U.S. patent application number 12/165193 was filed with the patent office on 2009-12-31 for flow diverters to enhance heat sink performance.
This patent application is currently assigned to Alcatel-Lucent Technologies Inc.. Invention is credited to Domhnaill Hernon, Marc Hodes, Shankar Krishnan, Alan Lyons, Alan O'Loughlin.
Application Number | 20090321046 12/165193 |
Document ID | / |
Family ID | 41446003 |
Filed Date | 2009-12-31 |
United States Patent
Application |
20090321046 |
Kind Code |
A1 |
Hernon; Domhnaill ; et
al. |
December 31, 2009 |
FLOW DIVERTERS TO ENHANCE HEAT SINK PERFORMANCE
Abstract
A heat sink includes a base and fins attached to the base. A
flow diverter is in contact with the base or at least one of the
fins and is configured to disturb a laminar flow region of a fluid
flowing adjacent to at least one of the fins or the base.
Inventors: |
Hernon; Domhnaill; (Meath,
IE) ; Hodes; Marc; (Dublin, IE) ; Lyons;
Alan; (New Providence, NJ) ; O'Loughlin; Alan;
(Dubllin, IE) ; Krishnan; Shankar; (Richland,
WA) |
Correspondence
Address: |
HITT GAINES, PC;ALCATEL-LUCENT
PO BOX 832570
RICHARDSON
TX
75083
US
|
Assignee: |
Alcatel-Lucent Technologies
Inc.
Murray Hill
NJ
|
Family ID: |
41446003 |
Appl. No.: |
12/165193 |
Filed: |
June 30, 2008 |
Current U.S.
Class: |
165/80.3 |
Current CPC
Class: |
F28F 2215/10 20130101;
B23P 15/26 20130101; H01L 2924/0002 20130101; F28F 13/02 20130101;
Y10T 29/4935 20150115; F28F 13/06 20130101; H01L 23/467 20130101;
F28F 3/02 20130101; H01L 2924/0002 20130101; H01L 2924/00
20130101 |
Class at
Publication: |
165/80.3 |
International
Class: |
F28F 7/00 20060101
F28F007/00 |
Claims
1. A heat sink comprising: a base; fins attached to said base; and
a flow diverter in contact with said base or at least one of said
fins and configured to disturb a laminar flow region of a fluid
flowing adjacent to at least one of said fins or said base.
2. The heat sink as recited in claim 1, wherein said flow diverter
is configured to divert said fluid from a greater distance above a
surface of said heat sink to a lesser distance above said
surface.
3. The heat sink as recited in claim 1, wherein said heat sink is
in thermal contact with a device configured to dissipate heat, and
said flow diverter is configured to direct said fluid from a region
of relatively lower power dissipation by said device to a region of
relatively greater power dissipation by said device.
4. The heat sink as recited in claim 1, wherein said flow diverter
comprises a duct between two of said fins.
5. The heat sink as recited in claim 1, wherein said flow diverter
is configured to produce unsteady flow in said fluid.
6. The heat sink as recited in claim 1, wherein said flow diverter
is located on said base between two of said fins.
7. The heat sink as recited in claim 6, wherein a height of said
flow diverter is less than a height of said fins.
8. The heat sink as recited in claim 6, wherein said flow diverter
has a streamlined profile.
9. The heat sink as recited in claim 1, wherein said flow diverter
is attached to said base or said fin and positioned upstream of
said fin and outside a space bounded by said fins.
10. The heat sink as recited in claim 1, wherein said flow diverter
is a monolithic feature of said heat sink.
11. The heat sink as recited in claim 1, further comprising an
opening in said surface, wherein said flow diverter is configured
to direct said fluid through said opening.
12. The heat sink as recited in claim 1, wherein said flow diverter
is an active element.
13. A method, comprising: providing a heat sink having a base and
fins attached thereto; placing a flow diverter in contact with said
fin or said base; and configuring said flow diverter to disturb a
laminar flow region of a fluid flowing adjacent to at least one of
said fins or said base.
14. The method as recited in claim 13, wherein said flow diverter
is configured to divert said fluid from a greater distance above
said base to a lesser distance above said base.
15. The method as recited in claim 13, further comprising placing
said heat sink in thermal contact with a device configured to
dissipate heat, wherein said flow diverter is configured to divert
said fluid from a region of relatively lower power dissipation by
said device to a region of relatively greater power dissipation by
said device
16. The method as recited in claim 13, further comprising
configuring a duct between two of said fins to divert said
fluid.
17. The method as recited in claim 13, further comprising
configuring said flow diverter to produce unsteady flow in said
fluid.
18. The method as recited in claim 13, further comprising locating
said flow diverter on said base between said fins and configuring
said flow diverter to have a height less than a height of fins.
