CA2203063A1

CA2203063A1 - Subsonic sound generator

Info

Publication number: CA2203063A1
Application number: CA 2203063
Authority: CA
Inventors: Bruce Yearham
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-04-18
Filing date: 1997-04-18
Publication date: 1998-10-18

Description

SUBSONIC SOUND GENERATOR
Field of the Invention This invention relates to the generation of a subsonic sound wave associated with a resonator tube whereby a gaseous medium is oscillated to improve an 5 industrial process. The invention finds application in cleaning boilers and heat exchangers by dislodging friable deposits. In combustion, rapidly oscill~ting sound waves improve the mi~ing of fuel and combustion air for more efficient utilization of fuels.
Mass heat transfer may also be improved by using sound waves to disturb a 10 thermal boundary layer surrounding a solid object in a gaseous medium and sound waves may also be used to accelerate the evaporation of liquids.

Background of the Invention In order to create a subsonic sound wave, a supply of air is delivered 15 intermittently into a resonator tube. This invention relates in part to the means used for creating an intermittent air delivery and will be referred to as a sound generator. Because the sound has a frequency of approximately 20 Hz, it cannot be heard by a human ear and it is therefore "subsonic".
One known form of sound delivery comprises an air chamber associated with 20 a compressed air supply. The air chamber is sealed by a flexible diaphragm which, in an extended position, causes a slide valve to move. The slide valve is in the form of a hollow cylinder in fluid communication with a resonator tube. The slide valve reciprocates outside a sleeve and both the slide valve and the sleeve have openings whereby ambient air is admitted into the resonator tube when the openings on the slide valve are in registration with the openings on the sleeve. In use, when ambient air is admitted, the pressure on the diaphragm is equalized and the diaphragm isrestored to a neutral unextended position thereby withdrawing the piston so that its openings are out of registration with the openings in the surrounding sleeve. The 5 reciprocating piston thus creates a sound pulse or intermittent air flow which is delivered to the resonator tube.
In another form of a sound generator known to the applicant, the piston movement is actuated by a compressed coil spring.
Both of the above-mentioned sound generators have limitations which result 10 in unreliable performance of the sound generator to accomplish their intended tasks.
In particular, the afore-mentioned forms of sound generator are not adjustable to compensate for changes in the ambient temperature which characterizes an optimumwavelength for the sound wave travelling through the resonator tube.

15 Summ~ry of the Invention In accordance with this invention, there is provided a sound generator comprising a direct current variable speed electric motor and an outer cylindrical sleeve operatively connected to said motor for rotation about its longitudinal axis.
An inner cylindrical sleeve is in fluid communication with an air supply and is 20 axially received in the outer cylinder which, in use, rotates outside the inner cylinder.
The inner and the outer cylinder have respective openings which come into and out of registration with each other upon rotation of the outer cylinder.

The air supply to the inner cylindrical sleeve is delivered intermittently to a resonator tube whenever said openings come into registration, the resonator tubebeing in fluid communication with a housing which receives the outer cylinder.
In accordance with another aspect of the invention, there is provided feedback means whereby the speed of the motor is adjusted in accordance with ambient conditions, the feedback means comprising a sensor for sensing vibrations on theresonator tube coupled to an electronic control means operatively connected to the motor.

Brief Description of the Drawings In order that the invention can better be understood, it is described in more detail below with reference to the accompanying drawings, in which:
Fig. 1 is a schematic drawing showing a subsonic sound generator in accordance with the invention associated with a resonator tube disposed inside a boiler wall; and Fig. 2 is a schematic sectional view drawn to a large scale of circled area 2 in Fig. 1.

Description of Preferred Embodiment A subsonic sound generator system is indicated generally by reference numeral 20 in Fig. 1 and includes a resonator tube 22 disposed horizontally in a boiler wall 24. The sound generator, in this application, is intended to be used to dislodgefriable deposits on the boiler wall to clean the boiler. As is common in the art, the resonator tube 22 is suspended by a pair of suspension springs 26 and the resonator tube is coupled to the boiler wall 24 by an extension tube 28 having a vibrationcompensator 30 disposed between the extension tube and the resonator tube to isolate the wall 24.
The free end of the resonator tube 22 remote from the wall 24 is in fluid communication with an intermittent air supply delivered to a housing 32 which houses a subsonic sound generator 34 which will be described further below with reference to Fig. 2.
The housing 32 is associated at one end with a direct current variable speed motor 36 and at another end with an air reservoir 38 supplied through a flexiblehose 40 with air from a compressor 42.
The air supply from the compressor 42 is delivered to a chamber or air receiver 44 and filtered through a suitable filtration unit 46. The compressor 42 delivers 250 to 750 CFM at 10-15 psi to the air receiver 44.
Referring now to Fig. 2, it will be seen that the air supply from the air receiver 44 is delivered to an inner cylinder 48 disposed axially inside an outer cylinder 50 both received in the housing 32. The outer cylinder 50 is mounted for rotation on longitudinally-spaced bearings 52 and driven by the motor 36.
The inner and the outer cylinders 48,50 have respective openings in the form of a longitudinally-extending slot 54 which come into and out of registration with each other upon rotation of the outer cylinder 50. When the slots 54 line up in registration with each other, a burst of air is allowed to escape through the outer cylinder 50 into the housing 32 and out of the resonator tube 22 where a sinusoidal sound wave is created, having a wave length of 17 metres at an ambient temperature of 20~C.
The length of the resonance tube is selected to accommodate a standing sonic quarter wave for oscillations of +/- 0.5 metre and the associated motor speed is5 selected so that the outer cylinder 50 rotates approximately 20 times per second, creating a sound wave having a frequency of 20 Hz and a pressure of 130-140 DB.
In order to compensate for temperature variations which result in commensurate changes in the wave length of the resulting sound wave, an accelerometer sensing device 56 (Fig. 1) is coupled to the resonance tube 22 and10 adapted to transmit an electronic signal to electronic control means 58 whereby the speed of the motor 36 is adjusted to vary the frequency of the sound wave. In this way, the power of subsonic air blasts into the boiler may be optimized for more efficient cleaning.
Conveniently, the electronic control means 58 is coupled to a solenoid valve 15 60 disposed to interrupt air flow in the air hose 40 and is also coupled to control the operation of the compressor 42. A bypass line 62 is provided around the solenoidvalve 60.
It will be understood that several variations may be made to the above-described embodiment of the invention and that the invention is not limited 20 thereby.

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