Liquid droplet generator

Abstract: A droplet generator (10) is provided for atomizing a fluid jet into a stream of droplets (60). The droplet generator comprises a housing (20) having a first end (22a), a second end (24), and an inner cavity (26). The second end of the housing has at least one orifice (70) herein. An acoustic transducer (30) is connected to the housing and has a first portion (32) located within the cavity and spaced a given distance from the second end (24) of the housing. The first portion (32) of the acoustic transducer and the second end (24) of the housing define a manifold (40) therebetween for receiving a fluid. A fluid supply (62) is connected to the acoustic transducer for supplying fluid under pressure to the inner cavity and into the manifold. The fluid passes from the manifold via the orifice (70) as a stream of fluid. A drive mechanism (50) is provided for driving the transducer (30) and causing the first portion of the transducer to impart acoustic energy to the fluid in the manifold, thereby creating velocity perturbations on the stream of fluid which are sufficient to atomize the fluid.

Description: GOVERNMENT RIGHTS The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of contract No. (F33615-89-C-2973) awarded by the U.S. Air Force. Background of the Invention The present invention relates to a liquid droplet generator of the kind as defined in the preamble of claim 1 or claim 12. Furthermore, the invention concerns a method for generating droplets as defined in the preamble of claim 8. The atomization of a jet or sheet of liquid is a process which, in most cases, requires energy to be added to the liquid. The added energy is converted into an increase in surface energy in the liquid as the initial liquid mass is separated into droplets. As the surface energy of the liquid increases, the surface area of the liquid likewise increases. Energy may be supplied for purposes of atomization from either a decrease in kinetic energy of the liquid or from an external source. UA-A-4 138 687 teaches a droplet generator and a method for generating droplets as defined in the preambles of claims 1 or 12 and claim 8, respectively. The ink jet dispenser which is shown therein is an atomizer with less efficiency. The electromechanically driven piston is mounted through a compliant mount to a nozzle plate. The top and bottom ends of a transducer are free to move up and down, so that when a piezoelectric material extends, the piston moves as a result of the inertial reaction of the other end of the piezoelectric transducer. The compliant mount is provided to prevent vibrations in the structure of the ink jet printer. Furthermore, the compliant mount also prevents the piston from placing a large compression on a manifold when a low frequency or steady voltage is applied to the transducer. One prior art process for atomizing a fluid involves impinging a fast moving air stream onto a slower moving fluid, such as a fuel to be burned in a combustor of a turbine engine. With this process, the kinetic energy of the injected air serves to tear the liquid into filaments and then into drops. Thus, a portion of the kinetic energy of the injected air is converted into an increase in surface energy in the atomized fluid. The prior art air injection process, when used to atomize a fuel to be burned in a turbine engine, is only effective when the engine is operating, since a source of high velocity air is needed for atomization. Further, higher engine operating temperatures, which result in greater engine operating efficiency, are difficult to achieve since excess air is added into the engine for purposes of atomization. Additionally atomization by use of injected air results in an inconsistent distribution of fuel spray in both time and space. As a result, the combustor is required to be longer than otherwise necessary to ensure that all the fuel is burned before the air/fuel mixture exits the combustor. The inconsistent distribution of fuel spray also results in a non-uniform combustion of the air/fuel mixture causing an increase in NOx pollutants being emitted from the engine. A further prior art atomization process involves the acoustic excitation of a circular liquid jet at an unstable wavelength. Rayleigh explained in 1878 that a circular fluid jet is unstable for azimuthally symmetric perturbations whose axial wavelength is longer than the circumference of the jet. This prior art process is based upon Rayleigh's theoretical work. The process involves placing small amplitude acoustic perturbations on a circular jet, wherein the perturbations have a wavelength longer than the circumference of the jet. The applied perturbations grow, due to an input of energy from surface tension, and break the jet into a stream of drops at the excitation frequency. This process adds little or no energy to the fluid. Thus, the surface area and surface