Field of the Invention

This invention pertains to apparatus for introducing acoustic vibrations into a process liquid.

Background of the Invention

Acoustic liquid processing involves the use of acoustic vibrational energy to treat a process liquid. Typical treatments include chemical reaction stimulation, sterilization, flotation enhancement, degassing, defoaming, homogenization, emulsification, dissolution, deaggregation of powder, biological cell disruption, extraction, crystallization, agglomeration and separation.

Typically, such treatments employ acoustic vibrational energy fre quencies in the ultrasonic range (i.e. above the human hearing threshold of about 16 kHz). Accordingly, acoustic liquid processing is sometimes called "ultrasonic processing" or "power ultrasound". More recently, the term "sonochemistry" has been applied to liquid processing techniques which use acoustic vibrations of any frequency. This invention pertains to the use of acoustic vibrations of any frequency, but is particularly useful at fre- quencies above 10 kHz.

A large body of literature has been written on the use of acoustic liquid processing for various applications. See for example "Sonochemistry: Theory, Applications and Uses of Ultrasound in Chemistry", by T.J. Mason and J.P. Lorimer, Ellis Horwood Limited, 1988; and "Practical Sonochemistry", by T.J. Mason, Ellis Horwood Limited, 1991.

In many processing applications, it is desirable to create a phenom¬ enon known as "cavitation" wherein the process liquid is subjected to intense acoustic energy. This creates small, rapidly collapsing voids in the liquid. Although the inventors do not wish to be bound by any specific theories, it is generally believed that extreme local temperatures (i.e. 5000° K) and pressures (i.e. 500 atm.) in the vicinity of the cavitational collapses are largely responsible for the processing action. Since the acoustic intensity necessary to produce cavitation becomes very large for acoustic

frequencies above 100 kHz in most liquids, this type of processing is typi¬ cally confined to frequencies below 100 kHz.

In some other processing applications, it is desirable to use forces associated directly with the acoustic field, such as acoustic radiation and agitation, to effect the processing action. Detailed aspects of these techniques and others are taught in literature such as U.S. Patent Nos. 5, 164,094 Stuckart; 4,673,512 Schram; 4,983, 189 Peterson et al.; and 5, 192,450 Heyman.

Prior art devices used in acoustic liquid processing have typically employed a flow-through duct arrangement to confine the process liquid within a selected treatment volume. A cylindrical flow-through duct ar¬ rangement is desirable in many applications, particularly those involving treatments requiring high acoustic intensities, because the acoustic energy is geometrically focused along the longitudinal axis of the cylinder. This has several advantages, including the ability to attain higher intensity acoustic vibrations within the focal region; confinement of intense cavitation away from equipment surfaces, thereby reducing surface erosion and trans¬ ducer decoupling problems; and, facilitation of the use of catalysts, fixed solid reagents, or sources of electromagnetic radiation (i.e. ultraviolet light) within the focal region for maximum utilization of the cavitational energy.

Prior art acoustic liquid processing devices incorporating a cylindrical duct design for confining the process liquid within a selected volume include

U.S. Patent Nos. 2,578,505 Carlin; 3,056,589 Daniel; 3,021, 120 Van der

Burgt; 3,464,672 Massa; 4,369,100 Sawyer; 4,433,916 HaU; 4,352,570 Firth; and 3,946,829 Mori et al. European Patent specification 0 449 008 Desbor- ough; and Japanese patent 3-151084 Murata also disclose such devices. Almost all prior art acoustic liquid processing devices have utilized piezoelectric or magnetostrictive transducers to generate acoustic vibrations for application to the process liquid. Most other known transducers have not been considered capable of delivering sufficient acoustic energy to the process liquid to perform the desired processing. See for example, Audio and

Ultrasonic Emitting Transducers, by K.A. Bunting, Electricity Council Research Centre, Capenhurst, U.K., 1989.

Most prior art cylindrical acoustic processing devices either have cylindrical magnetostrictive or piezoelectric transducers or have a plurality piezoelectric or magnetostrictive transducers at discrete locations spaced around the outside of a cylindrical chamber containing the process liquid. Each of these design aproaches have deficiencies which have hindered their successful implementation on a commercial scale.

