USP_20090224066_Ultrasonic atomizing nozzle methods for the food industry_VIP (1063672), страница 2
Текст из файла (страница 2)
Hence, as the operating frequency, f, increases, thenumber median drop siZe (dMQS) decreases.[0023] In order to form capillary Waves that are suitable forultrasonic atomiZation, it is desirable to suppress the formation of Waves that are not perpendicular to the solid surfacefrom Which the liquid ?lm absorbs vibrational energy. Inorder to suppress the formation of such non-perpendicularWaves, the largest diameter of any active noZZle element islimited.
More speci?cally, the diameter is limited to a lengththat is beloW one-fourth of the Wavelength, 7», of an acousticWave in the material from Which the atomiZing surface isformed.[0024] The Wavelength, 7», of an acoustic Wave in such amaterial is calculated as folloWs:LIC/fWhere c?he characteristic velocity at Which sound Wavespropagate through a ceramic material. Thus, for a givenoperational frequency, materials having higher characteristicvelocities, c, at Which sound Waves propagate therethroughcorrespond to longer Wavelengths. Hence, such materialsalloW for a larger noZZle diameter at a given frequency.[0025] When the diameter of the noZZle becomes so smallthat the noZZle becomes impractical to make or use, the practical operating frequency of the noZZle is reached.
As such, inmetallic noZZles according to the prior art (i.e., in noZZlesWhere the vibrating surface is metallic), the practical upperlimit of the operating frequency, f, is approximately 120 kHZ.HoWever, in noZZles according to embodiments of the presentinvention Where ceramics are used, the upper limit of the[0026]Keeping in mind the above-mentioned characteristics of ceramic materials, one of skill in the art Will appreciatethat, at a given operating frequency, f, ceramic noZZles can beoperated at a greater ?oW rate than their metallic counterparts.In other Words, the diameter of the noZZle can remain larger ina ceramic noZZle than in a metallic noZZle, as can stems, thearea of the atomiZing surface, and/or liquid feed ori?ces thatmay be included to lead liquid to the noZZle.[0027] As mentioned above, FIG. 1 is a longitudinal crosssectional vieW of an ultrasonic atomiZing noZZle arrangement10 according to a ?rst embodiment of the present invention.The noZZle 10 illustrated in FIG.
1 includes a rear horn 12 thatfunctions as an interface section. As such, the rear horn 12 iscon?gured to alloW the introduction of a liquid into the noZZle10.[0028] The rear horn 12 illustrated in FIG. 1 is directlyconnected to a liquid inlet 14. HoWever, the rear horn 12 maybe directly or indirectly connected to any component that WillalloW for How of a liquid into the noZZle 10. The liquid inlet14 may be af?xed to the rear horn 12 in any manner that Wouldbecome apparent to one of skill in the art upon practicing thepresent invention (e.g., a pressure seal or an adhesive).Although not illustrated in FIG.
1, the liquid inlet 14 is typically connected, either directly or indirectly, to a source ofliquid such as, for example, a tank containing Water based oroil based or solvent based food coating ingredients, in asolution or in a suspension mode.[0029]According to certain embodiments of the presentinvention, the rear horn 12 is either made entirely from aceramic material or portions of the rear horn 12 are made froma ceramic material. HoWever, according to other embodiments of the present invention, the rear horn 12 is fabricatedeither partially or entirely from a metal. For example, the rearhorn 12 may be made from silicon carbide (SiC) or aluminumoxide (A1203).[0030] The noZZle 10 illustrated in FIG. 1 also includes afront horn 16 that is con?gured to function as an atomiZingsection.
The front horn 16, according to certain embodimentsof the present invention, can include one or more portionsmade from a ceramic material (e.g., SiC or A1203) or can bemade entirely from one or more ceramic materials. The fronthorn 16 is con?gured to form drops of the liquid introducedinto the noZZle 10 through the rear horn 12. These drops can,according to certain embodiments of the present invention,have number median drop siZes (dN,O_5) of less than approximately 20 microns (e. g., approximately 17 microns),although larger drop siZes are also Within the scope of certainembodiments of the present invention. Also, according otherembodiments of the present invention, the front horn 16 iscon?gured to form drops of liquid having number mediandrop siZes of betWeen approximately 7 microns and approximately 10 microns.[0031]One of the advantages of the noZZle 10 illustrated inFIG.
