Electrohydrodynamic control device

Abstract

A fluidic device is disclosed, comprising an enclosed passage that is adapted to convey a circulating fluid. The enclosed passage comprises a flow unit having a first electrode and a second electrode offset from the first electrode in a downstream direction of a flow of the circulating fluid. The first electrode is formed as a grid structure and arranged to allow the circulating fluid to flow through the first electrode. The fluidic device may be used for controlling or regulating the flow of the fluid circulating in the enclosed passage, and thereby act as a valve opening, reducing or even closing the passage.

Claims

1. An electrohydrodynamic (EHD) device, comprising: an enclosed passage adapted to convey a circulating dielectric liquid; and a flow unit arranged in the enclosed passage, wherein the flow unit comprises: a first electrode; and a second electrode offset from the first electrode in a downstream direction of a flow of the circulating dielectric liquid, the first electrode and the second electrode being connectable to a voltage source; wherein the first electrode is formed as a grid structure and arranged to allow the circulating dielectric liquid to flow through the first electrode; wherein at least a portion of the enclosed passage is adapted to provide a thermal connection to allow transfer of heat between the circulating dielectric liquid and a surrounding of the EHD device; and wherein the enclosed passage defines a closed loop in which the circulating dielectric liquid circulates.

2. The EHD device of claim 1, wherein: the first electrode comprises bridges and joints forming the grid structure; at least a portion of at least one of the bridges has a maximum height in a direction parallel to a direction of the flow and a maximum gauge in a direction orthogonal to the direction of the flow; and said maximum height is larger than said maximum gauge.

3. The EHD device of claim 1, wherein the flow unit is arranged to cover at least part of a cross section of the enclosed passage.

4. The EHD device of claim 1, wherein the flow unit is arranged to cover an entire cross section of the enclosed passage.

5. The EHD device of claim 1, wherein the EHD device comprises an array of flow units arranged to have a lateral extension in a common lateral plane, wherein a downstream side of a first one of the flow units is in fluid communication with an upstream side of a second one of the flow units so as to allow the circulating dielectric liquid to pass through said first and second one of the flow units.

6. The EHD device of claim 1, wherein the enclosed passage is adapted to be thermally connected to a heat exchanger.

7. The EHD device of claim 6, wherein the heat exchanger is a heat sink or a heat source.

8. The EHD device of claim 1, wherein at least a portion of the enclosed passage is formed as a tube.

9. The EHD device of claim 1, wherein the second electrode is formed as a grid structure.

10. The EHD device of claim 1, wherein at least one of the first electrode and the second electrode comprises a suspension structure arranged to absorb thermally induced deformations in the first electrode or the second electrode, respectively.

11. The EHD device of claim 1, wherein the enclosed passage comprises a first chamber in fluid communication with a second chamber; and wherein the flow unit is adapted to be disposed in the first chamber or the second chamber of the enclosed passage.

12. The EHD device of claim 5, wherein the enclosed passage comprises a first chamber in fluid communication with a second chamber; and wherein the flow unit is adapted to be disposed in the first chamber or the second chamber of the enclosed passage.

13. A method of controlling a circulating dielectric liquid in an electrohydrodynamic (EHD) device, the method comprising: activating a flow unit so as to induce a flow of the circulating dielectric liquid in the EHD device, wherein the flow unit is arranged in an enclosed passage that is adapted to convey the circulating dielectric liquid, the flow unit comprising a first electrode and a second electrode that is offset from the first electrode in a downstream direction of a flow of the circulating dielectric liquid, the first electrode and the second electrode being connectable to a voltage source, wherein the first electrode is formed as a grid structure and is arranged to allow the circulating dielectric liquid to flow through the first electrode; wherein at least a portion of the enclosed passage is adapted to provide a thermal connection to allow transfer of heat between the circulating dielectric liquid and a surrounding of the EHD device; and wherein the enclosed passage defines a closed loop in which the circulating dielectric liquid circulates; and deactivating the EHD device so as to impede the flow of the circulating dielectric liquid in the EHD device.

14. The method of claim 13, wherein activating the flow unit comprises applying a voltage difference between the first electrode and the second electrode.

15. The method of claim 13, wherein the flow unit comprises: the first electrode comprises bridges and joints forming the grid structure; at least a portion of at least one of the bridges has a maximum height in a direction parallel to a direction of the flow and a maximum gauge in a direction orthogonal to the direction of the flow; and said maximum height is larger than said maximum gauge.

