Abstract:
A device and method for sono-chemical processing, including a reactor bounded by a substantially cylindrical wall, the reactor having: a reaction volume, defined by the wall; first and second magnetostrictors, associated with the reaction volume, the wall and the magnetostrictors designed and disposed such that the first magnetostrictor produces a first series of ultrasonic waves having a first frequency within the reaction volume, the second magnetostrictor produces a second series of ultrasonic waves having a second frequency within the reaction volume, wherein the second frequency exceeds the first frequency.

Description:
[0001]     This application draws priority from U.S. Provisional Patent Application Ser. No. 60/607,591, filed 8 Sep., 2004. 
     
    
     FIELD AND BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a method and device for effecting and enhancing chemical reactions and processes, and more particularly, to a method and device for producing water-and-hydrocarbon nano-emulsions.  
         [0003]     Emulsions containing water and diesel oil have drawn much interest as being ecologically clean fuels.  
         [0004]     The emulsification of two such immiscible liquids involves thermodynamically treating the liquids so as to destroy the cohesive forces within a liquid, so as to form extremely small droplets.  
         [0005]     The most efficient method to produce nano-emulsions involves achieving cavitation within the liquids to be emulsified. Cavitation is a well-known effect wherein, due to disruption of cohesive forces by an external mechanical action upon a liquid, bubbles are formed, which are immediately filled with gases that have been dissolved in the liquid, or with the vapor form of the liquid itself. Cavitation usually occurs in pipes carrying water, ship propellers operating at high RPM, centrifugal pumps pumping liquids, high-speed mixer blades, and similar devices.  
         [0006]     The emulsification of two immiscible liquids into nano-emulsions is best achieved in a reactor that is operationally connected to a transducer for obtaining electromagnetic high-frequency energy and converting it into mechanical oscillation (ultrasound). The generated ultrasound is radiated into the cavity of a reactor, thereby producing cavitation.  
         [0007]     All prior-art ultrasound processors utilize a considerable number of low-power, piezo-ceramic transducers glued onto the exterior walls of cylindrical reactors. This construction has an adverse effect of attenuating useful transmissions of high-intensity ultrasound energy. Moreover, the piezo-ceramic generators transmit low-energy ultrasound through the walls of the reactor, causing a considerable energy loss. Furthermore, the cavitation bubbles generated on the walls of the reactor cause an additional loss in ultrasound energy, as the gas bubbles absorb the ultrasound. Because of these shortcomings, the efficiency of the above reactors is considerably low, never achieving more than 25-30%.  
         [0008]     Because of the low useful energy generated by the ultrasound reactors of the prior art (e.g., the reactor disclosed in WO 97/02088 PCT), the emulsion production rates of such reactors are correspondingly low. Moreover, the average size of the droplets is several microns.  
         [0009]     To increase productivity, U.S. Pat. No. 5,384,508 teaches a tube that at every half-wavelength distance has a resonating ring whose average diameter equals the wavelength of the radiated ultrasound. Each of the rings is connected to a low-power, piezo-ceramic transducer. The length of the tube is optimized to the time necessary to process the material flowing through the tube.  
         [0010]     Each ring on the tube concentrates the ultrasound within a region associated with the ring. This arrangement, however, precludes the process from achieving high production rates, because most of the useful energy is absorbed by the considerable mass of the ring. Furthermore, the remaining useful energy is diminished by a sonotrode construction having poor acoustic properties. The shortcomings of the construction are further exacerbated by the high-amplitude oscillations, which cause material fatigue of the rings. Additionally, since the diameter of a ring is dictated by the wavelength of the ultrasound, it becomes technically impossible for a transducer having a power rating of 200-400 kW (the power rating cannot exceed 1 kW due to the accelerated fatigue of the construction materials) to be connected to a ring whose diameter is about 30 mm for operating at a frequency of 20 kHz. This narrow diameter further limits raw material flowrate, and, consequently, productivity. Therefore, the sonotrode construction employing such tubes and rings is useful only for processing materials that do not require generation of high-intensity ultrasound.  
         [0011]     U.S. Pat. No. 5,658,534 teaches an ultrasound processor having a tube of stainless steel that is 2.5 mm thick, and is connected to three equidistant transducers providing ultrasound having a power distribution of 0.3-1.0 W/cm 2 .  