1 is that it increases the rate at Which a liquid introducedinto the noZZle 10 may be atomiZed. As discussed above,because the ceramic material used in embodiments of thepresent invention have higher characteristic velocities atWhich sound Waves propagate therethrough, a larger frontnoZZle diameter is alloWable for a given frequency. Therefore,according to certain embodiments of the present invention,the front horn 16 is con?gured to alloW the liquid introducedSep. 10, 2009US 2009/0224066 A1into the nozzle 1 0 to ?oW through the nozzle 1 0 at a rate aboveshroud 11 and the rear shroud 13 provide a housing for theapproximately 600 ml per minute (10 gallons per hour).nozzle 10 and the O-rings 15 provide a plurality of sealsAccording to other embodiments of the present invention, thefront horn 16 is con?gured to alloW the liquid to ?oW throughWithin this housing.the nozzle 10 and the front horn 16 at a rate of approximatelysonic atomizing nozzle arrangement 10 illustrated in FIG.
1taken along line 3-3. As illustrated in FIG. 2, the rear horn 121200 ml per minute (20 gallons per hour).[0032]In the nozzle 10 illustrated in FIG. 1, the rear horn 12and the front horn 16 have substantially equal lengths. HoWever, according to other embodiments of the present invention, the rear horn 12 and the front horn 16 have differentlengths. According to certain embodiments of the presentinvention, a ceramic nozzle operates at 250 kHz and the rearhorn 12 and front horn 16 both have lengths equal to, forexample, 3M4, since horns of such length are substantiallyeasier to manufacture than horns having lengths of M4.According to certain other embodiments of the present invention, a ceramic nozzle operates at 120 kHz and both horns 12,16 have lengths of M4, Which are relatively practical to manufacture.[0033] The nozzle 10 illustrated in FIG.
1 also includes atransducer portion 18 that includes a pair of transducers thatare positioned in an intermediate section of the nozzle 10 thatis located betWeen the rear horn 12 and the front horn 16. Thetransducers in the transducer portion 18 are piezoelectrictransducers and are con?gured to promote ultrasonic-frequency mechanical motion in the front horn 16.
In otherWords, the transducers in the transducer portion 18 providethe mechanical energy to cause the atomizing surface 20located on the front horn 16 illustrated in FIG. 1 to vibrate atan ultrasonic frequency With su?icient amplitude to result inatomization. Although tWo transducers are discussed aboveas being included in the transducer portion 18 illustrated inFIG. 1, a single transducer and/or any other component orsystem that can be used to cause ultrasonic-frequencymechanical motion in the front horn 16 is also Within thescope of the present invention.[0034] The rear horn 12 and the front horn 16 each includea ?ange 22.
A cover, in the form of a ring 24, is positionedadjacent to each of the ?anges 22 illustrated in FIG. 1. Aplurality of fasteners, in the form of bolts 26, are also illustrated in FIG. 1 and connect the tWo rings 24.[0035] The above-discussed bolts 26 and rings 24 are components of a clamping mechanism that is positioned adjacentto the exterior surfaces of the rear horn 12 and front horn 16,respectively. This clamp is con?gured to keep the front horn16 and the rear horn 12 adjacent to the transducer portion 18.In addition, this clamp is also con?gured to apply predetermined compressive forces to the transducer/hom assembly,thereby assuring proper mechanical coupling amongst thevarious elements of the assembly.[0036] By using the clamp arrangement illustrated in FIG.1, the rear horn 12 and the front horn 16, one or both of Whichmay be made from a ceramic material, do not need to includethreaded holes that directly accommodate the bolts to be keptadjacent to each other.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
