U.S. patent application number 11/858080 was filed with the patent office on 2009-01-22 for heat pipe with composite wick structure.
This patent application is currently assigned to FOXCONN TECHNOLOGY CO., LTD.. Invention is credited to CHANG-SHEN CHANG, JUEI-KHAI LIU, HSIEN-SHENG PEI, CHAO-HAO WANG.
Application Number | 20090020269 11/858080 |
Document ID | / |
Family ID | 40263886 |
Filed Date | 2009-01-22 |
United States Patent
Application |
20090020269 |
Kind Code |
A1 |
CHANG; CHANG-SHEN ; et
al. |
January 22, 2009 |
HEAT PIPE WITH COMPOSITE WICK STRUCTURE
Abstract
A heat pipe (10) includes a metal casing (12) having an
evaporator section (121) and a condenser section (122). A major
wick structure (14) is disposed on an inner wall of the casing. At
least one assistant wick structure (16) is disposed in and contacts
with the major wick structure, and working medium fills in the
casing and saturates the major wick structure and the at least one
assistant wick structure. An average pore size of the major wick
structure corresponding to the evaporator section is smaller than
that of the major wick structure corresponding to the condenser
section. A diameter of a cross section of the at least one
assistant wick structure is smaller than a diameter of a cross
section of the major wick structure, and thus the at least one
assistant wick structure has a linear contact with the major wick
structure.
Inventors: |
CHANG; CHANG-SHEN;
(Tu-Cheng, TW) ; WANG; CHAO-HAO; (Tu-Cheng,
TW) ; LIU; JUEI-KHAI; (Tu-Cheng, TW) ; PEI;
HSIEN-SHENG; (Tu-Cheng, TW) |
Correspondence
Address: |
PCE INDUSTRY, INC.;ATT. CHENG-JU CHIANG
458 E. LAMBERT ROAD
FULLERTON
CA
92835
US
|
Assignee: |
FOXCONN TECHNOLOGY CO.,
LTD.
Tu-Cheng
TW
|
Family ID: |
40263886 |
Appl. No.: |
11/858080 |
Filed: |
September 19, 2007 |
Current U.S.
Class: |
165/104.26 ;
165/180 |
Current CPC
Class: |
F28D 15/046
20130101 |
Class at
Publication: |
165/104.26 ;
165/180 |
International
Class: |
F28D 15/00 20060101
F28D015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 18, 2007 |
CN |
200710075201.8 |
Claims
1. A heat pipe comprising: an elongated casing having an evaporator
section and a condenser section; a major wick structure disposed on
an inner wall of the casing, an average pore size of the major wick
structure corresponding to the evaporator section being smaller
than that of the major wick structure corresponding to the
condenser section; at least one assistant wick structure disposed
in and contacting with an inner wall of the major wick structure
and extending from the evaporator section to the condenser section,
a diameter of a cross section of the at least one assistant wick
structure being smaller than a diameter of a cross section of the
major wick structure, the at least one assistant wick structure
having a linear contact with the inner wall of the major wick
structure; and working medium filling in the casing and saturating
the major wick structure and the at least one assistant wick
structure.
2. The heat pipe of claim 1, wherein the at least one assistant
wick structure is a hollow tube made of sintered powder.
3. The heat pipe of claim 1, wherein the at least one assistant
wick structure is a hollow tube made of a plurality of woven metal
wires, and the metal wires are selected from a group consisting of
copper wires and stainless steel wires.
4. The heat pipe of claim 1, wherein the at least one assistant
wick structure comprises a plurality of assistant wick structures
spacing a distance from each other.
5. The heat pipe of claim 1, wherein the at least one assistant
wick structure comprises a plurality of assistant structures
contacting with each other.
6. The heat pipe of claim 1, wherein the at least one assistant
wick structure is a hollow tube with an inner diameter ranging from
0.5 mm to 2 mm.
7. The heat pipe of claim 1, wherein the major wick structure is
selected from the group of grooves, sintered powder, fiber and
screen mesh.
