U.S. patent application number 10/390773 was filed with the patent office on 2004-01-22 for vapor augmented heatsink with multi-wick structure.
Invention is credited to Siu, Wing Ming.
Application Number | 20040011509 10/390773 |
Document ID | / |
Family ID | 29553494 |
Filed Date | 2004-01-22 |
United States Patent
Application |
20040011509 |
Kind Code |
A1 |
Siu, Wing Ming |
January 22, 2004 |
Vapor augmented heatsink with multi-wick structure
Abstract
A heat transfer device includes a base chamber, a fin chamber,
and at least one fin. The chambers can be thermally coupled. The
heat transfer device also includes a wick structure. The wick
structure can include a multi-wick structure. The multi-wick
structure can include a three-dimensional wick structure and/or a
spatially varying wick structure.
Inventors: |
Siu, Wing Ming; (Kowloon
City, HK) |
Correspondence
Address: |
EDELL, SHAPIRO, FINNAN & LYTLE, LLC
1901 RESEARCH BOULEVARD
SUITE 400
ROCKVILLE
MD
20850
US
|
Family ID: |
29553494 |
Appl. No.: |
10/390773 |
Filed: |
March 19, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60380274 |
May 15, 2002 |
|
|
|
Current U.S.
Class: |
165/80.3 |
Current CPC
Class: |
F28D 15/046 20130101;
H01L 2924/0002 20130101; F28F 2215/10 20130101; Y10T 29/49353
20150115; H01L 2924/0002 20130101; F28D 15/0233 20130101; F28F 3/02
20130101; H01L 2924/00 20130101 |
Class at
Publication: |
165/80.3 |
International
Class: |
F28F 007/00 |
Claims
What is claimed is:
1. A heat transfer device, comprising: at least one base chamber;
at least one fin chamber; and at least one fin, the chambers being
thermally coupled and adapted to hold condensable vapor.
2. The heat transfer device of claim 1, wherein at least one fin is
solid.
3. The heat transfer device of claim 1, wherein the fin has at
least one side and is in thermal contact with at least one of the
base chamber and fin chamber.
4. The heat transfer device of claim 1, wherein the fin comprises
thermally conductive material.
5. The heat transfer device of claim 1, wherein the heat transfer
device includes at least one vapor path.
6. The heat transfer device of claim 1, further comprising a wick
structure.
7. The heat transfer device of claim 6, wherein the wick structure
can be formed integrally with a wall of the chambers.
8. The heat transfer device of claim 6, wherein the wick structure
can be formed separately from a wall of the chambers.
9. The heat transfer device of claim 6, wherein the wick structure
includes a multi-wick structure.
10. The heat transfer device of claim 9, wherein the multi-wick
structure includes a three-dimensional wick structure.
11. The heat transfer device of claim 9, wherein the multi-wick
structure includes a spatially varying wick structure.
12. The heat transfer device of claim 9, wherein the multi-wick
structure includes at least one bridging wick structure to provide
multiple liquid-flow-path.
13. The heat transfer device of claim 9, wherein the multi-wick
structure includes a combination of a groove, a mesh, an aggregated
powder wick, or a foam wick.
14. The heat transfer device of claim 9, wherein the multi-wick
structure includes a combination of a layered structure, a bar
structure, or a bridging wick structure.
15. The heat transfer device of claim 9, wherein the multi-wick
structure includes a wick structure with varying porosity.
16. The heat transfer device of claim 9, wherein the multi-wick
structure includes a wick structure with varying pore size.
17. The heat transfer device of claim 9, wherein the multi-wick
structure includes a wick with varying cross-sectional
geometry.
18. The heat transfer device of claim 9, wherein the multi-wick
structure includes a wick with varying dimensions.
19. The heat transfer device of claim 6, wherein the wick structure
includes a spatially varying wick structure.
20. The heat transfer device of claim 19, wherein the spatially
varying wick structure can be a groove structure with a spatially
varying pattern.
21. The heat transfer device of claim 6, wherein the wick structure
includes an aggregated powder wick.
22. The heat transfer device of claim 6, wherein the wick structure
includes a foam wick.
23. The heat transfer device of claim 6, wherein the wick structure
includes at least one groove.
24. The heat transfer device of claim 6, wherein the wick structure
includes a mesh wick.
25. The heat transfer device of claim 6, wherein the wick structure
includes a layered structure.
