KR20050085880A - Flexible graphite thermal management devices - Google Patents

Abstract

The invention provides to thermal management devices constructed from flexible graphite. In one embodiment, the thermal management device includes a wick structure inside a shell. In certain preferred embodiments, the wick structure is composed of a mass of expanded graphite. In another embodiment, the shell of the device includes flexible graphite and an optional wick structure. In certain preferred embodiments, the flexible graphite shell is fluid impermeable. The invention further includes methods of making the aforementioned thermal management devices.

Description

Thermal Management Device for Flexible Graphite {FLEXIBLE GRAPHITE THERMAL MANAGEMENT DEVICES}

FIELD OF THE INVENTION The present invention relates to thermal management devices, and more particularly, to devices comprising flexible graphite and methods of making such devices.

Thermal management devices such as heat pipes are devices known in the field of heat transfer. The heat pipe is essentially a closed heat transfer system, where a small amount of liquid in the sealed vacuum enclosure is circulated through the evaporation and condensation cycle. Heat entering the enclosure at one location on the case evaporates the liquid at that location, which produces vapor that travels to the cooler location on the case where condensed vapor condenses. The movement of the steam causes a small vapor pressure difference between the evaporator position and the condenser position. Heat transfer is achieved when the heat of vaporization that produces steam is essentially transferred by the steam to the condenser position, where heat at that location is provided as heat of condensation.

In order to continue the heat transfer, the condensate must be returned from the condenser to the evaporator, where evaporation takes place again. Although this return can be achieved by something as simple as gravity, capillary wicks have generally been used to make heat pipes relatively insensitive to gravity effects. Such a wick extends from a position near the condenser where water begins to form to a position in the evaporator necessary for evaporation.

With regard to the constituent material, the cases are traditionally made of copper or other metals, and the cases are structurally sufficient to withstand the vapor pressure in the heat pipes and to avoid inhaling reduced steam or non-condensable gases outside the heat pipe tape. It consists of walls of sufficient thickness to ensure.

Considerable efforts have been made to develop materials that are thermally conductive and act as capillary structures for wicks. Such most common materials are metal screens used in multiple layers, and metal powder sintered into a structure attached to a case. The thermal conduction properties of such wicks have been considered important to allow heat entering the heat pipe to be directed through the wick in the evaporator and to allow the liquid to evaporate within the wick. A thermal five configuration in which the wick is attached to the case wall at the evaporator is generally preferred to allow the input heat to directly access the liquid in the wick.

However, there are applications that are not satisfactory with existing heat pipe structures. Metal cases and metal wicks add weight, strength and electrical conductivity to heat pipes, but such metal cases and metal wicks are not available in some situations. Portable computers, so-called "laptops", are one application where traditional thermal pies are difficult to use. In such applications, weight and space are extremely important factors. Moreover, the price of metal cases and sintered wicks is a disadvantage in terms of the highly competitive market of portable computers. Moreover, the wick components from existing materials do not withstand corrosion. Therefore, there is a need to find new construction materials for heat pipes.

1 is a front view of the inner form of a cylindrical heat pipe;

2 is an exploded view of the elements of a vertical heat pipe.

3 is a front view of one particular embodiment of a heat pipe of the present invention in a heat spreader assembly.

4 is a cross-sectional view of one particular embodiment of a thermal management device having fins.

One embodiment of the present invention provides a thermal management device that includes a substantially fluid permeable shell and a wick structure within the shell. In certain preferred embodiments, the wick comprises a large amount of expanded graphite.

Another embodiment of the present invention provides a method of manufacturing a thermal management apparatus having a wick structure formed from a large amount of expanded graphite.

Another embodiment of the present invention provides a thermal management device having a shell constructed from flexible graphite.

In a further embodiment of the present invention, there is provided a method of manufacturing a thermal management apparatus having a shell constructed from flexible graphite, which will be apparent to those skilled in the art after reading this specification.

The thermal management devices of the present invention have a number of advantages over conventional devices in terms of good weight, acceptable strength, and satisfactory thermal conductivity. Moreover, the wick structure of the device of the present invention also has improved corrosion resistance compared to existing wick materials.

Additional features and advantages of the invention will be set forth in the description which follows, and one of ordinary skill in the art will readily understand in part from the description, or may practice the invention described herein, including the following description and claims and drawings. Will be recognized.

It is to be understood that the foregoing general description and the following detailed description represent embodiments of the invention and are intended to provide a schematic perspective or framework for understanding the nature and properties of the invention as they claim. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated and constituted as part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operations of the invention.

Graphite is characterized by a carbon laminate structure, that is, a structure consisting of laminated layers or layers of carbon atoms that are coupled with weak van der Waals forces. When considering the graphite structure, two axes or directions are usually mentioned, namely the "c" axis or direction, and the "a" axis or direction. For simplicity, the "c" axis or direction may be considered as perpendicular to the carbon layers. The "a" axis or direction may be considered as the direction parallel to the carbon layers or the direction perpendicular to the "c" direction. Graphite suitable for producing flexible graphite sheets has a high degree of orientation.

