This invention relates to an improved electrospray device and more particularly to an electrospray device which avoids excess accumulation of electrospray fluid.
Basic operation of electrosprays is well-known and characterized in a large number of publications and used in many applications. Most of these applications are distinguished by relatively short-duration operation, especially where the electrospray is emitted through one or more apertures in grids composed of some solid material. During electrospray operation, and particularly during startup or with certain applied voltages and/or liquid flowrates applied to the electrospray, the electrospray may deposit some amount of sprayed liquid upon the solid edges of the grids (overspray), especially proximate the aperture. Accumulated build-up of this deposited liquid adversely impacts performance of electrospray operation over time, particularly when low vapor pressure liquids are used. Because this accumulation is gradual and most applications are short-duration, performance impacts had been negligible and no solutions to liquid accumulation had been sought.
For extended electrospray operation e.g. for durations exceeding 100 hours, or for particular operating conditions, no effective means for transport/removal of accumulated liquid exists. Consequently, duration of electrospray operation is limited to the point where the accumulated liquid interferes with, and ultimately prevents, proper function. Proper function is restored by performing manual cleaning of accumulated liquid and/or replacement of affected components.
Frequent cleaning or replacement of components is costly, and for applications where cleaning or replacement is impossible, the duration of electrospray operation is limited to the time it takes for some critical buildup preventing proper operation.
It is therefore an object of this invention to provide an improved electrospray device.
It is a further object of this invention to provide such an improved electrospray device which prevents buildup of excess electrospray fluid.
It is a further object of this invention to provide such an improved electrospray device which prevents back spray and shorting due to electrospray fluid accumulation.
It is a further object of this invention to provide such an improved electrospray device which enables extended operation and enables use in environments where cleaning or replacement is not practical.
It is a further object of this invention to provide such an improved electrospray device which reduces time and cost for cleaning or replacement necessitated by electrospray accumulation.
It is a further object of this invention to provide such an improved electrospray device which provides improved operation by eliminating the effect of free surfaces in electric fields affecting electrospray.
It is a further object of this invention to provide such an improved electrospray device which enables smaller and more compact devices through denser arrays of electrospray emitters.
The invention results from the realization that an improved electrospray device which reduces excess electrospray accumulation is achieved by making the extractor plate and one or more accelerator plates and shaping plates from a porous, conductive medium for transporting excess, accumulated electrospray fluid away from the aperature(s) in the plates.
The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives.
This invention features an electrospray device including an electrospray emitter adapted to receive electrospray fluid, an extractor plate spaced from the electrospray emitter and having at least one aperture, and a power supply for applying a first voltage between the extractor plate and emitter for generating at least one Taylor cone emission through the aperture to create an electrospray plume from the electrospray fluid, the extractor plate including a porous, conductive medium for transporting excess, accumulated electrospray fluid away from the aperture.
In a preferred embodiment the emitter may include a capillary tube for delivering the electrospray fluid. The emitter may include an externally wetted needle. The emitter may include a porous core with a circular emission rim. The emitter may include a porous core with a linear emitter. The electrospray fluid may include an ionic liquid. The electrospray fluid may include a mixture of ionic liquid and a solvent. The porous, conductive medium may include a metal. The porous, conductive medium may include a sintered metal. The aperture may include a hole. The aperture may include a gap distance from the extractor plate. There may be an accelerator plate spaced from the extractor plate on the other side from the emitter. The power supply may provide a second voltage between the extractor place and the accelerator plate. The second voltage may have the same polarity as the first voltage. The second voltage may have the opposite polarity from the first voltage. There may be shaping plate for shaping the electrospray plume. The shaping plate may be disposed between the emitter and the extractor plate. The power supply may apply a voltage to the shaping plate similar to that applied to the emitter. The shaping plate may include a porous, conductive medium. The accelerator plate may include a porous, conductive medium. At least one of the extractor, accelerators, and shaping plates may be connected to a liquid storage.
Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:
Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer.
As explained in the Background, electrospray devices such colloid thrusters employ extraction and acceleration grids to create and accelerate liquid propellant as charged droplets and ions. A small fraction of the emitted propellant, usually much less than 1%, is intercepted by the grids where it may accumulate. The majority of this interception occurs during start up transients. Because the liquid is conductive, sufficient accumulation can bridge across high voltage gaps, and short the thruster, terminating its useful life or detrimentally altering the electrostatic field between the grids.
There is shown in
In accordance with this invention aperture plate 14 is made of a porous conductor. It is a conductor in order to contribute to the establishment of the electric field between emitter 10 and plate 14. In accordance with this invention it also must be porous. Metals are a good choice for plate 14, especially sintered metals. The porosity depends upon the viscosity and flowability of the electrospray fluid used. For example, using an electrospray fluid such as EMIIm available from Covalent Associates, Inc. plate 14 may be made of stainless steel and have a porosity of 0.5 μm. Using ionic fluid such as EMIBF4 available from Alfa Aesar the plate 14 may be made of stainless steel and have a porosity of 0.5 μm. If the electrospray fluid is EMIPF6 available from Sigma Aldrich then plate 14 may be made of stainless steel and have a porosity of 0.5 μm. By making plate 14 porous in accordance with this invention the excess electrospray fluid which would accumulate on plate 14 in and around hole 16 is instead wicked away and absorbed into the porous plate 14. The enlarged detail view of
In
In another alternative,
While thus far the porous plate 14 according to this invention has been shown with an aperture that is basically a hole or a round opening this is not a necessary limitation of the invention for as shown in
The action promoted by the porous structure of the aperture plate according to this invention is shown in
Although thus far the invention has been applied to a single aperture plate, typically the extractor plate of an electrospray device, this is not a necessary limitation of the invention. For example, as shown in
The invention is applicable to all manner of arrangements and configurations of aperture plates, shaping electrodes and the like. Some examples of the variety of aperture plates including extractor plates, accelerator plates, shaping electrodes and lenses which are accommodated by this invention are shown in
Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments.
In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant can not be expected to describe certain insubstantial substitutes for any claim element amended.
Other embodiments will occur to those skilled in the art and are within the following claims.
This application claims benefit of and priority to U.S. Provisional Application Ser. No. 61/137,410 filed Jul. 30, 2008 under 35 U.S.C. §§119, 120, 363,365, and 37 C.F.R. §1.55 and §1.78 incorporated herein by this reference.
Some work pertaining to this invention has been done under government contract: NASA NAS7-1407/Subcontract No. 1247199; United States Air Force FA8650-04-C2504; and HQ0006-05-C-7235. The Government may have certain rights under the subject invention.
Number | Date | Country | |
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61137410 | Jul 2008 | US |