U.S. patent application number 17/521273 was filed with the patent office on 2022-04-28 for capillary device for use in heat pipe and method of manufacturing such capillary device.
The applicant listed for this patent is Aavid Thermal Corp.. Invention is credited to Ryan James McGlen, John Gilbert Thayer.
Application Number | 20220128312 17/521273 |
Document ID | / |
Family ID | 1000006079007 |
Filed Date | 2022-04-28 |
View All Diagrams
United States Patent
Application |
20220128312 |
Kind Code |
A1 |
McGlen; Ryan James ; et
al. |
April 28, 2022 |
CAPILLARY DEVICE FOR USE IN HEAT PIPE AND METHOD OF MANUFACTURING
SUCH CAPILLARY DEVICE
Abstract
A capillary device (102) for use in a heat pipe in which heat is
transferred from at least one evaporation region to at least one
condensation region by means of evaporated working fluid is
disclosed. The capillary device comprises a body portion defining
chambers (108) containing powdered material (110) therein, wherein
at least part of the periphery of at least one said chamber is
porous to allow flow of condensed working fluid, by means of
capillary action, through said powdered material in said chamber
when flowing from a condensation region to an evaporation
region.
Inventors: |
McGlen; Ryan James;
(Northumberland, GB) ; Thayer; John Gilbert;
(Lancaster, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Aavid Thermal Corp. |
Wilmington |
DE |
US |
|
|
Family ID: |
1000006079007 |
Appl. No.: |
17/521273 |
Filed: |
November 8, 2021 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
16254684 |
Jan 23, 2019 |
11168944 |
|
|
17521273 |
|
|
|
|
14119814 |
Mar 14, 2014 |
|
|
|
PCT/EP2012/059681 |
May 24, 2012 |
|
|
|
16254684 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F28D 15/046 20130101;
F28D 15/04 20130101; Y10T 29/10 20150115; F28D 15/0233 20130101;
Y10T 29/49353 20150115; B23P 15/26 20130101; Y10T 29/49396
20150115 |
International
Class: |
F28D 15/04 20060101
F28D015/04; F28D 15/02 20060101 F28D015/02; B23P 15/26 20060101
B23P015/26 |
Foreign Application Data
Date |
Code |
Application Number |
May 24, 2011 |
EP |
11167303.4 |
Claims
1. A heat transfer pipe in which heat is transferred from an
evaporation region to a condensation region by means of working
fluid, the heat transfer pipe comprising: a body portion defining a
central channel, the central channel extending between and in fluid
communication with the evaporation region and the condensation
region; and a capillary structure within the body portion and
surrounding the central channel, wherein the capillary structure
comprises a plurality of spaced-apart porous protrusions extending
radially into the central channel with each protrusion separated
from an adjacent protrusion by a gap therebetween; wherein the heat
transfer pipe includes successive layers of metal powder that are
located over a donor material and have been melted by an energetic
beam, wherein the successive layers at least partially define the
plurality of porous protrusions.
2. A heat transfer pipe according to claim 1, wherein each porous
protrusion of the plurality of porous protrusions includes a hollow
interior and contains unfused metal powder within the hollow
interior.
3. A heat transfer pipe according to claim 2, wherein the
successive, melted layers of metal powder at least partially define
the hollow interiors.
4. A heat transfer pipe according to claim 2, wherein the unfused
metal powder is aluminum.
5. A heat transfer pipe according to claim 1, wherein the body
portion is formed from aluminum.
7. A heat transfer pipe according to claim 1, wherein each of the
gaps extends in a longitudinal direction parallel to the central
channel.
8. A heat transfer pipe according to claim 1, further comprising
lattice capillary structures positioned in the gaps between the
porous protrusions, wherein each of the capillary lattice
structures extends longitudinally along a length of the heat
transfer pipe between the evaporation region and the condensation
region.
9. A heat transfer pipe according to claim 8, wherein the lattice
capillary structures do not extend to the evaporation region.