Consider for example liquid processing devices having cylindrical piezoelectric transducer configurations as disclosed in U.S. Patent Nos. 3,464,672 Massa; or 3,056,589 Daniel; or, in Japanese Patent No. 3-151084 Murata. The rigid, fragile nature of most piezoelectric materials makes it difficult to manufacture large diameter transducers, which may restrict the volumetric capacity of the liquid processing device and/or the maximum acoustic intensity attainable along its longitudinal axis. Also, such transducers often require elaborate installation and mounting arrangements which add substantially to the cost of constructing and maintaining the liquid processing device. Also, large tensile stresses induced in the transducer may lead to mechanical fatigue and failure of the transducer. Instead of attempting to fabricate a single cylindrical transducer structure, one may alternatively mount a plurality of piezoelectric or mag¬ netostrictive transducers at discrete locations spaced around the outside of the cylinder which contains the process liquid. U.S. Patent Nos. 2,578,505 Carlin; 4,369, 100 Sawyer; and, 4,433,916 Hall; and, European Patent Appli- cation No. 0 449 008 Desborough disclose such arrangements. This ap¬ proach reduces problems with the transducer per se, compared to designs which use unitary cylindrical piezoelectric transducer elements. However, this approach introduces the new problem of efficiently coupling the acoustic vibrational energy from the individual transducers through the cylinder wall into the process liquid. The various prior art designs discussed

above propose slightly different schemes to address this problem. The practical effectiveness of these schemes is questionable.

The prior art liquid processing devices discussed above all have the deficiency that the available high power magnetostrictive and piezoelectric transducers have high acoustic impedances which are poorly matched to the acoustic impedances of process liquids. These high impedance transducers operate efficiently only in a narrow band of frequencies close to their own mechanical resonant frequencies. This impedance mismatch is a source of lost efficiency in all of these prior art devices. Furthermore, prior art hquid processing devices utilizing piezoelectric or magnetostrictive transducers require the transducer to operate at mechanical resonance, which precludes the generation of multiple or tunable frequencies by a single transducer, as may be desirable in some liquid processing applications. Summary of the Invention

In accordance with the preferred embodiment, the invention provides an acoustic liquid processing device in the form of a vessel having an interior wall for surrounding a process Hquid. An electrostatic film trans¬ ducer is attached to the interior wall to substantially envelop a selected volume of the process liquid. The transducer's acoustic impedance is approximately equal to that of the process liquid. The transducer is energized to subject the process liquid to acoustic vibration.

The acoustic vibrations generated by the transducer are preferably of an intensity sufficient to produce cavitation within the process liquid at points removed from the vessel's interior wall. In most cases the acoustic vibration is advantageously a resonant mode of the process liquid system.

The vessel is preferably cylindrical. In one embodiment, the vessel comprises a single cylinder which directly contains the process liquid; the transducer being attached to the cylinder's interior wall. In another embodiment, the vessel comprises dual, concentric inner and outer cylinders separated by an annular region containing a coupling liquid; the transducer

in this case being attached to the inner cylinder's outer surface, which in turn confines the process Hquid. The inner cyHnder's acoustic impedance approximately equals that of the process Hquid.

The transducer may advantageously be fabricated as a multi-layer structure, as described in U.S. Patent No. 4,885,783 Whitehead et al.

An acousticaUy transparent duct may be positioned within the vessel's interior wall to confine the process Hquid to a selected volume; in which case a coupling Hquid is provided between the duct and the interior wall. When applied to the single cyHnder embodiment mentioned above, the duct confines the process Hquid within the cyHnder. When appfied to the dual cyHnder embodiment, the duct confines the process Hquid within the inner cylinder.

In those embodiments which utilize a coupHng Hquid, the coupfing liquid's cavitation threshold preferably exceeds that of the process Hquid. An ultraviolet Hght source, soHd catalyst, and/or reagent may be axiaUy afigned within the interior wall to enhance the Hquid treatment process.

This invention is not subject to the deficiencies of prior art acoustic

Hquid processing devices. The invention addresses two key problems with the prior art as foUows:

(a) An acoustic Hquid processing device having an electrostatic film transducer attached to an inner waU of a vessel is easier to construct and maintain than prior art acoustic Hquid processing devices. Unlike the fragile cyHndrical piezoelectric materials used in U.S. Patent Nos. 3,464,672 Massa; or 3,056,589 Daniel; or Japanese