energy of the fluid is lower after break-up than before. Further, the size of the resulting drops produced by this process have a diameter approximately twice the diameter of the original jet. Thus, if small drops are desired, small nozzles or orifices must be used. Small nozzles, however, can be easily obstructed by particles carried by a fluid. Consequently, this process is disadvantageous for use where small droplets are desired. Further, this process will not induce atomization of a sheet of liquid. Accordingly, there is a need for an apparatus which is capable of adding energy to a liquid stream for purpose of atomization without employing high velocity air. There is a further need for an apparatus capable of employing acoustic energy for atomizing a liquid stream into a stream of droplets having a greater surface area and surface energy than that of the initial stream, and which is further capable of inducing atomization of a sheet of liquid. Summary of the Present Invention According to the invention this need is met by the method comprising the features of claim 8 and apparatus according to claim 1 or claim 12. According to the invention, a high energy, acoustic droplet generator is provided for imparting energy into a stream of liquid in the form of velocity perturbations for purposes of atomizing the fluid into a stream of droplets. Because energy is added to the liquid stream, the surface area of the surface energy of the resulting stream of droplets is greater than that of the initial liquid stream. In accordance with a first aspect of the present invention, a droplet generator is provided for breaking a fluid jet into a stream of droplets. The droplet generator comprises a housing having a first end, a second end, and an inner cavity. The second end of the housing has at least one orifice therein. An acoustic transducer is connected to the housing and has a first portion located within the cavity and spaced a given distance from the second end of the housing. The first portion of the acoustic transducer and the second end of the housing define a manifold therebetween for receiving a fluid. Fluid supply means are connected to either the housing or the acoustic transducer for supplying fluid under pressure to the inner cavity and into the manifold. The fluid passes from the manifold via the orifice as a stream of fluid. Drive means are provided for driving the transducer and causing the first portion of the transducer to impart acoustic energy to the fluid in the manifold, thereby creating velocity perturbations on the stream of fluid which are sufficient to atomize the fluid. The acoustic transducer according to the invention comprises the features of claim 1 or claim 12. A sealing means for sealing the piston to the housing and thereby forms a sealed chamber for receiving the fluid. At least a portion of the piston is positioned within the chamber and a section of the chamber is defined by the manifold. The piezoelectric means may comprise at least two piezoelectric crystals. The mount includes a centrally located stepped bore. Each of the piezoelectric crystals includes a centrally located bore extending therethrough, while the piston includes a centrally located threaded bore which extends at least partially therethrough. The connector means may comprise a bolt which extends through the bores in the mount and the piezoelectric crystals and threadedly engages with the threaded bore in the piston for connecting the mount, the piezoelectric crystals, and the piston to one another. The bolt preferably includes a centrally located passage extending therethrough. The piston includes at least one additional bore extending from an outer surface thereof to communicate with the centrally located passage extending through the bolt. The fluid supply means communicates with the passage in the bolt for supplying fluid through the passage and the at least one additional bore in the piston to the cavity and into the manifold. The drive means serves to drive the transducer at a natural frequency of the transducer. This causes large amplitude oscillations of the first portion of the transducer, thereby resulting in the first portion of the transducer imparting acoustic energy to the fluid in the manifold which results in large amplitude velocity perturbations on the stream of fluid. In one embodiment of the present invention, the housing includes a hollow main portion having first and second ends. The first end of the main portion defines the first end of the housing. A nozzle plate is connected to the second end of the hollow main portion. The nozzle plate defines the second end of the housing and has the at least one orifice formed therein. In a further embodiment of the present invention, the housing comprises a hollow main portion having first and second ends. The first end of the main portion defines the first end of the housing. An