US20120111542A1

US20120111542A1 - Coiled heat pipes and methods thereof

Info

Publication number: US20120111542A1
Application number: US13/292,671
Authority: US
Inventors: Joseph M. Fridy; Rabindra K. Bhalfacharyya; Stephen J. Makosey
Original assignee: Alcoa Inc
Current assignee: Howmet Aerospace Inc
Priority date: 2010-11-09
Filing date: 2011-11-09
Publication date: 2012-05-10

Abstract

A coiled heat pipe and methods of making a coiled heat pipe are provided. The coiled heat pipe includes a sealed-exterior coil and a plurality of interior-perforated coils. The exterior coil and the plurality of interior-perforated coils are be formed from a single aluminum sheet. The exterior coil is sealed and houses, or otherwise contains, a partial vacuum and a working fluid.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This non-provisional patent application claims the benefit and priority of U.S. Provisional Patent Application Ser. No. 61/411,687 filed on Nov. 9, 2010.

BACKGROUND OF THE INVENTION

Field of the Invention

Generally known heat pipes may include a sealed pipe, or tube, made of a material with a high thermal conductivity such as copper or aluminum. The air may be partially removed from the sealed pipe. A working fluid, or coolant, such as water, may be introduced into the sealed pipe. The heat pipe may further contain a wick, which may serve to exert a capillary pressure on the liquid phase of the working fluid. Without wishing to be bound by the theory, Applicants believe that heat pipes include a heat transfer mechanism that combines the principles of both thermal conductivity and phase transition to efficiently manage the transfer of heat between two solid interfaces.

SUMMARY OF THE INVENTION

In one illustrative embodiment, the present disclosure provides a coiled heat pipe. The coiled heat pipe may include an exterior coil and a plurality of interior-perforated coils. The exterior coil and the plurality of interior-perforated coils may be formed from a single aluminum sheet, which may be a 5xxx series aluminum. The exterior coil may house, or otherwise contain, a partial vacuum and a working fluid.
In another illustrative embodiment, the present disclosure provides a method of producing a coiled heat pipe. The method may include providing an aluminum alloy sheet and optionally heat treating the aluminum alloy sheet. A first portion of the aluminum alloy sheet may be perforated to form a perforated end. The perforated end may be coiled about itself to form a plurality of interior-perforated coils, having interior-perforated coil perimeters. The non-perforated end of the aluminum alloy sheet may be coiled about the plurality of interior-perforated coils to form a lap, and an exterior coil having a distal edge and exterior coil perimeters. The aluminum alloy sheet may be optionally etched with a solvent.
For purposes of summarizing the present coiled heat pipe and methods thereof, certain aspects, advantages, and novel features of the present coiled heat pipe and methods thereof have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any one particular embodiment of the coiled heat pipe and methods thereof. Thus, the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.
These and other embodiments of the present coiled heat pipe and methods thereof will also become readily apparent to those skilled in the art from the following detailed description of the embodiments having reference to the attached drawing figures, the coiled heat pipe and methods thereof not being limited to any particular embodiment(s) disclosed.

BRIEF DESCRIPTION OF THE DRAWING

For a fuller understanding of the disclosure, reference is made to the following description taken in connection with the accompanying drawing figures, in which:

FIG. 1 is an illustrative embodiment of a cross-sectional view of a coiled heat pipe;

FIG. 2 is an illustrative embodiment of a perspective-cross-sectional view of the coiled heat pipe of FIG. 1;

FIG. 3 is a flow chart showing one embodiment of a method of producing the coiled heat pipe;

FIG. 4 is an illustrative micrograph of an exemplary aluminum sheet after etching; and

