US20080175720A1

US20080175720A1 - Contoured electrodes for an electrostatic gas pump

Info

Publication number: US20080175720A1
Application number: US12/017,986
Authority: US
Inventors: Daniel J. Schlitz; Vishal Singhal
Original assignee: THORRN MICRO TECHNOLOGIES Inc
Current assignee: THORRN MICRO TECHNOLOGIES Inc
Priority date: 2007-01-23
Filing date: 2008-01-22
Publication date: 2008-07-24
Also published as: CN101622687A; KR20090107548A; JP2010517241A; WO2008091905A1; TW200903558A; EP2126956A1

Abstract

The present invention achieves high gas flow rates through an electrostatic pump having sharp and blunt electrodes with a corona discharge taking place in the gas gap in between the electrodes. According to certain aspects, the invention comprises a specially shaped blunt electrode that is contoured to maintain a constant or approximately constant distance between the sharp (corona) electrode and the neutralizing surface of the blunt electrode. The contour provides maximum electric field enhancement at the corona electrode and minimizes the electric field at the blunt electrode. This maximizes the non-arcing operating voltage and increases the maximum power output of the corona discharge. The contour also isolates neighboring corona electrodes, preventing their electric fields from interfering with one another and making it possible to increase the density of electrodes which further increases the pumping power of the device.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from U.S. Provisional Appln. No. 60/886,204 filed Jan. 23, 2007, the contents of which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to electrostatic gas pumps, and more particularly to methods and apparatuses for producing greater gas flow rates in an electrostatic pump.

BACKGROUND

An electrostatic gas pump consists of one or more sharp (corona) and blunt (neutralizing) electrodes. An electric field is applied between the two electrodes causing a partial breakdown of the gas, referred to as a corona discharge, near the sharp electrode. The discharge produces ions which are attracted to the neutralizing electrode. En route, the ions collide with neutral gas molecules creating pressure head and flow similar to that produced by a mechanical fan.
U.S. patent application Ser. No. 11/338,617, Jan. 23, 2006, titled “Electro-hydrodynamic Gas Flow Cooling System,” the contents of which are incorporated herein by reference in their entirety, dramatically advanced the state of the art of electrostatic gas pumps. Nevertheless, the present inventors recognize that certain opportunities for improvement remain. For example, in prior art pumps using corona electrodes, including those described in the above-described co-pending application, the blunt electrode is generally a flat or effectively flat surface. The flat surfaced electrode is not equidistant from the corona electrode. Hence, it does not provide additional field enhancement at the corona electrode and a higher voltage must be used to get the same ion current as a contoured electrode. The flat electrode does not confine the ionization region, so it will arc at a lower voltage and have less pumping power. Finally, the flat electrode does not isolate neighboring electrodes. This necessitates a much larger spacing between electrodes and again decreases the total ion current and pumping power.
Other prior art approaches fail to identify, appreciate and/or attempt to solve the problems recognized by the present inventors. For example, U.S. Pat. No. 6,888,314 dated May 3, 2005, and titled “Electrostatic fluid accelerator” describes isolating wire-type corona electrodes by placing them in between flat-plate blunt electrodes. This patent does not suggest contouring of the blunt electrode to enhance the electric field at the corona electrode. Further, the corona wire and plate electrode run parallel. The plate spacing is determined by electrical considerations. This patent does not suggest nor can it implement an embodiment where the corona wire runs perpendicular to the blunt electrodes. This prevents any embodiment of this invention from being optimized for flow, heat transfer, etc.
Accordingly, there remains a need in the art for a electrostatic gas pump that can address the problems identified by the present inventors, among others.

SUMMARY OF THE INVENTION

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures, wherein:

FIGS. 1A and 1B illustrate a contoured blunt electrode for use with a wire-type sharp electrode according to aspects of the invention;

FIGS. 2 and 3 illustrate possible embodiments of an electrostatic pump using a contoured blunt electrode such as that shown in FIG. 1;

FIGS. 4A to 4C show examples of extruded-type cross sections for a corona electrode that can be used together with a contoured blunt electrode according to aspects of the invention;

FIG. 5 illustrates a configuration of a corona electrode having protruding point-type electrodes that can be used in embodiments of the invention; and

