Dielectric barrier discharge device

Abstract

We provide a dielectric barrier discharge device. [Solution] The dielectric barrier discharge device comprises a dielectric nozzle surrounding an internal cavity. The dielectric nozzle has a first end, a second end opposite the first end, an inner side, and an outer side opposite the inner side. The internal cavity extends from the first end to the second end and has an open end at the second end of the dielectric nozzle. A first electrode is provided on the outside, and a second electrode is provided inside the internal cavity. A gas inlet is fluidly connected to the internal cavity, and a gap is provided between the second electrode and the inner side. The size of this gap may vary along the second electrode. A power supply is electrically connected to the first electrode and the second electrode.

Description

Technical Field

[0001] The present disclosure relates to the configuration of a dielectric barrier discharge device.

Background Art

[0002] A dielectric barrier discharge (DBD) device includes two electrodes, one of which is covered with a dielectric barrier material. The electrodes are connected to an AC power source that drives a discharge in the gap between the electrodes. The discharge causes ionization of the gas every half cycle of the electricity. The resulting plasma interacts with the surrounding air or other gas medium to induce a net flow called an ion wind or an electric wind. DBD devices are used, for example, as ozone generators, ultraviolet lamps, plasma generators, and aerodynamic flow control devices.

Summary of the Invention

Problems to be Solved by the Invention

[0003] Therefore, an object of the present invention is to provide a dielectric barrier discharge device.

Means for Solving the Problems

[0004] A dielectric barrier discharge device according to an example of the present disclosure includes a dielectric nozzle surrounding an internal cavity. The dielectric nozzle has a first end, a second end opposite the first end, an inner side, and an outer side opposite the inner side. The internal cavity extends from the first end to the second end of the dielectric nozzle and has an open end at the second end of the dielectric nozzle. A first electrode is provided on the outer side, and a second electrode is provided in the internal cavity. A gas inlet is fluidly connected to the internal cavity, and a gap extending between the second electrode and the inner side is provided. This gap can vary in size along the second electrode. A power source is electrically connected to the first electrode and the second electrode.

[0005] The present disclosure can include one or more of the individual features disclosed above and / or below alone or in any combination.

[0006] Various features and advantages of this disclosure will become apparent to those skilled in the art from the following detailed description. In this disclosure, the same reference numeral indicates the same element as where applicable, and reference numerals that are 100 or a multiple of 100 indicate a modified element that is understood to encompass the same features and advantages as the corresponding element. The drawings accompanying the detailed description are briefly described below. [Brief explanation of the drawing]

[0007] [Figure 1] This diagram shows the coaxial configuration of a dielectric barrier discharge device. [Figure 2] This diagram shows the convergence-divergence configuration of a dielectric barrier discharge device, in which an electromagnet coil is incorporated into the convergence-divergence structure. [Figure 3] Figure 2 shows the apparatus along with the electric field vector and magnetic field vector. [Figure 4] This figure shows another example of a convergence-divergence configuration for a dielectric barrier discharge device with a bobbin for magnets. [Figure 5] This figure shows the metal foil of the first electrode of the apparatus shown in Figure 2. [Figure 6] Figure 4 is a three-dimensional cross-sectional view of the apparatus. [Figure 7] This is a diagram showing a dielectric barrier discharge device with a frustoconical electrode. [Figure 8] This is a diagram showing a dielectric barrier discharge device having a conical electrode. [Figure 9] Figures (A), (B), and (C) show dielectric barrier discharge devices equipped with second electrodes of different heights. [Figure 10] Figures (A), (B), and (C) show dielectric barrier discharge devices equipped with first electrodes of different lengths. [Figure 11] This figure shows a dielectric barrier discharge device equipped with axial electrodes. [Modes for carrying out the invention]

[0008] Figure 1 shows a cross-sectional view of a dielectric barrier discharge device 20. In this example, device 20 is used as a thruster 22. The device in the example described later is also used as a thruster. This device is not limited to such applications and can be used in many other applications, such as a synthetic jet actuator for boundary layer control, an ozone generator, an ultraviolet lamp, and a plasma generator, but is not limited to these.

[0009] The apparatus 20 comprises a dielectric nozzle 24 having opposing first (inner) and second (outer) sides 24a / 24b and first and second opposing ends 24c / 24d. The second end 24d is open. For example, the dielectric nozzle 24 is made from a solid dielectric material, which is an electrical insulator that polarizes by the movement of positive and negative charges and net displacement when an electric field is applied. Many ceramics, mica, and quartz glass are considered dielectric materials. Other examples of dielectric materials include, but are not limited to, aluminum nitride, boron nitride, alumina, and borosilicates. A "dielectric nozzle" refers to a conduit structure made of a dielectric material that guides or modifies the flow of plasma by its shape and dielectric properties.

