Electrostatic-induction spray-charging nozzle system

• US 5,765,761 A
• Filed: 07/26/1995
• Issued: 06/16/1998
• Est. Priority Date: 07/26/1995
• Status: Expired due to Term

• Current Assignee: The University of Georgia Research Foundation, Inc.
• Original Assignee: The University of Georgia Research Foundation, Inc.
• Inventors: Cooper, Steven C., Law, S. Edward
• Primary Examiner(s): Kashnikow, Andres
• Assistant Examiner(s): Douglas, Lisa Ann
• Application Number:
  US08/506,725
• Time in Patent Office: 1,056 Days
• Field of Search: 239/690, 239/690.1, 239/700-8, 239/590, 118/629, 118/621
• US Class Current: 239/690.1
• CPC Class Codes: B05B 5/03 characterised by the use of gas , e.g. electrostatically assisted pneumatic spraying B05B5/04, B05B5/043, B05B5/047 take precedence
• CPC Class Codes: B05B 5/043 using induction-charging
• CPC Class Codes: B05B 5/0533 Electrodes specially adapted therefor; Arrangements of electrodes
• CPC Class Codes: B05B 5/1608 the liquid or other fluent material being electrically conductive

Abstract

The disclosed invention relates to electrostatic spraying systems for liquids and specifically to an improved spray-charging nozzle system having increased reliability, consistency, safety and power efficiency for long-term operation in harsh agricultural and industrial applications. The invention achieves these advantages by: a) management of the interaction of any externally-originating electric fields with the droplet-charging electric-induction field being applied within the nozzle, including partial or total exclusion of the former fields; b) maintenance of the charge-induction electric field at the droplet-formation zone by precluding or minimizing leakage of charge in all directions from the induction electrode; c) protection of electronic and nozzle components from damage due to inadvertent overcurrents; and d) facilitation of non-tedious, convenient, trouble-free inspection and cleaning of the nozzle under harsh field conditions.

Claims

1. An electrostatic induction spray-charging nozzle device, the device being adapted for use with an electrical power supply, a liquid source and a gas source upstream of a rearward end of the device, comprising:

an electrically insulative body portion having a first channel therethrough for carrying a liquid from the liquid source, and a second channel therethrough for carrying gas from the gas source;

a liquid orifice tip in the body portion, the liquid orifice tip having an aperture aligned to receive and discharge liquid from the first channel of the body portion, the liquid being discharged from the liquid tip so as to meet with the gas in a droplet formation zone and form an atomized spray cloud;

a cap removably coupled to a forward end of the body portion, the cap comprising a spray exit aperture substantially coaxial to the liquid orifice tip aperture, an electrode forming a portion of the aperture, and an electrical connector within the cap for connecting the electrode to the power supply;

the body portion containing (1) no seam through which fluid may communicate with the first channel and (2) no electrical path between the first channel and the exterior of the body portion through which electrical charge may leak from the electrode to the liquid in the first channel; and

at least one resilient seal located between the body portion and the cap and not in communication with the first channel in order to block any fluid communication between the liquid orifice tip of the body and the electrical connector in the cap.

2. The nozzle according to claim 1, wherein the liquid tip is formed integral to the body portion.

3. The nozzle according to claim 1, wherein the liquid tip is press fit into the body portion.

4. The nozzle according to claim 1, wherein the liquid tip comprises a material that is not readily flammable.

5. The nozzle according to claim 1, wherein the liquid tip comprises a PTFE-like material.

6. An electrostatic induction spray-charging nozzle device, being adapted for use with a liquid source and a gas source upstream of a rearward end of the device, the device coupled to an electrical power supply and to a reference voltage and comprising:

an electrically insulative body portion having a first channel therethrough for carrying a liquid from the liquid source, a second channel therethrough for carrying gas from the gas source, and a liquid orifice tip having an aperture aligned to receive and discharge liquid from the first channel of the body portion, the liquid discharging from the liquid orifice tip meeting with the gas in a droplet formation zone to form an atomized spray cloud that is ejected in a direction forward of the nozzle;

