WO2012160564A1 - Dispositif d'échange thermique - Google Patents

Dispositif d'échange thermique Download PDF

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Publication number
WO2012160564A1
WO2012160564A1 PCT/IL2012/050187 IL2012050187W WO2012160564A1 WO 2012160564 A1 WO2012160564 A1 WO 2012160564A1 IL 2012050187 W IL2012050187 W IL 2012050187W WO 2012160564 A1 WO2012160564 A1 WO 2012160564A1
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WIPO (PCT)
Prior art keywords
heat exchange
channel
fluid
channels
flow
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PCT/IL2012/050187
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English (en)
Inventor
Moshe Rosenfeld
Efi ZEMACH
Original Assignee
Ramot At Tel-Aviv University Ltd.
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Application filed by Ramot At Tel-Aviv University Ltd. filed Critical Ramot At Tel-Aviv University Ltd.
Priority to US14/119,940 priority Critical patent/US20140090818A1/en
Publication of WO2012160564A1 publication Critical patent/WO2012160564A1/fr

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F13/00—Arrangements for modifying heat-transfer, e.g. increasing, decreasing
    • F28F13/06—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by affecting the pattern of flow of the heat-exchange media
    • F28F13/12—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by affecting the pattern of flow of the heat-exchange media by creating turbulence, e.g. by stirring, by increasing the force of circulation
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F13/00—Arrangements for modifying heat-transfer, e.g. increasing, decreasing
    • F28F13/06—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by affecting the pattern of flow of the heat-exchange media
    • F28F13/08—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by affecting the pattern of flow of the heat-exchange media by varying the cross-section of the flow channels
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F3/00—Plate-like or laminated elements; Assemblies of plate-like or laminated elements
    • F28F3/12—Elements constructed in the shape of a hollow panel, e.g. with channels
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F7/00—Elements not covered by group F28F1/00, F28F3/00 or F28F5/00
    • F28F7/02—Blocks traversed by passages for heat-exchange media
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/34—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
    • H01L23/46—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements involving the transfer of heat by flowing fluids
    • H01L23/473—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements involving the transfer of heat by flowing fluids by flowing liquids
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
    • F28D21/00—Heat-exchange apparatus not covered by any of the groups F28D1/00 - F28D20/00
    • F28D2021/0019—Other heat exchangers for particular applications; Heat exchange systems not otherwise provided for
    • F28D2021/0028—Other heat exchangers for particular applications; Heat exchange systems not otherwise provided for for cooling heat generating elements, e.g. for cooling electronic components or electric devices
    • F28D2021/0029—Heat sinks
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F9/00—Casings; Header boxes; Auxiliary supports for elements; Auxiliary members within casings
    • F28F9/02—Header boxes; End plates
    • F28F2009/0285—Other particular headers or end plates
    • F28F2009/029—Other particular headers or end plates with increasing or decreasing cross-section, e.g. having conical shape
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F2260/00—Heat exchangers or heat exchange elements having special size, e.g. microstructures
    • F28F2260/02—Heat exchangers or heat exchange elements having special size, e.g. microstructures having microchannels
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/0001—Technical content checked by a classifier
    • H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Definitions

  • the present invention relates to a heat exchange device, and in particular to a miniature scale heat exchange device.
  • Heat transfer is a major obstacle in the miniaturization process of high power elements, such as CPUs, CPUs etc.
  • Conventional heat exchangers in general and heat sinks in particular that are based on fins and fans cannot cope with high power density within a reasonable volume limit.
  • existing air-based heat sinks need a volume of 200-2000cm 3 (not including the fan) to dissipate 100-150Watts. Therefore, alternative heat dissipating solutions are being sought being capable for heat removal from modern high power miniature devices.
  • Some of the most popular solutions utilize coolant flow through microchannels. Typically, such "channels based" heat exchange devices are relatively small, and can be in the sub- millimeter range.
  • the present invention provides for a novel technique utilizing one or more channels (e.g. micro-channels) configured to direct flow of a heat exchange fluid for providing high efficiency heat exchange.
  • channels e.g. micro-channels
  • liquid based heat exchange system are somewhat complex, require relatively high maintenance and generally undesirable near electronic equipment.
  • air is considered as the preferred coolant for electronic components, but due to its limitation in removing high heat fluxes, liquid is chosen in many applications of high power density.
  • conventional air cooling systems, and in particular systems utilizing microchannels are limited by the heat transfer of 350 Watt/m 2 - K.
  • the present application describes a novel approach for heat exchange techniques used for either heating or cooling a target element/device.
