AN ACOUSTIC APPARATUS AND METHOD

Abstract: A method and apparatus for introducing acoustic energy into a chamber are described. The apparatus comprises a member disposable near to a portion of the chamber to define a space therebetween, sealing means disposed in the space so as to define a cavity therein, and at least one acoustic means coupleable externally to the member so as, in use, to introduce acoustic energy into the cavity when the cavity contains a liquid metal and thereby into the chamber.

Description: An Acoustic Apparatus and Method This invention relates to acoustic apparatus, and more particularly to acoustic apparatus for introducing acoustic waves into a chamber containing a liquid. It is known that the introduction of ultrasonic energy into a liquid-filled chamber can lead to cavitation in the liquid - see for example "Sounding Out New Chemistry", by K Suslick and S Doktycz, New Scientist, pp50-53, 3 February 1990. One of the problems associated with the use of acoustic energy in such liquid-containing chambers is that of actually introducing the acoustic energy into the chamber. With relatively large chambers an acoustic transducer can be inserted into the chamber, but there is a limit to the type and the size of the chamber, below which some external method has to be found for introducing acoustic energy into the chamber from an external source. It is, for example, difficult to introduce acoustic transducers into pipes of process plant. According to a first aspect of the present invention, there is provided a method of introducing acoustic energy into a liquid-containing chamber, the method comprising the steps of forming a liquid metal filled cavity in contact with a portion of the chamber, and introducing acoustic energy into the cavity and thereby into the chamber. According to a second aspect of the present invention, there is provided a method of introducing acoustic energy into a liquid-containing chamber, the method comprising forming an annular, liquid metal filled region about a portion of the chamber, and introducing acoustic energy into the region and thereby into the chamber. The methods of the first and second aspects of the present invention may include the further step of solidifying the liquid metal in the cavity or region prior to or simultaneously with introducing acoustic energy into the chamber. According to a third aspect of the present invention, there is provided apparatus for introducing acoustic energy into a chamber, the apparatus comprising members means and said chamber wall portion; filling means to enable said closed cavity to be filled with liquid metal; at least one acoustic energy into the chamber through the cavity when the cavity is filled with metal. According to a fourth aspect of the present invention, there is provided apparatus for introducing acoustic energy into a chamber, wherein the member means comprises a metal member spaced apart from the chamber wall so as to define a space therebetween, said cavity being formed by sealing means interposed between the metal members and the chamber wall. The apparatus of the third and fourth aspects of the invention may, in use, have the liquid metal in the cavity or region solidified prior to or simultaneously with the introduction of acoustic energy. The metal used in the cavity according to the method and apparatus of the present invention is preferably a low melting point metal having a melting temperature below about 150°C. Various alloys of lead, tin, bismeth and other elements may be suitable. The metal in the cavity or region may be either liquid or solidified during use when introducing the acoustic energy. Solidified metal may subsequently be liquefied as required, for example to facilitate moving the apparatus along the chambers and re-solidified again before use if desired. Use of liquid metal also helps to accommodate awkward contours on the surface of the chamber such as welding joints or other projections. In such situations the liquid metal may flow around the awkward projection to accommodate it, after which the liquid metal may be solidified before introducing acoustic energy. It should be noted that the present invention provides a method and apparatus for introducing acoustic energy into a liquid-containing chamber. The acoustic energy may be at any frequency from very low frequencies to ultrasound. The cavity formed around the chamber may be by the annular member sealed to the chamber by flexible sealing means at opposite ends of the annular member, the cavity being defined between said seals. The cavity formed around the chamber may be completely contained within a flexible member which is constrained in a radially outwardly direction by a metal sleeve therearound. The chamber might comprise a duct, for example a pipe. The sealing means may comprise hollow rubber seals, endless fluid filled tubes, flexible lip seals or Λ 0' ring seals for example. The liquid or solid metal in the cavity is preferably in contact with the wall of the chamber. The sealing means may be composed of Viton (trade name) rubber or a fluoroelastomer in order to withstand the temperature of the liquid metal. The acoustic energy may be arranged such that the peak energy thereof occurs inside the chamber near to the inside surface of the chamber, and a node thereof occurs at the annular member. The invention will now be further described by way of example only with reference to the accompanying drawings, in which :- Figure 1 shows a medial sectional view of apparatus for introducing acoustic energy into a pipe; Figure 2 shows a view on the line II-II of Figure 1; Figure 3 shows a modified form of the apparatus of Figure 1; Figure 4 shows part of a modified form of the apparatus of Figure 3; Figure 5 shows part of another modification of the apparatus of Figure 1; Figure 6 shows part of yet another modified form of the apparatus of Figure 1; and Figure 7 which shows a medial sectional view of another embodiment of the apparatus according to the present invention. Referring now to Figures 1 and 2, an acoustic apparatus 10 is shown disposed about a chamber in the form of a liquid-filled metal pipe 12. The apparatus 10 comprises a thin metal annular sleeve 14 about the pipe 12 and defining an annular cavity or region 