         [0012]     The goal of the above construction is to create, within a material flow, a region of concentrated energy. This effect of energy concentration is sufficient to impart the reactor with a relatively high specific power.  
         [0013]     The above reactor, however, is complicated and expensive to build, demanding that transducers are strictly synchronized in phase. Moreover, the relatively small size of the concentrated energy region does not allow for emulsification or homogenization of materials in a continuous mode on an industrial scale.  
         [0014]     A standard homogenizer/emulsifier technology capable of processing materials in continuous mode utilizes a cell technology. This technology achieves characteristically low throughputs. For example, when emulsifying lipophilic materials having equal molecular weights, such cells are limited to a maximal flow rate of 5 liters/hour.  
         [0015]     Another commercially-available homogenizer, distributed by Cole-Palmer Ltd., has twelve transducers rated at 0.75 kW/hour that are capable of producing a combined 9 kW/hour ultrasound during a continuous production mode. The design utilizes standard sonotrodes, from which it follows that the design suffers from low production efficiency and from a high rate of erosion of the waveguides. Tests performed by the inventor show that this homogenizer fails to produce emulsions having a sufficiently low droplet size. Moreover, the design requires an unusually large reactor, because the twelve low-efficiency sonotrodes discharge a copious quantity of heat, thereby creating the need for an extremely large cooling system.  
         [0016]     It is evident from all of the above that the above-described prior art is fundamentally incapable of providing the high specific-energy required for industrial production of nano-emulsions, due, inter alia, to poor sonotrode efficiency. The reactors disclosed by the prior art also require frequent maintenance of the ultrasound-generating equipment due to rapid erosion thereof.  
         [0017]     Several reactor configurations have been used to produce nano-emulsions. U.S. Pat. No. 6,079,508 to Caza and U.S. Pat. No. 5,658,534 to Desborough teach reactors having a plurality of ultrasonic transducers placed around the reactor enclosure. The disparity of the longitudinal and the transversal dimensions of the reactor causes the ultrasonic energy to be distributed in a non-homogenous pattern, thereby decreasing the volume available for useful cavitation, and ultimately leading to a low product throughput.  
         [0018]     There is therefore a recognized need for, and it would be highly advantageous to have a method and device for producing nano-emulsions that achieves a higher yield and allows for a substantially higher production rate than methods known heretofore. It would be of further advantage if such a reactor would be simple in construction and would allow for continuous production of such nano-emulsions.  
       SUMMARY OF THE INVENTION  
       [0019]     According to the teachings of the present invention there is provided a device for sono-chemical processing, including a reactor bounded by a substantially cylindrical wall, the reactor having: (a) a reaction volume, defined by the wall; (b) a first magnetostrictor, associated with the reaction volume, and (c) a second magnetostrictor, associated with the reaction volume, the wall and the first magnetostrictor designed and disposed such that the first magnetostrictor produces a first series of ultrasonic waves having a first frequency within the reaction volume, the wall and the second magnetostrictor designed and disposed such that the second magnetostrictor produces a second series of ultrasonic waves having a second frequency within the reaction volume, wherein the second frequency exceeds the first frequency.  
         [0020]     According to further features in the described preferred embodiments, the first frequency and the second frequency are selected so as to achieve modulation between the first series of ultrasonic waves and the second series of ultrasonic waves.  
         [0021]     According to still further features in the described preferred embodiments, the reaction volume is for containing at least two immiscible fluids, and wherein the first magnetostrictor and the second magnetostrictor are disposed with respect to the wall, such that upon introduction of the fluids into the reaction volume, the first series of ultrasonic waves and the second series of ultrasonic waves act upon the fluids so as to produce a nano-emulsion.  
         [0022]     According to still further features in the described preferred embodiments, the second magnetostrictor is disposed below the reaction volume.  
         [0023]     According to still further features in the described preferred embodiments, the second magnetostrictor includes a wave guide, the wave guide being disposed in the wall, adjacent to a bottom surface of the reaction volume, the wave guide for directing the second series of ultrasonic waves into the reaction volume.  
         [0024]     According to still further features in the described preferred embodiments, the first frequency is in a range of 2 kHz, inclusive, to 10 kHz, inclusive.  
         [0025]     According to still further features in the described preferred embodiments, the first frequency is in a range of 2 kHz, inclusive, to 8.5 kHz, inclusive.  
