US20090014154A1

US20090014154A1 - Passive Thermal Management System

Info

Publication number: US20090014154A1
Application number: US12/091,337
Authority: US
Inventors: Philippe Schick; Daryl James
Original assignee: TIR Technology LP
Current assignee: TIR Systems Ltd; Koninklijke Philips NV
Priority date: 2005-11-09
Filing date: 2006-11-08
Publication date: 2009-01-15
Also published as: EP1946030A1; WO2007053939A1

Abstract

A traditional passive thermal management system can only be used effectively in a single orientation because it relies on the buoyancy of the heated air to create natural convection. A passive thermal management system is provided which includes means for transferring heat away from a heat source (10) in any orientation. The system comprises a heat pipe (14) which is thermally coupled to the heat source (10). The heat pipe (14) is capable of transferring heat away from the heat source (10), wherein this heat is transferred along the length of the heat pipe (14). Thermally coupled to the heat pipe (14) is a fin system (12), which provides a means for extraction of the heat from the heat pipe (14) and transfer of this heat to the environment thereby dissipating the heat generated at the heat source (10). The fin system (12) is configured to provide a desired level of heat transfer to the environment independent of the orientation of the thermal management system.

Description

FIELD OF THE INVENTION

The present invention pertains to thermal management and in particular to a passive thermal management system.

BACKGROUND

Typical thermal management devices, especially those designed to incorporate heat pipes, are designed for one orientation to ensure proper airflow for efficient performance of the device. For example, heat sinks can be used to extract heat from a heat source and are designed based on the proximate airflow conditions and can vary greatly in shape and construction. For applications that allow the inclusion of a fan, the design of a heat sink can provide tightly spaced fins to reduce size, while enabling air to pass freely. If the fan malfunctions, for example, air movement will likely be limited due to the spacing constraints, thus rendering the heat sink substantially ineffective. Passive thermal management devices rely on buoyancy driven flow, or natural convection. Essentially, the air is heated by the heat sink, resulting in a reduction in the density of the air, which allows this heated lower density air to rise, thus inducing airflow. This type of system typically requires larger spaces between fins associated with the heat sink, and the orientation and shape of those fins can be critical. If the fins are parallel to the gravitational vector, as the lower density air rises, it passes over the surface of the fins and increases the heat transfer coefficient. If the fins are oriented perpendicular to the gravitational vector, the lower density air will rise, however the flow of the air will typically not pass over the surface of the fins, and therefore will likely not improve the heat transfer coefficient.
U.S. Pat. No. 5,921,315 describes a heat pipe heat exchanger that is provided in the form of a serpentine heat pipe that does not have the ends of the individual tubes manifolded to one another via a straight pipe or via any other common connector. Instead, the heat pipes are connected via U-bends to form a continuous coil. The serpentine heat pipe may include integral condenser and evaporator portions separated by a divider to form a one-slab heat exchanger, or separate evaporator and condenser coils connected to one another by vapour and return lines to form a two-section heat pipe. The heat pipe heat exchanger may be formed in a continuous closed-loop pipe.
U.S. Patent Application No. 2005/0231983 describes a method and apparatus for using light emitting diodes for curing and various solid state lighting applications. The method includes a method for cooling the light emitting diodes and mounting the same on a heat pipe in a manner which delivers ultra high power in UV, visible and IR regions. Furthermore, the LED packaging technology utilizes heat pipes that perform efficiently in compact spaces. Much more closely spaced LEDs operating at higher power levels and brightness are possible because the thermal energy is transported in an axial direction down the heat pipe and away from the light-emitting direction rather than a radial direction in nearly the same plane as the “p-n” junction. A heat pipe is bonded to a heat sink that has fins that may be machined, or moulded in place. The fins on the heat sink may be either radial and/or at an angle in relation to the heat pipes and/or they may be axially disposed.
European Patent Application No. 02006194.1 describes an antenna for performing wireless transmission of voice or data to a base station connected to a basic network. The antenna is accommodated in a case in which a heat sink is provided. The heat sink is disposed at the rear surface of the case. The heat sink is disposed so as to form a predetermined tilt angle such that radiating fins of the heat sink are disposed to form an acute angle of about 45° with respect to, e.g., a direction of gravity in any one of the state of the vertically polarized wave and the state of the horizontally polarized wave. The heat sink is thermally coupled via the case to the high-frequency circuit portion within the accommodating portion of the case. Thus, even if the case is rotated 90° such that the antenna is set to either the direction of the vertically polarized wave and the direction of the horizontal polarized wave, the heat sink takes two substantially symmetrical positions where radiating fins are tilted about 45° with respect to the direction of gravity, while being thermally coupled to the high-frequency circuit portion.
U.S. Pat. No. 7,048,412 describes a lamp having LED sources that are placed about a lamp axis in an axial arrangement. The lamp includes a post with post facets where the LED sources are mounted. The lamp includes a segmented reflector for guiding light from the LED sources. The segmented reflector includes reflective segments each of which is illuminated primarily by light from one of the post facets (e.g., one of the LED sources on the post facet). The LED sources may be made up of one or more LED dies. The LED dies may include optic-on-chip lenses to direct the light from each post facet to a corresponding reflective segment. The LED dies may be of different sizes and colors chosen to generate a particular far-field pattern. This application further describes the use of heat pipes to increase thermal conduction away from LED sources and mounting of heat pipes to a heat sink. The heat sink, in one embodiment, consists of fins attached to the surface of the heat pipe.
U.S. Patent Application No. 2002/0179284 describes a device for enhancing cooling of electronic circuit components. A thin profile thermosyphon heat spreader mounted to an electronics package comprises a central evaporator in hydraulic communication with a peripheral condenser, both at least partially filled with liquid coolant. Performance is optimized by keeping the evaporator substantially full at all orientations while leaving a void for accumulation of vapour in the condenser. The device may further include means for cooling the condenser such as cooling fins and liquid-cooled jackets that surround the condenser.
The thermal management systems as defined in the prior art are primarily orientation dependent in order to enable appropriate functioning thereof. Therefore there is a need for a new passive thermal management system which can provide heat transfer independent of orientation and can enable the transfer of heat away from a heat source and dissipation of this heat to the environment.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a passive thermal management system. In accordance with an aspect of the present invention, there is provided a passive thermal management system for dissipating heat generated by a heat source, the thermal management system comprising: one or more heat pipes each having a length, each heat pipe thermally connected to the heat source, each heat pipe for transferring heat along its length away from the heat source; and a fin system thermally coupled to the one or more heat pipes, the fin system extracting heat from the one or more heat pipes and dissipating the heat therefrom, the fin system configured to provide a desired level of heat dissipation independent of orientation of the thermal management system.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a side view of a passive thermal management system according to one embodiment of the present invention which is coupled to a light-emitting diode heat source.