intermediate nozzle plate support is connected to the second end of the hollow main portion. A nozzle plate is connected to the nozzle plate support and has the one orifice formed therein. The nozzle plate and the intermediate plate define the second end of the housing. In accordance with a further aspect of the present invention, a method is provided for generating droplets from a stream of liquid. The method comprises the steps indicated in claim 8. The piezoelectric means may comprise at least two piezoelectric crystals. Preferably, the mount, the piezoelectric crystals, and the piston include bores as discussed above with regard to the first aspect of the present invention. The step of connecting the mount, the piston and the piezoelectric means to one another is performed by passing a bolt through the bores in the mount and the piezoelectric crystals and threadedly engaging the bolt with the bore in the piston for connecting the piezoelectric crystals, the mount and the piston to one another. The bolt includes a centrally located passage extending therethrough. The piston includes an additional bore extending from an outer surface of the piston to communicate with the centrally located passage extending through the bolt. The step of supplying fluid to the inner cavity and into the manifold is performed by passing fluid through the passage in the bolt and the additional bore in the piston to the cavity and into the manifold. The step of driving the transducer is performed at a natural frequency thereof causing large amplitude oscillations of the first portion of the transducer, thereby resulting in the first portion imparting acoustic energy to the fluid in the manifold which results in large amplitude velocity perturbations on the stream of fluid. Accordingly, it is an object of the present invention to provide a method and apparatus for imparting energy into a stream of liquid in the form of velocity and pressure perturbations for purposes of atomizing the liquid into a stream of droplets. It is a further object of the present invention to provide an acoustic droplet generator for imparting energy into a circular liquid stream for atomizing the liquid into a stream of droplets having a diameter much less than twice the diameter of the initial jet. It is an additional object of the present invention to provide an acoustic droplet generator for imparting energy into a sheet of liquid for atomizing the same. It is yet another object of the present invention to provide an acoustic drop generator for imparting energy into a liquid stream for atomizing the liquid into a stream of droplets having a surface area and surface energy greater than that of the initial stream. These and other objects and advantages of the present invention will be apparent from the following description, the accompanying drawings, and the appended claims. Brief Description of the Drawings Figure 1 is a side elevational view of the droplet generator of the present invention; Figure 2 is a partial-sectional view of the droplet generator shown in Figure 1; Figure 3 is a side elevational view of the transducer of the droplet generator shown in Figure 1; Figure 4 is an exploded perspective view of the droplet generator of the present invention; Figure 5 is a side elevational view of the housing of the droplet generator shown in Figure 1; Figure 6 is a cross-sectional view taken generally along section line 6-6 of Figure 5; Figure 7 is an end view of the droplet generator of Figure 1 illustrating a nozzle plate in accordance with a first embodiment of the present invention; Figure 8 is a generalized diagram of a stimulation driving circuit in accordance with the present invention; Figure 9 is a plan view of a nozzle plate in accordance with a second embodiment of the present invention; Figure 10 is an enlarged plan view of the slot of the nozzle plate shown in Figure 9; Figure 11A is a cross-sectional view taken generally along section line 11A-11A in Figure 10; Figure 11B is a cross-sectional view taken generally along section line 11B-11B in Figure 10; Figure 12 is a photograph of a stream of droplets formed by the droplet generator of the present invention while employing the nozzle plate shown in Figure 9; Figure 13 is an enlarged plan view of the slot of a nozzle plate formed in accordance with a third embodiment of the present invention; Figure 14 is a cross-sectional view taken generally along section line 14-14 in Figure 13; Figure 15 is a photograph of a stream of droplets formed by the droplet generator of the present invention while employing a nozzle plate having the slot shown in Figure 13; Figure 16 is an enlarged plan view of the slot of a nozzle plate formed in accordance with a fourth embodiment of the present invention; Figure 17 is a cross-sectional view taken generally along section line 17-17 in Figure 16; and, Figure 18 is a photograph of a stream of