16 inside an annular flexible member 18. The member 18 at its outer surface defines short sides 20,22 that are bonded to the inside of the sleeve 14, and has a continuous wall 24 at its inner surface in close contact with the pipe 12. An inlet 26 in the sleeve 14 allows the region 16 to be filled with a liquid metal. A number (eight are shown) of acoustic transducers 28 are coupled to the outside of the sleeve 14 in radially equi-spaced relationship. In operation, energising the transducers 28 causes acoustic energy to be transmitted firstly through the sleeve 14 into the liquid metal in the region 16, and then through the wall 24 and the pipe 12 where cavitation may be caused in the liquid in the pipe 12, if the energy transmitted is sufficiently high, and shown by bubbles 30 in Figure 1. The radial thickness of the region 16 can be arranged and the wavelength of the acoustic energy selected so that peak energy of the acoustic energy occurs just inside the wall of the pipe 12. The frequency of the acoustic energy may range from very low frequencies to greater than 20 kHz, i.e. from infrasound to ultrasound acoustic energy. The frequency of the acoustic energy in this case is about 20 kHz. Apart from mechanical effects of the imploding cavitation bubbles 30 in the liquid in the pipe 12, a raised temperature and pressure are produced in the liquid at the bubbles 30 which assist in dislodging any scale or corrosion, that might be adhering to the inside of the pipe 12 or dislodging any blockage which may have occurred. The raised temperature has the effect of locally increasing the reactive properties of any mild chemical reagent that might be introduced into the pipe 12 to assist in descaling the pipe 12. Although the flexible member 18 has been shown as having outer surface with short sides 20,22, this outer surface could be continuous in a flexible member 18a_ (see Figure 5) like the wall 24 but with the disadvantage of some attenuation of the acoustic energy from the transducers 28. Referring now to Figure 3, an apparatus 40 is shown similar in many respects to the apparatus 10 of Figure 1 in having a thin metal annular sleeve 44 disposed about a metal pipe 42. Two gas filled (eg air) flexible, endless sealing tubes 46, 48 are disposed inside the sleeve 44 in spaced apart relationship to define an annular cavity or region 49 therebetween into which a liquid metal is introduced through an inlet 50. A number (only two are shown) of acoustic transducers 28 are coupled to and disposed about the sleeve 44. The apparatus 40 operates in a similar manner to the apparatus 10 of Figures 1 and 2, but has the advantage that the liquid metal in the region 49 is in direct contact with the pipe 42, and hence reduces the loss of acoustic energy in the transfer from the liquid metal in the region 49 to the pipe 42. Instead of using the flexible sealing tubes 46,48 of Figure 3, conventional flexible lip sealing members 51,52 (see Figure 4) may be used in opposing relationship inside a thin metal annular sleeve 54 to define an annular region 56 about a pipe 58. Acoustic transducers 28 are coupled to and disposed about the sleeve 54 so as to send acoustic energy through the region 56 into and through the pipe 58. Figure 6 shows rubber doughnut seals 64, 65 as the sealing means. The seals 64, 65 are spaced apart inside a thin metal annular sleeve 68 defining an annular cavity or region 63 about a pipe 60. The annular region 63 may be filled with a liquid metal through an inlet 69. Acoustic transducers 28 are coupled to and disposed about the sleeve 68 so as to send acoustic energy through the region 63 into and through the pipe 60. The flexible members 18, 18a, the sealing tubes 46, 48 and the seals 64, 65 may alternatively comprise rubber or plastics material. For some applications, the transducers 28 might be mounted on metal waveguides or horns secured to the sleeves 14, 44, 54 and 68. Usually, when the invention is used for descaling the inside of a pipe, the transducers 28 will be arranged so that a node occurs at the sleeve 14, 44, 54, 68 and the peak energy occurs adjacent the internal surface of the pipe 12,42,58,60. Referring now to Figure 7, another embodiment of the present invention is shown comprising an annular sleeve 78 disposed about a liquid-containing pipe 70 and Λ 0' ring seals 75, the rubber λ O' ring seals 75 being seated in radial grooves located in seating blocks 74. The annular sleeve 78 and the seals 75 define an annular cavity 73 about the pipe 70, the cavity 73 being filled with a liquid metal through an inlet 79. An acoustic horn 84 is secured to the sleeve 78 and, in use, channels acoustic energy from an acoustic transducer 88 into the liquid metal, and thereby into the liquid 71 contained in the pipe 70 in order to remove a layer of contamination 82 from the internal surface of the pipe 70. In each of the embodiments described above with reference to Figures 1 to 7, the liquid metal may be solidified during use, that is when introducing the acoustic energy. Thus, in such embodiments, for metals which are liquid at ambient temperature, freezing may be required. For metals which melt at elevated temperature, the liquid metal may be introduced into the cavity or region at a temperature above the melting point and subsequently cooled to solidify the metal before use. It will be understood that although the invention has been described in relation to descaling or decontaminating a chamber in the form of a pipe or duct, the invention may be used with other chambers where it is necessary to inject acoustic energy into the chamber, not necessarily for descaling the chamber. Acoustic energy may be used for clearing blockages where, for example, solids have collected causing a stoppage or restriction of flow. Such solids may, for example, be from a slurry which is being pumped along the pipe. Solids from the slurry may settle-out if flow is not maintained for any reason and cause a blockage. If desired, fewer or more than eight acoustic transducers may be used depending on the application. It will be appreciated that the acoustic energy might have the effect of inducing chemical reactions to take place in the chamber that would otherwise not occur or would have occurred at only an extremely slow rate.