FIG. 2 illustrates a cross sectional view of half of a fin system used for the passive thermal management system of FIG. 1.

FIG. 3 illustrates a cross sectional view of a passive thermal management system of FIG. 1.

FIG. 4 illustrates a side view of a passive thermal management system according to another embodiment of the present invention.

FIG. 5 illustrates a cross sectional view of a passive thermal management system according to another embodiment of the present invention.

FIG. 6 illustrates a cross sectional view of a passive thermal management system according to another embodiment of the present invention.

FIG. 7 illustrates a side view of a passive thermal management system according to another embodiment of the present invention.

FIG. 8 illustrates a perspective view of a fin for use in the fin system of the passive thermal management system of FIG. 7.

FIG. 9 illustrates a perspective view of another fin for use in the fin system of the passive thermal management system of FIG. 7.

FIG. 10A illustrates a cross sectional view of a passive thermal management system according to one embodiment of the present invention.

FIG. 10B illustrates a cross sectional view of a fin for use in the fin system of the passive thermal management system of FIG. 10A.

FIG. 11A illustrates a cross sectional view of a passive thermal management system according to one embodiment of the present invention.

FIG. 11B illustrates a cross sectional view of a fin for use in the fin system of the passive thermal management system of FIG. 11A.

FIG. 12 illustrates a perspective view of a fin for use in a fin system according to one embodiment of the present invention.

FIG. 13 illustrates a cross sectional view of a passive thermal management system according to one embodiment of the present invention.

