Fluid sprinkling – spraying – and diffusing – Processes – Including electrostatic charging
Reexamination Certificate
2000-03-24
2001-11-20
Scherbel, David A. (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Processes
Including electrostatic charging
C239S690000, C239S695000, C239S696000, C239S102200, C361S227000, C128S204210
Reexamination Certificate
active
06318640
ABSTRACT:
The invention relates to a dispensing device for comminuting a liquid, means for supplying liquid for use in such device and the use of such a device, in particular, in medicine.
Dispensing devices are known which produce a finely divided spray of liquid droplets by electrostatic means(more properly referred to as ‘electrohydrodynamic’ means). Electrohydrodynamic sprayers have found use in many areas of industry, especially in agriculture for crop spraying, paint spraying in the automotive industry and also in medicine for the administration of medicaments by inhalation.
The droplet spray in such devices is generated by applying an electric field to a liquid located at a spray head or spray edge. The potential of the electric field is sufficiently high to provide comminution of electrically charged liquid droplets from the spray head. The electrical charge on the droplets prevents them from coagulating via mutual repulsion.
United Kingdom patent number 1569707 describes an electrohydrodynamic spray device principally for use in crop spraying. An essential component of the GB 1569707 spray device is a field intensifying electrode, cited adjacent the spray head and maintained at the same potential as the spray head. The field intensifying electrode is not supplied with liquid In use it is stated to reduce the incidence of corona discharge which interfere with spray production and thereby allows lower electric field strengths to be used during spray generation.
U.S. Pat. No. 4,703,891 describes a crop spraying apparatus for spraying liquids from a vehicle such as an aircraft or other airborne vehicle, having at least two sprayheads arranged to produce spray of positive charge at one sprayhead and negative charge at the other. The resulting charged sprays are then applied to the relevant crops.
In many circumstances it is desirable to partially or wholly remove the electric charge from droplet sprays produced by electrohydrodynamic comminution devices in a controlled manner. To date the principal method used to effect comminution discharge has required the use of a discharging electrode having a sharp or pointed edge and located downstream from the spray head. The discharging electrode produces a cloud of charged ions from the surrounding air having an opposite electrical charge of equal magnitude to that on the comminuted liquid spray. In use, the ion cloud is attracted towards, collides with and thereby neutralizes the liquid spray.
United Kingdom patent number 2018627B discloses an electrohydrodynamic spray device wherein the electric charge on the droplet spray is fully or partially removed by means of a discharge electrode. The UK 2018627B device is stated to provide discharged or partially discharged sprays for crop spraying purposes. European Patent number 0234842 discloses an electrohydrodynamic inhaler wherein the spray of charged droplets is similarly discharged by means of a discharge electrode. The droplets are discharged in order to facilitate droplet deposition into the respiratory tract as otherwise the electrically charged droplets would deposit onto the mouth and throat of the user.
A particular problem associated with the use of the sharp discharge electrode is that the highly mobile ion cloud from the discharge electrode often interferes with the commninution of the liquid spray. The inhaler device of EP 0234842 attempts to ameliorate the effects of the ion cloud at the spray head by using a neutral shield electrode located close to the spray head.
It is a primary feature of the present invention that a device for comminuting a liquid is provided, which corn minutes the liquid by electrohydrodynamic means and which produces a partially or fully electrically discharged comminution without the need for the sharp discharge electrode described above. The present device does not have the problems associated with the discharge electrode and hence it does not require the use of a neutral shield electrode.
Accordingly, there is provided a device for comminuting a liquid, which comprises at least two electrohydrodynamic comminution means arranged so that in use comminutions of opposing polarity are formed which are substantially admixed after formation.
The electrohydrodynamic comminution means may be any conventional electrohydrodynanic comminution means, for example those described in the above mentioned patent specifications.
Suitably, each comminution means comprises a comminution site, generally being a surface or edge, from which the liquid comminution is produced.
A preferred conmminution surface or edge is provided by a thin capillary tube, a nozzle or a slot defined by two parallel plates. However any comminution surface or edge described in the above mentioned patent specifications may be used.
The device generally comprises an even number of comminution means but this is not essential, the key factors are that at least two of the comminution means provide comminutions of opposing polarity and that the comminutions produced are ananged to substantially admix
Suitably, the device comprises 2,4 or 6 comminution means, however higher numbers can be used as required. An example of a device is that which has 2 comminution means. An example of a device is that which has 6 comminution means.
Suitably, each comminution means comprises a means for supplying liquid to the comminution site.
Appropriate means for supplying liquid to the comminution site include mechanical, electrical or electronic powered means such as pumps which ar capable of providing the required flow rate of liquid to the comminution site.
The comminution means of the invention can be used with a large range of flow rates, but generally operates with flow rates in the range of between 0.1 to 500 &mgr;L per second, such as 0.5 to 5 &mgr;L per second, especially for inhaled administration, or 10 to 200 &mgr;L per second, especially for agricultural use.
A suitable means for supplying the liquid includes a syringe pump or an electrically powered pump as described in EP 0029301.
It will be appreciated from the foregoing that the comminution means generally comprises a comminution site, a means for supplying a liquid to the comminution site and a means for electrically charging the comminution site to an electric potential sufficient to comminute the liquid in use.
Accordingly, in one particular aspect of the invention there is provided a device for comnrinuting a liquid, which comprises at least two electrohydrodynamic comminution means each comprising a comminution site, a means for supplying a liquid to the comminution site and a means for electrically charging the comminution site to an electric potential sufficient to comminute the liquid in use, wherein the comminution means are arranged so that in use comminutions of opposing polarity are formed which are then substantially admixed.
Suitably, each comminution means comprises a means for electrically charging the said comminution site to a potential sufficient to provide comminution of the liquid, the potential usually being of the order of 1-20 kilovolts.
The means for electrically charging the said comminution site, such as a surface or edge, may be provided by any conventional high voltage generator having the approat output, one particularly convenient generator being a piezoelectric generator.
The piezoelectric material for the generator may be chosen from several types, such as barium tianate ceramic, or pvdf polymers, which generate significant high-voltage electric charge displacement upon being pressurized. The choice and capacity may be so chosen as to offer control of the degree of pumping and/or atomization when operated.
The required voltage for use is provided when the piezo-electric generators are squeezed, and again (with opposite polarity) when the piezo-electric generators are released from pressure.
The arangement by which the comminutions are admixed enables the net charge on the admixed comminution to be either essentially neural, positive or negative. Generally, the residual positive or negative charges are less than the positi
Cobrin & Gittes
Electrosols Ltd.
Scherbel David A.
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