10. A heat transfer pipe according to claim 8, wherein the lattice
capillary structures are formed from a plurality of pores which
increase in size along lengths of the lattice capillary structures
from the condensation region to the evaporation region.
11. A heat transfer pipe according to claim 1, wherein the
successive layers at least partially define the body portion.
12. A heat transfer pipe in which heat is transferred from an
evaporation region to a condensation region by means of working
fluid, the heat transfer pipe comprising: a solid outer body
portion; a porous capillary structure within the outer body portion
extending between and in fluid communication with the evaporation
region and the condensation region; and a plurality of vapor flow
channels embedded in the capillary structure and extending between
and in fluid communication with the evaporation region and the
condensation region.
13. A heat transfer pipe according to claim 12, wherein the
plurality of vapor flow channels is spaced circumferentially around
an interior region of the porous structure.
14. A heat transfer pipe according to claim 12, wherein the heat
transfer pipe includes successive layers of metal powder that are
located over a donor material and have been melted by an energetic
beam, wherein the successive layers at least partially define the
porous capillary portion and the vapor flow channels.
15. A heat transfer pipe according to claim 12, further comprising
a fluid flow passage formed in the center of the porous capillary
structure and extending between and in fluid communication with the
evaporation region and the condensation region.
16. A heat transfer pipe according to claim 15, further comprising
a region of powder metal between the porous capillary structure and
the fluid flow passage.
17. A heat transfer pipe in which heat is transferred from an inlet
chamber to an outlet chamber by means of working fluid, the heat
pipe comprising: an outer body portion; and a porous capillary
structure positioned within the outer body portion between and in
fluid communication with the inlet chamber and the outlet chamber,
wherein the porous capillary structure has a porous rigid outer
wall and contains unfused powder material.
18. A heat transfer pipe according to claim 17, wherein the inlet
chamber and the outlet chamber are divided by the porous capillary
structure.
19. A heat transfer apparatus comprising: an evaporation chamber;
and a condensation chamber in fluid communication with the
evaporation chamber, wherein heat is transferred from the
evaporation chamber to the condensation region by means of working
fluid, wherein the evaporation chamber includes an outer
cylindrical body that defines an interior volume, a porous
capillary structure positioned within the interior volume adjacent
an interior surface of the outer cylindrical body, wherein the
porous capillary structure defines an interior annular chamber
enclosing a layer of unfused metal powder, an elongate escape
channel positioned between the interior surface of the outer
cylindrical body and the interior annular chamber, wherein the
elongate escape channel extends from an interior of the porous
capillary structure to a first opening in the porous capillary
structure, wherein the first opening is in fluid communication with
the interior volume and is formed at an end face of the porous
capillary structure, a plurality of spaced-apart circumferential
vapor channels interconnected by the elongate escape channel, and a
central bore surrounded by the interior annular chamber, wherein
the central bore extends between the end face and a second opening
of the porous capillary structure to the interior volume, wherein
the second opening is in fluid communication with the interior
volume and positioned opposite the end face.
20. A heat transfer apparatus according to claim 19, wherein the
evaporation chamber and the condensation chamber are in the form of
a loop heat pipe.
21. A heat transfer pipe comprising: an evaporation region; a
condensation region; a body portion extending between and in fluid
communication with the evaporation region and the condensation
region; and a capillary structure configured to direct working
fluid between the evaporation region and the condensation region;
wherein the capillary structure includes successive layers of metal
powder that have each been melted by an energetic beam to be
secured to one or more other layers of the successive layers.
22. The heat transfer pipe of claim 21, wherein the condensation
region includes a condenser plate, wherein the condenser plate
defines a donor material, wherein the successive layers of metal
powder include a first, melted layer of metal powder disposed on
the donor material and a second, melted layer of metal powder
disposed on the first layer of metal powder.
23. The heat transfer pipe of claim 22, wherein the first, melted
layer of metal powder and the second, melted layer of metal powder
define a rigid, porous structure that defines a portion of the
capillary structure.
24. The heat transfer pipe of claim 23, wherein the capillary
structure extends along an interior surface of the body
portion.
