WO2007079371A2

WO2007079371A2 - Perforated heat pipe material

Info

Publication number: WO2007079371A2
Application number: PCT/US2006/062591
Authority: WO
Inventors: Igor Touzov
Original assignee: Igor Touzov
Priority date: 2005-12-30
Filing date: 2006-12-24
Publication date: 2007-07-12
Also published as: WO2007079371A3

Abstract

Heat sealable mesh-like planar or 3D heat transferring material with improved weight characteristics has high surface area and air breathable surface uniquely advantageous to tasks of heat dissipation or harvesting. Material is heat sealable that allows customization and fitting operations not applicable to traditional heat spreading or dissipating devices. Intended areas of applications include electronics heat management, apparel, and medical devices.

Description

PERFORATED HEAT PIPE MATERIAL DESCRIPTION

RELATED APPLICATION DATA

[Para 1 ] This application is a continuation-in-part of each of:

(1 ) U.S. patent application Ser. No. 1 1 /306,530, filed Dec. 30, 2005, entitled "Heat pipes utilizing load bearing wicks", hereby incorporated by reference

(2) U.S. patent application Ser. No. 1 1 /306,529, filed Dec. 30, 2005, entitled "Perforated heat pipes", hereby incorporated by reference

(3) U.S. patent application Ser. No. 1 1 /307051 , filed Jan. 20, 2006, entitled "Process of manufacturing of spongy heat pipes", hereby incorporated by reference

(4) U.S. patent application Ser. No. 1 1 /307292, filed Jan. 31 , 2006, entitled "High throughput technology for heat pipe production", hereby incorporated by reference

(5) U.S. patent application Ser. No. 1 1 /307359, filed Feb. 02, 2006, entitled "Stretchable and transformable planar heat pipe for apparel and footwear, and production method thereof, hereby incorporated by reference

(6) U.S. patent application Ser. No. 1 1 /307865, filed Feb. 26, 2006, entitled "Multi- surface heat sink film", hereby incorporated by reference

Technical Field [Para 2] The invention provides essential improvement in field of heat transferring devices and materials. In particular it contributes to devices and materials design that rely on use of phase transitions of embedded substances such as gas and liquids. Fundamental advantage of instant invention is in area of applications requiring efficient heat transfer to or from ambient gaseous or liquid media: commonly air and water.

Background Art

[Para 3] Prior art accounts for wealth of designs addressing the problem of heat transfer and heat dissipation. Most common of them are liquid filled radiators that allow heavy duty exchange of heat between ambient media such as air, water or soil and target source/receiver of the heat. Areas of applications include automotive, refrigeration, heating and many other well known industries and products.

[Para 4] Critical disadvantage of described solution is its complexity and maintenance overhead. Core element therein is a pump that consumes energy to maintain flow of the liquid. In many modern applications described approach is simply unacceptable due to factors such as: power consumption, weight, size, and cost. One of examples is electronics cooling. This industry accounts for constant innovations that result in lighter, smaller and more efficient heat dissipation solutions than ever before.

[Para 5] Most common in today's market are heat sinks with active (forced) air circulation that often employ heat pipe device to improve heat transfer performance from source to fins/pins interfacing with airflow. There are hundreds of well known US and international patents that describe these devices, yet new designs continue to emerge. To keep this description in reasonable size and for ethical aspects no specific inventions will be cited here. [Para 6] Common problem presented in task of creation of compact heat dissipating design is ability to maximize heat transfer from fins/pins or other geometrical features to airflow created around them. At the same time power spent to create such airflow has to be minimal to extend energy efficiency and reduce noise pollution.

[Para 7] To excel in this trade-in thermal gradients present in all components of the design must be kept at minimum. This is usually achieved by use of materials with high thermal conductivity (aluminum, copper, graphite) and fine tuning geometry of overall design. In one of inventions (US patent application 20060272798) authors inherit geometry of liquid radiator yet substituting pump with heat pipe style device. In alternative, invention of Parish (US Patent 6,981 ,322) discloses dissipating device all surfaces of which embeds micro channels with actively pumped liquid. In this invention thermal gradients are nearly eliminated across whole assembly, yet power consumption of the pump supplying liquid to micro channels could be substantial.