[0010] A first electrode 26 is provided on the outer surface 24b of the dielectric nozzle 24. For example, the first electrode 26 is a conductive metal foil wound around the dielectric nozzle 24. Both the first electrode 26 and the dielectric nozzle 24 are cylindrical with respect to the nozzle central axis A and surround an internal cavity 28. The internal cavity 28 extends from the first end 24c to the second end 24d of the dielectric nozzle 24.

[0011] A second electrode 30 is provided in the internal cavity 28. In this example, the second electrode 30 has a cylindrical portion 30a centered on an axis A that is coaxial with the dielectric nozzle 24 and the first electrode 26. The first electrode 26 also includes an electrode post portion 26a, which includes a wire 26b housed in a dielectric shell 26c. The post portion 26a is positioned along axis A, coaxial with the cylindrical portion 30a and the dielectric nozzle 24.

[0012] The cylindrical portion 30a is positioned spaced apart from the inner surface 24a of the dielectric nozzle 24, and a gap 32 is formed between the second electrode 30 and the inner surface 24a. In this example, the gap 32 is an annular region centered on axis A and has a constant cross-sectional area along the length direction of the cylindrical portion 30a (in a radial plane perpendicular to axis A).

[0013] The dielectric nozzle 24 and the second electrode 30 are mounted by a backing plate 34. The backing plate 34 closes the first end 24c of the dielectric nozzle 24 and has one or more gas inlets 34a that are fluidly connected to the internal cavity 28. Although not shown, a gas source is fluidly connected to the backing plate 34 and supplies working gas to the internal cavity 28 through one or more gas inlets 34a. The working gas varies depending on the end application of the apparatus 20 and may be, but is not limited to, air, argon, hydrazine, or a mixture of these gases. The backing plate 34 also surrounds the axial side of the internal cavity 28, but the opposite axial end of the internal cavity 28 is open at the second end 24d of the dielectric nozzle 24.

[0014] The power supply 36 is electrically connected to the electrodes 26 / 30. For example, the power supply 36 is an AC power supply, but it may also include a DC bias power supply. In this example, the first electrode 26, including the post portion 26a, is located on the ground side of the circuit, and the second electrode, including the cylindrical portion 30a, is located on the voltage supply side of the circuit. When the power supply 36 is started by receiving a working gas, it generates plasma in the cavity 28. As indicated by arrow 38, the plasma is emitted from the open end 24d of the dielectric nozzle 24. All the devices described herein can be used with a variety of different working gases, thereby enabling multimode operation of the devices across a variety of thruster technologies.

[0015] Figure 2 shows a cross-sectional view of a selected portion of another example of apparatus 120. In this example, the dielectric nozzle 124 has a convergent-divergent shape, rather than being cylindrical like apparatus 20 in Figure 1. For example, the dielectric nozzle 124 defines a first section 142, a second section 144, and an axial throat 146 between the first section 142 and the second section 144. The first section 142 converges from the first end 24c to the throat 146. The second section 144 diverges from the throat 146 to the second end 24d. The throat 146 is the minimum cross-sectional area of ​​the internal cavity 128. In the illustrated example, the throat 146 is discretely formed with peaks at the vertices of the walls of the dielectric nozzle 124, but instead, the throat 146 could be widened axially in a "strip-like" shape by broadening the peaks. The first section 142 forms a convergence angle A1 with respect to the nozzle central axis A, and the second section 144 forms a divergence angle A2 with respect to the nozzle central axis A. The angles A1 / A2 can be adjusted to facilitate plasma focusing. For example, in absolute angles, the convergence angle A1 is equal to, greater than, or less than the divergence angle A2.