  • the technique of the present application is operable with respectively heating or cooling fluid which preferably provides a compressible flow (e.g. subsonic flow velocity of Mach number of the order of 0.5) being directed through channels of a heat exchange system.
  • a compressible flow e.g. subsonic flow velocity of Mach number of the order of 0.5
  • such heat exchange system and the fluid flowing therein are at times referred to herein below as respectively "cooling system” and “coolant”.
  • the invention should not be limited to the "cooling” embodiment and may be useful for heating as well. Accordingly, these terms should be interpreted broadly to cover both “cooling” and “heating” embodiments.
  • the technique of the present invention is based on the inventors' understanding that the coolant flow in a micro-channel is generally laminar, this is due to the small scale of the system which leads to relatively low Reynolds number.
  • the most efficient heat exchange mechanism is typically based on convention, i.e. transport of heat by transporting of hot fluid (i.e. liquid or gas) to a relatively cool region.
  • hot fluid i.e. liquid or gas
  • the inventors have found that more efficient heat exchange can be achieved by introduction of vortices into the flowing fluid.
  • creation of vortex ring (which will be described further below) in the fluid passing through a channel provides mixing of hot fluid from the vicinity of the channel's walls with cooler fluid flowing at the center of the channel and thus enables efficient heat exchange.
  • Vortex rings in general are toroidal regions of rotating fluid with concentrate vorticity, typically self- propagating through the same or different fluid. Vortex rings can be formed in various ways. One of the simplest formation methods is by injecting fluid through a nozzle or an orifice. However, in general, the formation of vortex ring is inherently unsteady. It has been shown that the presence of a large-scale vortex near a wall may induce an adverse streamwise pressure gradient along the wall leading to the formation of a secondary recirculation region followed by a narrow eruption of the near-wall fluid. The locally thickening of a boundary layer in the vicinity of the eruption provoked an interaction between the viscous boundary layer and the outer flow.
  • creation of a vortex ring within a channel provides mixing of fluid flowing at the periphery of the channel (i.e. near the walls) with the fluid flowing at the center of the channel.
  • the fluid flowing near the wall of the channel collects heat therefrom while being repeatedly replaced to provide efficient convection and thus efficient heat exchange.
  • the inventors have found that efficient heat transfer can be achieved by utilizing the phenomena associated with a flow of fluid within an enclosure (such as a channel) while generating vortex rings along the flow.
  • the vortex rings provide effective mixing of the fluid at the region where such phenomena occurs during the fluid flow through the channel, i.e. mixing the fluid flow components of the periphery of the channel (closer to the walls) with the fluid flow components at the center thereof.
  • the efficient mixing of fluid portions by a vortex ring during the fluid propagation through the channel provides for heat exchange by convection and thus increases the efficiency of heat exchange.
  • a heat exchange system configured according to the present invention provides significantly high efficiency for the same volume of the system.
  • a heat exchange system of the present invention can extract 15 Watt/cm 3 and beyond. This performance enables the use of relatively smaller heat exchange systems which can provide similar or higher power density dissipation.
  • the vortex rings created in a channel can survive in turbulent flow as well as in laminar flow of the fluid.
  • the effect of vortex rings enhancing heat transfer is generally more pronounced in laminar flow in which the mixing of fluid components is relatively low (mixing due to diffusion).
  • the technique and device of the present invention can be used to enhance heat transfer in both laminar and turbulent flow of the fluid.
  • the present invention thus provides a heat exchange channel (e.g. microchannel) of a certain cross-sectional dimension D.
  • the channel comprises inlet and outlet ports, and has at least one orifice having a predetermined cross-sectional dimension d. Passage of a fluid through the orifice affects a flow of the fluid through the channel by creating a vortex ring-like fashion of the flow within the channel.
  • the geometrical parameters of the channel and the orifice(s) therein are selected in accordance with the properties of the fluid to flow in the device, as well as the flow characteristic, in order to provide efficient generation of vortex rings within the channel. To this end, the more vortex rings are created, and the longer the distance they travel (or lifetime of the vortex rings), the better the heat exchange efficiency.
  • a heat exchange device may be formed by one or more heat exchange block units or blocks, where each of the blocks includes a certain number of channels (a single channel or an array of channels) including at least one orifice located at one end of the channel(s).
  • the heat exchange block unit is preferably made of a material composition having high heat conductivity, e.g. Copper, Aluminum or Stainless Steel, and is configured to be brought into thermal contact with a target element/structure to be heated/cooled.
