U.S. patent application number 11/306061 was filed with the patent office on 2006-09-07 for method of manufacturing wick structure for heat pipe.
Invention is credited to Ching-Tai Cheng, Chu-Wan Hong, Chang-Ting Lo, Jung-Yuan Wu.
Application Number | 20060198753 11/306061 |
Document ID | / |
Family ID | 36944288 |
Filed Date | 2006-09-07 |
United States Patent
Application |
20060198753 |
Kind Code |
A1 |
Hong; Chu-Wan ; et
al. |
September 7, 2006 |
METHOD OF MANUFACTURING WICK STRUCTURE FOR HEAT PIPE
Abstract
A method is disclosed to produce a wick structure for a heat
pipe. The wick structure is a sintered powder wick and is produced
by sintering process. A group of powders is firstly provided. The
group of powders is then classified into many sub-groups in terms
of powder size. At least one sub-group of the powders is selected
to form the wick structure via the sintering process. Thus, the
powders used to construct the wick structure are confined to
powders having a relatively narrower range of powder size in
relative to the group of powders as originally provided. This has
greatly reduced the complexity involved in the sintering process,
and as a result, the required sintering temperature and the
required time for the sintering process are easier to be
determined.
Inventors: |
Hong; Chu-Wan; (Shenzhen,
CN) ; Lo; Chang-Ting; (Shenzhen, CN) ; Cheng;
Ching-Tai; (Shenzhen, CN) ; Wu; Jung-Yuan;
(Shenzhen, CN) |
Correspondence
Address: |
NORTH AMERICA INTELLECTUAL PROPERTY CORPORATION
P.O. BOX 506
MERRIFIELD
VA
22116
US
|
Family ID: |
36944288 |
Appl. No.: |
11/306061 |
Filed: |
December 15, 2005 |
Current U.S.
Class: |
419/23 |
Current CPC
Class: |
B22F 3/1103 20130101;
B22F 1/0014 20130101; B22F 3/1035 20130101; F28D 15/046
20130101 |
Class at
Publication: |
419/023 |
International
Class: |
B22F 5/00 20060101
B22F005/00; B22F 3/10 20060101 B22F003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 4, 2005 |
TW |
094106550 |
Claims
1. A method of manufacturing a wick structure for a heat pipe
comprising steps of: providing a group of powders; classifying the
powders into multiple sub-groups in terms of powder size, the
sub-groups having powder sizes different from each other; selecting
at least one sub-group of the powders; and sintering the selected
powders to form said wick structure.
2. The method of claim 1, wherein the powders as provided are one
of copper powders, nickel powders, stainless steel powders and
ceramic powders.
3. The method of claim 1, wherein the powders as provided are
classified into the multiple sub-groups by passing through a series
of screens.
4. The method of claim 1, wherein, when more than one sub-groups of
the powders are selected, the selected sub-groups of the powders
are mixed in a prescribed ratio by weight.
5. A method of manufacturing a wick structure for a heat pipe
comprising steps of: providing multiple groups of powders with each
group having an average powder size different from that of each of
the other groups; selecting at least one group of powders from said
multiple groups; and sintering the selected powders to form said
wick structure.
6. The method of claim 5, further comprising a step of mixing the
selected powders in a prescribed proportion by weight before
sintering.
7. The method of claim 6, wherein the multiple groups of powders
are obtained by classification from an original group of powders
having the multiple groups of powders.
8. The method of claim 7, wherein the original group of powders is
classified into the multiple groups of powders by passing through a
series of screens.
9. The method of claim 7, wherein the powders are ceramic
powders.
10. The method of claim 7, wherein the powders are one of copper
powders, nickel powders and stainless steel powders.
11. A method for forming a wick structure for a heat pipe,
comprising: preparing a group of powders; separating the group of
powders into a plurality of sub-groups of powders according to a
size distribution of the powders, the sub-groups occupying
different regions of the size distribution, respectively; selecting
at least one of the sub-groups of powders and filling the selected
powders into a casing of the heat pipe; and heating the casing and
the selected powders to sinter the selected powders in the casing
to thereby obtain the wick structure in the casing of the heat
pipe.