25. The heat transfer pipe of claim 22, wherein the condenser plate
is an aluminum plate, wherein the first, melted layer of metal
powder is aluminum powder, and wherein the second, melted layer of
metal powder is aluminum powder.
26. The heat transfer pipe of claim 21, wherein the evaporation
region includes an evaporator plate, wherein the evaporator plate
defines a donor material, wherein the successive layers of metal
powder include a first, melted layer of metal powder disposed on
the donor material and a second, melted layer of metal powder
disposed on the first layer of metal powder.
27. The heat transfer pipe of claim 26, wherein the first, melted
layer of metal powder and the second, melted layer of metal powder
define a portion of the body portion.
28. The heat transfer pipe of claim 27, wherein the successive
layers of metal powder further include additional layers of melted,
metal powder that define the capillary structure, wherein the
capillary structure is disposed within the body portion.
29. The heat transfer pipe of claim 28, wherein the capillary
structure includes rigid, porous protrusions.
30. The heat transfer pipe of claim 21, wherein the body portion
also includes successive layers of metal powder that have each been
melted by an energetic beam to be secured to one or more other
layers of the successive layers of the body portion.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 16/254,684, filed Jan. 23, 2019, which is a
continuation of U.S. application Ser. No. 14/119,814, filed Mar.
14, 2014, which is a 371 of international PCT/EP2012/059681, filed
May 24, 2012, which claims priority to EP 11167303.4, filed May 24,
2011, issued as EP2715265, the entire contents of each of which are
incorporated herein by reference.
[0002] The present invention relates to a device for use in a heat
exchange apparatus and to a method of manufacturing such a device.
The invention also relates particularly, but not exclusively, to a
capillary device for use in a heat pipe.
[0003] Heat pipes are devices in which heat is rapidly removed from
a first region by means of evaporation of working fluid, and
subsequently released at a second location by means of condensation
of the working fluid.
[0004] A conventional loop heat pipe is shown in FIG. 1. The heat
pipe 2 comprises a cylindrical evaporator 4 having an inlet 6 for
condensed working fluid, the inlet 6 being in communication with a
compensation chamber 8, and a cylindrical vapour passage 10
communicating with an outlet 12 for enabling evaporated working
fluid to pass to a condenser 14. A capillary structure 16 surrounds
a gap 18 surrounding the inlet 6, and is in turn surrounded by the
vapour passage 10. The purpose of the compensation chamber 8 is to
ensure that the gap 18 is always filled with condensed working
fluid and to prevent over pressure within the loop heat pipe, since
condensed working fluid is displaced into the compensation chamber
as vapour is generated.
[0005] During operation of the heat pipe 2, heat in the vicinity of
the evaporator 4, for example generated by electronics operating in
a confined space, travels in the direction of arrows A to cause
evaporation of the working fluid in the capillary structure 16. The
evaporated working fluid then passes along vapour passage 10 and
outlet 12 to the condenser 14 where heat can be more easily removed
in the direction of arrows B and condensed working fluid is
returned via inlet 6 and compensation chamber 8 to fill the gap 18
surrounding the inlet 6. Condensed working fluid is then
transferred from the gap 18 to the vapour passage 10 through the
capillary structure 16 by means of capillary action. The capillary
structure 16 of the heat pipe 2 is manufactured by sintering of
fine metal powder and subsequent machining to form the flow
passages.
[0006] This arrangement suffers from the drawback that the
sintering technique can only be carried out on a limited range of
materials, and the complexity of possible shapes and dimensions of
flow channels is limited by the machining technique.
[0007] A conventional axially grooved heat pipe 16 is shown in FIG.
2. The heat pipe 16 has capillary structure 19 which is extruded
from a suitable material and comprises a plurality of axial grooves
20 surrounding a central channel 22. Vaporised working fluid
travels along the central channel 22 from a hot end of the heat
pipe 16 to a cold end, and condensed working fluid travels in the
opposite direction along grooves 20 by means of capillary action.
