Patent Application
20090277971
Not applicable
Not Applicable
Not Applicable
1. Field of Invention
This invention relates to ultrasonic atomization of low viscosity liquids including atomization of fuels for internal combustion engines.
2. Prior Art
Ultrasonic atomization is a well-known art and a description of an application of an ultrasonic device is found in a paper by J. N. Antonovich, entitled “Ultrasonic Atomization of Liquids” which appears in “Transactions of Ultrasonics” (February 1959, Pages 6-15) published by the United States Institute of Radio Engineers. Electromagnetic, magneto restrictive, and piezoelectric effects are known to produce ultrasonic vibrations.
The piezoelectric effect is achieved by applying a voltage to a material, which possesses a particular crystalline lattice (also called the piezo element or element). The electrons influence the element and cause its geometry to change. This change overall translates into contraction or expansion depending on the polarity of the voltage applied. A common material used to manufacture piezoelectric devices is Lead Zirconium Titanium (PZT), although many other materials are commercially available.
PZT is manufactured in many shapes and configurations depending on the application. A type of piezo actuator called a piezo bender is constructed of a thin, flexible substrate (often metallic) in which a thin layer of PZT is bonded. The PZT bonded to the substrate results in unimorphic, or bimorphic movement when electrified. Piezo benders are currently the most economical and commercially available piezoelectric actuators on the market.
An alternating electrical signal generator or driver circuit supplies an alternating voltage to the bender. During the positive cycle (or phase) of the signal the element expands causing the flexible metallic substrate to warp in a direction. As the voltage changes to the negative cycle, the element contracts and causes the substrate to warp in the opposite direction. A signal at 40.8 kHz repeats this warping action 40,800 times per second. The vibration at this rate is beyond the human range of hearing and is considered “ultrasonic”.
Liquid vibrating at ultrasonic frequencies form surface waves and a disruption in the surface tension of the liquid. Atomization of the liquid occurs when the proper amplitude of the ultrasonic vibration is achieved cresting the surface waves and breaking the surface tension, casting off minute droplets.
Piezoelectric materials have specifications disclosed by the manufacturer. The most important consideration is the operating temperature, as overheating will cause the piezo element crystalline lattice to disorientate and permanently lose any useable properties (known as the Curie temperature). To prevent the element from malfunctioning it is important to stay within the operating voltages and temperatures set forth by the manufacturer. Operating frequency, power consumption, and overall lattice distortion of the piezoelectric material are also considered when designing piezoelectric devices for liquid atomization.
Several issues arise concerning prior art, which are addressed by this invention. U.S. Pat. No. 3,860,173 issued Jan. 14, 1975 to Sata and U.S. Pat. No. 5,145,113 issued Sep. 8, 1992 to Burwell et al both employ liquid return capabilities to handle excess liquid (dripping) that has been improperly atomized. These devices rely on gravity to function properly and thus must be orientated accordingly. U.S. Pat. No. 4,799,622 issued Jan. 24, 1989 to Ishikawa et al utilizes an ultrasonic probe contacting the surface of the liquid supply channel, which is a source of frictional power loss and wear. U.S. Pat. No. 3,125,295 issued Mar. 17, 1964 to G. Moss et al requires a custom manufactured piezo element and offers no protection to the piezo element from direct heat related to combustion or open flame when used in combustion applications. U.S. Pat. No. 4,408,719 issued Oct. 11, 1983 to Last requires air flow as an addition function to perform the overall operation of atomization. U.S. Pat. No. 4,742,810 issued May 10, 1988 to Anders et al uses a powerful piezo element to drive multiple atomizing ports with no assurance each port will atomize at the same rate as other ports. U.S. Pat. No. 5,483,616 issued Jan. 9, 1996 to Chiu et al is subject to overheating, a problem common with ultrasonic atomizers. During operation, if the liquid is unavailable, the element will overheat in a matter of seconds and therefore requires a liquid level sensor to prevent this potential problem.
Cost is directly related to the power output, frequency response, density, material, and other factors used to manufacture piezo elements. Standard cylindrical and box shapes are more economical than custom shapes such as tubes and cones. Power is directly related to heat dissipation. The more electrical power a piezo element uses, the more heat must be dissipated in order to operate continuously.
In accordance with the embodiments, a piezo bender supplies vibration to an atomizer assembly at 40.8 kHz. An electrical signal is supplied by a conventional signal generator or driver circuit and is connected to the piezo bender by a conventional electrical connection means. The liquid is supplied from a source to the atomizer assembly via a transport line. A mounting body provides a means to support the electrical connectors, liquid supply connection, transport line and piezo bender. Vibration is transmitted from the piezo bender to the atomizer assembly via the transport line extension.