Patent No. 3-151084 Murata, electrostatic film transducers are rela¬ tively flexible and robust so that they may be easily conformed into developable surfaces such as cyHnders. This improves manufacturabiHty and maintainabifity in general, particularly for large diameter devices. Further, the flexible nature of electrostatic films allows them to support comparatively large ampfitudes of oscil-

lation without inducing high stresses which would otherwise lead to mechanical fatigue, (b) Electrostatic film transducers typicaUy have acoustic impedances comparable to the acoustic load presented by a process Hquid system over a wide range of frequencies. Therefore, the efficiency with which acoustic energy generated by an electrostatic film transducer can be coupled to a process Hquid system is relatively insensitive to changes in the acoustic properties of the transducer or load. This aUows apparatus according to the present invention to operate efficiently at one or more resonant frequencies of the process Hquid system. It also aUows the frequency of operation of the apparatus of the invention to be tuned in response to changes in conditions without significantly degrading the overaU efficiency of the appar¬ atus. The acoustic properties of the process Hquid system and/or the transducer may change with conditions, such as temperature. These operational characteristics cannot be practicaUy achieved with with prior art devices which use high impedance piezoelectric or magnetostrictive transducers which operate best only in a very narrow band around a single resonant frequency of the transducer.

Electrostatic film transducers are incapable of generating sufficient acoustic intensity for use in conventional acoustic Hquid processing devices. However, when used in the apparatus of this invention, an electrostatic film transducer is capable of producing acoustic pressures sufficient for acoustic Hquid processing. This is because the apparatus exploits the properties of such a transducer, which are inherently different from those of piezoelectric or magnetostrictive transducers, to reHably couple the transducer to a resonant mode of the process Hquid system. Resonant amplification aUows the generation of sufficient acoustic pressures to cause cavitation. A large diameter vessel may be used to achieve a desired degree of energy concen¬ tration in a region around an axis of the vessel.

Brief Description of the Drawings

Figure 1 is a simplified cross-sectional illustration of a prior art transducer.

Figures 2, 3 and 4 are simplified cross-sectional views of various prior art electrostatic film transducers.

Figure 5 is a cross-sectional view of an electrostatic transducer structure suitably mounted for use in accordance with the invention.

Figure 6 is a cross-sectional view of a cyHndrical embodiment of the invention in which the transducer is attached to the interior surface of the cyHndrical process vessel's outer waU.

Figure 7 is similar to Figure 6, with the addition of an interior duct for carrying the process Hquid.

Figure 8 is a cross-sectional view of another cyHndrical embodiment of the invention in which the transducer is positioned away from the cyHndrical process vessel's outer waU.

Figure 9 is similar to Figure 8, with the addition of an interior duct for carrying the process Hquid.

Figure 10 is similar to Figure 6, but shows a transducer having four discrete sections. Figure 11 is similar to Figure 6, but shows a select volume of process

Hquid undergoing cavitation.

Figure 12 is similar to Figure 11, with the addition of an axiaUy aHgned fixture for radiating electromagnetic energy into the region of cavitation. Figure 13 is a cross-sectional view along the longitudinal axis of an exemplary implementation of a Hquid processing device utifizing the Figure 8 transducer arrangement.

Figure 14 is a simplified electronic schematic diagram of one possible means for energizing transducers constructed in accordance with the invention.

Figures 15 and 16 respectively depict alternative spherical and elHptical embodiments of the invention in cross-section. Detailed Description of the Preferred Embodiment

Figure 1 depicts the basic structure of a typical prior art transducer: opposed electrically conducting plates 1 separated by dielectric 2 which has a thickness "d" and dielectric constant "ε". The electrostatic pressure "P" generated by applying a voltage difference "V" across plates 1 causes acoustic vibrations 3. The physical quantities of interest are given by the equation P = (εV ² )/(2d ² ). Accordingly, if voltage V is a sinusoid of frequency "f, then the electrostatic pressure P is a sinusoid of frequency 2f.