[Para 8] The Taiwan Patent Serial Number 861 1541 5 discloses a cooling device that is essentially planar heat pipe with one wall made in shape of folded fins. This design not only has minimal thermal gradients across all dimensions but also provides increase surface area for interfacing with airflow and increasing efficiency of heat dissipation from the device. In yet another design by Huang (US Patent 6,269,865) invention utilizes capillary type heat pipes interfacing with grid formed by interconnected capillaries that play role of radiator and effectively dissipates heat into adjacent airflow. Capillary effects carry essential role in function of such design. It requires close loop to be formed in order for bubble train inside the capillary to propel the liquid circulation.

[Para 9] The subject of present invention can be utilized in broad range of applications that also includes market of thermal management in garments and apparel. This area of use of heat pipes type devices in conjunction with human wearable apparel was exploited for sake of thermal stress management. Inventors suggested uses of various heat reservoirs to absorb the heat such as one described in US patent 6,763,671 , yet this and similar inventions provide short term benefits with expense of reduced mobility and added weight. [Para 10] Some of prior art inventions such as one described in US patent 5,269,369 suggest redistribution of heat between distinct pieces of apparel. While such ideas have numerous potential benefits, this design creates discomfort in dressing as well as causes faults in practical use of such apparel systems because of plurality of interconnections between moving parts.

Disclosure of Invention

[Para 1 l]The essence of this invention is to provide completely passive lightweight and highly efficient heat dissipating solution. The primary aspect of this invention is novel material that transfers heat from one location to another in form of latent heat of evaporation of embedded chemicals that undergo phase transitions between liquid and gaseous states. Unlike known prior art devices including planar and traditional heat pipes, this material is breathable. This means it allows ambient media (commonly air or water) to go through and not around its geometry.

[Para 12] In its simplest topological state as shown on Figure 1 the material of instant invention is planar sheet that has periodic and random through holes/perforations 1 covering almost entire surface. The area ratio of these perforations to entire area varies is based on application and commonly stays in 0.2 to 0.8 range.

[Para 1 3] The material has internal sealed volume 2 that contains chemical(s) 3 capable of undergoing phase transition from liquid 4 to gaseous or supercritical state 5. The volume 2 is shared by liquid 4 and gas 5. Supply of heat to the material increases evaporation of liquid 4 and raises the pressure of gas 5. Dissipation of heat from the material causes condensation of gaseous components of liquid 4 and reduction of the pressure. Gaseous phase 5 might also contain some non-condensing gases. The volume 2 may enclose some additional functional elements some of which are common to designs of heat pipes and are well known to engineers experienced in the art. Some examples of such elements are wicking materials, spacers, structural elements. Complete disclosure of internal structure is not essential for matter of the instant invention and is disclosed in co pending patent applications.

[Para 14] In its simplest implementation, as shown on Figure 2, inner volume 2 has no additional structural components except chemicals 3 (not shown). The shell 6 that surrounds volume 2 is thin continuous film. It separates inner volume 2 from ambient media. Because of large number of perforations 1 minimal curvature of the film 6 is inherently high. This makes geometrical structure of the material on local scale (distance between adjacent perforations 1) to be very stiff with respect to difference between inner and outer pressures, while allowing reduced thickness of film 6. At the same time on larger scale (approximately 10 average distances between adjacent perforations) the material behaves as soft and flexible.

[Para 1 5] Phase transitions and motion of gases 5 through volume 2 establish highly efficient heat transfer along the surface of the material making thermal gradients very small. Perforations 1 increase total surface area of the material nearly twofold and at the same time allow airflow to go through the surface of the sheet instead of going around. There are two well known effects from this topological advantage: (i) air resistance can be reduced by orders of magnitude thus creating lower backpressure for surrounding airflow; (ii) natural convection develops at very low Rayleigh numbers thus allowing to eliminate source of forced air and achieve totally passive cooling solution. [Para 1 6] In one embodiment the shell 6 of the material is heat sealable that makes it easy for user to cut and create any desired shape without allowing embedded chemicals 3 to escape. This advantage uniquely distinguishes the subject of this invention from known heat pipe devices. Unlike devices that must be used as is, the material of instant invention is highly customizable, and can be used more readily in broader range of applications. [Para 1 7] Design of the material of this invention allows for broad selection of chemicals 3. In one embodiment this chemical is water and no other gases is present in volume 2. This means that at normal ambient conditions volume 2 is evacuated. Yet the thickness of walls of the shell 6 is only few microns and whole structure of the material remains stable and does not collapses under the force of ambient pressure. No inner spacer or other supporting elements are necessary in this invention because high curvature of the shell 6 makes it highly stable event when it is very thin.

