WO2010090766A1 - Heat transfer device - Google Patents

Heat transfer device Download PDF

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Publication number
WO2010090766A1
WO2010090766A1 PCT/US2010/000357 US2010000357W WO2010090766A1 WO 2010090766 A1 WO2010090766 A1 WO 2010090766A1 US 2010000357 W US2010000357 W US 2010000357W WO 2010090766 A1 WO2010090766 A1 WO 2010090766A1
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WO
WIPO (PCT)
Prior art keywords
surface
coolant
magnetic field
liquid coolant
heat
Prior art date
Application number
PCT/US2010/000357
Other languages
French (fr)
Inventor
Jan Vetrovec
Original Assignee
Jan Vetrovec
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to US20719109P priority Critical
Priority to US61/207,191 priority
Priority to US12/584,490 priority patent/US20100071883A1/en
Priority to US12/584,490 priority
Application filed by Jan Vetrovec filed Critical Jan Vetrovec
Publication of WO2010090766A1 publication Critical patent/WO2010090766A1/en

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Classifications

    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28HEAT EXCHANGE IN GENERAL
    • F28DHEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
    • F28D15/00Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28HEAT EXCHANGE IN GENERAL
    • F28FDETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F23/00Features relating to the use of intermediate heat-exchange materials, e.g. selection of compositions
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28HEAT EXCHANGE IN GENERAL
    • F28FDETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F2250/00Arrangements for modifying the flow of the heat exchange media, e.g. flow guiding means; Particular flow patterns
    • F28F2250/08Fluid driving means, e.g. pumps, fans
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L33/00Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/48Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
    • H01L33/64Heat extraction or cooling elements
    • H01L33/648Heat extraction or cooling elements the elements comprising fluids, e.g. heat-pipes
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01SDEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00Semiconductor lasers
    • H01S5/02Structural details or components not essential to laser action
    • H01S5/024Cooling arrangements
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01SDEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00Semiconductor lasers
    • H01S5/02Structural details or components not essential to laser action
    • H01S5/024Cooling arrangements
    • H01S5/02407Active cooling, e.g. the laser temperature is controlled by a thermo-electric cooler or water cooling
    • H01S5/02423Liquid cooling, e.g. a liquid cools a mount of the laser
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01SDEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00Semiconductor lasers
    • H01S5/02Structural details or components not essential to laser action
    • H01S5/024Cooling arrangements
    • H01S5/02469Passive cooling, e.g. where heat is removed by the housing as a whole or by a heat pipe without any active cooling element like a TEC

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 electrically conductive liquids (including liquid metals) and ferrofluids. 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

TITLE: HEAT TRANSFER DEVICE

CROSS-REFERENCE TO RELATED APPLICATIONS:

This application claims priority from U.S. provisional patent application U.S. Ser. No. 61/207,191, filed on February 09, 2009. This patent application is a continuation-in-part patent application of: United States serial number 12/290,195 filed on October 28, 2008 and entitled HEAT TRANSFER DEVICE; and United States serial number 12/584,490 filed on September 05, 2009 and entitled HEAT TRANSFER DEVICE; the entire contents of all of which are hereby expressly incorporated by reference.

TECHNICAL FIELD

[001] This invention relates generally to heat removal from heat-generating components and more specifically to heat removal of heat at high flux.

BACKGROUND ART |002) 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.

10031 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

I of 37 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.

[004] 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.

[005] 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. [006] 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.

[007J 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.

[008] 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. [009] 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 to obtain desirable heat transfer coefficient with conventional coolants such as water, alcohol, or ethylene glycol. Liquid metal coolants have been also considered to attain target heat transfer coefficient. 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.

[001 OJ In summary, prior art does not teach a heat transfer device capable of removing heat at very 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.

DISCLOSURE OF THE INVENTION

[0011] 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.

[0012] 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).

|0013] 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. [0014] 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.

10015 j 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.

[0016] It is another object of the invention to provide means for cooling HGC.

[0017] It is still another object of the invention to provide means for temperature control of HGC.

[0018] It is yet another object of the invention to cool a semiconductor electronic components.

[0019] It is yet further object of the invention to cool semiconductor laser diodes.

[0020] It is a further object of the invention to cool LED for solid-state lighting. [0021] It is still further object of the invention to cool computer chips.

|0022] It is an additional object of the invention to cool photovoltaic cells.

[0023] These and other objects of the present invention will become apparent upon a reading of the following specification and claims.

BRIEF DESCRIPTION OF DRAWINGS

[0024] FIG. IA 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. 10025] FIG. IB is a cross-sectional view of an HTD in a plane transverse to coolant flow in accordance with one embodiment of the subject invention using a magneto- hydrodynamic drive.

