Patent Application
20150136867
The present invention relates to a nozzle assembly for agricultural use and, more particularly, to an induction charging nozzle assembly that preferably is based on an unmodified conventional hydraulic flat fan nozzle.
Uniform deposition and application of sufficient amounts of active material are very important when applying low-toxicity pesticides to crops (S. Gan-Mor et al., Improved uniformity of spray deposition in a dense plant canopy: methods and equipment, Phytoparasitica 24(1):57-67 (1996)). The importance of this high-quality coverage increases as regulations regarding pesticide residues become stricter and consumer demand for clean products becomes stronger. Currently, the use of hydraulic pressure to break the sprayed liquid into small droplets is the most commonly used technique for generating droplets in agricultural spraying; this technique uses hydraulic pressure on a liquid that flows thorough a metal or ceramic orifice to produce the spray. Introducing air streams to assist in transporting the droplets towards the target generally improves the deposition (Gan-Mor et al., 1996). The process can be further improved by introduction of short-range electrostatic forces when the droplets approach the target.
The use of electrostatic charging in this manner is very common in industrial processes such as liquid-spray painting, and the advantage of electrostatics is enhanced when high charge-to-mass ratios are achieved. When appropriate charging levels are applied in agricultural spraying, the coverage can be very uniform and large amounts of material can be deposited, especially on hard to reach areas such as the undersides of leaves on the lower parts of plants (S. E. Law, Agricultural electrostatic spray application: a review of significant research and development during the 20th century, Journal of Electrostatics 51: 25-42 (2001)). In contrast, if the charge level is poor no coverage improvement is achieved. Therefore it is important to be sure of obtaining considerable charge level and improvements of deposition when acquiring and using a commercially available electrostatic sprayer. Agricultural sprayers that use electrostatic charging in addition to air assisted spraying and achieve average of 150% improvement in spray deposit density, are offered commercially by ESS Inc., Watkinsville, Ga., USA. The ESS nozzles provide droplets smaller than 50 μm Volume Mean Diameter (VMD).
It is important to note that the producers of conventional hydraulic nozzles recommend the use of droplet sizes of more than 90 um VMD and to avoid the use of very small droplets, because of the possibility that massive drift might occur because of the long settling time of such droplets. For similar reasons, some jurisdictions prohibit droplets smaller than 90 um VMD. The use of electrostatic charging in pesticide spraying on agricultural targets is rare, for a variety of reasons.
It would be highly advantageous to have an induction charging nozzle assembly, for agricultural use, that is based on a conventional hydraulic nozzle, possibly with air assistance. Preferably, the induction charging nozzle assembly would provide charge-to-mass ratios of at least 0.8 mC/kg.
According to the present invention there is provided an induction charging nozzle assembly including: (a) an electrode including two branches; (b) a nozzle positioned relative to the electrode so as to spray an atomized spray of a liquid between the branches, the branches being substantially parallel at least along the portions thereof between which the spray passes; and (c) a power supply for applying an electric potential to the electrode relative to the liquid so that the liquid acquires an electrical charge when sprayed from the nozzle.
According to the present invention there is provided a method of spraying a liquid, including the steps of (a) forcing the liquid through an orifice of a nozzle, thereby creating an atomized spray; (b) directing the atomized spray between two substantially parallel branches of an electrode; and (c) electrically charging the atomized spray by applying an electric potential to the electrode relative to the liquid.
According to the present invention there is provided an induction charging nozzle assembly including: (a) an electrode; (b) a nozzle for spraying a liquid; (c) a power supply for applying an electric potential to the electrode relative to the liquid; (d) at least one electrically insulating supporting member for mounting the electrode relative to the nozzle so that the electric potential induces an electrostatic charge on an atomized spray of the liquid that is sprayed via the nozzle; and (e) a mechanism for keeping dry at least a portion of the electrode and at least a portion of each supporting member while the liquid is sprayed via the nozzle.
According to the present invention there is provided a method of spraying a liquid, including the steps of: (a) forcing the liquid through an orifice of a nozzle, thereby creating an atomized spray of the liquid; (b) applying an electric potential to an electrode relative to the liquid; (c) mounting the electrode relative to the nozzle, using at least one electrically insulating supporting member, so that the electric potential induces an electrostatic charge on the atomized spray; and (d) while the liquid is forced through the orifice, keeping dry at least a portion of the electrode and at least a portion of each supporting member.
