U.S. patent application number 11/164323 was filed with the patent office on 2006-10-05 for heat pipe with sintered powder wick.
Invention is credited to Ching-Tai Cheng, Chu-Wan Hong, Chang-Ting Lo, Jung-Yuan Wu.
Application Number | 20060219391 11/164323 |
Document ID | / |
Family ID | 37068931 |
Filed Date | 2006-10-05 |
United States Patent
Application |
20060219391 |
Kind Code |
A1 |
Hong; Chu-Wan ; et
al. |
October 5, 2006 |
HEAT PIPE WITH SINTERED POWDER WICK
Abstract
A heat pipe (10) includes a casing (12) and a sintered powder
wick (14) arranged at an inner surface of the casing. The sintered
powder wick is in the form of a multi-layer structure in a radial
direction of the casing and at least one layer is divided into
multiple sections in a longitudinal direction of the casing, and
the multiple sections have powder sizes different from each other.
The sections with large-sized powders are capable of reducing the
flow resistance to the condensed liquid to flow back while the
sections with small-sized powders are capable of providing a
satisfactory capillary force for moving the condensed liquid.
Inventors: |
Hong; Chu-Wan; (Shenzhen,
CN) ; Wu; Jung-Yuan; (Shenzhen, CN) ; Lo;
Chang-Ting; (Shenzhen, CN) ; Cheng; Ching-Tai;
(Shenzhen, CN) |
Correspondence
Address: |
NORTH AMERICA INTELLECTUAL PROPERTY CORPORATION
P.O. BOX 506
MERRIFIELD
VA
22116
US
|
Family ID: |
37068931 |
Appl. No.: |
11/164323 |
Filed: |
November 18, 2005 |
Current U.S.
Class: |
165/104.26 ;
165/104.21 |
Current CPC
Class: |
F28D 15/046
20130101 |
Class at
Publication: |
165/104.26 ;
165/104.21 |
International
Class: |
F28D 15/00 20060101
F28D015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 1, 2005 |
TW |
094110523 |
Claims
1. A heat pipe comprising: a casing; and a sintered powder wick
arranged at an inner surface of the casing; wherein the sintered
powder wick is in the form of a multi-layer structure in a radial
direction of the casing and at least one layer is divided into
multiple sections in a longitudinal direction of the casing, and
the multiple sections have powder sizes different from each
other.
2. The heat pipe of claim 1, wherein at least two layers of the
sintered powder wick are divided into multiple sections and the
sections of the two layers are constructed to have identical
lengths.
3. The heat pipe of claim 1, wherein at least two adjacent layers
of the sintered powder wick are divided into multiple sections and
at least two adjacent sections of the two layers in said radial
direction have powder sizes different from each other.
4. The heat pipe of claim 1, wherein at least two layers of the
sintered powder wick are divided into multiple sections and the
sections of the two layers are constructed to have different
lengths.
5. The heat pipe of claim 1, wherein the multiple layers of the
sintered powder wick have different thicknesses.
6. The heat pipe of claim 1, wherein each layer of the sintered
powder wick is divided into multiple sections.
7. The heat pipe of claim 6, wherein the sintered powder wick has a
three-layer structure and each layer is divided into three
sections.
8. The heat pipe of claim 1, wherein the sintered powder wick is
one of a sintered metal powder wick and a sintered ceramic powder
wick.
9. A method for manufacturing a heat pipe comprising steps of: (1)
providing a hollow casing; (2) inserting a mandrel into the casing,
and filling powders into said casing to form a layer of powder
under the control of the mandrel; (3) pre-sintering the layer of
powder at a first temperature and drawing out the mandrel; (4)
repeating the steps of (2) and (3) until at least two layers of
powder are formed inside the casing, wherein in forming one of the
at least two layers of powder, at least two groups of powder with
different powder sizes are used; and (5) sintering said at least
two layers of powder at a second temperature higher than the first
temperature, whereby a sintered powder wick with a multi-layer
structure is formed inside the heat pipe.
