EP2747892A1

EP2747892A1 - Spraying method and spray head comprising a laval nozzle and an annular induction electrode

Info

Publication number: EP2747892A1
Application number: EP11778721.8A
Authority: EP
Inventors: Boleslaw SOBKOWIAK; Ryszard KACPRZYK; Pawel Zylka; Tadeusz Pawlowski; Zygmunt Lada
Original assignee: Przemyslowy Instytut Maszyn Rolniczych
Current assignee: Przemyslowy Instytut Maszyn Rolniczych
Priority date: 2011-08-25
Filing date: 2011-09-30
Publication date: 2014-07-02
Also published as: WO2013028084A1; PL396084A1; PL224862B1

Abstract

Method for carrying out agrotechnical spraying with chemical substances, characterized in that pneumatic atomization is performed using a convergent - divergent nozzle (3) to which gas is supplied under pressure within the range from 1 to 5 x 10⁵ Pa, wherein in the divergent part of the nozzle (3) in the widest point it reaches speed a few times faster than the speed of sound, so that gas accelerated to ultrasonic speed disintegrates technological liquid flowing out from a capillary tube into drops of size from a few to a dozen micrometers, which are charged in an electrical field with a direct current voltage from a few hundred to 3 kilovolts, an annular electrode (7) is being supplied with voltage u_e no more that 70 percent of voltage u_p, at which electrical discharge begins to occur in the space between the annual electrode (7) and the capillary tube (4) for technological liquid.

Description

SPRAYING METHOD AND SPRAY HEAD COMPRISING A LAVAL NOZZLE AND AN ANNULAR

INDUCTION ELECTRODE

The object of invention is a method and a head for carrying out an agrotechnical spraying with chemical substances, especially with agrochemicals, that are used in the field of plant protection during cultivation.

The most important factor concerning plants protection during cultivation are sprayers equipped with pressure fan atomizers, operation of which is frequently supported, by different means, by air jet. Air jet support is applied in ejector atomizers equipped with a hole, through which flowing pressurized liquid sucks in the air. There are also known injector atomizers of design similar to ejector one, but the air is supplied from the compressor under different pressure. As a result, size of the generated drops is variable; it is increased together with the increase of wind speed to limit drifting the technological liquid beyond the secured area. Application of ejector and injector atomizers is used to enhance the index of coverage of plants with the technological liquid. Drops charged with air bubbles are large and break while hitting the plant, thus increasing the coverage index. There is also known a device for spraying supported by air jet that includes field beams equipped with air sleeve and fan providing parting and penetration of thick cultivations and improvement of plant coverage degree, and possibility to adapt the fine-drop atomizers during windy weather without the risk of liquid drifting.

From the American patent application US4004733, there is known a constructional solution for heads for providing aerosols, whose particles have non-zero electric charge, destined for electrostatic atomization of well and poor conducting liquids including agrotechnical liquids. The head is equipped with a chamber with spraying nozzle that use synergistic effect of internal pneumatic atomization of liquid particles supplied under pressure through a pipe channel, wherein the electric charge is generated as a result of electrical inductions using annular high current electrode. Electrical charge is introduced onto drops at the moment of their generation from continuous stream of liquid, the atomized liquid being kept at the earth potential. Induction electrode is supplied with direct voltage of selected positive or negative polarization and value from a few hundred V to 5 kV, generated in electronic direct current converter supplied for example form 12 V installation, all components of the high current system being built in directly into the nozzle. Other construction of spraying nozzle according to this patent description consists of connected together: cylindrical body and housing. In the body made of electrically conducting materials, for example metal, there is an axial channel guiding the atomized liquid, supplied under pressure from the back part of the body from the liquid tank. The body also comprise a coaxial, tapered towards the front of the body channel guiding a gas, for example the air, supplied under pressure from the back part of the body from the gas source, the channel can consist of many separate channels converging at the outlet from the body from the side of its connection with the housing. Dielectric housing mechanically connected with the body also comprise an internal channel, guided axially with respect to the liquid channel. From the body side, this channel is of constant diameter, while at the front outlet orifice, its diameter is reduced. The body houses outlets of channels guiding the liquid and gas corresponding to inlets of the channel in the housing where the liquid and gas are guided together. Jets of gas and liquid act together in the area of the housing channel of constant diameter, called the area of generating aerosol drops. In this area, part of kinetic energy of gas jet is consumed for rupturing the liquid jet into drops, i.e. atomization, and the remaining part of kinetic energy of gas jet causes convection of the generated drops outside the nozzle and generation of a screen on the channel for near-surface gas jet that does not contain drops of liquid. This jet separates jet of aerosol from the induction electrode and counteracts moistening of both the electrode and dielectric surfaces of outlet channel and the housing orifice. Annular induction electrode made of electrically conducting material, for example brass, is built into the housing and directly encloses the area of drops generation so that its back surface is located from the front side of the channels guiding the gas, and liquid and its front surface is located from the side of the outlet orifice of the housing at accurately set distance. Toroidally arranged lines of electric field forces, generated by induction electrode, concentrate in the area of drops generation, and because the gap between the electrode and centre of the drops generation area is very small, gradient of electrical field in this area is very high even for relatively low voltage polarizing the electrode. This leads to effective polarization of liquid drops even at relatively low voltages polarizing the induction electrode. The induction electrode is connected to high voltage source by means of high voltage conductor built into the head housing. Such nozzle provides generation of solid particles in airborne or not airborne liquefied drops of aerosols of typical size of particles at least 50 micrometers and larger from liquids, solutions and suspensions. Maximum value of charge transferred to aerosol particles in this solution is about 15% of limit value, resulting from Rayleigh's limitation (according to A. G. Bailey, „Electrostatic spraying of liquids", 1st ed., Taunton Research Studies Press, London, 1988) with aerosol particles diameter of 50 μητι and 26 % and 40 % for particle diameters of 75 m and 100 μιη respectively.

