WO2015008010A1

WO2015008010A1 - Acoustic cleaning apparatus

Info

Publication number: WO2015008010A1
Application number: PCT/GB2013/051918
Authority: WO
Inventors: David Haines
Original assignee: David Haines
Priority date: 2013-07-18
Filing date: 2013-07-18
Publication date: 2015-01-22

Abstract

An acoustic apparatus suitable for cleaning soot from a ship's boiler comprises a generator (13) which generates an acoustic signal in the infrasonic range of 0.001 –50 Hz, the acoustic generator being coupled to a first end of a waveguide (12) having a length substantially equal to a quarter of the wavelength of the generated acoustic signal, the second end (17) of the waveguide being open and adapted to radiate the acoustic signal towards the surface to be cleaned.In use, the waveguide (12) acts as a closed tube resonator due to the impedance mismatch between the air pressure inside the waveguide and the external air pressure. Hence, the waveguide resonates at the fundamental frequency and at odd multiples thereof, thereby amplifying the signal generated by the acoustic generator(13). Since the waveguide (12) is only a quarter of a wavelength, the apparatus is considerably smaller in size than known devices.

Description

ACOUSTIC CLEANING APPARATUS

This invention relates to cleaning apparatus which utilises sound waves to vibrate dust and other matter which has accumulated on a surface to be cleaned.

It is well known to use low frequency sound of 20 Hz or less to remove deposits of dirt, dust or soot etc from surfaces, such as inside exhausts, furnaces, boilers, economisers, silos and ducting etc.

GB2207543 and GB2261080 disclose known acoustic cleaning apparatus for cleaning boilers and economisers in ships. The apparatus comprises a rotary valve having an input connected via a duct to a source of compressed air having a pressure of 7 to 8 bar. The output of the rotary valve is connected via another duct to an elongate open-ended resonator tube fitted to the side of the boiler.

In use, the valve is rotated by a motor at 1200 rpm to produce a pulsed airflow having a frequency of 20 Hz: this pulsed airflow is delivered via the resonator tube to the boiler. The resonator has a length equal to a half a wavelength of the pulses, such that resonance occurs at the fundamental frequency and integer multiples thereof, thereby increasing the amplitude of the pulses delivered to the boiler. The pulses penetrate the interior of the boiler and contact the surfaces therein and dislodge any accumulated particles of soot. The particles are then carried out of the boiler with the convection airflow.

Whilst devices of the kind disclosed in the above-mentioned documents provide a degree of cleaning, we have now devised an acoustic cleaning apparatus having improved cleaning.

In accordance with the present invention, as seen from a first aspect, there is provided an acoustic cleaning apparatus comprising an acoustic generator coupled to a first end of an elongate waveguide, the second end of the waveguide being open and adapted to radiate an acoustic signal generated by said acoustic generator towards a surface to be cleaned, wherein the acoustic generator comprises a valve having an inlet for coupling to a source of pressurised gas, an outlet coupled to the first end of the waveguide and a valve member disposed between the inlet and outlet, means being provided for operating the valve member to modulate the flow of gas between the inlet and outlet at an operating frequency, the valve member being arranged to capture a volume of said pressurised gas from the inlet in a reservoir and to transfer the captured volume of gas to the outlet.

We have realised that a problem with the devices of the kind disclosed in the above- mentioned documents is that the inlet pressure drops significantly when the valve opens, resulting in a high volume gas flow carrying low energy pulses. The present invention solves this problem by preventing the inlet from being directly connected to the outlet, so that no significant pressure drop occurs. The valve member regulates and controls the flow of gas from the apparatus. The valve member collects and dispenses high pressure pockets of gas in pulses into the first end of the wave guide, the second end of waveguide being open and adapted to radiate the resultant high pressure wave towards the surface to be cleaned. The pulses can be varied in size, speed and number to vary the flow as required. Preferably, the waveguide has a length substantially equal to a quarter of the wavelength of the generated acoustic signal. In use, the waveguide acts as a closed tube resonator due to the impedance mismatch between the air pressure inside the waveguide and the external air pressure. Hence, the waveguide will resonate at the fundamental frequency and at odd multiples thereof, thereby amplifying the signal generated by the acoustic generator. Since the waveguide is only a quarter of a wavelength, the apparatus is considerably smaller in size than those of the known devices.