10. The method of claim 9, wherein the powders are one of metal
powders and ceramic powders.
11. The method of claim 9, wherein the powders are copper powders
and the first temperature is about 630 degrees Celsius.
12. The method of claim 9, wherein the powders are copper powders
and the second temperature is about 950 degrees Celsius.
13. The method of claim 9, wherein when forming each of the at
least two layers of powder, said at least two groups of powder with
different powder sizes are used.
14. A heat pipe for transmitting heat from one section of the heat
pipe to another section of the heat pipe comprising: a metal hollow
casing having an inner surface; and a sintered powder wick in the
casing and adjacent to the inner surface, the wick comprising a
plurality of layers along a radial direction of the casing and a
plurality of sections along a longitudinal direction of the casing,
wherein two neighboring sections of one of the layers have
different pore sizes.
15. The heat pipe of claim 14, wherein two neighboring sections of
two neighboring layers have different pore sizes.
16. The heat pipe of claim 14, wherein the heat pipe has an
evaporating section and a condensing section, and one of the
sections of the sintered powder wick is located and has a length
corresponding to the evaporating section and another of the
sections of the sintered powder wick is located and has a length
corresponding to the condensing section.
17. The heat pipe of claim 14, wherein the layers have different
thickness.
18. The heat pipe of claim 14, wherein the sections have different
lengths.
19. The heat pipe of claim 17, wherein the sections have different
lengths.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to apparatus for
transfer or dissipation of heat from heat-generating components
such as electronic components, and more particularly to a heat pipe
having a sintered powder wick.
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 "evaporating section") to
another section thereof (typically referring to as "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. Specifically, as 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
towards and carries the heat simultaneously to the condensing
section where the vapor is condensed into liquid 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 condensed liquid is then drawn back by the wick
structure to the evaporating section where it is again available
for evaporation.
[0003] 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 powder
combined to the inner wall of the casing by sintering process.
Among these wicks, the sintered powder wick is preferred to the
other wicks with respect to heat transfer ability and ability
against gravity of the earth.
[0004] In a heat pipe, the primary function of a wick is to draw
the condensed liquid back to the evaporating section of the heat
pipe under the capillary pressure developed by the wick. Thus, the
capillary pressure has become an important parameter to evaluate
the performance of the wick. Since it is well recognized that the
capillary pressure of a wick increases due to a decrease in pore
size of the wick, the sintered powder wick generally has a
capillary pressure larger than that of the other wicks due to its
very dense structure of small particles. In order to obtain a
relatively large capillary pressure for a sintered powder wick,
small-sized powders are often used so as to reduce the pore size
formed between the powders. However, it is not always the best way
to choose a sintered powder wick based on the size of powder,
because the flow resistance to the condensed liquid also increases
due to a decrease in pore size of the wick. The increased flow
resistance significantly reduces the speed of the condensed liquid
in returning back to the evaporating section and ultimately limits
the heat transfer performance of the heat pipe. As a result, a heat
pipe with a wick that has a too large or a too small pore size
often suffers dry-out problem at the evaporating section as the
condensed liquid cannot be timely sent back to the evaporating
section of the heat pipe.
[0005] Therefore, it is desirable to provide a heat pipe with a
sintered powder wick that can provide a satisfactory capillary
force and a reduced flow resistance to the condensed liquid so as
to effectively and timely bring the condensed liquid back to the
evaporating section of the heat pipe and thereby avoid the
undesirable dry-out problem at the evaporating section.
SUMMARY OF INVENTION
[0006] A heat pipe in accordance with a preferred 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 in the form of a multi-layer structure in a radial
direction of the casing and at least one layer is divided into
multiple sections in a longitudinal direction of the casing, and
the multiple sections have powder sizes different from each
other.