26. The heat transfer device of claim 6, further comprising a wick
structure adapted to store liquid so as to accommodate a liquid
flow variation.
27. The heat transfer device of claim 6, further comprising a wick
structure is disposed between opposing walls of a chamber.
28. The heat transfer device of claim 1, further comprising at
least one internal supporting structure to avoid collapsing of
chambers.
29. The heat transfer device of claim 28, wherein the internal
supporting structure includes at least one solid element.
30. The heat transfer device of claim 28, wherein the at least one
internal supporting structure element includes a wicking
structure.
31. The heat transfer device of claim 1, wherein at least one fin
includes at least one opening.
32. The heat transfer device of claim 31, wherein the opening
defines a plurality of geometries.
33. The heat transfer device of claim 31, wherein the opening
defines a plurality of dimensions.
34. The heat transfer device of claim 1, wherein at least one fin
includes an opening in an airflow downstream portion.
35. The heat transfer device of claim 1, wherein at least one fin
includes a cut-out on a side.
36. The heat transfer device of claim 35, wherein the cut-out
defines a plurality of geometries.
37. The heat transfer device of claim 35, wherein the cut-out
defines a plurality of dimensions.
38. The heat transfer device of claim 35, wherein the cut-out
defines a slit.
39. The heat transfer device of claim 35, wherein the side with the
cut-out thermally contacts at least one of the base chamber and the
fin chamber.
40. The heat transfer device of claim 1, wherein the at least two
fins comprise two interconnected fins.
41. The heat transfer device of claim 41, wherein the two
interconnected fins are connected by a baffle.
42. The heat transfer device of claim 1, further comprising at
least one phase change element.
43. The heat transfer device of claim 1, wherein the chambers form
an inverted T-shape.
44. The heat transfer device of claim 1, wherein the chambers form
a double inverted T-shape.
45. The heat transfer device of claim 1, wherein the chambers form
a U-shape.
46. The heat transfer device of claim 1, wherein the chamber form a
W-shape.
Description
CLAIM OF PRIORITY
[0001] This application claims priority under 35 USC .sctn.119(e)
to U.S. Provisional Application Serial No. 60/380,274, filed on May
15, 2002, and titled "VAPOR HEAT SINK," the entire contents of
which are hereby incorporated by reference.
TECHNICAL FIELD
[0002] This application relates to cooling devices, and more
particularly, to vapor augmented heat transfer devices.
BACKGROUND
[0003] As electronic components and devices get smaller with
increasing operational speed, generated heat becomes a major
obstacle of improving performance of electronic devices and
systems. A heatsink is a common device used to remove heat from a
heat-generating device to the ambient environment.
[0004] In many applications, heat generated from an electronic
device can be ejected into the air by heatsinks. Development of
heatsinks has been a major focus of thermal management in
electronic systems. The performance of a heatsink can be
represented by a total thermal resistance. A lower resistance value
represents a higher cooling/heat transfer performance. Conductive
resistance and convective resistance can affect the total thermal
resistance of a heatsink. Conductive resistance represents the
ability of a heatsink to diffuse heat from contact point with the
heat source to convective surfaces. In general, conductive
resistance can be minimized by having a short thermal conduction
path with a large cross-section area with highly conductive
material, e.g., aluminum or copper. Convective resistance
represents the ability of a heatsink to eject heat into the ambient
environment with a given air flow configuration. In general,
heatsink designs maximize the number of convective surfaces.
[0005] Heat pipes can be used to reduce conductive resistance,
since evaporated vapor carries heat from the evaporation zone and
releases the heat by condensation over the condensation surface.
For instance, a flat-plate heatpipe has been used to reduce the
spreading resistance at the base of a heatsink. Also, fins, which
are heatpipes arranged in an array configuration, thermally
connected with a solid base, can minimize conductive resistance
along the fins. A flat-plate heatpipe can be combined with other
heatpipes to form a base and fins.
SUMMARY
[0006] A heatpipe heatsink includes a heatsink in which both the
fins and the base can be interconnected heatpipe chambers. Such a
heatpipe heatsink can directly contact semiconductor chips, a
bottom portion of the base chamber can be a flexible, thermally
conductive sheet to provide good contact with surfaces of the
chips. Inter-connected chambers of a heatpipe heatsink can be
formed of ceramic material. The ceramic material can form the body
with a porous structure and an impermeable layer can cover the
porous ceramic body. Ceramic material can provide a more uniform
interconnected pore structure for the wick. Alternatively, a
heatpipe heatsink can be made by hot-pressing or sintering metal
powders and over-molding a thermally conductive polymer. The fin
chambers can have a pin array configuration for convective heat
transfer. Inter-connected chamber heatpipe heatsink for a
semi-conductor package can include channels as the wick structure.
