Thermal management for solid state high-power electronics

Abstract

The invention is for an apparatus and method for removal of waste heat from heat-generating components including high-power solid-state analog electronics such as being developed for hybrid-electric vehicles, solid-state digital electronics, light-emitting diodes for solid-state lighting, semiconductor laser diodes, photo-voltaic cells, anodes for x-ray tubes, and solids-state laser crystals. Liquid coolant is flowed in one or more closed channels having a substantially constant radius of curvature. Suitable coolants include liquid metals and liquids with low vapor pressure. The former may be flowed by magneto-hydrodynamic effect or by electromagnetic induction. The latter may be flowed by magnetic forces. Alternatively, an arbitrary liquid coolant may be used and flowed by an impeller operated by electromagnetic induction or by magnetic forces. The coolant may be flowed at very high velocity to produce very high heat transfer rates and allow for heat removal at very high flux.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. provisional patent applications U.S. Ser. No. 61/463,040, filed on Feb. 12, 2011 and entitled “Thermal Management for Solid State High-Power Electronics,” and U.S. Ser. No. 61/463,210, filed on Feb. 14, 2011 and entitled “Thermal Management for Solid State High-Power Electronics,” the entire contents of all of which are hereby expressly incorporated by reference This patent application is a continuation-in-part patent application of: U.S. Ser. No. 12/290,195 filed on Oct. 28, 2008 and entitled HEAT TRANSFER DEVICE; U.S. Ser. No. 12/584,490 filed on Sep. 5, 2009 and entitled HEAT TRANSFER DEVICE; and U.S. Ser. No. 12/932,585 filed on Feb. 28, 2011 and entitled THERMAL INTERFACE DEVICE; the entire contents of all of which are hereby expressly incorporated by reference.

FIELD OF THE INVENTION

This invention relates generally to a removal of heat from heat-generating component and more specifically to a removal of heat at high flux.

BACKGROUND OF THE INVENTION

The subject invention is an apparatus and method for removal of waste heat from heat-generating components including analog solid-state electronics, digital solid-state electronics, semiconductor laser diodes, light emitting diodes, photo-voltaic cells, vacuum electronics, and solid-state laser crystals.

There are many devices generating waste heat as a byproduct of their normal operations. These include analog solid-state electronic components, digital solid-state electronic components, semiconductor laser diodes, light emitting diodes for solid-state lighting, solid-state laser components, laser crystals, vacuum electronic components, and photovoltaic cells. Waste heat must be efficiently removed from such components to prevent overheating and consequential loss of efficiency, malfunction, or even catastrophic failure. Methods for waste heat management may include conductive heat transfer, convective heat transfer, and radiative heat transfer, or various combinations thereof. For example, waste heat removed from heat generating components may be transferred to a heat sink by a flowing heat transfer fluid. Such a heat transfer fluid is also known as a coolant.

Cooling requirements for the new generation of heat-generating components (HGC) are very challenging for thermal management technologies of prior art. For example, an ongoing miniaturization of semiconductor digital and analog electronic devices requires removal of heat at ever increasing fluxes now on the order of several hundreds of watts per square centimeter. Traditional heat sinks and heat spreaders have large thermal resistance contributing to elevated junction temperatures and thus reducing device reliability. As a result, removal of heat often becomes the limiting factor and a barrier to further performance enhancements. More specifically, a new generation of high-power semiconductors for hybrid electric vehicles and future plug-in hybrid electric vehicles requires improved thermal management to boost heat transfer rates, eliminate hot spots, and reduce volume, while allowing for higher current density.

High-brightness light emitting diodes (LED) being developed for solid-state lighting for general illumination in commercial and household applications also require improved thermal management. These new light sources are becoming of increased importance as they offer up to 75% savings in electric power consumption over conventional lighting systems. Waste heat must be effectively removed from the LED chip to reduce junction temperature, thereby prolonging LED life and making LED cost effective over traditional lighting sources.

Another class of electronic components requiring improved cooling are semiconductor-based high-power laser diodes used for direct material processing and pumping of solid-state lasers. Generation of optical output from laser diodes is accompanied by production of large amount of waste heat that must be removed at a flux on the order of several hundreds of watts per square centimeter. In addition, the temperature of high-power laser diodes must be controlled within a narrow range to avoid undesirable shifts in output wavelength.

Photovoltaic cells (solar electric cells and thermo-photovoltaic cells) are becoming increasingly important for generation of electricity. Such cells may be used with concentrators to increase power generation per unit area of the cell and thus reduce initial installation cost. This approach requires removal of waste heat at increased flux. Similarly, high-performance crystals used in solid-state lasers generate waste heat that may require removal at fluxes in the neighborhood of thousand watts per square centimeter.

Anodes in x-ray tubes are subjected to very high thermal loading. Rotating anodes are frequently used to spread the heat to avoid overheating. Such rotating anodes inside a vacuum enclosure are impractical for use in a new generation of x-ray tubes for use in compact and portable devices in medical and security applications. A compact and lightweight heat transfer component having no moving parts inside the vacuum is very desirable.

Current approaches for removal of waste heat at high fluxes include 1) spreading of heat with elements having high thermal conductivity and/or 2) forced convection cooling using liquid coolants. However, even with heat spreading materials having extremely high thermal conductivity such as diamond films and certain graphite fibers, a significant thermal gradient is required to conduct large amount of heat even over short distances. In addition, passive heat spreaders are not conducive to temperature control of the HGC. Forced convection methods for removal of waste heat at high fluxes may use microchannel heat exchangers or impingement jets operating at high flow rates to obtain desirable heat transfer coefficient with conventional coolants such as water, alcohol, or ethylene glycol. This results in a very high coolant consumption and requires a large pumping system. Known forced convection systems have many components, are bulky, heavy, and have geometries that require the coolant to make complex directional changes while traversing the coolant loop. Such directional changes are a potential source of increased flow turbulence causing higher pressure drop in the loop and, therefore, necessitate higher pumping power.

Metals have a thermal conductivity several orders-of-magnitude greater than water and organic liquids. Liquid (molten) metals have a viscosity comparable to that of water. As a result, liquid metals are excellent candidates for advantageous cooling in many demanding applications, especially where heat must be removed at high heat flux. Initially, liquid metal cooling was developed for thermal management of nuclear reactors on submarines in the 1950's. These large systems used eutectic alloy of sodium and potassium (also known as NaK) and in some cases, eutectic alloys of lead and bismuth. A large number of patents have been awarded in connection with these large-scale systems.

Liquid metal cooling for small commercial applications (e.g., electronics) is deemed to have been enabled by the discovery of a low melting point (−19° C.) eutectic alloy of gallium, indium, and tin (galinstan) (see, for example, U.S. Pat. No. 5,800,060). Galinstan is non-toxic, stable in air, and it wets well many materials. This opportunity was recognized in several recent disclosures, for example, U.S. Pat. Nos. 7,505,272, 7,697,291, 7,539,016, 7,764,499, 7,701,716, 7,672,129, 7,245,495, 7,861,769, and 7,131,286. To date, no devices based on these disclosures are known to have appeared on the market.

The above disclosures typically suggest a traditional layout for a thermal management system found already in the above mentioned nuclear systems: a heat exchanger (HEX) for receiving heat, HEX for rejecting heat, plumbing, and a pump. Such configurations may not self-contained and may be impractical for many applications because they may have a large size, may not sealed, may use incompatible materials, and may have large electromagnetic interference (EMI). In addition, above disclosures do not address the challenges of handling and pumping liquid metal, namely:

• • 1) Galinstan has a specific gravity of about 6.4, which means that galinstan flow loop may require nearly 7-times more pumping power to operate than a comparable water flow loop having the same flow velocity.
  • 2) Gallium alloys have a tendency to form amalgams with other metals, which may result in severe corrosion in commonly used engineering metals. In addition, the solid inter-metallic compounds produced by the corrosive action may form deposits inside the liquid metal flow channel, impeding the heat transfer, and possibly block the flow channels.
  • 3) Pumping of liquid metal with an electromagnetic pump may be very simple in theory, but it may be challenging in practice due to possible complex magneto-hydro-dynamic (MHD) boundary layers and MHD instabilities.
  • 4) Volumetric specific heat of liquid metal may be only about half of that of water. Hence, a liquid metal cooling loop may require higher flow velocities to carry away the same amount of heat as a comparable water loop with the same temperature rise. This means that, a liquid metal cooling loop operating at low velocity may not be much more effective (and may be actually less effective) than a comparable water loop.

The above indicates that for a superior performance, a liquid metal cooling hardware may not have an arbitrary configuration and/or arbitrary operating parameters.

In summary, prior art does not teach a heat transfer device capable of removing heat at very loads and high fluxes that is also compact, lightweight, self contained, capable of accurate temperature control, has a low thermal resistance, and requires very little power to operate. It is against this background that the significant improvements and advancements of the present invention have taken place.