  • a manifold arrangement is provided to direct input flow towards the inlet ports of the channels and to collect/evacuate output flow from the outlet ports of the channels to thereby provide flow of heat exchange fluid through the channels while avoiding mixing of input and output flows.
  • the heat exchange fluid may be air, being forced through the channels by one or more fans.
  • dimension of the orifice in the channel is about 66% of the cross- sectional dimension of the corresponding channel.
  • the heat exchange device configured to:
  • tube comprises a micro-channel.
  • the flow of the fluid within the micro-channel tube is a laminar one.
  • a heat exchange system of the present invention preferably includes an array of channels (e.g. micro-channels) arranged in a spaced-apart parallel relationship along an axis substantially perpendicular to the general flow direction (i.e. input direction). Each channel is configured as described above.
  • the input fluid flow is thus split into spatially separated flows through multiple channels respectively. Passage of the flow through the at least one orifice of the channels results in vortex ring-like fashion of the flow.
  • An outer surface of such a heat exchange system may be placed in contact with a surface of a target element/structure to be heated/cooled.
  • the vortex ring fashion of the flow increases mixing of the fluid portions within the channels and thus provides for convection type heat transfer within the fluid.
  • the device/system of the present invention may comprise miniature channels with one or more orifices in each channel.
  • a heating/cooling fluid preferably air, is forced through the orifices into the channels, generating a plurality of propagating compressible subsonic vortex rings. This set up enhances heat exchange significantly, allowing the use of very small volume heat exchangers using compressible fluid.
  • a heat exchange device comprising one or more channels having inlet and outlet ports to direct flow of a predetermined fluid to and from said one or more channels.
  • Said one or more channels comprise at least one channel having at least one orifice of a predetermined hydraulic diameter, a flow of said predetermined fluid through said orifice and through said channel thereby generating a vortex ring-like fashion of the flow within the channel.
  • the hydraulic diameter of said at least one channel may be between 100 to 1000 micrometers.
  • the device may be configures such that a ratio between a hydraulic diameter of said at least one channel and said predetermined hydraulic diameter of said at least one orifice is selected to be between 1.3 to 1.6. According to some embodiments this ratio may be equal to 1.5.
  • any one of the channels or orifice in the device may have a circular, rectangular or other polygonal cross section, and made of a thermally conductive material composition.
  • the said one or more channels may be made of at least one of the following materials: Copper, Aluminum and Stainless steel.
  • the heat exchange device may be configured to direct compressible flow of a predetermined heat exchange fluid through said at least one channel. Passage of the flow through said at least one orifice generates one or more vortex rings thereby providing efficient mixing of fluid portions from periphery of said channel with fluid portions from central region thereof.
  • the channels of the heat exchange device, or at least some of them, may be arranged together in one or more layers. Typically, at least one of said layers is configured to be in contact with a target element.
  • the inlet ports of the channels may be arranged to face a predetermined direction for fluid input.
  • the heat exchange device may comprise a manifold arrangement for directing input heat exchange fluid towards the inlet ports of said one or more channels.
  • a heat exchange system comprising one or more heat exchange blocks, at least one of the heat exchange blocks comprises a plurality of channels of a predetermined hydraulic diameter, each comprising at least one orifice of a predetermined hydraulic diameter. Passage of fluid through said channels and through said orifice therein generating vortex ring downstream of said orifice with respect to a general fluid flow direction through the channel, thereby increasing efficiency of heat exchange by convection of fluid within said channels.
  • a method for use in heat transfer to and from a target element comprises: providing a compressible laminar flow of a fluid through one or more channels being in contact with said target element, and directing said flow through at least one orifice located near an inlet port of said one or more channels, to thereby generate a vortex ring-like flow, providing high-efficiency heat transfer for a relatively small length of said one or more channels.
  • Fig. 1 illustrates a channel unit configured for use in a heat exchange device according to some embodiments of the present invention
  • Figs. 2A-2C illustrate an example of a specific configuration of a channel unit according to the invention (Fig. 2A) and simulation result of fluid flowing through the channel showing velocity map (Fig. 2B) and temperature map (Fig. 2C);
  • Figs. 3A-3G show simulation results exemplifying generation of vortex rings' train along a channel unit of the invention, the results are shown at different simulation times;
  • Fig. 4 shows a comparison of calculated Nusselt number for as a function of the ratio between the channel's hydraulic diameter and the orifice hydraulic diameter for three values of orifice diameter;
  • Fig. 5 shows a comparison of calculated efficiency between a heat exchange device according to the present invention and a standard microchannel heat exchange device
  • Fig. 6 shows a comparison between the thermal efficiency of heat exchange unit according to the present invention and of a standard channel based heat exchange device
  • Fig. 7 shows a comparison of heat flux per contact area relative to flow rate for single layer array of heat exchange units according to the invention and for a standard channels-based heat exchange system
  • Fig. 8 exemplifies a heat exchange device configured according to some embodiments of the present invention.