FIG. 14 illustrates a cross sectional view of a fin for use in a fin system of the passive thermal management system of FIG. 13.

FIG. 15 illustrates a blank for the manufacture of a fin according to one embodiment of the present invention.

FIG. 16 illustrates a fin manufactured from the blank illustrated in FIG. 15.

FIG. 17 illustrates a blank for the manufacture of a fin according to one embodiment of the present invention.

FIG. 18 illustrates a fin manufactured from the blank illustrated in FIG. 17.

FIG. 19 illustrates a passive thermal management system according to one embodiment of the present invention.

FIG. 20 illustrates a single fin of the fin system of the passive thermal management system illustrated in FIG. 19.

FIG. 21 illustrates a blank for the manufacture of the fin illustrated in FIG. 20.

FIG. 22A illustrates a side view of the fin illustrated in FIG. 20.

FIG. 22B illustrates an end view of the fin illustrated in FIG. 20.

FIG. 23 illustrates a cross sectional view of a passive thermal management system according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

The term “heat source” is used to define a source of heat from which the heat is to be extracted or transferred therefrom. A heat source can be an electronic device, light-emitting device, laser diode, light-emitting diode, semiconductor based device or other similar device as would be known to a worker skilled in the art, which is capable of heat generation.
As used herein, the term “about” refers to a +/−10% variation from the nominal value. It is to be understood that such a variation is always included in any given value provided herein, whether or not it is specifically referred to.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
The present invention provides a passive thermal management system which provides a means for transferring heat away from a heat source. The system comprises a heat pipe which is thermally coupled to the heat source. The heat pipe is capable of transferring heat away from the heat source, wherein this heat is transferred along the heat pipe. Thermally coupled to the heat pipe is a fin system, which provides a means for extraction of the heat from the heat pipe and transfer of this heat to the environment thereby dissipating the heat generated at the heat source. The fin system is configured to provide a desired level of heat transfer to the environment independent of the orientation of the thermal management system, for example the orientation of the thermal management system relative to the gravitational vector.
FIG. 1 illustrates a passive thermal management system according to one embodiment of the present invention. The thermal management system provides for the dissipation of heat that is generated by one or more light-emitting diodes 10 which are thermally coupled to the passive thermal management system, and more specifically a heat pipe 14. For example, the thermal connection between the one or more light-emitting diodes and a heat pipe can be provided via substantially direct contact, through a LED package or via a thermally conductive substrate upon which the one or more light-emitting diodes are mounted. The thermal management system comprises heat pipe 14 which is thermally connected to a fin system 12 which is configured as a sleeve of fins. Each of the fins of the sleeve of fins are substantially aligned along the length of a heat pipe. The sleeve of fins functions as a heat sink and thereby passively transfers heat from a heat pipe to the surrounding environment, thereby reducing the effect that the heat generated by the one or more light-emitting diodes has thereon.

Heat Pipe

The one or more heat pipes are configured to be in thermal contact with the one or more heat sources, wherein the one or more heat pipes are configured to transport the heat generated by the heat sources away therefrom.
A heat pipe is a device that can quickly transfer heat from one point to another. A typical heat pipe is formed from a sealed hollow tube, which is typically manufactured from a thermally conductive material, for example aluminium or copper, however other materials can be used as would be readily understood. A heat pipe contains a working fluid therein and an internal wicking structure which provides a means for liquid phase working fluid to return to the evaporator end of the heat pipe. A heat pipe is capable of heat transfer against the gravitational vector through an evaporation-condensation cycle of the working fluid with the aid of the internal wicking structure.
The wicking structure allows the capillary driving force to return the condensate of the working fluid to the evaporator end of the heat pipe. Different types of wicking structures are used depending on the application for which the heat pipe is being used including sintered, grooved or mesh structures. Working fluids can range from liquid helium for extremely low temperature applications to mercury for high temperature conditions.
For a thermal management system that includes multiple heat pipes, the heat pipes can be configured such that they are substantially similar or the heat pipes can be configured as substantially different. For example, the multiple heat pipes can be manufactured from the same or different materials, use the same or different working fluids and wicking structures. The selection of these materials for heat pipe manufacture can be dependent on the intended use of the thermal management system and the conditions for desired operation. A worker skilled in the art would readily understand how to select one or more appropriate heat pipes for the thermal management system, based on intended use.

