Low frequency electrostatic ultrasonic atomising nozzle

Abstract

The invention discloses a low-frequency electrostatic ultrasonic atomization nozzle that relates to an electrostatic atomizer in the field of agricultural engineering. The low-frequency electrostatic ultrasonic atomization nozzle comprises a transducer back cover, piezoelectric ceramics, a transducer front cover, an ultrasonic horn and a fastening screw. Furthermore, the fastening screw is set through the transducer back cover, the piezoelectric ceramics and the center round hole of the transducer front cover in sequence; a liquid inlet channel is designed in the axial center of the ultrasonic horn; an air intake channel is designed in a position that deviates from the axial center; the top of the ultrasonic horn is machined as a concave spherical surface; and a suspended ball is arranged on the concave spherical surface. Moreover, compressed air in the axial eccentric position is used for rotating the suspended ball at high speeds; a charging needle is electrified to generate an electric field for the suspended ball that the droplets generated by low-frequency ultrasonic atomization and can electrostatically atomize again, and it can make the droplets take on an electrostatic charge; finally, the electrified droplets are sprayed out from the nozzle. The low-frequency electrostatic ultrasonic atomization nozzle breaks through the bottleneck of a low-frequency ultrasonic atomization nozzle that struggles to generate ultrafine droplets and enables the droplets to take on static electricity to increase adhesion so that the droplets can attach to crops more efficiently.

Claims

1. A low-frequency electrostatic ultrasonic atomization nozzle, comprising: a back cover; an ultrasonic vibrator comprising a transducer back cover, piezoelectric ceramics, and a transducer front cover; an ultrasonic horn, the length of which is determined as the half-length of an ultrasonic wave, the ultrasonic horn comprising a liquid inlet channel configured in an axial center thereof and an intake channel configured at a position that deviates from the axial center of the ultrasonic horn, wherein the intake channel is configured to inject compressed air and has a concave spherical surface configured for levitating balls; a fastening screw, wherein the fastening screw is attached through center holes of the transducer back cover, the piezoelectric ceramics, and the transducer front cover in sequence; a levitating ball with a V-shaped annular groove on its outer surface that is made of a metallic conductor; a charging needle restrained by a spring and the V-shaped annular groove on the levitating ball that uninterruptedly charges the levitating ball; an insulating sleeve configured to insulate the charging needle; a bracket; and a socket connecting the bracket and the insulating sleeve; and a spring in the insulating sleeve and configured to ensure the charging needle uninterruptedly contacts the levitating ball, wherein the bracket is connected with flanges of the ultrasonic horn by set screws, and wherein the bracket fixes the socket.

2. The low-frequency electrostatic ultrasonic atomization nozzle of claim 1, wherein the depth of the annular groove on the outer surface of the levitating ball is 1-2 mm.

3. The low-frequency electrostatic ultrasonic atomization nozzle of claim 1, wherein the levitating ball and the charging needle are made of copper.

4. The low-frequency electrostatic ultrasonic atomization nozzle of claim 1, wherein the diameter of the insulating sleeve is 0.2-0.4 mm greater than the diameter of the spring and 0.05-0.1 mm less than the diameter of the socket, and wherein the spring is against the insulating sleeve to restrict reciprocating movement of the charging needle in the socket.

5. The low-frequency electrostatic ultrasonic atomization nozzle of claim 1, wherein two same-sized holes are respectively drilled in the bracket and the socket to enable a charged wire to pass through the socket and the bracket to directly charge the charging needle.

6. The low-frequency electrostatic ultrasonic atomization nozzle of claim 1, wherein the bracket is a rectangular frame, wherein the set screws comprise bolts and nuts, and wherein the ultrasonic horn is fitted with a gasket.

7. The low-frequency electrostatic ultrasonic atomization nozzle of claim 1, wherein the ultrasonic horn and the transducer back cover are made of insulating ceramic materials.

8. The low-frequency electrostatic ultrasonic atomization nozzle of claim 1, comprising a main part, wherein the main part comprises the transducer back cover, the piezoelectric ceramics, the transducer front cover, and the ultrasonic horn, and wherein a vibration frequency of the low-frequency electrostatic ultrasonic atomization nozzle is in a range of 20-100 kHz.

9. The low-frequency electrostatic ultrasonic atomization nozzle of claim 1, wherein the charging needle applies a static voltage of less than 500 V to the levitating ball.

