Abstract:
Acoustic resonators and systems for controlling the same to cause desired reactions and physical effects therein are described. Some aspects are directed to an acoustic cavitation resonator that can be placed under high static pressure and to which a set of ultrasonic drivers are coupled so as to cause cavitation in the resonator during operation. Inlet and outlet ports allow introduction of one or more fluid species into the resonator so that the desired processing of the fluids can be accomplished under pressure and in the presence of cavitation.

Description:
TECHNICAL FIELD 
       [0001]    The present application relates to resonators for applying acoustic energy to fluids contained therein. Specifically, the present application describes high-intensity acoustic resonator chambers, which may be used to apply acoustic energy to fluids flowing therethrough, and in some cases, flowing fluids under pressure, and in other cases, applying acoustic fields to cause cavitation within said fluids. 
       BACKGROUND 
       [0002]    It is known that acoustic fields can be applied to fluids (e.g., liquids, gases) within resonator vessels or chambers. For example, standing waves of an acoustic field can be generated and set up within a resonator containing a fluid medium. The acoustic fields can be described by three-dimensional scalar fields conforming to the driving conditions causing the fields, the geometry of the resonator, the physical nature of the fluid supporting the acoustic pressure oscillations of the field, and other factors. 
         [0003]    One common way to achieve an acoustic field within a resonator is to attach acoustic drivers to an external surface of the resonator. The acoustic drivers are typically electrically-driven using acoustic drivers that convert some of the electrical energy provided to the drivers into acoustic energy. The energy conversion employs the transduction properties of the transducer devices in the acoustic drivers. For example, piezo-electric transducers (PZT) having material properties causing a mechanical change in the PZT corresponding to an applied voltage are often used as a building block of electrically-driven acoustic driver devices. Sensors such as hydrophones can be used to measure the acoustic pressure within a liquid, and theoretical and numerical (computer) models can be used to measure or predict the shape and nature of the acoustic field within a resonator chamber. 
         [0004]    If the driving energy used to create the acoustic field within the resonator is of sufficient amplitude, and if other fluid and physical conditions permit, cavitation may take place at one or more locations within a liquid contained in an acoustic resonator. During cavitation, vapor bubbles, cavities, or other voids are created at certain locations at times within the liquid where the conditions (e.g., pressure) at said certain locations and times allow for cavitation to take place. 
         [0005]    For the sake of illustration,  FIG. 1  shows a simplified diagram of an acoustic resonator or cavitation system  10  according to the prior art. A resonator  100  contains a volume of fluid which is to be cavitated. An acoustic driver such as a PZT transducer  110  is fixed to a location on cavitation chamber  100 . The coupling is typically done by screw attachment or epoxy attachment of transducer  110  to chamber  100 . 
         [0006]    Transducer  110  is driven by an electrical driving signal generated by signal generator  120 , which provides an output signal that is amplified by amplifier  130 . The output of amplifier  130  is coupled to a conducting surface or electrode on transducer  110  to cause the transducer to vibrate, oscillate, or otherwise make an acoustic (e.g., ultrasonic) output. The acoustic output of transducer  110  is then transmitted to chamber  100  due to the acousto-mechanical coupling between transducer  110  and chamber  100 . 
         [0007]    Under certain conditions, the acoustic action of transducer  110  and chamber  100  set up an acoustic field within the fluid in chamber  100  that is of sufficient strength and configuration to cause acoustic cavitation within a region of chamber  100 . Specifically, under suitable conditions, acoustic cavitation of the fluid in chamber  100  may cause bubbles  199  or acoustically-generated voids as described above and known to those skilled in the art, to form within one or more regions of chamber  100 . The cavitation usually occurs at zones within the chamber  100  that are subjected to the most intense (highest amplitude) acoustic fields therein. 
         [0008]    Acoustic resonator  100  has been designed in a variety of shapes and sizes, and has been used in a variety of applications in the art. For example, resonators made of glass and steel have been devised. Also, resonators having metal walls with glass or quarts optical viewing ports have been devised. Additionally, resonators in the shape of cylinders, spheres, and other shapes have been devised. Furthermore, flow-through resonator systems have been devised, where a flowing fluid passes through the resonator by entering in an inlet fluid port and exiting by an outlet fluid port. 