droplets formed by the droplet generator of the present invention while employing a nozzle plate having the slot shown in Figure 16. Detailed Description of the Invention A droplet generator constructed in accordance with the present invention is shown in Figures 1 and 2, and is generally designated by the reference numeral 10. The droplet generator 10 includes a housing 20 having a substantially cylindrical main body portion 22 and an exit portion 24. Upper end 22a of the main body portion 22 defines a first end of the housing 20 and exit portion 24 defines a second end of the housing 20. Connected to the main body portion 22 of the housing 20 is an acoustic transducer 30. The transducer 30 includes a piston 32 (also referred to herein as a first portion of the transducer) located within an inner cavity 26 of the housing and spaced a given distance (e.g., between 0,254 mm (0.010 in.) and 0,635 mm (0.025 in.)) from an entrance surface 24a of the exit portion 24 of the housing 20. The piston 32 and the entrance surface 24a define a manifold 40 therebetween for receiving a fluid. Drive means 50 is connected to the transducer 30 for driving the transducer 30 and causing the piston 32 to impart acoustic energy to the fluid in the manifold 40, thereby creating high amplitude velocity perturbations on the outgoing stream of fluid which are sufficient to atomize the fluid into a stream of droplets 60, as shown in Figure 1. Because energy is added to the stream of droplets 60, the surface area and the surface energy of the droplets 60 is greater than that of the initial liquid mass from which the droplets are formed. A fluid supply 62 communicates with the acoustic transducer 30 through a fluid supply line 64 for providing pressurized fluid to the transducer 30. The fluid supplied to the transducer 30 passes from the transducer 30 into the inner cavity 26 and into the manifold 40. The fluid exits from the generator 10 via orifices or nozzles 70 formed within a nozzle plate 72, which comprises a first section of the exit portion 24 of the housing 20. In accordance with a first embodiment of the present invention, the orifices 70 are formed in the plate 72 as a linear array of spaced apart circular openings (see Figure 7), Referring to Figures 2, 3 and 4, the acoustic transducer 30 includes a mount 33 fixedly connected to the main body portion 22 of the housing 20 via bolts 33a. Positioned between the mount 33 and the piston 32 are two piezoelectric crystals 34 having an electrode 35 interposed therebetween. The electrode 35 extends through a slot 28 in the main body portion 22 for connecting with the drive means 50, as illustrated in Figure 1. As will be discussed in further detail below, the drive means serves to drive the transducer 30 for causing the piston 32 to oscillate relative to the exit portion 24 of the housing 20 and impart acoustic energy to the fluid in the manifold 40 to atomize the fluid. A bolt 38 (also referred to herein as connector means) is provided for connecting the piston 32, the mount 33, the piezoelectric crystals 34, and the electrode 35 to one another to form the transducer 30. The bolt 38 passes through a centrally located stepped bore 33b in the mount 33, a centrally located bore 34a in each of the piezoelectric crystals 34 and a bore 35a located in the electrode 35. The upper portion 38a of the bolt 38 seats in the stepped bore 33b in the mount 33, while the lower portion 38b threadedly engages with a centrally located threaded bore 32a in the piston 32. The transducer 30 further includes sealing means comprising an O-ring 39 for sealing the piston 32 to the main body portion 22 of the housing 20 and thereby forming a sealed chamber 42 for receiving the fluid. At least a portion of the piston 32 is positioned within the chamber 42 and a section of the chamber 42 is defined by the manifold 40. The bolt 38 includes a centrally located passage 38c extending therethrough, as shown in dotted line in Figure 2. The piston 32 includes an additional bore 32b extending from an outer surface 32c of the piston 32 for communicating with the centrally located passage 38c extending through the bolt 38. The fluid supply line 64 is connected to the mount 33 via connector 65 and communicates with the passage 38c in the bolt 38 for supplying fluid through the passage 38c and the additional bore 32b in the piston 32 to the sealed chamber 42 and into the manifold 40. The fluid supply means 62 preferably supplies fluid through line 64 at a pressure between 6,896 - 41,376 N/cm 2 (10-60 psi). In accordance with the preferred embodiment of the present invention, a nozzle support plate 74 is interposed between the nozzle plate 72 and the main body portion 22 of the housing 20. The support plate 74 comprises a second section of the exit portion 24 of the housing 20 and its upper surface defines the entrance surface 24a of the exit portion 24 of