19. The method as recited in claim 13, further comprising forming
said flow diverter, said base and said fins as a monolithic
structure.
20. The method as recited in claim 13, wherein said flow diverter
is an active element.
21. The method as recited in claim 13, wherein said fluid is air.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is related to U.S. patent
application Ser. No. ______ to Hernon, et al., entitled "Active
Heat Sink Designs", and which is commonly assigned with the present
application, and U.S. patent application Ser. No. ______ to Hernon,
et al., entitled "Monolithic Structurally Complex Heat Sink
Designs," both of which are hereby incorporated by reference as if
reproduced herein in their entirety.
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention is directed, in general, to heat
sinks.
BACKGROUND OF THE INVENTION
[0003] Heat sinks are commonly used to increase the convective
surface area of an electronic device to decrease the thermal
resistance between the device and cooling medium, e.g., air. Such
heat sinks generally employ fins or pins to exchange heat with a
fluid (air or liquid) flowing thereover. Some electronic components
dissipate enough power that air-cooled heat sinks are becoming
inadequate to sufficiently cool these devices. Liquid cooling adds
significant costs and reliability concerns to system designs, and
is thus undesirable in many cases. Methods of improving the heat
transfer efficiency of air-cooled heat sinks are needed to extend
their use to higher power components.
SUMMARY OF THE INVENTION
[0004] One embodiment is a heat sink that includes a base and fins
attached to the base. A flow diverter is in contact with the base
or at least one fin and is configured to disturb a laminar flow
region of a fluid flowing adjacent to at least one of the fins or
the base.
[0005] Another embodiment is a method that includes providing a
heat sink having a base and fins attached thereto. A flow diverter
is placed in contact with said fin or said base. The flow diverter
is configured to disturb a laminar flow region of a fluid flowing
adjacent to at least one of said fins or said base.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] Various embodiments are understood from the following
detailed description, when read with the accompanying figures.
Various features may not be drawn to scale and may be arbitrarily
increased or reduced in size for clarity of discussion. Various
features in figures may be described as "vertical" or "horizontal"
for convenience in referring to those features. Such descriptions
do not limit the orientation of such features with respect to the
natural horizon or gravity. The term "surface" unless otherwise
qualified applies to the combined surface of the heat sink, that
is, the surface of the base, fins and any projections therefrom.
Reference is now made to the following descriptions taken in
conjunction with the accompanying drawings, in which:
[0007] FIG. 1 illustrates a prior art heat sink;
[0008] FIG. 2 illustrates air flow regions between two fins of a
heat sink;
[0009] FIGS. 3-5 illustrate embodiments of a heat sink with various
configurations of a flow diverter; and
[0010] FIGS. 6 and 7 illustrate embodiments of a heat sink where
air flow is diverted vertically with respect to a base.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0011] Embodiments described herein reflect the recognition that
structural features may be used in heat sinks that decrease thermal
resistance between the heat sink and a fluid e.g., air. In some
embodiments, these structural features may be used to produce
unsteady flow of air, e.g., in selected portions of the heat sink
to disturb laminar flow near surfaces of the heat sink. In other
embodiments, features are formed that direct cooler, faster moving
air from one region of a heat sink to a region having hotter,
slower flow to increase the rate of heat transfer from the hotter
regions. In some embodiments, three dimensional (3-D) rendering and
investment casting may be employed to form such structural features
in a cost-effective manner.
[0012] FIG. 1 illustrates a prior art heat sink 100. Features of
the heat sink 100 include a base 110 and fins 120. The fins 120 of
such heat sinks are typically structurally uniform, e.g., there are
no projections or depressions in the surface of the fins 120 other
than surface roughness typical of the particular manufacturing
method.
[0013] An air stream 130 passes between the fins 120 with little
obstruction. It is thought that as air enters the space between two
fins, a boundary layer forms near the surfaces of the fins 120 and
the base 110. The boundary layer is a region of airflow adjacent to
a surface that contains a velocity gradient. The gradient arises
due to the fact that the velocity at the surface is about zero.
Outside the boundary layer, in the so-called "free-stream" region,
the velocity gradients are small or negligible. Therefore, the flow
must go from nearly zero velocity at the wall to the free-stream
velocity away from the wall within the boundary layer. The boundary
layer acts as a thermal insulator. Thus, in general, the thinner
the boundary layer, the lower the thermal resistance between the
flowing air and a heat sink element such as a fin 120.