The arrangement shown in FIG. 2 suffers from the drawback that the
range of shapes and sizes of grooves 22 is limited by extrusion
techniques, as a result of which the grooves 22 have channel widths
in the region of 0.1 to 1 mm wide. This dimension of channel width
is too large to provide sufficient surface tension to entrain
condensed working fluid when operating against gravity, as a result
of which this type of device can generally only be used in space
applications such as satellite cooling.
[0008] Preferred embodiments of the present invention seek to
overcome one or more of the above disadvantages of the prior
art.
[0009] According to an aspect of the present invention, there is
provided a capillary device for use in a heat transfer apparatus in
which heat is transferred from at least one first region to at
least one second region by means of working fluid, the capillary
device comprising a body portion defining at least one chamber
containing unmelted powdered material therein, wherein at least
part of the periphery of at least one said chamber is porous to
allow flow of condensed working fluid through said unmelted
powdered material in said chamber by means of capillary action.
[0010] By providing at least one chamber containing unmelted
powdered material therein, wherein at least part of the periphery
of at least one said chamber is porous to allow flow of condensed
working fluid through said unmelted powdered material in said
chamber, this provides the advantage in the case of a heat pipe
using capillary action to transport condensed working fluid, of
increasing fluid transfer by means of capillary action, while
minimising thermal conduction into the powdered material of the
chamber, which in turn minimises the effect of parasitic heating of
the working fluid passing through the powdered material. This in
turn improves the cooling performance of a heat pipe incorporating
the device.
[0011] The capillary device may be adapted to be used in a heat
pipe in which heat is transferred from at least one evaporation
region to at least one condensation region by means of evaporated
working fluid, and at least part of the periphery of at least one
said chamber may be porous to allow flow of condensed working
fluid, by means of capillary action, through said unmelted powdered
material in said chamber when flowing from a condensation region to
an evaporation region.
[0012] At least a portion of said body portion in the vicinity of
an evaporation region may have a porosity different from a porosity
of at least a portion of said body portion remote from said
evaporation region.
[0013] This provides the advantage of enabling the capillary action
to be tailored to the various parts of the device and fluid flow to
thereby be maximised.
[0014] The body portion may surround an elongate channel and at
least one said chamber may be located between at least part of said
channel and an evaporation region in use.
[0015] This provides the advantage of enhancing capillary action
and thereby increasing fluid flow, thereby enabling the apparatus
to be used when subject to gravity.
[0016] A plurality of said chambers may be spaced apart around the
periphery of, and protruding into, said channel.
[0017] The capillary device may further comprise at least one
vapour flow passage in said body portion for allowing flow of
evaporated working fluid from an evaporation region to a
condensation region.
[0018] At least part of the periphery of at least one said vapour
flow passage may be porous.
[0019] Said body portion may comprise at least one support portion
adapted to resist compressive forces applied to the capillary
device, wherein at least part of at least one said support portion
is porous to allow flow of condensed working fluid
therethrough.
[0020] By providing at least one support portion which can
contribute to the capillary action, this provides the advantage of
reducing the weight of the capillary device.
[0021] According to another aspect of the present invention, there
is provided a heat transfer apparatus comprising at least one
capillary device as defined above.
[0022] At least one said capillary device may be connected to a
plurality of condenser devices.
[0023] This provides the advantage of enabling a capillary device
to be constructed by means of selective melting of powdered
material to thereby enable a wider range of dimensions and
properties of capillary structure to be provided, while enabling
condenser devices manufactured according to simpler techniques such
as extrusion to be used.
[0024] According to a further aspect of the present invention,
there is provided a method of manufacturing a body portion of a
capillary device for use in a heat transfer apparatus in which heat
is transferred from at least one first region to at least one
second region by means of working fluid, the method comprising
forming successive layers of said body portion by means of
selective melting of powdered material by means of an energetic
beam, such that at least part of said body portion is porous to
enable flow of condensed working fluid therethrough.
[0025] By forming successive layers of said body portion by means
of selective melting of powdered material by means of an energetic
beam, this provides the advantage of enabling a wider range of
shapes of device to be constructed, and a wider range of materials
to be used. This is particularly advantageous in the case of heat
pipes which use capillary action to transfer condensed working
fluid from a condensation region to an evaporation region. For
example, the method of the present invention enables body portions
of complex shapes having voids or hollow portions to save weight to
be provided.