[Para 18] In yet another embodiment choice of chemical is automotive refrigerant Rl 34a. At elevated temperatures such as 100⁰C its pressure reaches 40atm. Yet the material shell 6 of only few microns thick easily holds such pressure. Combination of high internal pressure and high curvature of shell 6 surface makes the material very stiff on small scale, at the same time it remain flexible at larger scale.

[Para 19] The primary shape of the material is planar film, yet it may exist in variety of other shapes. In one embodiment the material's topology is corrugated sheet that has 3D structure with higher and lower regions arranged in chess order. Corrugation period is nearly matches average distance between perforations 1 . This highly corrugated surface resembles thin sponge. It has higher surface area per unit area of the material than the planar sheet.

[Para 20] Yet another embodiment uses three dimensional network like topology where the network nodes are natively distributed in complex 3D pattern and each node is interconnected with plurality of adjacent nodes. While above mentioned topologies are topological^ equivalent to planar mesh, the topology of present embodiment is strictly not planar. This topology provides notable benefits to heavy duty heat dissipating applications where high surface area must be achieved in minimal allocated space. Yet internal structure of the material with this topology is equivalent to structure of the other topological arrangements.

[Para 21] It is obvious to one experienced in the art of heat dissipating devices that nearly planar topology of original material can be easily transformed and shaped into more complex customized three-dimensional forms. These forms are usually optimized for particular geometry and functionality of targeted application. These transformations are easily achievable with the material of instant invention by means of bending, folding, heat- sealing and cutting the material to achieve desired end result.

[Para 22] In one example material's initial shape was selected to accommodate complex custom geometrical form of human body parts/organs. This custom shaped material can be further modified by above listed technique to fine tune size and shape of resulting medical device for particular patient. Example applications include forced thermal management of traumatized body parts/organs.

[Para 23] In yet another embodiment perforation pattern has preferred orientation with elliptic form of through holes oriented in one direction. This approach creates anisotropic effect with respect to amount of heat transferred in different directions. Changing pattern of perforation allows creation of custom heat distribution pattern as well as can be used to add artistic aspects to the design.

[Para 24] In another embodiment shown on Figure 3 the pattern of perforations 1 overlaps with pattern of junction points 7. Junction point 7 is permanent connection between opposite surface sides of the material. Functionally junction point 7 increases the curvature of shell 6 and improves local stiffness of the material while at the same time attributes to increase in its flexibility on larger scale. Pattern of junction points 7 used in this embodiment creates regions where average distances between opposite surfaces of the material become notably smaller that its average thickness. This creates regions 8 with profound capillary effect. It also causes liquid 4 to redistribute within volume 2 by dominantly occupying regions 8 and freeing remainder of volume 2 for gases 5. This segregation attributes to increase in overall heat transport performance of the material. [Para 25] Regions 8 can be created by use of junction points, or by use of perforations, or both. Because the material can be heat sealed, its perforation pattern, shape, and functional performance can be easily tuned and modified by means of in-process or after-process addition of both junction points and perforations. In one practical embodiment array of junction points is added to the material to create interface region for electronic device. This array makes several regions 8 that accelerate intake of liquid 4. Figure 4 illustrates the design. Contact regions 9 does not form a continuous surface, instead they are collection of small contact pads with tiny separations between them.

Brief Description of Drawings

[Para 26] Figure 1 shows external view on a sheet of the material. Numerous through perforations 1 form channels for air to pass through the layer. Ultra thin shell of the material is only few micron thick able to sustain mechanical and geometrical stability due to high local curvatures. View A shows 2D net-like topology, view B shows topology of rows formed by isolated patterns of perforations. Magnified view shows example of perforation pattern in arrangement of view B.