A disadvantage with the devices of the kind disclosed in the above-mentioned documents is that is that they are bulky in construction, due to the fact that the resonated tube will be approximately 8.75 m in length. The size also prevents the devices from being used in other cleaning applications. Hence, the waveguide of the present invention is preferably folded at one or more points along its length in order to reduce the overall size of the apparatus.

Preferably the waveguide comprises a plurality of straight sections interconnected by bends, for example of 180°.

Preferably the second end of the waveguide is flared in diameter. Preferably the waveguide is tubular. Alternatively, the waveguide may comprise an elongate hollow channel formed within a solid body.

Preferably the waveguide is circular in section.

Preferably the acoustic generator is arranged to generate an acoustic signal having a frequency in the infrasonic range of 0.001 - 50 Hz.

The second end of the waveguide may be disposed adjacent an external flow of gas, such as a convection current within a boiler. Alternatively, the apparatus may comprise means for generating an external flow of gas adjacent the second end of the waveguide. Preferably said external flow generating means comprises a suction source arranged to draw the dislodged particles into the apparatus. The wavelength of the signal is inversely proportional to the density of the medium in which the signal is propagating. Since the density of the medium (e.g. air) can change with pressure, temperature and humidity, means are preferably provided for varying the frequency of the signal generated by the acoustic generator to produce an acoustic signal having the desired cleaning wavelength.

Preferably means are provided for tuning the waveguide to the frequency of the acoustic generator, for example by varying the length of the waveguide or the impedance at a point along the length thereof. Preferably the frequency adjusting means is controlled by an output of a pressure, temperature or humidity sensor, which either senses the relevant parameter of the medium within the waveguide or the relevant parameter of the medium at or adjacent the surface to be cleaned: in the latter case, the frequency of the acoustic generator can thus be varied to provide a cleaning signal having the optimum wavelength for cleaning the surface.

Preferably the apparatus forms a self-contained unit comprising said acoustic generator and said waveguide, preferably provided within a common housing. Preferably the self-contained unit further comprises means for generating a flow of fluid along said waveguide and/or adjacent the said second end of the waveguide.

Preferably the apparatus comprises handles or straps enabling the apparatus to be worn or carried by a user.

In an alternative embodiment, the apparatus may comprise a sensor to monitor for the accumulation of matter on a surface, the output of the sensor being connected to a control device which actuates the acoustic generator if the output of the sensor indicates that the surface requires cleaning.

In accordance with the present invention, as seen from a second aspect, there a provided an acoustic generator comprising a valve having an inlet for coupling to a source of pressurised gas, an outlet coupled and a valve member disposed between the inlet and outlet, means being provided for operating the valve member to modulate a flow of gas between the inlet, wherein the valve member is arranged to capture a volume of said pressurised gas from the inlet in a reservoir and to transfer the captured volume of gas to the outlet. Preferably the valve member comprises said reservoir.

Preferably the valve member is displaceable from a first position in which the reservoir is connected to the inlet and second position in which the valve member is coupled to the outlet.

Preferably the valve member is rotated between said first and second positions.

Preferably the valve member comprises a plurality of reservoirs to increase the modulation frequency over the rotational frequency.

Embodiments of the present invention will now be described by way of examples only and with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a first embodiment of acoustic cleaning apparatus in accordance with the present invention; Figure 2 is a schematic diagram illustrating components of the apparatus of Figure 1 ;

Figure 3 is a perspective view of a portion of a waveguide of a second embodiment of acoustic cleaning apparatus in accordance with the present invention;

Figure 4 is a perspective view of a third embodiment of acoustic cleaning apparatus in accordance with the present invention; Figure 5 is a sectional view through an embodiment of acoustic generator of an acoustic cleaning apparatus in accordance with the present invention; and

Figure 6 is a sectional view through an alternative embodiment of acoustic generator of an acoustic cleaning apparatus in accordance with the present invention.