Fin System

The fin system is thermally coupled to the one or more heat pipes and configured to extract heat from the one or more heat pipes and dissipate this extracted heat to the environment. The fin system comprises one or more fins which are configured to enable the dissipation of heat independent of the operational orientation of the thermal management system.
For example, the fin system is configured to provide a desired level of heat dissipation wherein this desired level can be achieved independent of the orientation of the thermal management system relative to the gravitational vector. A desired level of heat dissipation by a thermal management system positioned in a particular orientation relative to the gravitational vector can be achieved if a desired level of convention can be obtained in that orientation, namely a desired level of air movement over the fin system, thereby enabling heat transfer to the air via the fin system and subsequently transport away from the thermal management system.
In one embodiment of the present invention, each of the one or more fins of the fin system are configured to enable air movement in a direction substantially parallel to the gravitational vector independent of the orientation of the fin system, such that the air moves over a portion or all of the surface area of the fins.
In one embodiment of the present invention, the thermal management system is operatively coupled to a lighting device, wherein the thermal management system comprises a fin system configured as a portion or the entire housing of the lighting device. The fin system can define the exterior surface area of a portion or all of the housing. In one embodiment the fin system can be configured to define the exterior surface area of a portion or all of the housing and additionally comprises exterior fins mounted on the exterior surface area thereof. These exterior fins may enhance the heat dissipation provided by the fin system.
In one embodiment of the present invention, the fin system comprises a plurality of fins, wherein a desired amount of the surface area of each of the fins is in environmental contact, for example in direct contact with air, and is configured to enable a desired level of heat to be transferred to the air via the fin system.
In one embodiment of the present invention, the one or more fins of the fin system can be configured in one, more than one or a combination of a plurality of shapes for example, planar, bi-planar, curved, conical, frusto-conical, cylindrical, or other configuration as would be readily understood by a worker skilled in the art. The selection of the shape of the one or more fins can be determined based on the desired level of heat transfer from the fins to the environment in one or more of the operational orientations.
In one embodiment of the present invention, the one or more fins of the fin system comprise one or more primary holes therethrough for insertion of the one or more heat pipes. In another embodiment, the one or more fins of the fin system comprise one or more secondary holes therethrough to enable fluid passage therethrough, for example to enable air, cooling fluid or other medium to pass therethrough.
In one embodiment of the present invention, the fin system comprises a plurality of similarly configured fins that are positioned in a stacked configuration with a predetermined separation therebetween.
The fin system can be manufactured from one or more of a variety of materials provided that these materials have a desired level of thermal conductivity and can retain a desired shape. For example, the fin system can be manufactured from aluminium, copper or other type of thermally conductive metal or alloy. The fin system may be manufactured from a thermally conductive polymer, ceramic, metal ceramic composite or other type of material as would be readily understood by a worker skilled in the art.
In one embodiment of the present invention, the fin system can be manufactured from multiple types of materials, which can be selected based on the desired functionality of portions of the fin system. For example, the portion of the fin system proximate to the one or more heat pipes may be formed from a weldable or solderable material, and the remainder of the fin can be manufactured from a thermally conductive polymer. Other materials and material configurations would be readily understood by a worker skilled in the art. For example, multi material fins may be used in situations where weight is a consideration, while maintaining a desired material in the vicinity of the thermal connection between a fin and a heat pipe.
The connection between the fin system and the one or more heat pipes can be enabled by one or more of a variety of methods. For example, the fin system and the one or more heat pipes can be connected by welding, brazing, interference connection, epoxy, soldering, thermally conductive adhesive or other means of connection as would be readily understood by a worker skilled in the art.
In one embodiment the thermal transfer between the heat pipe and the fin system can be enhanced with thermal grease or another highly thermally conductive material as would be readily understood by a worker skilled in the art.
The invention will now be described with reference to specific examples. It will be understood that the following examples are intended to describe embodiments of the invention and are not intended to limit the invention in any way.