         [0009]    However, previous resonator system designs have generally lacked utility and the design thereof has not been well-understood or optimally utilized. Traditional resonator systems rely on ad-hoc designs for the most part. The placement of the acoustic drivers on the resonators and the selection of the acoustic and fluid and ambient physical parameters and properties are also generally done in an ad-hoc way, and often rely of trial and error to achieve a desired outcome or semblance of an outcome. This is true in experimental laboratory settings as well as in industrial or biomedical applications, where persons designing and setting up the resonance system commonly rely on intuition or guesswork to implement the resonance systems. 
         [0010]    It has not been possible or practical in the prior art to achieve large acoustic standing waves and high quality factors (Q) in acoustic resonators, especially those having flowing fluid therein. Also, such resonator systems have not been optimized for use in cavitation environments or environments where a flowing fluid is under static or ambient pressure. 
       SUMMARY 
       [0011]    Aspects of the present disclosure are directed to acoustic resonators containing a fluid such as a liquid which is both flowing and under some pressure. Embodiments hereof provide methods for generating cavitation at some or many locations within the resonators in a controlled way so as to accomplish a processing step carried out in the resonator on the fluids therein. Among other features, the selection of the location of the acoustic drivers, the inlet and outlet ports, and the other physical parameters of the system are discussed and collectively made to enhance the processing of the fluid medium or other substances carried therein. Applications of the present systems and methods can be found in industrial, environmental, biomedical, scientific, and other fields. 
         [0012]    Some present embodiments are directed to an acoustic cavitation system, comprising an electrical driving circuit including a signal generator adapted to generate an electrical signal and an amplifier adapted to receive the electrical signal and generate an amplified driving signal for driving a plurality of transducer elements with respective driving signals at respective amplitudes thereof, a data processor coupled to said electrical driving circuit adapted for executing a sequence of programmed instructions and for controlling an operation of said electrical driving circuit, said plurality of transducer elements adapted to receive said respective driving signals and to provide respective acoustic outputs corresponding to the driving signals and amplitudes thereof, a resonator having resonator walls capable of withstanding a greater than ambient static pressure within said resonator, and comprising at least one fluid inlet port and at least one fluid discharge port, said resonator walls coupled to said plurality of transducer elements such that the acoustic outputs of said transducer elements cause an acoustic field in a volume defined by said resonator walls, and such that a given driving signal and amplitude configuration is adapted to cause cavitation within a fluid within said resonator, a fluid driving element adapted and arranged to cause flow of a fluid through said resonator, said flow being directed into at least one fluid inlet port of said resonator and exiting said resonator through at least one fluid discharge port, and a fluid pressure source adapted and arranged to cause a net positive static pressure within said resonator, operating cooperatively with said fluid driving element, such that a fluid flowing through said resonator experiences flow, pressure, and cavitation effects within said resonator in some or all of the volume defined by said resonator walls. 
         [0013]    Other embodiments are directed to a cavitation system for causing cavitation in a cavitation chamber of said system, comprising a cavitation chamber having rigid walls thereof, a first fluid inlet port in an inlet volume of said chamber for receiving a first fluid or mixture, a second fluid inlet port in said inlet volume of said chamber for receiving a second fluid or mixture, a mixing zone in which said first and second fluids or mixtures are mixed with one another, a plurality of acoustic drivers coupled to said rigid walls of said chamber for causing cavitation in a cavitation zone within said cavitation chamber, said cavitation zone being substantially in a portion of said chamber in which said mixing zone is located, and at least one fluid outlet port in an outlet volume of said cavitation chamber for discharging the first and second fluids or mixtures after they have undergone mixing and cavitation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    For a fuller understanding of the nature and advantages of the present concepts, reference is be made to the following detailed description of preferred embodiments and in connection with the accompanying drawings, in which: 
           [0015]      FIG. 1  illustrates an acoustic resonator system according to the prior art; 
           [0016]      FIG. 2  illustrates an exemplary cavitation system according to the present disclosure; 
           [0017]      FIGS. 3-5  illustrate exemplary embodiments of acoustic cavitation chambers or resonators that take an incoming fluid or mixture through an inlet port and cavitate the same before discharging the fluids or mixtures through an outlet port and where the general direction of fluid flow is parallel to a long axis of symmetry of the chamber; 
           [0018]      FIG. 6  illustrates an exemplary cavitation chamber that additionally allows mixing two or more fluids or mixtures therein, each entering through a respective inlet port; 
           [0019]      FIG. 7  illustrates an exemplary cavitation chamber or resonator having a plurality of inlet ports and a plurality of outlet ports, and in which the direction of fluid movement is generally perpendicular to a long axis of symmetry of the chamber; and 
           [0020]      FIG. 8  illustrates an exemplary cavitation chamber with a plurality of inlet and outlet fluid ports disposed at opposite ends thereof. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    As discussed above, it is useful to have acoustic resonators and chambers for conducting cavitation, which are equipped with flow-through capability to pass fluid through the resonator chamber. In addition, it is useful to have a well-designed resonator system for certain purposes, which may require controllable static pressure within the system, flow-through of a fluid medium, and custom or pre-configured or configurable acoustic driver placement. 