10026 J FIG 1C shows a ferromagnetic yoke that may be used to carry return flux between permanent magnets of the magneto-hydrodynamic drive of FIGs. IA and IB

[00271 FIG. 2A is an enlarged view of portion 2A of the HTD of FIG. 1 A. |0028] FIG. 2B is an enlarged view of portion 2B of the HTD of FIG. IB.

|0029] FIG. 3 is an enlarged view of alternative portion 2B of the HTD of FIG. IB showing a flow channels with surface extensions. [0030] FIG. 4 is an enlarged view of another alternative portion 2B of the HTD of

FIG. IB showing multiple flow channels arranges side -by-side.

(0031 J Fig. 5 is an enlarged view of portion 2A of the HTD of FIG. IA showing a mounting of a laser diode array HGC.

[0032] Fig. 6 is an enlarged view of portion 2A of the HTD of FIG. IA showing a mounting of a laser diode bar HGC.

[0033] Fig. 7 is an enlarged view of portion 2A of the HTD of FIG. IA showing a mounting of a light emitting diode HGC.

|0034] Fig. 8 is an enlarged view of portion 2A of the HTD of FIG. IA showing a mounting of a solid-state laser crystal HGC. 10035] FIG. 9 shows an alternative HTD body having internal passages for a secondary coolant.

[0036] FIG. 10 shows another alternative HTD body having external fins for heat transfer to gaseous coolant or ambient air.

[0037] FIG. HA is a side 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. [0038] FIG. 11 B is a side cross-sectional view of an HTD in a plane transverse to coolant flow in accordance with another embodiment of the subject invention wherein coolant flow is induced by a rotating magnetic field produced by a rotating magnet.

[0039] FIG. 12A is a side 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.

[0040] FIG. 12B is a side cross-sectional view of an HTD in a plane transverse to the flow loop in accordance with yet another embodiment of the subject invention wherein coolant flow is induced by a rotating magnetic field produced by stationary electromagnets. [0041 J FIG. 13 shows a suitable connection of electromagnets to a single phase alternating current supply.

10042] 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. [0043] FIG. 15A is a side cross-sectional view of an HTD in accordance with still another embodiment of the subject invention using an impeller.

[0044] FIG. 15B is a side cross-sectional view of an HTD in a plane transverse to coolant flow in accordance with still another embodiment of the subject invention using an impeller. [0045] FIG. 16A is a plan view of an HTD in accordance with a further embodiment of the subject invention having a planar flow loop.

|0046] FIG. 16B is a side cross-sectional view of an HTD in accordance with further embodiment of the subject invention having a planar flow loop.

[0047] FIG. 17A is a plan view of an HTD in accordance with a still further embodiment of the subject invention having a planar flow loop with an impeller.

[0048] FIG. 17B is a side cross-sectional view of an HTD in accordance with still further embodiment of the subject invention having a planar flow loop with an impeller.

[0049] FIG. 18 is a plan view of an alternative impeller of the HTD of FIG. 17A. [0050] FIG. 19A is a side cross-sectional view of an HTD in accordance with a yet further embodiment of the subject invention having an elongated flow loop.

[0051] FIG. 19B is a face view of an HTD in accordance with yet further embodiment of the subject invention having an elongated flow loop. [0052] FIG. 20 is a top view of an HTD in accordance with additional embodiment of the subject invention suitable for flat packaging.

[0053] FIG. 21 is a view 21-21 of the HTD of FIG. 20. [0054] FIG. 22 is a view 22-22 of the HTD of FIG. 21. [0055J FIG. 23 is a view 23-23 of the HTD of FIG. 21. [0056] FIG. 24 is a view of a ferromagnetic yoke that may be used in HTD of FIG.

20 to facilitate a return magnetic flux.

[0057] FIG. 25 is a view of the HTD of FIG. 20 being constructed from several layers of material.

|0058] FIG. 26A is a top view of a layer for construction of HTD of FIG. 25. [0059] FIG. FIG. 26B is a bottom view of a layer for construction of HTD of FIG.

25.

[0060] FIG. 27A is a view of HTD having fins on the top surface.

|0061] FIG. 27B is a view 27B-27B of the HTD of FIG. 27A.

[0062] FIG. 28A is a view of HTD having fins on the bottom surface. [0063] FIG. 28B is a view 28B-28B of the HTD of FIG. 28 A.

[0064J FIG. 29 is a cross-sectional view of a variant HTD having an MHD drive.

[0065] FIG. 30A is a cross-sectional view of a variant HTD having an alternative MHD drive.

[0066] FIG. 30B is a cross-sectional view 30B-30B of the HTD of FIG. 3OA. BEST MODE FOR CARRYING OUT THE INVENTION

|0067j 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.

[0068] Referring now to FIGS. IA and IB, 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. |0069] 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. [0070] 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, NY), 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 US Patent No. 5,800,060 issued to G. Speckbrock et al., on September 1, 1998. It is important that electrodes 130a and 130b (FIG. IB), 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 (Aug. 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 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.

[0071] 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, CA. FIG. 8 shows a mounting of HGC 1141V, 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. Patent No. 7,003,011.

[0072] Referring now again to FIGS. IA and IB, 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 (FIG 1C). 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. [0073] 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. IA and the arrows 124 in FIG. 2 A. 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."