[0016] The first electrode 126 is positioned on the outside 24b of the dielectric nozzle 124, and the second electrode 130 is positioned inside the internal cavity 128. In the illustrated example, the second electrode 130 is conical, more specifically cylindrical-conical. The term "cylindro-conical" refers to a shape in which a cone sits on top of a cylinder, and the diameter of the base of the cone is equal to the diameter of the cylinder. Therefore, the second electrode 130 has a cylindrical portion 131a that functions as the electrode base in the backing plate 34, and a conical portion 131b having an apex 131c. The combination of the shape of the second electrode 130 and the shape of the converging portion 142 of the dielectric nozzle 124 defines a gap 132 between the inside 24a of the dielectric nozzle 124 and the second electrode 130, the gap having a size (cross-sectional area) that changes along the axial direction of the second electrode 130. For example, the gap 132 is largest at the cylindrical portion 131a, and its size decreases continuously from the conical portion 131b to the throat 146. The change in the size of the gap 132, particularly the gradual narrowing of the gap 132 towards the apex 131c, plays a role in focusing the generated plasma to the throat 146 via an electron pressure gradient, thereby promoting an improvement in the power density and collimation (and consequently the plasma acceleration efficiency) of the generated plasma.

[0017] Furthermore, as shown in this example, the second electrode 130 extends through the throat 146 from the first section 142 to the second section 144. Only a short portion of the second electrode 130 extends through the throat 146. For example, the radial plane passing through the throat 146 intersects the second electrode 130 for a percentage of its total axial length. Such a configuration helps to further narrow the gap 132 in the throat 146, thereby allowing for further plasma focusing.

[0018] The device 120 also includes a magnet 140 that provides a magnetic field on the outside 24b of the dielectric nozzle 124 to accelerate the plasma discharged from the opening end 24d of the dielectric nozzle 124. The magnet 140 provides a magnetic field that serves to accelerate the plasma discharged from the opening end 24d of the dielectric nozzle 124. For example, the magnetic field generated by the magnet 140 captures the plasma downstream of the throat 146, thereby helping to reduce the loss of plasma due to neutralization inside the dielectric nozzle 124. The magnet 140 includes a coil 140a that surrounds the dielectric nozzle 124. In this example, the dielectric nozzle 124 functions as a bobbin around which the coil 140a is wound. In this regard, the magnet 140 is disposed within a triangular region defined by the inclination of the walls forming the sections 142 / 144 on the outside 24b of the dielectric nozzle 124. Thus, since the magnet 140 fits within the envelope of the outer peripheral contour of the dielectric nozzle 124, the device 120 is compact.

[0019] FIG. 3 again shows the device 120 (the elements are not labeled), where the electric field vector E and magnetic field vector B with respect to the plasma P are shown. The diverging portion 144 of the dielectric nozzle 124 functions as a discrete discharge region for the generated plasma P. The diverging portion 144 follows the diverging shape of both the electric field E and the magnetic field B starting from near the throat 146. Thus, the diverging portion 144 reduces the wall interaction with the plasma and at the same time improves the collimation of the plasma beam. Further, the magnet 140 bipolar diffuses ions and electrons as a downstream pair and finally separates them from the magnetic field. In contrast, in the "coaxial" configuration of the device 20 in FIG. 1, since the cross-sectional areas of the dielectric nozzle 24 and the gap 32 are constant respectively, the electric and magnetic fields diverge towards the wall where the plasma is neutralized, so there is a possibility of increased wall losses in the acceleration region.

[0020] The converging-diverging configuration of the device 120 in FIGS. 2 and 3 can provide greater electrical insulation and thus also improve performance compared to the "coaxial" configuration of the device 20 in FIG. 1. For example, the second electrode 30 with electrode sections 30a and 30b has a more complex shape and may cause an unwanted discharge in the gas passage flowing into the backing plate 34 and / or the cavity 28, resulting in a reduction in the power of the generated plasma plume emitted from the dielectric nozzle 24. However, the single second electrode 130 within the device 120 avoids such insulation complexity and thus reduces unwanted discharges, thereby maintaining more of the power of the generated plasma.

[0021] FIG. 4 shows another exemplary device 220 that is the same as the device 120 except for the magnet 240 (see also the cross-sectional 3D rendering of the device 220 in FIG. 6). Similar to the magnet 140, the magnet 240 is disposed outside the dielectric nozzle 124 at 24b. However, the device 220 further includes a bobbin 250. The bobbin 250 includes a cylinder 252 having a first flange 254a at a first axial end and a second flange 254b at a second axial end. The magnetic coil 240a is wound around the cylinder 252 of the bobbin 250. The dielectric nozzle 124 is disposed inside the cylinder 252 of the bobbin 250. The dielectric nozzle 252 is removable from the cylinder 252 if desired, for example, the dielectric nozzle 124 can be replaced with a dielectric nozzle of a different shape (e.g., a nozzle with different angles A1 / A2). However, depending on the end-use product, nozzle replacement may not be necessary, and in that case, the dielectric nozzle 124 can be more permanently fixed within the cylinder 252.