During operation, liquid from the source is urged through the transport line and emerges at the atomizer assembly. The electrical signal causes the piezo bender to vibrate. The liquid is atomized by the vibrating atomizer assembly without dripping.
Illustration
The mount body 24 is constructed of brass providing a means of electrically conductive rigid support for the piezo bender 20 and transport line 23. The mount body 24 is rectangular, measuring 15 mm long, 8 mm wide, and 10 mm thick. Attachment of the piezo bender 20 is achieved by embedding the edge of the piezo bender substrate 20B 1.5 mm deep into a slot 24B in the longitudinal end of the mount body 24, 2.5 mm from the bottom of the mount body 24, aligned perpendicularly with the longitudinal axis of the piezo bender substrate 20B, and then bonding the adjoining surfaces with silver solder.
Grounding of the alternating electrical signal is achieved through the mount body 24 and conducted through the silver solder attachment to the conductive piezo bender substrate 20B. An additional electrical connection is made to the piezo element 20A by soldering 21B a conductive wire 21A to a nodal location on the surface of the piezo element 20A near the mount body 24.
The nodal location is determined by the operating frequency and the natural harmonic of the piezo bender 20. The piezo bender substrate 20B is made of brass 18 mm in diameter, 0.38 mm thick with a concentrically bonded layer of piezo electric material (the piezo element) 20A 13 mm in diameter and 0.25 mm thick with a natural resonant frequency of 6800 Hz as provided by manufacturer specifications.
The operating frequency is selected at 40.8 kHz, the 6th harmonic of the natural resonant frequency of the piezo bender 20, therefore the closest nodal location to the mount body 24 is 3 mm from the attached edge of the piezo bender substrate 20B along its longitudinal axis. A 0.50 mm piezo bender substrate orifice 20C is drilled into the piezo bender substrate 20B, 15 mm from the mount body 24 along the piezo bender substrate 20B longitudinal axis, which is the furthest antinodal location existing on the piezo bender substrate 20B away from the mount body 24.
The transport line 23 is made of surgical hypodermic 304 stainless steel tubing with an outside diameter of 0.49 mm and inside diameter of 0.254 mm. 304 stainless steel has a Young's modulus approximately 195 Gpa and a density of 8.00 grams per cubic centimeters. The transport line 23 serves as two additional integrated functional components; the transport line spring 23B and the transport line extension 23C. The transport line 23 itself serves the purpose of transporting the liquid through its interior from the liquid supply connector 22 to the atomizing assembly 25.
The transport line inlet 23A is inserted 5 mm into a 0.50 mm diameter mount body orifice 24A, at a location 4.0 mm below and parallel with the longitudinal axis of the piezo bender 20, as shown in
The transport line spring 23B provides vibrational dampening to the attachment where it meets the mount body orifice 24A. In preferred embodiment shown by
The transport line extension 23C passes through the antinode piezo bender substrate orifice 20C and is attached to the piezo bender substrate 20B at this location with silver solder and extends perpendicularly 30 mm away from the piezo bender substrate 20B surface. The distance from the mount body 24 exterior where it intersects with the mount body orifice 24A, to the antinode piezo bender orifice 20C is 15 mm, giving the transport line spring 23B including the 90 degree bend the same length. The transport line extension 23C is perpendicular and concentrically aligned with the 0.50 mm active plate orifice 25B.
The transport line outlet 23D is inserted into the bottom of the active plate orifice 25B and extends until flush with the top of the active plate 25A. The transport line extension 23C is bonded to the active plate 25A by silver solder resulting in the transport line outlet 23D to communicate with the top surface of the active plate 25A.
As shown in
The passive plate 25D has six circular atomizing apertures 25E each 0.55 mm in diameter arranged symmetrically and radially, a distance of 1.5 mm around the axial center of the passive plate 25D. Both active plate 25A and passive plate 25D diameters are approximately 6.35 mm.
The atomizer spring leaves 25F are of a radial leaf type spring consisting of three identical leaves placed equidistantly around the periphery of the passive plate 25D. Each leaf is 0.75 mm wide and 7.5 mm long and spaced 0.75 mm away from the passive plate 25D with a shape contouring the passive plate 25D. The passive plate flanges 25G integrating the atomizing spring leaves 25F to the passive plate 25D protrude 1.5 mm away from the passive plate 25D, are parallel to the passive plate 25D, are symmetrically distributed radially around the axial center of the passive plate 25D, and are 0.75 mm wide with 0.2 mm fillets on the corners.