Channel wicks can be used in a heatpipe heatsink with an array of
tapered-hollow-pin fin chambers.
[0007] The wicking structure of a heatpipe heatsink is functionally
different from that of a more traditional heat pipe. In particular,
the vapor and liquid flow of a more traditional heatpipe is
generally one-dimensional, while in a heatpipe heatsink the vapor,
liquid flow is more like three-dimensional. As such, the mass flow
rate of the condensed liquid spatially varies in a heatpipe
heatsink, but not in a more traditional heatpipe. Consequently, a
modified wick structure can be used. A heatpipe heatsink with a
modified wick structure can further reduce its thermal
resistance.
[0008] A vapor-augmented heatsink can provide high thermal
performance by using a wick structure which considers the
three-dimensional characteristics of vapor and liquid flows within
the heatpipe chambers and by using the heatpipe chamber and the
solid convective element to minimize convective resistance.
[0009] The heat transfer rate across a heatpipe chamber directly
contributes to the conductive resistance of the vapor-augmented
heatsink. The heat transfer rate can be limited by the vapor flow
rate and liquid flow rate. Since the performance of heatpipe
chambers relates to three-dimensional fluid flows, the internal
configuration can accommodate three-dimensional vapor flow and the
three-dimensional liquid flow. Regarding the liquid flow, as the
vapor augmented heatsink is intended for the electronic market, the
heating (evaporation) zone typically has a high heat flux factor.
Coupled with the size of the vapor augmented heatsink, having a
high heat flux factor creates an illusion of needing a wicking
structure with high wicking-power, while providing sufficient lift
in relation to the size of the device. In general, wicking
structures that can sustain both high flow-rate and provide large
lift are difficult to achieve. However, in reality, only the
heating (evaporation) zone has a high wicking-power factor, and the
wicking power factor reduces with increasing distance from the
heating zone. Specifically, condensation occurs at a significantly
reduced heat-flux, and a high condensation flow rate is needed only
at the evaporation site where the condensate converges together.
Therefore, the wicking structure can vary according to the spatial
flow rate requirement in order to better balance the forces (i.e.,
capillary force, viscous force, and gravitational force) acting on
the liquid. Furthermore, the condensed liquid can flow back to the
evaporation zone through three-dimensional multiple
liquid-flow-paths, thereby shortening the travel distances. These
factors allow for the use of variable wicks with variable wicking
structures and/or variable thickness in the wicking structure.
[0010] Concerning the three-dimensional vapor flow, the vapor needs
to be spread across the chambers. In general, the cross-sectional
dimensions of the vapor cavity should be sufficiently large.
However, a smaller overall chamber size is required for allow more
convective surface area. Therefore, a thinner wick layer can
provide a larger vapor cavity inside the chamber. With a varying
wick structure, the thickness of the wick layer can be thinner at
locations other than the evaporation zone. For example, the fin
chamber can have a thinner wick structure since the amount of
condensed liquid is less there than at the location close to the
evaporation zone. As a result, the overall performance of the
vapor-augmented heatsink can be improved by considering both the
convective resistance and the conductive resistance.
[0011] In addition, in order to reduce the total thermal resistance
of heatpipe heatsinks, solid convective fins can be used. Since the
thickness or the size of a solid convective fin is generally
smaller than that of a heatpipe chamber, the convective resistance
can be reduced by using solid fins in a configuration to increase
the total number of convective surfaces with a small temperature
variation over the convective surfaces. In order to obtain a
convective surface with smaller temperature variation, at least one
side of a solid fin can thermally contact the heatpipe
chambers.
[0012] In addition to internal operations, the fin(s) of the
vapor-augmented heatsink can be configured to further reduce
convective resistance. Specifically, in a typical heatsink, the
base of the solid fin(s) serves to conduct heat away from the base
toward the tip of the fin(s), which, in a channel configuration,
increases the pressure drop in the air and thus diminishes the
ability of the air to remove the heat. However, in a
vapor-augmented heatsink, heat can be transported away from the
base through vapor condensation, and as a result, opening(s) can be
created on the solid fin(s). The opening(s) can reduce the pressure
drop in the air and can increase the convective heat transfer
similar to that of a pin-grid array or porous configuration.