[0074] 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. 9 shows an HTD body 102' having a second surface 108' formed as internal passages for flowing secondary liquid or gaseous coolant. 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. [0075] 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.

|0076] Referring now to FIGS. 1 IA and 1 IB, 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 Wl 1 available from FerroTec in Bedford, NH, 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.

|0077] The body 202 is similar to body 102 of HTD 100 (FIG. IA) 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. IA) 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).

|0078 J 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.

[0079| 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.

[0080] 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."

[0081] 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, NY, 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. 10082 J 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, NY, 1966). Electromagnet coils may have ferromagnetic cores such as practiced on electric motors for alternating current. 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. |0083| 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.

[0084 j 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. 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."

[0085] The HTD of the subject invention may be also practiced in a flat package.

Referring now to FIGS. 16A and 16B, there is shown an HTD 500 in accordance with further preferred embodiment of the subject invention comprising a body 576 and a rotating magnet assembly 596. The body 576 , which is preferably made of material having good thermal conductivity, is a generally flat member comprising a front face 586, back face 588, and an annular flow channel 598 therebetween. In one variant of the preferred embodiment, the channel 598 has a thickness in the range from 0.1 to 5 millimeters and an outside diameter in the range from 10 to 100 millimeters. The body is preferably constructed from materials having high thermal conductivity. Either one or both of the faces 586 and 588 may be in a thermal communication with a suitable heat sink. The channel 598 may be substantially filled with liquid coolant 516. The coolant 516 may be either an electrically conductive liquid and/or a ferrofluid. A heat-generating component (HGC) 114 may be attached to the front face 586 and arranged to be in a good thermal communication therewith. The magnet assembly 596 is rotationally suspended so that its plane of rotation is generally parallel to and in a close proximity to the back face 588. The magnet assembly 596 may also comprise a permanent magnet 592 and pole extensions 594a and 594b. Furthermore, the magnet assembly 596 may be affixed to a shaft 577 of an electric motor 574. A fan 590 may be also affixed to the shaft 577 of the electric motor 574.

[0086] In operation, the HGC 114 generates waste heat that is conducted to the front face 586 of the body 596 and, therethrough into the coolant 516. Electric motor 574 spins the magnet assembly 596, which generates a rotating magnetic field that penetrates though the back face 588 and interacts with the coolant 516. If the coolant 516 is electrically conductive, the rotating magnetic field couples to the coolant via eddy currents in a manner already describe in connection with the HTD 200. If the coolant 516 is a ferrofluid, the rotating magnetic field couples to the coolant magnetically in a manner already describe in connection with the HTD 200. In either case, rotation of the magnet assembly 596 causes the coolant 516 to flow around the annular flow channel 598 as indicated by the arrow 599. As a result, waste heat received by the coolant from HGC 514 is transported to other parts of the front face 586 and to the back face 588, and therefrom to a suitable heat sink. To facilitate improved removal of heat from the back face 588, fan 590 spun by electric motor may direct ambient air onto the back face 588. One skilled in the art will recognize that a rotating magnetic field suitable for causing the coolant 516 to flow around the annular flow channel 598 may be also produced by stationary electromagnets supplied with poly-phase alternating currents as already described in connection with the HTC 300. [0087J Referring now to FIGS. 17A and 17B, there is shown a heat transfer device

(HTD) 600 in accordance with yet further preferred embodiment of the subject invention. The HTD 600 is essentially the same as the HTD 500, except that in HTD 600 further comprises an impeller disk 668. In addition, the flow channel 698 is a disk-like (rather than annular) chamber. Furthermore, the coolant 616 used with HTD 600 may be any suitable liquid coolant. The impeller disk 668 is rotatably suspended inside the flow channel 698 on bearings 684 and substantially immersed in coolant 616. The impeller disk 668 may be made of an electrically conductive material and/or from a ferromagnetic material. In some variants of this embodiment the impeller disk 668 may have radial slots or perforations 678 such as shown in FIG. 18 to improve inductive coupling to the rotating magnetic field. The HTD 600 operates similarly to the HTD 500, except that the rotating magnetic field generated by the magnet assembly 596 couples to the impeller disk 668. If the impeller disk 668 is made of an electrically conductive material such as copper, the magnetic field may couple into it inductively via eddy current interaction. If the impeller disk 668 is made of ferromagnetic material such as steel, the magnetic field may couple into it magnetically. In either case, rotation of the magnet assembly 596 causes the impeller disk 668 to rotate, which in turn causes the coolant 616 to flow inside the chamber 698 as indicated by arrow 699.