12. The method of claim 11, wherein two sub-groups of powders are
selected, size ranges of the selected two sub-groups of powders are
at discontinuous regions of the size distribution of the
powders.
13. The method of claim 11, wherein the size distribution is a
normal distribution, and one sub-group of powders is selected which
includes a median of the normal distribution.
14. The method of claim 12, wherein a heating temperature and
period of time for the heating step are selected to melt the
selected powders of one of the two sub-groups substantially
entirely, which have a smaller powder size than the selected
powders of the other of the two sub-groups.
15. The method of claim 12, wherein one of the two sub-groups,
which has a smaller powder size has a weight less than that of the
other of the two sub-groups, which has a larger powder size.
16. The method of claim 15, wherein the other of the two
sub-groups, which has the larger powder size has a weight which is
five to twenty times of that of the one of the two sub-groups,
which has the smaller powder size.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to an apparatus for
transfer or dissipation of heat from heat-generating components
such as electronic components, and more particularly to a method of
manufacturing a wick structure for a heat pipe.
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"). The casing is made of high thermally
conductive material such as copper or aluminum. 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 powders
combined to the inner wall 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] Currently, a conventional method for making a sintered
powder wick includes filling a group of metal powders necessary to
construct the wick into a hollow casing which has a closed end and
an open end. A mandrel has been inserted into the casing through
the open end of the casing; the mandrel functions to hold the
filled powders against an inner wall of the casing. Then, the
casing with the powders is sintered at high temperature for a
specified time period to cause the powders to diffusion bond
together to form the wick. In the method, it requires a sintering
temperature (or temperature range) suitable for the sintering
process.
[0005] The group of powders to be formed as the wick can be
obtained by well-known method such as mechanical grinding.
Generally, the powders thus obtained are a mixture of powders with
different sizes due to a tolerance in producing the powders. That
is, the powders generally have a wide range of powder sizes. In
addition, the proportion between these different sized powders is
unknown before the sintering process. As a result, it is difficult
to determine the sintering temperature required by the sintering
process and how long the sintering process should take. The general
rule is that a lower sintering temperature and a shorter period of
time are required to sinter and interconnect the small-sized
powders in relative to the large-sized powders. If the sintering
temperature is much too lower or the time to carry out the
sintering process is much shorter than it should be, the powders as
applied to form the wick cannot be effectively diffusion bonded
together. To the contrary, if the sintering temperature is much too
higher or the time is much longer than what is indeed required, the
powders with relatively small sizes are apt to be overheated and
melt. When the powders with relatively small sizes have a large
proportion in the group of powders, the wick accordingly formed
will shrink significantly into a compact, high-density structure,
noticeably reducing the pore size of the wick and causing the pores
formed in the wick to be disconnected. The disconnected pores in
the wick cannot provide a continuous passageway for the condensed
liquid to return back along the wick.
[0006] Therefore, it is desirable to provide a method of
manufacturing a sintered powder wick by a sintering process. In the
method, both the required sintering temperature and the required
time for the sintering process can be easily determined and
controlled.
SUMMARY OF INVENTION
[0007] The present invention relates to a method of manufacturing a
wick structure applicable in a heat pipe. A preferred method
includes the following steps: (1) providing a group of powders; (2)
classifying the powders into multiple sub-groups in terms of powder
size, the sub-groups having powder sizes different from each other;
(3) selecting at least one sub-group of the powders; and (4)
sintering the selected powders to form the wick structure.
[0008] In the method, if the selected powders are consisted of more
than one sub-groups, these sub-groups are preferably mixed in a
prescribed proportion by weight. Thus, the powders used to form the
wick structure are confined to a relatively narrow range of powder
sizes, and before sintering, the proportion between these
sub-groups is already known. It is therefore easier to determine
both the required sintering temperature and the required time for
the sintering process.