[0013] The chambers can be formed by a material removal process,
such as machining and electro-discharge-machining; or a material
transforming process, such as stamping, drawing, casting, molding,
folding, laminating, sintering, or jointing of preformed elements;
or another material forming process known in the art. The wick
structure on the inner wall of the device can be formed (for
example, by molding or by lamination) at the same time as the
chamber. Alternatively, the wick structure can also be formed
separately by processes that are known in the art, for example, by
inter-connective process, such as mesh formed by wires, sintering
of powders, or powders with bonding material; or material forming
process, such as plating or coating, or porous foam forming; or
material removal process, such as machining or etching; or
combinations of processes that are known in the art. The solid
convective elements can be formed at the same time as the formation
of the chamber. Alternatively, the convective elements can also be
formed separately by material forming processes, such as casting,
molding, stamping, or machining, or other material forming or
removal processes that are known in the art. The thermal connection
between the separately formed convective elements and the chamber
can be done by material connection processes with or without
interfacial bonding material, such as soldering, brazing, welding,
thermal activated bonding, sonic activated bonding, pressure
activated bonding, adhesive bonding, or other process known in the
art. Working liquid can be introduced into the chamber before the
chamber is hermetically sealed. Furthermore, the condition inside
the chamber can allow evaporation of the working fluid at a
temperature between its freezing condition and critical
condition.
[0014] In a general aspect, a heat transfer device includes at
least one base chamber, at least one fin chamber, and at least one
fin. The chambers can be thermally coupled and adapted to hold
condensable vapor.
[0015] The implementation of the heat transfer device may include
one or more of the following features. The heat transfer device can
include at least one fin that is solid. The fin can have at least
one side and be in thermal contact with at least one the base and
fin chambers. The fin can be formed of thermally conductive
material.
[0016] The heat transfer device can include at least one vapor
path.
[0017] The heat transfer device can also include a wick structure.
The wick structure can be formed integrally with a wall of the
chambers. Alternatively, the wick structure can be formed
separately from a wall of the chambers. The wick structure can
include a multi-wick structure, a three-dimensional wick structure,
or a spatially varying wick structure.
[0018] The multi-wick structure can include at least one bridging
wick structure to provide multiple liquid-flow-path. Alternatively,
the multi-wick structure can include a combination of a groove, a
mesh, an aggregated powder wick, or a foam wick. Or, the multi-wick
structure can include a combination of a layered structure, a bar
structure, or a bridging wick structure. In another alternative,
the multi-wick structure can include a wick structure with varying
porosity or varying pore size. The wick can have a varying
cross-sectional geometry or varying dimensions.
[0019] The wick structure can include a spatially varying wick
structure. The spatially varying wick structure can be a groove
structure with a spatially varying pattern.
[0020] Alternatively, the wick structure can include an aggregated
powder wick, a foam wick, at least one groove, or a mesh wick. The
wick structure can include a layered structure.
[0021] The heat transfer device can further include a wick
structure adapted to store liquid so as to accommodate a liquid
flow variation.
[0022] The heat transfer device can further include a wick
structure is disposed between opposing walls of a chamber.
[0023] The heat transfer device can further include at least one
internal supporting structure to avoid collapsing of chambers. The
internal supporting structure can include at least one solid
element. Alternatively, the internal supporting structure element
can include a wicking structure.
[0024] The fin of the heat transfer device can include at least one
opening. The opening can define a plurality of geometries.
Alternatively, the opening can define a plurality of
dimensions.
[0025] The fin of the heat transfer device can include an opening
in an airflow downstream portion.
[0026] The fin of the heat transfer device can include a cut-out on
a side. The cut-out can define a plurality of geometries.
Alternatively, the cut-out can define a plurality of dimensions. In
another alternative, the cut-out can define a slit. The side with
the cut-out can thermally contact at least one of the base chamber
and the fin chamber.
[0027] The at least two fins of the heat transfer device can
include two interconnected fins. The two interconnected fins can be
connected by a baffle.
[0028] The heat transfer device can further include at least one
phase change element.
[0029] The chambers of the heat transfer device can form an
inverted T-shape, a double inverted T-shape, a U-shape, or a
W-shape.