FIG. 5 is an illustrative micrograph of an alternative exemplary aluminum sheet after etching.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 1 and 2 and in one embodiment of the present disclosure, a coiled heat pipe, also called a coiled heat tube, 100 is provided. The coiled heat pipe may include an exterior coil 105 and a plurality of interior-perforated coils 110. The exterior coil 105 and the plurality of interior-perforated coils 110 may be formed from a single aluminum sheet 115. The single aluminum sheet 115 may be formed from any aluminum alloy including without limitation: 1xxx series; 2xxx series; 3xxx series; 4xxx series; 5xxx series; 6xxx series; 7xxx series; or 8xxx series aluminum alloy.
In an embodiment, the single aluminum sheet 115 may have, at a first end, 120, a plurality of interior-perforated coils 110. While the coiled heat pipe 100 may include any number of interior-perforated coils 110 depending on a number of conditions, including without limitation: the size of the coiled heat pipe 100, the required volume of working fluid, and the necessary heat flux from the coiled heat pipe; typically, the coiled heat pipe 100 may include between 2 and 10, alternatively between 2 and 5, interior-perforated coils 110. In an embodiment, the plurality of interior-perforated coils 110 are concentrically coiled about themselves. In an embodiment, the plurality of interior-perforated coils 110 may be spaced apart such that first surfaces, 110 a, and second surfaces, 110 b, of the interior-perforated coils 110 may both function as wicking surfaces. Without limitation and in an embodiment, the spacing between first surfaces, 110 a, and second surfaces 110 b, may be a distance ranging from between about an eighth of a sheet thickness, alternatively from about 25 microns, to about a sheet thickness, typically about 250 microns. In a still further embodiment, a plurality of spacers (not shown) may be affixed to, disposed upon, or formed integral with, the first surfaces, 110 a, and/or the second surfaces 110 b, of the interior-perforated coils 110 to maintain the spacing between first surfaces, 110 a, and second surfaces 110 b. Without limitation, suitable spacers may include: protrusions, bumpers, or bumps; tabs; deliberate burrs; and the like.
The interior-perforated coils 110 may include a plurality of perforations 125. In an embodiment, the perforations 125 may be evenly distributed, or irregularly distributed, across a first end 120 of the coiled heat pipe 100. In an alternative embodiment, the perforations 125 may each have a diameter ranging from about three times the sheet thickness to about ten times the sheet thickness, alternatively from about 250 microns to about 2,500 microns. In a further embodiment, the perforations 125 have a total area fraction of 5 to 20 percent, based on the total area of the first end 120.
Continuing from, or otherwise extending in a first direction along an axis, X, away from, the first end 120 of the single aluminum sheet 115, may be a lap, or fin, 130. The lap, or fin, 130 may include a sealed lap portion 135 and an overlapped lap portion 140. In an embodiment, the sealed lap portion 135 may be adjacent to, extending from, or integral with, the first end 120, along the axis, X, in the first direction. In an embodiment, the overlapped lap portion 140 may be adjacent to, extending from, or integral with, the sealed lap portion 135, along the axis, X, in the first direction. In an embodiment, preferably at its distal end 145, the overlapped lap portion 140 may be doubled over, folded, overlapped, or otherwise re-directed over itself, and continues along the axis, X, in a second direction, which may be generally parallel to, and opposite of, the first direction.
Continuing from, or otherwise extending in the second direction along the axis, X, away from the overlapped lap portion 140, may be the exterior coil 105. The exterior coil 105 may continue to extend, preferably concentrically, about an outer-most interior-perforated coil 150. In this manner, the plurality of interior-perforated coils 110 may be housed within, disposed within, or otherwise contained by, the exterior coil 105. In an embodiment, outer perimeters of the exterior coil 155 a and outer perimeters of the interior-perforated coils 155 b may be co-planer, and generally aligned with each other, in a plane that overlays a Y axis, which is perpendicular to the X axis. The outer perimeters of the exterior coil 155 a and the outer perimeters of the interior-perforated coils 155 b may be sealed by hemming, seam welding, or fish tailing (e.g., squishing a portion of the perimeters 155 a, 155 b flat and folding the flatted portion over itself).
The exterior coil 105 may continue to extend until a distal end 160 of the exterior coil 105 extends adjacent to, and aligned with, the sealed lap portion 135. In an embodiment, the termination of the distal end 160 may define the termination of the sealed lap portion 135, and the initiation, or beginning, of the overlapped lap portion 140. In an embodiment, the sealed lap portion 135 may include a seal 165, preferably made by one or more welds, or as illustrated in FIGS. 1 and 2, by adhesive bonding. In an embodiment, the sealed lap portion 135 may include a welded seal 165 across three layers of the single aluminum sheet 115, wherein the three welded layers may include: a first layer 170 extending from the first end 120 in the first direction along the axis, X; a second layer 175 extending from the overlapped lap portion 140 in the second direction along the axis, X; and a third layer 180 of the exterior coil 105. Without limitation, adhesives suitable to form the seal 165 may include thermoplastics, epoxies, and any suitable adhesives resistant to the work fluid (not shown).