As mentioned above, the bonding force holding the layers of parallel carbon atoms together is only a weak Van de Waals force. Natural graphite overlaps the carbon layers or laminates to provide an expanded extension in the direction perpendicular to the layers (the “c” direction) to form an expanded or inflated graphite structure in which the laminate properties of the carbon layers are substantially maintained. It can be processed so that the space between them can be properly opened.

More specifically, the expanded graphite pieces can be expanded to have a final thickness or " c " dimension of 80 times or more of the original " c " direction dimension, or a sheet of adhesive or integrated sheet of expanded graphite (e.g., That is, without the use of a binder as a web, paper, strip, foil, mat, etc., generally referred to as "flexible graphite". Without the use of any binding material, the formation of graphite particles that expands into flexible graphite integrated to have a final thickness or “c” direction dimension of 80 times or more of the original “c” direction dimension by compression It is recognized that this is possible due to the mechanical interlocking or bonding achieved between the graphite particles.

In addition to the flexibility, the above-mentioned sheet material has thermal conductivity and thermal conductivity in comparison with natural graphite due to expanded graphite particles and graphite layers substantially parallel to the mating sheet surfaces resulting from significant high compression such as roll compaction. It has been known to have a high degree of anisotropy and fluid diffusion for electrical conductivity. The resulting sheet material therefore has good flexibility, good strength and high orientation.

In summary, the process of producing flexible, binderless anisotropic graphite sheet materials such as webs, papers, strips, tapes, foils, mats, etc. can be performed without binders under predetermined loads to produce substantially flat flexible integrated graphite sheets, Compressing or compressing expanded graphite particles having a " c " direction dimension of 80 times or more than the original particles. Expanded graphite particles, once compressed, generally in the form of a worm, will maintain an arrangement with the pressed form and the opposite major sheet surface. The density and thickness of the sheet material can be varied by controlling the degree of compaction. The density of the sheet material may be in the range of about 0.04 g / cc to about 2.0 g / cc. Flexible graphite sheet material exhibits a moderate degree of anisotropy due to the arrangement of graphite particles parallel to the opposing parallel major sheet surfaces by the degree of anisotropy which increases the roll compression of the sheet material to increased density. In the anisotropic material of roll compression, the thickness, ie, the direction perpendicular to the opposing parallel sheet surfaces, includes the "c" direction, and the directions along the length and thickness, ie, the directions parallel to the opposing major surfaces. Include the "a" directions, and the thermal and electrical properties of the sheet are very different in size for the "c" and "a" directions.

A method for producing a product from graphite particles has been proposed. For example, U.S. Patent No. 5,882,570 to Hayward, describes the steps of: drawing a flexible, uncoated graphite foil to small particle sizes, thermally thermally impacting the particles to swell the particles, Mixing the expanded graphite with a thermosetting phenolic resin, molding injection of the mixture to form low density blocks or other forms, and heat treating the blocks to thermoset the material. . The final blocks may be used as insulating materials in a furnace or the like.

WO 00/54953 and US Pat. No. 6,217,800 to Hayward further disclose processes related to the content of US Pat. No. 5,882,570. Hayward processes are quite limited in the raw materials used and the type of end product that can be produced. Hayward uses only raw material that has not been injected, and the final product can be formed only by mixing graphite particles with a large proportion of resins and by injection molding the mixture to produce a product, which product is then heated Cures.

For graphite, it is known that graphite consists of a layered plane of hexagonal arrays of carbon atoms or nets. The planes of this layered structure of hexagonally arranged carbon atoms are substantially flat and oriented so as to be equidistant substantially parallel to each other. Equivalent sheets or layers of substantially flat and parallel carbon atoms, often referred to as graphene layers or ground planes, are connected or bonded to one another, and the groups of sheets or layers are arranged in a crystalline form. Highly ordered graphite consists of crystals of considerable size. The crystals have well aligned or highly aligned carbon layers with respect to each other. In other words, highly ordered graphite has a highly desirable crystalline orientation. It should be noted that graphite has an anisotropic structure and thus exhibits high directional properties, ie thermal and electrical properties, and fluid diffusion.

The present invention may include providing a raw material, such as a sheet of flexible graphite material. The raw material typically comprises graphite in crystalline carbon form containing atoms covalently bonded with weak bonding agents between planes in flat layered structures. When obtaining raw materials such as the flexible graphite sheets mentioned above, graphite particles such as natural graphite pieces are typically treated by intercalating agents such as sulfur and nitrogen solutions, and the crystal structure of the graphite is graphite and intercal. Reacts to form a compound of rating agent. From now on, the treated graphite particles are referred to as "intercalated graphite particles". Upon exposure to high temperatures, the intercalating agent in the graphite decomposes and volatilizes, which intercalates the graphite particles in a direction perpendicular to the crystal plane of the graphite, i. To expand. The exfoliated graphite particles are worm-shaped in shape and are therefore commonly referred to as worms. The worms, unlike the original graphite pieces, may be formed into various shapes and cut together and squeezed together into flexible sheets, where small transverse openings can be provided by modifying mechanical collisions.