Referring to Figures 1 and 2 of the drawings, there is shown an acoustic cleaning apparatus 10 for fitting to a boiler or other article to be cleaned. The apparatus 10 is a self-contained unit within an external housing 11 , the apparatus 10 comprising an elongate tubular waveguide 12 having a first end coupled to an acoustic generator 13 and second end 17 coupled to an outlet port 18 on the housing 11. The acoustic generator 13 is arranged to generate an infrasonic signal having a wavelength of 50 Hz or less, although for exemplary purposes, the acoustic generator 13 is arranged to generate said signal having a wavelength of 20 Hz. The acoustic generator 13 is of the form disclosed in GB2207543 and comprises a rotary valve member (not shown) which is driven by a motor(not shown). However, it will be appreciated that the acoustic generator 13 may be of any suitable form known to persons skilled in the art.

The acoustic generator 13 further comprises an inlet which is connected to a source 14 of pressurised air such as a compressed air cylinder or an air compressor. In one embodiment, the source 14 pressurised air forms part of the apparatus 10 and is contained within the housing 11. However, in an alternative embodiment, the housing 11 may be provided with a port (not shown) for connecting to an external source of pressurised air. The outlet of the acoustic generator 13 is connected to the first end of the waveguide 12. Embodiments of acoustic generator 13 are described in Figures 5 and 6.

The waveguide 12 comprises an elongate circular-section tube, having a length between opposite ends thereof which is equal to one quarter of the wavelength of the signal output by the acoustic generator 13. It will be appreciated that a signal of 20 Hz in air at 30°C will have a wavelength of 17.46 m. Accordingly, the length of the waveguide 12 will be approximately 4.37m. The second end of 17 of the waveguide 12 is preferably outwardly-flared in diameter towards the point where it couples to the outlet port 18. The waveguide 12 comprises one or more bends of 180° at respective points along its length, in order to make the waveguide 12 as compact as possible to fit within the housing 11. The acoustic generator 13 is connected to a control unit 15, which is connected to one or more sensors 16, 19. In use in boiler cleaning applications, the apparatus 10 is fitted in-situ on or adjacent the boiler to be cleaned. The outlet port 18 is coupled to a corresponding port formed in the wall of the boiler. The acoustic generator 13 is then actuated to apply pulses of pressurised air at 7 to 8 bar from the source 14 into the waveguide 12, the pulses having a frequency of 20 Hz as hereinbefore described. The pulses of air produced by the acoustic generator 13 propagate along the waveguide 12 towards the second end 17 thereof. The difference in air pressure between the interior and exterior of the waveguide 12 produces change in impedance at the second end 17 of the waveguide 12. This change in impedance acts like a closed end to the waveguide 12, such that the generated signal is partially reflected at 180° out-of- phase with the incident signal. When this happens, the reflected pressure waves travelling back from the second end 17 of the waveguide 12 will exactly coincide with the waves travelling forward from the acoustic generator 13, such that the waves reinforce each other. In this manner, the waveguide 12 causes resonance at the operating frequency of the acoustic generator 13 and at odd multiples thereof.

The amplified signal propagates into the boiler and penetrates in and around obstructions to dislodge any particles accumulated thereon. The dislodged particles are then carried out of the boiler by the heat convection currents and/or any forced airflows therein. The apparatus 10 may be operated periodically as or when required. However, the sensor 16 may be arranged to monitor the interior of the boiler to actuate the apparatus when an accumulation of particles in the boiler is detected. Since the wavelength of the generated signal within the boiler is dependent upon pressure, temperature and humidity, the sensor 19 may be arranged to monitor one or more of these parameters and to adjust the frequency of the pulses generated by the acoustic generator 13, in order to maintain the optimum cleaning wavelength inside the boiler. It will be appreciated that any change in the frequency of the signal output by the acoustic generator 13 could cause a mismatch with the length of the waveguide such that the resonance is no longer optimised. Accordingly, means (not shown) may also be provided for varying the length of the waveguide 12 so that it is always one quarter of the wavelength of the generated signal. Alternatively, resonance may be maximised by varying the impedance of the waveguide at one or more points along its length.