         [0026]     According to still further features in the described preferred embodiments, the second frequency is in a range of 18 kHz, inclusive, to 40 kHz, inclusive.  
         [0027]     According to still further features in the described preferred embodiments, the second frequency is in a range of 18 kHz, inclusive, to 40 kHz, inclusive.  
         [0028]     According to still further features in the described preferred embodiments, the ratio of the first frequency to the second frequency is less than 1:2, inclusive.  
         [0029]     According to still further features in the described preferred embodiments, the ratio of the first frequency to the second frequency is in a range of 1:2, inclusive, to 1:10, inclusive.  
         [0030]     According to still further features in the described preferred embodiments, the first magnetostrictor is disposed so as to radiate the first series of ultrasonic waves radially inward into the reaction volume, thereby producing cavitation along a longitudinal axis of the reaction volume.  
         [0031]     According to still further features in the described preferred embodiments, the second magnetostrictor and the wave guide are disposed so as to focus the second series of ultrasonic waves towards a longitudinal axis of the reaction volume.  
         [0032]     According to still further features in the described preferred embodiments, the device further includes a flexible pad or gasket, disposed between the first and second magnetostrictors, for hermetically sealing between the wave guide and the reaction volume, and for enabling acoustical communication between the first and second magnetostrictors.  
         [0033]     According to still further features in the described preferred embodiments, the inside diameter of the flexible gasket is smaller than an inside diameter of a cylindrical portion of the wave guide.  
         [0034]     According to still further features in the described preferred embodiments, the inside diameter of the flexible gasket is smaller than the inside diameter of the cylindrical portion of the wave guide by at least 0.2 mm.  
         [0035]     According to another aspect of the present invention, there is provided a method of sono-chemical processing including the steps of: (a) providing a reactor bounded by a substantially cylindrical wall, the reactor having: (i) a reaction volume, defined by the wall; (ii) a first magnetostrictor, associated with the reaction volume, and (iii) a second magnetostrictor, associated with the reaction volume; (b) activating the first magnetostrictor to produce a first series of ultrasonic waves having a first frequency within the reaction volume, and (c) activating the second magnetostrictor to produce a second series of ultrasonic waves having a second frequency within the reaction volume, wherein the second frequency exceeds the first frequency.  
         [0036]     According to further features in the described preferred embodiments, the method further includes the steps of: (d) introducing a first fluid into the reaction volume, and (e) introducing a second fluid into the reaction volume, the second fluid being substantially immiscible with the first fluid, wherein the first frequency and the second frequency are selected such that the first and second series of ultrasonic waves produce a nano-emulsion of the fluids.  
         [0037]     According to still further features in the described preferred embodiments, the method further includes the step of: (f) selecting the first frequency and the second frequency so as to achieve modulation between the first series of ultrasonic waves and the second series of ultrasonic waves.  
         [0038]     According to still further features in the described preferred embodiments, the method further includes the step of: disposing the second magnetostrictor below the reaction volume.  
         [0039]     According to still further features in the described preferred embodiments, the method further includes the step of: withdrawing the nano-emulsion as a continuous process.  
         [0040]     According to still further features in the described preferred embodiments, the method further includes the step of: producing the nano-emulsion as a batch process.  
         [0041]     According to still further features in the described preferred embodiments, the activating of the magnetostrictors is performed to produce an acoustical pressure of at least 1 kg per square centimeter in the reaction volume.  
         [0042]     According to still further features in the described preferred embodiments, the acoustical pressure is within a range of 1 kg per square centimeter to 4 kg per square centimeter.  
         [0043]     According to still further features in the described preferred embodiments, the activating of the magnetostrictors is performed to effect, within the reaction volume, a specific energy of 1.4-4.2 W/cm3, so as to efficiently produce the nano-emulsion.  
         [0044]     According to still further features in the described preferred embodiments, the first fluid includes water and wherein the second fluid includes a hydrocarbon.  
         [0045]     According to still further features in the described preferred embodiments, the second fluid is primarily diesel fuel. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0046]     The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.  