A first basic induction charging nozzle assembly of the present invention includes an electrode with two branches (or two electrodes with one or more branches each), a nozzle and a power supply. The nozzle is positioned relative to the electrode(s) so as to spray an atomized spray of a liquid between the two branches, or between two of the branches. At least the portions of the two branches between which the spray passes are substantially parallel to each other. The power supply applies an electric potential to the electrode(s) relative to the liquid so that the liquid acquired an electrical charge when sprayed from the nozzle.
Preferably, the gap between the substantially parallel at least portions of the two branches between which the atomized spray passes is between about 20 mm and about 40 mm.
Preferably, the distance between the orifice of the nozzle and a surface defined by the parallel at least portions of the two branches between which the atomized spray passes is between about 10 mm and about 30 mm, and most preferably between about 16 mm and about 22 mm.
Preferably, the induction charging nozzle assembly also includes an air blower for directing a stream of air onto the electrode branches between which the atomized spray passes. The air blower is separate from the nozzle and most preferably the nozzle is outside the air blower. Also most preferably, the induction charging nozzle assembly also includes one or more electrically insulating supporting members for mounting the electrode(s) in the correct position relative to the nozzle. The air blower also directs the stream of air onto the supporting member(s).
Preferably, the nozzle is a hydraulic nozzle, i.e., a nozzle that uses the kinetic energy of the liquid that is forced therethrough to atomize the liquid, without air assistance. Most preferably, the nozzle is a flat fan hydraulic nozzle that is oriented relative to the electrode(s) so that the shape of the atomized spray that passes between the two electrode branches is a flat fan whose plane is substantially parallel to the two electrode branches.
Preferably, the induction charging nozzle assembly includes a substantially one-dimensional (linear or curved) array of a plurality of the nozzles. The array is substantially parallel to the electrode branches between which the nozzles' atomized sprays pass: each nozzle is positioned relative to the electrode(s) so as to spray its respective atomized liquid spray between the two electrode branches. Most preferably, the nozzles are spaced at least about 90 mm apart.
Preferably, the absolute value of the electric potential that is applied to the electrode(s) relative to the liquid is at least about 7 kV.
In a first basic method of the present invention for spraying a liquid, the liquid is forced through the orifice of a nozzle, thereby creating an atomized spray. The atomized spray is directed between two substantially parallel branches of one or more electrodes. The atomized spray is charged electrically by applying an electric potential to the electrode(s) relative to the liquid.
Preferably, the volume mean diameter of the atomized spray is between about 80 microns and about 140 microns.
Preferably, the electric potential is between about 8 kV and about 18 kV.
Preferably, the method also includes directing a stream of air onto the electrode branches to keep the electrode branches dry. Preferably, the speed of the air stream is between about 10 m/sec and about 90 m/sec. Most preferably, the speed of the air stream is between about 40 m/sec and about 80 m/sec. Also most preferably, the electrode(s) is/are mounted relative to the nozzle using one or more electrically insulating supporting members, and the air stream also is directed onto the supporting member(s) to keep dry at least a portion of each supporting member. Also most preferably, the air stream is directed onto the atomized spray in a manner that helps propel the atomized spray towards a target. In the present context, the target typically is an agricultural target and the liquid that is sprayed typically is an agricultural chemical such as a pesticide or a fungicide.
Preferably, the electrical charging of the atomized spray produces an electrically charged atomized spray that has a charge-to-mass ration of at least about 0.8 mC/kg.
A second basic induction charging nozzle assembly of the present invention includes an electrode, a nozzle for spraying a liquid, and a power supply for applying an electric potential to the electrode relative to the liquid. The electrode is mounted relative to the nozzle, using one or more electrically insulating supporting members, so that the electric potential induces an electrostatic charge on an atomized spray of the liquid that is sprayed via the nozzle. The assembly also includes a mechanism for keeping dry at least a portion of the electrode and at least a portion of each supporting member while the liquid is being sprayed via the nozzle. The preferred such mechanism is an air blower for directing a stream of air onto the electrode and the supporting member(s).
In a second basic method of the present invention for spraying a liquid, the liquid is forced through the orifice of a nozzle, thereby creating an atomized spray. An electric potential is applied to an electrode relative to the liquid. One or more electrically insulating supporting members are used to mount the electrode relative to the nozzle so that the electric potential induces an electrostatic charge on the atomized spray. While the liquid is being forced through the orifice to create the atomized spray, at least a portion of the electrode and at least a portion of each supporting member are kept dry, preferably by directing a stream of air onto the electrode and onto the supporting member(s).