Referring to Figure 3 of the drawings, in an alternative embodiment the waveguide comprises a passage 20 formed in a solid body 21 of a material. The passage 20 may be formed by forming corresponding channels in two body members, which are subsequently joined together. An advantage of this arrangement is that the waveguide will be extremely durable in construction and can withstand the large forces developed by the pressure wave. Referring to Figure 4 of the drawings, the apparatus may be portable and comprise one or more straps, which enable the apparatus to be carried or worn by a user. In this embodiment, the outlet 18 is coupled to an elongate flexible duct 31 which can be grasped by the user. In use, the duct 31 can be directed at surfaces to be cleaned, such as light fittings or ventilation ducts, to dislodge any dirt of dust particles thereon.

The apparatus preferably further comprises a second elongate flexible duct 32, which is connected to a suction source (not shown) provided in the apparatus. In this manner, the particles dislodged by the signal emitted from the tube 31 will be drawn into the apparatus for collection and subsequent disposal. Referring to Figure 5 of the drawings, an acoustic generator 13 suitable for use with the acoustic cleaning apparatus comprises a body provided with an inlet duct 50, which is connected to the source of pressurised air, and an outlet duct 51 which is connected to the first end of the waveguide 12. The inlet and the outlet ducts 50,51 extend parallel to each other from an inner face of the body 49. The inner face of the body 49 lies in a plane which extends parallel and adjacent the front face of a rotary valve member 52. The rotary valve member 52 comprises a circular body 53, which is rotated about its central axis A by a motor (not shown), such that the front face thereof rotates in a plane which extends perpendicular to the rotational axis A. The valve member 52 comprises a plurality of reservoirs or chambers 54, which are circumferentially spaced around the axis of rotation A and which comprise mouths or openings formed in the front face of the valve member 52. The chamber openings are disposed radially outwardly of the axis of rotation A by the same distance as the inlet and the outlet ducts 50,51. A seal (not shown) is disposed between the front face of the rotary valve member 52 and the inner face of the body 49.

In use the valve member 52 is rotated and pressurised air is applied to the inlet duct 50: the pressurised air fills one of the chambers 54 when the mouth of that chamber registers with the end of the inlet duct 50. Continued rotation of the valve member 52 causes the volume of pressurised air to be trapped inside the chamber 54 until the chamber reaches the outlet duct 51 , whereupon the pressurised air is released into the outlet duct 51 to produce a sudden and defined pressure wave. The process then continues for each chamber 54 and it will be appreciated that the frequency of the pressure waves applied to the outlet duct 51 will be dependent on the speed of rotation and the number of chambers.

It will be appreciated that the pressurised air cannot escape directly from the inlet to the outlet and hence no significant loss of pressure occurs: this enhanced pressure is then trapped as the valve member 52 rotates and hence an amplified and more defined pressure wave is generated.

Referring to Figure 6 of the drawings, an alternative embodiment of acoustic generator 13 suitable for use with the acoustic cleaning apparatus comprises a body 100 having a tubular side wall 101 and opposite end walls 102, 103 which define a cylindrical chamber 104. A cylindrical rotor 105 is rotatably mounted inside the chamber 104 by bearings 106, 107 fitted in the respective end walls 102, 103. An inlet duct 108 extends radially from the side wall 101. An outlet duct 109 also extends radially from the side wall 101 at a location disposed diametrically opposite the inlet duct 108. The inlet duct 108 is connected to the source of pressurised air, and the outlet duct 109 is connected to the first end of the waveguide 12.