Selection of an electrostatic film transducer for use in the present invention requires consideration of two key design criteria. First, in order for the electrostatic pressure P to generate substantial acoustic vibration 3, the impedances of the transducer must be weU matched to that of the acoustic load (in this case the process Hquid). Second, unlike conventional electrostatic transducers which are typicaUy used for radiating low acoustic pressure levels, electrostatic film transducers suitable for practicing the present invention must be capable of generating very high electrostatic pressures. This necessitates the use of large electrostatic fields, typicaUy at least ten milHon volts/meter. When subjected to such fields, any gases present in the dielectric wiU be prone to breakdown, unless the transducer is operating significantly to the left of the Paschen minimum product Pressure x Distance (Pd) curve for the gas in question (see for example Fig¬ ure 8 of U.S. Patent No. 4,885,783 and the description pertaining thereto). Figures 2 and 3 illustrate prior art techniques (both exemplified by

U.S. Patent No. 4,885,783 Whitehead et al) for satisfying the above design criteria. In Figure 2, conducting plates 1 are separated by a closed ceU foam dielectric in which biaxiaUy oriented gas bubbles 4 are suspended in a compHant structure 5. In Figure 3, conducting plates 1 are separated by regularly spaced compHant strips or nodules 6.

More particularly, the Figure 2 transducer utiHzes opposed plates 1 which are electrically coupled to an "energizing means" (i.e. electrical poten¬ tial "V" appHed across the plates). A compHant dielectric material 5 is dis¬ posed between the plates and in contact therewith. The dielectric material has a pluraHty of pockets 4 of approximate average depth "d" such that, for a gas existing within the pockets at a pressure "P", the product Pd is significantly less than the value required to achieve the minimum break¬ down voltage of said gas. In the case of the Figure 3 transducer, opposed first and second plates 1 are again electricaUy coupled to an energizing means which appHes an electrical potential "V" across the plates. A compHant dielectric material 6 disposed between the plates and in contact therewith separates the plates by a distance "d", thus aUowing a gas to exist between the plates at a pressure "P", such that the product Pd is sig¬ nificantly less than the value required to achieve the minimum breakdown voltage of the gas.

Manufacturing difficulties may estabHsh a practical lower bound for the dielectric stiffness which can be attained. In such cases, the effective stiffness of the overaU transducer structure may be reduced by utiHzing multiple layers of electrostatic film to form the transducer structure. This technique reduces the stiffness of the overaU transducer structure in direct proportion to the number of layers used. Such a multiple layer transducer structure is shown in Figure 4. Here, 5 dielectric layers composed of compHant strips 6 alternately separate the 6 conductive plates 1. The stiffness of the Figure 4 structure is theoreticaUy one-fifth that of the equivalent single layer structure shown in Figure 3.

Figure 5 illustrates a simple example of one possible means for mounting and protecting an electrostatic film transducer. Three-layer transducer structure 7, sealed and electricaUy insulated by layers 8, is fixed on one side to surface 9 by means of an adhesive bonding layer 10. A protective outer coating layer 11 is bonded by another adhesive layer 10 to

the opposite side of transducer 7. Protective coating layer 11 is designed to resist corrosive and/or erosive effects of the process Hquid.

Figure 6 depicts a cyHndrical embodiment of the invention in cross- section. CyHndrical process vessel housing 12 provides structural support for transducer 13 and encloses process Hquid 14. The design of housing 12 depends primarily on structural consideration of stresses imposed by the process Hquid pressure, vibration fatigue, mass loading, etc. A typical con¬ struction material for housing 12 is carbon steel. Transducer 13, which may be simUar in construction to the example shown in Figure 5, is bonded to the interior wall of cyHndrical housing 12 (i.e. the interior waU of the cyHndrical housing is analogous to surface 9 in Figure 5).

Figure 7 depicts the same structure as Figure 6, with the addition of an interior duct 15 for enclosing process Hquid 14. Duct 15 is designed to be approximately acousticaUy transparent so that it dissipates or reflects a minimal amount of the acoustic energy generated by transducer 13. This can be achieved by forming duct 15 of materials having mechanical impe¬ dance simUar to that of the process Hquid. Where possible, it is desirable to place duct 15 near a pressure antinode of the resonant system, as this will further minimize losses. The annular region between the outer surface of duct 15 and transducer 13 is fiUed with a coupHng Hquid 16 which transmits the acoustic vibrations from transducer 13 to duct 15 and thence to process Hquid 14. CoupHng Hquid 16 preferably has a high cavitation threshold (such as olive oU) to prevent unwanted cavitation therein. CoupHng Hquid 16 may be caused to circulate within the annular region between the outer surface of duct 15 and transducer 13 to act as a coolant for transducer 13 and/or process Hquid 14.