10. The low-frequency electrostatic ultrasonic atomization nozzle of claim 1, wherein the diameter of the levitating ball is in a range of from 13 mm to 17 mm.

11. The low-frequency electrostatic ultrasonic atomization nozzle of claim 1, wherein the charging needle applies a static voltage of less than 2000 V to the levitating ball.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present disclosure will be described with reference to the accompanying drawings, wherein like numbers reference like elements.

(2) FIG. 1 is the schematic diagram of the static ultrasonic atomization nozzle structure.

(3) FIG. 2 is a side view of the static ultrasonic atomization nozzle.

(4) FIG. 3 is a schematic exploded 3-D diagram of the electrostatic ultrasonic atomization nozzle.

(5) FIG. 4 is a diagram of the working process of the nozzle.

(6) FIG. 5 is the analysis of the force of the suspended ball.

(7) FIG. 6 is a schematic diagram of the atomization process of the droplets.

(8) FIG. 7 is a schematic diagram of the bottom structure of the electrostatic atomization nozzle.

(9) FIG. 8 is a schematic diagram of the bottom of the electrostatic atomization nozzle.

(10) FIG. 9 is a diagram of the nozzle bracket connection.

(11) FIG. 10 is a schematic diagram of the stent and the charging needle structure.

(12) FIG. 11 is a diagram of the nozzle drive circuit.

(13) FIG. 12 is a simplified model of the nozzle drive circuit.

(14) FIG. 13 is a waveform figure of the working principle of the nozzle drive circuit at different stages.

(15) In these figures, 1set; 2charging nozzle; 3ultrasonic horn; 4inlet channel; 5back cover; 6piezoelectric ceramic; 7intake channel; 8suspended ball; 9insulation sleeve; 10spring; 11bracket; 12tightening screw; 13bolt; 14gasket; 15nut 16nutrient solution; 17compressed air; 18front cover;

(16) L.sub.RFLchoke inductor; Sswitch; Cequivalent parallel capacitor (the sum of the switch tube input capacitor, the distributed capacitor and the external capacitor); L.sub.1series resonant inductor; C.sub.1series resonant capacitor; C.sub.pimpedance matching capacitor; Vgsdrive signal of the switch S; Vsvoltage waveform across the switch S; iscurrent flowing through the switch S; iscurrent flowing through the parallel capacitor C; icurrent flowing through the nozzle.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

(17) As shown in FIG. 1 and FIG. 2, the nozzle includes a horn 3, a front cover 18, a back cover 5, and piezoelectric ceramics 6 that generate ultrasonic vibrations. Among them, the vibration part of the nozzle is composed of three parts: a front cover 18, piezoelectric ceramics 6 and a back cover 5. The length of the horn 3 is a half-wavelength. The inlet channel 4 is designed in the axial center of the nozzle. The gas intake channel 7 is designed to deviate from the axial center at a certain position. The top of the nozzle is machined as a concave hemisphere and has a levitating ball 8 on it. The material of the levitating ball 8 is a metal conductor with a diameter of 15 mm and the outer surface of the levitating ball 8 has a V-shaped annular groove with a depth of approximately 1-2 mm. The top of the charging needle 2 is mounted in a V-shaped annular groove. The top of the charging needle 2 is provided with a spring 10 restraint, which ensures that the tip of the charging needle 2 can be in constant contact with the levitating ball 8. The surface of charging needle 2 has an insulation sleeve 9 mounted on the bracket 11 by a set 1. In addition, the bracket 11 is mounted at the node of the nozzle.

(18) The operation of the nozzle is shown in FIG. 4. In FIG. 4, the levitating ball 8 is close to the top end of the nozzle due to the gravity and pressing force from the charging needle 2. When the nozzle is working, under the piezoelectric ceramics 6 drive, the horn 3 and the piezoelectric ceramic 6 resonance, ultrasonic vibrations are produced along with a focused radiation field in the semi circular end. The levitating ball 8 overcomes gravity and the force from the charging needle 2, under the action of the sound radiation force, suspending it upwards. Thus, it forms a gap between the levitating ball 8 and the top face of the horn. The intake channel 7 is located in the eccentric axial position of the nozzle, and the diameter of the inlet channel 7 is approximately 1 mm. When the nozzle is operated, compressed air 17 is supplied with a flow rate of 50-100 m/s in the intake channel 7. The compressed air 17 drives the levitating ball 8 to rotate at high speeds so that the droplets do not stain the levitating ball 8. The high-speed rotation of the levitating ball 8 and many droplets collide so that the droplets are atomized again. The force analysis of the levitating ball 8 is shown in FIG. 5.