8. The heat pipe of claim 7, wherein the major wick structure
corresponding to the evaporator section of the heat pipe is one of
sintered powder and screen mesh, and the major wick structure
corresponding to the condenser section of the heat pipe is
grooves.
9. The heat pipe of claim 7, wherein the major wick structure
corresponding to the evaporator section of the heat pipe has two
layers stacked along a radial direction of the heat pipe, one layer
being grooves and the other layer being one of sintered powder and
screen mesh.
10. A heat pipe comprising: a metal casing having an evaporator
section and a condenser section; a porous major wick structure
disposed on an inner wall of the casing, an average pore size of
the major wick structure corresponding to the evaporator section
being smaller than that of the wick structure corresponding to the
condenser section; at least one assistant wick structure disposed
in an inner wall of the major wick structure, the at least one
assistant wick structure defining a plurality of pores
communicating an inside of the at least one assistant wick
structure with an inside of the major wick structure and a channel
in an inner space thereof; and working medium filling in the casing
and saturating the major wick structure and the at least one
assistant wick structure; wherein vapor in the metal casing flows
from the evaporator section to the condenser section via a space
between the major wick structure and the at least one assistant
wick structure, and condensate in the metal casing flows from the
condenser section to the evaporator section via the pores of the
major and the assistant wick structures and the channel of the
assistant wick structure.
11. The heat pipe of claim 10, wherein a diameter of the at least
one assistant wick structure ranges from 0.5 mm to 2 mm.
12. The heat pipe of claim 10, wherein the at least one assistant
wick structure is made of a plurality of woven metal wires selected
from a group consisting of copper and stainless steel wires.
13. The heat pipe of claim 10, wherein the at least one assistant
wick structure comprises a plurality of assistant wick structures
spaced from each other.
14. The heat pipe of claim 13, wherein the plurality of assistant
wick structures are evenly spaced from each other.
15. The heat pipe of claim 10, wherein the at least one assistant
wick structure comprises a plurality of assistant wick structures
contacting with each other.
16. The heat pipe of claim 10, wherein the major wick structure is
selected from the group of grooves, sintered powder, fiber and
screen mesh.
17. The heat pipe of claim 16, wherein the major wick structure
corresponding to the evaporator section of the heat pipe is one of
sintered powder and screen mesh, and the major wick structure
corresponding to the condenser section of the heat pipe is
grooves.
18. The heat pipe of claim 16, wherein the major wick structure
corresponding to the evaporator section of the heat pipe has two
layers stacked along a radial direction of the heat pipe, one layer
being grooves and the other layer being one of sintered powder and
screen mesh.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to a heat transfer
apparatus, and more particularly to a heat pipe having composite
capillary wick structure.
[0003] 2. Description of Related Art
[0004] Heat pipes have excellent heat transfer performance due to
their low thermal resistance, and are therefore an effective means
for transfer or dissipation of heat from heat sources. Currently,
heat pipes are widely used for removing heat from heat-generating
components such as central processing units (CPUs) of
computers.
[0005] A heat pipe is usually a vacuum casing containing therein a
working medium, which is employed to carry, under phase transitions
between liquid state and vapor state, thermal energy from an
evaporator section to a condenser section. Preferably, a wick
structure is provided inside the heat pipe, lining an inner wall of
the casing, for drawing the working medium back to the evaporator
section after it is condensed at the condenser section. In
operation, the evaporator section of the heat pipe is maintained in
thermal contact with a heat-generating component. The working
medium contained at the evaporator section absorbs heat generated
by the heat-generating component and then turns into vapor and
moves towards the condenser section where the vapor is condensed
into condensate after releasing the heat into ambient environment.
Due to the difference in capillary pressure which develops in the
wick structure between the two sections, the condensate is then
brought back by the wick structure to the evaporator section where
it is again available for evaporation.