         [0047]     In the drawings:  
         [0048]      FIG. 1  is a cross-sectional view of a reactor according to one embodiment of the present invention;  
         [0049]      FIG. 2  is a magnified view of a portion of the reactor in  FIG. 1 , showing a linear transducer and a sonotrode attached thereto;  
         [0050]      FIG. 3  is a top view of the reactor of  FIG. 1 ;  
         [0051]      FIG. 3A  is a side, cross-sectional view of the reactor cover;  
         [0052]      FIG. 4A  is a conceptual diagram of a system for producing nano-emulsions, the system including the inventive reactor;  
         [0053]      FIG. 4B  is a conceptual diagram of a system for producing nano-emulsions, the system including the inventive reactor and a homogenizing bath, and  
         [0054]      FIG. 5  is a graphical representation of A mod  as a function of time. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0055]     The principles and operation of the reactor according to the present invention may be better understood with reference to the drawings and the accompanying description.  
         [0056]     Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawing. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.  
         [0057]     As used herein in the specification and in the claims section that follows, the term “transducer” refers to a device that converts input electromagnetic or electrical energy into output energy in the form of ultrasound.  
         [0058]     As used herein in the specification and in the claims section that follows, the term “magnetostrictor” refers to a device that transforms high-frequency current into ultrasound.  
         [0059]     Emulsions composed of fuel and water are known to be difficult to produce and extremely unstable. Since the stability of emulsion improves with decreasing droplet size, production methods should preferably be directed towards producing emulsions of the smallest possible droplet size, while maintaining a high rate of production.  
         [0060]     The cavitation effect of ultrasound has been used in the production of emulsions. To maximize the eroding property of the cavitation, an additional effect of external hydrostatic pressure can be used. This effect substantially increases the energy of the cumulative jet action of the collapsing bubbles produced by cavitation. However, hydrostatic pressure can inhibit the much-desired bubble generation, decrease cavitation, and reduce the number of bubbles per unit of volume. High hydrostatic pressures can suppress the cavitation altogether.  
         [0061]     The use of hydrostatic pressure has been known to cause low emulsion yields in continuous production methods, therefore, it has been used only in batch production. It would be highly advantageous to achieve, in a continuous process, the increased erosion associated with external hydrostatic pressure in batch processes.  
         [0062]     When comparing characteristics of low and high frequencies of same power level, low frequencies, being inherently high in amplitude, produce high acoustical pressure, thereby creating large bubbles that are undesirable in the production of nano-emulsions. High frequencies, on the other hand, produce lower acoustical pressure and advantageously produce small bubbles. However, high-frequency ultrasonic waves are inherently low in amplitude and create droplets that have a distinct tendency to collapse.  
         [0063]     In the present invention, it has been surprisingly discovered that the most favorable form of ultrasound cavitation for producing nano-emulsions is created by adding the two frequencies, such that the ultrasonic waves characterized by each of the two frequencies are superimposed. Preferably, the first frequency and said second frequency are selected so as to achieve modulation between said first series of ultrasonic waves and said second series of ultrasonic waves.  
         [0064]     Without wishing to be limited by theory, it is believed that the beneficial effect is achieved by the high-amplitude, low frequency waves dividing the reactor volume into a multitude of minor regions, each oscillating at a high frequency. Thus, the high acoustical pressure replaces the effect of, and obviates the need for, an external hydrostatic pressure acting on the small bubbles formed by the high-frequency waves.  
         [0065]     The current invention also relates to a new type of high-power sonic processor that utilizes ultrasound cavitation generated by radiating two ultrasound frequencies at an optimal ratio between 1:2 and 1:10.  
         [0066]     Preferably, the range for the lower frequency is 2-10 kHz, and more preferably, 2-8.5 kHz. The range for the higher frequency is 18-40 kHz.  
         [0067]     As shown in  FIG. 1 , one inventive feature of reactor  108  is the incorporation of a linear transducer and an axial transducer. The axial transducer contains a cylindrical (or axial) magnetostrictor  1 , which includes a stack of ring plates. The ring plates have a thickness of 0.1-0.2 mm and are made of magnetostrictive materials preferably having an inwardly-directed stricture. One such material is nickel.  
         [0068]     One of the advantages of using nickel is that an oxidation layer, Ni 2 O 3 , formed either thermally or, preferably, by acid treatment, is an excellent insulator. This property allows the magnetostrictor to be stacked between fiberglass flanges  3 , and compressed by compression bolts  2 .  
         [0069]     The stacked construction of the magnetostrictor drastically decreases energy loss and increases heat conduction when compared to magnetostrictors constructed of plates that have been glued with Bakelite™ or organosilicon glues.  