         [0022]      FIG. 2  illustrates an exemplary acoustic resonator and cavitation system  20 . The system includes an electrical circuit  200  for driving the acoustic drivers  201   a  and  201   b  (which can be generalized to a plurality of acoustic drivers). The circuit is controlled by a controller or control processor or control computer  250 . A signal generator or waveform generator  260  provides a signal that is amplified by amplifier  270 , which is in turn computer-controlled by computer or processor  250 . As mentioned earlier, the driving output of amplifier  270  provides the electrical stimulus to cause transduction within transducers  201   a, b , which in turn cause acoustical field generation within resonator chamber  220 . 
         [0023]    The heavier lines of  FIG. 2  represent a fluid circuit that circulates a fluid to be acoustically cavitated in resonator or chamber  220 . The resonator  220  comprises a first end cap or end bell  222  at a first end thereof, and a second end cap or end bell  224  at a second end thereof. Said first and second ends of resonator  220  being substantially at opposite ends of said resonator  220  in some embodiments. Generally, a fluid is flowed in resonator  220 , sometimes under static pressure, and said fluid may be cavitated by acoustic transducers  201   a, b . As will be described further, the relative placement of the transducers and the fluid inlet and outlet ports in the system with respect to the acoustic field within the resonator  220  is arranged to achieve a desired outcome in processing the flowing pressurized fluid and/or materials suspended or dissolved therein. 
         [0024]    The fluid circuit includes a fluid driver (e.g., a pump such as a rotary or reciprocating pump)  201 . The pump  201  drives the fluid against the head loss in the fluid circuit portion of cavitation system  20 . A pressure gauge  202  may be installed at a useful location downstream of pump  201  to monitor the pressure at its highest value downstream of pump  201 . A filter  203  may be used inline with the flowing fluid to trap any impurities or dirt in the fluid. 
         [0025]    A solenoid or gate valve  204  may be used to secure the fluid flow in some cases or to isolate the resonator upstream of the resonator  220 . A second solenoid valve 206  is used to secure flow of the fluid or to isolate the resonator  220  in cooperation with valve  204 . 
         [0026]    Relief value  230  may be provided as a safety mechanism to relieve fluid from the system if the pressure of said fluid exceeds a pre-determined threshold. For example, the relief valve may be set to discharge fluid in a controlled way if the pressure within resonator  220  approaches a value that could jeopardize the integrity of the resonator or other system components. 
         [0027]    Fluid flow rate meter  208  may be used to sense and provide an indication of the rate of fluid flow (e.g., in cubic centimeters per second) through the fluid system. Because the fluid is generally incompressible, the fluid flow rate in the outlet portion of the system (as pictured) is substantially the same as the flow rate at the inlet to resonator  220 . 
         [0028]    A fluid holding, storage, surge or expansion tank or reservoir  240  is provided to contain an adequate amount of fluid and mediate any volumetric or pressure surges in the system. A temperature sensor (thermometer)  242  is used to provide an indication of the temperature of the fluid in the system. 
         [0029]      FIG. 3  illustrates another embodiment  30  or configuration of the present cavitation chambers. Liquid fluid  350  flows into an inlet volume  302  through an inlet port  352 . A main cavitation volume  300  receives said incoming liquid  350  from the inlet volume  302 . The main cavitation volume  300  of the chamber  30  may have a cylindrical shape and a generally circular cross section perpendicular to its cylindrical axis. The flow of liquid is generally to the right in  FIG. 3  and qualitatively flowing substantially parallel to a cylindrical axial axis of symmetry of chamber  30 , although it is to be understood that the flow may follow locally-variable paths and be subjected to turbulent movement at a local scale as well. The liquid  360  exits the chamber by flowing through exit volume  304  and out of the chamber from outlet port  362 . The main cavitation volume  300  and the inlet and outlet volumes  302  and  304  may be formed as a single unit. Alternatively the three volumes may be formed by joining the inlet and outlet volumes  302 ,  304  to the central main volume  300  at joining locations  303  and  305 . Joining locations  303  and  305  may be made by mechanically or otherwise coupling the various sections of cavitation chamber  30 . These may be joined or coupled by a threaded or bolted mechanism, or by braising or welding, depending on the application so as to form a liquid seal to contain the liquid of interest within cavitation chamber  30 . 