[0006] In order to draw the condensate back timely, the wick
structure provided in the heat pipe is expected to provide a high
capillary force and meanwhile generate a low flow resistance for
the condensate. In ordinary use, the heat pipe needs to be
flattened to enable the miniaturization of electronic products
incorporating the heat pipe, which may result in damage to the wick
structure of the heat pipe. When this happens, the flow resistance
of the wick structure is increased and the capillary force provided
by the wick structure is decreased, which in turn reduces the heat
transfer capability of the heat pipe. If the condensate is not
quickly brought back from the condenser section, the heat pipe will
suffer a dry-out problem at the evaporator section.
[0007] Therefore, it is desirable to provide a heat pipe with
improved heat transfer capability; wick structure of the heat pipe
will not be damaged and still can have a satisfied wicking force
when the heat pipe is flattened.
SUMMARY OF THE INVENTION
[0008] The present invention relates to a heat pipe for removing
heat from heat-generating components. The heat pipe includes a
longitudinal casing having an evaporator section and a condenser
section; a major wick structure is disposed on an inner wall of the
casing; at least one assistant wick structure is disposed in and
contacts with the major wick structure, and extends from the
evaporator section to the condenser section. Working medium fills
in the casing and saturates the major wick structure and the at
least one assistant wick structure. An average pore size of the
major wick structure corresponding to the evaporator section is
smaller than that of the major wick structure corresponding to the
condenser section. A diameter of a cross section of the at least
one assistant wick structure is smaller than a diameter of a cross
section of the major wick structure, and thus the at least one
assistant wick structure has a linear contact with the inner wall
of the major wick structure.
[0009] Other advantages and novel features of the present invention
will become more apparent from the following detailed description
of preferred embodiment when taken in conjunction with the
accompanying drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Many aspects of the present invention can be better
understood with reference to the following drawings. The components
in the drawings are not necessarily drawn to scale, the emphasis
instead being placed upon clearly illustrating the principles of
the present invention. Moreover, in the drawings, like reference
numerals designate corresponding parts throughout the several
views:
[0011] FIG. 1 is a longitudinal cross-sectional view of a heat pipe
in accordance with a first embodiment of the present invention;
[0012] FIG. 2 is a transverse cross-sectional view of a condensing
section of the heat pipe of FIG. 1 taken along line II-II;
[0013] FIG. 3 is a transverse cross-sectional view of an
evaporating section of the heat pipe of FIG. 1 taken along line
III-III;
[0014] FIG. 4 is similar to FIG. 3, but shows the evaporating
section according to a second embodiment of present invention;
[0015] FIG. 5 is a transverse cross-sectional view of the
evaporating section according to a third embodiment of the present
invention;
[0016] FIG. 6 is a transverse cross-sectional view of the
evaporating section according to a fourth embodiment of the present
invention;
[0017] FIG. 7 is a transverse cross-sectional view of the
evaporating section according to a fifth embodiment of the present
invention;
[0018] FIG. 8 is a transverse cross-sectional view of the
evaporating section according to a sixth embodiment of the present
invention; and
[0019] FIG. 9 is a transverse cross-sectional view of the
evaporating section according to a seventh embodiment of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0020] FIGS. 1-2 illustrate a heat pipe 10 in accordance with a
first embodiment of the present invention. The heat pipe 10
includes a round tube-like metal casing 12, and a variety of
elements enclosed in the metal casing 12, i.e., a major wick
structure 14, an assistant wick structure 16, and a working medium
(not shown).
[0021] The metal casing 12 is made of high thermally conductive
material such as copper or aluminum. The metal casing 12 has an
evaporator section 121, an opposing condenser section 122 along a
longitudinal direction of the heat pipe 10, and an adiabatic
section 123 disposed between the evaporator and condenser sections
121, 122. Two ends of the heat pipe 10 are sealed. The working
medium is saturated in the major and assistant wick structures 14,
16, and is usually selected from a liquid such as water, methanol,
or alcohol, which has a low boiling point and is compatible with
the major and assistant wick structures 14, 16. Thus, the working
medium can easily evaporate to vapor when it receives heat at the
evaporator section 121 of the heat pipe 10. The metal casing 12 of
the heat pipe 10 is evacuated and hermetically sealed after the
working medium is injected into the metal casing 12 and saturated
in the major and assistant wick structures 14, 16.
