Patent Application
20180361420
The present invention relates generally to an ultrasonic nozzle and more particularly it relates to an ultrasonic nozzle that utilizes an electrostatic apparatus and sonic levitation mechanism.
Ultrasonic atomization is the use of electronic ultra-high frequency oscillation principle. Besides, the ultrasonic generator working with a specific frequency of oscillation current produced a high-frequency power signal and converted the signal towards the ultrasonic mechanical vibration through the transducer. Moreover, the ultrasonic vibration is propagated through a medium that needs to be atomized, and it makes the formation of surface tension wave which is formed at the gas-liquid interface. Due to ultrasonic cavitation, the surface tension waves cause liquid molecule force and make the liquid become droplets from the liquid surface. It is the primary process of liquid atomization by using ultrasonic waves. The ultrasonic atomization can form many droplets size up to the micron level. The ultrasonic atomization has many advantages in the field of agricultural engineering because it can form small droplet size and has a wide range of applications in the field of agricultural engineering. Considering, the high-frequency ultrasonic atomization (working frequency above 1 MHz) can change the physical and chemical properties of the atomized liquid to a large extent. Therefore, it is not suitable for the field of atomization cultivation (Aeroponics system) and plant protection. However, the low-frequency ultrasonic atomization has less effect on the physical and chemical properties of the atomized liquid. But the main problem associated with low-frequency ultrasonic atomization is that it thin's too large droplets, resulting in reduced adhesion on the leaves and roots of the crops.
A large number of research studies have shown that the charge can reduce the liquid surface tension and atomization resistance. Moreover, when the droplets carry the same charge, under the action of the electric field, it will break the large liquid molecules into smaller droplets with more uniform diameter distribution. The electrostatic atomization has been widely used in many applications include pesticide spraying, industrial spraying, material preparation, fuel combustion, industrial dust and desulfurization, particle aggregation and separation, and many other fields. The advantage of electrostatic spray is that the droplet adhesion characteristics are excellent. However, because of the technical constraints, the electrostatic voltage of the critical voltage is between several kilo-volts to tens of thousands volt, which is called high-voltage electrostatic atomization. High-voltage electrostatic atomization has the following shortcomings: the voltage of high-voltage electrostatic atomization is between several kilo-volts to tens of kilo-volts, which is a great security risk for the operator; high-voltage static electricity that beyond a certain extent will hurt the crops, and low-voltage electrostatic will promote the growth of crops; the structure of high-voltage electrostatic spray is complex, demanding high manufacturing materials, especially insulation properties; the most important thing is that the high-voltage electrostatic needs high-cost equipment.
The present invention aims to overcome the shortcomings of the prior art and to provide a low-frequency electrostatic ultrasonic atomizer which produces ultrafine charged droplets under low-frequency ultrasound and low static voltage to improve the adhesion of droplets to the crop.
In order to achieve the above objects, the present invention adopts the following technical scheme:
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. The diameter of the fastening screw is smaller than the center hole of the piezoelectric ceramic to prevent the short circuit between the fastening screw and the piezoelectric ceramic, affecting the normal operation of the nozzle. The transducer back cover, the piezoelectric ceramics, and the transducer front cover constitutes the vibrator part of the low-frequency electrostatic ultrasonic atomizing nozzle. The length of the ultrasonic horn is arranged at the half-length of the ultrasonic wave, and the ultrasonic horn is provided with an inlet channel in the axial center. The rear part of the ultrasonic horn is provided with liquid in the radial direction which is connected to the liquid inlet channel. An intake channel is arranged at an offset position from the axial center. The rear portion of the ultrasonic horn is provided with compressed air in the radial direction connected to the intake channel. The top of the ultrasonic horn is machined into a concave spherical surface, and a levitating ball is arranged on the concave spherical surface. Furthermore, the radius of curvature of the levitating ball is the same as the radius of curvature of the concave spherical surface of the ultrasonic horn. This design can form a focused ultrasound suspension system which can generate more acoustic levitation force. Apart from this, the levitating ball is made of the metallic conductor. The outer surface of the levitating ball is arranged in the V-shaped annular groove, and the tip of the charging needle is provided in the V-shaped annular groove. The rear end of the charging needle is restrained by a spring so as to be in regular contact with the suspended ball; the charging needle is covered with an insulating sleeve, and it is mounted on the bracket by means of a set, and the bracket is mounted on the flanges of the ultrasonic horn by means of set screws. The flange is designed at the node of the ultrasonic horn.