It is desirable to insert duct 15 between transducer 13 and process Hquid 14 as shown in Figure 7 whenever process Hquid 14 is deemed incom¬ patible with transducer 13 due to potential corrosion, erosion, heat, etc. fac- tors which cannot effectively be controUed by the transducer's protective coating layer 11 alone. Duct 15 can also be used to confine process Hquid

14 to a select region aligned with the cyHndrical process vessel's longi¬ tudinal axis within which the intensity of the acoustic vibrations is greatest, thereby optimizing the use of the acoustic energy generated by transducer 13. Figure 8 depicts another cyHndrical process vessel in which transducer 13 is held a fixed distance "s" away from the internal waU of structural housing 12. This is achieved by mounting transducer 13 on an acousticaUy transparent cyHndrical support 17 mounted concentricaUy within housing 12 to define a gap of distance "s" between the respective inner and outer waUs of housing 12 and support 17. Transducer 13 is preferably mounted on the outer waU of support 17 to isolate it from process Hquid 14 (i.e. in this embodiment the process vessel's transducer-bearing "interior waU" is the outer waU of support 17). CoupHng Hquid 16 fills the annular region between housing 12 and transducer 13 and may again serve as a coolant for transducer 13 and/or process Hquid 14.

The Figure 8 embodiment aUows design freedom in positioning of transducer 13 relative to the acoustic system. SpecificaUy, transducer 13 can be placed somewhere other than on the inner surface of structural hous¬ ing 12, to more optimaUy drive the acoustic system. Figure 9 shows the addition of duct 15 to the Figure 8 embodiment.

As described above with reference to Figure 7, duct 15 can be used to isolate transducer 13 from process Hquid 14 and/or confine process Hquid 14 to a select region aHgned with the cyHndrical process vessel's longitudinal axis to optimize the use of the acoustic energy generated by transducer 13. The annular regions between (i) the outer surface of duct 15 and the inner surface of support 17; and, (n) transducer 13 and the inner surface of housing 12 are again filled with a coupHng Hquid 16 which transmits the acoustic vibrations from transducer 13 to duct 15 and thence to process Hquid 14. Figures 6, 7, 8, and 9 depict embodiments of the invention in which transducer 13 completely envelops process Hquid 14. However, simUar

processing results can be attained if transducer 13 comprises a plurality of discrete transducer elements spaced around the circumference of the process vessel to substantiaUy envelop the process Hquid. This notion is iUustrated in Figure 10, which is analogous to Figure 6, except that the single cyHndrical transducer 13 shown in Figure 6 is replaced with four discrete semi-cyHndrical transducer elements 18.

The Figure 10 embodiment may be used to improve the manufacturabUity of the device. The spacing "r" between individual transducer elements 18 should be kept as small as possible, as the reduction in overaU transducer area wiU cause a corresponding reduction in the maximum acoustic power which can be generated by the device. All of the transducer elements 18 should be operated in phase with one another.

The cyHndrical geometry of the embodiments described above and -Illustrated in Figures 6, 7, 8 and 9 focuses the transducer's acoustic energy towards the longitudinal axis of the cyHndrical process vessel. This is particularly useful where it is desired to produce cavitation in the process Hquid, because the focused acoustic energy faciHtates confinement of the cavitation region to a select volume or "cavitation zone" 19 (Figure 11) away from the surface of transducer 13 by appropriate selection of the transducer drive voltage V. By preventing cavitation from occurring near the surface of transducer 13 one may reduce problems such as acoustic decoupHng of the process Hquid from the transducer; and, cavitational erosion of the transducer's surface. Focusing the acoustic energy also reduces the magni- tude of the transducer osciUations required to attain a given pressure ampHtude within the "cavitation zone" 19.

By focusing the acoustic energy in a selected volume of the process Hquid one may also more efficiently combine acoustical energy treatment with other treatments. For example, Figure 12 lustrates how an elec- tromagnetic energy radiating device 20 such as an ultra-violet lamp mounted within a suitable housing 21 (i.e. a quartz tube) can be placed in

cavitation zone 19 for simultaneous cavitation and irradiation of the process Hquid in cavitation zone 19. For example, such an embodiment may be appHed in the treatment of chlorinated organic compounds as described in U.S. Patent No. 5, 130,031 Johnston. SimUarly, a fixed soHd catalyst or reagent may be mounted along the longitudinal axis of the cyHndrical process vessel for more efficient use of the acoustic energy (i.e. due to the observed tendency of acoustic energy to concentrate in regions occupied by such catalysts or reagents).

