U.S. patent application number 11/306530 was filed with the patent office on 2007-07-05 for heat pipes utilizing load bearing wicks.
Invention is credited to Igor Victorovich Touzov.
Application Number | 20070151709 11/306530 |
Document ID | / |
Family ID | 38223167 |
Filed Date | 2007-07-05 |
United States Patent
Application |
20070151709 |
Kind Code |
A1 |
Touzov; Igor Victorovich |
July 5, 2007 |
Heat pipes utilizing load bearing wicks
Abstract
This invention enables mechanical design of flexible and elastic
heat pipes. It provides structural solution that reduces
weight/performance ratio for traditional heat pipes and prevents
freeze damages.
Inventors: |
Touzov; Igor Victorovich;
(Cary, NC) |
Correspondence
Address: |
IGOR V TOUZOV
212 CRESTONE DRIVE
CARY
NC
27513
US
|
Family ID: |
38223167 |
Appl. No.: |
11/306530 |
Filed: |
December 30, 2005 |
Current U.S.
Class: |
165/104.26 |
Current CPC
Class: |
F28F 19/006 20130101;
F28D 15/0241 20130101; F28D 15/046 20130101 |
Class at
Publication: |
165/104.26 |
International
Class: |
F28D 15/00 20060101
F28D015/00 |
Claims
1. A capillary device formed by a set of braided or plaited
threads, wherein said braiding or plaiting forms plurality of
intrinsic channels with preferred direction coincident with
preferred direction of said braiding, and the term thread
represents a material in shape of wire, fiber, tow, yarns or alike,
and average cross section area of said plurality exceeds the area
of average opening between said threads in direction normal to said
preferred direction, and said plurality contains at least one
channel, and said structural, and a said device retain its
geometrical constraints under either external or internal pressure,
or under both internal and external pressure.
2. A heat pipe device having a capillary structure commonly known
as a wick, wherein the wick forms a spatial structure that provides
both capillary properties and interconnected gas permeable voids,
wherein said structure retains said properties under either
external or internal pressure, or under both internal and external
pressure.
3. A heat pipe device having a capillary structure commonly known
as a wick, wherein said wick structure utilizes capillary devices
of claim 1, and said device form spatial ordered pattern and
spatial orientations of said preferred directions form limited
number of well defined clusters.
4. A device of claim 2, wherein said wick is formed by braided
fibers or yarns.
5. A device of claim 2, wherein said wick is formed by plurality of
fabric sheets or by three dimensional woven or braided or knitted
fabric structure.
6. A device of claim 2, wherein the outer shell construction
utilizes a plurality of not smooth foil or sheets of thin material
with thickness of less then 1 mm each, and said plurality contains
at least one element.
7. A device of claim 6, wherein said shell is attached to said
wick.
8. A device of claim 2, wherein said wick is made of polymer
material.
9. A device of claim 2, wherein said wick is made of metal or
alloy.
10. A device of claim 2, wherein said wick is made of inorganic
fiber.
11. A device of claim 2, wherein said wick is made of carbon of
graphite fiber.
12. A device of claim 1, wherein said threads are made of polymer
material.
13. A device of claim 1, wherein said threads are made of metal or
alloy.
14. A device of claim 1, wherein said threads are made of inorganic
fiber.
15. A device of claim 1, wherein said threads are made of carbon of
graphite fiber.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a field of structural design of
heat pipes. It provides functional solution that reduces
weight/performance ratio for traditional heat pipes and improves
performance of flexible heat pipe designs.
PRIOR ART
[0002] Applications of heat pipes often become impractical due to
complexity associated with fitting these components into tightly
packed spaces or because of mobility restrictions they could cause.
Another implication is that systems can be utilized at temperatures
below freezing point of selected liquid. Liquid crystallization
might severely damage the shell of a heat pipe. It also disables
pipe functions until the liquid melts. Prior art (U.S. Pat. No.
4,194,559) exploit compromise solutions that prevent freeze damage
of the pipe in expense of added free volume that increases total
volume and weight of a solution.
[0003] Prior art (U.S. Pat. Nos. 4,279,294, 5,647,429, and
6,595,270) include attempts to utilize polymer materials such as an
aromatic polyamide fiber of extremely high tensile strength (Kevlar
fiber), polytetrafluoroethylene, nylon, or polyimides as a
construction material for outer shell of a flexible heat pipe. All
of them nevertheless require rigid geometry such as thick round
walls or imbedded spacers to prevent collapse of the pipes.
Invention U.S. Pat. No. 4,279,294 uses low boiling point liquid and
utilizes underground installation to prevent explosion of the pipe.
Devices of the other two inventions fail to account for high air
permeability of polymers that explains impractically short service
life of the inventions.
[0004] One prior art invention (U.S. Pat. No. 6,446,706) provides
highest performance among all competitors. It has form factor of a
tape with high unidimensional flexibility. Nevertheless design is
subject to freeze damage and its specific heat transfer performance
is reduced by presence of one or two layers of vapor transmitting
spacer material.
[0005] Another invention employs an array of rigid machined
capillars sealed between solid plates forming a flat heat pipe.
While this design provides very high performance it is inherently
solid and relies on load bearing shell. This design fails when the
pipe must operate at positive internal pressure.
DETAILED DESCRIPTION
[0006] This invention overcomes cited technical challenges
utilizing a soft shell and a load bearing wick structure in a heat
pipe design. Unlike competitive technologies it provides convenient
topological solution for compact designs, confined spaces, and
flexible solutions.