the housing 20. The nozzle support plate 74 includes a centrally located opening 74a through which the fluid passes before it exits through the orifices 70 in the nozzle plate 72. Bolts 76 pass through corresponding openings in the plates 72 and 74 and threadedly engage with corresponding openings 22b found in the main body portion 22 of the housing 20 to secure the plates 72 and 74 to the main body portion 22. Adhesive (not shown), such as an epoxy, may be interposed between the nozzle support plate 74 and the nozzle plate 72 for further securing and sealing the nozzle plate 72 to the nozzle support plate 74. The nozzle support plate 74 acts to increase the rigidity of the nozzle plate 72. A more rigid nozzle plate 72 allows for a more efficient conversion of the oscillatory effects of the piston 32 to fully periodically compress the fluid thereby forming pressure perturbations in the fluid within the manifold 40. While not shown in the drawings, the nozzle plate 72 may alternatively be attached directly to the main body portion 22 of the housing 20 via bolts 76. The drive means 50 preferably comprises the driving circuit 52 shown in Figure 8, and disclosed in US-A-3 868 698 (entitled "Stimulation Control Apparatus for an Ink Jet Recorder," issued February 25, 1975), the disclosure of which is incorporated herein by reference. Briefly, the driving circuit includes a differential amplifier 53, a power amplifier 54, a load resistor 55, and negative and positive feedback loops to the negative and positive input terminals 53a and 53b of the differential amplifier 53. The negative feedback loop extends from output terminal 53c of differential amplifier 53 back around to the negative input terminal 53a. The negative feedback loop therefore includes load resistor 55 and branches out into two branches at the output side thereof. One of these two negative branches includes only a resistor 56, whereas the other branch comprises a peak detector 57a, a differential amplifier 57b and a voltage dependent resistance 57c. The positive feedback loop extends from output terminal 53c back through an R-C network to the positive input terminal 53b. The positive feedback loop comprises resistors 58a and 58b and capacitors 59a and 59b connected in a wien bridge arrangement. The circuit 52 serves to drive the transducer 30 at a natural frequency thereof and to track that frequency as it changes normally due to heating or other causes during operation of the droplet generator 10. The transducer 30 normally has more than one natural frequency. Consequently, it is usually possible to drive the piezoelectric crystals 34 at more than one frequency. Additionally, several frequencies may be placed on the crystals 34 at the same time. Because the transducer 30 is driven at a natural frequency thereof, the amplitude of motion of the bottom surface 32d of the piston 32 is much greater than the amplitude of motion of the crystals 34 combined. Consequently, the oscillating bottom surface 32d of the piston 32 imparts sufficient acoustic energy to the fluid in the manifold 40 to create large amplitude velocity perturbations on the fluid which result in atomization of the fluid into a stream of droplets. Referring now to Figures 9, 10, 11A and 11B, a nozzle plate 80, constructed in accordance with a second embodiment of the present invention, is shown. The nozzle plate 80 is formed having a nozzle 82 through which fluid in the manifold 40 exits from the droplet generator 10. The plate 80 may be formed according to the process disclosed in US-A-4 528 070, the disclosure of which is incorporated herein by reference. The plate 80 comprises first and second layers of nickel 84 and 86, respectively, and an intermediate layer of beryllium-copper 88 interposed therebetween, see Figures 11A and 11B. As shown in Figures 10, 11A and 11B, the first layer 84 is formed with an entrance slot 84a through which the fluid first passes as it exits from the manifold 40. The second layer 86 is formed with an exit slot 86a through which the fluid exits from the generator 10 after passing through the entrance slot 84a. As shown in Figure 10, the entrance slot 84a is rotated from the exit slot 86a at an angle , which is approximately 4°. The entrance slot 84a has a length of approximately 5,588 mm (0,220 in.) and a width of approximately 0,1524 mm (0,006 in.), while the exit slot 86a has a length of approximately 5,334 mm (0,210 in.) and a width of approximately 0,0381 mm (0,0015 in.). The thickness of the plate 80 including the first, second and intermediate layers 84, 86 and 88, respectively, is approximately 0,254 mm (0,010 in.). A stream of droplets formed by a droplet generator 10 according to the present invention employing the nozzle plate 80 is shown in the photograph of figure 12. The droplet generator 10 included a nozzle support plate 74 having a thickness of approximately 6,35 mm (0,25 