         [0070]     Thus, during the assembly of the magnetostrictor, the plates are stacked according to a predetermined shape, and the inner diameter of the formed cylindrical stack is polished. Upon being thermally expanded, the stack is subsequently swaged on to a tube, or a cylinder (cylindrical wall)  4 , preferably manufactured of an ASTM 316SL stainless steel and having a thickness of preferably 2 to 3 mm.  
         [0071]     The optimal thickness of cylinder  4  has been found to be 3 mm, which is necessary for a reliable weld of the cylinder to flanges  3 , thereby ensuring strength required to resist the destructive forces of high-amplitude ultrasound oscillations while containing the oscillations within the cavity of cylinder  4  with minimal loss.  
         [0072]     The lower end of cylinder  4  is welded to a support flange  5 , which has an approximate thickness of about 10 mm and is manufactured of ASTM 306 or ASTM 316 stainless steel. Flange  5  has a diameter  5 A that is 20 mm larger than the inner diameter of flange  5 . Diameter  5 A serves to admit an external section of sealing gasket  6 , which seals the lower end of the ultrasonic chamber defined by flange  5  and an upper plate  7 . Gasket  6  is preferably manufactured from a hexafluoropropylene-vinylidene fluoride co-polymer (such as Viton®). Gasket  6  forms a seal between flange  5  and a lip  8 A of a mounting ring  8 , which serves as a structural mount of a reactor  9 .  
         [0073]     Axial magnetostrictor  1  has a coil  10  inserted through openings in magnetostrictor plates. The windings of coil  10  are perpendicular to the plates, i.e., parallel to the wall of cylinder  4 . Electrical contacts to the wiring of coil  10  are contained in a hermetically sealed outlet (not shown) located on the external surface of a cooling jacket  11  of magnetostrictor  1 . The wire insulation material is polytetrafluoroethylene (Teflon®), or any other similar material.  
         [0074]     Cooling jacket  11  is attached by a bolt  12  to flange  5 . A polytetrafluoroethylene gasket  13  can be tightened to form a seal between plate  7  and cylinder  4 . Gasket  13  also serves as an electrical insulator that disrupts the circuit formed by cylinder  4  and cooling jacket  11 , thereby preventing induction of any undesirable currents in the reactor housing.  
         [0075]     The height and volume of the reactor are determined by the desired power rating, which is also equivalent to the magnetostrictor inductivity, and to magnetostrictor resonance at the low frequency mode of operation.  
         [0076]     The high-frequency ultrasound is generated by a magnetostrictor  14 , which is a linear magnetostrictive transducer. Preferably, the ultrasonic waves have a frequency in the range of 18 to 40 kHz. More preferably, the frequency is in the range of 18 to 30 kHz, and most preferably, the frequency is in the range of 20 to 25 kHz. Magnetostrictor  14  has a rectangular cross section, and is soldered by silver or titanium to sound transformer  15  (preferably made of a Ti-4V-6Al titanium alloy). Sound transformer  15  has a M20 metric threaded opening, which accepts a joining pin  16  of matching thread. Magnetostrictor  14  with corresponding coil windings is contained within a casing  17 , which also serves as a cooling jacket.  
         [0077]     Another inventive feature of the invention is a sonotrode, or wave guide, having an innovative structure. Referring now to  FIG. 2 , the structure of sonotrode  18  is dictated by acoustical and design requirements. Sonotrode  18 , in addition to being the source of high-frequency ultrasound, also serves as the bottom part of the reactor, which ensures a hermetical closure of the working cavity of the reactor.  
         [0078]     Sonotrode  18  has a conical lower section  18 A, whose surface  18 D matches an upper surface of sound transformer  15 . In surface  18 D, there is an opening containing threaded pin  16 , which joins sound transformer  15  to sonotrode  18 . Surface  18 D and the matching sound transformer surface are substantially perfectly planar and highly polished.  
         [0079]     An upper section  18 B of sonotrode  18  is a cylinder whose base is disposed at the point of null amplitude, i.e., at the node of ultrasound waves radiated into the cavity of the reactor. The diameter of section  18 B is approximately 10 mm smaller than the diameter of a surface  18 C, thereby forming a ledge that seats gasket  6 , of thickness between 3-5 mm. The inner diameter of gasket  6  is 0.2 mm smaller than the diameter of section  18 B so as to achieve a tight fit as it seats on lip  8 A, thereby assuring a hermetically tight seal. The 0.2 mm difference in diameter also allows insulation of the inner diameter of the gasket and the cylindrical part of sonotrode  18  from the erosive action of cavitation bubbles.  
