Heat Transfer Using Ionic Pumps

Abstract

Heat transfer devices are based on using one or more ionic pumps to circulate a dielectric working fluid around a closed circulation path, which may be contained in a conduit. The working fluid may be a liquid or a gas. The ionic pumps are disposed along the closed circulation path. The pumps include an emitter and collector. When a voltage is applied to the emitter, the working fluid is ionized at the emitter. The ionized fluid is drawn electrostatically to the lower-voltage collector, which, through collision with molecules that in turn impart their momentum, creates a flow of the working fluid. This approach may be used with either positive or negative corona devices.

Description

BACKGROUND

1. Technical Field

This disclosure relates generally to heat transfer using ionic flow generators (ionic pumps).

2. Description of Related Art

There are many applications for devices that perform heat transfer. At large scales, this may be done with small bladed or screw-type or other mechanical impellors to actively move a working fluid that transfers heat from one location to another for exhaust or radiative dissipation (e.g., car engine radiator systems).

However, it is more difficult when reducing to a micro-scale, with dimensions on the order of a few mm. Traditional state-of-the-art solutions generally do not work at all on such small scales, or are too performance-limited in their ability to remove heat quickly enough from intense heat sources, such as those increasingly found in modern electronic devices.

Thus, there is a need for better approaches for small heat transfer devices.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the disclosure have other advantages and features which will be more readily apparent from the following detailed description and the appended claims, when taken in conjunction with the examples in the accompanying drawings, in which:

FIG. 1 shows a perspective view of an ionic heat transfer apparatus.

FIGS. 2 and 3 show different views of the two end caps of the ionic heat transfer apparatus of FIG. 1.

FIG. 4 shows the cable cover conduit of the ionic heat transfer apparatus of FIG. 1.

FIG. 5 shows perspective views of the two end caps with cable cover.

FIG. 6 shows a perspective view of the ionic heat transfer apparatus with attached electronics.

FIG. 7 shows a perspective view of another ionic heat transfer apparatus.

FIG. 8 shows a side view and bottom view of another ionic heat transfer apparatus.

FIG. 9 is a perspective view of a unit cell used to construct an ionic pump.

FIG. 10 is a perspective view of another ionic pump.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The figures and the following description relate to preferred embodiments by way of illustration only. It should be noted that from the following discussion, alternative embodiments of the structures and methods disclosed herein will be readily recognized as viable alternatives that may be employed without departing from the principles of what is claimed.

In one aspect, heat transfer devices are based on using one or more ionic pumps to circulate a dielectric working fluid around a closed circulation path, which may be contained in a conduit. The working fluid may be a liquid or a gas. The ionic pumps are disposed along the closed circulation path. The pumps include an emitter and collector. When a voltage is applied to the emitter, the working fluid is ionized at the emitter. The ionized fluid is drawn electrostatically to the lower-voltage collector, which, through collision with molecules that in turn impart their momentum, creates a flow of the working fluid. This approach may be used with either positive or negative corona devices. Pumps of this type may be made smaller and with different form factors compared to conventional mechanical pumps. As a result, the overall heat transfer device may be designed to address applications that are not feasible for more conventional pumps.

FIGS. 1-6 show an example. In this example, the apparatus includes a conduit for a closed circulation path, in the form of a cable cover with two end caps. FIG. 1 shows a perspective view of the assembled apparatus 100, with the two end caps 120, 130 and cable cover 110 in between. The end caps 120, 130 contain the pumps to circulate the working fluid. One end cap 120 makes thermal contact with the heat source, which in this example is electronics. The other end cap 130 closes the circulation path.

FIG. 1 also shows magnified cross-sectional views of the two end caps 120, 130. The right end cap 120 contains pumps (not shown in FIG. 1) and is also integrated with a heat sink 125. The heat source (not shown in FIG. 1) makes thermal contact with this end cap 120, transferring heat to the working fluid. As indicated by the arrows, the working fluid 140 circulates from the right end cap 120, down the length of the cable cover along one channel 112, through the left end cap 130, and back up the length of cable cover along a different channel 114, and back through the right end cap 120. The left end cap 130 is a return, that also contains pumps. The center 116 of the cable cover is hollow, so that cables may be routed to the electronics.