in.). The fluid supplied to the generator 10 comprised a formulation of water to glycerol in a weight ratio of 4:6. The fluid was supplied to the generator 10 at a pressure of approximately 21,17 N/cm 2 (33.6 psi). The drop generator transducer 30 was driven at a frequency of approximately 9.78 kHz, which was approximately equal to a natural frequency of the transducer 30. As shown in the photograph, the fluid, as it exits from the generator 10, first breaks into a plurality of horizontal filaments and then into a plurality of droplets. Referring now to Figures 13 and 14, a portion of a nozzle plate 90, constructed in accordance with a third embodiment of the present invention, is shown. The nozzle plate 90 includes a nozzle 92 through which fluid in the manifold 40 exits from the droplet generator 10. The nozzle plate 90 may be formed according to the process disclosed in US-A 4,528,070. The nozzle plate 90 includes first and second layers of nickel 94 and 96, respectively, and an intermediate layer of beryllium-copper 98 interposed therebetween, see Figure 14. As shown in Figures 13 and 14, the first layer 94 is formed with an entrance slot 94a through which the fluid first passes as it exits from the manifold 40. The second layer 96 is formed with an exit slot 97 through which the fluid exits from the generator 10 after passing through the entrance slot 94a. The entrance slot 94a is rotated from the exit slot 97 at an angle α (shown exaggerated in Figure 13), which is approximately 3.4°. The entrance slot 94a has a length of approximately 5,334 mm (0,210 in.) and a width of approximately 0,1524 mm (0,006 in.). The exit slot 97 is formed with a plurality of perturbations 97a, each having a length L 1 equal to approximately 1,016 mm (0,040 in.). The exit slot 97 has a length of approximately 6,096 mm (0,240 in.) and has a first width W 1 equal to 0,0762 mm (0,003 in.) and a second width W 2 equal to 0,0381 mm (0,0015 in.). The thickness of the plate 90 including the first, second and intermediate layers 94, 96 and 98, respectively, is approximately 0,254 mm (0,010 in.). A stream of droplets formed by a droplet generator 10 according to the present invention employing the nozzle plate 90 is shown in the photograph of Figure 15. The droplet generator 10 included a nozzle support plate 74 having a thickness of approximately 6,35 mm (0.25 in.). The fluid supplied to the generator 10 comprised a formulation of water to glycerol in a weight ratio of 4:6. The fluid was supplied to the generator 10 at a pressure of approximately 21,17 N/cm 2 (33.6 psi). The drop generator transducer 30 was driven at a frequency of approximately 5.55 kHz, which was approximately equal to a natural frequency of the transducer 30. As shown in the photograph, as the fluid sheet exits from the generator 10, it breaks into horizontal filaments and then into a plurality of droplets. Referring now to Figures 16 and 17, a portion of a nozzle plate 100, constructed in accordance with a fourth embodiment of the present invention, is shown. The nozzle plate 100 includes a nozzle 102 through which fluid in the manifold 40 exits from the droplet generator 10. The plate 100 may be formed according to the process disclosed in US-A-4 528 070. The plate 100 includes first and second layers of nickel 104 and 106, respectively, and an intermediate layer of beryllium-copper 108 interposed therebetween, see Figure 17. As shown in Figures 16 and 17, the first layer 104 is formed with an entrance slot 104a through which the fluid first passes as it exits from the manifold 40. The second layer 106 is formed with an exit slot 107 through which the fluid exits from. The entrance slot 104a has a length of approximately 5,334 mm (0.210 in.) and a width of approximately 0,0381 mm (0.0015 in.). The exit slot 107 includes a plurality of perturbations 107a, each having a length L a equal to 0,254 mm (0.010 in.). The exit slot 107 has a length of approximately 5,334 mm (0.210 in.) and a first width W a approximately equal to 0,0508 mm (0.002 in.) and a second width W b approximately equal to 0,0381 mm (0.0015 in.). The entrance slot 104a is offset from the exit slot 107 by a distance D which is approximately equal to 0,0254 mm (0.001 in.). The thickness of the plate 100 including the first, second and intermediate layers 104, 106 and 108, respectively, is approximately 0,254 mm (0.010 in.). A stream of droplets formed by a droplet generator 10 according to the present invention employing the nozzle plate 100 is shown in the photograph of Figure 18. The droplet generator 10 included a nozzle support plate 74 having a thickness of approximately 6,35 mm (0.25 in.). The fluid supplied to the generator 10 comprised a formulation of water to glycerol in a weight ratio of 4:6. The fluid was supplied to the generator 10 at a pressure of approximately 21,17 N/cm 2 (33.6 psi). The drop generator transducer 