(19) The atomization process of the droplet is shown in FIG. 6. The atomization process is divided into four stages:

(20) (1) The liquid becomes a liquid film at the top surface of the ultrasonic nozzle, as shown in FIG. 6 (a).

(21) (2) The liquid is atomized by ultrasonic action on the hemispherical atomized end face, as shown in FIG. 6 (b). The cavitation effect of the ultrasonic wave on the liquid results in the generation of micro-shocks to produce atomization. The high-frequency vibrating air flow with the turbulent, pulsed liquid film will be drawn into filaments and further broken into droplets and an aerosol spray.

(22) (3) The liquid is subjected to secondary atomization by the electric field generated by the charged levitating ball 8 as shown in FIG. 6 (c). High-voltage static electricity reduces the surface tension and viscous resistance of the liquid, causing the liquid to be easily broken into smaller droplets and making the droplet size distribution even more uniform. When the droplets are charged, they are easily atomized for a second time in the high voltage electrostatic field, which further reduces the droplet size. At the same time, for the charged droplets in the charge between the repulsion, the degree of dispersion increased. The charged droplets can be attracted to leaves with the opposite polarity of the charge so that they can be easily captured by the target under the action of polarization and gravitational forces.

(23) 4) The liquid is ejected by the centrifugal force of the aerodynamic force and the high-speed rotation of the levitating ball 8, which is shown in FIG. 6 (d).

(24) The lower end of the nozzle connection structure is shown in FIG. 7 and FIG. 8. A set screw 12 was used through the transducer back cover 5 and the piezoelectric ceramics 6 and connected to the tip of the ultrasonic horn 3 while fixing the piezoelectric ceramic 6 and the front and back covers. The diameter of the socket screw 12 is smaller than the radius of the center hole of the piezoelectric ceramics 6, and it can prevent a short circuit caused by contact between the socket screw and the piezoelectric ceramics, which might affect the normal operation of the nozzle.

(25) As shown in FIG. 8 and FIG. 9, the bracket 11 and the horn 3 are connected by bolts 13. This structure is simple, and it is easy to install and disassemble during maintenance. At the same time, it can increase the preload to prevent loosening and does not cause a connection material composition phase change. The gasket 14 is sandwiched between the nuts 15 and the ultrasonic horn 3, which prevents the nut 15 from loosening during the operation of the nozzle, increase the bearing area and prevent the screw 12 bolts from being damage.

(26) As shown in FIG. 10, the surface of the charging needle 2 is designed with an insulation sleeve 9 to prevent the spring 10 and set 1 from being in contact with electricity. The diameter of the insulation sleeve 9 is greater than the diameter of the spring 10 and less than the inner diameter of the socket 1, and the spring 10 can resist the insulation sleeve 9 so that the charging needle 2 reciprocates in the socket 1. The upper surface of the socket 1 is fixed to the bracket 11 by welding. At the same time, in the center of the bracket 11 and the socket 1, a small hole is designed to let the live wire pass deep into the socket 1 and be directly connected to the charging needle 2. It can make the charge needle 2 charged, to achieve the goal of electrostatic atomization.

(27) The driver circuit of the nozzle is shown in FIG. 11. The structure of the circuit is simple; it is a single-ended circuit, mainly composed of six parts: choke inductor L.sub.RFL, switch S, equivalent parallel capacitor C (the sum of the switch input capacitor, the distributed capacitor, and an external capacitor), series resonant inductor L.sub.1, series resonant capacitor C.sub.1, and impedance matching capacitor C.sub.P. The working principle is as follows: the square wave signal of working frequency f (nozzle series resonant frequency) controls the turning on or off of the switch S. At this time, switch S outputs a pulse voltage. The nozzle at both ends of the switching frequency f harmonic signal is suppressed, through the frequency selection network C-C.sub.1-L.sub.1-C.sub.p, and the base frequency signal is selected. In this way, two ends of the nozzle can be obtained with the square wave signal with the frequency of a sinusoidal AC signal. On the other side, the frequency selective network can be used to adjust the load impedance. Simply put, the switch S is operated by the active square wave signal cycle, the DC energy from the power supply can be converted to AC energy. The frequency selection network can only let the base frequency current flow, thus encouraging the nozzle to work.