The rotor 105 is rotated about its central axis A by a motor (not shown) connected to an external pulley 110. The rotor 105 comprises one or more radially extending reservoirs or chambers e.g. 11 1 , which comprise mouths or openings formed in the side face of the rotor 105. The chamber openings are arranged to successively register with the inlet 108 and outlet 109 as the rotor 105 turns. An annular seal (not shown) is disposed in slots 1 12 at each end of the rotor 105. In use the rotor 105 is rotated and pressurised air is applied to the inlet duct 108: the pressurised air fills one of the chambers e.g. 11 1 when the mouth of that chamber registers with the proximal end of the inlet duct 108. Continued rotation of the rotor 105 causes the volume of pressurised air to be trapped inside the chamber 11 1 until the chamber reaches the outlet duct 109, whereupon the pressurised air is released into the outlet duct 109 to produce a sudden and defined pressure wave. The process then continues for each other chamber and it will be appreciated that the frequency of the pressure waves applied to the outlet duct 109 will be dependent on the speed of rotation and the number of chambers. Further inlet and outlet ducts 108A, 109A may be positioned on the body 101 at a point disposed axially away from the aforementioned ducts 108, 109. These additional ducts 108A, 109A are arranged to register with one or more further radially extending reservoirs or chambers e.g. 11 1 A, which are positioned on the rotor 105 at a point disposed axially away from the aforementioned chambers e.g. 11 1. In use, the further ducts 108A, 109A may be connected in parallel with the ducts 108, 109, or they may be connected to the waveguide of a separate cleaning apparatus.

A cleaning apparatus in accordance with the present invention is compact and modular in construction, thereby enabling the apparatus to be used in a wide variety of applications including applications where the apparatus is fixed in-situ where the apparatus is portable.

Claims

An acoustic cleaning apparatus comprising an acoustic generator coupled to a first end of an elongate waveguide, the second end of the waveguide being open and adapted to radiate an acoustic signal generated by said acoustic generator towards a surface to be cleaned, wherein the acoustic generator comprises a valve having an inlet for coupling to a source of pressurised gas, an outlet coupled to the first end of the waveguide and a valve member disposed between the inlet and outlet, means being provided for operating the valve member to modulate the flow of gas between the inlet and outlet at an operating frequency, the valve member being arranged to capture a volume of said pressurised gas from the inlet in a reservoir and to transfer the captured volume of gas to the outlet.

An acoustic cleaning apparatus as claimed in claimed in claim 1 , in which the waveguide acts as a closed tube resonator in use and resonates at the fundamental frequency and at odd multiples thereof.

An acoustic cleaning apparatus as claimed in claimed in claims 1 or 2, in which the waveguide is folded at one or more points along its length in order to reduce the overall size of the apparatus.

An acoustic cleaning apparatus as claimed in claimed in claim 3, in which the waveguide comprises a plurality of straight sections interconnected by bends.

An acoustic cleaning apparatus as claimed in any preceding claim, in which the second end of the waveguide is flared in diameter.

An acoustic cleaning apparatus as claimed in any preceding claim, in which the waveguide is tubular.

An acoustic cleaning apparatus as claimed in any of claims 1 to 5, in which the waveguide comprises an elongate hollow channel formed within a solid body.

8. An acoustic cleaning apparatus as claimed in any preceding claim, in which the waveguide is circular in section.

9. An acoustic cleaning apparatus as claimed in any preceding claim, in which the acoustic generator is arranged to generate an acoustic signal having a frequency in the infrasonic range of 0.001 - 50 Hz.

10. An acoustic cleaning apparatus as claimed in any preceding claim, in which the acoustic generator is arranged to produce said signal in a continuous flow of gas along the waveguide, the flow serving to carry the signal towards the surface to be cleaned.

1 1. An acoustic cleaning apparatus as claimed in any preceding claim, in which the second end of the waveguide is disposed adjacent an external flow of gas.

12. An acoustic cleaning apparatus as claimed in any of claims 1 to 10, in which the apparatus comprises means for generating an external flow of gas adjacent the second end of the waveguide, the flow serving to carry the signal towards the surface to be cleaned.

13. An acoustic cleaning apparatus as claimed in claim 12, in which said external flow generating means comprises a suction source arranged to draw the dislodged particles into the apparatus, the flow serving to carry the signal towards the surface to be cleaned.

14. An acoustic cleaning apparatus as claimed in any preceding claim, in which means are provided for varying the frequency of the signal generated by the acoustic generator to produce an acoustic signal having the desired wavelength.

15. An acoustic cleaning apparatus as claimed in any preceding claim, in which means are provided for tuning the waveguide to the frequency of the acoustic generator.