[0007] 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, and filling powders into said casing to
form a layer of powder under the control of the mandrel; (3)
pre-sintering the layer of powder at a first temperature and
drawing out the mandrel; (4) repeating the steps of (2) and (3)
until at least two layers of powder are formed inside the casing,
wherein in forming one of the at least two layers of powder, at
least two groups of powder with different powder sizes are used;
and (5) sintering said at least two layers of powder at a second
temperature higher than the first temperature, whereby a sintered
powder wick with a multi-layer structure is formed inside the heat
pipe.
[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 longitudinal 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 a heat pipe
in accordance with a second embodiment of the present
invention;
[0011] FIG. 3 is a longitudinal cross-sectional view of a heat pipe
in accordance with a third embodiment of the present invention;
and
[0012] FIGS. 4A-4C are longitudinal cross-sectional views showing
the steps of a preferred method in manufacturing the heat pipe of
FIG. 1.
DETAILED DESCRIPTION
[0013] FIG. 1 illustrates a heat pipe 10 in accordance with a first
embodiment of the present invention. The heat pipe 10 includes a
casing 12 and a capillary wick 14 arranged at an inner surface of
the casing 12. The casing 12 includes an evaporating section 121
and a condensing section 123 at respective opposite ends thereof,
and a central section 122 located between the evaporating section
121 and the condensing section 123. The casing 12 is typically made
of high thermally conductive materials such as copper or copper
alloys. The wick 14 is saturated with a working fluid (not shown),
which acts as a heat carrier for carrying thermal energy from the
evaporating section 121 toward the condensing section 123 when
undergoing a phase transition from liquid state to vaporous state.
In more detail, heat that needs to be dissipated is transferred
firstly to the evaporating section 121 of the heat pipe 10 to cause
the working fluid saturated in the wick 14 to evaporate. Then, the
heat is carried by the working fluid in the form of vapor to the
condensing section 123 where the heat is released to ambient
environment, thus condensing the vapor into liquid. The condensed
liquid is then brought back, via the wick 14, to the evaporating
section 121 where it is again available for evaporation.
[0014] The capillary wick 14 is a sintered powder wick which is
formed by sintering small-sized powders, such as metal powders
including copper and aluminum, or ceramic powders under high
temperature. Along a radial direction of the casing 12, the wick 14
has a three-layer structure, which includes in sequence an outer
layer 141, an intermediate layer 142 and an inner layer 143. These
layers 141, 142, 143 are stacked together along the radial
direction of the casing 12 with the outer layer 141 being connected
to the inner surface of the casing 12. Furthermore, each layer of
the wick 14 is divided into three sections along a longitudinal
direction of the casing 12. For example, as for the inner layer
143, it includes sequentially a first section 1431, a second
section 1432 and a third section 1433 along the direction from the
evaporating section 121 to the condensing section 123. The three
sections of each layer of the wick 14 have powder sizes different
from one another, and these sections are consistent in length with
the evaporating, central and condensing sections 121, 122, 123 of
the casing 12, respectively. As for the inner layer 143, the first
section 1431 has the largest powder size, whereas the third section
1433 has the smallest powder size. Moreover, every three sections
of the three layers 141, 142, 143 of the wick 14 that correspond to
a single section of the casing 12 in the radial direction thereof
also have powder sizes different from one another. Thus, in this
embodiment, every three consecutive sections of the wick 14,
viewing in either the radial direction or longitudinal direction of
the casing 12, have powder sizes different from each other.
[0015] Since the powder size of the powders of the wick 14 also
determines the pore size formed between the powders, the pore sizes
defined by every three consecutive sections of the wick 14 also
differ from one another. According to the general rule that the
capillary pressure of a wick and its flow resistance to the
condensed liquid increase due to a decrease in pore size of the
wick, the sections that have large powder sizes among every three
consecutive sections, for example, the sections 1431, 1432 of the
inner layer 143, are capable of providing a reduced flow resistance
to the condensed liquid due to having relatively large pore sizes,
thereby reducing the resistance the condensed liquid encounters
when flowing through these sections. However, the other section
that has small powder size among the three consecutive sections,
for example, the section 1433 of the inner layer 143, is still
capable of maintaining a relatively high capillary force for the
wick 14. Thus, the multi-layer and multi-section structure of the
wick 14 is thus capable of simultaneously providing a satisfactory
capillary force and a reduced flow resistance for the condensed
liquid. As the flow resistance to the condensed liquid is reduced,
the condensed liquid is therefore capable of being timely brought
back to the evaporating section 121 of the heat pipe 10,
effectively avoiding the dry-out happening at that section.