[0014] FIG. 2 illustrates a schematic view of a nonlimiting model
of a fluid 210 flowing between two conventional fins 220 with an
opening 230 between them. By convention, the direction of flow of
the air stream 210 is downstream, and the opposite direction is
upstream. Within a region 240, the air stream 210 flows with
free-stream characteristics. Within a region 250 the air stream 210
flows with boundary layer characteristics. A transition region 260
marks a transition from free-stream characteristics to boundary
layer characteristics. The boundary layers begin at the opening
230. The thickness of the boundary layer region 250 increases with
increasing distance from the opening 230 to a point 270. The
boundary layer generally includes a laminar flow region 280
adjacent to the surface of the fin 220 that includes a region of
flow parallel to the surface. The laminar flow region may include
regions of non-ideal flow, e.g., not exactly parallel to the
adjacent surface. Such minor departures from ideal laminar flow are
considered laminar flow in the present discussion. The laminar flow
region 280 and may include a region of non-parallel flow. At the
point 270, the boundary layer region 250 is fully developed,
meaning that essentially all of the air flows in a region of
smoothly decreasing velocity gradient with increasing distance from
the fins 220. It is thought that the resistance of heat transfer
between the air stream 210 and the fins 220 decreases with
increasing boundary layer thickness, and more particularly with
increasing thickness of the laminar flow region 280. At the point
270, the heat transfer rate is thought to reach a minimum. Thus,
the thermal resistance is expected to increase from the opening 230
to a maximum at about the point 270.
[0015] Embodiments described herein reflect the recognition that a
laminar flow region adjacent a heat sink surface, e.g., a surface
of a fin or a base, may be disturbed using structural elements,
referred to herein as flow diverters. "Disturbed" as applied to a
laminar flow region means that the laminar flow region has flow
characteristics it would not have in the absence of the flow
diverter. Examples of disturbed laminar flow region include, e.g.,
thinning, flow separation, and flow non-parallel to the adjacent
surface.
[0016] Without limitation by theory, the flow diverters are thought
to produce vortexes or unsteady flow at the downstream side of the
flow diverters. Unsteady flow may include, e.g., vortices and
eddies, and transitional, turbulent, unstable, chaotic and resonant
airflow. In some cases, a low pressure region is thought to form on
the downstream side of a flow diverter. The low-pressure region is
thought to cause the fluid to flow in a manner that impinges on the
laminar flow region adjacent the surface, e.g., the laminar flow
region 280. Such diversion of, e.g., a fluid stream causes diverts
the fluid from a greater distance above the surface to a lesser
distance above the surface. Because the thermal resistance of the
heat sink is in part a function of the thickness of the laminar
flow region, the impinging may have the effect of increasing the
rate of heat transfer between the fluid and the heat sink. The flow
diverters may be configured to reduce thermal resistance of a
portion of a heat sink or the entire heat sink. For example, it may
be desirable to reduce thermal resistance of only a portion of a
heat sink located proximate a region of an electronic device that
generates more heat than other regions of the device.
[0017] FIG. 3A illustrates one embodiment of a heat sink 300 having
a base 310 and a fin 320 formed thereon. Flow diverters 330 are
attached to the fin 320. FIG. 3B illustrates the fin 320 in plan
view and sectional view. An fluid stream 340 flows past the flow
diverters 330. The fluid stream 340 may a gas or a liquid, and may
be used to transfer heat to or from a heat sink, depending on the
application. For simplicity of discussion a fluid stream is
referred to herein after as an air stream, while recognizing that
other gases or liquids may be used as a heat exchange medium.
Furthermore, heat is referred to as being extracted from the heat
sink, while recognizing heat could be extracted by the heat sink
from the fluid stream.
[0018] In this embodiment of FIG. 3A, the flow diverters 330 are
square cylindrical elements having a length equal to or less than
the height of the fin 320 above the base 310. The flow diverters
330 may have any desired cross-sectional profile, e.g., circular,
square or triangular. Any shape that has the effect of causing a
portion of the air stream 340 to impinge on a laminar flow region
proximate the surface of the base 310 or the fin 320 is within the
scope of this discussion. The flow diverters 330 are also
stationary with respect to the fin 320. In other embodiments, the
flow diverters 330 may be an active element as described in U.S.
patent application Ser. No. ______. (Hernon 1) There may be one or
a plurality of flow diverters 330 on a fin 320, and a particular
heat sink may have flow diverters 330 formed on one or a plurality
of fins 320. Flow diverters 330 may be spaced at regular or uneven
intervals on the fin 320, and when present on adjacent fins and
projecting into the same inter-fin space, may be aligned as
illustrated in FIG. 3C or staggered as illustrated in FIG. 3D.
[0019] The flow regime of air or other cooling fluid through a heat
sink may be characterized by a Reynolds number associated with the
heat sink and the flowing fluid. As known by those skilled in the
pertinent art, a Reynolds number describes the relationship between
inertial forces and viscous forces in a fluid system. Laminar flow
occurs when a fluid flows in parallel layers with little or no
disruption between the layers. This flow regime is associated with
a low Reynolds number. Turbulent flow is characterized by random
eddies, vortices and other flow fluctuations, and is associated
with a high Reynolds number. A transition regime between laminar
and turbulent flow may be characterized by more predictable but
non-uniform flow, such as vortices and eddies that are fairly
stable over time. Thus, providing a heat sink with flow diverters
may be viewed as increasing the Reynolds numbers associated with
flow of the cooling fluid through the heat sink.