30 was driven at a frequency of approximately 9.64 kHz, which is approximately equal to a natural frequency of the transducer 30. As shown in the photograph, the fluid breaks into a plurality of droplets as it exits from the nozzle 102 at an angle from vertical. By the present invention a method and apparatus are provided for imparting energy into a stream of liquid in the form of velocity perturbations for purposes of atomizing the liquid into a stream of droplets. Because energy is imparted into the stream of liquid, the liquid atomizes into a stream of droplets having a surface area and surface energy greater than that of the initial stream. It is believed that the droplet generator 10 of the present application may be employed in applications such as agricultural spraying, spray drying and fuel injection. For example, it is contemplated that the transducer 30 may be driven with a high voltage so as to create large amplitude oscillations of the piston 32. It is additionally contemplated that several piezoelectric crystal pairs can be employed, and each pair may be driven at a different frequency.

Claims: A droplet generator (10) comprising: a housing (20) having a first end (22a), a second end (24), and an inner cavity (26), said second end having at least one dispensing orifice (70); an acoustic transducer (30) having a first portion located within said cavity and spaced a given distance from said second end (24) of said housing, said first portion of said acoustic transducer and said second end of said housing defining a manifold (40) therebetween for receiving a fluid; a mount (33) for said transducer fixedly connected to said first end of said housing; a piston (32) substantially sealed within said cavity to substantially isolate said manifold and defining said first portion of said transducer; fluid supply means (62) connected to one of said housing and said acoustic transducer for supplying fluid under pressure into said manifold, said fluid passing from said manifold via said orifice (70) as a stream of fluid (60); said transducer including piezoelectric means (34) and being connected to said piston for causing said piston to oscillate relative to said second end (24) of said housing and impart acoustic energy to said fluid in said manifold, thereby creating velocity perturbations on said stream of fluid which are sufficient to atomize said fluid, characterized in that said transducer including said piezoelectric means (34) are positioned between said housing (20) and said piston (32) and that connector means (38) for rigidly securing said mount, said housing, said piston and said piezoelectric means to one another is provided, whereby said fluid is fully periodically compressed in said manifold by said piston against the fixed second end of said housing forming pressure pertubations to enhance the atomization of said fluid. A droplet generator as set forth in claim 1, characterized in that said piezoelectric means comprises at least two piezoelectric crystals (34). A droplet generator as set forth in claim 1, characterized in that said mount includes a centrally located stepped bore (33b); each of said piezoelectric crystals includes a centrally located bore (34a) extending therethrough; said piston includes a centrally located threaded bore (32a) which extends at least partially therethrough; and that said connector means (38) comprises a bolt which extends through said bores in said mount and said piezoelectric crystals and threadedly engages with said threaded bore in said piston for connecting said mount, said piezoelectric crystals, and said piston to one another. A droplet generator as set forth in Claim 1, characterized in that said bolt includes a centrally located passage (38c) extending therethrough; said piston includes at least one additional bore (32b) extending from an outer surface thereof to communicate with said centrally located passage extending through said bolt; and that said fluid supply means communicates with said passage in said bolt for supplying said fluid through said passage and said at least one additional bore in said piston into said manifold. A droplet generator as set forth in Claim 1, characterized in that said piezoelectric means (34) drives said transducer at a natural frequency thereof causing large amplitude oscillations of said piston, thereby resulting in said piston (32) imparting acoustic energy and periodically compressing said fluid in said manifold which results in large amplitude velocity and pressure perturbations on and in said stream of fluid. A droplet generator as set forth in Claim 1, characterized in that said housing (20) comprises: a hollow main portion having first and second ends, said first end of said main portion defining said first end of said housing; and a nozzle plate (72, 74) fixedly connected to said second end of said hollow main portion, said plate defining said