U.S. patent application number 14/797956 was filed with the patent office on 2016-01-14 for heat transport device.
This patent application is currently assigned to FUJIKURA LTD.. The applicant listed for this patent is FUJIKURA LTD.. Invention is credited to Mohammad Shahed AHAMED, Yuji SAITO, Phan THANHLONG.
Application Number | 20160010927 14/797956 |
Document ID | / |
Family ID | 55067324 |
Filed Date | 2016-01-14 |
United States Patent
Application |
20160010927 |
Kind Code |
A1 |
AHAMED; Mohammad Shahed ; et
al. |
January 14, 2016 |
HEAT TRANSPORT DEVICE
Abstract
A heat transport device having enhanced heat transport capacity
is provided. The heat transport device comprises an evacuated and
sealed container 2, and phase changeable working fluid encapsulated
in the container to transport heat a fiber wick 3 is laid on an
inner face of the container 2 in a longitudinal direction, and a
powder wick is formed on a surface of the fiber wick 3. A thickness
of the powder wick is five to ten times smaller than a diameter of
the fiber.
Inventors: |
AHAMED; Mohammad Shahed;
(Tokyo, JP) ; SAITO; Yuji; (Tokyo, JP) ;
THANHLONG; Phan; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJIKURA LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
FUJIKURA LTD.
Tokyo
JP
|
Family ID: |
55067324 |
Appl. No.: |
14/797956 |
Filed: |
July 13, 2015 |
Current U.S.
Class: |
165/104.26 |
Current CPC
Class: |
F28D 15/046 20130101;
F28D 15/0233 20130101 |
International
Class: |
F28D 15/04 20060101
F28D015/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 14, 2014 |
JP |
2014-143877 |
Claims
1. A heat transport device, comprising: a sealed container from
which air is evacuated; a working fluid that is encapsulated in the
container, and that circulates within the container while being
evaporated by being heated and condensed by removing heat
therefrom; a fiber wick that is formed by bundling a plurality of
fibers, and that is laid on an inner face of the container in a
longitudinal direction; and a powder wick that is formed on a
surface of the fiber wick by depositing particles whose grain
diameters fall within a range between 5 to 10 .mu.m that is five to
ten times smaller than a diameter of the fiber; wherein a thickness
of the powder wick is one to five times larger than the grain
diameter of the particle.
2. The heat transport device as claimed in claim 1, wherein the
sealed container includes a heating site heated by an external
heat, and a cooling site from which the heat is radiated to
outside, and wherein the powder wick is formed from the surface of
the fiber wick to an inner surface of the heating site of the
container.
3. The heat transport device as claimed in claim 1, wherein the
powder wick is formed entirely on the inner face of the sealed
container except for a portion on which the fiber wick is laid.
4. The heat transport device as claimed in claim 1, wherein a
diameter of the fiber is 50 .mu.m at smallest, and a grain diameter
of the particle is 10 .mu.m at largest.
5. The heat transport device as claimed in claim 3, wherein the
sealed container is made of metal material; wherein the fibers and
the particles include metal fibers and metal particles; and wherein
the metal fibers and the metal particles are fixed to an inner face
of the container by a sintering method.
6. The heat transport device as claimed in claim 1, wherein the
sealed container includes a flat container having a larger width
than a thickness.
Description
[0001] The present invention claims the benefit of Japanese Patent
Application No. 2014-143877 filed on Jul. 14, 2014 with the
Japanese Patent Office, the disclosure of which is incorporated
herein by reference in its entirety.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates to an art of a heat transport
device in which a phase-changeable working fluid in encapsulated in
a sealed container.
[0004] 2. Discussion of the Related Art
[0005] Various kinds of heat pipes and thermosiphon are known in
the art. For example, JP-A-2013-002640 describes a flat heat pipe
formed by flattening a tubular container holding working fluid
therein. In the flattened container, the working fluid is
evaporated when it is heated and condensed when it is cooled, and
the working fluid in the liquid phase is pulled by a capillary
pumping of a wick laid on an inner flat face.
[0006] According to the teachings of JP-A-2013-002640, a grooved
pipe in which a plurality of rows of grooves is formed on an inner
face, and a bear pipe having an unprocessed smooth inner face can
be used as the container. The wick is comprised of a layer of
carbon fibers or copper fibers laid on the inner surface, and a
metal powder layer covering the fiber layer.
