U.S. patent application number 16/626003 was filed with the patent office on 2021-05-27 for wick structures and heat pipe networks.
The applicant listed for this patent is Nokia Solutions and Networks Oy. Invention is credited to Akshat Agarwal, Nicholas M. JEFFERS, Rudi O'REILLY MEEHAN.
Application Number | 20210156619 16/626003 |
Document ID | / |
Family ID | 1000005398435 |
Filed Date | 2021-05-27 |
United States Patent
Application |
20210156619 |
Kind Code |
A1 |
Agarwal; Akshat ; et
al. |
May 27, 2021 |
WICK STRUCTURES AND HEAT PIPE NETWORKS
Abstract
A wick structure for a heat pipe network, the wick structure
comprising multiple channels defined by wall portions protruding
from a first surface of the wick structure and extending in an
axial direction along a length of the wick structure, wherein at
least one of the wall portions comprises a tapered termination.
Inventors: |
Agarwal; Akshat;
(Clonmagadden, IE) ; O'REILLY MEEHAN; Rudi;
(Dublin, IE) ; JEFFERS; Nicholas M.; (Wicklow,
IE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nokia Solutions and Networks Oy |
Espoo |
|
FI |
|
|
Family ID: |
1000005398435 |
Appl. No.: |
16/626003 |
Filed: |
May 15, 2018 |
PCT Filed: |
May 15, 2018 |
PCT NO: |
PCT/EP2018/062499 |
371 Date: |
December 23, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F28D 15/046 20130101;
F28D 15/0266 20130101 |
International
Class: |
F28D 15/02 20060101
F28D015/02; F28D 15/04 20060101 F28D015/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2017 |
EP |
17179184.1 |
Claims
1. A wick structure for a heat pipe network, the wick structure
comprising: multiple channels defined by wall portions protruding
from a first surface of the wick structure and extending in an
axial direction along a length of the wick structure, wherein at
least one of the wall portions comprises a tapered termination at a
junction between respective branches of the heat pipe network.
2. A wick structure as claimed in claim 1, wherein the wick
structure comprises a first wick portion in a first branch of the
heat pipe network and a second wick portion in a second branch of
the heat pipe network, wherein the termination of the wall portion
is provided in the region between the first wick portion and second
wick portion.
3. A wick structure as claimed in claim 1, wherein alternate wall
portions are provided with respective terminations.
4. A wick structure as claimed in claim 2, wherein a wall portion
has a curved profile.
5. A wick structure as claimed in claim 4, wherein the wall portion
is curved at said region between the first wick portion and the
second wick portion.
6. A heat pipe network comprising an evaporator section in fluid
communication with multiple heat pipe branches each comprising a
respective condenser section within the network, wherein a heat
pipe branch includes a wick structure on an internal surface
thereof to promote a fluid flow from the respective condenser
section to the evaporator section, the wick structure comprising
multiple channels defined by wall portions depending radially
inwards from an interior surface of a branch and extending in an
axial direction along a length of a branch, wherein at least one of
the wall portions comprises a tapered termination in a radial
direction with respect to the heat pipe branch, wherein the
termination of a wall portion is provided in the region of a
junction between two branches of the condenser section.
7. A heat pipe network as claimed in claim 6, wherein alternate
wall portions are provided with respective terminations.
8. A heat pipe network as claimed in claim 6, wherein a wall
portion has a curved profile.
9. A heat pipe network as claimed in claim 8, wherein the wall
portion is curved around a junction between two branches of the
condenser section.
10. A heat pipe network as claimed in any of claim 6, wherein the
heat pipe network is at least partially embedded in a heat
sink.
11. A method, comprising: depositing multiple layers of material to
additively manufacture a heat pipe network comprising a wick
structure with multiple channels defined by wall portions to depend
radially inwards from an interior surface of a heat pipe and to
extend in an axial direction along a length of a heat pipe, wherein
at least one of the wall portions terminates by tapering in a
radial direction at a junction between respective branches of the
heat pipe network.
12. A method as claimed in claim 11, further comprising forming a
heat sink around the heat pipe network.
13. A method as claimed in claim 11, forming wall portions such
that alternate wall portions terminate.
14. A method as claimed in any of claim 11, further comprising
forming wall portions with curved profiles.
Description
TECHNICAL FIELD
[0001] Aspects relate, in general, to a wick structure, a heat pipe
network and a method.