fixed second end of said housing and having said orifice formed therein. A droplet generator as set forth in Claim 1, characterized in that said housing (20) comprises: a hollow main portion having first and second ends, said first and second ends of said main portion defining said first and second ends of said housing, respectively; an intermediate nozzle plate support (72) rigidly connected to said second end of said hollow main portion; and, a nozzle plate (74) securely connected to said nozzle plate support, said nozzle plate having said orifice formed therein, and said nozzle plate and said intermediate plate defining said fixed second end of said housing. A method for generating droplets comprising: providing a housing (20) having a first end (22a), a second end (24), and an inner cavity, said second end having at least one dispensing orifice (70); providing an acoustical transducer (30); a mount (33) for said transducer fixedly connected to said first end of said housing; locating a first portion of said transducer within said cavity and defining a piston (32) spaced a given distance from the fixed second end (24) of said housing, said piston and said fixed second end of said housing defining a manifold (40) therebetween for receiving a fluid; supply fluid under pressure into said manifold; sealing (39) said piston within said cavity to substantially isolate said manifold; passing said fluid from said manifold via said orifice (70) as a stream of fluid (60); and driving said acoustical transducer (30) including piezoelectric means (34) and causing said piston (32) to impart acoustical energy to said fluid in said manifold, and so as to be periodically compressed forming pressure pertubations against said fixed second end (24) thereby creating velocity and pressure pertubations on and in said stream of fluid which are sufficient to atomize said fluid, characterized by rigidly fixing said acoustical transducer (30) to said housing (20) including to said first end, by positioning said transducer including said piezoelectric means (34) between said housing (20) and said piston (32) and by providing for connector means (38) for rigidly securing said mount, said housing, said piston and said piezoelectric means to one another. A method for generating droplets as set forth in Claim 8, characterized in that the step of driving said acoustical transducer (30) is performed by activating a piezoelectric means (34). A method for generating droplets as set forth in Claim 8, characterized in that said step of supplying fluid into said manifold includes passing said fluid through said transducer (30) and said piston (32), and then into said manifold. A method for generating droplets as set forth in Claim 8, characterized in that said step of driving said transducer (30) is performed at a natural frequency thereof causing large amplitude oscillations of said piston (32) of said transducer, thereby resulting in said first portion imparting acoustic energy to said fluid in said manifold (40) which results in large amplitude velocity perturbations on said stream of fluid. A droplet generator comprising: a housing (20) having a first end (22a), a second end (24), and an inner cavity, said second end having at least one dispensing orifice (70); a piston (32) substantially sealed within said cavity; an acoustical transducer (30) connected to one of said housing and said piston; said piston (32) being spaced a given distance from said second end (24) of said housing defining a manifold (40) therebetween for receiving a fluid; sealing means (39) positioned between said piston and said housing within said cavity to substantially seal and isolate said manifold from said first end (22a) of said housing; a mount (33) fixedly connected to said first end of said housing; and fluid supply means (62) connected to one of said housing and said piston for supplying fluid under pressure into said manifold, said fluid passing from said manifold via said orifice (70) as a stream of fluid (60); characterized in that said transducer (30) is positioned between said housing and said piston for causing said piston to oscillate relative to said second end (24) of said housing and impart acoustical energy to said fluid in said manifold, thereby creating velocity pertubations on said stream of fluid which are sufficient to atomize said fluid; and that connector means (38) for rigidly securing said mount, said housing, said piston and said transducer to one another is provided, whereby said fluid is fully periodically compressed in said manifold (40) by said piston against the fixed second end (24) of said housing forming pressure pertubations to enhance the atomization of said fluid.

Inventors: DRESSLER JOHN LAWRENCE, DRESSLER, JOHN LAWRENCE
Applicants: DRESSLER JOHN L, DRESSLER, JOHN LAWRENCE
Application year: 1993
Main classification: B05B17
IPC codes: F02M51, F02M69, B05B17