  • Fig. 9 exemplifies a heat exchange device made of a bulk material including multiple layers of microchannels according to some embodiments of the present invention.
  • Fig. 10 schematically illustrates a heat exchange device including several blocks/arrays of microchannel and configured to direct inlet and outlet flow to provide efficient heat exchange according to some embodiments of the present invention.
  • Figs. 11A-11B shoe two examples of heat exchange unit/channel according to embodiments of the present invention
  • Fig. 11A exemplifies a U-shaped channel
  • Fig. 11B exemplifies a multi-orifice channel.
  • the technique of the present invention is based on the inventor's understanding that one of the most effective heat transfer mechanisms is provided by convection. More specifically, formation of vortex rings in a flow of fluid along a channel provides mixing of fluid from the periphery of the channel with fluid flowing near a central region thereof. Such mixing enables evacuation and replacement of fluid portions exchanging heat with the channel's walls and thus provides heat exchange between the channels' walls (the environment) and the flow within the channel.
  • the present invention provides a heat exchange system utilizing one or more channels (e.g. microchannels) directing flow of a predetermined fluid (e.g. air or other compressible coolant) to provide heat exchange of a target structure with a heat/cold source and/or the surrounding.
  • a predetermined fluid e.g. air or other compressible coolant
  • the channels of are configured such that a flow of heat exchange fluid (coolant) therethrough generates vortex rings along the flow.
  • heat exchange fluid heat exchange fluid
  • the system and technique of the present invention are capable of heating or cooling of the target structure.
  • the heat exchange system and the fluid flowing therein are at times described herein below as respectively “cooling system” and “coolant”. It should however be understood that the invention should not be limited to the "cooling” embodiment and may be useful for heating as well.
  • vortex ring is a toroidal region of rotating fluid with concentrated vorticity moving through the same or different fluid.
  • Vortex rings are commonly created by fluid injections through a nozzle or an orifice into a wider region. It should be noted that vortex rings and the formation of such is inherently unsteady.
  • the heat exchange system of the present invention may include one or more basic heat exchange units or blocks, where each basic block includes one or more channels or microchannels associated with a common input port.
  • An example of such basic heat exchange unit is shown in Fig. 1 being generally designated 10.
  • the unit 10 includes an inlet 12 and an outlet 14, and at least one channel, single channel 20 being shown in the present not limiting example, having a cross-section dimension (hydraulic diameter) D for directing a flow of a predetermined heat exchange fluid there through.
  • the channel 20 is typically of a micrometric dimension, i.e. having a hydraulic diameter of 100-1000 micrometers.
  • the channel 20 includes at least one orifice, single such orifice 30 being shown in the present not limiting example placed therealong.
  • the orifice 30 is of a cross-sectional dimension (hydraulic diameter) d smaller than that of the channel 20 and may be of a circular-like (e.g. elliptic), rectangular or any other polygonal cross-sectional shape.
  • the orifice 30 may typically be of a hydraulic diameter d being about 0.8D to 0.5D.
  • a ratio between the cross-sectional dimension of the channel (having circular-like, rectangular or any other cross-sectional shape) along different axes (longitudinal and lateral) is between 0.8-1.2 and more preferably is almost 1.
  • the basic (micro) channel unit 10 may typically be of 1-5 millimeter in length, but may be longer in some applications, and typically utilizes compressible flow of coolant/fluid.
  • the fluid being air or any other gas (it should be noted the for simplicity, the term "air” is used herein below but should be interpreted broadly as referring to gas of any composition), or liquid, flows through the channel, preferably with subsonic velocity, i.e. Mach number of about 0.5-0.8 and in any case smaller than 1.
  • the coolant flow is typically of a relatively small Reynolds number being in the laminar range of 2500>Re>1500. This small Reynolds number results from the small cross-sectional dimension (diameter) of the channel 20 which, as indicated above, is typically of a micrometric dimension.
  • Figs. 2A-2C illustrate the specific configuration of a heat exchange unit 10 used in the numerical simulations (Fig. 2A), a resulting velocity map from such numerical simulation (Fig. 2B), and a resulting temperature map along the flow in the channel (Fig. 2C).
  • Fig. 2A illustrates a model of heat exchange unit 10 as used for the simulations below.