Various embodiments are herein described, by way of example only, with reference to the accompanying drawings, wherein:
The principles and operation of an induction charging nozzle assembly according to the present invention may be better understood with reference to the drawings and the accompanying description.
Referring now to the drawings,
The voltage difference imposed by DC power supply 28 between electrode 20 and ground is denoted in
ΔE is just one of the parameters involved in the design of assembly 10.
1. Branches 22 need not be parallel along their entire lengths. Branches 22 need to be parallel only along the portion of the gap between them that is traversed by spray 26.
2. Branches 22 need not be branches of the same electrode 20. Each branch 22 can be an electrode 20 in its own right, as long as both branches 22 are charged to the same potential ΔE relative to ground. Of course, if each branch 22 is part or all of a different electrode 20, that electrode 20 must be attached to the rest of assembly 10 by its own set of one or more insulating supporting members 22 (not shown in
3. Branches 22 can be either straight or curved.
A laboratory testing system was devised to determine optimal values of the system design parameters ΔE, L, h and v. Preliminary tests showed that induction charging of sprays 26 generated with flat-fan nozzles 12 was superior to all other test setups. Two parallel charging electrode branches 22 were found to provide relatively high charging levels, and trials to reduce the setup size led to preference for 80-degree nozzles 12. Laboratory limitations such as maximal drift and liquid handling led to preference of low-flow-rate nozzles 12. Therefore, flat-fan nozzles model TP8001 (by Teejet Technologies Inc. of Wheaton, Ill. USA) and yellow Albuz AX18002 nozzle (by CoorsTek, Inc., Evreux, France) were selected. The preliminary tests also showed that the ambient air speed next to the nozzle edge had a, positive influence on the charge levels.
The dependent parameter that was monitored was the current, I, produced by the laboratory setup.
The charge-to mass ratio was easily determined by dividing the current by the liquid flow rate. The measured flow rates at a pressure of 4 bar were 0.55 and 0.7 l/min for the Teed TP8001 nozzle and the yellow Albuz AX18002, respectively. A variable-speed radial blower provided ambient air velocities ranging from 5 to 65 m/min at the blower outlet, which was rectangular, measuring 5×24 cm, and located 10.0 cm from the nozzle tip. A metal mesh screen made of 0.5 mm wires with 2×2 mm square openings was positioned 24 cm from the nozzle tip, and was used for collecting the electric charges from the droplets in the air jet. The screen was placed 3.0 cm above a plastic bowl that served to collect the spray fluid, which subsequently was drained. The bowl was insulated, and the current, I, from the screen and the bowl was monitored with a UT 58 meter (Uni-Trend Group Ltd., Hong Kong, China) which, after some modification and calibration provided an accuracy of ±1 μA. With every test setup five repetition of the reading were sampled.
Several parameters influence the current on the mesh, which was defined as the dependent variable. In the light of the difficulty of simultaneously conducting experiments, analyzing the results, and presenting the findings with respect to all the above independent parameters, preliminary tests were conducted to determine which parameters had a weak influence, and to set their optimal values as unvarying parameter. The first set of tests addressed the influence of the distance between the electrode branches and the nozzles (the parameter h). The electrode potential, ΔE was 20 kV and the air speed, v, was 60 m/s. Table 1 shows, for two spacings between the electrode branches (the dimension L), that the distance between the electrode branches and the nozzles had a weak influence on the current, I, which was delivered by the spray cloud. For electrode branch to nozzle distances between 16 and 20 mm maximal currents were 13 to 14 μA, for the two electrode branch spacings shown in Table 1. Therefore, a distance of 19 mm between the electrode branches and the nozzle was selected for the subsequent tests. This selection enabled the following simpler analysis.
The following parameters were found to exert substantial influence on the current delivered by the charged cloud: the electrodes spacing, L; the electrode potential, ΔE; and the air speed, v.
A field system was developed, based on the results obtained with the laboratory setup. Because several nozzles were needed in the field system, the influence of the proximity between the nozzles was evaluated. Generally, the current delivered by each nozzle was reduced when two or more nozzles were placed next to each other and the induction charging technology of the present invention was used. The current decreased as the distance between adjacent nozzles decreased, however, since the current reduction did not vary linearly with this distance, an optimal distance of 90 mm between the centers of adjacent nozzles was selected.
