U.S. patent application number 11/478392 was filed with the patent office on 2007-04-26 for heat pipe with sintered powder wick.
This patent application is currently assigned to Foxconn Technology Co., Ltd.. Invention is credited to Chuen-Shu Hou, Tay-Jian Liu, Chao-Nien Tung.
Application Number | 20070089860 11/478392 |
Document ID | / |
Family ID | 37984263 |
Filed Date | 2007-04-26 |
United States Patent
Application |
20070089860 |
Kind Code |
A1 |
Hou; Chuen-Shu ; et
al. |
April 26, 2007 |
Heat pipe with sintered powder wick
Abstract
A heat pipe includes a casing and a sintered powder wick
arranged at an inner surface of the casing. The sintered powder
wick is made of spherical metal powder (300), the spherical metal
powder having an apparent density ranging from 3.3 g/cm.sup.3 to
4.8 g/cm.sup.3 to reduce micro pores of the sintered powder wick
and improve ability of heat transfer of the heat pipe.
Inventors: |
Hou; Chuen-Shu; (Tu-Cheng,
TW) ; Liu; Tay-Jian; (Tu-Cheng, TW) ; Tung;
Chao-Nien; (Tu-Cheng, TW) |
Correspondence
Address: |
PCE INDUSTRY, INC.;ATT. CHENG-JU CHIANG JEFFREY T. KNAPP
458 E. LAMBERT ROAD
FULLERTON
CA
92835
US
|
Assignee: |
Foxconn Technology Co.,
Ltd.
Tu-Cheng City
TW
|
Family ID: |
37984263 |
Appl. No.: |
11/478392 |
Filed: |
June 28, 2006 |
Current U.S.
Class: |
165/80.4 ;
165/104.26; 29/890.032 |
Current CPC
Class: |
F28D 15/046 20130101;
Y10T 29/49353 20150115; B22F 1/0011 20130101; B22F 3/1103 20130101;
B22F 2998/00 20130101; B22F 2998/00 20130101; B22F 1/0096
20130101 |
Class at
Publication: |
165/080.4 ;
165/104.26; 029/890.032 |
International
Class: |
F28D 15/04 20070101
F28D015/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 21, 2005 |
TW |
94137042 |
Claims
1. A heat pipe comprising: a casing; working fluid received in the
casing; and a wick structure sintered at an inner surface of the
casing, the wick structure comprising spherical metal powder, the
spherical metal powder having an apparent density ranging from 3.3
g/cm.sup.3 to 4.8 g/cm.sup.3.
2. The heat pipe of claim 1, wherein fine powder acting as an
additive is added to the spherical metal powder to improve the
strength of the wick structure, wherein the fine powder have a
particle size smaller than that of the spherical metal powder.
3. The heat pipe of claim 2, wherein a weight of the fine powder is
1.about.10% of a weight of the metal powder.
4. The heat pipe of claim 1, wherein a particle diameter of the
spherical metal powder ranges from 80 .mu.m to 300 .mu.m.
5. The heat pipe of claim 4, wherein the particle diameter of the
spherical metal powder ranges from 100 .mu.m to 250 .mu.m.
6. The heat pipe of claim 1, wherein a particle diameter of the
spherical metal powder ranges from 30 .mu.m to 300 .mu.m.
7. The heat pipe of claim 1, wherein the spherical metal powder is
made from superfine powder having a particle diameter below 10
.mu.m.
8. A method for manufacturing a heat pipe comprising steps of:
providing a hollow casing; inserting a mandrel into the casing;
filling spherical metal powder into a space between the mandrel and
the inner surface of the casing, wherein an apparent density of the
spherical metal powder ranges from 3.3 g/cm.sup.3 to 4.8
g/cm.sup.3; and conducting sintering process to the casing and the
filled spherical metal powder, whereby a sintered wick structure
made of the spherical metal powder is formed inside the casing.
9. The method for manufacturing a heat pipe as in claim 8, wherein
each of the spherical metal powder consists of superfine powder
having a particle diameter below 10 .mu.m and sintered at
600.about.800 degrees Celsius.
10. The method for manufacturing a heat pipe as in claim 8, wherein
fine powder acting as an addictive supplement is added to the
spherical metal powder to improve the strength of the wick
structure, the fin powder having a particle diameter smaller than
that of the spherical metal powder.
11. The method for manufacturing a heat pipe as in claim 10,
wherein a weight of the fine powder is 1.about.10% of a weight of
the metal powder.
12. The method for manufacturing a heat pipe as in claim 8, wherein
a particle diameter of the spherical metal powder ranges from 80
.mu.m to 300 .mu.m.
13. The method for manufacturing a heat pipe as in claim 8, wherein
the particle diameter of the spherical metal powder ranges from 100
.mu.m to 250 .mu.m.