BACKGROUND
[0002] Electronic devices include heat generating components which
can be densely packed. This may be particularly apparent in the
case of telecommunications equipment for example, where high data
throughput to service a network along with the miniaturization of
equipment as a result of advancing technology can result in a dense
array of components with high heat flux.
SUMMARY
[0003] According to an example, there is provided a wick structure
for a heat pipe network, the wick structure comprising multiple
channels defined by wall portions protruding from a first surface
of the wick structure and extending in an axial direction along a
length of the wick structure, wherein at least one of the wall
portions comprises a tapered termination. The wall portions can
therefore extend or depend radially inwardly from an interior
surface of the heat pipe. A wall portion can terminate in the
region of a junction of the heat pipe with another heat pipe of the
network. A junction is formed at the intersection of two or more
heat pipes. The region of a junction is an area around an
intersection between two or more heat pipes.
[0004] The wick structure can comprise a first wick portion
configured to be located in a first heat pipe and a second wick
portion configured to be located in a second heat pipe and the
termination of the wall portion can be provided in the region
between the first wick portion and second wick portion. Alternate
wall portions can be provided with respective terminations. A wall
portion can have a curved profile. A wall portion can be curved at
said region between the first wick portion and the second wick
portion.
[0005] According to an example, there is provided a heat pipe
network comprising an evaporator section in fluid communication
with multiple heat pipe branches each comprising a respective
condenser section within the network, wherein a heat pipe branch
includes a wick structure on an internal surface thereof to promote
a fluid flow from the respective condenser section to the
evaporator section, the wick structure comprising multiple channels
defined by wall portions depending radially inwards from an
interior surface of a branch and extending in an axial direction
along a length of a branch, wherein at least one of the wall
portions can comprise a tapered termination in a radial direction
with respect to the heat pipe branch.
[0006] A termination of a wall portion can be provided in the
region of a junction between two branches of the condenser section.
Alternate wall portions can be provided with respective
terminations. A wall portion can have a curved profile. A wall
portion can be curved around a junction between two branches of the
condenser section. A heat pipe network can be at least partially
embedded in a heat sink.
[0007] According to an example, there is provided a method,
comprising depositing multiple layers of material to additively
manufacture a heat pipe network comprising a wick structure with
multiple channels defined by wall portions to depend radially
inwards from an interior surface of a heat pipe and to extend in an
axial direction along a length of a heat pipe, wherein at least one
of the wall portions terminates by tapering in a radial direction.
A heat sink can be formed around the heat pipe network. Wall
portions can be formed such that alternate wall portions terminate.
Wall portions can be formed with curved profiles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Embodiments will now be described, by way of example only,
with reference to the accompanying drawings, in which:
[0009] FIG. 1 is a schematic representation of a heat pipe
network;
[0010] FIGS. 2a-c are schematic representations of a junction from
the heat pipe network according to an example;
[0011] FIG. 3 is a schematic representation of a wick structure for
a junction in a heat pipe network according to an example;
[0012] FIGS. 4a-b are schematic representations of a wick structure
for a junction in a heat pipe network according to an example;
[0013] FIGS. 5a-b are schematic representations of a wick structure
for a junction in a heat pipe network according to an example;
[0014] FIG. 6 is a schematic representation of a wick structure for
a junction in a heat pipe network according to an example;
[0015] FIG. 7 is a schematic representation of a wick structure for
a junction in a heat pipe network according to an example; and
[0016] FIG. 8 is a schematic representation of a wick structure for
a junction in a heat pipe network according to an example.
DESCRIPTION
[0017] Example embodiments are described below in sufficient detail
to enable those of ordinary skill in the art to embody and
implement the systems and processes herein described. It is
important to understand that embodiments can be provided in many
alternate forms and should not be construed as limited to the
examples set forth herein.
[0018] Accordingly, while embodiments can be modified in various
ways and take on various alternative forms, specific embodiments
thereof are shown in the drawings and described in detail below as
examples. There is no intent to limit to the particular forms
disclosed. On the contrary, all modifications, equivalents, and
alternatives falling within the scope of the appended claims should
be included. Elements of the example embodiments are consistently
denoted by the same reference numerals throughout the drawings and
detailed description where appropriate.
[0019] The terminology used herein to describe embodiments is not
intended to limit the scope. The articles "a," "an," and "the" are
singular in that they have a single referent, however the use of
the singular form in the present document should not preclude the
presence of more than one referent. In other words, elements
referred to in the singular can number one or more, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises," "comprising," "includes," and/or
"including," when used herein, specify the presence of stated
features, items, steps, operations, elements, and/or components,
but do not preclude the presence or addition of one or more other
features, items, steps, operations, elements, components, and/or
groups thereof.