FIG. 2 shows different views of the end cap 120 on the heat source side. The top left is a perspective view of the end cap 120. The bottom left is a sectioned perspective view. The bottom right is a cross-sectional side view. The end cap 120 contains eight ionic pumps 150, which are shown as small squares, with an arrow entering or exiting each pump in the top perspective view. The end cap 120 has an annular cavity 122. In FIG. 2, the bottom four pumps 150 pump the working fluid from channel 114 into the cavity 122, and the top four pump fluid out of the cavity into channel 112, as shown by the arrows. The end cap is integrated with a heat sink 125. The circulation path for the working fluid is contained in the base of the heat sink 125. The center hole 126 allows cables to pass through.

FIG. 3 shows the end cap 130 on the return side. The views in FIG. 3 are the same as in FIG. 2: perspective view, sectioned perspective view and cross-sectional side view. The end cap is rotated 180 degrees relative to the orientation in FIG. 1, so that the ionic pumps 150 are visible. The end cap 130 also contains eight ionic pumps 150 that pump fluid into and out of an annular cavity 132. In FIG. 3, the top four pumps 150 pump the working fluid from channel 112 into the cavity 132, and the bottom four pump fluid out of the cavity into channel 114, as shown by the arrows. Cables may pass through the center hole 136.

FIG. 4 shows the cable cover conduit 110. As shown in the cross section, the central opening 116 is where the cable goes. The annulus outside of the center opening 116 is divided into two chambers or channels 112, 114. Fluid flows from the heat source to sink along one channel 112 and in the reverse direction along the other channel 114, as shown by the arrows. The cable cover also includes heat radiating ribs 117 to dissipate heat.

FIG. 5 shows magnified views of the two end caps 120, 130 with a short section of cable cover 110 to show the circulation path across the boundary of these components. Some pumps 150 are also visible.

FIG. 6 shows a perspective view of the apparatus, with electronics 190 contacting the heat sink 125 and end cap 120 and also with the cable 180 inserted into the cable cover 110. Heat is transferred from the electronics 190 to the heat sink 125 for dissipation. Heat is also transferred to the working fluid which circulates through the cable cover 110 to dissipate the heat.

FIG. 7 shows an alternate design in which the main section of the conduit is flat, rather than round. This design includes a flat main conduit section 710, and two end caps 720, 730. Conduit 710 has two channels 712, 714. Both end caps 720, 730 contain ionic pumps 750 to circulate the working fluid. One end cap 720 makes thermal contact with the heat source and also includes an integrated heat sink 725. The other end cap 730 closes the circulation path. The working fluid circulates through end cap 720, down through channel 712, through end cap 730, and back up through channel 714, as shown by the arrows in FIG. 7. The conduit 710 has fins 717 to dissipate heat from the working fluid. The walls of the conduit 710 could dissipate heat by convection or radiation, even without fins.

The designs shown in FIGS. 1-7 are merely examples. It will be understood that other designs will be apparent. For example, the ionic pumps do not have to be located in the end caps. They could be disposed at other locations along the closed circulation path, for example along the length of the cable cover 110 or conduit 710. The conduits could be different sizes, lengths, shapes and cross-sections. They could also be made from different materials: plastic or metal for example. They could be either rigid or flexible. In some cases, they may be RF transparent. Different working fluids may be used, including both liquids and gases. Examples of liquids include Flourinert, deionized water, hydrofluorocarbons and refrigerants. Examples of gases include inert gases, noble gases, helium, nitrogen, argon, neon, krypton and xenon. In some cases, the working fluid has a dynamic viscosity of not more than 5 centiPose (cP) and/or a temperature thermal conductivity of at least 0.02 W/mK.

FIG. 8 shows an alternate design in which the closed circulation path is located in the base of a heat sink. FIG. 8 shows a side view and a bottom view of this design. A heat source 890 (e.g., an integrated circuit) is mounted to the base 810 of a heat sink. The heat sink has fins 817 to dissipate the heat. In the base of the heat sink, there is a closed circulation path 812. A working fluid flowing through the circulation path 812 provides a more uniform temperature in the base of the sink, thus reducing the spreading resistance. Ionic pumps, marked by circle P's, move the fluid around the circulation path 812. In the example of FIG. 8, the black paths are the closed circulation path 812 and the circle P's are the ionic pumps.