14. The method for manufacturing a heat pipe as in claim 8, wherein
a particle diameter of the spherical metal powder ranges from 30
.mu.m to 300 .mu.m.
15. The method for manufacturing a heat pipe as claim 8, wherein
the spherical metal powder is made from superfine powder having a
particle diameter below 10 .mu.m.
Description
BACKGROUND
[0001] 1. Field
[0002] The present invention relates generally to heat pipes as
heat transfer/dissipating device, and more particularly to a heat
pipe with a sintered powder wick.
[0003] 2. Description of related art
[0004] Heat pipes have excellent heat transfer properties and
therefore are an effective means for transfer or dissipation of
heat from heat sources. Heat pipes are widely used for removing
heat from heat-generating components such as computer central
processing units (CPUs). A heat pipe is usually a vacuum tube
containing a working fluid therein, which is employed to carry
thermal energy from one section of the heat pipe (typically
referred to as the "evaporating section") to another section
thereof (typically referred to as the "condensing section") via
phase transitions between a liquid state and a vapor state of the
working fluid. The tube is made of a highly thermally conductive
material such as copper or aluminum. Preferably, a wick structure
is provided inside the heat pipe, lining an inner wall of the tube,
for drawing the working fluid back to the evaporating section after
it has condensed in the condensing section. Specifically, as the
evaporating section of the heat pipe is maintained in thermal
contact with a heat-generating component, the working fluid
contained in the evaporating section can absorb heat generated by
the heat-generating component and turn into vapor. Due to the
difference in vapor pressure between the two sections of the heat
pipe, the vapor moves towards the condensing section where the
vapor is condensed into liquid, releasing the heat into ambient
environment in the process; the heat is then dispersed by, for
example, fins thermally contacting the condensing section. Due to
the difference of capillary pressure in the wick structure between
the two sections, the condensed liquid is then drawn back by the
wick structure to the evaporating section where it is again
available for evaporation.
[0005] FIG. 3 illustrates a wick structure in accordance with
related art, provided for a heat pipe and mainly composed of water
atomized irregular copper powder 100 with low apparent density. The
powder 100 has irregular shape particle and the apparent density
ranges from 2.5 g/cm.sup.3 to 3.3 g/cm.sup.3, thereby forming a
plurality of micro pores 110 in the powder. Capillary pressure is
related to interfacial tension, pore size and contact angle by the
following equation: (Pc)=(2.times..sigma..times.cos .theta.)/r
where [0006] Pc=capillary pressure; [0007] s=interfacial tension;
[0008] r=radius of pore; [0009] .theta.=contact angle.
[0010] It can be seen from the above equation that the smaller the
effective pores 110 sizes the higher the capillary pressure. A flow
resistance to working liquid also increases due to a decrease in
pores 110 sizes of the wick structure. The working fluid and
non-condensation gas in the heat pipe is prone to adhere into the
pores 110 having higher capillary pressure and is prevented flowing
out of the pores 110 of the wick structure, thereby causing a lack
of the working fluid available for heat transfer and reducing the
heat transfer performance of the heat pipe. Therefore, the powder
100 is often sintered at a predetermined temperature to eliminate
the micro pores 110 of the wick structure. FIG. 4 shows a
microstructure of a wick structure formed by sintering the powder
particles 100 having a relatively high green density and sintered
at a relatively low temperature. FIG. 5 shows a microstructure of a
wick structure formed by sintering the powder particles 100 having
a relatively low green density and sintered at a relatively high
temperature. Compared with the FIG. 5, most of the micro pores 110
of the FIG. 4 is not eliminated. The micro pores 110 can be
eliminated only at the relatively high temperature (see FIG. 5).
However, when the conventional water atomized irregular copper
powder 100 is sintered at the high temperature, not only the number
of the micro pores 110 is reduced but also a total porosity of the
sintered wick structure is reduced. The reduction of the total
porosity of the sintered structure adversely affects the
performance of the heat pipe.
[0011] Therefore, there is a need for a heat pipe with a sintered
powder wick which can solve the above problems.
SUMMARY OF THE INVENTION
[0012] A heat pipe in accordance with an embodiment of the present
invention includes a casing and a sintered powder wick arranged at
an inner surface of the casing. The sintered powder wick is made of
spherical metal powder, the spherical metal powder having an
apparent density ranging from 3.3 g/cm.sup.3 to 4.8 g/cm.sup.3 to
reduce micro pores of the sintered powder wick and improve ability
of heat transfer of the heat pipe.