[0007] In the heat pipe taught by JP-A-2013-002640, menisci of the
liquid phase working fluid are formed among the powers of the
powder layer, and a liquid level in the powder wick lowered as a
result of evaporation of the working fluid is raised by a capillary
pumping of menisci. Such capillary pumping force is enhanced by
narrowing clearances among the powders. In the heat pipe of this
kind, the working fluid in the liquid phase is allowed to flow back
smoothly to an evaporation site through clearances among the metal
fibers where a flow resistance is small. However, the working fluid
has to flow back over the long distance to a heated site at one end
of the container, and then the working fluid evaporated by the heat
generating device contacted to the heated site has to flow upwardly
through the powder layer having a certain thickness to escape from
an outer surface of the powder layer. This increases a thermal
resistance between the heated site and the working fluid in the
heat pipe taught by JP-A-2013-002640. Thus, conventional heat pipes
have to be improved to enhance heat conductivity by reducing
thermal resistance to transport heat by the working fluid.
SUMMARY OF THE INVENTION
[0008] The present invention has been conceived nothing the
foregoing technical problems, and it is therefore an object of the
present invention is to enhance heat transport capacity of a heat
transport device by reducing a thermal resistance to transfer heat
to working fluid.
[0009] The present invention is applied to a heat transport device
having an evacuated and sealed container, and phase changeable
working fluid is encapsulated in the container to transport heat.
In order to achieve above-mentioned objective, according to the
present invention, a fiber wick formed of fibers is laid on an
inner face of the container in a longitudinal direction, and a
powder wick is formed on a surface of the fiber wick. Grain
diameters of the particles fall within a range between 5 to 10
.mu.m that is five to ten times smaller than a diameter of the
fiber, and a thickness of the powder wick is one to five times
larger than the grain diameter of the particle.
[0010] The sealed container includes a heating site heated by an
external heat, and a cooling site from which the heat is radiated
to outside. According to one aspect of the present invention, the
powder wick may be formed from the surface of the fiber wick to an
inner surface of the heating site of the container.
[0011] According to another aspect of the present invention, the
powder wick may also be formed entirely on the inner face of the
sealed container except for a portion on which the fiber wick is
laid.
[0012] Specifically, a diameter of the fiber is 50 .mu.m at
smallest, and a grain diameter of the particle is 10 .mu.m at
largest.
[0013] The sealed container may be made of metal material, and
metal fibers and metal particles may be used to form the fiber wick
and the powder wick. In this case, the metal fibers and the metal
particles are fixed to an inner face of the container by a
sintering method.
[0014] Optionally, the sealed container may be formed into a flat
container having a larger width than a thickness.
[0015] In the heat transport device of the present invention,
longitudinal clearances among the fibers serve as straight flow
passages of the working fluid in the liquid phase, and diameters of
passages are not varied partially. For this reason, the working
fluid is allowed to flow smoothly back to the heating site through
the fiber wick so that the thermal resistance in the heat transport
device can be reduced to enhance heat transporting performance.
Further, the powder wick on the fiber wick is formed of fine
particle to create strong pumping forces at menisci to pump up the
working fluid to the surface of the powder wick where the
evaporation of the working fluid takes place. For this reason, the
working fluid is also allowed to flow back smoothly to the heating
site so that thermal resistance in the heat transport device can be
further reduced to enhance heat transporting performance. In
addition, since the thickness of the powder wick is significantly
thinner than fibers of the fiber wick, the thermal resistance
between the working fluid penetrating into the powder wick and an
external heat source can be reduced so that heat transport
performance of the heat pipe can be further enhanced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Features, aspects, and advantages of exemplary embodiments
of the present invention will become better understood with
reference to the following description and accompanying drawings,
which should not limit the invention in any way.
[0017] FIG. 1 is a perspective view showing a preferred example of
the heat transport device formed into a flat heat pipe;
[0018] FIG. 2 is a cross-sectional view of the flat heat pipe;
[0019] FIG. 3 is a schematic illustration showing a surface of the
fiber wick and particles adhering thereto;
[0020] FIG. 4 is a schematic illustration showing a situation of
measuring a thermal resistance of the heat pipe; and
[0021] FIG. 5 is a graph indicating measurement results of thermal
resistance in the heat pipe according to the preferred example and
the conventional heat pipe according to the comparative
example.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0022] Hereinafter, a preferred example of the heat transport
device according to the present invention will be explained in more
detail with reference to the accompanying drawings. Referring now
to FIG. 1, there is schematically shown a heat pipe 1 as a heat
transfer device adapted to transport heat by the known principle. A
sealed container 2 of the heat pipe 1 is formed by flattening a
metal pipe to have a wider width than a height, and working fluid
is encapsulated therein liquid-tightly. The working fluid is
evaporated when it is heated at a predetermined temperature, and
condensed when it is cooled by a predetermined temperature. In
order to pull the condensed working fluid to a heating site by
capillary pumping, a fiber wick 3 is laid on an inner flat surface
of the flattened container 2. For example, a steel pipe, an
aluminum alloy pipe, a copper pipe can be used to form the
container 2, and the copper pipe having the highest heat
conductivity is most suitable. Specifically, a bear metal pipe in
which an inner surface thereof is unprocessed is used to form the
container 2.