16. The method of claim 13, wherein deactivating the EHD device comprises turning off the flow unit, and the EHD device is in an operational mode when the flow through the flow unit is reduced or eliminated.

17. The method of claim 14, wherein deactivating the EHD device comprises reducing or removing a voltage difference between the first electrode and the second electrode.

18. The method of claim 14, wherein the first electrode comprises bridges and joints forming the grid structure; at least a portion of at least one of the bridges has a maximum height in a direction parallel to a direction of the flow and a maximum gauge in a direction orthogonal to the direction of the flow; and said maximum height is larger than said maximum gauge.

19. The method of claim 13, wherein the enclosed passage is adapted to be thermally connected to a heat exchanger and the heat exchanger comprises at least one of a heat sink or a heat source.

20. The method of claim 13, wherein the enclosed passage comprises a first chamber in fluid communication with a second chamber; and wherein the flow unit is adapted to be disposed in the first chamber or the second chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of embodiments of the present invention. Reference will be made to the appended drawings, on which:

(2) FIG. 1 schematically illustrates a fluidic device comprising an enclosed passage and a flow unit according to an embodiment of the invention;

(3) FIGS. 2a and b are schematic cross sections of a fluidic device according to some embodiments;

(4) FIG. 3 is a schematic diagram of a fluidic device according to an embodiment, wherein the enclosed passage is thermally connected to heat exchangers;

(5) FIG. 4 is a schematic perspective view of a first and second electrode of a flow unit according to an embodiment;

(6) FIGS. 5a-d show cross sectional portions of the first and second electrode of a flow unit according to an embodiment;

(7) FIGS. 6a and b are schematic views of an array of flow units according to embodiments of the invention;

(8) FIGS. 7a and b are top views of an electrode of a flow unit provided with a deformation structure according to embodiments of the invention; and

(9) FIG. 8 is a cross section of a flow unit according to an embodiment, comprising a stack of a plurality of electrodes.

(10) All the figures are schematic, generally not to scale, and generally only show parts which are necessary in order to elucidate the invention, whereas other parts may be omitted or merely suggested.

DETAILED DESCRIPTION OF EMBODIMENTS

(11) FIG. 1 shows a fluidic device 1 comprising an enclosed passage 200, e.g. forming a loop, and a flow unit 100. The enclosed passage 200 may e.g. be formed as a tube or channel wherein the end is connected to the beginning so as to allow for a continuous and repeated flow of a circulating fluid in a closed loop system. The flow unit 100 may be arranged to cover an entire cross section of the enclosed passage 200, as indicated in FIG. 1, or to cover only a part of the cross section so as to allow fluid to pass at the side of the flow unit 100. By arranging the flow unit 100 to cover the entire cross section of the passage 200, all fluid has to pass through the flow unit 100 in order to circulate. This allows for an improved control of the flow.

(12) The fluidic device 1 may be operated in at least two different states: an activated state, and a deactivated or off-state. In the activated state, the flow unit 100 may be operated by means of a potential difference inducing a flow through the flow unit 100 and hence a circulating flow in the enclosed passage 100. In the off-state, the flow 100 may be operated at a zero potential difference, or at a potential difference resulting in a reduced or zero net flow of fluid through the flow unit 100, so as to impede or even stop the circulation of the fluid in the enclosed passage. The flow unit 100 may hence be operated as a control valve regulating the flow in the enclosed passage.

(13) FIGS. 2a and b show a fluidic device 1 according to embodiments that may be similarly configured as the embodiment discussed in connection with FIG. 1. According to the embodiment depicted in FIG. 2a, the enclosed passage may be defined by a first chamber 210 and a second chamber 220 that are separated by a dividing wall 215 or septum. The dividing wall 215 may comprise gaps or local passages connecting the first chamber 210 and the second chamber 220 with each other, thereby defining a closed loop in which the fluid may circulate. The fluid may circulate through the first chamber 210, enter the second chamber 220 via one of the gaps in the dividing wall 215, passing through the second chamber 220 and enter the first chamber via the second one of the gaps in the wall 220 (the circulating fluid is indicated by arrows in FIG. 2a).

(14) At least one of the chambers, such as e.g. the first chamber 210 may comprise a flow unit 100 as previously described. The flow unit 100 may be configured to induce a flow in the fluid when operated in the activated state, and to impede or reduce a flow in the fluid when operated in a deactivated state or at a reduced voltage difference as compared to the activated state. Thus, the flow unit 100 may be used for affecting or controlling the circulation of the fluid between the first chamber 210 and the second chamber 220.