Also from the American patent application No. US005765761A there is known a device with electroaerosol nozzle counteracting the settlement of charged aerosol drops on the nozzle body by introduction of internal electrostatic screen built into the nozzle and having specified electrical potential with the systems protecting the nozzles and the high voltage supply systems against generation and effects of short circuit currents as well as the methods of screening electric field generated locally inside the heads by induction electrode against the influence of external electrical fields.

Despite many attempts, electrostatic spraying with technological liquid within the area of plants protection has not yet been introduced. Current trials consisted in placing electric charge on liquid drops generated by atomizers emitting drops of diameters more than a few dozens of microns to a few hundred microns, so of too large weight, where the gravitational forces and inertial forces dominate over the forces of electrostatic attraction. Barrier of wide application of electrostatic technologies - except the processes of electrostatic painting known in the art - is also represented by difficulties related to spraying liquids in high capacity agricultural devices. Thus, there are no technical solutions that enable generating electroaerosol jet with high electric charge and at high speed of particles that are able to penetrate compact and high crops and which are relatively resistant to drifting. Despite many-year-long development of techniques and technologies of plant protection using agrochemical, the following problems could have not been solved in satisfactory way:

- uniform spraying of high and compact crops such as corn and energetic plants. Technologies of spraying with additional air jet do not suffice in such cases.

- uniform spraying of all part of a plant, especially top and bottom surfaces of leaves. The object of the invention is to remove or to limit the current inconveniences by developing a new technical solution.

The method consists in that the pneumatic atomization is performed using convergent - divergent nozzle, to which gas, preferably air, is supplied, under pressure within the range from 1 to 4 bar, where within the convergent part of the nozzle it gains speed and reaches at the narrowest point the critical speed equal to the speed of sound and in the divergent part in the widest point it reaches speed a few times faster than the speed of sound, so that gas accelerated to ultrasonic speed disintegrates the technological liquid flowing from the capillary tube into drops of size from a few to a dozen micrometers, of which the particles charge in the electrical field with direct current of voltage from a few hundred to 3 kilovolts, the annular electrode being supplied with voltage no more than 70 percent of voltage at which electrical discharge begins to occur in the space between the annual electrode and capillary tube with technological liquid.

The matter of the head according to invention consists in that it contains gas channel, gas nozzle, capillary tube, channel supplying the technological fluid, outlet chamber with annular electrode connected via a conductor with high voltage feeder, outlet chamber housing with port hole that is characterized in that the gas channel represents a bent hose with one end equipped with seat for supplying pressurized gaseous agent and the other end connected to the convergent - divergent nozzle. The convergent - divergent nozzle is divided to four segment arranged along one axis, the first segment being in a shape of convergent truncated cone with element of a cone of acute angle within the range from 55 degrees to 65 degrees, the second element of the nozzle being in a shape of short cylindrical cylinder at the spot, where the convergent - divergent nozzle diameter is the smallest, the third segment of the nozzle being in a shape of divergent truncated cone with element of a cone of acute angle within the range from 35 degrees to 25 degrees, the fourth segment being in a shape of cylindrical cylinder at the spot, where the convergent - divergent nozzle diameter is the biggest. Moreover, the convergent - divergent nozzle is introduced into the outlet chamber and the channel supplying the technological liquid is in a shape of bent hose with one end equipped with seat for supplying the technological liquid under pressure of 1 to 5 bar and the other end is connected to capillary tube positioned concentrically coaxially inside the convergent - divergent nozzle, the end of the capillary tube being introduced into the outlet chamber interior.