FIG. 6 illustrates an electrostatic pump having a plurality of contoured blunt electrodes respectively paired with a plurality of point-like corona electrodes according to other possible embodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference to the drawings, which are provided as illustrative examples of the invention so as to enable those skilled in the art to practice the invention. Notably, the figures and examples below are not meant to limit the scope of the present invention to a single embodiment, but other embodiments are possible by way of interchange of some or all of the described or illustrated elements. Moreover, where certain elements of the present invention can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the present invention will be described, and detailed descriptions of other portions of such known components will be omitted so as not to obscure the invention. In the present specification, an embodiment showing a singular component should not be considered limiting; rather, the invention is intended to encompass other embodiments including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover, applicants do not intend for any term in the specification or claims to be ascribed an uncommon or special meaning unless explicitly set forth as such. Further, the present invention encompasses present and future known equivalents to the known components referred to herein by way of illustration.
According to certain general aspects, the present invention uses a specially shaped blunt electrode having substantial portions of its leading surface located a constant, or near constant, distance from the corona electrode. Typically, the leading surface comprises the surface that is closest to the corona electrodes, and is the portion of the blunt electrode where the majority of the electric field lines either originate or terminate (depending on the polarity).
FIGS. 1A and 1B illustrate certain aspects of the invention in an electrostatic pump having a blunt electrode 102 and corona electrode 104. The blunt electrode 102, rather than having a flat shape as in the prior art, has a contoured neutralizing surface 106 facing the corona electrode 104.
More particularly, as shown in FIG. 1B, which is taken along sectional line 1B-1B in FIG. 1A, surface 106 of blunt electrode 102 facing corona electrode 104 is contoured such that the distance d between a given point on corona electrode 104 is substantially the same at all points on surface 106 of blunt electrode 102 that directly underlie that point. Accordingly, as shown in FIG. 1A, for a given length of the corona electrode 104, the contour of the neutralizing surface 106 of the blunt electrode 102 is similar to a portion of the inside of a hollow partial cylinder, the partial cylinder having a height corresponding to the given length.
The angle θ in FIG. 1A, when d is substantially the same between all points on surface 106 from a given point on corona electrode 104, can thus be considered as defining the size of an arc with the corona electrode 104 as the center. Theoretically, the angle θ can be any value greater than 0° and up to 360°. In general, the inventors note that the electric field enhancement at the corona electrode increases as θ increases. The isolation between neighboring corona electrodes (not shown) afforded by the contoured blunt electrode also increases as θ increases. However, the present inventors further recognize that as θ is increased beyond 180°, some of the ions begin to be attracted in the upstream direction and exert a detrimental effect on the gas flow. Therefore, positive aspects of increasing θ, increased ion current and better isolation, are preferably weighed against the negative aspects to arrive at an appropriate geometry for a particular application.
In example implementations of the principles of the invention in an electrostatic gas pump, the present inventors recognize that consideration should be given to the electrostatic air flow path through the device. For example, passageways through the blunt electrode(s) should be provided while maintaining the general contoured shape.
FIG. 2 illustrates one example embodiment of an electrostatic gas pump according to aspects of the invention. In this example, pump 200 employs a series of parallel blunt electrode fins 202 that run perpendicular to the corona electrodes 204. As can be seen, each fin 202 has a contoured neutralizing surface facing each of the corona electrodes as described above in connection with FIGS. 1A and 1B. The spacing between the blunt electrode fins 202 define channels 206, and the overall configuration of the provides an array of multiple, parallel electrostatic discharges between the electrodes. The channels 206 further allow gas to flow efficiently through the device as a result of the electrostatic pumping action, in the direction illustrated by the large arrows. This embodiment also shows an array of corona wires implementing the corona electrodes 204.
FIG. 3 illustrates another example embodiment of an electrostatic gas pump according to the invention. In this example, pump 300 includes walls 308 running parallel to direction of the corona electrodes 304 that define separated channels 306 for the flow of gas in between the blunt electrode fins 302 and further between each of their contoured neutralizing surfaces. The walls 308 further help to maintain a high electric field concentration over all portions of the corona electrode, particularly in the region between the contoured fins. The walls 308 also help to reduce the electric field at the blunt electrode and to provide additional electrical isolation between neighboring corona electrodes 304.