[0030] The details of one or more embodiments are set forth in the
accompanying drawings and the description below. Other features
will be apparent from the description and drawings and from the
claims.
DESCRIPTION OF DRAWINGS
[0031] FIG. 1A is an isometric view of a vapor-augmented heatsink
with an inverted "T" heatpipe chamber.
[0032] FIG. 1B is a cross-sectional view of the vapor-augmented
heatsink of FIG. 1A, along section A-A. showing one view of an
embodiment of a mesh wicking structure.
[0033] FIG. 1C is a cross-sectional view of the vapor-augmented
heatsink if FIG. 1A, along section B-B, showing another view of the
embodiment of the mesh wicking structure of FIG. 1B.
[0034] FIG. 2A is a sectional view of the embodiment of a
multi-wick wicking structure with a special groove on the bottom
plate of the vapor-augmented heatsink of FIG. 1A taken along
section A-A.
[0035] FIG. 2B is a sectional view of the embodiment of a
multi-wick wicking structure with a special groove on the bottom
plate of the vapor-augmented heatsink of FIG. 1A, taken along
section B-B.
[0036] FIG. 3A is a sectional view of a third embodiment of a
grooved wicking structure with mesh layer on the bottom plate of
the vapor-augmented heatsink of FIG. 1A, taken along section
A-A.
[0037] FIG. 4A is a sectional view of a fourth embodiment of a
multi-wick wicking structure of the vapor-augmented heatsink of
FIG. 1A, taken along section A-A.
[0038] FIG. 4B is a sectional view of the fourth embodiment of the
multi-wick wicking structure of the vapor-augmented heatsink to
shown one
[0039] FIG. 5A is a sectional view of a fifth embodiment of another
multi-wick wicking structure of the vapor-augmented heatsink of
FIG. 1A, taken along section A-A.
[0040] FIG. 5B is a sectional view of the fifth embodiment of the
multi-wick wicking structure of the vapor-augmented heatsink of
FIG. 1A, taken along section B-B.
[0041] FIG. 5C is a sectional view of the fifth embodiment of the
multi-wick wicking structure of the vapor-augmented heatsink of
FIG. 1A, taken along section C-C.
[0042] FIG. 6A is a sectional view of the vapor-augmented heatsink
of FIG. 1A, showing a wick configuration with liquid reservoirs,
taken along section D-D.
[0043] FIG. 6B is a sectional view of the vapor-augmented heatsink
of FIG. 1A showing the wick configuration with liquid reservoirs,
taken along section B-B.
[0044] FIG. 7A is a sectional view of the vapor-augmented heatsink
of FIG. 1A, showing the wick configuration with solid-liquid phase
change elements, taken along section A-A.
[0045] FIG. 7B is a sectional view of the vapor-augmented heatsink
of FIG. 1A, showing the wick configuration with solid-liquid phase
change elements of FIG. 7A, taken along section B-B.
[0046] FIG. 8A is an isometric view of a vapor-augmented heatsink
with a double inverted "T" heatpipe chamber.
[0047] FIG. 8B is a sectional view of the vapor-augmented heatsink
with a double inverted "T" heatpipe chamber of FIG. 8A taken along
section 8B-8B.
[0048] FIG. 8C is a sectional view of the vapor-augmented heatsink
with a double inverted "T" heatpipe chamber of FIG. 8A taken along
section 8C-8C.
[0049] FIG. 8D is a sectional view of the vapor-augmented heatsink
with a double inverted "T" heatpipe chamber of FIG. 8A taken along
section 8D-8D.
[0050] FIG. 8E is a sectional view of the vapor-augmented heatsink
with a double inverted "T" heatpipe chamber of FIG. 8A taken along
section 8E-8E.
[0051] FIG. 9 is a front view of a vapor-augmented heatsink with a
"U" heatpipe chamber.
[0052] FIG. 10 is a front view of a vapor-augmented heatsink with a
"W" heatpipe chamber.
[0053] FIG. 11A is a sectional view of the multi-wick wicking
structure of the vapor-augmented heatsink of FIG. 1A taken along
section A-A with a wick having a spherical shape.
[0054] FIG. 11B is a sectional view of the multi-wick wicking
structure of the vapor-augmented heatsink of FIG. 1A, taken along
section B-B with a wick having a plurality of shapes.
[0055] FIGS. 12-14 are side views of a fin including at least one
opening of a vapor-augmented heatsink having a plurality of
geometries and/or dimensions.