16. An acoustic cleaning apparatus as claimed in claim 15, in which the waveguide is tuned to the frequency of the acoustic generator by means arranged to vary the length of the waveguide or the impedance at a point along the length thereof.

17. An acoustic cleaning apparatus as claimed in claims 15 or 16, in which the frequency adjusting means is controlled by an output of a pressure, temperature or humidity sensor, which either senses the relevant parameter of the medium within the waveguide or the relevant parameter of the medium at or adjacent the surface to be cleaned.

18. An acoustic cleaning apparatus as claimed in any preceding claim, in which the apparatus forms a self-contained unit comprising said acoustic generator and said waveguide.

19. An acoustic cleaning apparatus as claimed in claim 18, in which said acoustic generator and said waveguide are provided within a common housing.

20. An acoustic cleaning apparatus as claimed in claim 18 or 19, in which the self-contained unit further comprises means for generating a flow of fluid along said waveguide and/or adjacent the said second end of the waveguide.

21. An acoustic cleaning apparatus as claimed in any of claims 18 to 20, in which the apparatus comprises handles or straps enabling the apparatus to be worn or carried by a user.

22. An acoustic cleaning apparatus as claimed in any preceding claim, in which the apparatus comprises a sensor to monitor for the accumulation of matter on said surface, the output of the sensor being connected to a control device which actuates the acoustic generator if the output of the sensor indicates that the surface requires cleaning.

23. An acoustic cleaning apparatus as claimed in any preceding claim, in which the valve member comprises a reservoir arranged to capture a volume of said pressurised gas.

24. An acoustic cleaning apparatus as claimed in claim 23, in which the valve member is displaceable from a first position in which the reservoir is connected to the inlet and second position in which the valve member is coupled to the outlet.

25. An acoustic cleaning apparatus as claimed in claim 24, in which the valve member is rotated between said first and second positions.

26. An acoustic cleaning apparatus as claimed in claim 25, in which the valve member comprises a plurality of reservoirs to increase the modulation frequency over the rotational frequency.

27. An acoustic cleaning apparatus as claimed in claims 25 or 26, in which the or each reservoir comprises a mouth for coupling to the inlet and outlet, the mouth being directed axially of the rotational axis of the valve member.

28. An acoustic cleaning apparatus as claimed in claims 25 or 26, in which the or each reservoir comprises a mouth for coupling to the inlet and outlet, the mouth being directed radially of the rotational axis of the valve member.

29. An acoustic generator as claimed in any of claims 23 to 28, in which the volume of said reservoir is arranged to reduce between said inlet and outlet.

30. An acoustic cleaning apparatus as claimed in any preceding claim, in which the waveguide has a length substantially equal to a quarter of the wavelength of the acoustic signal generated by said acoustic generator.

31. An acoustic generator comprising a valve having an inlet for coupling to a source of pressurised gas, an outlet coupled and a valve member disposed between the inlet and outlet, means being provided for operating the valve member to modulate a flow of gas between the inlet, wherein the valve member is arranged to capture a volume of said pressurised gas from the inlet in a reservoir and to transfer the captured volume of gas to the outlet.

32. An acoustic generator as claimed in claim 30, in which the valve member comprises a reservoir arranged to capture a volume of said pressurised gas.

33. An acoustic generator as claimed in claim 31 , in which the valve member is displaceable from a first position in which the reservoir is connected to the inlet and second position in which the valve member is coupled to the outlet.

34. An acoustic generator as claimed in claim 32, in which the valve member is rotated between said first and second positions.

35. An acoustic generator as claimed in claim 31 , in which the valve member comprises a plurality of reservoirs to increase the modulation frequency over the rotational frequency.

36. An acoustic generator as claimed in claims 31 or 32, in which the or each reservoir comprises a mouth for coupling to the inlet and outlet, the mouth being directed axially of the rotational axis of the valve member.

37. An acoustic generator as claimed in claims 31 or 32, in which the or each reservoir comprises a mouth for coupling to the inlet and outlet, the mouth being directed radially of the rotational axis of the valve member.

38. An acoustic generator as claimed in any of claims 31 to 36, in which the volume of said reservoir is arranged to reduce between said inlet and outlet.