EXAMPLE 1

FIG. 1 illustrates a passive thermal management system according to one embodiment of the present invention. The thermal management system provides for the dissipation of heat that is generated by one or more light-emitting diodes 10 which are thermally coupled to the passive thermal management system, and more specifically heat pipe 14. For example, the thermal connection between the one or more light-emitting diodes and a heat pipe can be provided via substantially direct contact, through a LED package or via a thermally conductive substrate upon which the one or more light-emitting diodes are mounted. The thermal management system comprises heat pipes 14 which are thermally connected to a fin system 12 which is configured as a sleeve of fins. Each of the fins of the sleeve of fins are substantially aligned along the length of a heat pipe. The sleeve of fins functions as a heat sink and thereby passively transfers heat from a heat pipe to the surrounding environment, thereby reducing the effect that the heat generated by the one or more light-emitting diodes has thereon.
In the embodiment illustrated in FIG. 1, the fin system comprises two half sections 16, one of which is illustrated in FIG. 2. These half sections may be manufactured using an extrusion technique or other manufacturing technique as would be readily understood. Two of these half sections are coupled together, for example by one or more bolts, clamps or other coupling device, to form the fin system 12. The fin system surrounds a heat pipe 14 such that the fin system is in thermal contact therewith, as illustrated in FIG. 3, wherein this thermal contact therebetween may be enhanced by thermal grease or other thermal transfer enhancing substance as would be readily understood by a worker skilled in the art. In this manner, heat generated by the one or more light-emitting diodes is transported away therefrom by the heat pipe to the fin system and is subsequently transferred to the surrounding environment.
In one embodiment of the present invention, a plurality of passive thermal management systems as illustrated in FIG. 1 can be configured in a circle for example. In this configuration, however, the fin systems may isolate the central region which they surround. This configuration can reduce the heat dissipation provided by the fin system 20 as the fins within the central region are not necessarily exposed to air movement. Therefore, in one embodiment of the present invention and as illustrated in FIG. 4, the heat pipes 22 can be bent in a manner that the central region 21 is exposed enabling air to move therethrough, thereby increasing the dissipation of heat by the fin system, said heat being generated by a heat source 24.
In another embodiment of the present invention the fin system can be formed as an extrusion with a sun type configuration which comprises a plurality of fins 26 as illustrated in FIG. 5. In this configuration the fins 26 of the fin system can run along the length of the heat pipe 28. In one embodiment of the present invention the fin system can be manufactured with a slightly smaller internal opening compared to the heat pipe diameter. This relative size configuration between the fin system and the heat pipe, can provide a substantially tight interference connection between the heat pipe and the fin system and thereby may enhance thermal connection therebetween. In one embodiment the fin system is manufactured from a thermally conductive material with elastic properties which can enable the insertion of a heat pipe into the internal opening of the fin system. These materials can include metals and alloys provided that during the required deformation for heat pipe insertion, the stresses induced within the material remain within the elastic region. In an alternate embodiment of the present invention, the fin system as illustrated in FIG. 5 can be manufactured from a material which has a desired thermal expansion coefficient, wherein the fin system is appropriately heated for insertion of the heat pipe into the internal opening. As would be readily understood, the thermal coefficient must be selected such that under operational conditions the fin system does not expand an amount that can diminish the thermal transfer between the fin system and the heat pipe below a predetermined level.
In one embodiment of the present invention wherein there are two or more heat pipes within the thermal management system, the fin system comprising a plurality of fins 32 and can be configured to wrap around the heat pipes 30 as illustrated in FIG. 6. This embodiment of the fin system can be formed by extrusion, casting or other method as would be readily understood by a worker skilled in the art.

EXAMPLE 2

In another embodiment of the present invention, the thermal management system comprises a fin system including two or more flat plate fins 34 that are thermally connected to one or more heat pipes 36 transverse to the length of each of heat pipes as illustrated in FIG. 7. These plate fins can be manufactured with one or more holes 38 therein for the insertion of a heat pipe therethrough as illustrated in FIG. 8.
In another embodiment, the plate fins can be manufactured with a plurality of holes 41 for the insertion of heat pipes and additionally include secondary holes 40 and 42 therein which can enable the passage of air therethrough, as shown in FIG. 9. The secondary holes 40 and 42 in adjacent plate fins can be aligned along the length of the heat pipes. Alternately the secondary holes in adjacent plate fins can be offset thereby providing a means for changing the direction of air movement along the length of the heat pipe, wherein the change in directional movement of the air may enhance heat transfer from the fins to the air, for example.