[0056] FIGS. 15 and 16 are side views of a fin including at least
one cut-out of a vapor-augmented heatsink having a plurality of
geometries and/or dimensions.
[0057] Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION
[0058] Referring to FIG. 1A, a vapor-augmented heatsink 100
includes a base chamber 110, a fin chamber 120, and solid fins 130.
The fins 130 and the heat source contact portion 103 (see FIG. 1B)
of the base chamber 110 can be made of thermally-conductive
material, such as copper or aluminum, while another remaining
portion 103, 104 of the base chamber 110 and other chambers can be
made of a solid material, such as metals, ceramics, and plastics,
depending on application requirements. The base chamber 110 can
absorb heat from the heat source 101 (as shown in FIGS. 1B and 1C),
such as an electronic device. The heat can evaporate the liquid
inside the base chamber 110. Vapor can be generated and can carry
the heat to other surfaces of the base chamber 110 and surfaces of
fin chamber 120 by condensation. The distributed heat can be
diffused into the fins 130 and eventually, convected into the
ambient environment by airflow over the fins 130. Wire mesh wick
structures 119, 129 can be applied over the internal walls 102 of
the fin chamber 120 and the base chamber 110, respectively. The
condensed liquid can be pulled back to the evaporation zone or heat
source contact portion 103 by capillary force along the wicks 119,
129. Generally, both base chamber 110 and fin chamber 120 are under
vacuum pressure so that internal supporting structure(s) (not
shown) prevent collapse of the chambers 110, 120. The supporting
structure(s) can include wicking structures. Besides the reduction
of conductive resistance, convective resistance can be reduced by
fin design. Each solid fin 130 conducts heat from two sites, the
contact 131 with the fin chamber 120 and the contact 132 with the
base chamber 110, to provide more uniform temperature convective
surfaces 133 on the fin 130 for improved heat dissipation.
Furthermore, openings 134 at the lower part of the fin can provide
an additional impingement effect on the base as air flows downward
and can reduce the back pressure and pressure drop for the airflow.
As a result, a large portion of the airflow can pass through the
fins and along the base without escaping the heatsink halfway
through before reaching the base chamber 110. Better flow ducting
effect can be achieved by adding baffles (not shown) at the sides
of the fins to guide the airflow downward.
[0059] To optimize liquid flow and vapor flow, a spatially varying
wick structure can be used. In general, the liquid flow rate along
the base chamber 110 is higher than that along the fin chamber 120.
A wicking structure at the bottom portion of base chamber 110 can
include a groove structure 140 applied on the bottom plate of the
base chamber 110 so that the wicking-power along the bottom plate
can converge the liquid toward the evaporation zone 103, as shown
in FIGS. 2A and 2B. The major grooves 141, 145 channel liquid away
from the sides 146, 167. Grooves 142, 143, 144 bridge the liquid
across grooves 141 and 145 and pull the liquid toward center. By
putting a mesh structure 119 on top of this groove structure layer
140, the condensed liquid can be pulled back to the evaporation
zone at the center. Instead of using mesh, groove structures 151,
152 can be applied over the internal walls. Referring to FIG. 3,
vertical grooves 151 and horizontal grooves 152 can be provided
inside the fin chamber 120, while horizontal grooves 152 and groove
structure 140 can be provided inside the base chamber 110. In order
to provide a higher wicking-power along the bottom portion of the
base chamber 110, a mesh layer 153 can be applied to groove
structure 140.
[0060] For higher heat dissipation, a more complex multi-wick
structure, such as the wick structure configuration shown in FIGS.