[0022] The major wick structure 14 is provided around an inner wall
of the metal casing 12 and extends along the longitudinal direction
of the metal casing 12 of the heat pipe 10. The major wick
structure 14 is tube-shaped in profile, and usually selected from a
porous structure such as grooves, sintered powder, screen mesh, or
bundles of fiber, which enable the major wick structure 14 to
provide a capillary force to drive condensed working medium at the
condenser section 122 of the heat pip 10 to flow towards the
evaporator section 121 thereof. In this embodiment, the major wick
structure 14 includes a first portion 142 applied to the evaporator
section 121 of the metal casing 12 of the heat pipe 10 and a second
portion 141 applied to the condenser section 122 and the adiabatic
section 123 of the metal casing 12. The first portion 142 of the
major wick structure 14 is sintered powder wick, and the second
portion 141 of the major wick structure 14 is groove wick. An
average pore size of the first portion 142 of the major wick
structure 14 is smaller than that of the second portion 141 of the
major wick structure 14. According to the general rule, the
capillary pressure of the wick structure and its flow resistance to
the condensed fluid increase due to a decrease in pore size of the
wick structure; the first portion 142 of the major wick structure
14 corresponding to the evaporator section 121 of the heat pipe 10
is thus capable of providing a capillary pressure gradually
increasing from the condenser section 122 toward the evaporator
section 121, and a flow resistance gradually decreasing from the
evaporator section 121 toward the condenser section 122.
[0023] The assistant wick structure 16 is an elongated hollow tube,
which is attached to an inner wall of the major wick structure 14
and extends along the longitudinal direction of the metal casing
12. The assistant wick structure 16 is formed by weaving a
plurality of metal wires, such as copper or stainless steel wires.
Alternatively, the assistant wick structure 16 may be formed by
sintering an amount of powders. A channel 163 is defined in an
inner space of the assistant wick structure 16 for passage of
condensed working medium. The channel 163 has a diameter ranging
from 0.5 mm to 2 mm. A plurality of pores 161 are formed in a
peripheral wall of the assistant wick structure 16, which provides
a capillary action to the working medium and communicates an inside
(not labeled) of the assistant wick structure 16 with an inside
(not labeled) of the major wick structure 14. A composite wick
structure is thus formed in the metal casing 12 of the heat pipe
10. The assistant wick structure 16 has a ring-like transverse
cross section. A diameter of the assistant wick structure 16 is
much smaller than a diameter of the major wick structure 14. The
assistant wick structure 16 has an adjacent portion contacting with
the inner wall of the major wick structure 14, and a distal portion
spaced a distance from the inner wall of the major wick structure
14 along a radial direction of the heat pipe 10.
[0024] In operation, the evaporator section 121 of the heat pipe 10
is placed in thermal contact with a heat source (not shown), for
example, a central processing unit (CPU) of a computer, that needs
to be cooled. The working medium contained in the evaporator
section 121 of the heat pipe 10 is vaporized into vapor upon
receiving the heat generated by the heat source. Then, the
generated vapor moves via a space between the major and assistant
wick structures 14, 16 of the heat pipe 10. After the vapor
releases the heat carried thereby and it is condensed into
condensate in the condenser section 122, the condensate is brought
back by the major wick structure 14 to the evaporator section 121
of the heat pipe 10 for being available again for evaporation.
Meanwhile, the condensate resulting from the vapor in the condenser
section 122 is capable of entering into the assistant wick
structure 16 easily due to the capillary action of the assistant
wick structure 16 and then can move through the channel 163 to the
evaporator section 121. As a result, the condensate is drawn back
to the evaporator section 121 rapidly and timely, thus preventing a
potential dry-out problem occurring at the evaporator section 121.
In addition, the working medium can not be accumulated in a bottom
portion of the major wick structure 14 of the heat pipe 10 under an
action of gravity. This prevents the increase of the flow
resistance of the heat pipe 10, which is caused by the accumulation
of the working medium in a specific place of the heat pipe. The
heat transfer capability of the heat pipe 10 is thus increased.