SUMMARY OF THE INVENTION

The present invention provides a heat transfer device (HTD) wherein a coolant flows in a closed channel with a substantially constant radius of curvature. This arrangement offers low resistance to flow, which allows to flow the coolant at very high velocities and thus enables heat transfer at very high rate while requiring relatively low power to operate. HTD of the subject invention may be used to cool HGC requiring removal of waste heat at very high heat flux. Such HGC may include solid-state electronic chips, semiconductor laser diodes, light emitting diodes for solid-state lighting, solid-state laser components, laser crystals, optical components, vacuum electronic components, and photovoltaic cells. Heat removed by HTD from HGC may be transferred to a heat sink or environment at a reduced heat flux. For example, HTD may transfer acquired heat to a structure, heat pipe, secondary liquid coolant, phase change material (PCM), gaseous coolant, or ambient air.

In one preferred embodiment of the present invention, the HTD comprises a body having a first surface, a second surface, and a closed flow channel. The first surface is adapted for receiving heat from a heat generating component and the second surface is adapted for transferring heat to a heat sink. The flow channel has a substantially constant radius of curvature in the flow direction. An electrically conductive liquid coolant is flowed inside the flow channel by means of a magneto-hydrodynamic (MHD) effect (MHD drive).

In another preferred embodiment of the present invention, electrically conductive liquid or ferrofluid coolant may be used and flowed by the means of a moving magnetic field. Moving magnetic field induces eddy currents in the electrically conductive coolant that, in turn, provide force coupling to the coolant (inductive drive). Alternatively, moving magnetic field directly couples into the ferrofluid (magnetic drive). Suitable moving magnetic field may be generated by a rotating magnet.

In yet another preferred embodiment of the present invention, the moving (rotating or traveling magnetic) magnetic field may be generated by stationary electromagnets operated by alternate current in an appropriate poly-phase relationship. In a still another embodiment of the present invention, the coolant is an arbitrary liquid flowed in a closed channel with a substantially constant radius of curvature. The coolant flow is induced by a rotating impeller (impeller drive) spun by a flow of secondary coolant, mechanical means, moving magnetic field, or by electromagnetic induction.

Accordingly, it is an object of the present invention to provide a heat transfer device (HTD) for removing waste heat from HGC. The HTD of the present invention is simple, compact, lightweight, self-contained, can be made of materials with a coefficient of thermal expansion (CTE) matched to that of the HGC, requires relatively little power to operate, and it is suitable for large volume production.

It is another object of the invention to provide means for cooling HGC.

It is still another object of the invention to provide means for temperature control of HGC.

It is yet another object of the invention to cool a semiconductor electronic components.

It is yet further object of the invention to cool semiconductor laser diodes.

It is a further object of the invention to cool LED for solid-state lighting.

It is still further object of the invention to cool computer chips.

It is an additional object of the invention to cool photovoltaic cells.

These and other objects of the present invention will become apparent upon a reading of the following specification and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side cross-sectional view of a heat transfer device (HTD) in accordance with one embodiment of the subject invention using a magneto-hydrodynamic drive.

FIG. 1B is a cross-sectional view of an HTD of FIG. 1A in a plane transverse to coolant flow.

FIG. 2A is an enlarged view of portion 2A of the HTD of FIG. 1A.

FIG. 2B is an enlarged view of portion 2B of the HTD of FIG. 1B.

FIG. 3 is an enlarged view of alternative portion 2B of the HTD of FIG. 1B showing a flow channels with surface extensions.

FIG. 4 is an enlarged view of another alternative portion 2B of the HTD of FIG. 1B showing multiple flow channels arranges side-by-side.

FIG. 5 is an enlarged view of portion 2A of the HTD of FIG. 1A showing a mounting of a laser diode array HGC.

FIG. 6 is an enlarged view of portion 2A of the HTD of FIG. 1A showing a mounting of a laser diode bar HGC.

FIG. 7 is an enlarged view of portion 2A of the HTD of FIG. 1A showing a mounting of a light emitting diode HGC.

FIG. 8 is an enlarged view of portion 2A of the HTD of FIG. 1A showing a mounting of a solid-state laser crystal HGC.

FIG. 9A shows an alternative HTD body having internal passages for a secondary coolant.

FIG. 9B shows a variant of an alternative HTD having an internal passage for flowing a secondary coolant.

FIG. 10 shows another alternative HTD body having external fins for heat transfer to gaseous coolant or ambient air.

FIG. 11A is a cross-sectional view of an HTD in accordance with another embodiment of the subject invention wherein coolant flow is induced by a rotating magnetic field produced by a rotating magnet.

FIG. 11B is a side cross-sectional view of the HTD of FIG. 11A in a plane transverse to coolant flow.

FIG. 12A is a cross-sectional view of an HTD in accordance with a yet another embodiment of the subject invention wherein coolant flow is induced by a rotating magnetic field produced by stationary electromagnets.

FIG. 12B is a side cross-sectional view of the HTD of FIG. 12A in a plane transverse to the flow loop.

FIG. 12C is a side cross-sectional view of an alternative HTD having stationary electromagnets with a return flux yoke

FIG. 13 shows a suitable connection of electromagnets to a single phase alternating current supply.

FIG. 14 shows a variant to the HTD in accordance with a yet another embodiment of the subject invention wherein the electromagnets are arranged to generate translating magnetic field.

FIG. 15A is a side cross-sectional view of an HTD in accordance with still another embodiment of the subject invention using an impeller.

FIG. 15B is a side cross-sectional view of the HTD shown in FIG. 15A.

FIG. 15C is a side cross-sectional view of an HTD in accordance with a variant of embodiment of the subject invention shown in FIG. 15A.

FIG. 15D is a side cross-sectional view of the HTD shown in FIG. 15C.

FIG. 16 is a side cross-sectional view of an HTD in accordance with a further embodiment of the subject invention suitable for cooling by impingement flow.

FIG. 17 is a side view of an HTD in accordance with a yet further embodiment of the subject invention suitable for cooling multiple heat generating components.

FIG. 18A is a cross-sectional view 18A-18A of the HTD shown in FIG. 17.

FIG. 18B is a cross-sectional view 18B-18B of the HTD shown in FIG. 18A.

FIG. 19 is an isometric view of the HTD of FIG. 17 with portions of selected outer elements removed to expose the inner elements and showing additional components.

FIG. 20 is an exploded isometric view of the HTD of FIG. 17 showing additional components.

FIG. 21 is an isometric view of the HTD of FIG. 19 indicating the flow paths of secondary coolant.

FIG. 22 is an isometric view with three-quarter cross-section of the HTD of FIG. 19.

FIG. 23 is an isometric view of an inverter assembly with two HTD's of FIG. 17 installed, in accordance with a still further preferred embodiment of the subject invention.

FIG. 24 is a side cross-sectional view 24-24 of the inverter assembly of FIG. 23.

FIG. 25 is an exploded isometric view of the inverter assembly of FIG. 23.

FIG. 26 is a side view of an HTD in accordance with a variant of the HTD of FIG. 17 having an externally driven impeller.

FIG. 27A is a cross-sectional view 27A-27A of the HTD shown in FIG. 26.

FIG. 27B is a cross-sectional view 27B-27B of the HTD shown in FIG. 27A.

FIG. 28 is a side view of an HTD in accordance with another variant of the HTD of FIG. 17 having an impeller driven by a rotating magnetic field.

FIG. 29A is a cross-sectional view 29A-29A of the HTD shown in FIG. 28.

FIG. 29B is a cross-sectional view 29B-29B of the HTD shown in FIG. 29A.

FIG. 30 is a side view of an HTD in accordance with another variant of the HTD of FIG. 17 having a magneto-hydrodynamic pump.

FIG. 31A is a cross-sectional view 31A-31A of the HTD shown in FIG. 30.

FIG. 31B is a cross-sectional view 31B-31B of the HTD shown in FIG. 31A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Selected embodiments of the present invention will now be explained with reference to drawings. In the drawings, identical components are provided with identical reference symbols in one or more of the figures. It will be apparent to those skilled in the art from this disclosure that the following descriptions of the embodiments of the present invention are merely exemplary in nature and are in no way intended to limit the invention, its application, or uses.