[Para 27] Figure 2 shows capillary channels that adsorb liquid 4 clearing passages for transport of gases 5. [Para 28] Figure 3 shows region of joint points. View A shows detail view on perforation 1 , while view B is detailed view of joint point 7.

[Para 29] Figure 4 shows interface pad 9 created by array 8 of joint points 7.

Modes for Carrying Out the Invention

[Para 30] in one example the preferred embodiment was produced through the following process. High temperature silicone stamp was produced with extended features forming the pattern of the perforations 1. Tin replica was created from the stamp using molding process with thickness of produced film of 500 microns. Tin film was deoxidized and electroplated in caustic conditions with copper to 0.5 micron. Then rinsed with distilled water and placed in acidic electroplating bath to deposit 2.5 micron of copper. Resulting film was cut by one edge and placed in 23O⁰C silicone oil bath to remove tin inside. Resulting copper shell 6 is tinned on inside. It was placed in antifreeze bath at -3O⁰C and filled with Rl 34a to 20% of inner volume. Remaining open edge was sealed using heat seal equipment set to 23O⁰C. [Para 31] Resulting piece of material has thickness of 600 microns. It was tested to 100⁰C for several hours, floats in the water. The material was cut using heat seal equipment to 5"x4" and tested on subject of heat dissipation to stationary air without any sources of forced air. The sample was compared against sheet of aluminum of the same size. Temperature of the heat source was compared and found to be 275% higher for the aluminum plate than for the sample.

[Para 32] In another example material was produced by different technique. A layer of TPSiV, -thermoplastic elastomer (TPSiV is a product of Dow Corning Company), the film is covered with a layer of felt of the same composition, all elements are maintained below -3⁰C, liquid refrigerant such as 1 ,2-dichloro-l ,1 ,2,2-tetrafluoroethane (R-1 14) or butane is dispensed to saturate the felt, second layer of TPSiV film is placed on top of the assembly, hot stamp with mesh pattern is pressed against the assembly at pressure in excess of 44atm at 295⁰C, after setting time the stamp is cooled.

[Para 33] Described process creates sealed flat material with mesh pattern of through perforations. Upon temperature increases internal pressure caused by refrigerant evaporation reshapes flexible shell material and creates vapor transfer channels. The size of the pattern is defined by two factors in addition to artistic perception: o vapor pressure of selected liquid at desirable operating temperature of the pipe o the material properties and the wall thickness for selected outer films [Para 34] Use of smaller separations allows for use of thinner material film and higher internal pressure.

[Para 35] Invented heat pipe can be custom cut to desired shape without need for special equipment using standard hot knife and a wise or a clamp. The pipe sheets or decals can be sewed together or to any fabric using standard sewing equipment. This makes the product suitable for general apparel manufacturing.

[Para 36] In another example the material is produced from two rolls of fine copper foil tined on one side. The foils are arranged vertically facing tined side of each other. The foils are passed through hot rolling stamps heated nearly to 23O⁰C and surface lubricated with high temperature silicone oil with anticorrosion additives to prevent oxidation. The pattern of perforations and (optional joint points 7) is created in a way that seals the cut edges. In one example this process can use modified equipment for expanded metal production. [Para 37] Perforated sandwich of two foils is chilled to -3O⁰C and liquid refrigerant Rl 34a is pumped between the foils with moderate excessive pressure. This step is performed right before the assembly passes between two cold rolling stamps with fixed separation between them. The separation is set to desired percentage of volume 2 to be occupied by liquid 4. In example: foil thickness is 3 micron, target material thickness is 600 micron, part of volume occupied by liquid 4 is 1 5% (percent), and average separation between the plates is 53 microns. This step ejects excessive amount of refrigerant from the assembly. The second set of stamps is adjacent to set of hot rollers that seal the edges.

[Para 38] Described process produces continuous film of the material. The film is sealed on its leading edge and periodically at specific intervals (e.g. one meter) to create individually sealed domains. Parameters of the process can be tuned to satisfy desired production throughput requirements.