Graphite starting materials suitable for use in the present invention but for flexible sheets are highly graphite carbonaceous materials that can intercalate halogen as well as organic and inorganic acids and then expand upon exposure to heat. It includes. These highly graphite carbonaceous materials most preferably have a degree of graphitization of about 1.0. As used herein, the term "degree of graphitization" is referred to as a value according to the following formula:

Where d (002) is the spacing between the carbon graphite layers of the crystalline structure, measured in kPa. The spacing “d” between the graphite layers is measured by standard X-ray diffraction techniques. Positions of diffraction peaks corresponding to (002), (004) and (006) Miller Indices are measured, and standard least square techniques to derive an interval that minimizes the total error for all these peaks. To be employed. Examples of highly graphite carbonaceous materials include natural graphites from various raw materials as well as other carbonaceous materials such as carbons by methods such as chemical vapor deposition and the like. In many examples, natural graphite is preferred.

Graphite starting materials for the flexible sheets used in the present invention may contain non-carbon components, as long as the crystal structure of the starting materials can be peeled off to maintain the required degree of graphitization. In general, any carbon-containing material having a degree of graphitization and having a peelable crystal structure is suitable for use in the present invention. Such graphite preferably has an ash content of 20 weight percent or less. In certain circumstances, the graphite used will have a purity of at least about 94%. In other preferred circumstances, the graphite used will have a purity of at least about 99%.

A common method for producing graphite sheets is described in US Pat. No. 3,404,061 to Shane et al., Which is incorporated herein by reference. In a typical implementation of the method by Shane et al., Natural graphite pieces are intercalated by dispersing the pieces in a solution comprising a mixture such as a mixture of nitric acid and sulfuric acid, the mixture being 100 pph of the weight of the graphite pieces (pph). ) Is advantageous by the level of about 20 to 30 pieces of intercalating agent solution weight. Intercalating solutions include oxidizing agents or other intercalating agents known in the art. Examples may include oxidants and oxidizing mixtures, mixtures such as solutions containing nitric acid, potassium chlorate, chromic acid, potassium permanganate, potassium chromate, potassium dichromate, perchloric acid, concentrated nitric acid and chlorate , Mixtures such as chromic acid and phosphoric acid, sulfuric acid and nitric acid, or strong organic acids such as trifluoroacetate, and mixtures of strong oxidants that can be dissolved in organic acids. Alternatively, the potential can be used to oxidize the graphite. Chemical microcomponents that can be induced into graphite crystals using electrolyte oxidation include sulfuric acid as well as other acids.

In a preferred embodiment, the intercalating agent is sulfuric acid, or a mixture of sulfuric acid and phosphoric acid, and an oxidizing agent solution such as nitric acid, perchloric acid, chromic acid, potassium permanganate, hydrogen peroxide, iodic acid or peroxic acid, and the like. Intercalating solutions may sometimes contain metal halides such as ferric chloride and ferric chloride mixed with sulfuric acid, or halides such as bromine and sulfuric acid solutions or bromine solutions in organic solvents.

The amount of intercalating solution may be about 20 to about 150 pph, and typically about 50 to about 120 pph. After the graphite pieces are intercalated, any excess solution is typically discarded from the pieces and the pieces are washed with water. Alternatively, the amount of intercalating solution may be limited between about 10 and about 50 pph, which allows the washing step to be eliminated as disclosed in US Pat. No. 4,895,713, which is incorporated herein by reference.

The intercalating solution treated graphite flake particles may be contacted with a reducing organic agent, optionally selected from alcohols, sugars, aldehydes and esters, for example by blending, which may be intercalated at temperatures ranging from 25 ° C. to 125 ° C. Reacts with the surface film to oxidize the calcifying solution. Specific organic agents suitable are hexadecanol, octadecanol, 1-octanol, 2-octanol, dekilk alcohol, 1, 10 decanediol, dealkylaldehyde, 1-propanol, 1,3 propanediol, ethylene glycol, Polypropylene glycol, dextrose, fructose, lactose, sucrose, potato starch, ethylene glycol monostearic acid, glycerol monostearic acid, dimethyl oxylate, diethyl oxylate, methyl formate, ethyl formate, ascorbic acid And lignin-derived compounds such as sodium lignosulphate. The amount of organic reducing agent is typically about 0.1-5% by weight of graphite flake particles.