[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 DRAWINGS
[0010] FIG. 1 is a flow chart of a preferred method in accordance
with the present invention, for manufacturing a wick structure
applicable in a heat pipe;
[0011] FIG. 2 is a graph of the powder size distribution of a group
of powders as provided by the method of FIG. 1;
[0012] FIGS. 3-5 are schematic diagrams of one example of the
present invention, showing in different stages of two sub-groups of
the powders in forming the wick structure by using the method of
FIG. 1; and
[0013] FIGS. 6-7 are schematic diagrams of another example of the
present invention, showing in different stages of one sub-group of
the powders in forming the wick structure by using the method of
FIG. 1.
DETAILED DESCRIPTION
[0014] FIG. 1 shows a preferred method in accordance with the
present invention for producing a porous wick structure that can be
suitably applied to heat pipes or other heat transfer devices such
as vapor chamber-based heat spreaders. The wick structure is
constructed from small-sized powders and a sintering process is
required to form the wick structure. Firstly, a group of powders is
provided, for example, by mechanical grinding a metal stock.
Typically, the powders thus obtained are consisted of powders with
various different sizes. The sizes of the powders may in fact range
widely, for example, from several to hundreds of micrometers, based
on the extent of preciseness and tolerance involved in the
production of the powders. Thus, the powders as thus originally
obtained are not suitable for being immediately used to construct
the wick structure since it has a wide range of powder size and
will raise uncertainty to the determination of the sintering
temperature and time required by the sintering process. Thus, in
this method, the powders are then classified into many sub-groups
based on their powder sizes with each sub-group has a relatively
narrow range powder sizes, as will be discussed in more details
later. For easier understanding, in this embodiment, the powders
used to construct the wick as originally obtained are presumed to
have powder sizes ranging from 20 to 400 mesh. The "mesh" used
herein represents the number of openings defined in per unit area
of a standard screen. Standard screens are well known apparatus
widely used to classify objects (such as powders or the like) based
on their sizes. If a standard screen is used to classify powders,
the number of openings in per unit area of the standard screen is
usually used to indicate the powder size of the powders that pass
through the standard screen. In this regard, it can be inferred
that the powders having a powder size of 20 mesh are larger than
those having a powder size of 400 mesh. For illustrative purpose,
the powder size distribution of the powders illustrated in FIG. 2
is generally in the form of a normal distribution.
[0015] Since the powders as originally obtained are generally not
immediately suitable for the sintering process, the powders
subsequently are divided into multiple sub-groups in terms of
powder size. The aforementioned standard screens will serve the
purpose of the classification job. Specifically, the powders are
brought to pass through a series of standard screens that have
different meshes (i.e., openings) in per unit area thereof. For
example, if the powders are brought to sequentially pass through a
series of standard screens that have 200, 140, 100, and 40 meshes
respectively in per unit area thereof, the powders will be
classified five sub-groups, i.e., the sub-group A having a powder
size of 200-220 mesh, the sub-group B having a powder size of
140-200 mesh, the sub-group C having a powder size of 100-140 mesh,
the sub-group D having a powder size of 40-100 mesh and the
sub-group E having a powder size of 20-40 mesh, as shown in FIG. 2.
In this figure, the X-coordinate represents the powder size of the
five sub-groups of the powders and the Y-coordinate represents the
powder distribution (by weight) of each sub-group of the powders.
It can be seen from this figure that a majority of the powders has
a powder size of 100-140 mesh.
[0016] After the original group of powders is divided into these
sub-groups, at least one sub-group of the powders is selected to
form the wick structure. Selecting which group or groups of the
powder to form the wick, however, is mainly based on what kind of
characteristic the wick structure is intended to have. For example,
if the wick structure to be formed is intended to have a large
capillary force, sub-groups A-C with small-sized powders are
generally preferred. To the contrary, if the wick structure to be
formed is intended to have a large permeability, then sub-groups
C-E with large-sized powders are helpful. If multiple sub-groups of
powders are selected, they should be mixed in certain proportions
by weight, respectively. Finally, the selected sub-groups of
powders are thoroughly mixed and sintered at a required temperature
for a required period of time to form the intended wick
structure.