EXAMPLE 3

FIG. 10A illustrates a configuration of the passive thermal management system for dissipating heat generated by a heat source located at end 45 according to another embodiment of the present invention. The thermal management system comprises one or more heat pipes 46 and a fin system comprising a plurality of curved fins 44. A single curved fin of the fin system is illustrated in FIG. 10B. The shape of the fins of the fin system is configured wherein the cool air enters into the passive thermal management system at a first velocity in a first direction 48 and is subsequently slowed, increasing thermal transfer thereto. The heated air thereafter exits the thermal management system at a second velocity in a second direction 50.
FIG. 11A illustrates a configuration of the passive thermal management system for dissipating heat generated by a heat source located at end 56 according to another embodiment of the present invention. The thermal management system comprises one or more heat pipes 58 and a fin system comprising a plurality of curved fins 54. A single curved fin of the fin system is illustrated in FIG. 11B. The shape of the fins of the fin system is configured wherein the cool air enters into the passive thermal management system at a first velocity in a first direction 60 and is subsequently increase in speed, thereby providing a means for the heated air to exit the fin system at an accelerated second speed in a second direction 62, which is substantially parallel to the gravitational vector. In particular the exiting direction of the heated air is substantially parallel to the gravitational vector and in a direction which is similar to that which would be passively induced by this gravitational vector and therefore heat removal may be enhanced.

EXAMPLE 4

FIG. 12 illustrates a fin for use in the fin system according to another embodiment of the present invention. The fin can be configured as a cone having a secondary hole 74 therein in addition to the holes 72 manufactured for the insertion of the heat pipes. The secondary hole can provide a location for the heated air to pass along the length of the heat pipe, wherein for a stack of a plurality of this fin configuration, this secondary hole can be aligned. These aligned secondary holes can thereby enable air movement in a manner similar to that of a chimney. This configuration of a fin of the fin system can provide a means for enabling a level of air movement along the length of the heat pipe and along the fins as well, thereby enhancing heat dissipation into the environment.

EXAMPLE 5

FIG. 13 illustrates a cross sectional view of a thermal management system according to another embodiment of the present invention, wherein in this figure the heat source is positioned at end 69 of the heat pipes. The thermal management system comprises heat pipes 70 and a series of fins stacked in order that holes therethrough are aligned enabling both heat pipe insertion and heat air movement along the length of the heat pipes.
As illustrated in FIG. 13, cool air can enter the thermal management system at a first velocity in a first direction 64, wherein this cool air can be slowed down proximate to the heat pipe thereby enabling heat transfer thereto, and subsequently accelerated and directed towards an exit hole and thereby exits the thermal management system in a direction 66, which is substantially parallel and in substantially the opposite direction to the gravitational vector.
FIG. 14 illustrates a perspective view of a fin for use in the fin system as illustrated in FIG. 13. This fin comprises two sloped portions 75 and 77 and a flat portion 73 which comprises holes 78 for the insertion of the heat pipes. This fin configuration can provide a means for capturing air moving along the length of the heat pipe and redirecting this air along the surface of the fin which may provide a means for enhancing heat transfer from the fins to the moving air. This configuration of the fin can further provide a means for the air to increase in velocity towards the centre of the fin cross section subsequent to the redirection at the flat portion 73, wherein the heat air can exit though aperture 76. This configuration can enable the heated air to travel along the length of the heat pipe in a manner that can enhance the exit velocity thereof.
FIG. 15 illustrates a blank from which a fin can be formed, wherein the fin is substantially configured as a flat disc. FIG. 16 illustrates a fin formed from the blank illustrated in FIG. 15, after punching and bending into a three dimensional configuration. During the punching process, aperture 76 and heat pipe insertion holes 74 can be formed.
FIG. 17 illustrates another blank from which a fin can be manufactured. This blank comprises a number of stress relief cuts 82 and 80 which can provide a means for limiting stress build-up within the fin during the formation process, which may cause ripping and/or tearing of the blank. FIG. 18 illustrates a final fin shape which can be manufactured from the blank illustrated in FIG. 17. During the punching process, aperture 84 and heat pipe insertion holes 86 can be formed and upon punching the fin can be bent into this configuration.