         [0030]    As described earlier, numerous components may be connected to the cavitation chamber  30  forming a cavitation system having fluid and electrical parts, which are not all shown in  FIG. 3  for simplicity. In addition, various coatings and surface treatments may be applied to the interior surfaces of the liquid-containing volumes of cavitation chamber  30  as needed to allow improved wetting of said surfaces for example. As discussed before, other materials, reactants, liquids, gases, or solids may be injected into or mixed with the primary cavitating fluid so that cavitation effects can operate on said mixed, dissolved, or entrained materials. 
         [0031]    Cavitation chamber of  FIG. 3  may be coupled to a plurality of acoustic drivers  310 , which are in turn powered as discussed above by corresponding driving power connections  320 . The plurality of acoustic drivers  310  may be driven with a common (shared) driving signal through connections  320  to each of the respective drivers or transducers  310 , or each driver or transducer  310  may receive a unique and respective driving signal, or groups of drivers or transducers  310  may be grouped and each group thereof driven as a whole using a same or similar driving signal. In operation, piezo-electric ultrasound transducer elements  310  may be driven in a way to cause a desired cavitation condition within the liquid contained in or moving through volume  300  of the cavitation chamber  30 . Of course, the cavitation may take place in a cavitation zone  330  that can include some or all of the interior volume of portion  300  of said chamber, depending on the design, driving and operational conditions. A plurality of cavitation bubbles  340 , voids, or bubble clouds or bubble groups may be caused to form in cavitation zone  330  of chamber  30 . The bubbles  330  may be convected or move with a fluid flow as the fluid passes from inlet port  352  to outlet port  362  of chamber  30 . 
         [0032]    In some embodiments, cavitation zone  330  extends to about a certain radius about the axial axis of the cylindrical cavitation chamber, and may extend in length to a certain length along said axis of the chamber. While not necessarily exactly cylindrical in shape, the cavitation zone formed hereby may take a general shape if averaged over time that resembles a cylindrical volume or a capsule shaped volume or elongated egg volume within the cavitation chamber&#39;s overall fillable volume. In some specific embodiments, the cavitation zone  330  is greater in volume than five percent (5%) of the volume of the cavitation chamber. In other embodiments, the cavitation zone has a volume greater than ten percent (10%) of the volume of the cavitation chamber. In yet other embodiments the cavitation zone has a volume greater than twenty five percent (25%), fifty percent (50%), or even greater than seventy five percent (75%) of the volume of the cavitation chamber. Finally, the cavitation zone may be made to include greater than ninety percent (90%), or substantially the entirety of the volume of the cavitation chamber. 
         [0033]      FIG. 4  illustrates another exemplary embodiment of a cavitation chamber  40  having a main cavitation section or volume  400  and an inlet section  402  and an outlet section or volume  404 . The features and operation of cavitation chamber  40  are substantially similar to those described above with respect to chamber  30  of  FIG. 3 . However, in the chamber of  FIG. 4 , the end volumes  402  and  404  have a generally cylindrical shape so that their ends are substantially flat rather than curved as in the previous figure. Fluid  420  enters the inlet section  402  through an inlet port  430  and exits at  422  through discharge port  432  from exit volume  404 . The fluid in the main volume  400  undergoes cavitation in some volume  410 . It should be understood that cavitation bubbles  420  will mainly form in cavitation volume  410 , but the nature of this phenomenon is that some cavitation events could occur in other portions of the fluid volume. The actual location of the volume where most of the cavitation takes place is in practice determined by the design of the cavitation chamber  40 , the fluids therein, and the placement and driving of the acoustic transducers. 
         [0034]      FIG. 5  illustrates another cavitation chamber  50  having a main cavitation volume  500  having inlet and outlet volumes  502  and  504  respectively. The incoming fluid  510  is received through inlet port  512  and the exiting fluid  520  exits through discharge port  522 . The flow of fluid in chamber  50  is therefore generally from left to right in  FIG. 5 . Note that in the present embodiment, the fluid ports  512  and  522  are not disposed in the respective end walls of their inlet and outlet volumes  502  and  504 . Instead, the fluid ports  512  and  522  are disposed in a side wall of volumes  502  and  504  respectively. Cavitation primarily takes place in a cavitation zone  540  that then develops cavitation bubbles  550 . 