The use of swelling agents applied immediately before, during or after intercalating may also provide improvements. These improvements may be reduced peel temperature and increased expansion volume (referred to as "worm volume"). The swelling agent in this respect will be an organic material that is sufficiently soluble in the intercalating solution to achieve an improvement in expansion. More particularly, organic materials of this type containing carbon, hydrogen and oxygen may preferably be used exclusively. Carboxylic acid has been known to be particularly effective. Suitable carboxylic acid acids useful as swelling agents can be selected from aromatic, aliphatic or cycloaromatic, straight chain or branched chains, saturated unsaturated monocarboxylic acids, dicarboxylic acid and polycarboxylic acid, wherein the polycarboxylic acid has at least one carbon atom The carboxylic acid acids are sometimes soluble in an intercalating solution in an amount effective to adjust up to about 15 carbon atoms and provide a measurable improvement of one or more stripping forms. Suitable organic solvents can be used to improve the solubility of the organic expanding agent in the intercalating solution.

Representative examples of saturated aliphatic carboxylic acid acids are represented by the formula H (CH ₂ ) _N COOH, wherein n is an integer from 0 to about 5, including form, acet, propyne, butyne, pentanone, hexanon, and the like. Mountains. Instead of carboxylic acid, anhydrides, or reactive carboxylic acid derivatives such as alkyl esters may also be used. Representative examples of alkyl esters are methyl form and ethyl form. Sulfuric acid, nitric acid and other known aqueous intercalating agents have the ability to ultimately break down formic acid into water and carbon dioxide. Because of this ability, formic acid and other sensitive swelling agents are advantageously contacted with the graphite pieces prior to the immersion of the graphite pieces in the aqueous intercalating agent. Representative examples of dicarboxylic acid acids are aliphatic dicarboxylic acid having 2-12 carbon atoms, more specifically oxalic acid, fumaric acid, malonic acid, maleic acid, succinic acid, glutaric acid, adipic acid, 1,5- Pentanedicarboxylic acid, 1-6-hexanedicarboxylic acid, 1,10-decanecarboxylic acid, cyclohexane-1, 4-dicarboxylic acid, and aromatic carboxylic acid such as phthalic acid or lerephthalic acid. Representative examples of alkyl esters are dimethyl oscillate and diethyl oxylate. Representative examples of cycloaliphatic acids are cyclohexane carboxylic acid acids, and representative examples of aromatic carboxylic acid acids are benzoic acid, naphthaic acid, anthranilic acid, p-aminobenzone acid, salicylic acid, o-, m- and p-tolyl Acids, methoxy and ethoxybenzone acids, acetoacetamidobenzone acids, and acetamidobenzone acids, phenylacetate acids and naphtanic acids. Representative examples of hydroxy aromatic acids include hydroxybenzone acid, 3-hydroxy-1-naphthaic acid, 3-hydroxy-2-naphthaic acid, 4-hydroxy-2 naphthaic acid, 5-hydroxy- 1-naphthaic acid, 5-hydroxy-2-naphthaic acid, 6-hydroxy-2-naphthaic acid, 7-hydroxy-2-naphthaic acid. Representative of the polycarboxylic acid acids is citric acid.

Intercalating solutions are typically aqueous and may contain about 1 to 10% swelling agent amount, which amount is effective to enhance exfoliation. In embodiments in which the expanding agent is contacted with graphite pieces before or after immersion in an aqueous intercalating solution, the expanding agent is mixed with the graphite by a suitable means such as a V-blender, the expanding agent typically being Amount from about 0.1% to about 10% by weight.

After intercalating the graphite pieces, the intercalated graphite pieces coated with the intercalating agent are blended with an organic reducing agent, the blend being 25 ° C. to accelerate the reaction of the reducing agent with the intercalating coding. Exposure to temperatures in the range of from 125 ° C. The heating cycle is up to about 20 hours, for shorter heating cycles, for example at least about 10 minutes, for temperatures higher than the above mentioned range.

Therefore, treated graphite particles are sometimes referred to as "intercalated graphite particles". When exposed to high temperatures, for example at least about 160 ° C., sometimes from about 700 ° C. to 1200 ° C. or higher, the intercalated graphite particles are inherently c-direction, ie perpendicular to the crystal plane of the constituent graphite particles. Expands by 80 to 1000 times its volume. Expanded ie exfoliated graphite particles are often referred to as worms because they are worm-shaped in shape. The worms, unlike the original graphite pieces, may be formed into various shapes and cut together and squeezed together into flexible sheets, where small transverse openings can be provided by modifying mechanical collisions.