Preferably, the convergent - divergent nozzle is made of dielectric material.

Preferably, the capillary tube is made of conducting material and is connected with earthed pole of high voltage feeder.

Preferably, the annular electrode is connected with the not earthed pole of high voltage feeder.

Preferably, the outlet chamber housing is made of dielectric material.

Maximum value of charge transferred to aerosol particles generated using the method according to the invention is about 5 % of limit value, resulting from Rayleigh's limitation for particles of diameter 10 pm (according to A. G. Bailey, „Electrostatic spraying of liquids", 1st ed., Taunton Research Studies Press, London, 1988).

Because of that, performing the spraying using the method according to invention enables:

- introducing aerosol jet of technological liquid in to the area of compact crops to whole depth because of high kinetic energy of particles;

- increasing uniformity of stalks and both sides of leaves coverage due to large turbulences in the jet, that force the leaves to move and change and equalize the exposure to aerosol jet;

- increasing, with respect to the spraying with aerosol without electrification of drops, the amount of substance deposited on the leaves due to electrostatic forces;

- applying smaller doses of active substances due to better uniformity of coverage;

- performing the spraying with significantly reduced amount of working fluid, that in effect reduces the consumption of plant protection substances by 20-30%;

- working liquid and air are supplied under adjusted and controlled pressure to the heads and are converted in these heads into an aerosol jet, which moreover is charged electrostatically, of physical parameters distinguishing it from jets currently known and applied in the technique of plants protection.

Differences are as follows: - aerosol jet is of many time higher, ultrasonic, initial speed of stream, that is obtained by means of constructional features of the head. This results in significantly higher kinetic energy of the stream that enables penetration of compacted and high plants along the whole depth of crops, up to even 4 m high,

- spectrum of technological liquid drops in the aerosol is characterized by about 10-time smaller diameter, thus about 1000-time lower weight that in currently applied solutions. Because of that, more uniform coverage of plants sprayed with working fluid is obtained due to: significantly increased number of drops per unit of volume of technological fluid and electrostatic attraction of drops to all parts of sprayed plants, also to bottom surfaces of leaves,

- high kinetic energy of the aerosol jet causes high turbulences of air in the sprayed crops, many time higher than in known technologies of spraying, which fact together with electrostatic attraction and increased number of drops, additionally improves the uniformity of coverage with technological fluid of all part of sprayed plants,

- a few time reduction of water volume used as a carrier for plant protection preparation as well as the option to perform operations with small or even very small superficial dose of preparations.

Moreover, the solution according to the invention allows reducing losses amounting 1000 PLN / ha related to insufficient protection of crops against pests, such as European corn borer preying in a lower parts of high plants, which within a region of intensive cultivation causes loss of yield reaching 30%. The invention is presented in the embodiment on the drawing, where fig. 1 represents the head in diagrammatic, cross sectional partial view, fig. 2 - graph with the characteristics of current I flowing between the annular electrode and voltage U applied to the annular electrode, i.e. I = f (U), fig. 3 - graph with characteristics of charge relation Q/m of particle weight m and voltage applied to the annular electrode, i.e. (Q/m) = f (U).

To explain how to use the invention, the nature of interaction between the particle with charge of technological liquid and the earthed object is given. Particle of weight m and charge Q moves along a trajectory determined by inertia force vectors F_m=m a, and electric force F_e=Q E, where: a - acceleration, E - value of local intensity of electric field. Influence of electric field onto the particle trajectory determines the forces relationship F_e/ F_m = (Q/m)(E/a), thus the value of parameter (Q/m), characteristic for the particle, determines the option to influence with electrical filed E on its motion. The higher value of parameter (Q/m), the higher influence on the electrical forces trajectory F_e. In order for the electrical forces to act, particle with charge Q must be in the electrical field of intensity E. In case of charged particles, present near the conducting and earthed objects, the basic source of field is so called "mirrored charge". If a particle with charge (+)Q is present at a distance (+)x from the conducting surface of earthed object, it is subjected to a force like from charge (-)Q present at a distance (-)x from the object surface. Charge (+)Q "sees" behind the conducting object surface "mirrored charge" of value (-)Q. Occurrence of charge (-)Q leads to appearance of force attracting the particle with charge (+)Q to the surface of earthed object - Coulomb's law. Each charged particle is attracted by a conducting and earthed object. This phenomenon is used in the processes of electrostatic coating of surfaces such as spraying, painting. Force from the mirrored charge depends on the second power of Q particle charge. For the electrical forces action to appear that attract the technological fluid particle, aerosol drop must provided with Q charge. To do that, particles are subjected to electrification.

