IE46068B1 - Ultrasonic atomizer - Google Patents

Description

The present invention relates to ultrasonic transducers and to apparatus employing same for achieving efficient combustion of fuels. An example of same is found in the U.S. Patent to H.L. Berger, 3,861,852, issued January 21, 1975.

A problem associated with transducers of the type used as atomizers in fuel burner assemblies is the non-uniform delivery of fuel to an atomizing surface of the atomizer with consequent non-uniform distribution of fuel from same. It has been discovered that with such prior art atomizers, fuels which have low surface tension, for example, hydrocarbon fuels, begin to atomize within a fuel passage leading to the atomizing surface through an ultrasonic horn of the transducer. This premature atomization creates bubbles within the fuel passage. The bubbles eventually work their way to the atomizing surface and their arrival at the atomizing surface results in a temporary interruption in fuel flow to portions of the surface. Non-uniform distribution of fuel over the surface results. The bubble remains intact for a short period of time on the atomizing surface and thus the surface area beneath the bubble during the interval Is not wet with fuel.

According to the present invention there is provided an ultrasonic atomizer comprising an ultra46063 - 3 sonic horn formed with a liquid supply passage extending to an atomizing surface of the horn, at least a portion of the passage being lined by a decoupling sleeve for acoustically isolating the surface of the passage from liquid flowing in the passage.

Advantageously the said portion of the passage terminates a small distance from the atomizing surface. Preferably the sleeve is made of polytetrafluoroethylene.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawing wherein the sole Figure is a side view, partly in section of a piezoelectric ultrasonic atomizer.

Referring to the drawing, an ultrasonic atomizer is seen as including a front 12 and a rear 13 ultrasonic horn and a driving element 14 comprising a pair of piezoelectric discs 15, 16 and an electrode 18 positioned therebetween, excited by high frequency electrical energy fed thereto from a terminal 18A.

The driving element 14 is sandwiched between flanges 19, 20 of the horns 12, 13 and securely clamped therein by means of a clamping assembly that includes a mounting ring 21 {for securing the assembly to other apparatus) and a plurality of assembly bolts 22 which pass through holes in the electrode 18 and the flanges 19 and 20 into threaded openings in the mounting ring 21. The assembly bolts 22 are electrically isolated from the electrode 18 fay means of insulators 23.

The atomizer 11 further Includes a fuel tube 24 for introducing fuel into a passage 34 within the front horn 12 and a pair of sealing gaskets 26, 27 compressed between horn flanges 19, 20.

The horns 12, 13 are of good acoustic conduct- 4 ing material such as aluminium titanium or magnesium; or alloys thereof such as Ti-6A1-4V titanium-aluminium alloy, 6O61-T6 aluminium alloy, 7025 high strength aluminium alloy, AZ 61 magnesium alloy and the like; the discs 15, 16 are of lead-zirconate-titanate such as those manufactured by Vernitron Corporation or of lithium niobate such as those manufactured by Valtec Corporation; the electrode 18 is of copper; the terminal 18A, mounting ring 21 and assembly bolts 22 are of steel; the insulators 23 are of nylon, polytetrafluoroethylene or some other plastics material with good electrical insulating properties; and, the sealing gaskets 26, 27 are of silicone rubber.

The front horn 12 is seen as including a large' diameter portion 28, a small diameter portion 30 so as to form an amplification shoulder 31, a flanged tip 32 with an atomizing surface 33, a central passage 34 for delivering fuel to the atomizing surface 33 and an internally mounted decoupling sleeve 35. The decoupling sleeve 35 is made of polytetrafluoroethylene which does not couple well acoustically to the material of the front horn 12.

As noted previously, in prior art atomizers fuel can begin to atomize within the fuel passage leading to the atomizing surface. This premature atomization creates voids within the fuel passage at the fuel-wall inter-face which leads to the formation of bubbles within the fuel passage. The bubbles eventually work their way to the atomizing surface, and their arrival at the atomizing surface results in a temporary interruption in fuel flow to a portion of the surface and non-uniform distribution of fuel over the surface results. The bubbles remain intact for a short period of time on the atomizing surface and thus the surface area beneath the bubble during that period is not wet with fuel. The net effect of this non46068 - 5 uniform and constantly varying distribution of fuel on the surface is a spatially unstable spray of fuel, a condition which leads to unstable combustion.

The foregoing problem is eliminated by the provision of the decoupling sleeve 35 within the fuel passage 34 that extends up to 1/32 of an inch of the atomizing surface 33. The sleeve 35 is made of a plastics material, is a press fit into the passage 34 and extends inwardly to the large diameter portion 28.

The difference in acoustical transmitting properties between the material of the sleeve 35 and the front horn 12 is such that the vibrating motion of the horn 12 is not Imparted to the fuel within the fuel passage 34 encompassed by the sleeve 35.

A method of making the ultrasonic transducer shown in the drawings forms the subject of and is claimed in Patent Specification No. 46066.

Claims (4)

1. CLAIM Si10

1. An ultrasonic atomizer comprising an ultrasonic horn formed with a liquid supply passage extending to an atomizing surface of the horn, at least a portion of the passage being lined by a decoupling sleeve for acoustically isolating the surface of the passage from liquid flowing in the passage.

2. An atomizer according to claim 1 in which the said portion of the passage terminates a small distance from the atomizing surface.

3. An atomizer according to claim 1 or claim 2 in which the sleeve is made of plastics material.

4. An atomizer according to claim 3 in which the plastics material is polytetrafluoroethylene.