(15) Alternatively, or additionally, the enclosed passage 200 may form a single chamber as shown in FIG. 2b. In such case, the flow may circulate within the chamber defined by the enclosed passage, as indicated by the arrows. The flow unit 100 may be arranged to induce the flow, preferably at a position relatively close or adjacent to a wall portion of the chamber. From such position, the flow unit 100 may induce a motion or flow of the fluid in a direction along the wall portion, thereby causing the fluid to circulate accordingly.

(16) FIG. 3 is a schematic representation of a system or fluidic device according to an embodiment that may be similarly configured as any one of the previously described embodiments. In FIG. 3, the enclosed passage is represented by line 200 and the flow unit by the box 100. The enclosed passage may be connected to one or several heat exchangers C, H allowing heat to be added or removed from the fluid. The connection may e.g. be thermal and/or fluidic, and the heat transferring means C, H may e.g. comprise a heat sink C and/or a heat source H.

(17) FIG. 4 shows an example of a flow unit 100 of a fluidic device according to embodiments similar to the embodiments of FIGS. 1 to 3. The flow unit 100 may comprise a first electrode, or emitter 110, comprising bridges 111 and joints 112 forming a grid that allows a fluid to flow through the emitter 110. The emitter 110 may have a lateral extension in a plane perpendicular to the intended flow direction, which is indicated by an arrow in FIG. 4. According to this embodiment, the second electrode, or collector 120, comprises bridges 121 and joints 122 that are arranged in a similar grid the one described with reference to the emitter 110. Consequently, the collector 120 may have a lateral extension in a plane perpendicular to the direction of the flow such that both the emitter 110 and the collector 120 are parallel to each other. Although not illustrates in FIG. 4, it will be appreciated that the second electrode 120 may be provided in other shapes and configurations than a grid. The second electrode 120 may e.g. be formed as, or comprise, one or several wires (which may have a main direction of extension in a plane essentially parallel with the first electrode 110) or pillars, needles, cylinders or rods that may be oriented e.g. along the direction of the flow.

(18) As indicated in the present figure, the emitter 110 and the collector 120 may be arranged spaced apart from each other in the flow direction by a positive distance d. The spacing may e.g. be maintained by a support arrangement, or grid spacer 130 (not shown in FIG. 4) being arranged between the emitter 110 and the collector 120. A relatively narrow gap d may be desirable since such gap may provide a relatively high electric field and thus enhance the electrohydrodynamic effect affecting the flow rate. The use of a grid spacer 130, which may have a well defined thickness, may advantageously reduce the risk of a shortcut or breakdown between the emitter 110 and the collector 120. As will be discussed in more detail below, the grid spacer 130 may e.g. have a similar configuration as the emitter 110 and/or the collector 120, i.e. comprising a grid of bridges 111, 121 and joints 112, 122. The grid spacer 130 may however have other configurations as well, such as e.g. being formed as a frame supporting the lateral edges of the emitter 110 and/or collector 120.

(19) It will also be realised that the grid may have one of a broad variety of shapes, wherein the edges and the joints e.g. may form a grating, a net, a hole pattern, a honeycomb structure, or other structures or patterns suitable for admitting a flow through the emitter 110 and/or collector 120.

(20) FIGS. 5a-d show cross sections of a portion of the emitter 110 and collector 120 of a flow unit similarly configured as the flow units described with reference to any one of the previous figures. The cross section is taken through three pairs of the bridges 111, 121 and along a plane parallel to the flow direction. According to this embodiment, the bridges 111 of the emitter 110 is arranged at a constant distance d from the bridges 121 of the collector 120, wherein the bridges 111 of the emitter have a maximum height h.sub.1 in the flow direction and a maximum gauge w.sub.1 in a direction orthogonal to the flow direction. The maximum height h.sub.1 is greater than the maximum gauge w.sub.1 so as to enable a relatively stable and rigid grid structure that can carry a relatively large load in the flow direction without a risk of deforming or collapsing, and yet have a relatively large open area allowing the fluid flow. According to this embodiment, the collector 120 may be formed of a grid having a similar relationship between the maximum height h.sub.2 and the maximum gauge w.sub.2 of the bridges 121. The ratio between the maximum height h.sub.1, h.sub.2 and the maximum gauge w.sub.1, w.sub.2 may e.g. be larger than 1, and more preferably larger than 2.