[0026] The selective melting of powdered material may provide
melted powdered material and unmelted powdered material, and said
body portion may define at least one chamber containing unmelted
powdered material therein, wherein at least part of the periphery
of at least one said chamber is porous.
[0027] The powdered material encapsulated in at least one said
chamber may be the same material as the powdered material from
which the successive layers are formed.
[0028] This provides the advantage of increasing the ease and speed
of manufacture of the capillary device.
[0029] The method may be a method of manufacturing a capillary
device adapted to be used in a heat pipe in which heat is
transferred from at least one evaporation region to at least one
condensation region by means of evaporated working fluid, wherein
at least part of the periphery of at least one said chamber is
porous to allow flow of condensed working fluid, by means of
capillary action, through said powdered material in said chamber
when flowing from a condensation region to an evaporation
region.
[0030] The body portion may define at least one chamber, and the
method may further comprise encapsulating powdered material in at
least one said chamber to allow flow of condensed working fluid, by
means of capillary action, through said powdered material in said
chamber when flowing from a condensation region to an evaporation
region.
[0031] The method may further comprise directing at least one
stream of powdered material to a location at which said powdered
material is melted by means of the energetic beam.
[0032] This provides the advantage of increasing the range of
locations at which the device can be used.
[0033] At least one said stream of said powdered material may be
constrained in a stream of inert gas.
[0034] Preferred embodiments of the invention will now be
described, by way of example only and not in any limitative sense,
with reference to the accompanying drawings, in which:
[0035] FIG. 1 is a schematic diagram of a conventional loop heat
pipe;
[0036] FIG. 2 is a cross sectional view of a conventional axially
grooved heat pipe;
[0037] FIG. 3 is a perspective view of a flat heat pipe of a first
embodiment of the present invention with an upper evaporator plate
thereof removed;
[0038] FIG. 4 is a schematic view of a process for forming the heat
pipe of FIG. 3;
[0039] FIG. 5 is a detailed view of region C of the heat pipe of
FIG. 4;
[0040] FIG. 6 is a detailed view of part of a heat pipe of a second
embodiment of the present invention;
[0041] FIG. 7 is a side cross sectional view of a capillary device
of an axially grooved heat pipe of a third embodiment of the
present invention;
[0042] FIG. 8 is a side cross sectional view, corresponding to FIG.
7, of a capillary device of an axially grooved heat pipe of a
fourth embodiment of the present invention;
[0043] FIG. 9 is a side cross sectional view, corresponding to FIG.
8, of a capillary device of a fifth embodiment of the present
invention;
[0044] FIG. 10 is a side cross sectional view, corresponding to
FIG. 9, of a capillary device of a sixth embodiment of the present
invention;
[0045] FIG. 11 is a side cross sectional view, corresponding to
FIG. 10, of a capillary device of a heat pipe of a seventh
embodiment of the present invention;
[0046] FIG. 12 is a schematic view of a heat transfer apparatus of
an eighth embodiment of the present invention;
[0047] FIG. 13 is a perspective view of a heat transfer apparatus
of a ninth embodiment of the present invention;
[0048] FIG. 14 is a side cross sectional view of an evaporation
apparatus of the heat transfer apparatus of FIG. 13;
[0049] FIG. 15 is a perspective view of a heat transfer apparatus
of a tenth embodiment of the present invention;
[0050] FIG. 16 is a view of an evaporation apparatus and a
condenser apparatus of the heat transfer apparatus of FIG. 15 with
an adiabatic section of the heat transfer apparatus removed;
and
[0051] FIG. 17 is a schematic view of a heat transfer apparatus of
an eleventh embodiment of the present invention.