an electrode cap removably coupled to a forward end of the body portion, the cap comprising a spray exit aperture substantially coaxial to the liquid orifice tip aperture, an electrode forming a portion of the aperture and disposed in the vicinity of the droplet formation zone to create an electric field for electrically charging the atomized spray cloud as it is ejected to a location forward of the nozzle, and an electrical connector within the cap for connecting the electrode to the power supply;

the body portion containing (1) no seam through which fluid may communicate with the first channel and (2) no electrical path between the first channel and the exterior of the body portion through which electrical charge may leak from the electrode to the liquid in the first channel; and

at least one resilient seal located between the body portion and the cap and not in communication with the first channel in order to block any fluid communication between the liquid orifice tip of the body and the electrical connector in the cap; and

an electric field barrier disposed between the electrode and the charged spray cloud, for decoupling the electric field of the ejected spray cloud from the electric field of the droplet charging zone.

7. The device according to claim 6, wherein the electric field barrier is coupled to the reference voltage.

8. The device of claim 7, in which the electric field barrier is generally disk-shaped and has a spray exit aperture.

9. The device of claim 7, in which the electric field barrier is generally cup-shaped and has a spray exit aperture.

10. The device of claim 6, in which the electric field barrier is generally disk-shaped and has a spray exit aperture.

11. The device of claim 10, wherein the electric field barrier is adapted to form an air gap.

12. The device of claim 11, wherein the electric field barrier further comprises a conductive material applied to the electric field barrier adjacent the air gap in order to modify the electric field interception characteristics of the electric field barrier.

13. The device of claim 6, in which the electric field barrier is generally cup-shaped and has a spray exit aperture.

14. The device of claim 6, in which the electric field barrier and the coupling of the electric field barrier to the reference voltage are disposed entirely within the electrode cap and in which the electrode and the coupling of the electrode to the electric power supply are disposed entirely within the electrode cap, such that the electrode cap and the body share no electrical pathways.

15. The device of claim 14, further comprising a first charge conductor disposed in the body and coupled to the reference voltage, and a second charge conductor disposed in the body and coupled to the electrical power supply, both charge conductors disposed at predetermined locations in the body, such that when the body is coupled to the electrode cap, the first charge conductor makes electrical contact with an electrical coupling of the field barrier, and the second charge conductor makes electrical contact with an electrical coupling of the electrode only when the body is at a preselected angular position with respect to the electrode cap.

16. The device of claim 6, further comprising a current leakage reduction channel insert coupled to the electrode cap at the spray exit aperture, the insert extending forward of the electrode and extending rearward of the electrode to form the forward wall of the gas plenum chamber region.

17. The device of claim 16, in which the channel insert comprises two parts, a first part extending forward from the electrode and a second part extending rearward from the electrode.

18. The device of claim 17, in which the channel insert parts comprise a PTFE-like material.

19. The device of claim 18, in which the surface of the second channel part comprises at least one groove for lengthening the upstream surface path between the electrode and the liquid.

20. The device of claim 6, wherein the external surface of the electrode cap includes a groove disposed therein, the device further comprising a band received in the electrode cap external surface groove for interrupting charge leakage paths.

21. The device of claim 20, wherein the band comprises a PTFE-like material.

22. An electrostatic induction spray-charging nozzle device, having a first channel therethrough for carrying a liquid from a liquid source, a second channel therethrough for carrying a gas from a gas source, the two channels meeting in a droplet formation zone, and the device being further coupled to a liquid supply tube for carrying liquid to the first channel, to an electrical power supply, and to a reference voltage, the device comprising:

(a) a body portion through which the first channel is disposed, for carrying into the droplet formation zone the liquid to be atomized into spray droplets by gas carried by the second channel;