  • the figure shows a section of the unit 10 from a central axis 22 to the walls 20 of the channel, i.e. the diameter D of the channel 20 is thus shown as D/2 and the diameter d of the orifice 30 is shown as d/2.
  • a coolant 40 is forced through the inlet 12 of the unit and is removed from the channel through the outlet 14 thereof.
  • Several numerical simulations considered the channel's length L of 6 millimeter. It should however be noted that the length L of the channel may be either longer or shorter than this specific value used in the simulations. The numerical simulation conducted by the inventors provided substantially similar results for various channel lengths.
  • the temperature of the input air was considered as 30°C and the walls temperature of the channel was 70°C.
  • Fig. 2B shows simulation results in the form of a velocity map of a compressible fluid flowing through the unit 10.
  • the flow is characterized by Reynolds number of 1500.
  • the channel section shown in this figure is of 2 millimeter length downstream of the orifice 30 with respect to the fluid flow direction through the channel.
  • a series of vortex rings V1-V3 is formed downstream of the orifice 30.
  • the vortex rings propagate with the flow through the channel 20 and provide effective mixing of fluid portions from the periphery of the channel (near the wall) with fluid portions close to the longitudinal axis of the channel (the central region of the channel). This is due to the proximity of the vortex rings to the walls which induces the eruption of the boundary layer into the core flow region.
  • the numerical (computer) simulations reveal formation of vortex rings due to the fluid passage through the orifice 30 into the channel 20.
  • the vortex rings are formed while being attached to the orifice and thereafter propagating downstream along the channel generating an inherently unsteady flow (although the inflow is steady).
  • the vortex rings V1-V3 are associated with flow vorticity mixing fluid potions from different layers relative to the channel wall, and thus enable significant heat transfer by convection.
  • a flow characterized by low Reynolds number is a laminar flow, where the viscosity of the fluid is a significant factor.
  • Such laminar flow in the vicinity of the channel's walls creates boundary layers of fluid which do not mix very well.
  • the formation of vortex rings in the heat exchange unit configured according to the present invention provides significant (effective) mixing and thus enables heat transfer in the form of convection. Additionally, interactions of the vortex rings with the walls of the channel induce eruption of counter-vorticity fluid that stops the formation of the vortex ring and disconnects it from the orifice, and thus allows the formation of subsequent vortex ring, and so on.
  • An additional major mechanism that enhances the disconnection of the vortex rings and the generation of a propagating train of vortex rings is the baroclinic torque that introduces instability and thus cause continuous formation of vortex rings.
  • Fig. 2C In this simulation the walls of the channel are at a temperature of 40°K above the temperature of the coolant flowing in the channel.
  • the dark regions shown in the figure correspond to higher temperatures while the lighter regions correspond to colder temperatures (i.e. the coolant temperature).
  • the formed vortex rings V1-V3 mix warm air (coolant) flowing near the walls with colder air flowing at the central regions, thereby increasing the flow temperature within the channel significantly beyond the temperature of the air (coolant) injected therein. This indicates a significant heat transfer from the walls into the flowing coolant due to the mixing action of the propagating vortex rings.
  • a flow through an orifice may generate a jet-like flow which exists for a transient time and dies out leaving the flow laminar and layered.
  • the inventors have found that by selecting properly the orifice size (diameter or area) relative to the channel size (diameter or area) and/or generating subsonic compressible flow (with an orifice Mach number of the order of 0.5-0.8), a train of vortex rings is continuously formed, even in the steady state, as a result of the interaction between the formed vortex ring and the adjacent walls.
  • the effect is also a result of the baroclinic torque due to the compressibility of the coolant (e.g. air).
  • the inventors have found that this effect applies at any scale, where the compressibility of the fluid and an appropriate relation between the hydraulic diameters of the orifice and the channel is applied.
  • the most relevant scale of a heat exchange unit or system utilizing the technique of the invention is the sub- mm (micro) scale.
  • the flow of almost any coolant is laminar and appropriate selection of compressible coolant is simple.
  • providing the heat exchange unit in a micrometric scale enables increasing of contact area between the heat exchange fluid and the surface(s) of the system, utilizing plurality of such units, with the target element/structure to be cooled/heated.
  • FIG. 3A shows the vorticity map of the flow at a certain time during the formation of a vortex ring v3 and a while after the formation of vortex rings VI and V2 which are propagating through the channel. Due to the bounded flow within the channel, the growth of the created vortex ring v3 is limited by the wall of the channel. This causes creation of a second vorticity center v3' shown in Fig.
  • FIG. 3C which while propagating is combined with vortex ring v3 to form a larger vortex ring V3 as shown in Fig. 3E.