(28) A simple summary of the ultrasonic atomization drive circuit in the various stages of the work process is as follows:

(29) First, choke inductance L.sub.RFL ndds to be large enough to allow only the DC signal to pass through, while the AC signal has a large impedance, thereby suppressing the AC signal through. This causes the supply current not to drastically change when the switch is turned on or off. Therefore, the input current can be considered as a constant flow.

(30) Second, the fundamental frequency resonant circuit quality factor needs to be high enough. The flow passing through the ultrasonic nozzle can be regarded as a sine wave.

(31) Finally, the conduction resistance of switch S is ignored, and switch S can instantaneously complete the process of turning on or off, which is the time for switch tube S to rise or fall to zero.

(32) As shown in FIG. 12 and FIG. 13, the drive circuit is simplified for analysis where V.sub.gs is the driving signal of switch S, V, is the voltage waveform across switch S, i.sub.s the current flowing through switch S, i.sub.c is the current flowing through parallel capacitor C, and i is the current flowing through the nozzle.

(33) Stage I (t.sub.0tt.sub.1)

(34) Before moment t.sub.0, switch S is turned on, and DC voltage V.sub.DC charges the choke inductance L.sub.RFC and lets it store energy. Parallel capacitor C beside switch S is short-circuited. Switch tube S, resonant inductance L.sub.1, resonant capacitor C.sub.1, and the nozzle form a series resonant circuit. At time t.sub.0, switch S is disconnected. As the inductor current cannot be mutated, the current flowing through switch S is instantaneously turned to parallel capacitor C next to switch S. The voltage across parallel capacitor C rises gradually from zero. At this point, parallel capacitance C, resonant inductance L.sub.1, resonant capacitor C.sub.1 and the nozzle together constitute a series resonant circuit. The energy stored in choke inductance L.sub.RFC previously is transferred to the resonant circuit. As current i.sub.C decreases, Vs reaches the highest value until it is reduced to zero; when i.sub.C changes from zero to negative, parallel capacitor C begins to discharge; when the discharge of parallel capacitor C is complete, then the current flowing through the RF choke i.sub.1 equals to current i in the resonant circuit, and switch S turns on immediately and enters the next stage. At this time, switch S becomes a zero current, zero voltage switch, and the switching conduction loss is almost zero.

(35) Stage II (t.sub.1tt.sub.2)

(36) At time t.sub.2, switch S is turned on and shunt capacitor C is shorted. According to the Kirchhoff current law, the current of choke inductance L.sub.RFC is divided into two conditions, one flow goes through switch S, and the other goes through the nozzle. As resonant current i gradually decreases, current i.sub.S flowing through switch S is increasing. The resonant circuit consists of series resonant capacitor C.sub.1, series resonant inductance L.sub.1, and the nozzle. Resonant capacitor C.sub.1 and resonant inductor L.sub.1 store energy during the exchange; one reaches the maximum, the other just falls down to zero. When resonant capacitor C.sub.1 reaches the resonant peak, resonant current i drops to zero. Thereafter, resonant capacitor C.sub.1 is discharged to resonant inductor L.sub.1, and resonant current i is reversed. The circuit then beings the next high-frequency cycle of working stage I.

(37) This low-frequency electrostatic atomization nozzle drive circuit has the following advantages: 1. The parasitic parameters of the circuit can be effectively absorbed. The junction capacitance of the switch tube is absorbed by the parallel capacitor of the resonant circuit, which can effectively reduce the influence of parasitic parameters on the circuit performance. 2. The circuit working efficiency is high. From the above analysis, current i.sub.S flowing through switch S, and voltage Vs across tparallel capacitance C of the switch are not present at the same time. Thus, at any one time, the product of i.sub.S and V.sub.S is zero, and the loss of switch S is almost zero. The ideal efficiency is 100%, and the actual efficiency reaches up to 90% or more.

(38) The embodiment is a preferred embodiment of the present invention, but the invention is not limited to the above-described embodiments. It will be apparent to those skilled in the art that any obvious modifications, substitutions, or variations are intended to be within the scope of the present invention without departing from the spirit of the invention.