(b) an electrode cap comprising a dielectric material and having a forward end, a rearward end, the rearward end coupled to the body, further having a spray exit aperture through which the atomized liquid is discharged as a charged spray cloud;

(c) an electrode coupled to the electrical power supply and disposed within the electrode cap adjacent the droplet formation zone, for electrically charging the spray in the droplet formation zone; and

(d) an electrically conductive grounding element electrically coupled to ground and in contact with the liquid stream and positioned at a selected distance upstream of the liquid orifice tip comprising a conductor inserted into the liquid supply tube and extending a selected distance downstream toward the liquid orifice tip to achieve a selected electrical resistance between the liquid jet of the droplet formation zone and the grounding element as determined by the resistance from the tip of the inserted conductor to ground, the liquid resistivity, the liquid supply tube resistivity, and the insertion distance downstream.

23. The device of claim 22 further comprising an electric field barrier means disposed between the electrode and the charged spray cloud and coupled to the reference voltage, for decoupling the electric field of the ejected spray from the electric field of the droplet charging zone.

24. The device of claim 22 comprising a PTFE-like material disposed on the nozzle surface between the electrode and ground to reduce current leakage.

25. An electrostatic induction spray-charging nozzle device, having a first channel therethrough for carrying a liquid from a liquid source, a second channel therethrough for carrying gas from a gas source, the two channels meeting in a droplet formation zone, and the device being further coupled to a liquid supply tube for carrying liquid to the first channel, to an electrical power supply, and to a reference voltage, the device comprising:

(a) a body portion through which the first channel is disposed, for carrying into the droplet formation zone the liquid to be atomized into spray droplets by gas carried by the second channel;

(b) an electrode cap comprising a dielectric material and having a forward end, a rearward end, the rearward end coupled to the body and coupled to the electrode cap, further having a spray exit aperture through which the atomized liquid is discharged from the body as a charged spray cloud;

(c) an electrode coupled to the electrical power supply and disposed within the electrode cap adjacent the droplet formation zone, for electrically charging the spray in the droplet charging zone;

(d) electric field barrier means disposed between the electrode and the charged spray cloud and coupled to the reference voltage, for decoupling the electric field of the ejected spray from the electric field of the droplet charging zone;

(e) a current leakage reduction means coupled to a surface of the nozzle;

(f) a short-circuit prevention and charge leakage reduction mechanism including;

(i) an electrically conductive grounding element electrically coupled to ground;

(ii) an electrically conductive insertion element, having a known resistance and electrically coupled to the grounding element, for inserting into the liquid supply tube to a preselected distance toward the liquid jet; and

(iii) a tube coupling coupled to the grounding element and to the liquid supply tube and having an aperture through which the insertion element may pass from outside the tube coupling into the liquid supply tube;

the preselected distance of insertion of the insertion element determining the resistance of an electrical path from the liquid jet to ground for controlling nozzle charge leakage; and

(g) an anti-drip auto-purge mechanism including a valve assembly coupled to the upstream end of the liquid supply tube, the valve assembly having a first position and a second position, wherein adjustment of the valve assembly from the first to the second position exposes the liquid supply tube to a change in pressure that evacuates the nozzle of liquid.

26. An electrostatic induction spray-charging nozzle device for use with a liquid source and a gas source comprising:

an electrode cap having a forward end, a rearward end, and an interior channel in the vicinity of which the liquid and gas from the liquid and gas sources meet to form an atomized spray, and having an electrode disposed adjacent the interior channel for electrically charging the atomized spray together with a conductor for connecting the electrode to a power supply, wherein the interior channel forms an internal nozzle charge leakage path, and the exterior surface of the electrode cap forms a first portion of an external nozzle charge leakage path, the charge leakage originating at the electrode;

a body portion coupled to the rearward end of the electrode cap and having an exterior surface forming a second portion of an external nozzle charge leakage path, and a liquid channel leading to a liquid orifice tip irremovably connected to the body portion;

a surface treatment having low surface wettability applied to a surface of the nozzle for interrupting a charge leakage path;

the body portion containing (1) no seam through which fluid may communicate with the liquid channel and (2) no electrical path between the liquid channel and the exterior of the body portion through which electrical charge may leak from the electrode to the liquid in the liquid channel; and

at least one resilient seal located between the body portion and the cap and not in communication with the liquid channel in order to block any fluid communication between the liquid orifice tip of the body and the electrical connector in the cap.