When the nozzle does not work, because of gravity and charge injection pressure, the levitating ball firmly attached to the top of the nozzle. However, when the nozzle is at work, under the drive of the piezoelectric ceramics, the front and back cover of the vibrator produce ultrasonic vibration, resonate with the horn, and generate the focused radiation sound field at the semicircular end. The sound field makes the levitating ball overcome the gravity and the force from the charging needle, and let the ball suspend upward to form a gap between the levitating ball and the top face of the horn. At the same time, the levitating ball goes with high-speed rotation by the eccentric aerodynamic effect. In order to ensure that the ball can produce acoustic suspension phenomenon, the front of the nozzle is designed as a concave spherical surface, resulting in a focused ultrasound suspension system to form greater acoustic leeway.
There is an intake channel in the eccentric axial position of the nozzle, and the diameter of the inlet channel is about 1-2 mm. In the nozzle work, the flow rate of 50-100 m/s of compressed air is passed into the intake channel. Acted by compressed air, the levitating ball goes with high-speed rotation, so that the droplets cannot stick on the suspended ball. Meanwhile, high-speed rotation of the levitating ball colliding with droplets makes droplets atomized again.
The depth of the annular groove on the outer surface of the levitating ball is 1-2 mm. 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. The spring can resist the insulation sleeve and restrict the charging needle to reciprocate in the socket.
The ultrasonic horn and transducer back cover is made of insulated ceramic materials. This ensures that the electrostatic field generated by the levitating ball does not affect the normal operation of the piezoelectric ceramics.
The levitating ball and the charging needle are made of copper. The surface of the charging needle is provided with an insulation sleeve to prevent the spring and sleeve from coming into direct contact with the charge. The diameter of insulation sleeve is higher than the spring diameter 0.2-0.4 mm and less than the sleeve diameter 0.05-0.1 mm. It can ensure that the charging needle and the levitating ball have regular contact. The upper surface of the socket is fixed to the bracket by welding. At the same time, a small hole is formed at the center of the contact of the holder and the sleeve so that the live wire can go into the socket and connect directly the charging needle to ensure the charging needle charged.
The bracket is a rectangular frame. The bracket and the horn are connected with bolts. The nuts and the ultrasonic horn are fitted with gaskets. The brackets and horns are bolted and have a simple structure to facilitate disassembly during installation or repairing time. At the same time, there are gaskets between nuts and the horn of the nozzle to prevent the nuts from loosening during operation.
The main body of the ultrasonic vibration consists of the horn, piezoelectric ceramics, the front cover of the transducer, back cover of the transducer and the socket screw. The frequency of the main body is 25-30 kHz. The charging needle applies a static voltage of less than 500-2000 V to the suspended ball.
The nozzle drive circuit consists of choke inductor LRFC, switch S, equivalent parallel capacitor C, series resonant inductance L1, series resonant capacitor C1 and impedance matching capacitor CP.
The nozzle drive circuit is simple and efficient, which is a single-ended circuit and mainly composed of six parts: choke inductor LRFL, switch S, equivalent parallel capacitor C (sum of switch input capacitor, distributed capacitor and external capacitor), series resonant inductor L1, series resonant capacitor C1, and impedance matching capacitor CP. The operating principle is as follows: the square wave signal of working frequency f (nozzle series resonant frequency) control the turning on and turning off of the switch S. At this time, switch S pole output pulse voltage. Through the frequency selection network C-C1-L1-CP, the nozzle at both ends of the switching frequency f harmonic signal is suppressed, and the base frequency signal is selected. In this way, the two ends of the nozzle can be obtained the square wave signal with the frequency of sinusoidal AC signal. In addition, the frequency selective network can be used to adjust the load impedance. Simply put, when 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. Frequency selection network can only let the base frequency current flow, thus encouraging the nozzle to work.
A simple analysis for ultrasonic atomization drive circuit in the three stages of the work process:
Firstly, the choke inductance LRFL needs 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 changes when the switch is turned on or off. Therefore, the input current can be considered as a constant flow.
Secondly, the fundamental frequency resonant circuit quality factor needs to be high enough. The flow passing through the ultrasonic nozzle can be regarded as the sine wave.
Finally, the conduction resistance of the switch S is ignored. And switch S can instantaneously complete the process of turning on or off, that is the time for switch tube S to rise or fall to zero.
Compared with the similar type of atomizer, the invention has the following technical effects:
1. By low-frequency ultrasonic atomization, electrostatic atomization, and centrifugal, the liquid is atomized several times, so this nozzle can produce finer electrified droplets, increasing possibility of adsorbing by plant. Levitating ball in the sound field achieves suspension under the action from the radiation. And in the eccentric aerodynamic action, the levitating ball goes with high-speed rotation, so that the charged droplets in the centrifugal force under the high-speed can fly out and droplets do not stick to the ball. The liquid is vibrated by the ultrasonic horn for the first atomization process. Under the action of the electrostatic field, the droplets are subjected to the second atomization. Finally, the droplets collide with the levitating ball at high speed for the third atomization. The liquid in the first atomization, the particle size is less than 60 microns, and the electrostatic secondary atomization required voltage significantly reduced, easy to achieve low-voltage electrostatic atomization. The droplets were high-speed spray out by the centrifugal force and aerodynamic compound effect after the third atomization.