         [0035]    A positive pressure may be applied to the cavitation system  50  by pressurizing the fluid system, e.g., by using a pump as shown earlier in  FIG. 2 . In this embodiment, the flow generally moves parallel to (along) the long axis of symmetry of the cavitation chamber. 
         [0036]      FIG. 6  illustrates a cavitation chamber  60  that allows cavitation in a cavitation zone  612  to generate cavitation bubbles  614  and other cavitation related phenomena. A first fluid  602  is input through a first inlet port  610  to inlet volume  600 . A second fluid  604  is input through a second inlet port  640  to inlet volume  600  as well. The first and second inlet ports  610 ,  640  are located at different positions in the body of inlet volume  600 , for example, one being at the end of the inlet volume  600  and the other being in a side wall of inlet volume  600 . 
         [0037]    Once the first and second fluids have entered the cavitation chamber  60  they are allowed to mix with one another. The first and second fluids mix at a desired location in the chamber  60 . For example, the first and second fluids may undergo mechanical mixing as well as enhanced mixing due to the cavitation in cavitation zone  612  of the chamber. The fluid  606  exits after mixing and cavitation have taken place. As mentioned above, the entire fluid flow, mixing, and cavitation processes may take place under a static or baseline pressure, e.g., a positive, greater than ambient pressure, and the static pressure can be provided by a pump or gas loading apparatus. 
         [0038]      FIG. 7  illustrates yet another embodiment of a cavitation chamber  70  equipped with a plurality of inlet ports  730  and outlet or discharge ports  732 . Acoustic transducers  740  are driven by driving signals on lines  750  as appropriate, and the driving of the transducers can be accomplished as discussed earlier. 
         [0039]    Once the fluid  702  comes into the chamber  700  it undergoes cavitation in cavitation zone  710  and yields a plurality of bubbles  720  in cavitation zone  710 . In this embodiment, the flow generally crosses (flows across) the chamber in a direction perpendicular to the long axis of symmetry of the chamber. 
         [0040]      FIG. 8  illustrates a cavitation chamber  80  having a generally cylindrical metal shell  800 . To the metal shell  800  are attached a plurality of acoustic drivers or transducers  820 . Fluid  810  to undergo cavitation enters the chamber through a plurality of inlet ports  812 . The inlet ports may be in fluid communication with an inlet plenum. Similar outlet ports may deliver the output fluid at the exit end of the chamber through a similar outlet plenum. Once again, as with other embodiments described herein, the entire fluid system, or the portions thereof that are experiencing cavitation in chamber  80  may be provided with a static fluid pressure so that the cavitation takes place under a baseline or bias static fluid pressure. 
         [0041]    The selection of the locations for the fluid ports may be made at least in part relative to the locations of the acoustical driving transducers on the body of the cavitation chambers. Also, the selection of the location ports may be made at least in part relative to the locations of a characteristic feature of the acoustic fields within the cavitation chambers. 
         [0042]    The present fluid ports can be constructed as necessary for a given application. In some embodiments, the fluid ports of the preceding drawings are formed by tapping a threaded opening into a selected location in a wall of the cavitation chambers. Fittings and sealants and gaskets may be employed to form fluid-tight seals in the fluid ports. The fluid-tight seals may be constructed and designed to withstand a substantial positive net pressure within said cavitation chambers. Steel, titanium or other metal alloys may be employed to make such fittings for structural integrity. 
         [0043]    As discussed in this disclosure, the fluid within the cavitation chamber may be placed under a static or DC pressure that is greater than the atmospheric ambient pressure of the system. In some aspects, pre-pressurizing the fluid in the cavitation chambers will cause a more violent cavitation bubble collapse, and more favorable reactions driven by said cavitation are encouraged. 
         [0044]    The present invention should not be considered limited to the particular embodiments described above, but rather should be understood to cover all aspects of the invention as fairly set out in the attached claims. Various modifications, equivalent processes, as well as numerous structures to which the present invention may be applicable, will be readily apparent to those skilled in the art to which the present invention is directed upon review of the present disclosure. The claims are intended to cover such modifications.