[0025] In the present invention, the assistant wick structure 16
cooperates with the major wick structure 14 to form the composite
wick structure, which increases the capillary force inside the heat
pipe 10. Thus, the heat transfer capability of the heat pipe 10 is
increased. The assistant wick structure 16 is distributed along the
longitudinal direction of the heat pipe 10 and has a smaller
diameter than that of the major wick structure 14. As a result, the
assistant wick structure 16 can not easily be damaged by the
flattening process of the heat pipe 10. On the other hand, the
average pore size of the first portion 142 of the major wick
structure 14 corresponding to the evaporator section 121 of the
heat pipe 10 is smaller than that of the second portion 141 of the
major wick structure 14 corresponding to the condenser section 122
and the adiabatic section 123 of the heat pipe 10. The major wick
structure 14 provides a capillary pressure gradually increasing
from the condenser section 122 toward the evaporator section 121,
and a flow resistance gradually decreasing from the evaporator
section 121 toward the condenser section 122.
[0026] FIGS. 4-9 schematically show the evaporator section 121 of
the heat pipe 10 in accordance with some additional embodiments of
the present invention. Except for the first portion of the major
wick structure 14, other parts of these embodiments are the same as
the first embodiment. In FIG. 4, the first portion 142a of the
major wick structure corresponding to the evaporator section 121 is
screen mesh wick which is planar-shaped in an unfurled state. FIGS.
5-7 show that the first portion of the major wick structure has two
stacked layers. Referring to FIG. 5, a first layer 141b of the
first portion is groove wick formed on the inner wall of the casing
12, and a second layer 142b is sinter powder wick contacting with
an inner surface of the first layer 141b. A portion of the second
layer 142b is filled in the grooves of the first layer 141b, and
the other portion forms a cylindrical-shaped inner surface. The
assistant wick structure 16 contacts the inner surface of the
second layer 142b of the first portion of the major wick structure.
As shown in FIGS. 6 and 8, the major wick structure has a first
layer 141c being groove wick and a second layer 142c being screen
mesh wick. The second layer 142c is planar shaped in an unfurled
state. Thus, the second layer 142c contacts to the first layer 141c
in part, and is spaced from the grooves of the first layer 141c of
the major wick structure. In FIGS. 7 and 9, the major wick
structure also has a first layer 141d being groove wick and a
second layer 142d being screen mesh wick. The difference of these
two embodiments over the third embodiment of FIG. 5 is that the
second layer 142d is square-wave shaped in an unfurled state. The
second layer 142d is received in the grooves of the first layer
141d. Thus, the second layer 142d forms an inner surface defining a
plurality of recesses (not labeled) along a circumferential
direction of the heat pipe.
[0027] Although, as shown in these embodiments, only the major wick
structure 14 at the evaporator section 121 has various types of
configuration, it is understood that the major wick structure 14 at
the condenser section 122 and the adiabatic section 123 also can
have various types of configuration. In addition, the heat pipe 10
may include more than one assistant wick structure 16. Theses
assistant wick structures 16 may be evenly and tidily attached to
the inner wall of the major wick structure 14 (as shown in FIGS.
8-9) or randomly arranged on the inner wall of the major wick
structure 14. In addition, these assistant wick structures 16 may
be spaced by a distance (as shown in FIG. 9) or intimately contact
with each other (as shown in FIG. 8). In the above embodiments from
FIG. 1 to FIG. 9, the assistant wick structure 16 has a linear
contact with the major wick structure 14.
[0028] It is to be understood, however, that even though numerous
characteristics and advantages of the present invention have been
set forth in the foregoing description, together with details of
the structure and function of the invention, the disclosure is
illustrative only, and changes may be made in detail, especially in
matters of shape, size, and arrangement of parts within the
principles of the invention to the full extent indicated by the
broad general meaning of the terms in which the appended claims are
expressed.
* * * * *