[0020] Unless otherwise defined, all terms (including technical and
scientific terms) used herein are to be interpreted as is customary
in the art. It will be further understood that terms in common
usage should also be interpreted as is customary in the relevant
art and not in an idealized or overly formal sense unless expressly
so defined herein.
[0021] Efficient cooling of components is an important
consideration since there may be strict temperature limits for
reliability in a system. On the flip side of this, the volume
occupied by a cooling solution should be minimal for multiple
deployment options. In order to meet these criteria, a heat pipe
network can be used.
[0022] Heat pipes typically comprise an evaporator section where
heat from a heat generating component causes liquid in the heat
pipe to evaporate. The vapor travels through the heat pipe to a
condenser section where a heat sink allows dissipation of the heat
from the heat pipe, condensing the vapor back to liquid. The liquid
then travels back to the evaporator section typically along a wick
structure which may take several different forms.
[0023] Heat pipes can be constructed from common metal processing
techniques which constrains them to simply shaped designs that are
extrusions of two-dimensional objects (rectangular, circular,
etc.), implying they typically have a uniform cross-section
throughout the length of the heat pipe.
[0024] An example of a heat pipe network is shown in FIG. 1 in
which three components 101, 103, 105 generate varying amounts of
heat, Q.sub.1, Q.sub.2 and Q.sub.3 respectively. Each component is
provided with a customized heat pipe network 107 based on heat
generated from that component, while being isolated from other
components. A heat pipe network with several junctions enables this
approach by allowing efficient use of the space available.
[0025] In the example shown in FIG. 1, heat pipes are encased in a
heat sink 109 which dissipates heat from the heat pipes to the
atmosphere. The heat generated by the three components varies and
the network approach caters to the needs of each component while
minimizing the volume occupied.
[0026] The junctions in such a network of heat pipes form an
important part of the network, serving to distribute the heat from
the component to a larger surface area, and a wick structure is
used to allow liquid from the condenser section to return to the
evaporator section without disrupting the flow of hot vapour along
the core of a heat pipe. If liquid flow is blocked, it may lead to
the liquid pooling at the junction, thereby disrupting the fluid
flow cycle in the heat pipe and leading to a dry out. This can
occur at junctions (e.g. between two merging heat pipes) where
complex wick structures meet and cause impediments to the efficient
flow of liquid.
[0027] According to an example, an additively manufactured heat
pipe is provided which comprises a wick structure with a complex
inner geometry that enables the efficient flow of a condensed fluid
at a junction in a heat pipe network, thereby reducing the risk of
pooling at the junction.
[0028] FIG. 2 is a schematic representation of a junction from a
heat pipe network according to an example. The number of heat pipes
combining in such a section may vary. An isometric view of a heat
pipe junction 207 in which two heat pipes 203, 205 combine to form
one 201 is shown in FIG. 2(a). To discuss an internal wick
structure at the junction 207 according to an example, a
cross-section of the heat pipe is taken, as shown in FIG. 2(b).
This section is then unwrapped along the dotted line, as indicated
by the `scissor` symbol in FIG. 2(b). An illustration of the heat
pipe when unwrapped is shown in FIG. 2(c), with the dotted line
along which it was unwrapped shown for clarity. In FIG. 2, the heat
pipe junction 207 is shown without any wick structure. In an
example, a wick structure can be located on the inner wall 206 of
the heat pipe.
[0029] FIG. 3 is a schematic representation of a wick structure for
a junction in a heat pipe network according to an example. The wick
structure 307 comprises multiple channels 305 defined by wall
portions 303 depending or extending radially inwardly from an
interior surface 309 of a heat pipe and extending in an axial
direction along a length of the heat pipe. A wall portion 303 may
extend the full length of the heat pipe, or partway as desired. In
an example, at least one of the wall portions terminates, and in
the example of FIG. 3 the termination is by way of tapering 304, in
a radial direction, along a portion of the length of a wall
portion. Furthermore, the terminated wall portions are limited to
those in the region of the junction 311. Thus, when the section of
FIG. 3 is reconstructed to form a pipe, the terminated portions
will be situated at the junction 207 of the heat pipe as depicted
in FIG. 2a. Thus, at the intersection of the two heat pipes 203,
205 shown in FIG. 2a, the terminating wall portions do not
interfere or provoke a complex or cumbersome inner geometry that
may cause pooling of fluid leading to a reduction or failure in
effectiveness of the heat pipe network.