It has been noted in U.S. Patent No. 5, 164,094 Stuckart that a piezoelectric polymer such as PVDF may be suitable for use as a transducer in an acoustic separation apparatus. The use of PVDF solves the aforementioned problems inherent to piezoelectric ceramics because PVDF is a relatively flexible and durable planar material. However, it is hindered in its use in this appHcation because of its relatively low acoustic output. Figure 13 shows how the transducer arrangement described above in relation to Figure 8 may be implemented in a process Hquid system. Structural housing 12 is equipped with flanges 30 at either end for connection to external piping system 31 which conveys process Hquid 14. Inner, acousticaUy transparent support waU 17 is also equipped with flanges 32 at each end. Inner waU 17 is held rigidly in concentric aHgnment with housing 12 by compressing flange 32 between flanges 30 via bolted joint 33. Gaskets 34 prevent leakage of coupHng Hquid 16 and/or process Hquid 14 to the external environment. Transducer 13 mounted on inner waU 17 is suppHed with electrical energy from energizing means 28 via cables 29 which penetrate the sealed system through grommetted port 35 in housing 12. Elastic deformation of inner waU 17 aUows for pressure equaHzation between coupHng Hquid 16 and process Hquid 14.

Figure 14 shows schematicaUy one example of a means for energizing the transducer. Signal source 36 outputs a sinusoidal signal at the desired frequency(s) which is then amplified by amplifier 37. The low- voltage output from amplifier 37 is fed to the primary side of transformer 38 which

raises the voltage of the signal by an amount proportional to the transformer's turns ratio. The resultant high-voltage signal is then fed from the secondary side of the transformer to tuning inductor 39 which has a characteristic inductance "L", and thence to transducer 40 which has a characteristic capacitance "C". Tuning inductor 39 and transducer (capacitor) 40 together form a resonant circuit which operates in electrical resonance at the desired circular frequency "ω" (rad/s) in accordance with the relation: L = l/(ω ² C) . Voltage "V" across the transducer 13 is the same voltage "V as shown in Fig. 1. In some appUcations it may be desirable to pressurize the process

Hquid. One reason for doing this is to increase the cavitation threshold, and thereby allow the use of higher acoustic pressures without causing cavitation (i.e. for use in appUcations such as acoustic agglomeration where high acoustic pressures are desirable, but cavitation is detrimental). Another reason for doing this is to increase the intensity of the cavitation bubble coUapse (which generaUy increases the effectiveness of the cavitation processing action). If the process Hquid is pressurized in any embodiment which employs a coupHng Hquid (i.e. any of the Figure 7-12 or 14-16 embodiments), then it wUl be necessary to equaHze the pressure between the process and coupHng Hquids. The pressure equaHzing means could be as simple as a providing an elastic membrane between the coupHng Hquid and the process Hquid. In some cases, the waU separating the coupHng and process Hquids could itself constitute such a membrane, if mounted correctly. It wiU in most cases be desirable to excite one or more resonant modes of the acoustic system. The creation of standing waves is necessary in certain appUcations of the invention (i.e. acoustic agglomeration) and in general aUows the development of much higher acoustic pressures in the process Hquid than those directly produced by the transducer. The degree to which the pressure is amplified at resonance depends on the quaHty factor "Q" of the resonant system, which in turn depends upon the total

damping in the system. In order to obtain the highest Q possible in the resonant system it is desirable to keep the internal damping of the transducer as low as possible.

As wiU be apparent to those skilled in the art in the Hght of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. For example, in appUcations requiring very high acoustic intensities, it may be desirable to construct a process vessel which sphericaUy envelops the process Hquid to further enhance the focusing of the acoustic energy. Figure 15 depicts a spherical embodiment of the invention in cross-section. Spherical process vessel housing 12 provides structural support for trans¬ ducer 13 and encloses process Hquid 14. Process Hquid 14 is circulated through the focal region of vessel 12 via duct 41 which penetrates vessel 12 through grommetted port 42. The region between the outer surface of duct 41 and transducer 13 is fiUed with a coupHng Hquid 16 which transmits the acoustic vibrations from transducer 13 to duct 41 and thence to process Hquid 14. In other appUcations it may be desirable to construct a process vessel which elHpticaUy envelops the process Hquid. Figure 16 depicts an elHptical embodiment of the invention in cross-section. Elliptical process vessel housing 12 provides structural support for transducer 13 and encloses process Hquid 14. The scope of the invention is to be construed in accordance with the substance defined by the foUowing claims.