         [0080]     The outer diameter of gasket  6  matches a recessed diameter of flange  5 , thereby assuring that sonotrode  18  is perfectly centered relative to axial magnetostrictor  1 . Mounting ring  8  presses gasket  6  into place, thereby preventing any unwanted contact between the metal of sonotrode  18  and the inner surface of cylinder  4 . Gasket  6  also serves to provide a flexible, cushioning joint between the sonotrodes, thus enabling vertical vibrations to pass between the two sonotrodes and establishing an acoustical coupling therebetween.  
         [0081]     Section  18 B contains a concave radiating surface  18 E having a radius  18 R, calculated to enable sonotrode  18  to radiate continuous acoustical currents, to prevent the surface from being eroded by cavitation, and to optimize transmission of ultrasound into the reactor cavity. Sonotrode  18  is preferably made of a Ti-4V-6Al titanium alloy (or a similar alloy) or of ASTM 316SL stainless steel (or a similar alloy), both of which possess excellent resonance properties.  
         [0082]     When utilizing raw materials which are suspensions and powders, section  18 B is provided with a circumferential ledge characterized by the difference of diameters  18 F for accommodating a ring of Viton® rubber to keep particles from entering the weak oscillation region, located between cylindrical surface of sonotrode  18  and cylinder  4 , and to prevent the region from being blocked by powder aggregates.  
         [0083]     A casing  19  is mounted on a support plate  21  that is fixed to ring  8  by struts  22 . The length of struts  22  equals the length of conical lower section  18 A. The upper ends of struts  22  have adjustable rubber adaptors  23 , allowing for centering the reactor relative to the linear transducer.  
         [0084]     Upper plate  7  of cooling jacket  11  has threaded pins  7 B and a seat for accommodating a rubber gasket  24 . A reactor cover  7 C is mounted by means of by pins  7 B and rubber seal  24 .  
         [0085]     Reactor cover  7 C has seals  32 , through which are mounted two intake tubes  25  and an output tube  26 , as shown in  FIG. 3A . The tubes have an inner diameter of 8 mm and an outer diameter of preferably about 10 mm, which has been determined to equal the width of the cavitation-free region in the cylindrical transducer, thus preventing cavitation that would erode the tube material. Furthermore, this diameter creates diffraction of ultrasound waves at the openings of the tubes which does not distort the focus of the ultrasound waves nor interferes with the conductance of the waves from the walls of the reactor inwards to the center thereof. The above tubes enter reactor cover  7 C at radially-disposed points, as shown in  FIG. 3 , allowing the tubes to enter cavitation-free regions within the reactor cavity, and approximately 15 mm from the wall of cylinder  4 .  
         [0086]     Output tube  26  has an orifice whose diameter is four times smaller than the total square area of the cross-sections of intake tubes  25 . This specific criterion assures a backpressure of approximately 1.5 to 2.5 atmospheres at a raw material delivery rate of 8 to 12 liters per minute. This pressure substantially increases the erosive property of ultrasound, which is beneficial to the dual-frequency ultrasound production of emulsions, suspensions, and similar materials. Reactor cover  7 C is preferably equipped with a sleeve for mounting a manometer  27 .  
         [0087]     The cooling of magnetostrictors  1 ,  14  is accomplished by externally-supplied water controlled to flow at a flow rate of approximately 3 liters per minute, and at a temperature below 15 degrees C. The cooling can be also accomplished by a pump-driven recirculating system.  
         [0088]     Cooling jackets  11  and  17  are connected in series, wherein, as illustrated in  FIG. 1 , water from discharge tube  30  of jacket  17  enters inlet  28  on jacket  11 . Spent water exits discharge tube  29  to return to the recirculating system. The above-mentioned serial connection of cooling jackets is based on the principle of superimposing waves having different wavelengths. This effect divides the reactor volume into mobile regions, or domains, each having specifically modulated high frequencies at the center and specifically modulated low frequencies at the boundary. This effect successfully avoids the creation of undesirable low frequencies at the outer regions of the reaction volume.  