[0023] The wick 3 is formed by bundling fibers. For example, metal
fibers such as copper fibers or inorganic fibers such as carbon
fibers can be used to form the wick 3. According to the preferred
example, a diameter of each fiber 3a is larger than 50 .mu.m, and
several hundreds of fibers 3a are bundled to form the wick 3. The
fibers may be twisted to be prevented from being loosened, however,
it is preferable to bundle the straight fibers without twisting to
reduce pressure loss in flow passages formed among the fibers.
Optionally, the fibers may be bundled by a not shown banding band.
Given that the copper fibers are used to form the wick 3, the
copper fibers may be sintered together and to be fixed onto an
inner face of the container 2 in a longitudinal direction.
[0024] As depicted in FIGS. 2 and 3, particles 4 are deposited on a
surface of the fiber wick 3. According to the preferred example,
copper powers whose maximum grain diameter is smaller than an
average diameter of the fiber 3a (50 .mu.m at minimum) are used as
the particles 4. Specifically, diameters of the particles 4 fall
within a range from 5 to 10 .mu.m, and other metal powders may also
be used instead of copper powder. The particles 4 thus covering the
surface of the fiber wick 3 serves as the claimed powder wick. A
thickness of the powder wick formed of the particles 4 is
determined in such a manner to ensure capillary pumping force to
pull the working fluid and specific surface area to expedite
evaporation of the working fluid. To this end, specifically, one to
five layers of the particles 4 is/are formed on the top surface of
the fiber wick 3. That is, a thickness of the powder layer is one
to five times larger than the grain diameter of the particles 4.
The thickness of the powder layer is adjusted to a desired value by
pouring the particles 3 into the container 2 in an amount
sufficient to cover the surface of the fiber wick 3, and then
discharging surplus particles 4 from the container 2. Consequently,
clearances among the fibers 3a forming the fiber wick 3 are filled
with the particles 4, and a top surface of the powder wick is
formed into a smooth surface.
[0025] The powder wick may be formed not only on the top face of
the fiber wick 3 but also entirely on the inner face of the
container 2 (except for the portion on which the fiber wick 3 is
laid). Especially, it is preferable to cover the inner surface of
the container 2 from a heating site 2H heated by the heat
generating element to the top surface of the fiber wick 3 by the
powder wick. In this case, a thickness of the portion of the powder
wick covering the inner face of the container 2 may not only be
equal to that of the portion covering the top surface of the fiber
wick 3 but also be different from that of the portion covering the
top surface of the fiber wick 3. The particles 4 may be fixed to
the top surface of the fiber wick 3 and the inner face of the
container 2 by an appropriate method. For example, the particles 4
may be fixed to the top surface of the fiber wick 3 and the inner
face of the container 2 by a sintering method. In this case, since
the grain diameter of the particle 4 is smaller the diameter of the
fiber 3a, a sintering temperature of the particles 4 is lower than
that of the fibers 3a.
[0026] An example of fixing the particles 4 onto the top surface of
the fiber wick 3 will be explained hereinafter. As described, a
copper tubular pipe in which both ends are opened is used to form
the sealed container 2. Appropriate number of the copper fibers 3a
to form the fiber wick 3 is laid on the inner face of the tubular
pipe in the longitudinal direction using a predetermined jig (e.g.,
a center rod) to situate the bunch of the fibers 3a at a desired
position while keeping into a desired configuration. Then, the
tubular pipe thus holding the fibers 3a is sintered to fix the
fibers 3a to one another and to the inner face of the tubular pipe
at approximately 1000 degrees C. under an inert atmosphere. After
the copper fibers 3a are fixed to the inner surface of the tubular
pipe, the jig is withdrawn from the tubular pipe. In this
situation, both ends of the tubular pipe are still opened. Then,
one of the end portions of the tubular pipe is closed using a
predetermined tool, and the copper particles 4 is fed into the
tubular pipe from the other opening end in an amount sufficient to
form the powder wick. Thereafter, surplus of the copper particles 4
is discharged from the tubular pipe by tapping or knocking the
closed end thereof while situating the opening end thereof
downwardly. In this situation, however, a necessary amount of the
copper powders 4 to form an unsintered powder layer is still
adsorbed to the top surface of the fiber wick 3 by a surface energy
of the copper powder 4 or by an attraction between the copper pipe
and the copper powder. In this situation, the tubular pipe is
sintered again at approximately 600 degrees C. under an inert
atmosphere to fix the copper powder layer to the top surface of the
fiber wick 3 and to the inner face of the tubular pipe.