[0052] Referring to FIG. 3, a flat heat pipe 102 of a first
embodiment of the present invention is formed from aluminium and
has an upper evaporator plate 124 (FIG. 4), a lower condenser plate
104 and solid side walls 106. Porous chambers 108 formed from
aluminium are arranged between the upper evaporator plate 124 and
the lower condenser plate 104, and unmelted aluminium powder 110 is
provided inside the chambers 108. The regions 112 between the
chambers 108 form a vapour space 109 covered by a layer 122 on the
underside of upper evaporator plate 124 such that working fluid
such as water is caused by the upper evaporator plate 124 to
evaporate and transfer heat via the vapour space 109 to the lower
condenser plate 104, and condensed working fluid passes by
capillary action through the walls of the chambers 108 and the
powdered aluminium 110 in the chambers 108 back to the upper
evaporator plate 124. The powdered aluminium 110 enhances fluid
flow due to capillary action, but thermal conduction through the
powdered aluminium 110 is limited, as a result of which the
parasitic heating effect on condensed working fluid passing through
the aluminium powder 110 is minimised. This in turn maximises the
amount of heat removed from the upper evaporator plate 124 by
evaporation of the working fluid.
[0053] The formation of the heat pipe 202 of FIG. 3 is shown in
detail with reference to FIGS. 4(a) to 4(h). Initially, as shown in
FIG. 4(a), a solid sheet of aluminium is provided, to form lower
condenser plate 104 and a layer 114 of powdered aluminium is placed
on the donor material, as shown in FIG. 4(b). A high intensity
energy beam (not shown) such as a laser beam is then directed onto
the layer 114 of powdered material and the path of the beam
controlled to selectively melt the layer of powder in the selected
regions to form rigid porous regions 116 forming the base of the
vapour space 109, separated by regions 118 of unfused powder
material which forms the powdered aluminium 110 in the chambers
108. Further layers of powdered aluminium are added and selectively
melted in FIGS. 4(c) to 4(e) to form porous side walls 120 of the
chambers 108. Similarly, porous upper walls 122 of the vapour space
109 can be formed on the lower surface of solid upper evaporator
plate 124 as shown in FIGS. 4(f) to 4(h).
[0054] As shown in greater detail in FIG. 5, each of the chambers
108 encapsulates unmelted powdered material 110, and the vapour
space 109 encloses a volume of working fluid at reduced pressure.
In use, heat is removed from the upper evaporator plate 124 by
evaporation of the working fluid enclosed in chambers 108 and
transferred to the lower condenser plate 104 by condensation of the
working fluid. The condensed working fluid can pass through the
porous walls 120 of chambers 108 into the unfused powder material
110 and returned to the upper evaporator plate 124 through the
powder material 110 by means of capillary action.
[0055] Referring to FIG. 6, in which parts common to the embodiment
of FIGS. 3 to 5 are denoted by like reference numerals but
increased by 100, a heat pipe of a second embodiment of the present
invention differs from the arrangement shown in FIGS. 4 and 5 in
that one or more support struts 228a, 228b, 228c extend through the
interior of one or more of the chambers 208 to assist in capillary
transfer of condensed working fluid between the condenser 204 and
evaporator 224 plates and to enhance the mechanical strength of the
heat pipe. The struts may be a single solid strut 228a, a 3D CAD
generated micro capillary strut 228b, or a combination strut 228c
consisting of a 3D micro capillary core 230 having a sintered
structure 232 mounted on its outer walls. The struts 228b, 228c
provide the advantage that by tailoring the 3D CAD geometry and the
sintering and/or selective laser melting treatment, the capillary
structure can be formed with a graded porosity and permeability,
which allows customisation of the mass flow rate of the condensed
working fluid around the device. In an alternative arrangement, the
sintered structure can be provided on the inside of the strut 228c
and the 3D CAD capillary structure on the external surface of the
strut.