Flexible graphite sheets and foils are adhesive with good processing strength and are suitably pressed by a rolling compression to a thickness of about 0.05 mm to 4.00 mm and a density of 0.1 to 1.5 grams per g / cc. About 1.5% to 30% by weight of the ceramic additive may be blended into intercalated graphite pieces as described in US Pat. No. 5,902,762 to provide resin injection into the final flexible graphite product (the patent is Merged by reference in the specification). The additive comprises ceramic fiber particles having a length of about 0.1 mm to 1.5 mm. The width of the particles is suitably about 0.05 to 0.001 mm. Ceramic fiber particles are non-responsive and non-adhesive to graphite and are suitable at temperatures of about 1100 ° C., preferably about 1400 ° C. or higher. Suitable ceramic fiber particles are formed of softened quartz glass fibers, carbon and graphite fibers, zirconia, boron nitrogen, silicon carbide and magnesium fibers, calcium metasilicate fibers, calcium aluminium silicate fibers, aluminum oxide fibers and the like.

Flexible graphite sheets may also sometimes be resin treated, and the absorbed resin after the treatment improves the waterproofing and processing strength (ie, firmness) of the flexible graphite sheet as well as the form "fixation" of the sheet. Suitable resin contents are preferably at least about 5% by weight, more preferably about 10 to 35% by weight, suitably up to about 60% by weight. Particularly useful resins in the practice of the present invention are acrylic-, epoxy- and phenolic-based resin-based, or mixtures thereof. Suitable epoxy resin systems include resin systems of diglycidyl ether or bisphenol A (EGEBA) and other multifunctional resin systems, phenolic resins that may be used include resol and novolak phenol. In certain preferred embodiments, the glass transition temperature of the resin is compatible with the temperature of use of the thermal heat management device. Nevertheless, the graphite sheet prepared above can be cut or trimmed to form the desired product. Resin treated flexible graphite is also referred to as "resin infused flexible graphite" or "injected flexible graphite".

The present invention will be described centering on the aforementioned figures of heat pipes, but the invention is not limited to heat pipes only and is applicable to other types of thermal management devices such as, for example, steam chambers. Possible similar or similar reference characters will be used to describe similar or similar elements in the figures.

1 is a front view of the interior of a cylindrical heat pipe, generally indicated at 10. 1 shows a cylindrical heat pipe 12 arranged in a vertical orientation with respect to the general path of the working fluid flow. The heat pipe 12 includes a shell 14 and a wick structure 16. Optionally, the heat pipe 12 may include at least one fluid passageway 18 outside of the wick structure 16, which is also indicated by arrow E. The heat pipe 12 may also include at least one fluid passage 20 into the interior of the wick structure 16, which is also indicated by arrow I. The wick structure 16 may also include a number of nearly radiant fluid passages, which allow the working fluid to move from the passage 18 through the wick structure 16 to the passage 20. Optionally, the heat pipe 12 also includes an evaporator 22 and a condenser 26 at opposite ends of the heat pipe 12.

Heat pipe 12 may include mating element 28 for heat source 30. Optionally, the mating element 28 is located at the same heat pipe 12 end as in the evaporator 22. In certain preferred embodiments, the mating element 28 has a surface in contact with the surface of the heat source 30, the surface of the mating element 28 optionally being in contact with the mating element 28. ) Is a mirror image of the surface. In other preferred embodiments, the mating element 28 also contacts the outer portion of the heat pipe 12. Contact between mating element 28 and heat pipe 12 may improve heat transfer from heat source 30 to heat pipe 12. Suitable constituent materials of mating element 28 include at least flexible graphite, copper, aluminum, and combinations thereof. Examples of suitable materials for mating element 28 include eGRAF ^™ HS 400 from Graftech Inc. One example of the heat source 30 is a computer chip.

As shown in FIG. 1, the heat pipe 12 may also include a number of fins 32 located on at least a portion of the shell 14. Optionally, the fins 32 are located on at least the end of the pipe 12 where the condenser 26 is located. In the embodiment of the heat pipe 12 comprising fins 32, the fins 32 are preferably composed of flexible graphite. Other suitable materials of the fins 32 may include copper, aluminum, and any combination of the previously named materials. The pins 32 are not limited to the embodiment shown in FIG. 1. Any suitable configuration of the pins 32 may be used as part of the present invention. For example, the fins 32 can include a base and a combination of elements of a plurality of distant fins extending vertically away from the heat pipe 12. Embodiments of the invention may also include a fan for moving air through the fins 32 to assist with the loss of heat absorbed by the fins 32.

As shown in FIG. 1, heat is generated in the heat source 30. Heat generated in the heat source 30 is transferred to the heat pipe 12 and evaporates the working fluid at least in the evaporator 22. The vapor phase of the working fluid flows through the passage 20 to the condenser 26 as indicated by arrow I. The vapor working fluid condenses in liquid form in the condenser 26 and the heat removed from the working fluid as a result of the condensation is transferred to the fins 32 and lost to the surrounding environment. The liquid form of the working fluid flows back to the evaporator 22 along the passage 18 in the direction indicated by arrow E. FIG. Typical flow mechanisms for delivering liquid working fluid from condenser 26 to evaporator 22 include at least gravity, capillary action, or a combination thereof.