EXAMPLE 6

FIG. 19 illustrates a thermal management system according to another embodiment of the present invention wherein the thermal management system comprises a plurality of fins 90 which form the fin system which are thermally connected to the heat pipes 88. These fins are configured as having a shape similar to that of a roof. A single fin according to this embodiment is illustrated in FIG. 20, wherein this fin can be fabricated as a planar element and bent along a single axis, thereby forming a bi-planar fin. The fin comprises a plurality of primary holes 100 configured to receive the heat pipes of the thermal management system and a centrally located hole 98.
In a first orientation, the thermal management system is oriented such that the heat pipes are substantially parallel to the gravitational vector and the heat source is positioned at end 96 of the thermal management system. In this orientation, as illustrated in FIG. 19, the centrally located secondary hole 98 associated with the fins of the fin system, essentially acts as a chimney for heated air movement through and subsequently out of the thermal management system in direction 94. In this orientation cool air can be drawn from the side of the thermal management system substantially in direction 92, wherein heating and acceleration of the air occurs along the surface of the fins and the heated air is subsequently expelled out the ‘chimney’ or centrally located secondary hole. This configuration of the fin system of the thermal management system can provide a means for the top fins of the fin system, namely the fins proximate to the exit hole or secondary hole, to receive cold air and thus aid in improving the thermal transfer efficiency of the fin system, as these upper fins are not simply receiving air previously heated by lower fins of the fin system.
When the thermal management system is oriented in the opposite direction to that illustrated in FIG. 19, cool air can enter the thermal management system through the centrally located hole, be heated along the surface of the fins and subsequently exit the thermal management system out the side of thereof.
In another orientation, for example when the heat pipes are oriented perpendicular to the gravitational vector, the fins of the fin system can substantially act as a series of vertical fins, thereby providing a means for all the fins of the fin system to draw in air that has not been pre-heated by other fins associated with the fin system.
FIG. 21 illustrates a punched blank from which a fin for use with the passive thermal management system as illustrated in FIG. 19 can be formed and FIG. 22A illustrates a front view of the fin after bending into the desired configuration. In one embodiment of the present invention, portions 101 of the blank can be removed which can provide a means for reducing stresses induced within the blank during the bending process and may further reduce buckling or tearing of the blank during bending.
FIG. 22B illustrates an end view of the fin wherein the bend can be formed at an angle 102, which can be determined based on the desired air flow through the thermal management system having a fin system comprising fins of this configuration. In one embodiment, angle 102 can be between about 40° to about 140°. In another embodiment, angle 102 can be between about 60° to about 120°. In yet another embodiment, angle 102 can be between about 80° to about 100°. The geometric configuration of the holes that are punched or formed within the blank are designed in order that upon bending of the fin, an appropriate hole geometry is realized for a desired heat pipe to be inserted while providing a desired level of thermal contact between the heat pipe and the fin. For example, in one embodiment the holes can be punched as ellipses wherein upon bending, and subsequent viewing from above, the holes may appear as circles. As would be readily understood by a worker skilled in the art, the shape of the holes created for the insertion of a heat pipe, is directly dependent on the selection of angle 102.