27. The device of claim 26, wherein the surface treatment is a cylindrical band applied to the exterior surface of the nozzle.

28. The device of claim 27, wherein the cylindrical band comprises a PTFE-like material.

29. The device of claim 26, wherein the surface treatment is a cylindrical channel insert applied to the interior channel of the electrode cap.

30. The device of claim 29, wherein the cylindrical channel insert comprises a PTFE-like material.

31. The device of claim 26, wherein the surface treatment is a coating applied circumferentially about the exterior of the nozzle.

32. The device of claim 31, wherein the coating comprises a PTFE-like material.

33. The device of claim 26, wherein the surface treatment is a tape applied circumferentially about the exterior of the nozzle.

34. The device of claim 33, wherein the tape comprises a PTFE-like material.

35. An electrostatic induction spray-charging nozzle system for generating a charged spray from a liquid jet fed from a liquid source upstream of the nozzle device with reduced charge leakage, comprising:

an electrostatic spray-charging nozzle;

a liquid supply tube having an external portion for carrying liquid from the liquid source and an internal portion disposed within the nozzle for carrying the liquid from the external portion of the liquid supply tube to the nozzle jet, the portions of the liquid supply tube having a preselected combined length and cross-sectional liquid column area, and formed of a preselected material; and

an electrical conductor placed in the liquid supply tube a preselected distance from the nozzle, extending a preselected distance in the liquid, and electrically coupled to electrical ground;

wherein the combined length, cross-sectional area, and material of the portions of the liquid supply tube, and the material and distance of the conductor to the liquid tip are selected such that the electrical resistance of an electrical path from the liquid jet to ground has a preselected value.

36. The device of claim 35 further comprising an electrical resistor placed between the conductor in the liquid supply tube and electrical ground.

37. An electrostatic induction spray-charging nozzle device, having a liquid supply channel therethrough for carrying a liquid from a liquid source to a liquid orifice tip, a second channel therethrough for carrying a gas from a gas source, the two channels meeting in a droplet formation zone, and the device being further coupled to a liquid supply tube for carrying liquid to the liquid supply channel, to an electrical power supply, and to a reference voltage, the device comprising:

(a) a body portion through which the liquid supply channel is disposed, for carrying into the droplet formation zone the liquid to be atomized into spray droplets by gas carried by the second channel;

(b) an electrode cap comprising a dielectric material and having a forward end, a rearward end, the rearward end coupled to the body, further having a spray exit aperture through which the atomized liquid is discharged as a charged spray cloud;

(c) an electrode coupled to the electrical power supply and disposed within the electrode cap adjacent the droplet formation zone, for electrically charging the spray in the droplet formation zone;

(d) an electrically conductive grounding element electrically coupled to ground and in contact with the liquid stream and positioned at a selected distance upstream of the liquid orifice tip; and

(e) selectable porting to the liquid supply channel, upstream of the liquid orifice tip, for purging the channel of spray liquid to prevent electrical current between the electrode and ground through the liquid channel.

38. The device of claim 37 in which the selectable porting empties a portion of the liquid supply channel of spray liquid and fills the channel with a gas to prevent dripping from the liquid orifice tip and to prevent electrical current between the electrode and the upstream spray liquid.

39. The device of claim 37 in which the selectable porting is adapted to replace the spray liquid with an alternate liquid for the purpose of cleaning the liquid channel and reducing electrical current from the electrode.

40. The device of claim 37 where the selectable porting is adapted to replace the spray liquid with an alternate liquid and empty the alternate liquid from the nozzle.