[0056] Referring to FIG. 7, a capillary device 240 for use in an
axially grooved heat pipe of a third embodiment of the present
invention is shown. The capillary device 240 is built up by means
of selected laser melting of aluminium powder to build up
successive layers on a solid donor plate 242 for placing in contact
with a heat source, a solid aluminium housing 244, and a capillary
structure 246 comprising circumferentially separated porous
aluminium protrusions 248 protruding into a central elongate
channel 250. By use of the selective laser melting technique used
to form the capillary structure 246, the porous protrusions 248 can
be separated by smaller channel widths than in the case of the
known arrangement shown in FIG. 2, as a result of which the
protrusions 248 and gaps 252 therebetween generate significantly
enhanced capillary action compared with the arrangement shown in
FIG. 2, thereby enabling the heat pipe to operate under the
influence of gravity and have improved heat transfer
performance.
[0057] In operation, one end of the capillary device 240 is placed
in contact with a heat source, and the other end is placed in
contact with cooling means to form a condenser. The heat source
causes the working fluid to evaporate, and evaporated working fluid
travels along the central channel 250 to the condenser. Condensed
working fluid travels along the axial gaps 252 between protrusions
248, and is drawn through the porous protrusions 248 by capillary
action at the hot end of the heat pipe to maintain the flow of
condensed working fluid to the evaporator. The porous protrusions
248 and gaps 252 cooperate to enhance the capillary action to the
extent that the capillary action can overcome the effects of
gravity.
[0058] Referring to FIG. 8, in which parts common to the embodiment
of FIG. 7 are denoted by like reference numerals but increased by
100, a capillary device 340 of a heat pipe of a fourth embodiment
of the present invention differs from the arrangement shown in FIG.
7 in that porous protrusions 348 are hollow and contain unfused
aluminium powder to enhance the capillary action of flow of
condensed working fluid through the porous walls of the protrusions
348 and the powder contained in the protrusions 348.
[0059] FIG. 9 shows a capillary device 440 of a heat pipe of a
fifth embodiment of the present invention, in which parts common to
the embodiment of FIG. 8 are denoted by like reference numerals but
increased by 100. The capillary device 440 of FIG. 9 differs from
the arrangement shown in FIG. 8 in that a lattice capillary
structure 454 is formed in longitudinal gaps 452 between porous
protrusions 448 by means of a selective laser melting or sintering
process to form capillary pores having characteristic dimensions
below 50 microns at the condenser end of the heat pipe to draw
condensed working fluid into the capillary structure. At the
condenser, there is also a transition from sintered capillary to
lattice within the channel, and as the lattice moves towards the
evaporator region, the minimum characteristic dimension is graded
to produce open channels with minimum characteristic dimension that
are suitable to allow passage of evaporated working fluid. At the
evaporator, the lattice may be removed completely to remove any
restriction to flow of evaporated working fluid into the vapour
channel along the centre of the heat pipe. By grading the pore size
along the length of the heat pipe, the means in which it interacts
with the working fluid can be manipulated. At the condenser end of
the heat pipe, the capillary structure 454 is tailored to draw in
and become flooded with condensed working fluid, and the adiabatic
region of the heat pipe is tailored to provide a high mass flow
rate of fluid from the condenser to the evaporator regions. At the
evaporator region, the capillary structure 454 is tailored to allow
much larger surface heat fluxes to be input over this region.
Through the thickness of the evaporator capillary structure, its
properties are graded to allow the vapour to easily pass from the
capillary structure 454 into the vapour space and also to provide a
flow of liquid fluid to the vapour generation sites.
[0060] Referring to FIG. 10, a selective laser melting process is
used to build up a capillary device 540 as a single solid component
having vapour flow channels 556 for passage of evaporated working
fluid. To improve heat transfer, the vapour flow channels 556 are
entirely embedded within a porous capillary structure 558, in order
to increase the evaporation heat transfer surface area around the
walls of the vapour flow channels 556. Since it is no longer
necessary to machine the vapour flow channels 558, the shape and
flow path into the device is unlimited.
[0061] Referring to FIG. 11, in which parts common to the
embodiment of FIG. 10 are denoted by like reference numerals, a
capillary device 640 differs from the arrangement shown in FIG. 10
in that the porous capillary structure 658 in which the vapour flow
channels are formed encapsulates aluminium powder material 660 and
has a radial inner wall 662 surrounding a central fluid flow
passage 664.