The circulation path(s) 812 can be implemented in many different ways. There may be a single path with a single active pump, or there may be a single path with multiple pumps. Alternatively, there may be multiple paths, with each closed circulation path having one or more pumps. The circulation path(s) may have different shapes, and the ionic pump(s) may be placed at different locations along the paths. One advantage of using ionic pumps is that the pumps are small enough that they may be built into the heat sink base 810, although that is not required.

FIGS. 9-10 describe example designs of ionic pumps that may be used for the heat transfer devices described above. In the following, ionic pumps may be referred to ionic flow generators or ionic air flow generators (when the fluid is air). In these examples, the working fluid is air, but they are not limited to air.

In one aspect, the emitter and/or collector of an ionic air flow generator are formed by conductors joined to a dielectric substrate, such as by metal deposited on a glass or ceramic substrate. One conductor, which is shaped to form the high-voltage emitter with sharp edges or other features to concentrate charge, is joined to one side of the dielectric substrate. Another conductor, which is shaped to form the grounded low-voltage collector with rounded edges that reduce field concentration, is joined to the opposite side of the dielectric substrate. The dielectric substrate is not solid between the emitter and collector. It is shaped with voids that form an air gap between the emitter and collector. Thus, when a voltage is applied to the emitter, air is ionized at the emitter. The ionized air is drawn electrostatically to the grounded collector, which, through collision with neutral molecules that in turn impart their momentum, creates a flow of air through the air gap. This approach may be used with either positive or negative corona devices.

For example, the dielectric substrate may start as a solid piece of glass or ceramic substrate. The surfaces of the substrate may be etched, scored or otherwise pre-conditioned. Conductors are deposited on opposite sides of the substrate. The surface shape of the substrate may be used to form structures in the conductors, such as sharp edges for the emitter or rounded edges for the collector. Dielectric between the conductors is removed, creating an air gap for air flow.

In one approach, sharp-edged groove(s) are made in one side of the substrate. Depositing the conductor into the grooves then forms ridges in the conductor, which functions as the emitter. Conductive material is also deposited on the other side of the substrate and patterned using standard lithography processes, thus forming the collector. After the conductors are deposited, substrate material between the conductors may be removed to create a path for air flow between the emitter and collector.

In a different approach, smooth, concave grooves are made in the substrate, and depositing the conductor into the groove then forms rounded surfaces in the conductor, which functions as the collector. Conductor is also applied to the opposite side with standard lithography techniques and shaped to form sharp edges, such as from a square cross section. This then functions as the emitter. After the conductors are deposited, substrate material between the conductors may be removed to create a path for air flow between the emitter and collector.

FIG. 9 shows an example of an ionic air flow generator. FIG. 9 is a perspective view of a unit cell 900 used to construct the air flow generator. In this example, the unit cell has an area of 1 mm×1 mm, and a thickness of slightly less than 1 mm. Air flow generators of different sizes may be constructed by assembling arrays of these units cells. The unit cell 900 includes two conductors 910 and 930, separated by a dielectric substrate which takes the form of spacers 920 in the final device. During construction, the two conductors 910, 930 are deposited onto a solid dielectric substrate, such as a glass or ceramic substrate. Dielectric is removed to create an air gap 925 between the two conductors 910, 930. The conductors 910, 930 include an emitter and collector, respectively. Some of the dielectric substrate remains to form the spacers 920, which maintains a consistent spacing for the air 925 gap between the emitter and collector.

Conductor 910 is predominantly flat. The flat surface areas in the corners of this unit cell for conductor 910 are joined to the spacers 920. The conductor 910 is also shaped to function as an emitter. It typically includes features that concentrate charge, such as points or edges. In this example, the conductor 910 is formed with a ridge 912 that has a sharp edge, which functions as the emitter. The radius of curvature of the ridge preferably should be as tight as possible, and preferably not larger than 30 um. This example uses a line-plane geometry. Other types of linear raised structures may also be used. If the emitter were formed as raised point structures (such as cones or pyramids), rather than raised linear structures (such as ridges), that would implement a point-plane geometry. Raised point structures preferably should also have feature sizes and curvature radii not larger than 30 um. Conductor 910 also includes holes 915 to allow air flow.