  • the formed vortex ring V3 detaches from the orifice forming an additional sub-ring v3" (Fig. 3F), which combines to V3 (Fig. 3G), and an additional vortex ring v4 which will eventually form a newly developed vortex ring while propagating through the channel.
  • the created vortex rings separate from the orifice due to their interaction with the channel walls and due to the compressibility (low Mach number, between 0.5-0.8) of the flow providing baroclinic torque.
  • the fluid rotation induces radial eruption of the flow from the boundary layer into the core flow. This eruption mechanism continues while the vortex rings propagate and convects heat from the walls' surface into the core of the flow. This eruption mechanism plays a role in continuous generation of vortex ring.
  • multiple vortex rings are typically generated even when the channel' s walls are relatively far and the eruption mechanism is weak, and the effect of the baroclinic torque may be sufficient.
  • the inventors have found that a ratio between the hydraulic diameters of the orifice and the channel plays a role both in the continuous formation of the vortex ring and in their interaction with the walls providing efficient convection.
  • the inventors have found that at a ratio of about D/d ⁇ 1.5 (hydraulic diameter d of the orifice is about 66% of the hydraulic diameter D of the channel) the generation of the vortex ring is continuous (forming a steady state) and the convection is efficient, providing effective heat transfer from/to the walls.
  • the size and the generation frequency of the vortex rings can be controlled.
  • the disconnection of the vortex rings from the orifice is obtained by the baroclinic production of counter-vorticity and the development of a nonlinear global interaction with the walls.
  • Table 1 compares several simulation results for various orifice and channel diameters exemplifying the performance of the technique of the present invention.
  • the Table 1 presents the Nusselt number Nu defined by the ratio between heat transfer by convection and by conduction measuring the heat that can be dissipated under similar conditions, and a ratio between the Nusselt number of a heat exchange unit according to the invention and the resulting Nusselt number of a channel of the same hydraulic diameter without an orifice Nu s .
  • the Nusselt number is defined as where D c k an nei is the hydraulic diameter of the channel, k is the heat conductivity and h is the heat transfer coefficient defined as Where Q is the heat extracted from a channel with a wetted area A and T wa u and T in i et are the wall and inlet temperatures respectively.
  • the above Table 1 also presents the heat flux and the required air flow rat e in the case of a single layer of channels placed next to one another on a surface of 1cm 2 forming together a heat exchange device as will be described more specifically further below.
  • Nusselt number i.e. heat exchange efficiency
  • the heat exchange unit of the invention comprising channel(s) with orifice(s) for different ratios between the channel's hydraulic diameter and the orifice hydraulic diameter, for three values of orifice diameter.
  • the Nusselt number compares the amount of heat transferred by convection relative to the amount of heat transferred by conduction.
  • the heat exchange unit of the present invention provides for efficient heat transfer by convection also for ratios from 1.3 to 1.6.
  • Fig. 5 shows a comparison between the Nusselt number achieved by the above described unit of the invention with respect to a standard microchannel utilizing substantially laminar flow.
  • the heat exchange performance parameter values (Nusselt number, Nu) are presented with respect to the flow rate Q [liter/minute].
  • Q the flow rate
  • the figure shows the thermal efficiency as a function of the geometrical parameter of the channel expressed by a ratio between the channel's length and diameter.
  • the thermal efficiency shown herein is defined by the actual temperature difference between the inlet fluid and the outlet fluid divided by the temperature difference of the fluid at the walls (in this example 40°C) which is the maximum temperature yield that can occur in the fluid.
  • the thermal efficiency of the heat exchange unit of the invention increases significantly as the channel's length increases, displaying values up to 38%, while standard channels show linear increase of thermal efficiency with respect to the length, reaching only up to 24%.
  • Fig. 7 shows a comparison of a single layer of heat exchange unit of the invention relative to the standard channels.
  • the figure shows the dependence of heat flux per contact area (q mean ) on the flow rate, where several corresponding coefficients of performance (COP) are indicated by labels for equal heat fluxes of both cases.
  • Fig. 8 exemplifies such heat exchange device 100 including a plurality (ten in the present not limiting example) of heat exchange units configured as described above and being aligned one next to the other to form a basic heat sink unit.
  • the adjacent microchannels 20 are channels made within (embedded) or placed on a bulk material, preferably made of metal(s) having high heat conductivity, and configured to direct heat exchange fluid (e.g. air or other coolants) to provide heat exchange to a target element.
  • the heat exchange device is to be attached to the target element or placed in direct contact therewith, e.g.
  • the microchannels 20 are arranged in a single layer close to the surface of the bulk material to be in touch with the target element.