Optionally, the heat pipe 12 may be operated at a pressure less than atmospheric pressure. By adjusting the pressure inside the heat pipe 12, the temperature at which the working fluid will evaporate inside the heat pipe 12 may be adjusted to a specific change in temperature combined with the heat generated by the heat source 30. For example, if the working fluid is water and the heat pipe 12 operates at a plasticized pressure, the water will evaporate at a temperature of about 100 ° C. or less.

A first embodiment of a heat pipe is shown in FIG. 2 and is generally indicated at 40. Optionally, the heat pipes 40 may be arranged in a vertical orientation with respect to the path of movement of the working fluid. However, the heat pipes 40 may be arranged in any configuration. Heat pipe 40 includes a shell, which includes two sheet materials 44u and 44l. Sheets 44u and 44l are located on opposite ends of heat pipe 40. Sheet 44l may be referred to as an evaporator, and sheet 44u may be referred to as a condenser.

The heat pipe 40 also includes a wick structure 46. As shown, the wick structure 46 includes four different plate structures 46a-46d. It should be appreciated that the heat pipe 40 is not limited to any particular number of plates. In the structure of the plate structures 46a to 46d, the flow path of the working fluid is preferably changed from one plate to an adjacent plate. For plates 46a-46d, it can be seen that the flow path of plate 46a is approximately exactly opposite of the flow path of the working fluid through plate 46b. For example, plate 46a has a central opening and spokes such as flow paths extending radially outward from the central opening. In contrast, plate 46b includes a center hub and spokes such as support members that extend radially outward from the wing center hub. Moreover, plate 46c preferably provides a flow path that supplements the flow path of plate 46b. The same relationship holds for the plates 46c and 46d. The wick structure 46 is configured in such a way that the working fluid is delivered into the heat pipe 40 at least through capillary action.

In an embodiment of the invention, the heat pipe 12 preferably comprises a shell 14 which is substantially fluid permeable, preferably the shell 14 is an airtight enclosure and the wick structure 16 is It is inside the shell 14. Optionally, the shell 14 of the heat pipe 12 may be constructed from flexible graphite. Optionally, the shell 14 has a density of at least 1.6 g / cc, typically at least about 1.7 g / cc, more typically at least about 1.9 g / cc, more typically at least about 2.0 g / cc It is composed of flexible graphite having a.

The flexible graphite used to form the shell 14 may or may not be resin infused flexible graphite. Moreover, the shell 14 may comprise a sheet of one or more flexible graphite sheets. In another embodiment of the shell 14, the inner surface of the shell 14 may comprise at least one channel, preferably a plurality of channels. By airtight herein is meant a vacuum used to remove at least some, preferably substantially all, of the fluid that has not moved from the shell 14. Fluid that does not move herein means at least a fluid, such as air, present in the shell 14 that is not a working fluid.

In the case where the shell 14 is composed of flexible graphite, various techniques may be used to form a shell of a desired shape. For example, pressing may be used to form the flexible graphite sheet into the desired shape for the shell 14. Typical pressures used to compress flexible graphite may be about 4 bars or less, typically about 2 bars or less. In the second technique, an adhesive may be used to form flexible graphite into the desired shape for the shell 14. In certain preferred embodiments, the adhesive does not dissolve in the working fluid or vice versa. In a third technique, the flexible graphite is rolled into a cylindrical shape, the length seam of the heat pipe 12 is formed through compression or adhesion, and a plug is used in each of the axial openings of the cylinder to form the shell 14. Can be.

In another technique, one or more flexible graphite sheets may be rolled into a tubular shape, and the ends of the tube may be plugged to form a shell 14. Optionally, the sheets may be raised to form channels on the inner surface of the shell 14. In another alternative, the flexible graphite sheets may be wrinkled. In another technique, flexible graphite sheets may be wrapped around the mandrel to form the shell 14. When wrapping sheets, the sheets can be wrapped in any configuration, such as but not limited to wrapping the sheets in a spiral manner. In the techniques mentioned above, flexible graphite sheets may or may not be resin injected. In the resin-infused sheets, the resin can be processed before or after the shell 14 formation.

In another embodiment, the shell 14 consists of three-dimensional pieces of flexible graphite. A passage is processed into the pieces. Preferably the passage does not extend completely through the piece. The opening end of the passage can be sealed by any one of the aforementioned techniques of adhesive, compression or plug.

In certain preferred embodiments, the wick structure 16 comprises a permeable material, more preferably a large amount of expanded graphite, more preferably a flexible graphite having a density of only about 1.5 g / cc. Flexible graphite is used herein to describe the large amounts of expanded graphite that have been formed into sheets. More preferably, the flexible graphite of the wick structure 16 has a density of only about 1.1 g / cc, more preferably 1.0 g / cc or less, and most preferably only a density of about 0.5 g / cc. Have It is more preferred that the flexible graphite has a density of at least about 0.25 g / cc. An example of such flexible graphite is Graftech Inc.'s GRAFOIL ^ⓡ residing in Lakewood, Ohio.