[0016] As illustrated in the first embodiment, the three layers
141, 142, 143 of the wick 14 almost have identical thicknesses and
each section of every layer almost exactly covers the corresponding
section of the casing 12 in length. However, some other
configurations may also be suitable for the wick 14 of the heat
pipe 10. For example, according to a second embodiment of the
present invention as illustrated in FIG. 2, a heat pipe 20 is shown
that has a multi-layer sintered powder wick 24 with each layer
having a different thickness, the inner layer 243 being the
thinnest, the intermediate layer 242 being the thickest and the
outer layer 241 having an intermediate thickness therebetween.
Similarly, according to a third embodiment of the present
invention, FIG. 3 illustrates a heat pipe 30 in which the sections
of two adjacent layers of the wick are arranged in a staggered
manner. In other words, the sections of neighboring layers of the
wick are constructed to have different lengths. However, it should
also be recognized that it is not necessary that all of the layers
141, 142, 143 of the wick 14 be in a multi-section configuration.
Some of them may also have a uniform structure, i.e., having a
uniform powder size and therefore a uniform pore size distribution
through their entire lengths.
[0017] The heat pipe 10 as disclosed in the first embodiment can be
made by using the method as illustrated in FIGS. 4A-4C. In order to
form the multi-layer and multi-section wick 14, multiple groups of
powder with different powder sizes are prepared in advance. First
of all, a first mandrel 40a is inserted into the casing 12 with a
space (not labeled) formed between the casing 12 and the first
mandrel 40a. Then, three groups of powder with different powder
sizes from each other are sequentially filled into the space with
the later filled group of powder being stacked on the earlier
filled group of powder along the longitudinal direction of the
casing 12, thereby defining a first layer of powder that is to be
constructed as the outer layer 141 of the wick 14, as shown in FIG.
4A. The first mandrel 40a is used to control the thickness of the
first layer of powder. Thereafter, second and third mandrels 40b,
40c with smaller diameters than that of the first mandrel 40a are
respectively and successively used, as the powders with different
sizes are continued to be filled into the casing 12, to control and
form second and third layers of powder, which are to be
respectively constructed as the intermediate and inner layers 142,
143 of the wick 14, as shown in FIGS. 4B-4C. In order to keep the
powders in place and prevent, after the corresponding mandrel 40a,
40b or 40c is drawn out, the powders from dropping into the hollow
space that is originally occupied by the corresponding mandrel 40a,
40b or 40c, each layer of powder is pre-sintered by heating the
layer of powder with the corresponding mandrel 40a, 40b or 40c and
the casing 12 at a suitable temperature. The suitable temperature
is, for example, about 630 degrees Celsius when the powders are
copper powders. After the pre-sintering, the corresponding mandrel
40a, 40b or 40c used to control the thickness thereof is drawn out
of the casing 12. Finally, after the powders necessary to construct
the wick 14 are all filled into the casing 12 and pre-sintered, the
casing 12 with the powders is subject to heat with a high
temperature, fox example, about 950 degrees Celsius when the
powders are copper powders, to thereby sinter the powders together
whereby the heat pipe 10 with the multi-layer and multi-section
wick 14 arranged along the inner surface of the casing 12 is
obtained. In this method, in order to prevent the later filled
small-sized powders from falling into spaces defined between
particles of the former filled large-sized powders, partitioning
means such as a layer of polymeric bonding agent can be applied
over the interface between every two adjacent groups of powder. The
bonding agent can be decomposed by subsequently applying heat
thereto.
[0018] 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.
* * * * *