonics pages in sequence, the arrows take you from the main Ultrasonics Page (with full index) to Pages A, 1, 1A, 2, 3, 4, and this page 5, Glossary Page, Cleaning Page, and Bibliography Pages 1, 2, 3, and 4 (see Index, above).



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