Conductor 930 is also predominantly flat and the flat surface areas in the corners of this unit cell of conductor 930 are joined to the spacers 920. The conductor 930 is shaped to form a collector, typically avoiding features with points or edges. It also includes holes 935 to allow air flow. The holes 935 are designed to avoid corners and edges. The holes 935 are pill-shaped with rounded ends, rather than rectangular with corners. The edges of the holes are also rounded, particularly the edges on the side facing the emitter. Preferably, they have less curvature than the emitter ridge. This reduces the risk of unwanted arcing or breakdown.

FIG. 10 is a perspective view of another design for an ionic fluid flow generator pump. This device 1000 includes two conductors 1010 and 1030, separated by a dielectric 1020. During construction, the two conductors 1010, 1030 are deposited onto a solid dielectric substrate, such as a glass or ceramic substrate. In FIG. 10, the collector conductor 1030 is on the top surface of the dielectric 1020, and the emitter conductor 1010 is on the bottom surface of the dielectric 1020. Dielectric is removed to create an aperture 1025 in the dielectric substrate. Conductor 1010 includes an emitter with one or more emitter stripes 1012 suspended across the aperture 1025. In this example, there are two emitter stripes. Conductor 1030 includes a collector with multiple collector stripes 1032, also suspended across the aperture 1025. The aperture 1025 includes isolation notches 1015, which increase the creep distance between the emitter and collector.

In this example, both the emitter stripes 1012 and the collector stripes 1032 are supported by the dielectric 1020 only on the two ends of the stripes after the dielectric material has been removed. There are no mid-stripe supports. However, the length of the stripes is short enough that there is no appreciable sag, and the dielectric 1020 maintains a consistent spacing for the air gap 1025 between the emitter stripes 1012 and collector stripes 1032. In alternate designs, the emitter and/or collector stripes may be supported, for example by forming a conductive trace supported along its entire length by a stripe of underlying dielectric. In the design of FIG. 10, the emitter stripes and collector stripes are arranged in a regular pattern, and they are oriented perpendicular to each other.

The collector stripes 1032 are rounded to avoid concentrating the electric field. In one approach, they are fabricated by scoring rounded grooves into the substrate. Metal is applied to both sides of the dielectric 1020. The metal deposited into the rounded grooves is patterned by etching, thus forming the rounded collector stripes 1032. The metal deposited on the opposite surface of the dielectric 1020 is patterened by etching to create sharp edges, thus forming the emitter stripes 1012.

The resulting collector stripes 1032 have cross sections without corners or, at least the surfaces facing the emitter are rounded. In contrast, the emitter stripes 1012 are formed with edges. In one approach, standard lithography is used to pattern the emitter stripes 1012 on the dielectric substrate. The resulting cross section is typically rectangular or trapezoidal, with corners. The corners preferably have a radius of curvature not greater than 30 um.

In other examples, embodiments of a similar structure may include two substrates with respective conductors created separately, and joined together as a subsequent step, or constructed such that air flow is routed in a lateral direction across the surface of the insulative substrate rather than through perforations in the substrate or in the applied conductors.

Further details and examples of ionic pumps are provided in International Application No. PCT/US22/22334, “Ionic Air Flow Generator,” filed Mar. 29, 2022, which is incorporated by reference herein in its entirety.

Although the detailed description contains many specifics, these should not be construed as limiting the scope of the invention but merely as illustrating different examples. It should be appreciated that the scope of the disclosure includes other embodiments not discussed in detail above. Various other modifications, changes and variations which will be apparent to those skilled in the art may be made in the arrangement, operation and details of the method and apparatus disclosed herein without departing from the spirit and scope as defined in the appended claims. Therefore, the scope of the invention should be determined by the appended claims and their legal equivalents.

Claims

1. An ionic heat transfer apparatus comprising: a conduit containing a closed circulation path, wherein the conduit is configured to make thermal contact with a heat source; andone or more ionic pumps disposed along the closed circulation path, configured to circulate a dielectric working fluid around the closed circulation path, wherein circulation of the working fluid transfers heat away from the heat source.

2. The ionic heat transfer apparatus of claim 1, wherein the conduit has a surface structure configured to radiatively and/or convectively dissipate heat from the working fluid.