[0027] The working fluid is selected from water, ammonia, alcohol
etc. having good hydrophilic property to the copper tube and the
copper powder 4, and according to the preferred example, water is
used as the working fluid. For example, the container 2 can be
filled with the working fluid by evacuating air therefrom, and
pouring an appropriate amount of the working fluid thereinto. Then,
the opening end of the container 2 is closed. Alternatively, the
container 2 may also be filled with the working fluid by pouring an
excessive amount of the working fluid into the tubular pipe while
boiling the working fluid by heating the container 2 to evacuate
air from the container 2, and then closing the opening end of the
container 2.
[0028] In the heat pipe 3 shown in FIGS. 1 to 3, the working fluid
in the liquid phase penetrates into the fiber wick 3. The working
fluid in the heating site 2H is heated by the heat "Q" of the heat
generating element that is brought into contact to an outer face of
the heating site 2H. The vapor of the working fluid flows toward a
cooling site 2C while transporting the heat "Q" in the form of
latent heat, and the heat "Q" is then radiated from the cooling
site 2H. Consequently, the working fluid is condensed again into
the liquid phase. Optionally, a portion between the heating site 2H
and the cooling site 2C may be insulated from an external heat. To
this end, the powder wick is formed on the inner face of the
container 2 between the heating site 2H and the cooling site 2C
through the heat insulating portion.
[0029] The working fluid is condensed on the inner face of the
container 2. Given that the powder wick of the copper powder 4 is
formed on the inner face of the container 2, the working fluid is
allowed to spread throughout the inner surface through the powder
wick so that hydrophilicity of the inner surface can be enhanced.
Consequently, the condensed working fluid is allowed to penetrate
into the fiber wick 3 efficiently to be pulled toward the heating
site 2H. In addition, the condensed working fluid is also allowed
to flow back partially to the heating site 2H through the powder
wick formed of the fine copper powder 4.
[0030] The condensed working fluid is returned to the heating site
2H to be evaporated mainly through the fiber wick 3. In the heating
site, the working fluid is evaporated and hence an amount of the
working fluid in the liquid phase is decreased. However, the
working fluid in the liquid phase is returned continuously from the
cooling site 2C through the fiber wick 3, and pumped up to a
surface of the powder wick formed of the finer copper powder 4
where the evaporation of the working fluid takes place by the
capillary pumping of menisci among the powder copper powder 4.
Thus, the working fluid is circulated efficiently within the heat
pipe 1 while changing phase to enhance heat transporting
performance of the heat pipe 1. Especially, according to the
preferred example, the thickness of the powder wick is five to ten
times thinner than the average diameter of the copper fibers 3a so
that the thermal resistance to transport heat to the working fluid
at the evaporating site can be reduced. For this reason, the
thermal resistance in the heat pipe 1 can be reduced entirely so
that the heat transporting performance of the heat pipe 1 can be
enhanced.
[0031] Here will be explained a comparison result of thermal
resistance between the heat pipe 1 according to the preferred
example shown in FIGS. 1 to 3 and a conventional heat pipe
according to a comparison example. Specifically, the heat pipe
according to a comparison example is provided with the fiber wick 3
but not provided with the powder wick. The remaining structures of
the heat pipes used in the measurement are similar to each other.
Lengths, widths and thicknesses of both heat pipes are 150 mm, 9.1
mm and 1.0 mm respectively. In the measurement, a square heater 5
(15 mm each side) adapted to change a temperature thereof
electrically is attached to the heating site 2 of each heat pipe,
and a portion of each heat pipe within 50 mm from a leading end of
the cooling site 2C is attached to a copper radiator plate 6 to be
cooled. During the measurement, the heating site 2C of each heat
pipe were heated at an operating temperature of 60 degrees C. while
changing a thermal input thereto, and a surface temperature Th of
the heating site 2C of each heat pipe and a surface temperature of
the cooling site Tc of each heat pipe were measured respectively by
a same sensor.
[0032] Measurement results are shown in FIG. 5. As can be seen from
FIG. 5, the thermal resistance ((Th-Tc)/W(.degree. C./W)) of the
heat pipe according to the preferred example falls within a range
from 0.5 (.degree. C./W) to 0.6 (.degree. C./W) under a condition
that the thermal input is 10 to 18 W. By contrast, the thermal
resistance of the heat pipe according to the comparison example is
larger than that of the heat pipe according to the preferred
example over the entire range of the thermal input. In addition, a
dry out of the heat pipe according to the preferred example is
caused at around 18 W of thermal input. By contrast, a dry out of
the heat pipe according to the comparison example is caused at
around 16 W of thermal input. Thus, thermal resistance of the heat
pipe according to the preferred example is reduced significantly to
enhance heat transporting performance.
[0033] It is understood that the invention is not limited by the
exact construction of the foregoing preferred example, but that
various modifications may be made without departing from the spirit
of the inventions.
* * * * *