Electrification of particles consists in introducing surplus charge Q on them. The method of induction that use the phenomenon of electric induction is used for the electrification of particles from solid and liquefied conducting materials: In case of nozzles with pneumatic spraying, it is preferred to apply induction method. Said method allows to limit the space where strong electric field is present. This property allows in turn to:

- apply voltage sources of significantly lower values of voltages comparing to other methods, for example discharging. Leads to easier and more reliable operation of the whole high voltage supply system, i.e. induction electrode, cables, connectors and feeder,

- reduce the possibility of electric leak,

- apply high voltage feeders of small power - important mostly from the point of view of operators safety.

The principle of aerosol particles electrification using the electric induction method consists in that the cone of jet of conducting liquid is subjected to strong electrical field E, generated in the area limited by two electrodes, between which high direct voltage is applied. One electrode, located at the earth potential is represented by a capillary tube together with the jet cone of electrically conducting fluid, the other is annular electrode connected to high voltage feeder output.

Electrical field E at the surface of the cone induces charge in it of superficial density proportional to field E. Air jet flow around the nozzle guiding the sprayed liquid disintegrates it into drops. Electrical charge covering major part of aerosol drop generated on the surface of the cone is of similar density as on the liquid cone. After breaking apart of the drop from the cone surface, charge of the drop remains constant and the jet of generated drops carries the charge of pole opposite to the pole on the induction electrode. The arrangement with inductive electrification shows the option to increase the degree of insulation of annular electrode using concentric jet of compresses air that preclude the contact with the jet of flow or formation of conducting bridges.

Maximum value of charge carried by drop depends on the drop size i.e. surface subjected to action of electrical field E and intensity of field E in the place of drops generating and breaking apart. The need to obtain high value of parameter (Q/m) requires introduction of relatively large charge Q on to the particle, this fact in turn necessitates the application of field E of possibly high intensity. Maximum value of field E is limited by the electrical strength of air and on the head of given geometry can be specified by voltage U_p, at which electrical discharges shall appear in the zone: annular electrode - capillary tube. Spark and corona discharge can be observed. Discharges are accompanied by sudden increase of induction electrode supply current that is fed by high voltage feeder. Characteristics given in the fig. 2 allows to determine voltage U_p above which electric discharges appear what in turn leads to limitation of maximum value of parameter (Q/m) given in the fig. 3.

Voltage U_e supplied to the annular electrode under operational conditions U_e is specified as: U_e = 0.70 x U_p .

Value of voltage U_p is determined experimentally based on examinations of dependencies of supply current / from voltage U for the annular electrode using the method given in the fig. 2.

The described method of electrification has been used in the head according to the invention.

The head comprises the metal body 1 that include such elements as gas channel 2, convergent - divergent nozzle 3, capillary tube 4, channel 5 supplying the technological liquid, outlet chamber 6 with annular electrode 7 connected by means of conductor 8 with high voltage feeder, housing 9 of the outlet chamber 6 with port hole. Gas channel 2 is made of bent hose with one end is equipped with seat 10 to supply the gaseous agent and the other end is connected to convergent - divergent nozzle 3, the convergent - divergent nozzle 3 consisting of four segments located along one axis, the first segment 1 1 of the nozzle 3 being in a shape of convergent truncated cone with element of a cone of acute angle within the range from 55 degrees to 65 degrees, the second element 12 of the nozzle 3 being in a shape of short cylindrical cylinder at the spot where the nozzle diameter is the smallest, the third segment 13 of the nozzle 3 being in a shape of divergent truncated cone with element of a cone of acute angle within the range from 35 degrees to 25 degrees, the fourth segment 14 of the nozzle 3 being in a shape of cylindrical cylinder at the spot where the convergent - divergent nozzle 3 diameter is the biggest, at the same time the end of the convergent - divergent nozzle 3 is introduced into the outlet chamber 6 and the channel 5 supplying the technological liquid is in a shape of bent hose with one end equipped with seat 15 and the other connected to capillary tube 4 positioned concentrically coaxially inside the convergent - divergent nozzle 3, the end of the capillary tube 4 being introduced into the outlet chamber 6.

