U.S. patent application number 11/306422 was filed with the patent office on 2007-01-11 for flat type heat pipe.
Invention is credited to Ching-Bai Hwang, Jin-Gong Meng.
Application Number | 20070006993 11/306422 |
Document ID | / |
Family ID | 37597270 |
Filed Date | 2007-01-11 |
United States Patent
Application |
20070006993 |
Kind Code |
A1 |
Meng; Jin-Gong ; et
al. |
January 11, 2007 |
FLAT TYPE HEAT PIPE
Abstract
A flat type heat pipe (10) is disclosed which includes a metal
casing (12) and a wick structure (16) arranged inside the metal
casing. The metal casing has an evaporating section (123) and a
condensing section (124). The wick structure extends from the
evaporating section towards the condensing section of the metal
casing and has a first section in conformity with the condensing
section of the metal casing and a second section in conformity with
the evaporating section of the metal casing. The first section has
a pore size larger than that of the second section of the wick
structure. The wick structure includes a metal foam.
Inventors: |
Meng; Jin-Gong; (Shenzhen,
CN) ; Hwang; Ching-Bai; (Shenzhen, CN) |
Correspondence
Address: |
NORTH AMERICA INTELLECTUAL PROPERTY CORPORATION
P.O. BOX 506
MERRIFIELD
VA
22116
US
|
Family ID: |
37597270 |
Appl. No.: |
11/306422 |
Filed: |
December 28, 2005 |
Current U.S.
Class: |
165/104.26 ;
257/E23.088 |
Current CPC
Class: |
F28D 15/046 20130101;
H01L 2924/00 20130101; H01L 2924/0002 20130101; F28D 15/0233
20130101; H01L 2924/0002 20130101; H01L 23/427 20130101 |
Class at
Publication: |
165/104.26 |
International
Class: |
F28D 15/04 20060101
F28D015/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 8, 2005 |
CN |
200510035938.8 |
Claims
1. A flat type heat pipe comprising: a metal casing having an
evaporating section and a condensing section; and a wick structure
made of a metal foam and arranged inside the metal casing, the wick
structure extending from the evaporating section towards the
condensing section of the metal casing and having a pore size
gradually increasing from the evaporating section towards the
condensing section of the metal casing.
2. The heat pipe of claim 1, wherein the wick structure extends
along a longitudinal direction of the heat pipe and occupies a
central region of an interior chamber defined in the metal
casing.
3. The heat pipe of claim 1, wherein the wick structure extends
along a longitudinal direction of the heat pipe and is located near
a sidewall of the metal casing.
4. The heat pipe of claim 1, wherein the metal casing defines a
plurality of grooves in an inner surface thereof.
5. The heat pipe of claim 4, wherein the grooves extend along a
longitudinal direction of the metal casing and at least one of the
grooves have a width gradually increasing from the evaporating
section towards the condensing section of the metal casing.
6. A flat type heat pipe comprising: a metal casing including a top
plate and a bottom plate cooperating with the top plate to define a
chamber inside the metal casing, the metal casing having an
evaporating section and a condensing section; and a wick structure
located inside the casing and occupying a portion of the chamber,
the wick structure having a first section in conformity with the
condensing section of the metal casing and a second section in
conformity with the evaporating section of the metal casing;
wherein the wick structure is sandwiched between the top and bottom
plates of the metal casing and said first section has a pore size
larger than that of the second section of the wick structure.
7. The heat pipe of claim 6, wherein the wick structure is in the
form of a metal foam.
8. The heat pipe of claim 6, wherein the metal casing has a
plurality of grooves formed in an inner surface thereof.
9. The heat pipe of claim 8, wherein the grooves each have a width
gradually increasing from the evaporating section towards the
condensing section of the metal casing.
10. The heat pipe of claim 6, wherein the wick structure occupies a
central portion of the chamber.
11. The heat pipe of claim 6, wherein the wick structure occupies a
side portion of the chamber.
12. A heat pipe, comprising: an elongated casing having a flat
plate, a plurality of grooves formed in an inner surface of the
casing along a longitudinal direction thereof; and a metal foam
received in the casing and extending along the longitudinal
direction thereof, the metal foam having a pore size which is
gradually increased along the longitudinal direction of the casing,
wherein the grooves and the metal foam cooperate as a wick
structure for the heat pipe for moving a condensate in the heat
pipe.
13. The heat pipe of claim 12, wherein at least one of the grooves
has a width which is gradually increased along the longitudinal
direction of the casing.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to an apparatus for
transfer or dissipation of heat from heat-generating components,
and more particularly to a flat type heat pipe applicable in
electronic products such as personal computers for removing heat
from electronic components installed therein.