[0088] Referring now to FIGS. 19A and 19B, there is shown a heat transfer device (HTD) 700 in accordance with still further preferred embodiment of the subject invention and suitable for cooling semiconductor laser diode bars in densely packed arrays. HTD 700 is similar to HTD 300', except that in HTD 700 the flow channel 704 and the opening 764 are elongated. In particular, the HTD 700 comprises a body 702 having an opening 764. A plurality of semiconductor laser diode 150 are installed into a substrate 148, which is attached to the body 702 and in a good communication therewith. The flow channel 704 containing liquid coolant 716 has a generally rectangular configuration, but other suitable configurations may be also practiced. Suitable liquid coolant 716 may be an electrically conductive liquid or a ferrofluid. Coil assemblies 732a-d each comprise two coils, one on the outside the body 702 and one inside the opening 764. Preferably, the coils in each assembly are positioned so that the magnetic field they generate crosses the channel 704 at substantially normal incidence. The coil assemblies 732a-d are fed poly-phase alternating currents arranged to produce magnetic field traveling in the direction of arrow 722, thereby inducing the coolant 716 to flow inside the channel 704 in the same direction. The laser diodes 150 are operated to produce optical output 152 while also generating waste heat. The coolant 716 flowing inside the channel 704 removes waste heat from the laser diodes 150 and transfers it to second surface 708 inside the opening 764. The opening may contain suitable heat sink such as secondary liquid coolant, gaseous coolant, or phase change material. It can be appreciated that the HTD 700 is conducive to stacking of multiple HTD units vertically and horizontally to produce large arrays that may be required for direct material processing or pumping of solid-state lasers.

|0089) Referring now to FIGs. 20-23, there is shown a heat transfer device (HTD) 800 in accordance with additional preferred embodiment of the subject invention and suitable for compact packaging. HTD 800 comprises a body 802 with a first surface 806 adapted for receiving waste heat from the HGC 114 and a second surface 808 adapted for transferring heat from the HTD 800 to a heat sink (not shown). In particular, the second surface 808 is arranged to be in a good thermal communication with a heat sink. Suitable heat sinks include a structure, heat pipe, secondary liquid coolant, phase change material (PCM), gaseous coolant, or ambient air. Fluid used as a heat sink may employ natural convection or forced convection to remove heat from the second surface 808. The second surface 808 may also include surface extensions such as fins or ribs to enhance heat transfer therefrom.

[0090] The body 802 is preferably made of material having high thermal conductivity. Examples of suitable materials are provided above in connection with the HTD 200. The body 802 further comprises a cylindrical chamber 897 and a fluid transfer passage 866. The cylindrical chamber 897 has a cylindrical surface 875, ceiling surface 811, and base surface 867 (FIG. 21). The cylindrical surface 875 has a substantially constant radius of curvature. The fluid transfer passage 866 includes a radial passage 839, tangential passage 835, vertical passage 841, and an injector passage 837. The cylindrical chamber 897 has a height "H" and diameter "D". Note that the diameter "D" is two (2) times the radius of curvature. The height "H" may be substantially smaller than the diameter "D". For example, the height "H" may be ten times smaller than the diameter "D". The preferred range for the diameter "D" is 10 to 100 millimeters. The preferred range for the height "H" is one thirtieth (1/30-th) to one sixth (1/6-th) of the diameter "D". The tangential passage 835 is fluidly coupled to the cylindrical surface 875 of the chamber 897 and preferably positioned to be generally tangential to it (FIG. 22). The injector passage 837 is fluidly connected to center of the base surface 867 of the cylindrical chamber 897 and oriented generally perpendicular to the base surface 867 (FIG. 21). The radial passage 839 is fluidly connected to the injector passage 837. The vertical passage 841 is fluidly connected to the tangential passage 835 and to the radial passage 839. The chamber 897 and the passages 835, 837, 839, and 841 are filled with a suitable liquid coolant 816. Suitable liquid coolant is either a ferrofluid or an electrically conductive liquid. Preferred liquid coolant 116 is liquid metal. Examples of suitable liquid coolants are provided above in connection with the HTD 200. The ceiling surface 811 may be generally parallel to the first surface 811. Preferably, the separation of the first surface 806 and the ceiling surface 811 is very small so that heat generated by HGC 114 can be efficiently conducted to the coolant 816 inside the chamber 897. Preferably, the separation of the surfaces 806 and 811 is substantially less than 1 millimeter. In some embodiments of the invention, the separation of the surfaces 806 and 811 may be on the order of 0.1 millimeter. The ceiling surface 811 may also include a pointed protrusion 895 generally positioned opposite to the injector passage 837 (FIG. 21). HTD 800 further comprises electromagnet coils 832a, 832b, and 832c, which may be positioned on the top surface 807 preferably with approximately 120 degree spacing. Preferably, the electromagnet coils 832a, 832b, and 832c include ferromagnetic flux returns. The coils and their respective flux return 831 may be arranged as shown in FIG. 24 so that magnetic field 860 produced within coolant 816 has a radial component. Preferably, HGC 114 is positioned generally above the center of the chamber 897 and in a good thermal communication with the surface 806. Preferably, HGC is mounted onto the surface 806. For example, HGC 114 may be mechanically clamped, bonded, soldered, or brazed onto the surface 806. Alternatively, HGC 114 may be attached to any other external surface of the body 802 and arranged to be in a good thermal communication with the coolant 116.