An electrostatic charging system was designed and constructed for a vineyard sprayer obtained from Degania Sprayers Inc. (Degania, Israel). The geometry of the charging electrodes was set in accordance with the optimal setup found in the laboratory, and the charging potential was set at 10.5 kV. The hydraulic pressure was set at 10 bar as an optimal value, in the light of the laboratory findings and the manufacturer's recommendations. The air velocity at the outlets was 68 m/s and the air blower outlet dimensions were 165×42 mm. Insulating the electrodes was of major importance: whereas in the laboratory the electrodes were hooked to an insulated gauge, the setup of the field unit was rather complicated. A technique for insulating the electrodes was incorporated using continuous drying process of blowing dry air jets onto the plastic electrode holders. This continuous drying of the plastic electrode holders is believed to be an important factor in obtaining the requisite high level of electrostatic charging.
Three sets of measurements were taken: (a) Current measurements on a 100×100 cm mesh screen located 1.2 m from the blower outlet. (b) Simulated tests of deposition on hard-to-reach areas were conducted by using a grounded metal cylinder measuring 5 cm in diameter and 14 cm in length as a target. Water-sensitive paper was attached to the front and to the back of the cylinder, to provide a simulated assessment of the influence of the charge, as described by Law (2001). The cylinder was connected to a 100 cm metal bar and moved across the stream at approximately 0.8 m/s, with the sprayer stationary. (c) Deposition on grape clusters and leaves by a vineyard sprayer was assessed by using a fluorescent tracer for coverage evaluation, according to Maclntyre-Allena et al., Confirmation by fluorescent tracer of coverage of onion leaves for control of onion thrips using selected nozzles, surfactants and spray volumes, Crop Protection 26:1625-1633 (2007), with only the top outlet of one side equipped with the electrostatic system and operated during the test.
Current measurements on a (1×1) in screen located 1.2 m from the air blower outlet showed a current of up to 12 μA for two yellow Albuz AX18002 flat fan nozzles. This current was almost doubled, and reached a level of 22 μA, when the screen was located 70 cm from the air blower outlet.
The results of a simulation test of deposition on hard-to-reach areas, which involved a target in the form of a grounded metal cylinder measuring (50×140) mm in diameter×length with water-sensitive paper attached to its front and back, are shown in
Distribution of spray deposit on grape clusters achieved by spraying with a vineyard sprayer was evaluated by using a fluorescent tracer, with only the top outlet of one side operative and equipped with the field electrostatic system. The deposit distributions on the rear of the cluster for spraying without and with charging (numbers of droplets per cm2) are shown in Tables 3 (uncharged spraying) and 4 (charged spraying), respectively. Table 5 shows the results for the underside of leaves, without and with charging.
Compared with uncharged spraying, the use of charged spraying provided more than five times as many droplets per unit area on the rear of grape clusters and more than twice as many droplets per unit area on the undersides of leaves. The statistical differences are significant for both the rear of grape clusters and the undersides of leaves. The uncharged deposition on the front of clusters was already in excess; therefore, significant improvement in this area as a result of using charged spraying was neither needed nor evident.
The air speed seems to be the most important independent parameter for design purposes: the blown air provides continuous drying of the electrode holders, optimal air speed facilitates reduction of the distance between the induction electrode and the nozzle outlet, and optimal air speed minimizes charge leakage from the spray cloud to the induction electrode. This charge leakage can be determined by measuring the potential drop on the charging electrode when the liquid flow is opened, since the resistors on the high-voltage line are of known value. Since the influence of charge leakage is already implicit in the above results it has not been analyzed separately. Straightforward measurements showed that increasing the flow rate by raising the pressure or by using nozzles with higher flow rates increased the charging level. Additional measurements showed that the spacing between two adjacent nozzles has strong influence, and that reduction of this spacing considerably reduce the charge level per nozzle. This means that a design with a smaller number of nozzles of higher flow rate provides higher charging levels than a larger number of nozzles of lower flow rate.
The charge-to-mass ratios provided by the present invention are approximately three times higher than the highest charge-to-mass ratio obtained conventionally, and the benefit was clearly demonstrated in the simulation test by placing water-sensitive papers on the rear of a cylinder, as shown in
While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made. Therefore, the claimed invention as recited in the claims that follow is not limited to the embodiments described herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2013/053650 | 5/7/2013 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61688088 | May 2012 | US |