[0017] An example of forming a wick structure in a heat pipe by
selecting the powders of sub-groups B and D is illustrated in FIGS.
3-5. The powders 10 of sub-group D and the powders 20 of sub-group
B are preferably mixed in a ratio by weight of 5:1 to 20:1. When
the two sub-groups B and D are mixed, the small-sized powders 20
are nested in the spaces (not labeled) formed between the
large-sized powders 10, as illustrated in FIG. 3. Although it is
not shown in the drawings, it is well known by those skilled in the
art that the powders 10, 20 after mixed are then filled into a
casing of the heat pipe and a mandrel is typically used to hold the
powders 10, 20 against an inner wall of the casing. The casing is
then placed into an oven and the powders 10, 20 are subsequently
sintered. Before the sintering process, the powder sizes of the
selected powders (i.e., sub-groups B and D) and the proportion
between them by weight are already known. Furthermore, the powders
used to construct the wick structure are limited to the selected
sub-groups each having a relatively narrower range of powder sizes.
It is therefore easier to determine the sintering temperature
required by the sintering process. On this basis, the required time
for the sintering process can also be easily determined. As the
sintering process is conducted under the determined sintering
temperature and time, the small-sized powders 20 of the sub-group B
become to melt and gradually turn into a molten state, as
illustrated in FIG. 4. At this time, however, the large-sized
powders 10 of the sub-group D are almost intact except that their
outer surfaces are melted. After the selected powders are sintered
under the determined sintering temperature for the determined
period of time, the wick structure is formed, wherein the
large-sized powders 10 are interconnected together by a plurality
of necks 20' which are formed from the small-sized powders 20, as
illustrated in FIG. 5. Meanwhile, a plurality of voids 30 is formed
between the large-sized powders 10. These voids 30 are communicated
with each other so as to form a continuous, liquid passageway. In
this example, the small-sized powders 20 are helpful to form the
necks 20' between the large-sized powders 10. In order for easier
illustration and understanding, in the drawings the large-sized
powders 10 are presumed unchanged throughout the sintering process.
In this example, since the proportion of the powders 20 of the
sub-group B in the mixture is controlled, the melting of the
powders 20 will not cause the mixture to have an excessive
shrinkage which may result in a disconnection between the voids 30.
The required temperature and time for the sintering process in this
example are selected to melt the powders 20 substantially entirely
and the outer surfaces of the powders 10.
[0018] Another example of forming a wick structure by selecting
only one group of the powders, such as group C, is illustrated in
FIGS. 6-7. The powders 40 of group C have a powder size of 100-140
mesh, larger than the powder size of group B (140-200 mesh) but
smaller than the powder size of group D (40-100 mesh). In this
case, since only one sub-group of the powders is selected to form
the wick structure, the sintering temperature and time required in
the sintering process is quite easy to be determined. As the
sintering process is conducted, the outer surfaces of the powders
40 become to melt, and meantime the powders 40 as a whole become to
shrink and the contacting surface between neighboring powders
increases, as illustrated in FIG. 4. After the sintering process,
the powders 40 are connected together by the melted outer surfaces
thereof. Meanwhile, a plurality of voids 50 is defined between the
powders 40. The required temperature and time for the sintering
process in this example are selected to melt the outer surfaces of
the powders 40. The selected group C of the powders has a range of
powder size which is located at a middle of the distribution and
includes a median of the distribution of FIG. 2.
[0019] Following the above-mentioned examples, a wick structure may
also be constructed by selecting, for example, the sub-groups B and
C, the sub-groups C and E, or the sub-groups B, C and D. A wick
structure having a multi-layer structure may also be formed, for
example, one layer thereof being formed by selecting the powders of
sub-groups B and D, and the other layer thereof being constructed
from the group C, thus forming a gradient in capillary force
between these layers of the wick structure. Further, the powders
used to construct the wick structure may be copper powders, nickel
powders, stainless steel powders, ceramic powders or combinations
thereof.
[0020] 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.
* * * * *