|0091] In operation, the HGC 114 is in a good thermal contact with the surface 806 and it is operated as intended. The operation of HGC 114 generates waste heat that is transported from the HGC 114 through the surface 806 into the body 802 and through the surface 811 into the coolant 816 inside the chamber 897. The electromagnet coils 832a,

832b, and 832c are supplied with poly-phase alternating currents to produce a time varying magnetic field with a rotating component. Magnetic field produced by the electromagnet coils 832a, 832b, and 832c engages the coolant 816 inside the chamber 897 in the manner already described in connection with the HTD 200 and 300, and causes the coolant 816 inside the chamber 897 to rotate in the direction of arrows 887 (FIG. 22). Rotation of the coolant 816 inside the chamber 897 substantially increases the rate of heat transfer from the surface 811 into the coolant 816.

[0092J Centrifugal force generated by the rotation within the coolant 816 forces the coolant toward the cylindrical surface 875 (FIG. 22). As a result, the hydrostatic pressure in the coolant 816 may be higher in the zone near the surface 875 of the chamber 897 than it is near the chamber center. A portion of the coolant 816 near the surface 875 flows into the tangential passage 835 as indicated by arrows 889. The coolant entering the tangential passage 835 may be decelerated therein, which may result in an increased hydrostatic pressure. The coolant then flows through the tangential passage 835 into the vertical passage 841, and it flows therethrough (as indicated by arrow 891) into the radial passage 839 (FIG. 21 and 23). The hydrostatic pressure in the coolant inside the vertical passage 841 may be greater then the hydrostatic pressure in the coolant inside the central portion of the chamber 897. As a result, the coolant flows (as indicated by arrow 893) through the radial passage 839 into the injector passage 837, and it flows therethrough (as indicated by arrow 885) into the central portion of the chamber 897. Coolant injected into the central portion of the chamber 897 from the injector passage 837 may substantially impinge on to the surface 811 and it may thereby increase the heat transfer rates at this location. In particular, the surface 811 may include the protrusion 895 formed to redirect the coolant flow from the injector passage 837 into a direction indicated by arrows 883. As a result, substantial portion of the injected coolant may flow generally along the surface 811. Furthermore, the protrusion 895 may be shaped to substantially avoid a stagnation point in the injected flow. Preferably, the injection passage 837 is aligned with the protrusion 895 (if present) so that the coolant flow is evenly spread in azimuthal direction. Rotation of the coolant 816 inside the chamber 897 may further entrain the injected flow causing it to rotate as indicated by arrows 881 (FIG. 22). Heat acquired by the coolant 816 from the surface 811 is transported by the coolant to other parts of the body 802. Heat may be removed from the body 802 through the surface 808 and transferred to a suitable heat sink. Alternatively, heat may be removed from the body 802 through the surface 807 and transferred to a suitable heat sink. [0093] In a variant of the HTD 800, the electromagnet coils 832a-c may be omitted, and a rotating magnet may be used to generate suitable rotating magnetic field such as, for example, may be practiced with the HTD 500 (FIGs 16A and 16B).

[0094] To facilitate ease of production, the body 802 of the HTD 800 may be constructed from several elements. Referring now to FIG. 25, the body 802' comprises the elements 802a, 802b, and 802c. The elements 802a and 802c may be formed as flat members.

The element 802b may be formed to include the chamber 897 and the passages 835, 837, 839, and 841 (FIGs. 26A and 26B). The elements 802a, 802b, and 802c may be joined by adhesive bonding, fusion bonding, diffusion bonding, soldering, brazing, or other suitable means to form the body 802'.

|0095] Referring now to FIGs. 27A and 27B, there is shown an HTD 800'. The HTD 800' is essentially the same at the HTD 800, except that the surface 807 is equipped with fins 877 adapted for transferring heat to a fluid. For example, the fins may be cooled by air via natural convection or via forced convection. [0096] Referring now to FIGs. 28A and 28B, there is shown an HTD 800". The

HTD 800" is essentially the same at the HTD 800, except that the surface 808 is equipped with fins 877 adapted for transferring heat to a fluid. For example, the fins may be cooled by air via natural convection or via forced convection.

[0097[ Referring now to FIG. 29, there is shown an HTD 900 suitable for flowing a liquid coolant 916 by means of MHD effect. HTD 900 comprises a body 902, permanent magnets 930a and 930b, electrodes 929a and 929b, and electric conductors 926a and 926b.