DESCRIPTION OF RELATED ART
[0002] Heat pipes have excellent heat transfer performance due to
their low thermal resistance, and therefore are 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. A
heat pipe is usually a vacuum casing containing therein a working
fluid, which is employed to carry, under phase transitions between
liquid state and vapor state, thermal energy from one section of
the heat pipe (typically referring to as the "evaporating section")
to another section thereof (typically referring to as the
"condensing section"). Preferably, a wick structure is provided
inside the heat pipe, lining an inner wall of the casing, for
drawing the working fluid back to the evaporating section after it
is condensed at the condensing section. The wick structure
currently available for heat pipes includes fine grooves integrally
formed at the inner wall of the casing, screen mesh or bundles of
fiber inserted into the casing and held against the inner wall
thereof, or sintered powders combined to the inner wall of the
casing by sintering process.
[0003] In operation, the evaporating section of the heat pipe is
maintained in thermal contact with a heat-generating component. The
working fluid contained at the evaporating section absorbs heat
generated by the heat-generating component and then turns into
vapor. Due to the difference of vapor pressure between the two
sections of the heat pipe, the generated vapor moves and carries
the heat simultaneously towards the condensing section where the
vapor is condensed into condensate after releasing the heat into
ambient environment by, for example, fins thermally contacting the
condensing section. Due to the difference of capillary pressure
developed by the wick structure between the two sections, the
condensate is then brought back by the wick structure to the
evaporating section where it is again available for
evaporation.
[0004] 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. Also, the wick structure is expected to provide a
high permeability at the condensing section of the heat pipe in
order for the condensate resulting from the vapor in that section
to enter into the wick structure more easily. However, the wick
structure provided in the conventional heat pipe generally has a
uniform pore size distribution over its entire length. This
uniform-type wick structure cannot satisfy these requirements. If
the condensate is not timely brought back from the condensing
section, the heat pipe will suffer a dry-out problem at the
evaporating section.
[0005] Therefore, it is desirable to provide a heat pipe with a
wick structure which can draw the condensate back from its
condensing section to its evaporating section effectively and
timely.
SUMMARY OF INVENTION
[0006] The present invention relates to a flat type heat pipe. The
heat pipe includes a metal casing and a wick structure arranged
inside the metal casing. The metal casing has an evaporating
section and a condensing section. The wick structure extends from
the evaporating section towards the condensing section of the metal
casing and has a first section in conformity with the condensing
section of the metal casing and a second section in conformity with
the evaporating section of the metal casing. The first section has
a pore size larger than that of the second section of the wick
structure.
[0007] In the heat pipe, the first section of the wick structure
generates a relatively low resistance for the condensate as it
flows in the condensing section, and the second section of the wick
structure is still capable of maintaining a relatively high
capillary force for drawing the condensate back from the condensing
section towards the evaporating section. Meanwhile, the condensate
in the condensing section is capable of entering into the wick
structure easily due to a relatively high permeability of the first
section of the wick structure. As a result, the condensate is drawn
back to the evaporating section rapidly and timely, thus preventing
the potential dry-out problem occurring at the evaporating
section.
[0008] 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 DRAWINGS
[0009] FIG. 1 is a transverse cross-sectional view of a heat pipe
in accordance with a first embodiment of the present invention;
[0010] FIG. 2 is a longitudinal cross-sectional view of the heat
pipe of FIG. 1, taken along line II-II thereof;
[0011] FIG. 3 is a transverse cross-sectional view of a heat pipe
in accordance with a second embodiment of the present
invention;
[0012] FIG. 4 is a plan view of a portion of a metal casing of the
heat pipe of FIG. 3, showing an interior of the metal casing;
and
[0013] FIG. 5 is a transverse cross-sectional view of a heat pipe
in accordance with a third embodiment of the present invention.
DETAILED DESCRIPTION
[0014] FIG. 1 illustrates a flat type heat pipe 10 in accordance
with a first embodiment of the present invention. The heat pipe 10
has a plate-type configuration and includes a metal casing 12. The
metal casing 12 includes a top plate 121 and a bottom plate 122
cooperating with the top plate 121 to define a chamber 14 in the
metal casing 12. A wick structure 16 is provided inside the heat
pipe 10, occupying a central region of the chamber 14. The wick
structure 16 is so dimensioned as to fit between the top and bottom
plates 121, 122 of the metal casing 12. The metal casing 12 is made
of high thermally conductive material such as copper or aluminum.
The heat pipe 10 is evacuated and hermetically sealed after a
working fluid (not shown) is injected into the chamber 14 of the
metal casing 12. The working fluid is saturated in the wick
structure 16 and is usually selected from a liquid such as water or
alcohol, which has a low boiling point and is compatible with the
wick structure 16. The wick structure 16 is a porous structure and
is in the form of a metal foam.