2. The drive circuit structure is simple with high efficiency. The parasitic parameters of the circuit are effectively used. 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. The circuit produces little heat in the process of working, which is able to drive the nozzle for a long time. At the same time, it has a high degree of reliability and can reduce the use of maintenance costs in the process and improve production efficiency.
The present disclosure will be described with reference to the accompanying drawings, wherein like numbers reference like elements.
In those figures, 1—set; 2—charging nozzle; 3—ultrasonic horn; 4—inlet channel; 5—back cover; 6—piezoelectric ceramic; 7—intake channel; 8—suspended ball; 9—insulation sleeve; 10—spring; 11—bracket; 12—tightening screw; 13—bolt; 14—gasket; 15—nut 16—nutrient solution; 17—compressed air; 18—front cover;
LRFL—choke inductor; S—switch; C—equivalent parallel capacitor (sum of switch tube input capacitor, distributed capacitor and external capacitor); L1—series resonant inductor; C1—series resonant capacitor; Cp—impedance matching capacitor; Vgs—the drive signal of the switch S; Vs—the voltage waveform across the switch S; is—the current flowing through the switch S; ic—current flowing through the parallel capacitor C; i—current flowing through the nozzle.
As shown in
The operation of the nozzle is shown in
The atomization process of the droplet is shown in
(1) The liquid becomes a liquid film at the top surface of the ultrasonic nozzle. As shown in
(2) The liquid is atomized by ultrasonic action on the hemispherical atomized end face. As shown in
(3) The liquid is subjected to secondary atomization by the electric field generated by the charged levitating ball 8. As shown in
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
The lower end of the nozzle connection structure is shown in
As shown in
As shown in
The driver circuit of the nozzle is shown in
A simple summary for ultrasonic atomization drive circuit in the various stages of the work process:
Firstly, the choke inductance LRFL needs 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 changes when the switch is turned on or off. Therefore, the input current can be considered as a constant flow.
Secondly, the quality factor of the fundamental frequency resonance circuit needs to be high enough that the flow through the ultrasonic nozzle can be regarded as a sine wave.
Finally, the conduction resistance of the switch S is ignored. And switch S is instantaneous opened or closed, that is the time that switch S rise or fall to zero.
As shown in
(t0≤t≤t1) Stage I
Before t0 moment, the switch S is turned on, and the DC voltage VDC charge the choke inductance LRFC and let it storage energy. The parallel capacitor C beside the switch S is short-circuited. Switch tube S, resonant inductance L1, resonant capacitor C1, and nozzle form a series resonant circuit. At time t0, switch S is disconnected. As the inductor current cannot be mutated, the current flowing through the switch S is instantaneously turned to the parallel capacitor C next to the switch S. The voltage across the parallel capacitor C rises gradually from zero. At this point, the parallel capacitance C, resonant inductance L1, resonant capacitor C1 and the nozzle together constitute a series resonant circuit. The energy stored in the choke inductance LRFC previously is transferred to the resonant circuit. As the iC current decreases, the Vs reaches the highest value until it is reduced to zero; when iC changes from zero to negative, the parallel capacitor C begins to discharge; when the parallel capacitor C discharge complete, then the current flowing through the RF choke i1 equals to the current i in the resonant circuit, and the switch S turns on immediately and enters the next stage. At this time, the switch S with the zero current, zero voltage switch, and the switching conduction loss is almost zero.
(t1≤t≤t2) Stage II
At time t2, the switch S is turned on and shunt capacitor C is shorted. According to the Kirchhoff current law, the current of the choke inductance LRFC is divided into two conditions, one flowing goes through the switch S, and the other goes through the nozzle. As the resonant current i gradually decrease, the current is that flowing through the switch S is increasing. The resonant circuit consists of series resonant capacitor C1, series resonant inductance L1, and nozzle. The resonant capacitor C1 and the resonant inductor L1 stored in the energy exchange, one reaches the maximum, the other just down to zero. When the resonant capacitor C1 reaches the resonant peak, the resonant current i drops to zero. Thereafter, the resonant capacitor C1 is discharged to the resonant inductor L1, and the resonant current i is reversed. And so on, the circuit work into the next high-frequency cycle of the working stage I.
This low-frequency electrostatic atomization nozzle drive circuit has the following advantages: 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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201610198692.4 | Apr 2016 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2016/080434 | 4/28/2016 | WO | 00 |