The body 902 is very similar to the body 802 of the HTD 800 (FIGs 20-23) except that the surfaces of the chamber 997 and the passages 935, 937, 939, and 941 may be made from materials that have a low electrical conductivity or that are electrically insulating. Alternatively, the surfaces of the chamber 997 and the passages 935, 937, 939, and 941 may be coated with an electrically insulating coating. Furthermore, the coolant 916 is an electrically conductive liquid. Suitable coolants have been described above in connection with the HTD 100. Preferred electrically conductive liquid coolant 916 include liquid metals and their alloys. In addition, the body 902 includes electrodes 930a and 930b arranged to be in electrical contact with the coolant 916, and a means for supplying the electrodes with electric current. For example, the electrode 930a may be electrically connected to the electrical conductor 926a and the electrode 930b may be electrically connected to the electrical conductor 926b, with the conductors 926a and 926b being electrically connected to a suitable source of direct electric current. The magnets 929a and 929b may be positioned in the proximity of the body 902 to provide a magnetic field with field lines 960 generally passing through the chamber 997 and the coolant 916 therein. The magnets 929a and 929b and the electrodes 929a and 929b should be positioned so that a vector of the electric current flowing between the electrodes has a substantial component orthogonal to the magnetic field lines 960. Preferably, the magnets 929a and 929b and the electrodes 929a and 929b should be positioned so that the vector of electric current flowing between the electrodes would be substantially orthogonal to the magnetic field lines 960. For example, magnets may produce a magnetic field that, is substantially perpendicular to the ceiling surface 911, and the electrodes draw an electric current that is substantially parallel to the ceiling surface 911. A yoke 931 made of soft ferromagnetic material (e.g., iron or soft steel) may be used to provide a flux return for the magnets 929a and 929b. HGC 114 may be mounted on the body 902 in the same manner as described in connection with the HTD 800. In a variant of the HTD 900, the permanent magnets 929a and 929b may be replaced by electromagnets.

[0098| The operation of HTD 900 is similar to the operation of the HTD 800, except that the motive force for rotating and flowing the coolant 916 inside the chamber 997 is generated by MHD effect. In particular, a direct electric voltage is applied to the electric conductors 926a and 926b. As a result, direct electric current is passed between the electrodes 930a and 930b through the coolant 916 substantially immersed in the magnetic field generated by the magnets 929a and 929b. The interaction between the electric current and the magnetic field generates a force acting on a portion of the coolant causing it to rotate in the chamber 997 and flow through the passages 935, 937, 939, and 941 in the manner already described in connection with the HTD 800. As a result, heat is being removed from the HGC 114 and transferred to a suitable heat sink.

[0099J In some variants of the invention, the HGC 114 may be operated (at least in- part) by a direct current electric power. Providing that the voltages and current of the HGC 114 and the electrodes 926a and 926b are compatible, the HGC may be electrically connected in series with the electrodes. If electromagnets are used in lieu of the permanent magnets 930a and 930b, and their voltages and currents are compatible with the HGC 114, the HGC may be electrically connected in series with the electromagnets.

[00100] Referring now to FIGs. 30A and 30B, there is shown an HTD 900' which is a variant of the HTD 900 (FIG 29). The HTD 900' is very similar the HTD 900 except that the permanent magnets 930a' and 930b', and the electrodes 929a' and 929b', are arranged to provide MHD pumping effect to the coolant 916 inside the radial passage 939.

100101] The operation of HTD 900' is similar to the operation of the HTD 900, except that the MHD motive force is applied to the coolant 916 inside the radial passage 939. In particular, a direct electric voltage is applied to the electric conductors 926a' and 926b'. As a result, direct electric current is passed between the electrodes 930a' and 930b' through the coolant 916 substantially immersed in the magnetic field generated by the magnets 929a' and 929b. The interaction between the electric current and the magnetic field generates a force acting on a portion of the coolant 916 causing it to flow through the passages 935, 937, 939, and 941, and being injected from the injector passage 937 into the chamber 997 where it impinges onto the ceiling surface 911. Draining of the coolant 916 from the chamber 997 via the tangential passage 935 induces a rotation to the coolant 916 inside the chamber 997. Coolant drained into the tangential passage flows to the radial passage 939 where it is being pumped again. Coolant impinging onto the ceiling surface 911 allows for efficient removal of heat therefrom. As a result, heat is being removed from the HGC 114 and transferred to a suitable heat sink.

[00102] The invention may be also practiced with a coolant suitable for boiling heat transfer. Coolant suitable for boiling heat transfer may be formed by mixing a suitable liquid having a high vapor pressure into a ferrofluid. For example, kerosene-based ferrofluid may be mixed with a suitable fluorocarbon (Freon) refrigerant, keton (such as acetone), or with alcohol (such as ethanol or methanol). Another example, water-based ferrofluid may be mixed with ammonia refrigerant or with suitable alcohol. The coolant flow channel or chamber 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. |00103] 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.

|00104] 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. [00105] 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. [00106] 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.

|00107] 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.

IOO1O8| Different aspects of the invention may be combined in any suitable way. |00109] 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.