Referring now to FIGS. 1A and 1B, there is shown a heat transfer device (HTD) 100 in accordance with one preferred embodiment of the subject invention. HTD 100 comprises a body 102, magnets 128a and 128b, electrodes 130a and 130b, and electrical conductors 126a and 126b. The body 102 further comprises a first surface 106 adapted for receiving heat from a heat generating component (HGC), a second surface 108 adapted for rejecting heat to a heat sink, and a flow channel 104. The body 102 is preferably made of material having high thermal conductivity. Preferably, such a material may also have a low electrical conductivity or such a material may be dielectric. Suitable materials for construction of the body 102 may include silicon, berylia, silicon carbide, and aluminum nitride. A heat generating component (HGC) 114 may be also attached to the first surface 106 and arranged to be in a good thermal communication therewith. HGC 114 may be, but it is not limited to a solid-state electronic chip, semiconductor laser diode, light emitting diodes (LED), solid-state laser crystal, optical component, x-ray tube anode, or a photovoltaic cell. If desired, the body 102 may be made from material having a coefficient of thermal expansion (CTE) matched to the CTE of the HGC 114. In some variants of the subject invention the body 102 can be a composite unit made of several suitably joined different materials. The second surface 108 is arranged to be in a good thermal communication with a heat sink (not shown). Suitable heat sinks include a structure, heat pipe, secondary liquid coolant, phase change material (PCM), gaseous coolant, or ambient air. When a fluid used as a heat sink, it may employ natural convection or forced convection to remove heat from the second surface 108. The second surface 108 may also include surface extensions such as fins or ribs to enhance heat transfer therefrom.

Referring now to FIGS. 2A and 2B, the HGC 114 may be thermally coupled to the first surface 106 with a suitable joining material 120. Preferably, joining material 120 has a good thermal conductivity. Suitable joining materials include solder, thermally conductive paste, epoxy, liquid metals, and adhesive. Alternatively, HGC 114 may be diffusion bonded onto surface 106. As another alternative, the HGC 114 may be mechanically attached onto surface 106. The flow channel 104 comprises an outer surface 110 and an inner surface 112. Each of the surfaces 110 and 112 may have a width “W” and they may be separated from each other by a distance “H”. Preferably, the surface 110 has a constant radius of curvature “R” and the inner surface 112 has a radius “R minus H” (“R−H”). For example, surfaces 110 and 112 may each be cylindrical and mutually concentric, thereby giving the flow channel 104 a general shape of a hollow cylinder with an outer radius “R”, and an inner radius “R−H”, and height “W”. More generally, the flow channel may have a shape of a toroid, which is a geometrical object generated by revolving a geometrical figure around an axis external to that figure. For example, the geometrical figure revolved may be a polygon. In particular, the geometrical figure may be a rectangle having a width “W” and height “H”. Because the channel forms a closed loop, it may be also referred to in this disclosure as the “closed flow channel.” Preferred range for the width “W” is 0.1 to 20 millimeters, but dimensions outside this range may be also practiced. Preferred range for the outer radius of curvature “R” is 5 to 25 millimeters, but dimensions outside this range may be also practiced. Preferably, the distance “H” is chosen so that the channel 104 has a hydraulic diameter (=2WH/(W+H)) about five (5) micrometers to three (3) millimeters, and most preferably about ten (10) micrometers to one (1) millimeter. In addition, surfaces 110 and 112 should be made very smooth. Preferably, surfaces 110 and 112 are finished to surface roughness of less than 8 micrometers root-mean-square value, and most preferably to surface roughness of less than 1 micrometer root-mean-square value. Surfaces of the flow channel 104 may also have a coating to protect them from corrosion. The first surface 106 may be generally tangential to the outer surface 110 and separated from it by a distance “S” (FIG. 2B). Preferred range for the distance “S” is 0.1 to 1 millimeter, but dimensions outside this range may be also practiced.

The flow channel 104 contains a suitable electrically conductive liquid coolant 116. Preferably, the flow channel 104 is not entirely filled with the liquid coolant and at least some void space free of liquid coolant is provided inside the channel to allow for thermal expansion of the coolant. Preferably, the liquid coolant 116 has a good thermal conductivity, low viscosity, and low freezing point. Suitable liquid coolants 116 include selected liquid metals. For the purposes of this disclosure, the term “liquid metal” shall mean suitable metals (and their suitable alloys) that are in a liquid (molten) state at their operating temperature. Liquid metals have a comparably good thermal conductivity while being also electrically conductive and, in some cases have a relatively low viscosity. Examples of suitable liquid metals include mercury, gallium, indium, bismuth, tin, lead, potassium, and sodium. Ordinary or eutectic liquid metal alloys may be used. Examples of suitable liquid eutectic metal alloys include Indalloy 51 and Indalloy 60 (manufactured by Indium Corporation in Utica, N.Y.), galinstan (obtainable from Geratherm Medical AG in Geschwenda, Germany). Galinstan is a nontoxic eutectic alloy of 68.5% by weight of gallium, 21.5% by weight of indium and 10% by weight of tin, having a melting point around minus 19 degrees Centigrade. Examples of suitable liquid metal alloys may be also found in the U.S. Pat. No. 5,800,060 issued to G. Speckbrock et al., on Sep. 1, 1998. It is important that electrodes 130a and 130b (FIG. 1B), and surfaces of the flow channel 104 are made of materials compatible with the coolant 116. In particular, it is well know that liquid gallium and its alloys severely corrode many metals. Prior art indicates that certain refractory metals such as tantalum and tungsten may be stable in gallium. See, for example, “Effects of Gallium on Materials at Elevated Temperatures,” by W. D. Wilkinson, Argonne National Laboratory Report ANL-5027 (August 1953). To protect against corrosion, surfaces of the flow channel 104 may be coated with suitable protective film. Prior art indicates that TiN and certain organic coatings may be stable in gallium. If a protective coating is additionally dielectric, the body 102 may be constructed from electrically conductive materials. In particular, TiN and diamond-like coating (DLC) may provide suitable protection to metals such as aluminum and copper from corrosion by gallium. Diamond-like coating may be obtained from Richter Precision in East Petersburg, Pa.

The outer surface 110 may also include extensions 118 to increase the contact area between the surface 110 and liquid coolant 116 (FIG. 3). Suitable form of surface extension 118 includes fins and ribs. Alternatively, multiple flow channels 104a-104e may be employed (FIG. 4). In some variants of the subject invention, a portion of the HGC 114 may form a portion of the outer surface 110 of the flow channel 104. In such variants of the invention, the liquid coolant 116 may directly wet a portion of the surface of the HGC 114. FIG. 5 shows a mounting of HGC 114′, which is an array of semiconductor laser diodes (or laser diode bars) 150 imbedded in a substrate 148 and producing optical output 152. Suitable array of semiconductor laser diode bars imbedded in a substrate known as “silver bullet laser diode assembly submodule” and as “golden bullet laser diode assembly submodule” may be obtained from Northrop-Grumman Cutting Edge Optronics in St. Charles, Mo. FIG. 6 shows a mounting of HGC 114″, which is a laser diode bar producing optical output 152. Suitable laser diode bar known as “unmounted laser diode bar” may be obtained from Northrop-Grumman Cutting Edge Optronics in St. Charles, Mo. FIG. 7 shows a mounting of HGC 114′″, which is a high-power light emitting diode producing optical output 153. Suitable high-power light emitting diode known as “Luxeon® K2” may be obtained from Philips Lumileds Lighting Company, Sun Valley, Calif. FIG. 8 shows a mounting of HGC 114^iv, which is a solid-state laser crystal receiving optical pump radiation 151 and amplifying a laser beam 155. Suitable solid-state laser crystal may be in the form of a thin disk laser as, for example, described by Kafka et al., in the U.S. Pat. No. 7,003,011.

Referring now again to FIGS. 1A and 1B, the magnets 128a and 128b are arranged to generate magnetic field that traverses the flow channel 104 in a substantially radial direction in the proximity of electrodes 130a and 130b. Double arrow line 160 indicates preferred directions of the magnetic field. Magnets 128a and 128b are preferably permanent magnets, and most preferably rare earth permanent magnets. Alternatively, magnets 128a and 128b may be formed as electromagnets. As a yet another alternative, magnets 128a and 128b may be pole extensions of a single magnet. A yoke 131 made of soft ferromagnetic material (e.g., iron or soft steel) may be provided to carry return flux between magnets 178a and 178b. Electrodes 130a and 130b are in electrical contact with the liquid coolant 116 and are arranged so that electric current may be passed through the coolant 116 in the region between the magnets 128a and 128b, and in a direction generally orthogonal to magnetic field direction. Electrodes 130a and 130b may be connected to external source of direct electric current via electric conductors 126a and 126b respectively. The HTD 100 may further include a magnetic shield (not shown) to prevent adverse effect of magnetic field generated by magnets 128a and 128b on HGC 114 and/or nearly components.