  • the microchannels 20 (or at least some of them) are formed with orifices 30 of smaller diameter located near the inlets region 45 of the respective channels 20.
  • the heat exchange unit 100 may be of a typical size of 3x6.5x0.65mm (LxWxH), however it should be noted that the size depends on the number of basic units of the device and may differ to provide heat exchange to target elements of different dimensions.
  • the heat exchange device may also include channels (microchannels) arranged in a number of layers within a bulk material forming a heat sink.
  • a heat exchange device 100 made of a bulk material (e.g. Copper, Aluminum, Stainless Steel or any other heat conductive material) including multiple layers (for example ten layers) of microchannels 20 in it, where each layer includes a plurality (e.g. twenty) basic units (microchannels) 20.
  • the microchannels (or at least some of them) are configured with one or more orifices (not specifically shown here) as described above to thereby provide flow of heat exchange fluid while generating plurality of vortex rings within the channel 20 and thus increase the heat exchange performance.
  • several such blocks can be placed on the surface of a heat source (target element), as will be described further below with reference to Fig. 10.
  • the heat exchange device 100 is configured as a heat sink made of a material composition having reasonable or high heat transfer properties (heat conductivity and heat capacity coefficients).
  • Preferred materials may be copper, stainless steel or aluminum, but other materials can be also used.
  • Some embodiments may utilize a Silicon based heat exchange device which offers compatibility with micromachining and micro fabrication techniques widely used in the semiconductor producing processes in the electronics industries.
  • one of the most effective heat exchange fluids which may be used in the invention is air (or other gas based heat exchange fluids) providing sufficient thermal properties and compressible flow. It should be noted that an important parameter affecting the efficiency of the heat exchange device is a sufficient supply of air into the inlet(s) and effective evacuation of the air from the outlet(s) directly into the surroundings (or alternatively evacuation through an exhaust- manifold) after exchanging heat with the target element.
  • Fig. 10 exemplifying a heat exchange device 200 including a plurality of heat sinks 100 configured as exemplified in Fig. 9 and including an air directing system 150 for supply and evacuation of the heat exchange fluid.
  • the heat exchange device 200 of this specific but not limiting example includes six blocks 100 (heat sinks) each including 10 layers of 30 microchannels per layer placed on a thermally conductive surface 180 and 160 to be brought in contact with a target element. Every two adjacent blocks 100 face each other so that the inlet region of cold air is the same for two adjacent blocks. The same applies for the hot-air exit region on the opposite side of the blocks 100. Air is directed into the device 200 with the appropriate gauge pressure through a manifold 120 into the inlet reservoir 150.
  • the air/coolant flows through the orificed-microchannels transferring heat from the walls as described above.
  • the hot air in the non-limiting example of cooling system, flows out of the blocks 100 into the isle between two adjacent blocks and subsequently to the outlet 140 of the device and out to the surroundings.
  • the air, or any other coolant which may be used can be directed into and out of the device utilizing conventional techniques, for example by one or more fans, however other arrangements of air supply and evacuation may be used.
  • the heat exchange device 200 exemplified above may be configured with various size and geometry appropriate for efficient attachment to the corresponding target element (e.g. CPU, GPU, Laser cavity or any other heat source, or alternatively a target to be cooled).
  • the device may have a dimension of approximately 26x32x10mm and in such physical dimension it is expected to dissipate 2.5Watt/°C or 0.4Watt/cm 2 -°C or 0.4Watt/cm 3 -°C in accordance with the surface area being in touch with the target element.
  • the heat exchange device of the invention may be controlled to adapt to varying operating conditions, for example, increasing or decreasing the flow to provide high heat dissipation when needed and reducing noise or energy consumption when less heat needs to be dissipated.
  • the heat exchange device may be associated with a flow generating unit (e.g. one or more blowers/fans) configured to provide inlet flow and/or to evacuate outlet flow.
  • the flow generating unit may include a control unit configured for managing operation thereof.
  • the control unit may include an inlet pressure sensor, cold and hot air temperature sensors, and one or more sensors for detecting the temperature of the target element. The control unit can control the flow by increasing/reducing blower speed or by any other technique for varying the inlet or outlet pressure in accordance with the measured temperatures.
  • the inventors have found that a train of vortex rings can be generated by a continuous inflow in compressible subsonic air flow through an appropriately configured orifice with adjacent channels' walls.
  • the unsteady propagating vortices enhance substantially the heat transfer capabilities even in the case of low Reynolds number flows (e.g. in small scale system) where conventional heat sinks perform poorly.