INDUSTRIAL APPLICABILITY

[00110] The invention is applicable to cooling of 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. The invention provides a heat transfer component containing coolant flowing at high velocities in narrow channels, thereby enabling high heat transfer coefficient at flow channel wall. As a result, the invention is capable of removing waste heat at very high heat flux. This capability allows operating heat-generating components (such as listed above) at very high power density with a reduced risk of overheating and consequential loss of efficiency, malfunction, or even catastrophic failure. The channel wall may have a substantially constant radius of curvature in the direction of the flow, thereby reducing resistance to the flow and allowing operation at relatively low power consumption.

Claims

CLAIMSWhat is claimed is:
1. A heat transfer device comprising: a) a body having a first surface, a second surface, and a cylindrical chamber; said cylindrical chamber formed within said body; said cylindrical chamber having a cylindrical surface, a ceiling surface, and a base surface; said cylindrical surface having a central axis of symmetry, a radius of curvature, and azimuthal direction; said radius of curvature being substantially constant; said ceiling surface and said base surface each being substantially flat and substantially perpendicular to said central axis; said first surface being adapted for receiving heat from a heat generating component; said first surface being generally parallel to said ceiling surface; said second surface being adapted for transferring heat to a heat sink; b) a fluid transfer passage within said body; said passage having a proximal end and a distal end; said proximal end being fluidly coupled to said cylindrical chamber through said cylindrical surface; said distal end being fluid coupled to said cylindrical chamber through said base surface; said distal end being directed substantially perpendicular to said base surface; c) a liquid coolant substantially filling said chamber and said passage; said liquid coolant being selected from the group consisting of ferrofluid and electrically conductive liquid; and d) a means for flowing said liquid coolant through said fluid transfer passage; said means using an effect selected from the group consisting of a magnetohydrodynamic (MHD) effect and a rotating magnetic field effect.
2. The heat transfer device of Claim 1, wherein said proximal end is directed substantially tangential to said cylindrical surface.
3. The heat transfer device of Claim 1, wherein said liquid coolant is electrically conductive and wherein said means for flowing said liquid coolant using an MHD effect comprises: a) a permanent magnet generating a magnetic field within at least a portion of said liquid coolant within said fluid passage; said magnetic field being generally perpendicular to the long dimension of said passage; and b) a pair of electrodes for drawing electric current through said portion of said liquid coolant in a direction substantially perpendicular to the direction of said magnetic field.
4. The heat transfer device of Claim 1, wherein said liquid coolant is electrically conductive and wherein said means for flowing said liquid coolant using an MHD effect comprises: a) a permanent magnet generating a magnetic field within at least a portion of said liquid coolant within said cylindrical chamber; said magnetic field arranged to have a substantial vector component perpendicular to said ceiling surface; and b) a pair of electrodes for drawing electric current through said liquid coolant immersed in said magnetic field; said electrodes arranged to draw electric current having a direction substantially parallel to the direction of said ceiling surface.
5. The heat transfer device of Claim 1, wherein said means for flowing said liquid coolant using a rotating magnetic field effect comprises a plurality of electromagnets fed with poly-phase alternating current and arranged to generate a time varying magnetic field; said magnetic field having a vector component within said chamber; said vector component arranged to rotate in said azimuthal direction.
6. The heat transfer device of Claim 5, wherein said liquid coolant is a ferrofluid and wherein said time varying magnetic field within said coolant includes magnetic field values of less than 50 Gauss (0.005 Tesla).
7. A heat transfer device comprising: a) a body having a first surface, a second surface, and a cylindrical chamber; said cylindrical chamber having a cylindrical surface, a ceiling surface, and a base surface; said cylindrical surface having a constant radius of curvature; said ceiling surface and said base surface each being substantially flat and substantially perpendicular to said cylindrical surface; said first surface arranged to be generally parallel to said ceiling surface and arranged to be in a good thermal communication with a heat generating component; said second surface arranged to be in a good thermal communication with a heat sink; b) a fluid transfer passage within said body; said passage having a proximal end and a distal end; said proximal end being fluidly coupled to said cylindrical chamber through said cylindrical surface and arranged to be generally tangential to said cylindrical surface; said proximal end being fluidly coupled to said cylindrical chamber through said base surface and arranged to be generally perpendicular to said base surface; said passage being substantially filled with liquid coolant; c) a liquid coolant substantially filling said cylindrical chamber and said fluid transfer passage; d) a means for flowing said liquid coolant through said fluid transfer passage; said means selected from the group consisting of an MHD drive, an inductive drive, and a magnetic drive.
8. The heat transfer device of Claim 7, wherein said liquid coolant is electrically conductive and wherein said MHD drive comprises: a) a permanent magnet generating a magnetic field within at least a portion of said liquid coolant; and b) a pair of electrodes for drawing electric current through said portion of said liquid coolant in a direction substantially perpendicular to the direction of said magnetic field.