One way in which the density of flexible graphite can be measured is the immersion density test. In this test, the flexible graphite sample is weighted and recorded. The sample is then immersed in a predetermined volume of water. The volume of water dispersed by immersion of the sample is recorded. Density is determined by dividing the weight of the sample by the volume of water dispersed. The density calculation method is not limited to the immersion density test mentioned above.

The flexible graphite of the wick structure 16 may be resin injected or non resin injected flexible graphite. This is the case when the structure 16 is resin injected. In certain preferred embodiments, structure 16 is injected in a manner that induces voids in structure 16. Under such circumstances, resin injection is more desirable to enhance capillary flow and / or diffusion of the working fluid.

Optionally, the flexible graphite wick structure 16 may further include metal wires that are integrated at least into segments of the wick structure 16. Examples of suitable metal wires include copper, aluminum, stainless steel, titanium, and combinations thereof. The metal wire can be integrated into the wick structure 16 in a variety of ways.

One way is that the metal wire is wrapped around at least a portion of the exterior of the wick structure 16. In a second manner, the metal wire is adhesively bonded to at least a portion inside or outside the wick structure 16. In a third scheme, a laminate of flexible graphite and metal wire is formed. At least a portion of the laminate includes a metal wire.

The wick structure 16 may also include one or more flexible graphite sheets. Moreover, each flexible graphite sheet may include about two or more flexible graphite layers.

In one particular embodiment, the wick structure 16 comprises a pleated flexible graphite sheet. Preferably, the wrinkles include fine wrinkles. More preferably, the fine wrinkles have a size of about 1 mm or less. Crinkle gears may be used for pleat formation. This embodiment of the wick structure 16 may include a second flexible graphite sheet. In some circumstances, the second flexible graphite sheet is free of wrinkles.

In another embodiment, the wick structure 16 includes at least one channel. The channel (channels) may comprise a first portion of a size that facilitates vapor flow, and a second portion of a size that facilitates liquid flow. The wick structure 16 may be raised to form channels in the structure 16. The size of the channels may be uniform or vary. If the channels vary in size, some channels may be sized to facilitate vapor flow and others may be sized to facilitate liquid flow. For structure 16, in one embodiment, wick structure 16 is attached to evaporator 22 of heat pipe 12.

As an alternative, the wick structure may be constructed from a material other than expanded graphite. Suitable alternative materials include metals such as aluminum, copper, iron, nickel, titanium, and combinations thereof. Alternative materials may be used instead of expanded graphite or in combination with expanded graphite.

The heat pipe 12 may also include a moving liquid that circulates inside the shell 14. Preferred examples of the working fluid include at least one of methanol, ethanol, other alcohols, water, and fluorocarbons (e.g., Freon ^ⓡ). In one embodiment, the construction of the heat pipe includes evacuating the shell-wick structure assembly of the heat pipe, and refilling the heat pipe with at least enough fluid to fill the wick structure 16 with voids.

In certain preferred embodiments, the amount of working fluid in the heat pipe 12 is sufficient to saturate the wick structure 16. More preferably, the amount of working fluid filled in the shell 14 comprises about 10% more than the amount needed to saturate the wick structure 16.

The amount of working fluid may optionally comprise about 20% more than the amount needed to saturate the wick structure 16. In another embodiment, the amount of working fluid in the heat pipe 12 includes the volume of the condenser 26, more preferably about 10% more than the volume of the condenser 26. One technique for evacuating the shell 14 is to draw space on the interior of the shell 14. The function of vacuuming the shell 14 is to remove large amounts of remaining air or other non-moving fluid from the shell 14.

In one preferred embodiment, the air inside the heat pipe reaches an equilibrium state of liquid and vapor. As heat enters the evaporator, this equilibrium moves to the steam side and increases the internal pressure of the heat pipe. Under increased pressure, steam can diffuse into the condenser, with slightly lower temperatures causing the steam to condense the latent heat of evaporation. The condensed fluid is then transferred back to the evaporator, preferably by capillary force or diffusion or gravity developed in the wick structure 16.

Continuous cycling of the working fluid transfers large amounts of heat with low thermal gradients. Preferably, the operation of the heat pipe is passive driven by the heat transferred. Advantages of passive operation include good reliability and good useful life.

The heat pipe of the present invention may be included in a heat spreader assembly, indicated generally at 50 in FIG. 3. The assembly 50 includes a heat pipe 52. In certain preferred embodiments, the heat pipe 52 comprises at least one of a shell or wick structure composed of flexible graphite as described above.

As shown in FIG. 3, the assembly 50 also optionally includes a base unit 54. Base unit 54 is preferably located at the end of the assembly, which assembly includes a condenser although not shown. Suitable materials that make up the base unit 54 include flexible graphite, copper, aluminum, and combinations thereof. Base unit 54 includes a surface 56 that may be used to attach to a plurality of pins of assembly 50, although not shown. Moreover, assembly 50 may include mating element 58. Preferably, the mating element 58 is located at the end of the heat pipe 52 with the evaporator and in contact with the heat source. Suitable materials that make up the mating element 58 include materials that will be the same as the materials of the mating element 28 mentioned above.

