Fluid sprinkling – spraying – and diffusing – Processes – Including electrostatic charging
Reexamination Certificate
2000-04-20
2001-10-16
Scherbel, David A. (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Processes
Including electrostatic charging
C239S690100, C239S692000, C239S706000
Reexamination Certificate
active
06302331
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to devices and methods for controlling the delivery and the delivery direction of an aerosol, and particularly to a method and apparatus for induced aerosol flow in an electrohydrodynamic (EHD) sprayer.
2. Background
The use of electrohydrodynamic (EHD) apparatus to produce aerosols is well known. Recently, we have recognized that EHD devices are extremely useful to produce and deliver aerosols of therapeutic products.
In typical EHE) devices fluid delivery means deliver fluid to be aerosolized to a nozzle maintained at high electric potential. One type of nozzle used in EHD devices is a capillary tube that is capable of conducting electricity. An electric potential is placed on the capillary tube which charges the fluid contents such that as the fluid emerges from the tip or end of the capillary tube a so-called Taylor cone is formed. This cone shape results from a balance of the forces of electric charge on the fluid and the fluid's own surface tension. Desirably, the charge on the fluid overcomes the surface tension and at the tip of the Taylor cone, a thin jet of fluid forms and subsequently and rapidly separates a short distance beyond the tip into an aerosol. Studies have shown that this aerosol (often described as a soft cloud) has a fairly uniform droplet size and a high velocity leaving the tip but that it quickly decelerates to a very low velocity a short distance beyond the tip.
EHD sprayers produce charged droplets at the tip of the nozzle. Depending on the use, these charged droplets can be partially or fully neutralized (with a reference or discharge electrode in the sprayer device) or not. The typical applications for an EHD sprayer without means for discharging or means for partially discharging an aerosol would include a paint sprayer or insecticide sprayer. These types of sprayers may be preferred since the aerosol would have a residual electric charge as it leaves the sprayer so that the droplets would be attracted to and tightly adhere to the surface being coated. However, with EHD apparatus used to deliver therapeutic aerosols, it is preferred that the aerosol be completely electrically neutralized prior to inhalation by the user to permit the aerosol to reach the pulmonary areas where the particular therapeutic formulation is most effective.
The preferred orientation of EHD sprayers is with the nozzle vertical and located above the object to receive the aerosol. This nozzle orientation eliminates, for practical purposes, the problems associated with the fluid dispensed from the nozzle tip collecting on or wicking up the outside of the capillary tube and associated fluid delivery means. If the fluid flows up the outside of the nozzle from the tip, it is no longer available to be sprayed and represents a loss in efficiency of the device. Moreover, fluid on the outside surfaces of the capillary tube may accumulate and suddenly flow back to the tip where it may disrupt the Taylor cone. These disruptions and any other disruptions of the Taylor cone may result in a large variation in the size and size distribution of the aerosol droplets which is particularly undesirable in pulmonary drug delivery.
When administering pharmaceuticals to a patient these limitations on orientation of the EHD apparatus result in either the patients having to tilt their head backwards or to lie on their back when the aerosol is delivered on axis with the nozzle. Alternatively, the EHD apparatus can deliver the aerosol vertically on axis with the nozzle and an elbow means can change the direction of aerosol flow to deliver the aerosol nearly horizontally. With this change in direction of the aerosol, there often is an appreciable loss in the quantity of the aerosol. The loss in quantity is a result of the fluid impacting and depositing on the walls of the delivery device, particularly in the vicinity of the elbow, instead of reaching the patient. One device for reducing disruptions of the Taylor cone and for reducing the loss in quantity of fluid impacting the walls is described in a co-owned U.S. patent application filed of even date herewith and entitled “High Mass Transfer EHD Aerosol Sprayer”, which application is hereby incorporated by reference. Therefore, an EHD aerosol sprayer is needed where the aerosol delivery direction can be controlled and wherein the Taylor cone can be stabilized to prevent disruption. Of particular need, is an EHD aerosol sprayer that can spray substantially horizontally and deliver the aerosol without appreciable wetting of the delivery device.
SUMMARY OF THE INVENTION
The invention described herein provides an aerosol delivery method and system for solving the problems discussed above by producing a charged EHD aerosol, discharging the aerosol and inducing a flow in the discharged aerosol in a desired direction without substantial wetting of the device.
In a preferred embodiment the delivery system includes a spray nozzle for dispensing the fluid to be aerosolized and negatively charging the aerosol droplets, a discharge electrode generally proximate the spray nozzle for generating a positive ion stream which intercepts and electrically neutralizes the negative aerosol droplets while also imparting a desired movement on the aerosol in a direction generally away from the discharge electrode, and at least one first reference electrode between the spray nozzle and the discharge electrode for modifying the electric field between the spray nozzle and the discharge electrode. Preferably, the discharge electrode is positioned proximate the spray nozzle such that the ion cloud intercepts the aerosol at a short distance, for example less than about 4 centimeters and more preferably less than 2 centimeters from the spray nozzle tip before the aerosol cloud has had a chance to disperse to a large degree.
Optionally, at least one second reference electrode may be placed near the discharge electrode on the side opposite of the first electrode. Optionally, at least one third electrode may also be placed near the spray nozzle on the side opposite the first reference electrode.
The spray nozzle is usually placed at a potential of between one and twenty kilovolts, with three to six kilovolts being the preferred voltage range. The placing of a negative potential on the spray nozzle results in the aerosol being negatively charged. To electrically discharge the aerosol, a positive potential of between one and twenty kilovolts, and with a preferred voltage of three to six kilovolts, is placed on a discharge electrode. The charges could be reversed on the spray nozzle and the discharge electrode, however, the positive ions from the discharge electrode appear to be much more effective than would negative ions in imparting movement (induced flow) to the aerosol.
Preferably, the discharge electrode includes a sharp point or edge where a positively charged ion cloud is originated to discharge the aerosol and move it in the desired direction. In a preferred embodiment, the axis of the spray nozzle and the axis of the discharge electrode are at an angle of less than about 120 degrees (between 0 degrees and 180 degrees) and more preferably in the range of 30-90 degrees. Larger angles may also be useful, but at angles approaching 180 degrees (the electrodes thereby being substantially opposed) the movement of the aerosol would be substantially toward the spray nozzle. In most uses, this would not be desirable to direct the charged aerosol substantially toward the discharge electrode, as the droplets are readily attracted to the electrode surface which reduces the aerosol delivery efficiency of the sprayer. If the discharge electrode becomes wetted with aerosol under these conditions, an undesired secondary spray can result at the discharge electrode. It is also undesirable to direct the discharge ion cloud substantially toward the spray nozzle as these ions can disrupt the EHD aerosol generation process.
Between the spray nozzle and the discharge electrode is a first reference electrode. The first
Chongsiriwatana Songsdhit
Dvorsky James E.
Battelle Pulmonary Therapeutics, Inc.
Bissell Barry S.
Nguyen Dinh Q.
Scherbel David A.
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