  • This allows obtaining high heat transfer in small scale employing air (or other gases) without the need to revert to liquids.
  • the heat-sink based on the present invention have at least one order of magnitude less volume, reaching a value of 0.4Watt/cm 3 -°C (and beyond), a value more than 30 times higher than in conventional air based fin solutions, thus allowing the extension of air-cooling beyond present limits.
  • the use of gases has a huge advantage over the use of liquids in simplifying the heat exchanger, substantially increasing reliability and decreasing maintenance costs, resulting in cheaper systems and better return on investment.
  • a longer channel may be configured by providing multiple orifices arranged in a spaced-apart relationship along the channel with a distance between them being selected to allow generation of vortex ring from each of the orifices.
  • Fig. 11A shows a basic unit 10 including a microchannel 20 configured with three orifices 30 located along the channel forming a row of vortex rings' generation regions along the channel. The orifices 30 may be located at a distance selected to be higher than a lifetime distance of the generated vortex rings. This configuration provides continuous generation of vortex rings along the channel length where otherwise the vortex rings would die out while propagating.
  • Fig. 11A shows a basic unit 10 including a microchannel 20 configured with three orifices 30 located along the channel forming a row of vortex rings' generation regions along the channel.
  • the orifices 30 may be located at a distance selected to be higher than a lifetime distance of the generated vortex rings. This configuration provides continuous generation of vortex rings along the channel length where otherwise the vortex rings would die
  • U-shaped channel unit 10 including a U- shaped channel (microchannel) 20 configured with an orifice 30 in each of its arms.
  • Such microchannel unit 10 may be used for increasing the effective length of the channel while providing heat exchange to a target element having relatively short contact surface along at lease one of its surfaces.
  • This configuration of the microchannels provides for a heat exchange device with "cross-channels" such that the inlet and outlet of the fluid are on the same surface (separated by a manifold to keep hot and cold fluid unmixed).
  • the heat exchange device as described above, or one or more channels/microchannels thereof may be integrated as channels passing through, or as separate layers, into electronic circuit architectures, being located between layers of heat generating components to effectively remove heat and resolve hot-spot regions.
  • liquid based heat exchange fluid may be utilized and is not limited to air or other gasses.
  • compressible flow of the fluid is preferred although incompressible flow may also be used.
  • the present invention provides a novel technique for heat exchange utilizing flow of appropriate fluid in the vicinity of a target element/structure to be heated/cooled.
  • the technique of the invention preferably utilizes laminar and compressible (subsonic) flow through one or more channels while providing continuous generation of vortex rings along the flow.
  • the vortex rings provide mixing of the fluid between the periphery and central regions of the channel and thus increase efficiency of heat exchange by convection.

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Abstract

L'invention concerne un dispositif d'échange thermique; ledit dispositif comprend un ou plusieurs canaux comportant des orifices d'entrée et de sortie conçus pour diriger l'écoulement d'un fluide prédéterminé vers lesdits un ou plusieurs canaux et depuis ceux-ci. Lesdits un ou plusieurs canaux du dispositif comprennent au moins un canal ayant au moins un orifice d'un diamètre hydraulique prédéterminé, conçu de telle sorte qu'un écoulement dudit fluide prédéterminé par ledit orifice et à travers ledit canal confère à l'écoulement un régime de type anneau tourbillonnaire à l'intérieur du canal pour assurer un transfert thermique efficace par le fluide.
PCT/IL2012/050187 2011-05-23 2012-05-23 Dispositif d'échange thermique WO2012160564A1 (fr)

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EP2913616A4 (fr) * 2012-10-25 2015-12-02 Toyota Motor Co Ltd Échangeur de chaleur
JP6107905B2 (ja) * 2015-09-09 2017-04-05 株式会社富士通ゼネラル 熱交換器
US11003808B2 (en) * 2015-09-30 2021-05-11 Siemens Industry Software Inc. Subtractive design for heat sink improvement
US20170097180A1 (en) * 2015-10-01 2017-04-06 Hamilton Sundstrand Corporation Heat transfer tubes
US11920874B2 (en) * 2021-02-09 2024-03-05 Ngk Insulators, Ltd. Heat exchange member, heat exchanger and heat conductive member
WO2023113924A1 (fr) * 2021-12-13 2023-06-22 Microsoft Technology Licensing, Llc. Systèmes et procédés de refroidissement en deux phases de composants électroniques
WO2024052473A1 (fr) * 2022-09-09 2024-03-14 Diabatix N.V. Procédé mis en œuvre par ordinateur pour concevoir un dissipateur thermique

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