Sprayed liquid is supplied via capillary tube 4 in to the zone of decompressed gas in the outlet chamber 6 supplied through the convergent - divergent nozzle 3 made of dielectric material. Drops of aerosol generated at the end of capillary tube 4 are being electrified in strong electrical field generated between the capillary tube 4 made of conducting material and the annular electrode 7 made of stainless steel supplied from direct high current source of low power by means of the conductor 8 connected to it via bolt 16. Body 1 from side of the outlet chamber 6 is covered from outside by means of the housing 9 made of dielectric material. The housing 9 also protects the annular electrode against direct contact with operating personnel and drops of back jet of charged aerosol particles (returning from the head).

In the head, channel 5 supplying the technological liquid and channel 2 supplying for example air, are of varying cross sections, with necking and bends of hoses that provide turbulent flow and vortexes in the supplied agents. Individual feeders are used to supply induction electrodes of the heads, each head is equipped with own feeder. Such solution allows:

- increasing reliability of the whole system operation, because damage of high voltage system (flooding - immobilization) of one head does not influence the operation of the others;

- increasing operating personnel safety due to lowering the nominal power of high voltage feeder;

- increasing safety and reliability by shortening the high voltage cabling to minimum; high voltage feeders are located in the closest vicinity of the spraying heads located on the sprayer construction surface.

Claims

1. The method for carrying out agrotechnical spraying with chemical substances, especially with agrochemicals consisting in atomization of technological conducting liquids using spraying nozzle using the effect of pneumatic atomization of liquid particles, in which electrical charge is transferred onto the drops at the moment of their generation as a result of electrical induction by means of high voltage annular electrode supplied with direct voltage and the liquid is maintained at the earth potential, characterized in that the pneumatic atomization is performed using convergent - divergent nozzle (3), to which gas, preferably air is supplied, under pressure within the range from 1 to 5 bar, wherein in the convergent part of the nozzle (3) it gains speed and reaches at the narrowest point the critical speed equal to the speed of sound and then in the divergent part of the nozzle (3) in the widest point it reaches speed a few times faster than the speed of sound, so that gas accelerated to ultrasonic speed disintegrates the technological liquid flowing out from the capillary tube into drops of size from a few to a dozen micrometers, of which the particles charge in the electrical field with direct current of voltage from a few hundred to 3 kilovolts, the annular electrode (7) being supplied with voltage U_e no more that 70 percent of voltage U_Pi at which electrical discharge begins to occur in the space between the annual electrode (7) and capillary tube (4) with technological liquid.

2. Head for carrying out agrotechnical spraying with chemical substances, especially with agrochemicals, comprising a gas channel, gas nozzle, capillary tube, channel supplying the technological liquid, outlet chamber with annular electrode connected with the high voltage feeder, outlet chamber housing with port hole, characterized in that the gas channel (2) is made of bent hose with one end equipped with seat (10) to supply the gaseous agent and the other end connected to convergent - divergent nozzle (3), the convergent - divergent nozzle (3) comprising four segments located along one axis, the first segment ( 1 ) of the nozzle (3) being in a shape of convergent truncated cone with element of a cone of acute angle within the range from 55 degrees to 65 degrees, the second element (12) of the nozzle (3) being in a shape of short cylindrical cylinder at the spot where the nozzle diameter is the smallest, the third segment (13) of the nozzle (3) being in a shape of divergent truncated cone with element of a cone of acute angle within the range from 35 degrees to 25 degrees, the fourth segment (14) of the nozzle (3) being in a shape of cylindrical cylinder at the spot where the convergent - divergent nozzle (3) diameter is the biggest, while the end of the convergent - divergent nozzle (3) is introduced into the outlet chamber (6), and the channel (5) supplying the technological liquid being in a shape of bent hose, with one end equipped with a seat (15) and the other connected to capillary tube (4) positioned concentrically coaxially inside the convergent - divergent nozzle (3), the end of the capillary tube (4) being introduced into the outlet chamber (6).

3. Head according to claim 1 , characterized in that the convergent - divergent nozzle (3) is made of dielectric material.

4. Head according to claim 1 , characterized in that the capillary tube (4) is made of conducting material and is connected with earthed pole of high voltage feeder.

5. Head according to claim 1 , characterized in that the annular electrode (7) is connected with not earthed pole of high voltage feeder.

7. Head according to claim 1 , characterized in that the housing (9) of the outlet chamber (6) is made of dielectric material.