4A and 4B, can be used. Since the distribution of heat is by
condensation of generated vapor, the condensed liquid can also be
distributed over the internal surfaces of chambers 110 and 120. The
condensed liquid can be pulled along the wick structure layers 111
and 121, which contact with the chamber walls 102, by capillary
force back to the evaporation zone 103. Since the heat flux can be
significantly reduced by the heat spreading effect, the liquid flow
rate can be relatively low that an ordinary wicking-power
structure, such as wire mesh, can be used. As the liquid is pulled
closer to the evaporation zone 103, the mass flow rate can increase
since the liquid converges from a large surface area to a smaller
evaporation area. Therefore, at most of surfaces, only an ordinary
wick structure (e.g., wire mesh, grooves, sintered powder layer, or
foam structure layer) can be applied for the wick layers 111, 121
and can pull the liquid flow toward the evaporation zone 103. On
the other hand, at regions 112, 122 close to the evaporation zone,
a higher wicking-power structure, such as many layers of wire mesh,
grooves, powders, foam structure, or a combination therefore, can
be used. Additionally, wick structure bridges 113, 123 can also be
applied within chambers 110, 120 to provide a short distance with
three dimensional multiple liquid-flow-paths for the liquid flow
back to the evaporation zone 103 instead of flowing along only
internal surfaces. The structure of the wick structure bridges 113,
123 (the three-dimensional multiple liquid-flow path wick
structures) can be a higher wicking-power structure, such as many
layers of wire mesh, grooves, powders, foam structure, or a
combination thereof. These bridges may also be combined with
structural columns (not shown) to provide the necessary supporting
functions. Vapor flow can affect heat distribution over the chamber
surface. As the vapor flows through the vapor cavity of the
chambers, there can be significant temperature difference between
the evaporation zone 103 and the condensation surfaces if the
pressure drop along the vapor flow path is large. If a wider vapor
cavity can be used with a thinner wick structure, the resulting
pressure drop can be reduced so that a final condensation
temperature at the chamber surface can be close to the temperature
at the evaporation zone 103. As a result, the overall high heat
dissipation performance can be increased.
[0061] Referring to FIGS. 5A, 5B, and 5C, another multi-wick
structure includes an ordinary wick structure layer 111 on the
bottom surface of the base 110 and a high wicking-power structure
layer 112 in the region close to the evaporation zone 103. A high
wicking-power structure can also be used for the wicking layer 115
around the sides of the base, as shown in FIG. 5B. Another high
wicking-power structure bar 116 at the middle and across the base,
perpendicular to the fin chamber 120 can be included. Both high
wicking-power structure layer 115 and high wicking-powered
structure bar 116 can be the height of the vapor chamber so that
the layer 115 and bar 116 can serve as wicking bridges (the
three-dimensional multiple liquid-flow-path wick structure) between
the top surface and the bottom surface of the base 110. Another
high wicking-power structure bar 114 can cross the base,
perpendicular to the wicking bar 116 at the middle of the base. The
height of wicking bar 114 can be less than the height of the
chamber so that a gap 105 can be created for vapor flow. The
wicking layer 115 along the side can channel the condensed liquid
around the side of the base 110 to the ends of the wicking bars
114, 116. Wicking bars 114, 116 can share the total mass flow of
liquid and pull the liquid back to the evaporation zone 103.
Similarly, wicking layer 125 can be applied along the side of the
fin chamber 120 and the bridging and channeling wicking bar 124 can
be applied at the middle of the fin chamber 120 from top to the
bottom, as shown in FIG. 5A.
[0062] Heat source 101 can dissipate heat into the base chamber
110. In a steady state situation, the amount of power dissipating
is relatively constant so that the amount of vapor generation is
also constant. In normal operating conditions, the condensed liquid
flow back to the evaporation zone is constant and equal to the mass
evaporation rate in order to maintain the balance of the heat of
evaporation and the heat input from the heat generating electronic
device 101. However, in some electronic device applications, the
heat dissipation rate is not steady and varies rigorously. If the
heat dissipation rate suddenly increases, the required increment of
the liquid flow may not be matched immediately. As a result, the
equilibrium temperature of the evaporation zone 103 can shift so
that the device may over-heat due to drying-out. Liquid reservoirs
117 can be introduced at the far end of the base chamber, as shown
in FIGS. 6A and 6B. The reservoirs 117 can hold an amount of
liquid, which can be pulled toward the evaporation zone 103 since
the wicking-power of the reservoirs 117 is relatively low in
comparison to ordinary wick 112.
[0063] Referring FIGS. 7A and 7B, solid-liquid phase change
elements 118 can be used to prevent drying-out due to a sudden
increase of heat dissipation from the heat source 101. The phase
change elements 118 can be small containers in which solid-liquid
phase change materials can be disposed. The phase change material
can be specifically selected to limit the evaporation zone
temperature at a predetermined temperature so that the melting
temperature of the phase change material is below the maximum
allowable temperature for the electronic device and higher than the
normal running temperature of the vapor-augmented heatsink 100.