In an embodiment, the exterior coil 105 may be sealed and may house, or otherwise contain, a partial vacuum (not shown) and a working fluid (not shown). In an embodiment, the partial vacuum may have a pressure ranging from about 0.003 Torr to about 0.1 Torr. The working fluid (not shown) may be any fluid having a sufficient boiling point to readily undergo liquid to gas, and gas to liquid, phase transitions during the intended working conditions of the heat pipe 100. In a preferred embodiment, the working fluid (not shown) may have as high a heat capacity as possible such that the it absorbs as much heat as possible during each phase transition. Without limitation, suitable working fluids (not shown) may include: water, ethanol, acetone; butane, pentanone, sodium, mercury, other organic compounds, and combinations thereof.
The followings are the definitions of the terms used in this application:
As used herein, the term “thermomechanically processing” means the deformation, or heat treatment, of a metal with the intent to change the properties or microstructure of the metal.
As used herein, the term “grain size” means the size of an individual crystal within the metal.
As used herein, the term “grain shape” means the mean shape of an individual crystal within the metal.
As used herein, the term “wicking” means the transport of a fluid through capillary action.
As used herein, the term “grain boundaries” means those regions within the metal where two or more grains abut.
As used herein, the term “continuous etchable phase” means a phase which is susceptible to be etchable by a chemical agent and not into disjoint regions.
With reference to FIG. 3, a schematic flow chart is provided, which illustrates an embodiment of a method for producing a coiled heat pipe 300, and which may be further understood with reference to FIGS. 1 and 2. The method 300 may include providing a single aluminum alloy sheet 115 in step 305, and then optionally heat treating the single aluminum alloy sheet 115 in step 310. In an alternative embodiment, the single aluminum alloy sheet 115 may be thermomechanically processed in step 315 before it is optionally heat treated in step 310. At least a first portion of the heat treated aluminum alloy sheet may be perforated in step 320. The first portion may be coiled about itself in step 325 to form a first end 100 having a plurality of interior-perforated coils 110. A non-perforated end of the single aluminum alloy sheet may be coiled about the plurality of interior-perforated coils in step 330 to form a lap, or fin, 130, and an exterior coil 105. In optional step 335, the single aluminum alloy sheet 115 may be etched with a solvent. In step 340, a proximate end 185 of outer perimeters of the exterior coil 155 a and outer perimeters of the interior-perforated coils 155 b may be sealed, a vacuum may be applied to a distal end 190 of outer perimeters of the exterior coil 155 a and outer perimeters of the interior-perforated coils 155 b, a working fluid may be introduced to the proximate end 185. In step 345 both ends may be sealed.
In step 305, an aluminum alloy is provided. Suitable aluminum alloys may include without limitation: 1xxx series; 2xxx series; 3xxx series; 4xxx series; 5xxx series; 6xxx series; 7xxx series; or 8xxx series aluminum alloy, including aluminum-magnesium alloy having between about 2.5 wt. % to about 12 wt. % magnesium.
In optional step 310, the aluminum alloy may be heat treated to produce a continuous etchable phase on the grain boundaries. In an embodiment, the aluminum alloy may be heated from between about 10 hours to about 10 days, and at a temperature ranging between about 120° C. to about 180° C. The temperature of heating may be variable during the duration of heating or may remain substantially constant throughout the heating step.
In optional step 315, the aluminum alloy may be thermomechanically processed by either deformation, or heat treatment, of a metal with the intent to change the properties or microstructure of the metal to produce grain size and shape suitable for wicking. Suitable mechanical processing techniques may include, without limitation: hot rolling; cold rolling; extrusion; or forging. Suitable thermal processing may include, without limitation: annealing; recrystallization; or recovery. In an embodiment, the aluminum alloy may be heat treated form between about 10 seconds to about 3 hours, and at a temperature ranging between about 280° C. to about 480° C. The temperature of heating treating may be variable during the duration of heating or may remain substantially constant throughout the heating step. In another embodiment, the grain size of the aluminum alloy may range from about 10 microns to about 500 microns.
In step 320, at least a first portion of the aluminum alloy may be perforated to form a perforated end. The perforation may be prepared by any suitable means including, without limitation: precision puncture using a punch; chemical etching; and an embossing roll.