Wick
[0007] FIG. 1 shows schematic the structure of the wick. Preferred
embodiment of the invention uses a wick 1 is formed by braided
fiber. The yarns are braided to form plaits along preferred
direction of the pipe. Each yarn could be formed by braided fiber
or tows. 6-tow maypole braided construction is a good example for
one of many possible yarn designs.
[0008] The total wick structure accounts for small (capillary 3)
and large (passages 2) gaps. The capillary are formed by
fiber-fiber gaps and inner-yarn tubes, Inner yarn tube is formed
when small number of carriers (4-8) are used in rotary or maypole
braiding. The passages are formed by yarn-yarn and braid-braid
spacing. This construction has high mechanical stability and yet
flexible. Its capillary channels are suitable for efficient
transport of a liquid, and intrinsic passages allow for vapor
transport and efficient liquid-vapor interaction.
[0009] Plaiting ensures anisotropic capillary properties that
increase liquid transport rates. The braids are shaped to allow
free passages 2 for vapor in spaces between the yarns. At the same
time each plait performs capillary functions by transporting liquid
through channels formed by adjacent yarns 3 and inside the yarn.
Twisted braiding increases capillary efficiency since adjacent
twists of braids create shortcuts that significantly reduce
effective capillary length.
[0010] FIG. 2 show one of possible yarn constructions. This yarn is
created by braiding six fibers 4 using a maypole braider. This
braid allows for intrinsic channel 5 along the braid axis. The
whole yarn works as a capillary size tube with porous walls. The
size of the pores 6 is smaller than the size of the channel. When
used in conjunction with a liquid that has low surface angle on the
material of the fiber, the yarn quickly absorbs the liquid through
the walls. When wetted the walls behave as a solid surface. The
surface angle of the liquid on this surface is zero degree. This
make internal channel an ideal capillary for quick transport of the
liquid along the yarn.
Shell
[0011] Unlike traditional wicks the structure of braided wick
easily withstands both positive and negative external and internal
pressure. In addition to benefits such as good recovery from ice
formation, it enables use of thing foils and flexible films for the
shell construction. Use of low pressure refrigerant liquids
accounts of negative pressure gradient across the shell. Prior art
designs utilize thick wall plates or tubes to counteract this
pressure. They also incorporate spacers to prevent collapse of a
heat pipe.
[0012] The wick of this invention eliminates the need in all these
elements. A thin foil (e.g. 50 gauge aluminum foil) can be uses as
a sole constructive element of the pipe shell as shown on FIG. 3.
The wick 1 forms a sheet with yarns 3 weaved or braided together
alike a fabric. Refrigerant liquid is carried mostly by the yarns
while vapor is transported through the channels 2 and pores formed
by the fabric. Ultra thin metal foil 7 is well supported by the
wick.
[0013] The only real limitation for the foil thickness is absence
of pinholes as mechanical strength of even 5 micron aluminum is
sufficient to resist 1 bar of air pressure when placed on top of
the wick of this invention. To eliminate effect of production
pinholes a laminate of two layers of capacitor grade aluminum foil
is created with total laminate thickness of 12 microns. The
laminate 7 under pressure forms corrugated patterns 8 alike well
known "diamond plate". This embossed pattern serves two critical
roles for the matter of this invention. First, it forms coplanar
mechanical contact 9 with the wick that dramatically increases
wick's mechanical stability. Second, it makes highly efficient
thermal contact with surfaces of the yarns. Each yarn walls are
saturated with refrigerant liquid that makes said thermal contact
highly stable and efficient.
[0014] The load bearing ability of the wick allows for its
efficient use with medium and high pressure refrigerant fluids.
Prior art designs of heat pipes for high pressure applications
accounts for thick walls or round pipe or external constraints
(underground installation). The wick of this invention allows to
avoid these design solutions as they contribute to higher weight
and reduced usability.
[0015] The shell for positive pressure designs can be furnished by
organic or inorganic polymers, fiber reinforced materials, or other
composites. Dense yarn structure of the wick allows the shell
material to be glued or molded into the surface of the wick. Other
well known methods of lamination can be used as well. Alternatively
layer or layers composing the shell can be interweaved with the
wick surface, or sewed with the wick, or any other well known
technique of mechanical attachment can be employed to secure the
shell on the wick.
[0016] Typical topology of surface for the invented wick has weaves
every 1 mm or less. Foil of Aluminum Alloy 2014-T6 100 micron thick
will be able to sustain 1700 psi pressure. The wick material for
this high pressure scenario can be steel fiber or carbon fiber.
Most refrigerant has critical pressure below 1700 psi that allow
for use of broader spectrum of wick materials.
[0017] The thin shell design of this invention under positive and
negative pressure forms intrinsic corrugations of the surface this
makes entire assembly flexible enough to allow in place bending and
curling of the pipe. The shape factor for the pipe can be selected
as a sheet, tape, sleeve or any others as only one factor defines
this shape -the wick cross section.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1. Cross-section of schematic structure of the wick
(top), and its appearance from outside (below).
[0019] FIG. 2. Construction of braided yarn with intrinsic cavity
(left), yarn appearance is similar to thread but have braiding
(right).
[0020] FIG. 3. Oriented braided wick constrained between shell
layers. Top view (top left), front view (bottom left), side view
(center). Details (right) shows deformation of shell surface (top)
and persistence of intrinsic cavities (bottom).
* * * * *