In operation, electric current is passed though the liquid coolant 116 between electrodes 130a and 130b. Because at least a portion of the coolant 116 is immersed in magnetic field having a vector component orthogonal to the electric current flowing though the coolant 116, a magneto-hydrodynamic (MHD) effect causes the coolant 116 to flow in the direction indicated by the arrow 122 in FIG. 1A and the arrows 124 in FIG. 2A. As a result, flow of coolant 116 forms a closed flow loop. Because the closed flow loop has a substantially constant radius of curvature and the walls of the flow channel 104 are smooth, the flow of coolant 116 encounters relatively little resistance. As a result, very high flow velocities of coolant 116 can be sustained with a relatively small amount of motive power. This disclosure may refer to the means for flowing the coolant by MHD effect as an “MHD drive.”

The HGC 114 is operated and its waste heat is allowed to transfer through the first surface 106 into the body 102 and conducted to the outer surface 110 of the flow channel 104. The second surface 108 is maintained at a temperature substantially below the temperature of the HGC 114. Liquid coolant 116 flowing at high velocity enables a very high heat transfer coefficient on the surface 110. Heat is transferred from the surface 110 into the liquid coolant 116, transported by the coolant 116, and deposited into other parts of the body 102. Heat deposited into other parts of the body 102 is conducted to the second surface 108 and transported therefrom to a suitable heat sink. Using the above process, HTD 100 removes heat from the HGC 114 and transfers it to a heat sink or environment. FIG. 9A shows an HTD body 102′ having a second surface 108′ formed as internal passages for flowing secondary liquid or gaseous coolant. FIG. 9B shows an HTD body 102′″ having a second surface 108′″ formed as an internal passages for flowing secondary liquid or gaseous coolant 185 in a secondary coolant passage 167 placed along the flow channel 104. The secondary coolant passage 167 may be also formed as a plurality of channels. Such channels may be generally straight and parallel. Alternatively such channels may be serpentine-like. Preferably, the secondary coolant 185 is flowed in the direction (indicated by arrows 179) generally opposite to the direction of the flow inside the flow channel 104 (indicated by arrows 124). FIG. 10 shows an HTD body 102″ having a second surface 108″ formed as external fins for transferring heat to a liquid coolant, gaseous coolant, or ambient air.

Temperature of the HGC 114 may be controlled by controlling the flow velocity of the coolant 116. The latter can be accomplished by controlling the current drawn through the coolant 116 via electrodes 130a and 130b. For example, by drawing more current through the coolant 116, the coolant flow velocity may be increased, and the HGC waste heat may be removed at a lower temperature differential between the HGC and the heat sink. Conversely, by drawing less current through the coolant 116, the coolant velocity may be decreased, and the HGC waste heat may be removed at a higher temperature differential between the HGC and the heat sink. Thus, by drawing more current through the coolant 116, the temperature of the HGC 114 may decreased, and by drawing less current through the coolant 116, the temperature of the HGC 114 may be increased. An automatic closed-loop temperature control of the HGC 114 can be realized by sensing HGC temperature (for example, with a thermocouple) and using this information to appropriately control the current drawn through the coolant 116. In particular, if the HGC 114 is an LED, its temperature may be inferred from the output light spectrum. A means for sensing the LED light spectrum may be provided for this purpose. If the HGC 114 is a semiconductor laser diode, its temperature may be inferred from the output light center wavelength. A means for sensing the semiconductor laser diode output light center wavelength may be provided for this purpose. If the HGC 114 has electric currents flowing therethrough, HGC temperature may be determined from certain current and/or voltages supplied to or flowing through in the HGC. If the coolant used in the HTD 100 is susceptible to freezing (solidifying) due to ambient conditions during inactivity, the HTD may be equipped with an electric heater to warm the coolant up to at least its melting point. HGC 114 may be also operated to warm up the HTD.

Referring now to FIGS. 11A and 11B, there is shown a heat transfer device (HTD) 200 in accordance with another preferred embodiment of the subject invention. HTD 200 is similar to HTD 100, except that in HTD 200 the coolant 216 inside the flow channel 204 may be an electrically conductive liquid or a ferrofluid. In addition, the flow of the coolant 216 is caused by a rotating magnetic field. The flow channel 204 in HTD 200 may be of the same construction as the flow channel 104 in HTD 100. Ferrofluids are composed of nanoscale ferromagnetic particles suspended in a carrier fluid, which may be water, an organic liquid, or other suitable liquid. Certain water-based ferrofluids such as W11 available from FerroTec in Bedford, N.H., are also electrically conductive. Ferrofluids using a liquid metal or liquid metal alloy as a carrier fluid have been reported in prior art; see, for example, an article by J. Popplewell and S. Charles in New Sci. 1980, 97(1220), 332. The nano-particles are usually magnetite, hematite or some other compound containing iron, and are typically on the order of about 10 nanometers in size. This is small enough for thermal agitation to disperse them evenly within a carrier fluid, and for them to contribute to the overall magnetic response of the fluid. The ferromagnetic nano-particles are coated with a surfactant to prevent their agglomeration (due to van der Waals and magnetic forces). Ferrofluids may display paramagnetism, and are often referred as being “superparamagnetic” due to their large magnetic susceptibility. It should be noted that ferrofluid may become magnetically saturated at a rather low magnetic fields of less than 0.1 Tesla (1,000 gauss). Alternatively, liquid coolant 216 may comprise a liquid having significant paramagnetic, diamagnetic, or ferromagnetic properties.

The body 202 is similar to body 102 of HTD 100 (FIG. 1A) except that it has a round central opening 264. In addition, the magnets 128a and 128b, the electrodes 130a and 130b, and the electric conductors 126a and 126b (FIG. 1A) are omitted. The body 202 further comprises a first surface 206 adapted for receiving heat from HGC 114, a second surface 208 adapted for transferring heat to a suitable heat sink. Furthermore, the body 202 may be also constructed from a variety of materials preferably having high thermal conductivity. For example, the body 202 may be constructed from copper, copper-tungsten alloy, aluminum, molybdenum, silicon, and silicon carbide. The body 202 may also be constructed in-part or in-whole from ferromagnetic materials to provide return for magnetic flux lines and/or to shield adjacent components from magnetic field. Depending on the choice of coolant 216, the surfaces of the flow channel 204 may require appropriate protective coating to prevent corrosion. HTD 200 further comprises a magnet 234 rotatably suspended inside the opening 264 and positioned so that a significant portion of magnetic field lines cross the flow channel 204. The label “N” designates the north pole of the magnet and the label “S” designates the south pole of the magnet 234. The magnet 234 and the ferromagnetic material in the body 202 (if used) are preferably arranged so that when the magnet 234 is rotated, a given portion of the coolant 216 is alternatively exposed to large variations in magnetic field level, and most preferably to a magnetic field with alternating direction. When the coolant 216 is a ferrofluid, the variations in magnetic field amplitude should include magnetic field level substantially lower than its saturation magnetic field. Preferably, the magnetic field within said coolant may include magnetic field values of less than 50 Gauss (0.005 Tesla).

Operation of HTD 200 is similar to the operation of HTD 100 except that the flow of the coolant 216 is caused by different means than flow of the coolant 116 in HTD 100. In particular, magnet 234 is rotated in the direction of arrow 238 to generate a rotating magnetic field. The magnet 234 may be rotated mechanically by a shaft 236 that may be coupled to an external drive such as an electric motor. For example, if the surface 208 is cooled by air (see, e.g., FIG. 10) supplied by a fan driven by an electric motor, the magnet 234 may be attached to the output shaft of that motor. Alternatively, the magnet 234 may be rotated by means of a magnetic coupling to an external rotating magnetic component. As another alternative, the magnet 234 may be rotated by a rotating magnetic field generated by electromagnets. As a yet another alternative, the magnet 234 may be rotated by a turbine operated by a secondary coolant flowing through the central opening 264.

If the coolant 216 is an electrically conductive liquid, time varying magnetic field produced by the rotation of the magnet 234 induces eddy currents in the electrically conductive coolant 216. Such eddy currents, interact with the rotating magnetic field produced by the magnet 234 thereby establishing a force coupling between the rotating magnet 234 and the coolant 216. As a result, rotating magnet 234 exerts a force onto the coolant 216 causing the coolant 216 to flow inside the flow channel 204 in the direction of the arrow 222 thereby forming a flow loop. This disclosure may refer to the means for flowing an electrically conductive coolant by rotating magnetic field as an “inductive drive.” Additional information about eddy current devices may be found in “Permanent Magnets in Theory and Practice,” chapter 7.6: Eddy-Current Devices, by Malcolm McCraig, published by Pentech Press, Plymouth, UK, 1977; and in “An Introduction to Magnetohydrodynamics,” chapter 5, section 5.5: Rotating Fields and Swirling Motions, by P.A. Davidson, published by Cambridge Texts in Applied Mathematics, Cambridge University Press, Cambridge, UK, 2001.