9. The heat transfer device of Claim 7, wherein said inductive drive comprises a plurality of electromagnets fed with poly-phase alternating current and arranged to generate a time varying magnetic field; said magnetic field having a vector component within said chamber; said vector component arranged to rotate in said azimuthal direction.
10. The heat transfer device of Claim 7, wherein said electrically conductive liquid is liquid metal.
11. The heat transfer device of Claim 7, wherein said cylindrical chamber has a height defined by the separation of said ceiling surface and said base surface; said height is selected to be in the range of one fifteenth (1/15-th) to one third (1/3-rd) of the size of said radius of curvature.
12. The heat transfer device of Claim 7, wherein said constant radius of curvature is between 5 and 50 millimeters.
13. The heat transfer device of Claim 7, wherein said coolant comprises a substance having a high vapor pressure.
14. A heat transfer device comprising: a) a body having a first surface, a second surface, and a chamber; said chamber formed as a hollow cylinder having an inner cylindrical surface and an outer cylindrical surface; said outer cylindrical surface having a central axis of symmetry, a first constant radius of curvature, and azimuthal direction; said inner cylindrical surface having a second constant radius of curvature and being substantially concentric with said outer cylindrical surface; said first surface being 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 arranged to be in a good thermal communication with a heat sink; b) a liquid coolant substantially filling said chamber; said liquid coolant being selected from the group consisting of ferrofluid and electrically conductive liquid; and c) a means for flowing said liquid coolant in said azimuthal direction; said means selected from the group consisting of an MHD drive, an inductive drive, a magnetic drive, and an impeller drive.
15. The heat transfer device of Claim 13, wherein said liquid coolant is electrically conductive and wherein said MHD drive comprises: a) a permanent magnet generating a magnetic field within at least a portion of said liquid coolant; and b) a pair of electrodes for drawing electric current through said portion of said liquid coolant in a direction substantially perpendicular to the direction of said magnetic field.
16. The heat transfer device of Claim 13, wherein said inductive drive comprises a plurality of electromagnets fed with poly-phase alternating current and arranged to generate a magnetic field rotating in said azimuthal direction.
17. The heat transfer device of Claim 13, wherein said inductive drive comprises a permanent magnet arranged to rotate in said azimuthal direction.
18. The heat transfer device of Claim 13, wherein said impeller drive comprises an impeller arranged to rotate in said azimuthal direction.
19. The heat transfer device of Claim 13, wherein said magnetic drive comprises a time varying magnetic field having a vector component rotating in said azimuthal direction.
20. The heat transfer device of Claim 19, wherein said liquid coolant is a ferrofluid and wherein said time varying magnetic field within said coolant includes magnetic field values of less than 50 Gauss (0.005 Tesla).
21.
22. The heat transfer device of Claim 13, wherein said electrically conductive liquid is liquid metal.
23. The heat transfer device of Claim 13, 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 1000 micrometers.
24. The heat transfer device of Claim 13, wherein said first constant radius of curvature is between 5 and 25 millimeters.
25. The heat transfer device of Claim 13, wherein said coolant comprises a substance having a high vapor pressure.
26. A method for transferring heat from a heat generating component to a heat sink comprising the steps of: a) providing a body having a first surface, a second surface, and a cylindrical chamber; said cylindrical chamber formed within said body; said cylindrical chamber comprising a cylindrical surface having a central axis of symmetry, a constant radius of curvature, and an azimuthal direction; said first surface being in a good thermal communication with a heat generating component; said second surface being in a good thermal communication with a heat sink; d) providing a liquid coolant substantially filling said cylindrical chamber; said liquid coolant being selected from the group consisting of ferrofluid and electrically conductive liquid; e) providing a drive means for flowing said liquid coolant in said cylindrical chamber in the azimuthal direction of said cylindrical surface; said drive means selected from the group consisting of an MHD drive, inductive drive, magnetic drive, and impeller drive. f) receiving heat from said heat generating component; g) transferring heat to said coolant; h) flowing said liquid coolant in said azimuthal direction; and i) transferring heat from said liquid coolant to a heat sink.
27. The method for transferring heat of Claim 26, further comprising the steps of: immersing said liquid coolant in a rotating magnetic field.
28. The method for transferring heat of Claim 26, further comprising the steps of: immersing said liquid coolant in a magnetic field; and drawing an electric current through said liquid.
PCT/US2010/000357 2008-09-08 2010-02-09 Heat transfer device WO2010090766A1 (en)

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US12/584,490 2009-09-05

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DE102018202679A1 (en) * 2018-02-22 2019-08-22 Osram Gmbh Optoelectronic component

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US7126822B2 (en) * 2003-03-31 2006-10-24 Intel Corporation Electronic packages, assemblies, and systems with fluid cooling
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US20090126922A1 (en) * 2007-10-29 2009-05-21 Jan Vetrovec Heat transfer device

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US7126822B2 (en) * 2003-03-31 2006-10-24 Intel Corporation Electronic packages, assemblies, and systems with fluid cooling
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EP3261197A4 (en) * 2015-02-16 2018-11-21 Mitsubishi Electric Corporation Semiconductor laser light source device, semiconductor laser light source system, and image display device
DE102018202679A1 (en) * 2018-02-22 2019-08-22 Osram Gmbh Optoelectronic component

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