[0015] As shown in FIG. 2, the metal casing 12 has an evaporating
section 123 and an opposing condensing section 124 along a
longitudinal direction of the heat pipe 10. The evaporating and
condensing sections 123, 124 occupy two end portions of the heat
pipe 10, respectively. Although it is not shown in the drawings, it
is well known by those skilled in the art that two ends of the heat
pipe 10 are sealed. The wick structure 16 extends in the
longitudinal direction of the heat pipe 10 and has a pore size that
gradually increases from the evaporating section 123 towards the
condensing section 124.
[0016] In operation, the evaporating section 123 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 fluid contained in the evaporating
section 123 of the heat pipe 10 evaporates into vapor upon
receiving the heat generated by the heat source. Then, the
generated vapor moves, via the other region of the chamber 14
without being occupied by the wick structure 16, towards the
condensing section 124 of the heat pipe 10. After the vapor
releases the heat carried thereby and turns into condensate in the
condensing section 124, the condensate is brought back by the wick
structure 16 to the evaporating section 123 of the heat pipe 10 for
being available again for evaporation.
[0017] In the present heat pipe 10, the capillary forces and the
flow resistances generated by different sections of the wick
structure 16 are different. The general rule is that the larger a
pore size a wick structure has, the smaller a capillary force and
the lower a flow resistance it provides. A first section of the
wick structure 16 in conformity with the condensing section 124 of
the heat pipe 10 has a pore size larger than that of a second
section of the wick structure 16 in conformity with the evaporating
section 123 of the heat pipe 10. Thus, the first section of the
wick structure 16 generates a relatively low resistance for the
condensate as it flows in the condensing section 124, and the
second section of the wick structure 16 is still capable of
maintaining a relatively high capillary force for drawing the
condensate back from the condensing section 124 towards the
evaporating section 123. Meanwhile, the condensate resulting from
the vapor in the condensing section 124 is capable of entering into
the wick structure 16 easily due to a relatively high permeability
of the first section of the wick structure 16. As a result, the
condensate is drawn back to the evaporating section 123 rapidly and
timely, thus preventing a potential dry-out problem occurring at
the evaporating section 123.
[0018] The metal foam used to form the wick structure 16 may be
made of such materials as stainless steel, copper, copper alloy,
aluminum alloy and silver. The wick structure 16 may be formed
independently of the metal casing 12 and then inserted into the
metal casing 12. Typically, the metal foam of the wick structure 16
is fabricated by expanding and solidifying a pool of liquid metal
saturated with an inert gas under pressure. The porosity of the
foam after solidification may be in a wide range, subject to the
levels of pressure applied during the fabrication process.
Electroforming is another typical method for fabricating the metal
foam, which generally involves steps of providing one kind of
porous material such as polyurethane foam, then electrodepositing a
layer of metal over the surface of the polyurethane foam and
finally heating the resulting product at a high temperature to get
rid of the polyurethane foam to thereby obtain the porous metal
foam. Still another fabrication method for the metal foam, called
die-casting process, is also widely used, which generally includes
steps of providing one kind of porous material such as polyurethane
foam, filling ceramic slurry into the pores of the porous
polyurethane foam and then solidifying the ceramic slurry therein,
then heating the resulting product at a high temperature to get rid
of the polyurethane foam to obtain a matrix of porous ceramic,
thereafter filling metal slurry into the pores of the ceramic
matrix and finally getting rid of the ceramic material after
solidification of the metal slurry to thereby obtain the porous
metal foam. However, there are still some other methods suitable
for fabrication of the metal foam. Fox example, the metal foam can
be made by steps of filling a kind of bubble-generating material
such as metallic hydride into metal slurry to generate a large
number of bubbles distributing randomly throughout the metal slurry
and solidifying the metal slurry to thereby obtain the metal foam
with a plurality of pores therein.
[0019] FIG. 3 illustrates a flat type heat pipe 20 in accordance
with a second embodiment of the present invention. In addition to
the wick structure 16 that is in the form of a metal foam, the heat
pipe 20 also includes a plurality of fine grooves 201
longitudinally defined in an inner surface of the casing 22. These
grooves 201 altogether function as another wick structure
cooperating with the original wick structure 16 so as to obtain a
higher capillary force inside the heat pipe 20. Furthermore, each
of the grooves 201 may have a varying width throughout the heat
pipe 20. As particularly shown in FIG. 4, each groove 201 has a
width gradually increasing from the evaporating section 223 towards
the condensing section 224 of the heat pipe 20. This particular
design of the grooves 201 can reduce flow resistance to the
condensate as it flows in the condensing section 224 of the heat
pipe 20.
[0020] FIG. 5 illustrates a flat type heat pipe 30 in accordance
with a third embodiment of the present invention. In this
embodiment, two wick structures 16 are arranged inside the heat
pipe 30 with each being located near a sidewall of the heat pipe
30. Thus, the central region of the chamber of the heat pipe 30
functions as a vapor channel for passage of vapor generated inside
the heat pipe 30 from the evaporating section to the condensing
section.
[0021] 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.
* * * * *