(21) The cross section of the bridges 111 of the emitter 110 may comprise a downstream portion 113 having a tapered shape forming an edge or a point 114 facing the collector 120. The tapered shape may e.g. be manifested as an edge or narrow end 114 extending along the downstream portion 113 of the bridge 111, or one or several protrusions having a shape conforming to e.g. a tip, needle, pyramid, dome, etc. As the emitter 110 is subjected to an electric potential difference, there may be an electric field concentration at the edge 114 of the tapered portion 113 which may facilitate or promote emission of electrons.

(22) Correspondingly, the portion of the bridges 121 of the collector 120 which face the emitter 110 may be provided with a dedicated shape or surface structure for enhancing collection of the emitted electrons. The bridges 121 and/or joints 122 of the collector 120 may e.g. be provided with a concave surface portion 123 increasing the surface area, and/or a structured surface comprising microscopic protrusions and/or recesses 124 increasing the active surface area. The structures 124 may e.g. be formed by molding, electroplating, surface treatment or by selectively adding and/or removing material by e.g. abrasive blasting, etching, milling, grinding, etc.

(23) FIG. 5a shows an example embodiment wherein the emitter 110 and the collector 120 are formed by screen printed Pt paste which has been sintered at about 800° C. so as to form a grid of bridges having a maximum height h.sub.1, h.sub.2 of about 100-200 μm and a maximum gauge w.sub.1, w.sub.2 of about 50 μm. As shown in FIG. 2b, the collector 120 has been equipped with a micro-structured surface portion 124, facing the emitter 110, by means of micro-blasting, wherein the surface is bombarded with sharp, micrometer-sized particles so as to increase the area of the surface.

(24) The flow units 100 in FIGS. 5b-d are similar to the flow unit 100 described with reference to FIG. 5a. According to FIG. 5b, the emitter 110 is further provided with a tapered upstream portion 117, forming a relatively sharp edge 118 directed towards the fluid flow so as to reduce the flow resistance and hence enhance the flow through the emitter 110. As indicated in FIGS. 5c and d, the collector 120 may further define channels 126 extending through the bridges 121 and/or the joints 122 (not shown) of the grid in order to decrease the flow resistance. The channels 126 may e.g. be effected by etching, such as e.g. reactive ion etching, wet etching, etc.

(25) FIG. 6a shows an array 10, or pump assembly, comprising a plurality of flow units 100. The flow units 100 may be arranged in a cell structure comprising a lid part 18 and a bottom part 19. In FIG. 6a, the outline of each cell 11 of the cell structure is indicated by a dashed line, whereas a cell 11 comprising a flow unit 100 is indicated by diagonal cross-hatching. The array 10 may comprise a first opening 12 for supply of fluid to the array 10. The first opening 12 may e.g. be arranged in the lid part 18. Further, a second opening 11 for outputting the fluid may be arranged in the bottom part 19 (indicated by a dashed line). According to the present embodiment, the array 10 may comprise e.g. five flow units 100 arranged in every second cell 11 of the cell structure. The flow units 100 may be arranged in a same direction or orientation such that the direction of flow of the fluid is essentially parallel for each one of the flow units 100. The cells 11 may be in fluid communication with one or several other cells 11 so as to allow a fluid to flow between the cells, preferably from one cell 11 to a neighbouring cell 11. During operation, a fluid may enter the cell structure via the first opening 12 and pass through a first flow unit 100 to a second flow unit 100 via neighbouring or intermediate cell 11, and eventually exit the cell structure through the second opening 14. Thus, the first opening 12 may be arranged, during operation, to receive fluid from an upstream side of the enclosed passage or loop, whereas the second opening 14 may be arranged to deliver fluid to a downstream side of the enclosed passage.

(26) FIG. 6b is a cross sectional side view of an array 10 that is similarly configured as the array 10 of FIG. 6a. The array 10 of flow units 100a, 100c, 100e is arranged in cells 11a, 11c, 11e defined by a lid part 18 and a bottom part 19 comprising cell separating walls 17. The cells 11a, 11b, 11c, 11d, 11e are connected to each other by means of channels 16 adapted to let a flow of fluid pass from a downstream side of a flow unit 100a, via an empty cell 11b, to an upstream side of a neighbouring flow unit 100c. Each flow unit 100a, 100c, 100e comprise a first electrode 110, such as e.g. a grid shaped emitter, and a second electrode 120, such as e.g. a metal plate provided with a through-hole.

(27) During operation, fluid may be entered through a first opening 12 and brought in fluid contact with the first electrode 110 of the flow cell 100a arranged in cell 11a. The fluid may be brought to flow by means of an electric field induced between the first electrode 110 and the second electrode 120, and continue through the channel 16 and the neighbouring, empty cell 11b to the next flow unit 100c. This process is repeated until the fluid reaches the second opening 14, through which it may exit the array 10.