Implementation details such as suitable materials, dimensions and voltages applied to the corona and/or blunt electrodes so as to obtain the desired electrostatic gas pumping action can be derived by those skilled in the art from the teachings of co-pending application Ser. No. 11/338,617. For example, the above described corona electrodes can be comprised of a thin wire and the blunt electrodes can be comprised of a heat sink fin material such as aluminum. In one example implementation using corona wind as the electrostatic gas pumping mechanism, the distance d between the corona electrode and blunt electrode surface (i.e. electrode gap) is about 30 mm, the corona electrode wire has a diameter of about 0.5 mm, the voltage applied to the electrode is about 20 kV, and blunt electrode fins have a thickness of about 1 mm. In a micro-scale corona wind example, the distance d is about 2 mm, the corona electrode wire has a diameter of about 2 microns, the voltage is about 1500 V, and the blunt electrode fin has a thickness of about 0.2 mm, and is approximately a semi-cylinder contour (i.e. θ is about 180 degrees).
In certain embodiments, the present inventors have recognized that it is desirable to make the electrode gap as small as possible. For example, the inventors have demonstrated electrostatic air pumps with gaps from 0.5 to 3 mm and voltages from 1200 to 5000 V. Eventually, the gap can be lowered to 100 μm with a operating voltage of several hundreds of volts while still maintaining a similar pumping outputs as the larger gaps. Corona wire spacing (e.g. separation of parallel corona electrodes 204 and 304) is approximately equal to twice the gas gap. As the gap decreases, wire spacing can also decrease.
It should be noted that the present invention can be practiced in many different ways and in different configurations than described in the examples above. For example, while round-shaped corona wires can be used in conjunction with the blunt electrode embodiments of FIGS. 1-3, other types of corona electrode configurations are possible in conjunction with the blunt electrodes according to the invention.
For example, FIGS. 4A, 4B and 4C show cross sections of various prismatic shapes of corona electrodes that can be used either singularly as in FIG. 1 or in linear arrays as in FIGS. 2 and 3. FIGS. 4A and 4B show elliptical (e.g. circular) and rectangular (e.g. square) shaped cross sections, respectively, of a wire that can be used to implement the corona electrode. FIG. 4C shows a knife edge or razor blade cross section of an extruded shape that is used to implement the corona electrode, rather than a wire. It should be apparent that other shapes are possible, such as hexagonal.
FIG. 5 shows an array of point-type corona electrode configurations, in which the corona electrode is implemented by a supporting member 502 with a plurality of sharp points 504 protruding therefrom. Note that in the case of the configuration of FIG. 5, or other type of electrode where only a portion of the electrode is creating the corona, the contoured blunt electrode should preferably be a constant or nearly constant distance from the corona region of the sharp electrode, and not necessarily all portions of the electrode.
Another possible embodiment involving a plurality of individual point-type corona electrodes is shown in FIG. 6. As shown in FIG. 6, an electrostatic gas pump 600 includes contoured blunt electrodes 602 that are configured in sets of four fins that together resemble the inside portion of a hollow sphere facing the respective corona electrode 604. While different in configuration and layout as the pumps in FIGS. 2 and 3, the operating concept is the same as in the wire-type electrodes described earlier. The contoured surfaces of the blunt electrodes 602 are a constant or near constant distance from the corona creating region of the point-type corona electrodes 604, except that the overall contour of the blunt electrode is spherical instead of cylindrical as in FIGS. 1-3.
The present inventors recognize that the contoured electrode described herein, by virtue of its geometry, creates the maximum the electric field enhancement at the corona electrode. High field enhancement gives this invention many advantageous attributes. First, it results in a lower turn-on voltage for a given gas gap and corona electrode size. Second, since the gas only breaks down where the electric field is high, a high field enhancement confines the ionization region closely to the corona electrode. This makes it more difficult for the corona discharge to transform to an arc as the voltage is increased. Thus, the voltage operating window is larger. Delay of arcing as voltage increases also leads to a higher ion density from a given corona electrode. This increases the pumping power of the device since pumping power is proportional to the voltage multiplied by ion current.
A second major advantage of the contoured electrode is that the electric field lines between the corona electrode and the contoured electrodes are better confined to the region in between the electrodes. The field lines from neighboring electrodes do not interfere. Corona electrodes can be place together more closely and still have the high field enhancement necessary to produce a high quality corona discharge and gas flow. The higher density of electrodes leads to a larger ion current in a given area and results in larger gas flow rates.
Yet another advantage of the contoured electrode is that with pumps having a plurality of corona electrodes, for example those shown in FIGS. 2 and 3, the spacing between the blunt electrode fins has very little effect on the ion current and pumping power. This gives the designer the freedom to set that spacing such that it optimizes other parameters, such as flow rate, heat transfer and such.
Although the present invention has been particularly described with reference to the preferred embodiments thereof, it should be readily apparent to those of ordinary skill in the art that changes and modifications in the form and details may be made without departing from the spirit and scope of the invention. It is intended that the appended claims encompass such changes and modifications.