[0022] Therefore, the bobbin 250 and coil 240a are located outside the triangular region defined on the outer side 24b of the dielectric nozzle 124. This configuration may result in a larger "footprint" than when the coil 240a is located within the triangular region, but it may offer manufacturing advantages due to the integration of the bobbin 250. For example, the bobbin 250 and backing plate 34 can be formed from a single monolithic part, thereby reducing the number of parts and assembly steps.

[0023] Figure 5 shows a portion of the first electrode 126 separated from the apparatus 120. The outer surface 24b of the dielectric nozzle 124 is a double frustum of a cone, with one frustum formed by the wall of the converging section 142 and the other frustum formed by the wall of the diverging section 144. The first electrode 126 is formed from, but is not limited to, a metal foil 127. The foil 127 is supplied as a sheet and can then be cut to match the shape of the frustum. For example, the foil 127 is cut into arc-shaped segments 129, and these segments are joined together to correspond to the shape of the frustum, thereby allowing the foil 127 to be wrapped around the dielectric nozzle 124 without wavy or twisted. In this way, the foil 127 is laid flat on the outer surface 24b, promoting uniformity of the generated electric field.

[0024] Figure 7 shows another example of a dielectric barrier discharge apparatus 320. Similar to apparatus 20, apparatus 320 has a cylindrical dielectric nozzle 24, but the second electrode 330 in the internal cavity 28 is a frustoconical shape with sloping sides. Coupled with the walls of the dielectric nozzle 24, this frustoconical shape provides a variable-size gap 332 that functions similarly to the gap 132 described above. Also in this example, the first electrode 26 is a copper mesh and can be sealed with a polymer material such as epoxy.

[0025] The axial lengths of the magnets described herein can ultimately be selected, at least in part, based on the shape of the magnetic field B for more optimal plasma acceleration. However, in the case of a convergent-divergent configuration, a magnet that completely overlaps the second electrode in the axial direction is considered to provide a divergent magnetic field shape corresponding to the divergent portion 146 of the nozzle 124, as already described above.

[0026] Figure 8 shows another exemplary apparatus 420 having the elements described above. However, in this example, the second electrode 430 is perfectly conical and provides a variable-size gap 432 that functions similarly to the variable-size gap 132 described above.

[0027] Figures 9A, 9B, and 9C show additional examples of the electric field profile in the apparatus 420 and how to adjust the resulting plasma acceleration force, and these teachings can be applied to other examples herein. For example, the dielectric nozzle 24 defines the cylinder height (hc), and the second electrode 430 defines the electrode height (h2) from the cone base 430a to the apex 430b, where the electrode height (h2) is lower than the cylinder height (hc). For example, in Figure 9A, the electrode height (h2) is at least twice as low as the cylinder height (hc). In Figure 9B, the electrode height (h2) is more than once as low as the cylinder height (hc), and at most 1.3 times lower. In Figure 9C, the electrode height (h2) is equal to the cylinder height (hc).

[0028] Furthermore, as shown in Figures 10A, 10B, and 10C, the axial length and position of the first electrode 26 can be changed to adjust the electric field shape. In Figure 10A, the first electrode 26 has the same spread as the dielectric cylinder 24. In Figure 10B, the first electrode 26 is positioned on the open end 24d side of the dielectric nozzle 24 and extends from the open end 24d to about one-third of the length of the dielectric nozzle 24. In Figure 10C, the first electrode 26 is positioned on the open end 24d side of the dielectric nozzle 24 and extends from the open end 24d to about two-thirds of the length of the dielectric nozzle 24. Similar to the magnetic field B, the length and axial position of the first electrode 26 can ultimately be selected, at least in part, based on the shape of the electric field E for more optimal plasma acceleration.

[0029] Figure 11 shows a side view of another example of apparatus 520. Apparatus 520 is similar to apparatus 320, but in this example, the first electrode 526 includes a plurality of electrode strips 527 arranged circumferentially spaced around the outer surface 24b of the dielectric cylinder 24. These strips 527 are axially elongated (relative to the central axis of the dielectric cylinder 324) and uniformly spaced apart circumferentially from each other by a distance longer than the width of the strip 527. Apparatus 520 can be used to pyrolyze and accelerate hydrazine or other liquid-storable propellants. The number of strips 527, the width of the strips, and the spacing between the strips can also be adjusted to control the density of the current arc filament. For example, the apparatus of the present invention can be used as an alternative to catalyst-based hydrazine configurations to pyrolyze hydrazine in arc filaments generated within the apparatus and to add electrostatic or electromagnetic volume forces.