In step 325, the perforated end, formed in step 320, may be coiled about itself to form a plurality of interior-perforated coils, the interior-perforated coils may have interior-perforated coil outer perimeters. With reference to FIGS. 1-3, and without limitation, in an embodiment, the perforated end, formed in step 320, may be coiled about itself to form a plurality of interior-perforated coils 120, the interior-perforated coils 120 may have interior-perforated coil outer perimeters 155. The interior-perforated coils 120 and the interior-perforated coil outer perimeters 155 may be of the form and structure as detailed above.
In step 330, the non-perforated end of the aluminum alloy may be coiled about the plurality of interior-perforated coils in step 330 to form a lap, and an exterior coil having an distal end and exterior coil outer perimeters. With reference to FIGS. 1-3, and without limitation, in an embodiment, the non-perforated end of the aluminum alloy may be coiled about the plurality of interior-perforated coils in step 330 to form a lap 130, and an exterior coil 105 having an distal end 160 and exterior coil outer perimeters 155. The interior-perforated coils 120 and the interior-perforated coil outer perimeters 155 may be of the form and structure as detailed above. For example and without limitation, in an embodiment, coiling the non-perforated end of the aluminum alloy about the plurality of interior-perforated coils in step 330 to form a lap may additional form the sealed lap portion 135, the overlapped lap portion 140, and the distal end 160 of the exterior coil 105. The sealed lap portion 135, the overlapped lap portion 140, and the distal end 160 of the exterior coil 105 may be of the form and structure as detailed above.
In an optional step 335, the aluminum alloy may be etched with a solvent that may dissolve the continuous etchable phase on the grain boundaries to produce the metal structure with a grooved wicking surface. In various embodiments, the solvent used may depend on the type of continuous etchable phase present on the aluminum alloy, and may include, without limitation: nitric acid, such as, without limitation nitric acid in a concentration of about 20% to about 70%; or caustic NaOH. In another embodiment, the duration of the etching step may be from about 5 minutes to about 90 minutes, and at a temperature ranging from about 30° C. to about 90° C., alternatively from about 70° C. to about 80° C. The temperature during etching may be variable during the duration of heating or may remain substantially constant throughout the etching step. Optionally, the continuous etchable phase on the grain boundaries may be strained to deform the grain boundaries in the direction of the strain before the etching step. In one embodiment, the straining may be done by rolling.
FIG. 4 is an illustrative micrograph of an exemplary aluminum sheet after etching. Without wishing to be bound by the theory, Applicant believes that the optional etching step results in the removal of the semi-continuous Mg bearing phase at the grain boundaries, which provides a continuous network of micron-scale grooves that may cover a substantial portion of the etched surface. FIG. 5 is an illustrative micrograph of an alternative exemplary aluminum sheet after etching. Without wishing to be bound by the theory, Applicant believes that the optional etching step removes the Mg bearing phase for several grain widths into the sheet, which increases the sheet's ability to act as a wicking surface. In an embodiment, the Mg bearing phase may extend into the sheet a depth ranging from about 50 to about 100 microns. Further, without wishing to be bound by the theory, Applicant believes that because the Mg bearing phase is not entirely continuous, after etching, the surface grains may be held in place by connections that were originally holding the Mg bearing phase.
With reference again to FIGS. 1-3, in step 340, a vacuum may be applied to a proximate end 185 of outer perimeters of the exterior coil 155 a and outer perimeters of the interior-perforated coils 155 b. and a working fluid may be introduced to a distal end 190 of outer perimeters of the exterior coil 155 a and outer perimeters of the interior-perforated coils 155 b. In an embodiment, a vacuum may be pulled from a proximate end 185 of outer
In step 340, a proximate end 185 of outer perimeters of the exterior coil 155 a and outer perimeters of the interior-perforated coils 155 b may be sealed. Then, a vacuum may be applied to a distal end 190 of outer perimeters of the exterior coil 155 a and outer perimeters of the interior-perforated coils 155 b. Then, a working fluid (not shown) may be introduced to the proximate end 185 by insertion through the seal. Following introduction of the working fluid (not shown), the proximate end 185 and the distal end 190 may be sealed. In an embodiment, the seals may be made by any suitable method including crimping, welding, folding, and the like.
In an alternative embodiment, in step 340 the proximate end 185 of outer perimeters of the exterior coil 155 a and outer perimeters of the interior-perforated coils 155 b may be sealed. A working fluid (not shown) may be introduced though the distal end 190. The working fluid (not shown) may be heated until its vapor pressure exceeds atmospheric pressure. After sufficient time, the vapor pressure of the heated working fluid may force a substantial amount of the air out, and the distal end 190 may be sealed.
While specific embodiments of the coiled heat pipe and methods thereof have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the coiled heat pipe and methods thereof which is to be given the full breadth of the claims to be appended and any and all equivalents thereof.