Claims

1. An apparatus comprising:

a corona electrode; and

a blunt electrode separated from the corona electrode by a gas gap;

wherein the blunt electrode has a neutralizing surface facing the corona electrode that is contoured so that respective distances between a point on the corona electrode and all points of the neutralizing surface directly underlying the point are substantially constant.

2. An apparatus according to claim 1, wherein the neutralizing surface is further contoured to maximize an electric field enhancement at the corona electrode and increase a maximum power output of a corona discharge occurring in the gas gap.

3. An apparatus according to claim 1, wherein the neutralizing surface faces the corona electrode for a given length thereof, the contour defining a partial hollow cylinder having a height corresponding to the given length and a radius corresponding to the substantially constant distance.

4. An apparatus according to claim 1, wherein the blunt electrode includes a plurality of fins, each fin having a neutralizing surface that faces the corona electrode for a respective given length thereof, the contour of each neutralizing surface defining a partial hollow cylinder having a height corresponding to the respective given length and a radius corresponding to the substantially constant distance.

5. An apparatus according to claim 1, wherein the corona electrode is comprised of a point protruding from a supporting member, and wherein the blunt electrode includes a plurality of fins, each fin having a neutralizing surface that faces the point, the contour of each neutralizing surface defining a partial hollow cylinder having a radius corresponding to the substantially constant distance, and wherein the contours of the plurality of fins collectively define a partial sphere having the radius.

6. An apparatus according to claim 1, wherein the corona electrode is comprised of a plurality of points protruding from a supporting member, and wherein the blunt electrode includes a plurality of fins, each fin having a neutralizing surface that faces a respective one of the points, the contour of each neutralizing surface defining a partial hollow cylinder having a radius corresponding to the substantially constant distance.

7. An electrostatic gas pump apparatus comprising:

a plurality of corona electrodes; and

a plurality of blunt electrode fins,

wherein each blunt electrode fin has a neutralizing surface facing certain of the corona electrodes, the neutralizing surface being contoured so that respective distances between a point on the corona electrode and all points of the neutralizing surface directly underlying the point are substantially constant.

8. An apparatus according to claim 7, wherein the neutralizing surface faces the corona electrode for a given length thereof, the contour defining a partial hollow cylinder having a height corresponding to the given length and a radius corresponding to the substantially constant distance.

9. An apparatus according to claim 7, wherein each neutralizing surface of each of the fins faces a respective one of the corona electrodes for a respective given length thereof, the contour of each neutralizing surface defining a partial hollow cylinder having a height corresponding to the respective given length and a radius corresponding to the substantially constant distance, the height corresponding to a thickness of the fin.

10. An apparatus according to claim 9, wherein the corona electrodes are arranged substantially parallel to each other and separated by a corona electrode spacing.

11. An apparatus according to claim 9, wherein the corona electrodes are arranged substantially parallel to each other and separated by a corona electrode spacing, and the fins are arranged substantially parallel to each other, and substantially perpendicular to the corona electrodes, and separated by a fin spacing.

12. An apparatus according to claim 11, wherein the fin spacing between the fins define corresponding channels for the flow of gas caused by an electrostatic discharge between the electrodes.

13. An apparatus according to claim 11, further comprising walls that are arranged parallel to the corona electrodes and connect the blunt electrode fins, each wall separating a corresponding adjacent pair of neutralizing surfaces in each of the fins.

14. An apparatus according to claim 13, wherein the fin spacing between the fins and the walls between the adjacent pairs of neutralizing surfaces define corresponding channels for the flow of gas caused by an electrostatic discharge between the electrodes.

15. An apparatus according to claim 7, wherein the neutralizing surface is contoured so as to isolate neighboring corona electrodes, preventing their electric fields from interfering with one another and thereby increasing the pumping power of the electrostatic pump apparatus.

16. An electrostatic pump apparatus, comprising:

an array of corona discharge regions, wherein each discharge region includes a contoured neutralizing surface of a blunt electrode.

17. An apparatus according to claim 16, wherein the array comprises a plurality of corona electrodes arranged substantially in parallel to each other and a plurality of blunt electrode fins arranged substantially in parallel to each other and substantially perpendicular to the corona electrodes, the corona discharge regions being respectively located at intersections between the corona electrodes and blunt electrode fins.

18. An apparatus according to claim 17, wherein the neutralizing surface in each corona discharge region faces the corona electrode and is contoured so that respective distances between a point on the corona electrode and all points of the neutralizing surface directly underlying the point are substantially constant.

19. An apparatus according to claim 17, wherein the neutralizing surface in each corona discharge region is contoured so as to isolate it from neighboring corona discharge regions, preventing their electric fields from interfering with one another and thereby increasing the pumping power of the electrostatic pump apparatus.

20. An apparatus according to claim 17, further comprising walls that are arranged parallel to the corona electrodes and connect the blunt electrode fins, each wall separating a corresponding adjacent pair of neutralizing surfaces in each of the fins.