[0030] While the illustrated examples illustrate combinations of features, it is not necessary to combine all of them to realize the advantages of the various embodiments of this disclosure. In other words, a system designed according to the embodiments of this disclosure does not necessarily include all the features shown in any of the figures, or all the parts schematically shown in the figures. Furthermore, selected features of one embodiment can be combined with selected features of another embodiment.

[0031] The above description is illustrative and not limiting in nature. It will be apparent to those skilled in the art that variations and modifications to the examples disclosed will not necessarily deviate from this disclosure. The scope of legal protection granted by this disclosure can only be determined by considering the following claims.

Claims

1. A dielectric nozzle surrounding an internal cavity, having a first end, a second end opposite to the first end, an inner surface, and an outer surface opposite to the inner surface, wherein the internal cavity extends from the first end to the second end, and the internal cavity has an open end at the second end, The aforementioned outer upper first electrode, The second electrode in the internal cavity, A gas inlet fluidly connected to the aforementioned internal cavity, The gap extending between the second electrode and the inner surface, A power supply electrically connected to the first electrode and the second electrode, A dielectric barrier discharge device equipped with the following features.

2. The dielectric barrier discharge apparatus according to claim 1, characterized in that the size of the gap changes along the second electrode.

3. The dielectric barrier discharge apparatus according to claim 1, characterized in that, when the power supply is in operation, it generates plasma from the gas flowing into the internal cavity from the gas inlet, and the plasma is emitted from the open end of the internal cavity.

4. The dielectric barrier discharge apparatus according to claim 1, characterized in that the dielectric nozzle is arranged around a central nozzle axis extending from the first end to the second end, the dielectric nozzle defines a first section, a second section, and an axial throat between the first section and the second section, the first section converges from the first end toward the throat, the second section diverges from the throat toward the second end, and the throat is the minimum cross-sectional area of ​​the internal cavity.

5. The dielectric barrier discharge apparatus according to claim 3, characterized in that the second electrode is conical and extends from the first section to the second section through the throat.

6. The dielectric barrier discharge apparatus according to claim 1, characterized in that the second electrode is conical in shape.

7. The dielectric barrier discharge apparatus according to claim 1, characterized in that the second electrode is cylindrical-conical in shape.

8. The dielectric barrier discharge apparatus according to claim 1, further comprising an electromagnet on the outside of the dielectric nozzle, wherein the electromagnet includes a coil surrounding the dielectric nozzle.

9. The dielectric barrier discharge apparatus according to claim 8, further comprising a bobbin having a cylinder with a first flange at a first axial end and a second flange at a second axial end, wherein the coil is wound around the cylinder of the bobbin.

10. The dielectric barrier discharge apparatus according to claim 9, characterized in that the dielectric nozzle is arranged inside the cylinder of the bobbin.

11. The dielectric barrier discharge apparatus according to claim 8, characterized in that the coil is wound around the dielectric nozzle.

12. The dielectric barrier discharge apparatus according to claim 1, characterized in that the dielectric nozzle is arranged around a central nozzle axis extending from the first end to the second end, the dielectric nozzle is cylindrical, the second electrode includes a cylindrical portion, and the dielectric nozzle and the cylindrical portion are coaxial around the central nozzle axis.

13. The dielectric barrier discharge apparatus according to claim 12, wherein the first electrode further comprises an electrode post portion including a wire housed within a dielectric shell, and the electrode post portion is arranged along the central nozzle axis such that it is coaxial with the dielectric nozzle and the cylindrical portion.

14. The dielectric barrier discharge apparatus according to claim 1, characterized in that the second electrode is frustoconical in shape.

15. The dielectric barrier discharge apparatus according to claim 1, characterized in that the dielectric nozzle defines a nozzle height (h1) in the axial direction, and the second electrode defines an electrode height (h2) from the base to the tip in the axial direction, wherein the electrode height (h2) is smaller than the nozzle height (h1).

16. The dielectric barrier discharge apparatus according to claim 15, characterized in that the first electrode is positioned toward the second end of the dielectric nozzle.

17. The dielectric barrier discharge apparatus according to claim 15, characterized in that the first electrode is cylindrical.

18. The dielectric barrier discharge apparatus according to claim 1, characterized in that the first electrode includes a plurality of electrode strips arranged at circumferential intervals around the outer edge of the dielectric nozzle.

19. The dielectric barrier discharge apparatus according to claim 1, further comprising a magnetic ring provided on the dielectric nozzle and surrounding the second end.

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