If the coolant 216 is a ferrofluid, magnetic field produced by the rotating magnet 234 directly couples into the coolant 216 and flows it inside the flow channel 104 in the direction of the arrow 222. Rotational speed of the magnet 234 may used to control the flow velocity of the coolant 216. Thus, controlling the rotational speed of the magnet 234 allows to control the rate of heat removal from the HGC 114 and, thereby to control the HGC temperature. This disclosure may refer to the means for flowing ferrofluid coolant by rotating magnetic field as “magnetic drive.”

Referring now to FIGS. 12A and 12B, there is shown a heat transfer device (HTD) 300 in accordance with yet another preferred embodiment of the subject invention. HTD 300 is essentially the same as HTD 200, except that in HTD 300 the rotating magnetic field for flowing the liquid coolant 216 is generated by stationary electromagnet coils 332a, 332b, and 332c, rather than a rotating magnet 234. The coils 332a, 332b, and 332 are preferably installed inside the central opening 264 as shown in FIG. 4A, and supplied with poly-phase alternating electric currents. Phases of the alternating currents supplied to the coils 332a, 332b, and 332c are set so that the combined magnetic field produced by the coils has a rotating component. For example, the electromagnet coils 332a, 332b, and 332c may be connected in a delta or star (Y) configuration as is often practiced in the art of three-phase alternating current systems (see, for example, “Standard Handbook for Electrical Engineers,” D. G. Fink, editor-in-chief, Section 2: Electric and Magnetic Systems, Three-Phase Systems, Tenth Edition, published by McGraw-Hill Book Company, New York, N.Y., 1968) and supplied with an ordinary three-phase alternating current. Rotating magnetic field couples into the coolant in an already described manner and causes the coolant 216 to flow around the closed loop.

One skilled in the art can appreciate that there is a variety of electromagnet coil configurations fed by poly-phase alternating currents that can produce a time varying magnetic field with a rotating component (see, for example, “Magnetoelectric Devices, Transducers, Transformers, and Machines,” by Gordon D. Slemon, Chapter 5: Polyphase Machines, published by John Willey & Sons, New York, N.Y., 1966). Electromagnet coils may have ferromagnetic cores such as practiced on electric motors for alternating current. FIG. 12C shows a heat transfer device (HTD) 300″ which is variant of the HTD 300. The HTD 300″ has electromagnet coils 332a, 332b, and 332c mounted on a flux return 333 located outside the HTD body 202′. The flux return 333 is preferably made of suitable soft ferromagnetic material. The body 202′ is preferably made from non-magnetic material except for the core portion 203, which is preferably made from a suitable soft ferromagnetic material. Suitable soft ferromagnetic material may include iron, silicon steel, or vanadium permendur. Preferably, suitable soft ferromagnetic material may be provided in form of thin sheets.

If only a single phase current is available, electromagnet coils 332a, 332b, and 332c may be combined with a capacitor 356 as shown, for example, in FIG. 13 to produce a suitable rotating magnetic field. There is a variety of similar connections practiced in the art of single phase electric motors. Frequency of the alternating currents supplied to the electromagnet coils 332a, 332b, and 332c may be used to control the flow velocity of the coolant 216. Thus, controlling the frequency of the alternating currents allows to control of the rate for heat removal from the HGC 114 and the HGC temperature. Typical range for alternating current frequency is from 1 to 1000 cycles per second. Alternatively, the coolant flow velocity may be controlled by controlling the electric current supplied to the electromagnets.

FIG. 14 shows an HTD 300′ that is a variant to the HTD 300 wherein the electromagnet coils 332a, 332b, and 332c are arranged to generate a traveling magnetic field rather than a rotating magnetic field. In particular, the electromagnet coils 332a, 332b, and 332c are arranged as often practiced in the art of linear electric motors and supplied with poly-phase alternating current in appropriate phase relationship. The resulting magnetic field is traveling generally in a linear path and it couples into the electrically conductive or ferrofluid coolant in the manner already described in connection with the HTD 300. It can be appreciated by those skilled in the art that the traveling magnetic field may cause the coolant 216 to flow even if the flow channel 204 may not have a substantially constant radius of curvature.

Referring now to FIGS. 15A and 15B, there is shown a heat transfer device (HTD) 400 in accordance with still another preferred embodiment of the subject invention. HTD 400 is similar to HTD 100, except that in HTD 400 the flow channel 404 is formed by a gap between the outer surface 410 of body 402 and a cylindrical surface 444 of an impeller 440. The impeller 440, which may have a shape of a cylinder is a rotatably suspended on bearings 442 and it may be magnetically or inductively coupled to external actuation means. Alternatively, the impeller may be driven by mechanical means. The body 402 further comprises a first surface 406 adapted for receiving heat from a heat generating component (HGC), a second surface 408 adapted for rejecting heat. The flow channel 404 contains a liquid coolant 416. The coolant 416 preferably has a good thermal conductivity and low viscosity. For example, coolant 416 may be substantially water, or alcohol, or mixture of water and alcohol, aqueous solution of ethylene glycol, or a refrigerant such as Freon.

The coolant 416 may also comprise a fluid containing nanometer-sized particles (nanoparticles) also known as nanofluid. Nanofluids are engineered colloidal suspensions of nanoparticles in a base fluid. The nanoparticles used in nanofluids may be typically made of metals, oxides, carbides, or carbon nanotubes. Common base fluids may include water and ethylene glycol. Nanofluids may exhibit enhanced thermal conductivity and the convective heat transfer coefficient compared to the base fluid.

In operation, external actuation means may be used to spin the impeller 440. Due to its finite viscosity, at least a portion of the coolant 416 is entrained by the cylindrical surface 444 and travels with it, thereby establishing a flow loop. If desired, the cylindrical surface 444 may have surface extensions (for example, ridges, grooves, or surface irregularities) to better entrain the coolant. Rotational speed of the impeller 440 may be used to control the velocity of the coolant 416. Thus, controlling the rotational speed of the impeller 440 allows to control the HGC temperature. This disclosure may refer to the means for flowing a coolant by a rotating impeller as an “impeller drive.”

Referring now to FIGS. 15C and 15D, there is shown a heat transfer device (HTD) 400′ which is a variant of the HTD 400. The HTD 400′ is similar to HTD 400, except that the HTD 400′ additionally comprises an inlet port 405 and an outlet port 407 installed in the body 402′. The inlet port 405 allows for the liquid coolant 416 to be fed from an outside source into the flow channel 404′, The outlet port 407 allows for the liquid coolant 416 to be drained from the flow channel 404′ to the exterior of the HTD 400′. Furthermore, the second surface 408′ may not be relied on for rejecting heat.

In operation, liquid coolant 416 is fed from an external supply through the inlet port 405 into the flow channel 404′, it is caused to flow under the HGC 114, and it is drained out of the flow channel 404′ through the outlet port 407. External actuation means are provided to spin the impeller 440. Due to the finite viscosity of the coolant 416, at least a portion of the coolant 416 may be entrained by the cylindrical surface 444 of the impeller 440 and may travel with it. As a result, the flow of coolant 416 from the inlet port 405 to the outlet port 407 may be significantly enhanced. Preferably, the cylindrical surface 444 may have surface extensions (for example, ridges, grooves, or surface irregularities) to better entrain the coolant. Furthermore, the high rotational speed of the impeller 440 may cause and/or enhance the turbulence in the liquid coolant 416. As a consequence, heat transfer from HGC 114 to the coolant 416 may be significantly enhanced. In particular, for a given flow rate of liquid coolant 416 into the inlet port 405, action of the rotating impeller 440 may significantly enhance heat transfer over what may be achievable with a stationary impeller. The heat acquired by the liquid coolant 416 from the HGC 114 is removed from the HTD 400′ by the flow of liquid coolant 416 drained through the outlet port 407. Controlling the rotational speed of the impeller 440 allows one to control the temperature of HGC 114. If desired, a portion 404a of the flow channel 404 may be narrowed down to reduce a flow of liquid coolant 416 therethrough.

One important application of the HTD 400′ may be in cooling semiconductor chips in electronic inverters used in hybrid electric vehicles. In particular, the liquid coolant 416 may be an engine coolant supplied by the engine cooling loop.

Referring now to FIG. 16, there is shown an HTD 500 in accordance with a further preferred embodiment of the subject invention comprising a body 502 having a flow channel 504 with a flow diverter 565. The flow channel 504 has a generally constant radius of curvature except for the flow channel portion in proximity of the HGC 114. In particular, in proximity of the HGC 114 the flow channel 504 includes the flow director 565 arranged to redirect the flow of the coolant 516 indicated by arrows 524 in a generally radial direction and to impinge into the channel wall just under the HGC 114. As a result, the heat transfer just under the HGC 114 may be substantially enhanced.