The active plate flange 25C configuration is the same as the passive plate flange 25G configuration, but rotationally offset allowing the terminating ends of the atomizing spring leaves 25F to rest on the active plate flanges 25C. Furthermore, the active plate 25A and passive plate 25D are concentrically aligned. The atomizing spring leaves 25F are equally bent downward from the integrated passive plate flanges 25G, which results in a parallel 0.2 mm atomizer gap 25H between the top surface of the active plate 25A and the bottom surface of the passive plate 25D as shown in
As shown in
A typical mode of operation illustrated by
Liquid from a liquid supply 30 (
The liquid exits the transport line outlet 23D emerging at the top surface of the active plate 25A where it floods the atomizer gap 25H (
The piezo bender 20 (
In
The aforementioned action is repeated 40,800 times per second causing the liquid present in the atomizing gap 25H to atomize and eject through the atomizing apertures 25E in the passive plate 25D and the periphery of the atomizing gap 25H between the active plate 25A and passive plate 25D.
Secondary atomization occurs on the top surface of the passive plate 25D where liquid, which has migrated from the atomizing gap 25H through the atomizing apertures 25E, receives vibration from the passive plate 25D.
The opposing movement of the active plate 25A and passive plate 25D allows for atomization to occur more efficiently and therefore with less power compared to other piezoelectric atomizers currently available.
The atomizer gap 25H between the active plate 25A and passive plate 25D being of close proximity, provides adequate surface area for the liquid to cling to, due to surface tension while the atomization occurs.
Liquid being supplied to the atomizing assembly at or below the rate of atomization produces a dripless result in any orientation.
Reciprocating motion of the active plate 25A and passive plate 25D is not the only vibrational force acting upon the liquid. The active plate 25A and passive plate 25D exhibit surface transversal vibrations in the form of standing waves, which additionally assist in the atomization process.
An alternative embodiment as shown in
A second alternative embodiment illustrated by
A third alternative embodiment illustrated by
Alternative atomizer assembly embodiments exploring the shape, size, construction, and materials of the active plate 25A and the passive plate 25D provide a variety of atomizing results in regards to operating frequency, droplet size, flow capacity, spray pattern, temperature threshold, lifespan, and economy.
The objective of these embodiments is to overcome problems previously presented by the prior art. The embodiments produce ultrasonic atomization of low viscosity liquids, at a rate of 0.45 liters per hour, utilizing 6 watts of power at 40.8 kHz frequency.
The embodiments described achieve atomization using economical piezo benders that operate continuously well below the Curie temperature. Operation does not rely on gravity, and can have any orientation. It operates with a wide frequency response, eliminating the need for precision electrical signal control. Atomization occurs a distance away from the heat sensitive piezo bender element, allowing atomization to occur directly in an open flame or heat source. Other advantages of the embodiments are listed as follows:
(a) The mounting support can be made of lightweight, economical materials such as plastic or ceramic.
(b) The overall size of the embodiments can be made very compact and easily integrated into other devices.
(c) The utilization of inexpensive off-the-shelf piezo benders allows for rapid manufacturing.
(d) The liquid is atomized with low wattage consumption.
(e) The piezo bender provides low heat dissipation for continuous operation even when running dry. It won't overheat.
(f) The +/−5% bandwidth response allows for use of inexpensive low tolerance driver circuits.
(g) The dripless atomizer assembly is operational in any orientation. There is no need for an overflow or liquid return reservoir.
(h) The atomizer assembly can be made of high temperature, corrosion resistant materials and extended directly into a heat source without exposing the piezo element to heat or liquids.
(i) There is no frictional contact of parts resulting in low wear and long life of the components.
(j) It operates with low liquid supply pressure.
(k) Changes to the passive plate aperture design can provide a variety of spray patterns and droplet sizes.
(l) The reciprocal vibrating action of the atomizer assembly provides an efficient atomization of liquids.
(m) It operates at multiples of harmonics of the piezo benders natural frequency allowing for more versatile atomizing results.
The embodiments illustrate the use and operation for applications requiring liquid atomization. However, with minor ramifications to the embodiments, the applications of use include but are not limited to, fragrance dispensers, agricultural pesticide sprayers, semiconductor spin coating, textile pigmentation, and medical disinfectants. Since the cost of production, power consumption, and weight is significantly lower than piezoelectric atomizers currently commercially available, and in conjunction with its dripless atomizer assembly features, these embodiments would be beneficial to markets that require atomization of liquids on a consumable or disposable basis.
Although the description above provides many specifications, these should not be construed as limiting the scope of the embodiments but as merely providing illustrations of some of the presently preferred embodiments. For example, the means of mount support could be made of rigid non conductive plastic thereby requiring an alternative means of conducting the electrical signal to the piezo transducer. Soldered wires, spring brushes, or metallic plates could very easily be incorporated to provide electrical connection to the signal generator. As mentioned, the transport line spring and radial leaf springs of the plate head can be configured in any shape, which provides resonance from a variety of materials. Thus the scope of the embodiments should be determined by the appended claims and their legal equivalent, rather than by the examples given.