[0030] Thus, as shown in FIG. 3, the upper part 301 of the heat
pipe has a uniform cross section on approach to the junction. At
the junction, some of the wall portions 303 are gradually tapered
304 to termination. That is, the wall portions 303 reduce in height
in a radial direction to the interior surface 309 of the heat pipe.
The taper may be gradual and continuous as shown, or stepwise with
or without discontinuities. A termination may be such that the wall
portion remains proud of the interior surface to some degree.
According to an example, this can be done for each of the upper
heat pipes 203, 205 in a network which combine into a single lower
heat pipe 201 (which may itself then combine with another pipe and
so on).
[0031] This provides an improvement from heat pipes of constant
cross-section since a clear path is provided for some of the
channels which take liquid to the evaporator section of the
network. Furthermore, while some channels are terminated, the
tapered design minimizes contamination of the vapour core by the
sudden leakage of liquid from the wick into the core. In an
example, to minimize any inefficiencies due to the terminating
channels, a junction with this cross-section can be placed at a hot
spot in the heat pipe network. The available heat can be used to
evaporate the liquid in the terminating channels, thereby
minimizing the adverse effect of the junction. A wick structure as
shown in FIG. 3 may be manufactured using conventional
manufacturing techniques such as extrusion for example or by
additive fabrication as described below.
[0032] FIG. 4 is a schematic representation of a wick structure for
a junction in a heat pipe network according to an example. As shown
in FIG. 4a, alternate wall portions, e.g. 410, 411, are terminated,
not just those that are in the region of a junction, as shown in
FIG. 3. Intermediate wall portions (to those which terminate), e.g.
405, 415, are, in the example of FIG. 4, curved such that they join
a wall portion in the lower heat pipe while the remaining wall
portions are tapered down to terminate as shown and as described
above with reference to FIG. 3. This structure is advantageous in
that liquid from all channels in the upper heat pipe is allowed to
flow into the lower heat pipe.
[0033] As can be seen in FIG. 4b, the height 406 of wall portions
in this example is constant since, during normal operation, the
channels for liquid returning to the evaporator section created by
the wick structure are not expected to be full of liquid.
Therefore, the decrease in total volume available for the liquid to
occupy as the liquid moves from multiple heat pipes 203, 205 to a
single, common heat pipe 201 does not hinder operation of the heat
pipe.
[0034] However, an area of further performance gain according to an
example can be to vary the height of the wick structure such that
the transition to a lower available volume as the liquid moves from
multiple heat pipes to a single, common heat pipe is made more
gradual or so that channel of increased height is provided to
accommodate an increased volume of liquid.
[0035] FIG. 5 is a schematic representation of a wick structure for
a junction in a heat pipe network according to an example. As
noted, while the heat pipe wick channels are not expected to be
full of liquid at all times during the operation, there might be a
scenario at the peak of performance when the channels are close to
being full. Thus, in the example of FIG. 5 the height 510 of the
wall portions is increased at the junction as can be seen in FIG.
5b in order to accommodate an increase in the volume of liquid at
the junction region. In the example of FIG. 5, each alternate wall
portion is combined such that liquid from all the channels 501
flows into the lower pipe 503 as shown in FIG. 5a. In this example,
the height 510 of the wicks is higher at the junction to increase
the available volume for liquid from multiple pipes to flow into a
single pipe. The variation in height can be continuous as shown, or
may be in the form of a step and so on.
[0036] According to an example, a heat pipe network as described
above with reference to FIGS. 2 to 5 can be generated using an
additive manufacturing process. Such additive manufacturing enables
heat pipes with complex inner geometries to be fabricated. For
example, multiple layers of a material, such as metal, can be
deposited using a rendering apparatus, such as a 3D printer for
example, in order to additively manufacture a heat pipe network
comprising a wick structure. The heat pipe network can be provided
within a heat sink, which can be additively manufactured at the
same time (such that the network is built up within the heat sink),
or added after the network has been fabricated.
[0037] According to an example, directing a flow of condensed fluid
in a wick structure efficiently into the lower heat pipe can be
extended to heat pipes with other wick structure designs. In an
example, one such design is that of a sintered wick. This can be
composed of sintered metal powder.