Referring now to FIGS. 17, 18A, 18B, and 19 through 22, there is shown an HTD 600 in accordance with a yet further preferred embodiment of the subject invention. The HTD 600 comprises a body 602, jacket 689, bushing 657, 3-phase armature 683, and 3-phase coils 632a, 632b, and 632c. The body 602 is generally formed as a hollow cylinder having a smooth circular bore and an exterior surface. The body 602 is preferably made of material having high thermal conductivity, such as, but not limited to copper, aluminum, molybdenum, copper-tungsten alloy, silicon carbide (SiC), silicon (Si), aluminum nitride (AlN), beryllium oxide (BeO), boron nitride, as well as metal matrix composites comprising of graphite or graphine. If the body 602 is made of copper or aluminum alloys, its surfaces in contact with the liquid metal 616 should be protected with a suitable anticorrosion coating such as, but not limited to, titanium nitride (TiN) coating or diamond like coating (DLC). The exterior surface of the body 602 may also have three flat surfaces 606 for mounting HGC 614 and for receiving heat. The exterior surface of the body 602 may be equipped with channels 667 for flowing a secondary coolant indicated by arrow(s) 679. A family of suitable secondary coolants may include, but is not limited to, water, ethylene glycol, alcohol, antifreeze, Freon, air, or other suitable fluids.

The jacket 689 is generally formed as a hollow cylinder with inner diameter sized to closely fit over the exterior surface of the body 602. The jacket 689 may be made of soft ferromagnetic material. To limit losses due hysteresis, the jacket is preferably made of silicon steel. For improved resistance to corrosion by the secondary coolant 679, the jacket 689 may be made of ferritic stainless steel, such as the American Iron and Steel Institute (AISI) grades 405, 429, 430, 434, 436, and 446. The jacket 689 has three openings 671 (FIG. 20) designed to align with the flat surfaces 606 on the body 602 when the jacket 689 is installed over the body. In addition, the jacket 689 may have a groove 619. The jacket 689 may be installed over the body 602 and affixed to it using brazing, soldering, swaging, adhesive bonding, or any other suitable joining techniques. When the jacket 689 is installed over the body 602, the groove 619 connects the secondary coolant flow channels 667 of the exterior of the body 602. Alternatively, a circumferential groove connecting the channels 667 may be provided directly on the external surface of the body 602.

When the jacket 689 is installed over the body 602, one or more HGC 614 may be affixed onto the surface 606 of the body 602. The HGC 614 may be a semiconductor chip die with a Si, SiC, or other suitable substrate. Alternatively, the HGC 614 may be semiconductor chip packaged in suitable casing. For example, each surface 606 may receive two HGC 614, one being an insulated gate bipolar transistor (IGBT) and the other a diode, such as may be used in switching high electric currents. In particular, such IGBT-diode combination may be used to construct electronic inverters for producing 3-phase output from a DC input.

The HGC 614 may be affixed to the surface 606 by soldering, adhesive bonding, or other suitable joining technique. If the body 602 is made of SiC, AlN, BeO or alike, the surface 606 may be equipped with suitable metallic coating to facilitate soldering. If the body 602 is made of electrically conductive material and electrical insulation between HGC 614 and the body 602 is required, a thin (for example, 100-micron thick) wafer 693 of suitable electrically insulating material (for example, AlN) may be placed between the HGC 614 and the surface 606. The diameter of the body 602 is preferably made 4 to 10 times the cross-sectional width of the HGC 614 in FIG. 18A.

The bushing 657 may be generally formed as a hollow cylinder with an outside diameter to fit the bore of the body 602 and an inside diameter to fit over the 3-phase armature 683. The bushing 657 has groove 673. Preferably the groove 673 has a rectangular shape and it is wide and shallow. The groove 673 may be at least as wide as the HGC 614. For example, in some variants of the subject invention, the groove 673 may be 12 millimeters wide and 1 millimeter deep. The bushing 657 is preferably made of electrically insulating material such as plastic, glass-filled epoxy, glass ceramic (such as Macor), or ceramic. However, the bushing 657 may be also made from metal. When necessary, portions of the metal bushing 657 should be protected with a suitable anticorrosion coating to avoid corrosion by liquid metal 616. The bushing 657 may be installed and affixed into the bore of the body 602 by using adhesives, or by press fitting, or the combination of both, or by any other suitable technique. When the bushing 657 is installed in the bore of the body 602, the grove 673 and a portion of the bore form a flow channel 604.

The flow channel 604 may be either partially or entirely filled with a suitable liquid metal 616. The liquid metal 616 may be injected into the flow channel by a hypodermic needle via a small delivery hole 607 in the bushing 657. A grove in the cylindrical surface of the bushing 657 may be used instead of the hole 607. After the flow channel is filled to a desirable level, the delivery hole 607 may be plugged with suitable material. For example, the hole may be plugged with suitable adhesive.

The 3-phase armature 683 is arranged to receive the 3-phase coils 632a, 632b, and 632c. The coils may be electrically joined in a standard delta connection and connected to a 3-phase power supply. The armature 683 is preferably made from soft ferromagnetic material having low hysteresis, such as silicon steel. Most preferably, the armature is made from silicon steel sheets (also known as transformer plates). This approach reduces eddy current loss. The HTD 600 may also include an end cap 691 and a mounting screw 687 (FIGS. 19-22).

In operation, the 3-phase coils 632a, 632b, and 632c may be energized with a 3-phase alternating current (AC) to produce electromagnetic field (EM) in the armature 683, the jacket 689, and the gap therebetween. The EM field may have a rotating component. The liquid metal 616 may be in the flow channel 604 located the gap between the armature 683 and the jacket 689, and it may be exposed to the EM field. Because the liquid metal 616 is electrically conductive, the EM field may generate eddy currents therein, thus establishing a force coupling between the liquid metal 616 and the EM field. As a result, the liquid metal 616 may be made to flow in the channel 604 (FIGS. 18A and 18B) in the direction indicated by arrows 624 (FIG. 18A). Concurrently, a secondary coolant streams 679 may be injected into channels 667a and 667b (FIGS. 18B and 21) and flow up to the groove 619 where they may merge, follow the groove 619 to the channels 679c and exit as a coolant stream 679′.

The HGC 614 may be operated as intended, thus producing waste heat, which is conducted through the joining material 620, the electrical insulator 693 (if used), and surface 606 into the body 602. The heat may be then transported from the portion of body 602 adjacent to the HGC 614 into the liquid metal 616 and carried away by the flow. The heat may be then transported from the liquid metal 616 into the portion of the body 602 adjacent to the channels 667, and therefrom into the coolant stream 679 flowing through the channels. The liquid metal 616 may remove heat at high flux from the portion of body 602 adjacent to the HGC 614 with very low thermal resistance and carry it into the portion of the body 602 adjacent to the channels 667. The combined area of the channels 667 wetted by the coolant stream 679 may be arranged to be many times (preferably 10 to 30 times) larger then the area of the HGC 614 thermally contacted to the surface 606. This arrangement may make it possible to transfer heat into the coolant stream 679 with a low thermal resistance. As a result, the HTD 600 may enable removal of high load heat at high flux from HGC 614 and transfer it to the secondary coolant stream 679 with very low resistance. Because the flow channel 604 has a constant curvature, the liquid metal 616 can be flowed at high velocity (up to several meters per second) with only modest motive power.

As already noted above, the HGC 614 may comprise IGBT and diode such as may be used in electronic inverters for producing 3-phase output from a DC input. Such inverters may be used, for example, in hybrid electric vehicles, all-electric vehicles, photovoltaic power plants, and wind power plants. Referring now to FIGS. 23, 24, and 25, there is shown an inverter assembly 601 in accordance with a still further preferred embodiment of the subject invention. The inverter assembly 601 may comprise two HTD 600 mounted on a coolant manifold 627 (FIGS. 24 and 25) and integrated with an electronic inverter card 661 populated with control chips, bus bars, and terminals. The coolant manifold 627 may comprise two ports 613 and coolant tubes 673. The ports 613 comprise three coolant passages 659 and a gasket 645. The HTD 600 may be inserted into the ports 613 so that the passages 659 of the ports are aligned with the coolant channels 667 of the HTD for feeding coolant stream 679 to and from the HTD 600. The HTD is help in place in the port 613 by the combination of the mounting screw 687 and the end cap 691. For clarity, FIGS. 23-25 do not show the electrical connections between the inverter card 661 and the HGC 614 on the HTD 600. Spacers 681a and 681b may be sued to hold the armature 683 in place. Because the inverter in a hybrid electric vehicle handles only transient loads, the HTD 600 drive (excitation of the 3-phase coils 632a, 632b, and 632c) may be only activated on demand, such as when the vehicle is accelerating. In an all-electric vehicle, the HTD 600 may be operated continuously. A temperature sensor may be provided to on the HTD 600 or on the HGC 614 to warn of overheating. An “over-temperature” signal from the sensor may be used to shut down the inverter or to limit its power throughput.