[0013] The present invention in another aspect, relates to a method
for manufacturing a sintered heat pipe. The preferred method
includes steps of (1) providing a hollow casing; (2) inserting a
mandrel into the casing; (3) filling spherical metal powder into a
space between the mandrel and the inner surface of the casing,
wherein an apparent density of the spherical metal powder ranges
from 3.3 g/cm.sup.3 to 4.8 g/cm.sup.3; and (4) conducting sintering
process to the casing and the filled spherical metal powder,
whereby a sintered wick structure made of the spherical metal
powder is formed inside the casing.
[0014] Other advantages and novel features of the present invention
will become more apparent from the following detailed description
of the embodiment when taken in conjunction with the accompanying
drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Many aspects of the present device 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 device. Moreover, in the drawings, like reference numerals
designate corresponding parts throughout the several views.
[0016] FIG. 1 is a microstructure of powder particles of a heat
pipe in accordance with a preferred embodiment of the present
invention;
[0017] FIG. 2 is a graph of a permeation rate distribution of
different types of powder, wherein the permeation rate is changed
with time;
[0018] FIG. 3 is a scanning electron micrograph of a wick structure
formed by sintering a water atomized irregular copper powder;
[0019] FIG. 4 is a scanning electron micrograph of a wick structure
formed by sintering the water atomized irregular copper powder
having a relatively high green density and sintered at a relatively
low temperature; and
[0020] FIG. 5 a scanning electron micrograph of a wick structure
formed by sintering the water atomized irregular copper powder
having a relatively low green density and sintered at a relatively
high temperature.
DETAILED DESCRIPTION OF THE INVENTION
[0021] A heat pipe in accordance with an embodiment of the present
invention includes a casing, a sintered powder wick structure
arranged at an inner surface of the casing and working fluid filled
with the casing. A method of manufacturing the heat pipe comprises
following steps: (1) inserting a mandrel into the casing; (2)
filling spherical metal powder 300 such as copper or aluminum
powder into a space between the mandrel and the inner surface of
the casing, wherein an apparent density of the spherical metal
powder 300 ranges from 3.3 g/cm.sup.3 to 4.8 g/cm.sup.3; (3)
heating the filled spherical metal powder 300 together with the
casing at a high temperature, whereby the filled spherical metal
powder 300 is sintered and diffusion bonded to the inner surface of
the casing and particles of the powder after the sintering have
approximately the same diameters to enhance the performance of the
heat pipe.
[0022] In this embodiment, the spherical metal powder 300 having
high apparent density is manufactured by mechanical method, such as
cutting, crushing, chipping, etc. Particle diameter of the
spherical metal powder 300 ranges from 80 .mu.m to 300 .mu.m,
wherein 100 .mu.m.about.250 .mu.m is preferable. Fine powder having
a diameter smaller than that of the spherical metal powder and
acting as an additive is added to the spherical metal powder 300 to
improve the sintering strength of the wick structure. The fine
powder has a weight which is 1.about.10% of a weight of the metal
powder 300.
[0023] FIG. 1 shows, in an enlarged scale, a structure of particles
of the spherical metal powder 300 formed in accordance with an
alternative method of the present invention, rather than the
afore-mentioned mechanical method such as cutting, crushing,
chipping, etc. According to this alternative method, each particle
of the spherical metal powder 300 consists of superfine powder 200
having a particle diameter below 10 .mu.m. The superfine powder 200
is processed by controlling parameters of a pressure granulator or
centrifugal granulator, to thereby obtain the spherical metal
powder 300 with high consistency. A particle diameter of the
spherical metal powder 300 formed according to this method ranges
from 30 .mu.m to 300 .mu.m. The super fine powder 200 is
pre-sintered at a suitable temperature, for example, about
600.about.800 degrees Celsius, whereby densification temperature of
the spherical metal powder 300 is dropped significantly. At the
same time, number of micro pores in the spherical metal powder 300
is reduced and flowability of the spherical metal powder 300 is
increased to prevent a bridging effect of the spherical metal
powder 300 during the filling of the spherical metal powder 300
into the casing.
[0024] FIG. 2 shows a permeation rate distribution of three
different types of powder with a porosity of 47%. The three
different types of powder comprises the spherical metal powder 300,
water atomized irregular copper powder and penniform electrolyte
power. It is obviousness that the spherical metal powder 300 has a
superior permeation rate to another two types of powder.
[0025] The present invention provides the spherical metal powder
300 for forming the sintered wick structure of the heat pipe having
various advantages over the heat pipe having water atomized
irregular copper powder in accordance with the related art. For
example, one advantage is capable of improving ability of heat
transfer by using of the spherical metal powder 300 having high
apparent density. Another advantage is to reduce micro pores of the
spherical metal powder 300 by pre-sintered processing. In addition,
the flowability of the spherical metal powder 300 is better than
the water atomized irregular copper powder 100.
[0026] 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.
* * * * *