[0038] FIG. 6 is a schematic representation of a wick structure for
a junction in a heat pipe network according to an example. Sintered
metal wicks 601 can be manufactured by packing small metal
particles between the inner heat pipe wall and a mandrel in powder
form. This assembly is then heated until the metal particles are
sintered to each other and to the inner wall of the heat pipe. The
resulting structure can be thought of as isotropic along the inner
wall of the heat pipe.
[0039] According to an example, a sintered region can be shaped or
modified such that it pre-empts a change in shape of the heat pipe,
providing a more gradual change in direction for the liquid. The
capillary pressure generated by the wick will keep the fluid from
leaking out of the sintered region.
[0040] FIG. 7 is a schematic representation of a wick structure for
a junction in a heat pipe network according to an example. As shown
in FIG. 7, the sintered wick structure 701 along the inner wall of
the junction in the heat pipe is shaped 705 to pre-empt the
termination of the heat pipe and provide a gradual change in
direction to the liquid at the junction region. In the example, of
FIG. 7, this is accomplished by providing an area 703 devoid of
sintered material and by profiling the sintered material above the
junction as shown to have a generally sinuous nature so as to avoid
any discontinuities that would otherwise interrupt the natural flow
of fluid in the wick structure.
[0041] FIG. 8 is a schematic representation of a wick structure for
a junction in a heat pipe network according to an example. In the
example of FIG. 8, a sintered region 800 (whose directionality
typically cannot be controlled using conventional manufacturing
processes) is fabricated and made anisotropic. The directional
sinter 801, 803 provides a path of least resistance to the liquid
in the wick, thereby directing it `around` the junction, generally
in direction D, in order to avoid the effects of liquid pooling
reducing the effectiveness of the network.
[0042] The sintered material can be the same material used for the
heat pipe and/or a heat sink. The anisotropic property of the
sintered material at the region of a junction can be provided
using, for example, selective laser sintering.
[0043] Accordingly, a heat pipe network with several junctions can
be provided by providing complex and bespoke wick structures for
the inner walls of the junction. The wick structures allow the
seamless flow of liquid from the condenser section to the
evaporator section of the heat pipe.
[0044] According to an example a wick structure for a heat pipe
network can comprise a first wick portion, a second wick portion
and a third wick portion and being configured to allow a flow of a
liquid from the first wick portion and the second wick portion to
the third wick portion wherein the wick structure further comprises
irregularities provided at least at a region between the first wick
structure and the third wick structure and configured to assist the
flow of the liquid from the first wick structure to the third wick
structure.
[0045] In an example, the first wick portion can be provided on the
inner wall of, for example, heat pipe 203, the second wick portion
can be provided on the inner wall of, for example, heat pipe 205,
and the third wick portion can be provided on the inner wall of,
for example, heat pipe 201. Irregularities provided at least at the
region 207 between the first wick structure and the third wick
structure can be a in the form of a tapered structure as described
with reference to FIGS. 3 to 5 for example, or a sintered structure
as described with reference to FIG. 7 or 8 for example. That is,
the irregularities configured to assist the flow of the liquid from
the first wick structure to the third wick structure can channels
with tapered wall portions as described with reference to FIGS. 3
to 5 for example, or an anisotropic sintered structure as described
with reference to FIG. 7 or 8 for example.
[0046] In an example, the wick structure can further comprise
irregularities provided at least at a region between the second
wick structure and the third wick structure and configured to
assist the flow of the liquid from the second wick structure to the
third wick structure.
[0047] The wick structure can comprise channels defining walls and
the irregularities can include terminations in the wall portions.
In an example, the wick structure can comprise terminations in
alternate wall portions.
[0048] In another example, the wick structure can comprise a
sintered material and the irregularities can include an area devoid
of sintered material configured to provide gradual change in the
direction of the flow of the liquid and/or a region of sintered
material configured to provide a path of flow having a resistance
to flow which is lower than a resistance of flow of an adjacent
area, as shown in FIG. 8 for example.
[0049] In an example, a wall portion of a channel can have a
constant height, or may have a varying height.
[0050] The present embodiments can be realised in other specific
apparatus and/or methods. The described embodiments are to be
considered in all respects as illustrative and not restrictive. In
particular, the scope of the disclosure is indicated by the
appended claims rather than by the description and figures herein.
All changes that come within the meaning and range of equivalency
of the claims are to be embraced within their scope.
* * * * *