[0062] A heat transfer apparatus 700 of a further embodiment of the
present invention is shown in FIG. 12. The apparatus 700 has a main
body 704 divided by a porous capillary structure 702, having porous
rigid walls and containing unmelted powdered material, into an
inlet chamber 706 and an outlet chamber 708. Liquid working fluid
introduced through an inlet 710 enters the capillary structure 702
via the inlet chamber 706 and is heated by heat passing through the
side wall of the main body 704. The heated working fluid then
passes in heated liquid or vapour form via the outlet chamber 708
and through an outlet 712.
[0063] Referring to FIGS. 13 and 14, a heat transfer apparatus 800
of a ninth embodiment of the present invention is in the form of a
flanged loop heat pipe comprising an evaporation chamber 802
cooperating with a condensation loop 804 and a cylindrical
compensation chamber 806. As shown in more detail in FIG. 14, the
evaporation chamber 802 has an outer cylindrical body 808 in which
a porous capillary structure 810 defines a complex 3D vapour flow
network 812 comprising a series of circumferential vapour channels
814 interconnected by an elongate escape channel 816. The capillary
structure 810 also defines an annular chamber 818 enclosing
unmelted metallic powder material 820. The chamber 818 surrounds a
central bore 822 which is closed by an end face 824 of the
capillary structure 810 and a solid wall 826. By manufacturing the
capillary structure 810 by means of selective melting of metallic
powder to form successive layers, complex 3D capillary structures
having a wider range of dimensions and properties can be
provided.
[0064] In operation, the evaporation device 802 cooperates with the
compensation chamber 806 such that the central bore 822 of the
evaporation device 802 is filled with condensed working fluid which
passes into the capillary structure 810 and unmelted metallic
powder 820 within the chamber 818 by means of capillary action.
When the evaporation chamber 802 is brought into contact with a
source of heat (not shown), working fluid evaporates from the
radially outer parts of the capillary structure 810 and passes into
the vapour flow network 812 and out of the fluid vapour escape hole
816 into condensation loop 804 where it is condensed by means of
cooling at a location separated from the heat source. Condensed
working fluid then passes into the end of the compensation chamber
806 remote from the evaporation chamber 802.
[0065] FIGS. 15 and 16 show a heat pipe 900 in which an evaporation
section 902, manufactured in successive layers by means of
selective melting of metallic powder, is connected, by means of a
curved adiabatic section 904, to a much longer extruded condenser
section 906 having a flow channel design 910 which matches that of
the evaporation section 902. The evaporation section 902 has a
grooved capillary structure 908, which may contain unmelted
metallic powder, having enhanced performance which therefore
enables larger amounts of heat to be input into the evaporator
section 902, thereby enabling the device 900 to cool smaller, high
power devices. Evaporated working fluid passes along a central
channel (not shown) of the curved adiabatic section 904 to the
longer condenser section 906, while condensed working fluid passes
along a capillary structure (not shown) contained in the curved
adiabatic section 904 to the capillary structure 908 of the
evaporation section 902.
[0066] FIG. 17 shows a heat transfer apparatus 1000 of an eleventh
embodiment of the present invention in which a single central
evaporator section 1002 having a capillary structure (not shown),
manufactured in successive layers by means of selective melting of
powdered metallic material using an energetic beam, is connected to
multiple, larger condensation sections 1004, each of which is
manufactured by means of conventional extrusion methods.
[0067] It will be appreciated by persons skilled in the art that
the above embodiments have been described by way of example only
and not in any limitative sense, and that various alterations and
modifications are possible without departure from the scope of the
invention as defined by the appended claims. For example, as an
alternative to a selective laser melting process, electron beam
melting may be used. In addition, as an alternative to selective
melting of a layer of powdered material, a stream of powdered
material may be directed by means of inert gas to the location at
which the powdered material is melted by the energy beam. This
enables a wider range of applications of the process to be used.
Furthermore, in addition to aluminium, other powdered materials
such as metals, metal alloys or polymer materials may be used.
* * * * *