Referring now to FIGS. 26, 27A, and 27B, there is shown an HTD 700 in accordance with a variant to the HTD 600 of the subject invention. The HTD 700 may be very similar to the HTD 600 except that the flow of liquid metal 716 is facilitated by an impeller 740 rather than EM field. The bushing 657 for HTD 600 (FIGS. 18A and 18B) is omitted. The impeller 740 may be formed as a cylinder mounted on a shaft 715 rotatably suspended in plugs 721 and 723. The plugs 721 and 723 may include low friction or antifriction bearings (not shown) to allow for rotation of the shaft 715 with only little torque. The plugs 721 and 723 may be made of plastic (for example, Nylon) or other suitable material and they may be press-fitted into the bore of the body 702. O-rings 749 may be provided to ensure good seal. Selected surfaces of the plugs 721 and 723, the body 702, and the impeller 740 may form the flow channel 704 filled with liquid metal 716. Suitable seal may be provided around the shaft 715 in the plug 723 to prevent the liquid metal 716 from leaking. Alternatively, the HTD 700 may be positioned with the end of the shaft 715 protruding through the plug 723 pointing up.

The cylindrical surface of the impeller 740 may be smooth or it may have grooves or dents to better engage the liquid metal 716 and to mix it. Suitable grooves may be circumferential, axial, crisscross, may form a pattern, or be random in size and/or direction. Additional grooves may be added onto the flat sides of the impeller 740 to bring in liquid metal 716 and to allow formation of a lubricating film between the impeller 740 and the plugs 721 and 723. This embodiment of the subject invention allows for using alternative liquids to the liquid metal 716. For example, the liquid metal 716 may be substituted with a coolant comprising substantially water, or alcohol, or mixture of water and alcohol, or Freon, or nanofluid. The impeller 740 may be formed from metal, plastic, ceramic, glass, or other suitable material. The jacket 789 may be formed from plastic, rubber, metal, or ceramic. If the jacket 789 is formed from ductile material, it may be press-fitted, shrunk-fitted, or swaged over the body 702. The body 702 may be formed the same way as the body 602 of FIGS. 17, 18A, 18B, and 19 through 22.

In operation, the shaft 715 is rotated as indicated by the arrow 746. Rotation of the shaft 715 may be accomplished by external means such as, but not limited to electric motor, internal combustion engine, hydraulic motor, compressed air turbine, and wind turbine. The impeller 740 induces the liquid metal (or alternative coolant, if used) to flow inside the channel 704 in the direction indicated by arrows 724 (FIG. 27A). As in the HTD 600, waste heat from HGC 714 is transported into the flow of liquid metal 716 (or alternative coolant, if used) and therefrom to the secondary coolant stream 779 flowing through the channels 767.

Referring now to FIGS. 28, 29A, and 29B, there is shown an HTD 800 in accordance with a variant to the HTD 700 of the subject invention. The HTD 800 may be very similar to the HTD 700 except that the impeller 840 is rotated by a 3-phase electromagnet formed by the armature 831 and 3-phase coils 832a, 832b, and 832c. The impeller 840 may be mounted on a shaft 815 rotatably suspended in bearings 809 installed in the plugs 821. Alternatively, the shaft 815 may be stationary, and the impeller 840 may be rotatably mounted on the shaft 815 via a suitable bearing. The bearings 809 may be friction bearings made of suitable low-friction material such as Nylon or Teflon, or they may be formed as antifriction bearings with suitable rolling elements, or they may be formed as jewel bearings such as used in precision instruments. This embodiment of the subject invention allows for using alternative liquids to the liquid metal 816. For example, the liquid metal 816 may be substituted with a coolant comprising substantially water, or alcohol, or mixture of water and alcohol, or Freon, or nanofluid. The impeller 840 may be formed similarly to the impeller 740 but it may also comprise a squirrel cage electrical conductor such as practices in rotors of certain 3-phase motors. Suitable armature formed from a ferromagnetic material may be also included the impeller 840. Alternatively, the impeller 840 may comprise a permanent magnet having a magnetization substantially in a radial direction of the impeller 840. The armature 831 may be formed from a soft ferromagnetic material having low hysteresis such as silicon steel. Preferably, the armature 831 may be formed from transformer plates.

The HTD 800 may operate in the same manner as the HTD 700, except that the motive power to the impeller 840 is provided by the EM field generated by the 3-phase coils 832a, 832b, and 832c fed by a 3-phase AC current in concert with the armature 831.

Referring now to FIGS. 30, 31A, and 31B, there is shown an HTD 900 in accordance with a variant to the HTD 600 of the subject invention. The HTD 900 may be very similar to the HTD 600 except that the liquid metal 916 inside the flow channel 904 is now flowed by magneto-hydro-dynamic (MHD) effect generated by electrodes 930aa, 930ab, 930ba, and 903bb, and permanent magnet 929. In particular, the permanent magnet 929 has a magnetization indicated by the arrow 943. The permanent magnet 929 is preferably substantially formed from samarium-cobalt or from neodymium-iron-boron materials. The bushing 947 may be very similar to the bushing 657 of the HTD 600, except that it has a provision for installation of the electrodes 930aa, 930ab, 930ba, and 903bb. The bushing 947 is preferably made of electrically insulating material such as, but not limited to plastic, Macor®, ceramic, or glass. The jacket 989 is preferably made of soft ferromagnetic material preferably having high magnetic saturation, such as, but not limited to, iron, low carbon steel, vanadium supermendur, or Hiperco®. For improved resistance to corrosion by the secondary coolant 979, the jacket 989 may be made of ferritic stainless steel, such as the American Iron and Steel Institute (AISI) grades 405, 429, 430, 434, 436, and 446.

To prevent corrosion by liquid metal 916, the electrodes 930aa, 930ab, 930ba, and 903bb should be made of corrosion resistant material preferably being also a good electrical conductor, such as, but not limited to molybdenum, tungsten, niobium, or tantalum. Alternatively, the electrode may be made of copper or copper alloy and it may be plated with a suitable refractory metal such as, but not limited to molybdenum, tungsten, niobium, tantalum, rhenium, osmium, and iridium. The body 902 is preferably made of materials having high thermal conductivity and, low electrical conductivity or being dielectric. Suitable materials for the body 902 may include, but are not limited to silicon carbide, silicon, aluminum nitride, and BeO (beryllia). The electrodes 930aa, 930ab, 930ba, and 903bb may be held in place with suitable adhesive such as, but not limited to epoxy or polyacrylate cement. The liquid metal 719 may be delivered into the channel 904 though the electrode slots in the bushing 947 prior to installation of the last electrode.

In operation, the electrodes 930aa and 930ba (FIG. 31B) may be connected to a source of direct current so that electric current may be flowed through the portion of liquid metal 916 between the electrodes 930aa and 930ba. This portion of the liquid metal is also immersed in the magnetic field generated by the magnet 929. Magnetic field lines are indicated by arrows 925 in FIGS. 31A and 31B. The interaction between the electric current and the magnetic field in the liquid metal 916 generates a force on the liquid metal 916 causing it to flow in the direction indicated by the arrows 924. In some variants of the invention, the electrodes 930ab and 930bb may be omitted. However, if the electrodes 930ab and 930bb are used, they may be also connected to a source of direct current so that electric current may be flowed through the portion of liquid metal 916 between the electrodes 930ab and 930bb. Care should be exercised to as to the polarity of the electric current connections to the electrodes 930aa, 930ab, 930ba, and 903bb to ensure that the MHD forces onto the liquid metal 916 have a consistent direction. In some variant of the invention, the electrode pairs 930aa-930ba and 930ab-903bb may be electrically connected in series. For example, the electrodes 930ba and 930bb may be electrically connected with suitable “jumper” conductor to connect the electrode pairs 930aa-930ba and 930ab-903bb in series. In this case, the electrodes 930aa and 930ab may be connected to a source of direct current.

The HTD 900 may operate in the same manner as the HTD 600, except that the motive power to the liquid metal 916 is provided by the MHD effect generated by electrodes 930aa, 930ab, 930ba, and 903bb, and permanent magnet 929 in HTD 900 instead of the EM field generated by the coils 632a-c in HTD 600.

An alternative liquid metal alloy disclosed by Brandeburg et al. in the U.S. Pat. No. 7,726,972 and having reportedly extended useful temperature range may be also usable with the subject invention. The Brandeburg's alloy differs from the commercially available Gallium-Indium-Tin (GaInSn) alloy in that its composition additionally includes 2%-10% Zinc (Zn). A preferred composition of the new alloy, referred to herein as GaInSnZn, contains approximately 3.0% Zn. Like the known alloy GaInSn, the new alloy GaInSnZn is liquid at ambient temperatures, but unlike GaInSn, the new alloy GaInSnZn has a substantially lower melting point. According to Brandeburg et al., the temperature scan analysis of the new alloy GaInSnZn exhibits a melting point of −36.degree C., and experimental testing has shown that it operates satisfactorily in the subject apparatus at temperatures as low as −40.degree C. A further advantage of the new alloy GaInSnZn relative to the known alloy GaInSn is that the constituent element Zinc is relatively low in cost compared to the other elements of the composition, thereby lowering the cost of the alloy, even as its melting point is significantly lowered.