EXAMPLE 7

FIG. 23 illustrates a passive thermal management system according to another embodiment of the present invention, wherein the passive thermal management system is coupled to a lighting device. The thermal management system provides for the dissipation of heat that is generated by one or more light-emitting diodes 200 which are thermally coupled to the passive thermal management system, and more specifically one or more heat pipes 202, 203. For example, the thermal connection between the one or more light-emitting diodes and the one or more heat pipes can be provided via substantially direct contact, through a LED package or via a thermally conductive substrate upon which the one or more light-emitting diodes are mounted. The thermal management system comprises one or more heat pipes 202, 203 which are thermally connected to a fin system 204. The fin system 204 is configured as the housing of the lighting device and in this configuration the fin system 204 forms as an exterior surface area. In one embodiment of the present invention this fin system can further comprise one or more external fins which may enhance heat transfer from the fin system to the environment.
In one embodiment heats pipe 202 of the thermal management system can be straight and transfer heat to the end 206 of the fin system 204. In another embodiment of the present invention, one or more of heat pipe 203 may be bent in order that thermal connection between the heat pipe and the fin system can be provided along a portion of the length of the heat pipe, which can enhance heat transfer to the fin system. In another embodiment of the present invention, the thermal management system can comprise both bent and straight heat pipes.
In one embodiment of the present invention, the fin system which forms the housing can comprise one or more openings therein thereby enabling environmental access to the interior volume 212 defined in part by the fin system 204, thereby aiding in the dissipation of any heat that may have otherwise been partially trapped within this interior volume. The one or more openings can be configured as holes or slits or other configurations as would be readily understood by a worker skilled in the art.
As illustrated in FIG. 23, the fin system 204 can retain or mate with a transparent window 208 which may cover the optics 210 associated with the one or more light-emitting diodes.
It is obvious that the foregoing embodiments of the invention are exemplary and can be varied in many ways. Such present or future variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims

1. A passive thermal management system for dissipating heat generated by a heat source, the thermal management system comprising:

(a) one or more heat pipes each having a length, each heat pipe thermally connected to the heat source, each heat pipe for transferring heat along its length away from the heat source; and

(b) a fin system thermally coupled to the one or more heat pipes, the fin system extracting heat from the one or more heat pipes and dissipating the heat therefrom, the fin system configured to provide a desired level of heat dissipation independent of orientation of the thermal management system.

2. The passive thermal management system according to claim 1, wherein said fin system comprises a plurality of fins, said fins aligned about parallel with the length of the one or more heat pipes.

3. The passive thermal management system according to claim 1, wherein said fin system comprises a plurality of fins, said plurality of fins positioned in a stacked configuration with a predetermined separation therebetween.

4. The passive thermal management system according to claim 3, wherein said fins are aligned about perpendicular with the length of the one or more heat pipes.

5. The passive thermal management system according to claim 3, wherein each of said fins comprise one or more primary holes therein for insertion of a heat pipe.

6. The passive thermal management system according to claim 3, wherein each of said fins comprise one or more secondary holes therein for enabling fluid to pass therethrough.

7. The passive thermal management system according to claim 3, wherein said fins are configured in a shape selected from the group comprising planar, bi-planar, curved, conical, cylindrical and frusto-conical.

8. The passive thermal management system according to claim 3, wherein said fins are have a cross section which comprises two sloped portions and one flat portion.

9. The passive thermal management system according to claim 3, wherein said fins are formed from a material selected from the group comprising aluminium, copper, metal, alloy, ceramic, metal ceramic composite and thermally conductive polymer.

10. The passive thermal management system according to claim 3, wherein said fins are formed from two or more thermally conductive materials.

11. The passive thermal management system according to claim 1, wherein the fin system is thermally coupled to the one or more heat pipes using a method selected from the group comprising welding, brazing, interference connection, epoxy, soldering and thermally conductive adhesive.

12. The passive thermal management system according to claim 3, wherein each of said fins are configured as a bi-planar fin comprising a centrally located secondary hole therein.

13. The passive thermal management system according to claim 12, wherein each of said fins comprise one or more holes therein, each of the one or more holes for insertion of one of the one or more heat pipes.

14. The passive thermal management system according to claim 12, wherein each the bi-planar fin has two planes which an intersection angle therebetween, said intersection angle ranges between about 40 degrees and about 140 degrees.

15. The passive thermal management system according to claim 13, wherein said intersection angle ranges between about 60 degrees and about 120 degrees.

16. The passive thermal management system according to claim 13, wherein said intersection angle ranges between about 80 degrees and 100 degrees.

17. The passive thermal management system according to claim 1, wherein the passive thermal management system is coupled to a lighting device and wherein the fin system is configured as a portion of a housing for the lighting device.

18. The passive thermal management system according to claim 17, wherein the fin system is configured to form an entire housing for the lighting device.