When there is a sudden increase of dissipating heat from the
electronic device, the evaporation rate can increase and the
equilibrium temperature at the evaporation zone can increase. When
the temperature at the evaporation zone reaches the melting
temperature of the phase change material, the phase change element
118 can absorb heat by melting. As a result, the evaporation rate
does not keep increasing so as to prevent dryout. When the heat
dissipation rate decreases so that the absorbed heat can gradually
be released to the liquid by re-solidification of the phase change
element 118, the equilibrium at the evaporation zone 103 can shift
back to the normal operating condition.
[0064] The geometry of the fin chamber 120 and base chamber 110 as
previously described was a single inverted "T". In FIGS. 8A to 8E,
the vapor-augmented heatsink includes a double inverted "T". The
arrangement of the multi-wick structure is similar to that for the
single inverted "T" configuration. Assuming the heat source 101 can
be located at the center of the base 110 of the vapor-augmented
heatsink 100, the heat can evaporate the liquid inside the chamber,
vapor can be generated, and the vapor can carry the heat to other
surfaces of base chamber and surfaces of the two fin chambers by
condensation. The condensed liquid can be pulled along the wick
structure layer 111 and 121 by capillary force. As the liquid is
pulled closer to the evaporation zone 103, the mass flow rate can
increase since the liquid can converge from a large surface area to
a small evaporation area. Therefore, at most of the surfaces, an
ordinary wicking structure, such as wire mesh, groove, sintered
powder, foam structure, can be used for the wicking layers 111 and
121, and can pull the liquid. At the regions 112, 122 close to the
evaporation zone 103, a higher wicking-power structure, such as
many layers of wire mesh, grooves, powders, foam structure, any
combination of them, can be used. In addition, additional wicking
bridges 113, 123, which provide the three-dimensional multiple
liquid-flow-path, can also be applied between the base surface and
other surface to provide a shorter travel distance for the liquid
flow back to the evaporation zone 103. The structure of the wicking
bridges 113, 123 can be of a higher wicking-power structure, such
as many layers of wire mesh, grooves, powders, foam structure, or a
combination thereof. Additional high wicking-power elements 114,
115, 116 can be added around the sides of the base and across the
base to enhance the liquid pulling back to the evaporation zone
103. Liquid reservoirs 117 and solid-liquid phase change elements
118 can be introduced to avoid dryout with an increase of
dissipation power from the heat source 101.
[0065] In FIGS. 9 and 10, a "U" shape and a "W" shape,
respectively, heatpipe chamber configuration can be included in the
vapor-augmented heatsink. An internal multi-wick structure can
follow the same principles as with the single inverted "T" and
double inverted "T" heatpipe chamber configurations described
above.
[0066] Referring to FIG. 11A, the multi-wick wicking structure 111
of the vapor-augmented heatsink includes a wick having a
semi-circular shape 161.
[0067] Referring to FIG. 11B, the multi-wick wicking structure 111
of the vapor-augmented heatsink includes a wick having a plurality
of shapes 123, 163.
[0068] Referring to FIGS. 12-14, the fin 130 of the vapor-augmented
heatsink can include at least one opening 171 having a plurality of
geometries and/or dimensions. In FIG. 12, for instance, the
openings 171 have the same shape (geometry), i.e., circular, and
have the same dimensions, i.e., are of a similar size. In another
example, in FIG. 13, the openings 171, 172, 173 again have the same
shape (geometry), i.e., circular, but, the openings 171, 172, 173
vary in size (dimension), i.e., diameter. In yet another example,
in FIG. 14, the openings 171, 174, 175 have different shapes
(geometries), i.e., triangular, circular, and square, and vary in
size (dimension).
[0069] Referring to FIGS. 15 and 16, the fin 130 of the
vapor-augmented heatsink can include at least one cut-out 181, 182,
183, 184, 185 having a plurality of geometries and/or dimensions.
In FIG. 15, for instance, the fin 130 includes a plurality of
cut-outs 181, 182, 183 having the same shape (geometry), i.e.,
rectangular, but have different sizes (dimensions). In another
example, in FIG. 16, the fin 130 includes a plurality of cut-outs
181, 184, 185 having different shapes (geometries), i.e.,
rectangle, semi-circle, quarter-circle, and having different sizes
(dimensions).
[0070] A number of implementations have been described.
Nevertheless, it will be understood that various modifications may
be made without departing from the spirit and scope.
[0071] Accordingly, other embodiments are within the scope of the
following claims.
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