[Para 39] In yet another example, three-dimensional network topology of the invention was produced by following technique. Production process for the structure begins with making a wick layout. This may be done via broad range of techniques including weaving, plaiting, braiding, knitting, cutting, forming, molding, stretching, or any other process that arranges wick material into desired linear, planar, or three dimensional arrangement. In some implementations it is possible that temporary spacers or other hardness features are embedded into such arrangement to stabilize it during production phase. [Para 40] Second step of production process is priming. This step may be repeated several times until desired properties are achieved. A primer is viscous usually polymeric or inorganic composite or solution that is sprayed on all surfaces of the wick creating a coat or other chemicals. The same can be achieved by submersing wick arrangement into bath of priming solution. Composition of the primer depends on many factors such as the wick material, layout density, desired product characteristics, and chemicals 3. In one scenario liquid butyl was used as a primer. In another scenario elecroless 1 micrometer copper film was deposited on. It is well known how to optimize composition of the primer to achieve necessary tackiness, penetration depth, thickness etc. Materials of the primer may vary. In one example gradient coat of two primers was achieved, when approximately one half of sponge like wick was coated with silicone carbide ceramic while the rest was coated with silicone rubber.

[Para 41] Third step of the process is addition of liquid refrigerant. This step may be performed as a second step of the sequence if chemical and process compatibility with primer allows it (e.g. when water is used as the refrigerant liquid it may be possible to exclude this step when water based primer is employed). In case when this step follows priming procedure, part of the wick arrangement is trimmed or striped to allow quick infusion of the refrigerant into the wick. Created opening then sealed with identical or alternative primer compound or using other techniques.

[Para 42] Following step of the process creates additional layers of coat on top of the primer. This step in some modifications of the process can be used instead of or be interchanged with the priming step. This step can be repeated several times to achieve desired thermal and mechanical characteristics of the product. There are many well known techniques through which it can be achieved and detailed description of those is not part of this invention. As an example electroplating of chrome can be performed to provide high longevity and durability to the product. Process must be performed under conditions that prevent escape of refrigerant and permeation of gases into the wick structure. When methanol used as a refrigerant electroplating was performed in sealed bath at pressure matching boiling point of refrigerant.

[Para 43] Another example involves molding of ceramic composite. The process was performed by deposition of putty of molding compound on surface of product and baking whole assembly in pressurized oven (required pressure can be computed from required molding temperature and phase transition characteristics of refrigerants). [Para 44] Yet in another example bromobutyl rubber was used as a final coat. Vulcanization was performed under pressure in bath of mineral oil. [Para 45] Yet another method of production is disclosed in co-pending US patent application 1 1 /307292 and incorporated here by reference.

Industrial Applicability

[Para 46] Invented material has broad application area. Because of its high efficiency in dissipating heat to ambient media it can be used in design of heat sinking and heat harvesting devices. Its primary beneficiary in this sector will be electronics cooling and alternative energy sources.

[Para 47] Since the material has heat sealing properties and air breathable it is equally suitable for area of apparel and garment design. Its ability to spread heat will reduce thermal stress of wearier and have unlimited operating time. Benefit of this invention is < effective combination of natural ability of a body to redistribute/manage heat and efficient heat exchange properties of the apparel system combined with its primary functions. [Para 48] Each apparel article according to this invention can be uniquely designed for a specific use scenario. This makes them comfortable, practical, lightweight, and reliable. The material is employed to increase heat exchange between the body surface and a heat source/recipient (in most scenarios ambient air).

[Para 49] The material can be permanently imbedded into or form by itself the apparel structure. This improves apparel durability and reduces its weight. Preferred chemical 3 for the material in this application area is medium pressure commercial refrigerant, while low or high pressure refrigerants and other liquids are not excluded. Use of medium pressure refrigerants allows to overcome problem associated with high gas permeability of polymer materials. Preferred shape of the invention for apparel application is a planar mesh or a planar ribbon with flaps. Spatial or 3D mesh structures are also the subject of these applications. [Para 50] The mesh shape allows for significant airflow through the material that allows for effective integration into apparel and other systems by sewing, gluing, molding, or fastening through the voids 1 of the material, while preserving breathable properties of the product.