In one embodiment of assembly 50, all three shells of heat pipe 52, base 54 and mating element 58 are comprised of flexible graphite, such as eFraf ^™ from Graftech Inc. In certain preferred embodiments, the flexible graphite for at least one of the pipe 52, the base 54, and the element 58 includes a laminate. The laminate is flexible graphite sheets of high density (in certain embodiments, at least about 1.6 g / cc, more preferably at least about 1.7 g / cc, more preferably at least about 1.9 g / cc) bonded together with cement It can be configured as. Alternatively, the flexible graphite laminate can be composed of a plurality of resin infused flexible graphite sheets that are thermally compressed and processed to form a substantially single structure.

4 shows a cross-sectional view of an embodiment of thermal management apparatus 60 and heat source 70. The device 60 includes a shell formed from the lower base 62 in contact with the heat source 70. Preferably, base 62 is made of a conductive material such as copper, aluminum, or an alloy thereof. The shell further includes an upper element 66 comprising flexible graphite. Upper element 66 and lower element 62 may be coupled at interface 64 by any suitable technique, such as using an adhesive such as epoxy. In certain preferred embodiments, the device 60 includes a number of pins 32 extending from the top surface of the element 66.

Optionally, the device 60 also includes one or more inner support elements 68. The inner support elements are not limited to any particular form or any particular material in construction. The support elements 68 may be composed of a conductive material such as copper, aluminum, expanded graphite, or a combination thereof. In alternative embodiments, the support elements 68 may include one or more pins extending downward from the upper element 66.

The invention also applies to other types of thermal management devices such as steam chambers. Vapor chambers are similar to heat pipes in many respects. Vapor chambers, such as heat pipes, utilize the latent heat of evaporation of the working fluid to transfer heat from the heat source to a cooler location than the heat source. In operation, the working fluid in the vapor chamber evaporates at several locations inside the vapor chamber, moves together to a cooler position within the vapor chamber, and condenses at such a cooling position.

In certain preferred embodiments, the vapor chamber comprises at least one shell similar to the shell of the heat pipe. Under these circumstances, the shell of the vapor chamber contains flexible graphite. Typically, the vapor chamber also contains a working fluid. The working fluid of the vapor chamber may be the same as the working fluid of the heat pipe as described above. Optionally, the vapor chamber may include one or more inner supports. Preferably, the inner supports are composed of some type of heat conducting material such as flexible graphite, copper, aluminum, or combinations thereof. Optionally, at least a portion of the outer surface of the vapor chamber may include a number of fins as described for the heat pipes.

Claims (20)

A substantially fluid permeable shell; A wick structure inside the shell, comprising a large amount of expanded graphite; And Working fluid circulating inside the shell Thermal management device comprising a. The method of claim 1, And wherein the wick structure further comprises a metal wire integrated into at least one segment of the wick structure. The method of claim 1, And the graphite comprises graphite infused with resin. The method of claim 1, The mass of expanded graphite comprises one or more flexible graphite sheets, at least one of the sheets having a density of only about 1.5 g / cc. The method of claim 1, And the constituent material of the shell comprises flexible graphite. The method of claim 5, The shell further comprising an outer surface, at least a portion of the outer surface having a plurality of fins extending from the outer surface. The method of claim 1, And the working fluid comprises at least one of alcohol, water, and fluorine carbide. The method of claim 1, And wherein the wick structure further comprises a plurality of channels. The method of claim 8, Wherein the plurality of channels comprises a first portion of the channel sized to facilitate vapor flow, and a second portion sized to facilitate liquid flow. As a manufacturing method of a thermal management apparatus, Forming a large amount of expanded graphite into a wick structure; And Inserting the wick structure into the shell of the thermal management apparatus Method of manufacturing a thermal management device comprising a. The method of claim 10, Forming a large amount of the expanded graphite into one or more flexible graphite sheets. A substantially fluid permeable shell, the constituent material of the shell comprising flexible graphite; and Working fluid circulating inside the shell Thermal management device comprising a. The method of claim 12, And a wick structure inside the shell. The method of claim 12, And the shell comprises a substantially tight enclosure. The method of claim 12, And wherein the density of the flexible graphite of the shell comprises at least about 1.6 g / cc. The method of claim 12, And the shell comprises a plurality of flexible graphite layers. The method of claim 12, And said flexible graphite of said shell further comprises a resin. The method of claim 12, The shell further comprising an outer surface, at least a portion of the outer surface having a plurality of fins extending from the outer surface. The method of claim 12, And the shell has an inner surface comprising a plurality of channels. The method of claim 12, And a plurality of internal track pattern elements inside the shell.