         [0089]     The outer boundary of each such region consists of low-frequency waves that have a significantly higher amplitude than the high-frequency waves inside the mobile domains, and, therefore, a significantly-higher acoustical pressure. Acoustical pressure of consistent frequency has the same beneficial effect as external hydrostatic pressure in increasing the energy of cumulative jets that are constantly being created by the collapsing of the cavitation bubbles. The effect of high frequency waves is instrumental in causing the bubbles to collapse, thereby increasing the cavitation effect as well as the number of cavitation loci.  
         [0090]     Assuming the following definitions for the two (higher-frequency and lower-frequency) wave functions: 
    t=time;     x i =displacement of an individual wave function, x i =x i (t);     x=total displacement, x=x 1 +x 2 ;     A=amplitude;     ω=angular frequency;     ω av =average angular frequency, ω av =½·(ω 1 +ω 2 );     ω mod =modulation angular frequency, ω mod =½·(ω 1 −ω 2 ), and     φ=oscillation initial frequency,     then if A 1 =A 2 =A; φ 1 =φ 2 =0, and ω 1 ≠ω 2 , 
 
 x   1   =A   1 ·sin ω 1   t  
 
 x   2   =A   2 ·sin ω 2   t  
 
 The total displacement, x, is equal to x 1 +x 2 =A(sin ω 1 t−sin ω 2 t). Solving, we obtain: 
 
 x= 2 A  cos[(ω 1 −ω 2 ) t/ 2]·sin[(ω 1 −ω 2 ) t/ 2]. 
 
 Since x=x 1 +x 2 =A mod (t)·sin ω av t, we obtain: 
 
 A   mod ( t )=2 A  cos ω mod   t.  
   
 
         [0100]     The function A mod  is shown graphically in  FIG. 5 , as a function of time. Also shown are T av  and T beat , defined by: 
        T av  is the oscillation period with ω av , and 
 
 T beat  is the half-period of the amplitude variation. 
       
 
         [0102]     As used herein in the specification and in the claims section that follows, the term “modulation” and the like, refers to a wave function having properties substantially as defined by the equation, A mod (t)=2A cos ω mod t, as developed hereinabove.  
         [0103]     The dual ultrasound frequency produced by the reactor of the present invention is manifested by the considerably higher erosive—and therefore, more productive—capabilities of the ultrasound processor with respect to reactors of the prior art. The effect has been tested in a production of diesel-water emulsion having droplets whose mean particle size is between 70-300 nm. The two-frequency reactor provides for nano-emulsion production rates of at least 5 liters per minute.  
         [0104]     According to another aspect of the present invention, the fuel-water emulsion is preferably manufactured by using the reactor of the present invention in a system schematically illustrated in  FIG. 4A . Water from a tank  101  and diesel from a tank  102  are pumped by metering pumps  107  directly to an ultrasonic reactor  108 , which has been illustrated in detail in  FIG. 1 . Ultrasonic waves of differing frequencies are applied to the diesel-water, as described hereinabove. The nano-emulsion produced in reactor  108  is stored in storage tank  109 .  
         [0105]     In another embodiment of the invention, the fuel-water emulsion is manufactured by using the reactor of the present invention in a system schematically illustrated in  FIG. 4B . Water and water-additives are stored in tank  101 . A mixture of diesel fuel and oil-soluble additives are stored in tank  102 . Diesel oil is stored in tank  110 . Pumps  107  deliver contents of the tanks to an ultrasonic bath  111 , where the fluids mix into a homogenized mixture. The mixture is transferred by pump  112  to reactor  108 . Ultrasonic waves of differing frequencies are applied to the diesel-water, as described hereinabove. The nano-emulsion produced in reactor  108  is stored in storage tank  109 .  
         [0106]     The processes in the above embodiments can be carried out either in batch mode, semi-batch mode, semi-continuous mode, or in continuous mode.  
         [0107]     The diesel fuel and/or the water preferably contain at least one surfactant. Surfactants of particular suitability for use in conjunction with the nano-emulsion device and method of the present invention have been described in our co-pending U.S. Patent Application Ser. No. 60/607,591, which is incorporated by reference for all purposes as if fully set forth herein.  
         [0108]     Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, no citation or identification of any reference in this application shall be construed as an admission that such reference is available as prior art to the present invention.