[Para 51 ] The shape of ribbon with flaps similar to one shown in magnified view on Figure 1 allows convenient integration of the material into apparel and other systems by sewing or gluing or laminating through the flaps. The flaps may also contain perforations 1 of various patterns including the mesh patterns.

[Para 52] Sheets of the material of planar of foam/sponge like 3D meshes can be utilized as a thermal barrier for fire protection, building thermal insulation, energy harvesting by heat pumps, and other traditional thermal applications.

[Para 53] The mesh structure of the invention contributes to high transport efficiency of capillary wicks. The small area of segments created by the mesh is compensated by two or three dimensional flow pattern of the mesh. This allows for large geometrical dimensions of the heat pipes with minimal degradation of their efficiency.

Claims

What i s clai med is:

[Claim 1 ] A composite material comprising at least of the following elements: a) hermetic outer shell, b) sealed inner volume evenly spread through the volume of the material, c) chemical(s) capable of undergoing phase transition between Liquid State and Gas State,

wherein a form of the material is topological^ equivalent to net or mesh, wherein said topology extends into either unidimensional or two-dimensional or three-dimensional structural form, wherein said net or mesh aggregates substructures designed to transport heat by means of transport of said chemical(s), wherein said shell if placed in air would be able to pass air flow through the volume of geometrical bounding envelope by means of interconnected network of voids formed by said outer shell, and the terms mesh and net comprise either ordered, or unordered, and periodic, or non-periodic compositions.

[Claim 2] A material of claim 1 , wherein said shell has composition suitable for heat-seal operation and local application of outer pressure and heat cause formation of hermetic seam in said sealed inner volume.

[Claim 3] A material of claim 1 , wherein said inner volume has pattern of channels of small cross section area and channels of large cross section area, wherein said small area is small enough to cause profound capillary effect on said chemical in liquid state.

[Claim 4] A material of claim 1 wherein said inner volume is segmented on plurality of individually sealed sub-volumes and said sub-volumes form pattern of rows evenly or not evenly distributed.

[Claim 5] A method of creation of said shell of material of claim 1 that differentiates by using a step of deposition of one compound on plurality of surface segments of a body, wherein said body embeds plurality of channels or capillaries randomly or orderly arranged through the volume or on a single surface, and wherein said compound forms solid film without completely filling up said channels or capillaries.

[Claim 6] A method of material of claim! that differentiates by using a step of extrusion of closed profile wherein said chemical(s) is disposed at the time of extrusion into inner volume of this extrusion in either liquid or gaseous, supercritical or any transient state.

[Claim 7] A material of claim 1 , wherein said mesh is two-dimensional lattice.

[Claim 8] A material of claim 1 , wherein said net is a three-dimensional pattern with thickness of five (5) millimeters or more.

[Claim 9] A material of claim 1 , wherein said network of voids contains pattern of straight through holes.

[Claim 1 0] A material of claim 1 , wherein said shell forms a two dimensional ornament or picture or other artistic elements.

[Claim 1 I ] A material of claim 1 , wherein said shell contains a polymer based composite.

[Claim 1 2] A material of claim 1 , wherein said shell contains a metal film.

[Claim 1 3] A material of claim 1 , wherein said shell contains inorganic material.

[Claim 1 4] A material of claim 1 , wherein said shell contains nano-particles, nano- composites, nano-ciay or other functional additives that reduce gas impermeability.

[Claim 1 5] A device made of the material of claim 1 that further comprises interface pad(s) for connection to sources of heat or cold.

[Claim 1 6] An electrical assembly comprising plurality of electrical elements, optional set of heat absorbing devices, and differentiated by containing at least one part made of material of claim 1 , wherein said material is in thermal contact with more than one of said elements.

[Claim 1 7] A detail made of material of claim 1 that is integrated in apparel. [Clai m 1 8] A detail made of material of claim 1 that is integrated in protective garment. [Claim 1 9] A detail made of material of claim 1 that is integrated in footwear. [Claim 20] A detail made of material of claim 1 topological^ fit to human body part or organ.