(28) As indicated in FIGS. 6a and b, the flow units 100 may be oriented in the same direction, allowing the fluid to pass through each flow unit 100 in the same flow direction. Such arrangement of the flow units 100 may require a channel 16 and, according to the present example, an intermediate empty cell 11b, 11d for “reversing” the flow exiting at the downstream side of a first flow unit 100 before it can enter at the upstream side of a second flow unit 100.

(29) FIG. 7a shows a deformation structure 115 of a grid acting as e.g. an emitter 110 in a flow unit 100 according to embodiments of the present invention. The grid comprises bridges 111 and joints 112 in accordance with the previously described embodiments. As indicated in FIG. 7a, the deformation structure 115 is composed of bridges 111 that are curved in a plane normal to the flow direction. The curved shape may e.g. be formed during manufacturing of the bridges 111, or induced by e.g. thermal stresses occurring during use of the flow unit 100. The curved shape may also comprise a weakened portion, e.g. a portion having a reduced gauge, so as to make it easier to deform upon heat induced stresses. As the material of the grid may expand with an increasing temperature, the bridges 111 of the deformation structure 126 may be compressed by compressive forces acting in the length direction of the bridges 111. By length direction should be understood the direction of extension between a first joint and a second joint. Thereby the lateral expansion of the grid may be absorbed by the deformation structure 115 and thermally induced stresses reduced so that the emitter 110 other than the deformation structure 115 may keep its original shape despite thermal expansion. It should however be understood that the forces acting on the bridges 111 of the deformation structure 115 also, or alternatively, may be caused by e.g. a torsional moment, or torque, acting on the structure.

(30) FIG. 7b shows a similar deformation structure 125 as described with reference to FIG. 8a, wherein the deformation structure 125 is formed of bridges 121 of a collector 120 of a flow unit 100 according to an embodiment. It will however be understood that the flow unit 100 may be provided with deformation structures 115, 125 arranged in any one, or several, of the emitter 110, the collector 120, and the support structure 130.

(31) The deformation structure 115, 125 may be provided in an emitter 110 and/or collector 120 that is attached to a support structure 130, wherein in the support structure 130 may have a coefficient of thermal expansion (CTE) that differs from the CTE(s) of the emitter 110 and/or collector 120. In case the emitter 110 and/or collector 120 is/are rigidly attached to the support structure 130, the risk for deformations, such as e.g. bending and flexures, and damages such as fractures, disconnected or loosening joints etc. may be reduced by the deformation structure 115, 125. Thereby, reliability and useful life of the flow unit 100 may be increased.

(32) FIG. 8 shows a cross section of flow unit 200 comprising a stacked structure of three first electrodes 110 and three second electrodes 210 according to any one of the previously described embodiments. The cross section is taken along the direction of the flow (indicated by an arrow in FIG. 8) and across a respective bridge 111, 121 of the grids of the electrodes 110, 120. A grid spacer 130 is arranged to separate the emitter 110 and the collector 120 electrodes from each other in the direction of the flow. According to this embodiment, the emitters 110 and collectors 120 may comprise e.g. Pt, Au, or stainless steel forming e.g. the bulk material or a surface coating.

(33) The grid spacer 130 may e.g. be formed as a grid supporting the emitters 110 and the collectors 120. As illustrated in FIG. 8, the grid spacer 130 may comprise a peripheral frame of bridges to which the edge portions of the emitter 110 and the collector 120 are attached by e.g. welding, soldering or gluing. Alternatively, or additionally, the grid spacer 130 may comprise other spacing structures such as pillars or spacers, etc. The grid spacer 130 may also comprise one or several spacing members, such as e.g. additional bridges or pillars, supporting the centre portions of the emitter and collector. The grid spacer 130 may also comprise a deformation structure 115, 125 (not shown) similar to the deformation structure described with reference to FIGS. 8a and b.

(34) The spacing d of the emitter and collector may be determined by the height of the bridges of the grid spacer 130, which may hence determine the magnitude of the electric field induced between the emitter 110 and the collector 120. The distanced between the emitter 110 and the collector 120 may e.g. be within the range of 10 μm and 1000 μm.

(35) Further, the grid spacer 130 may comprise an alignment structure for facilitating alignment of the emitters 110 and the collectors 120, and/or alignment of the flow units 100 in the array.