While the preferred Brandeburg's alloy composition includes 3% Zinc as described in the preceding paragraph, it should be appreciated that acceptable results for many liquid metal rotary connector applications may be achieved with a GaInSnZn alloy, where Zinc is present in a concentration range of 2%-10%. Also, alloys additionally containing up to 5% Bismuth (Bi) will provide acceptable results in the subject application. The following table sets forth three potential GaInSnZn alloy compositions, with Zinc present in concentrations of 3%, 5% and 7%, along with lower and upper ranges for each of the constituent elements.

	Gn	In	Sn	Zn	Bi
	3% Zn	66.4%	20.9%	9.7%	3.0%
	5% Zn	65.1%	20.4%	9.5%	5.0%
	7% Zn	63.7%	20.0%	9.3%	7.0%
	Lower	60%	18%	8%	2%	0%
	Upper	70%	22%	12%	10%	5%

The HTD 700 and HTD 800 of the subject invention may be also practiced with a liquid coolant suitable for boiling heat transfer in lieu of the liquid metal 716 and 816 respectively. Coolant suitable for boiling heat transfer may include suitable fluorocarbon (Freon) refrigerant, keton (such as acetone), or alcohol (such as ethanol or methanol), or ammonia. The coolant flow channel 704 and 804 respectively may also include a void that is substantially free of liquid and may contain gases and/or vapors at a predetermined pressure. The void space allows for thermal expansion of the coolant and for formation of vapor bubbles from liquid coolant while avoiding excessive buildup of pressure inside the flow channel.

In operation, when the coolant suitable for boiling heat transfer receives heat, a portion of the high vapor pressure liquid undergoes nucleate boiling. Vapor bubbles are swept by the flow of coolant. Centrifugal force induces hydrostatic pressure within coolant, which may make the vapor bubbles buoyant. As a result, vapor bubbles may move away from the heat input surface and into the bulk flow of coolant, where they may collapse and deposit thermal energy.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” and “includes” and/or “including” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

The terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. For example, these terms can be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies.

The term “suitable,” as used herein, means having characteristics that are sufficient to produce a desired result. Suitability for the intended purpose can be determined by one of ordinary skill in the art using only routine experimentation.

Moreover, terms that are expressed as “means-plus function” in the claims should include any structure that can be utilized to carry out the function of that part of the present invention. In addition, the term “configured” as used herein to describe a component, section or part of a device includes hardware and/or software that is constructed and/or programmed to carry out the desired function.

Different aspects of the invention may be combined in any suitable way.

While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the present invention as defined in the appended claims. Furthermore, the foregoing description of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the present invention as defined by the appended claims and their equivalents. Thus, the scope of the present invention is not limited to the disclosed embodiments.

Claims

1. A heat transfer device comprising:

a) a body having a first surface, a second surface, and a chamber; said chamber being formed as a hollow cylinder comprising an inner cylindrical surface and an outer cylindrical surface; said outer cylindrical surface comprising a central axis of symmetry, a first constant radius of curvature, and an azimuthal direction; said inner cylindrical surface comprising a second constant radius of curvature; said inner cylindrical surface being substantially concentric with said outer cylindrical surface; said first surface is arranged to be in a good thermal communication with a heat generating component; said first surface being generally tangential to said outer cylindrical surface with only a small separation between the two; said second surface is arranged to be to be in a good thermal communication with a heat sink;

b) a liquid coolant substantially filling said chamber; and

c) a means for flowing said liquid coolant in said azimuthal direction.

2. The heat transfer device of claim 1, wherein two times the height of said hollow cylinder multiplied by the difference between said first constant radius of curvature and said second constant radius of curvature, divided by the sum of said height and said difference is in the range of 10 to 2000 micrometers.

3. The heat transfer device of claim 1, wherein said first constant radius of curvature is between 5 and 25 millimeters.

4. The heat transfer device of claim 1, wherein the difference between said first constant radius of curvature and said second constant radius of curvature is in the range of 10 to 2000 micrometers.

5. The heat transfer device of claim 1, wherein said liquid coolant is a liquid metal and wherein said means for flowing said liquid coolant in said azimuthal direction comprise an MHD drive comprising:

a) a permanent magnet generating a magnetic field within at least a portion of said liquid coolant; said magnetic field having a substantial component in a radial direction of said hollow cylinder; and

b) a plurality of electrodes for drawing electric current through at least a portion of said liquid coolant in a direction substantially parallel to said central axis of symmetry.

6. The heat transfer device of claim 1, wherein said liquid coolant is a liquid metal and wherein said means for flowing said liquid coolant in said azimuthal direction comprise a plurality of electromagnets; said electromagnets adapted for generating a magnetic field rotating in said azimuthal direction in response to excitation by poly-phase alternating current.

7. The heat transfer device of claim 1, wherein said means for flowing said liquid coolant in said azimuthal direction comprise on impeller; said impeller arranged to form at least a portion of said inner cylindrical surface; and said impeller arranged to rotate with respect to said body; and said impeller arranged to substantially rotate about said central axis of symmetry.

8. A heat transfer device comprising: a body, an impeller, and liquid coolant;

a) said body having a first surface, a second surface; (i) said first surface being arranged to be in a good thermal communication with a heat generating component; (ii) said second surface being arranged to be to be in a good thermal communication with a heat sink;

b) said impeller being rotatably suspended inside said body;

c) said impeller and said body being arranged to form a chamber; (i) said chamber being formed as a hollow cylinder comprising an outer cylindrical surface and an inner cylindrical surface; (ii) said outer cylindrical surface comprising a first constant radius of curvature; (iii) said inner cylindrical surface comprising a second constant radius of curvature (iv) said outer cylindrical surface of said chamber being substantially formed by said body; (v) said inner cylindrical surface of said chamber being substantially formed by said impeller; (vi) said inner cylindrical surface comprising an axis of rotational symmetry; (vii) said chamber being substantially filled by said liquid coolant; and

d) said impeller arranged to rotate substantially about said axis of rotational symmetry.

9. The heat transfer device of claim 8, wherein said first surface being generally tangential to said outer cylindrical surface with only a small separation between the two.

10. The heat transfer device of claim 8, wherein the difference between said first constant radius of curvature and said second constant radius of curvature is less than about 2,000 micrometers.

11. The heat transfer device of claim 8, further comprising a means to rotate said impeller about said axis of rotational symmetry.

12. The heat transfer device of claim 8, further comprising a plurality of electromagnets fed with poly-phase alternating current; said electromagnets being arranged to generate an electromagnetic field rotating substantially about said axis of rotational symmetry; said electromagnetic field being arranged to operatively couple to said impeller; said electromagnetic field arranged to rotate said impeller substantially about said axis of rotational symmetry.

13. The heat transfer device of claim 12, further comprising a permanent magnet; said permanent magnet being mechanically coupled to said impeller; and said permanent magnet being arranged to operatively couple to said electromagnetic field.

14. The heat transfer device of claim 12, further comprising an electromagnetic coil; said coil being mechanically coupled to said impeller; and said coil being arranged to operatively couple to said electromagnetic field.

15. A method for transferring heat from a heat generating component to a heat sink comprising the steps of:

a) providing a body, an impeller, and liquid coolant; said body comprising a first surface and a second surface; said impeller rotatably installed in said body; said impeller and said body arranged to form together a chamber; said chamber shaped generally as a hollow cylinder; said chamber being substantially filled with said liquid coolant;

b) rotating said impeller;

c) causing said liquid coolant to flow substantially azimuthally inside said cylindrical chamber;

d) transferring heat from a heat generating component into said liquid coolant;

e) transporting heat in said liquid coolant; and

f) transferring heat from said liquid coolant to a heat sink.

16. The method for transferring heat of claim 15, wherein said impeller substantially forms an inner cylindrical surface of said hollow cylinder.

17. The method for transferring heat of claim 15, further comprising the steps of:

a) providing a heat generating component arranged to be in a good thermal communications with said body; and

b) providing a heat sink arranged to be in a good thermal communications with said body.

18. The method for transferring heat of claim 15, further comprising the step of providing a means for rotating said impeller.

19. The method for transferring heat of claim 18, wherein said a means for rotating said impeller comprise a plurality a plurality of electromagnets adapted for operation with poly-phase alternating current.

20. The method for transferring heat of claim 18, wherein said a means for rotating said impeller are selected from the group of electric motor, rotating magnetic field, hydraulic motor, and a turbine.