Claims: Claims 1. A method for introducing acoustic energy into a liquid-containing chamber as hereinbefore defined, the method comprising the steps of: forming a cavity in operable contact with a portion of the chamber; filling the cavity with a liquid metal and introducing acoustic energy into the cavity and thereby into the chamber. 2. A method as claimed in Claim 1, wherein the cavity forms an annular cavity about a portion of the chamber. 3. A method as claimed in either Claim 1 or 2, wherein the acoustic energy is arranged such that the peak energy thereof is arranged to occur inside the chamber near to the inside surface of the chamber. 4. A method as claimed in claim 3, wherein the energy causes cavitation of the liquid in the chamber. 5. A method as claimed in any one of the preceding Claims wherein the acoustic energy is arranged so that a node thereof occurs in the cavity. 6. A method as claimed in any one of the preceding Claims, wherein the liquid in the chamber is provided with a chemical reagent to assist in descaling the inside surface of the chamber. 7. A method as claimed in any one of the preceding Claims, wherein the liquid metal in the cavity is arranged to be in direct contact with the wall of the chamber . 8. A method as claimed in any one of the preceding Claims, wherein a portion of the chamber is circular in cross-section, and the acoustic energy is introduced through a plurality of transducers spaced around the cavity. 9. A method as claimed in any one of the preceding Claims, wherein the chamber comprises a duct or pipe. 10. A method as claimed in any one of the preceding Claims, wherein the acoustic energy has a frequency from very low frequencies to about 20 kHz. 11. A method according to anyone preceding claim further including the step of solidifying the liquid metal prior to the introduction of the acoustic energy. 12. Apparatus for introducing acoustic energy into a chamber, the apparatus comprising member means disposable near to a portion of a wall of the chamber so as to define a closed cavity between said member means and said chamber wall portion; filling means to enable said closed cavity to be filled with liquid metal; at least one acoustic energy producing means compilable to an outer surface of the member means so as, in use to introduce acoustic energy into the chamber through the cavity when the cavity is filled with metal. 13. Apparatus as claimed in claim 12 wherein the member means comprises a metal member spaced apart from the chamber wall so as to define a space therebetween, said cavity being formed by sealing means interposed between the metal member and the chamber wall. 14. Apparatus as in claim 13 wherein the metal member is an annular member, the space defined is an annular space and the sealing means are disposed between the metal member and chamber wall in spaced-apart relationship so that the cavity defined is an annular cavity. 15. Apparatus as claimed in any one of preceding Claims 12 to 14, wherein the sealing means comprise flexible sealing members. 16. Apparatus as claimed in Claim 15, wherein the sealing members comprises endless fluid-filled tubes. 17. Apparatus as claimed in Claim 15, wherein the sealing members comprise rubber doughnut seals. 18. Apparatus as claimed in Claim 15, wherein the sealing members comprise flexible lip sealing members. 19. Apparatus as claimed in Claim 15, wherein the sealing members comprise x O' ring seals. 21. Apparatus as claimed in any one of Claims 15 to 20, wherein the flexible sealing members are composed of Viton™ rubber or a fluoroelastomer . 22. Apparatus as claimed in any one of Claims 12 to 21, wherein the chamber portion is circular in cross-section, and a plurality of acoustic means are spaced around the member means. 23. Apparatus as claimed in Claim 22, wherein the chamber comprises a duct or pipe. 24. Apparatus as claimed in any one of Claims 12 to 23 wherein, in use, the liquid metal is directly in contact with the chamber. 25. Apparatus according to any one preceding claim from 12 to 24 wherein, in use, the liquid metal is solidified in the cavity prior to introducing acoustic energy.

Inventors: JENNINGS HOWARD TIMOTHY, WISE ROGER JEREMY, JENNINGS, HOWARD, TIMOTHY, WISE, ROGER, JEREMY
Applicants: BRITISH NUCLEAR FUELS PLC, JENNINGS HOWARD TIMOTHY, WISE ROGER JEREMY, JENNINGS, HOWARD, TIMOTHY, WISE, ROGER, JEREMY
Application year: 1998
Main classification: G10K11
IPC codes: B08B9, G10K11