3. The ionic heat transfer apparatus of claim 2, wherein the surface structure comprises fins.

4. The ionic heat transfer apparatus of claim 1, wherein each ionic pump has a cross-sectional flow area of not more than 4 mm2.

5. The ionic heat transfer apparatus of claim 1, wherein the conduit is flexible.

6. The ionic heat transfer apparatus of claim 1, wherein the conduit is RF transparent.

7. The ionic heat transfer apparatus of claim 1, wherein the working fluid has a dynamic viscosity of not more than 5 centiPose (cP).

8. The ionic heat transfer apparatus of claim 1, wherein the working fluid has a room temperature thermal conductivity of at least 0.02 W/mK.

9. The ionic heat transfer apparatus of claim 1, wherein the working fluid is Flourinert, deionized water, a hydrofluorocarbon or a refrigerant.

10. The ionic heat transfer apparatus of claim 1, wherein the working fluid is an inert gas, a noble gas, helium, nitrogen, argon, neon, krypton or xenon.

11. The ionic heat transfer apparatus of claim 1, wherein the conduit is an elongate conduit with two channels between two ends of the conduit, the working fluid flows through a first of the channels in one direction along the conduit and flows through a second of the channels in an opposite direction along the conduit, one end of the conduit makes thermal contact with the heat source, and circulation of the working fluid transfers heat away from the heat source

12. The ionic heat transfer apparatus of claim 11, wherein one of the ends of the conduit makes thermal contact with a heat sink.

13. The ionic heat transfer apparatus of claim 11, wherein the conduit comprises an end cap containing at least one of the ionic pumps.

14. The ionic heat transfer apparatus of claim 11, wherein the conduit comprises one or two end caps that contain all of the ionic pumps.

15. The ionic heat transfer apparatus of claim 11, wherein at least one of the ionic pumps is disposed along a length of the conduit.

16. The ionic heat transfer apparatus of claim 11, wherein the conduit comprises a cable cover.

17. The ionic heat transfer apparatus of claim 1, wherein at least one of the ionic pumps comprises: a dielectric substrate having a first side and an opposing second side and an aperture through the dielectric substrate;a first conductor comprising an emitter with one or more emitter stripes, wherein each emitter stripe is suspended across the aperture in the dielectric substrate and has two ends deposited on and supported by the first side of the dielectric substrate; anda second conductor comprising a collector with multiple collector stripes, wherein each collector stripe is suspended across the aperture in the dialectic substrate and has two ends deposited on and supported by the opposing second side of the dielectric substrate;wherein the dielectric substrate maintains a gap between the emitter and collector, and a voltage applied to the emitter ionizes working fluid at the emitter and the ionized working fluid is drawn to the collector thereby creating a flow of working fluid through the gap.

18. The ionic heat transfer apparatus of claim 17 wherein: the ends of the emitter stripes comprise patches that are deposited on and supported by the first side of the dielectric substrate on opposite sides of the aperture, the patches on each side of the aperture are electrically connected to each other and to an emitter electrode;the ends of the collector stripes comprise patches that are deposited on and supported by the second side of the dielectric substrate on opposite sides of the aperture, the patches on each side of the aperture are electrically connected to each other and to a collector electrode;

19. The ionic heat transfer apparatus of claim 1, wherein at least one of the ionic pumps comprises: a dielectric having a first side;a conductor joined to and supported by the first side of the dielectric, the conductor also shaped to form a first electrode comprising either an emitter or a collector; anda second electrode comprising the other of emitter and collector, wherein the emitter and collector are positioned opposing each other such that a voltage applied to the emitter ionizes working fluid at the emitter and the ionized working fluid is drawn to the collector thereby creating a flow of working fluid.

20. The ionic heat transfer apparatus of claim 1, wherein at least one of the ionic pumps comprises: a dielectric frame;a conductor joined to and supported by the frame, the conductor also shaped to form a first electrode comprising either an emitter or a collector; anda second electrode comprising the other of emitter and collector, wherein the emitter and collector are positioned opposing each other such that a voltage applied to the emitter ionizes working fluid at the emitter and the ionized working fluid is drawn to the collector thereby creating a flow of working fluid.