Claims

1) A coiled heat pipe comprising: an exterior coil and a plurality of interior-perforated coils, wherein the exterior coil and the plurality of interior-perforated coils are formed from a single aluminum sheet.

2) The coiled heat pipe of claim 1, wherein the aluminum sheet is a 5xxx series aluminum.

3) The coiled heat pipe of claim 1, wherein the exterior coil is sealed and contains: a partial vacuum and a working fluid.

4) The coiled heat pipe of claim 3, wherein the working fluid is selected from the group consisting of water, ethanol, acetone; butane, pentanone, sodium, mercury, other organic compounds, and combinations thereof.

5) The coiled heat pipe of claim 1, wherein the plurality of interior-perforated coils includes at least two interior-perforated coils.

6) The coiled heat pipe of claim 1, wherein a first end of the single aluminum sheet forms the plurality of interior-perforated coils and the first end is contained within the exterior coil, and a second end of the single aluminum sheet is sealed to a portion of the exterior coil.

7) The coiled heat pipe of claim 1, wherein the plurality of interior-perforated coils each include a first and second surface, and the plurality of interior-perforated coils are spaced apart such that the first and second surfaces may both function as wicking surfaces.

8) The coiled heat pipe of claim 1, wherein the interior-perforated coils further comprise spacers selected from the group comprising: bumps, tabs, deliberate burrs, and the like.

9) The coiled heat pipe of claim 1, further comprising a lap extending from the exterior coil.

10) A method of producing a coiled heat pipe comprising:

providing an aluminum alloy sheet;

optionally heat treating the aluminum alloy sheet;

perforating a first portion of the aluminum alloy sheet to form a perforated end;

coiling the perforated end about itself to form a plurality of interior-perforated coils, having interior-perforated coil outer perimeters;

coiling a non-perforated end of the aluminum alloy sheet about the plurality of interior-perforated coils to form a lap, and an exterior coil having a distal end and exterior coil outer perimeters; and

optionally etching the aluminum alloy sheet with a solvent.

11) The method of claim 10, wherein the heat treating produces a continuous etchable phase on the aluminum alloy sheet, and wherein the solvent dissolves the continuous etchable phase on the aluminum alloy sheet.

12) The method of claim 11, further comprising: thermomechanically processing the aluminum alloy sheet to produce grains having a size and a shape suitable for wicking, wherein the heat treating produces a continuous etchable phase on the grain boundaries, and wherein the solvent dissolves the continuous etchable phase on the grain boundaries.

13) The method of claim 10, further comprising: sealing the distal end of the exterior coil to a portion of the exterior coil; sealing interior-perforated coil perimeters and the exterior coil perimeters to form a sealed-exterior coil.

14) The method of claim 13, further comprising: removing at least a portion of the gas within the coiled heat pipe; and filling at least a portion of coiled heat pipe with a working fluid, wherein the working fluid is selected from the group consisting of water, ethanol, acetone, sodium, mercury, and combinations thereof.

15) The method of claim 13, wherein the free edge of the exterior coil is sealed to a portion of the exterior coil by a method selected from group consisting of welding and adhesive bonding.

16) The method of claim 13, further comprising: removing the lap.

17) The method of claim 10, wherein the continuous etchable phase is magnesium bearing, and the solvent is nitric acid.

18) The method of claim 18, wherein the etching step is from about 5 minutes to about 90 minutes at a temperature range of about 30° C. to about 90° C.

19) The method of claim 12, wherein the grain size ranges from about 10 microns to about 500 microns.

20) The method of claim 12, further comprising the step of straining the continuous etchable phase on the grain boundaries, by rolling, to deform the grain boundaries in the direction of the strain before the etching step.