Passive Thermal Management System
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.
Latest Patents:
The present invention pertains to thermal management and in particular to a passive thermal management system.
BACKGROUNDTypical 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 INVENTIONAn 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.
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.
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 SystemThe 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 1In the embodiment illustrated in
In one embodiment of the present invention, a plurality of passive thermal management systems as illustrated in
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
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
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
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
As illustrated in
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
When the thermal management system is oriented in the opposite direction to that illustrated in
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.
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
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.
Type: Application
Filed: Nov 8, 2006
Publication Date: Jan 15, 2009
Applicant:
Inventors: Philippe Schick (Vancouver), Daryl James (Coquitlam)
Application Number: 12/091,337
International Classification: F28F 7/00 (20060101); F28D 15/00 (20060101);