[0020] Turbulent flow is generally associated with greater
resistance to flow of fluid. In the context of heat sinks, greater
flow resistance translates to a greater pressure drop across the
heat sink. In some cases, a greater pressure drop is undesirable.
In such cases, the flow diverters 330 may be configured to produce
non-uniform flow, but not turbulent flow. In general, such a
configuration must be determined experimentally for a combination
of cooling fluid, velocity of the fluid, and the configuration of
the heat sink.
[0021] FIG. 3B illustrates unsteady flow of an air stream 340 over
the flow diverters 330. The flow diverters 330 are thought to form
a low-pressure region 350 downstream of the flow diverters 330 due
to, e.g., flow separation. The low pressure region 350 may produce
a standing wave or vortexes 360 at the downstream side of the flow
diverters 330 depending on, e.g., the Reynolds number associated
with the geometry of the heat sink 300 and the velocity of the air
stream 340. The standing wave or vortexes 360 include a flow
direction component normal the surface of the fin 320. This normal
flow may have the effect of compressing the laminar flow region
proximate the surface of the fin 320, thus reducing the thermal
resistance between the fin 320 and the air stream 340.
[0022] FIG. 3C illustrates an embodiment in which the flow
diverters 330 are configured to cause air flow through the heat
sink 300 to be resonant. In this nonlimiting example, the flow
diverters 330 cause a standing pressure wave resulting in regions
of differing pressure, e.g., low pressure regions 370 and high
pressure regions 380. The formation of the standing wave is
expected to occur at a range of velocity of the air stream 340 that
is dependent on the geometry of the fins 320 and the flow diverters
330. The flow diverters 330 may be configured to form the low
pressure regions 370 and the high pressure regions 380 at positions
that result in reduction of the thermal resistance between the fins
320 and the air stream 340 near a portion of the heat sink 300 at
which lower thermal resistance between the heat sink 300 and the
air stream 340 is desired.
[0023] FIG. 3D illustrates an embodiment in which the flow
diverters 330 are placed on opposing faces of fins 320 in a
staggered configuration. In some cases, it is thought that
staggering the flow diverters 330 may aid the formation of a
desired air flow characteristic, e.g., unsteady or resonant air
flow, at a particular flow velocity of the air stream 340.
Configurations of the flow diverters 330 may be combined in any
desired manner within a heat sink to result in the desired flow
characteristics. A configuration may be determined, e.g., by
wind-tunnel analysis or numerical modeling.
[0024] Turning to FIG. 4A, illustrated is an embodiment of a heat
sink 400 including a base 410 and a fin 420 thereon. A number of
flow diverters 430 are placed at the leading edge of the fin 420.
These flow diverters 430 present a 2-D profile to an air stream (in
the plane of the fin 420), in contrast to the flow diverters 330,
which present a 1-D profile. In some cases, the length of the flow
diverters 430 in the plane of the fin 420 is less than about 2 the
height of the fin 420. Thus, multiple flow diverters 430 may be
placed in a line with space between them, as illustrated in FIG.
4A. In some cases, flow diverters 435 may be placed on the fin 420
downstream of the leading edge of the fin 420 instead of or in
addition to the flow diverters 430.
[0025] FIG. 4B illustrates the fin 420 in plan view and sectional
view. An air stream 440 flows past the flow diverters 430. The flow
diverters 430 cause unsteady flow on the downstream side,
illustrated without limitation as vortexes 450. In this case, the
vortexes 450 have a more complex motion due to the fact that the
flow diverters 430 present a two-dimensional cross-section to the
air stream 440. The vortexes 450 are thought to have a direction
component parallel and a direction component normal to the surface
of the fin 420. It is believed that in some flow regimes this
motion is particularly effective at reducing thermal resistance
between the fin 420 and the air stream 440.
[0026] As mentioned above, flow diverters 435 may be placed
downstream of the leading edge of the fin 420 in addition to the
flow diverters 430. These downstream flow diverters 435 may be
aligned with upstream flow diverters 430 or they may be staggered,
as illustrated, causing air to take a more tortuous path between
the fins 430.
[0027] Turning to FIG. 5A, illustrated is a heat sink 500 having a
base 510 and two fins 520. A flow diverter 530 is attached to the
base 510 between the fins 520. The flow diverter 530 has, e.g., a
triangular cross section in the plane of the base, but could have
any other desired cross section, such as circular, elliptical,
square, or a more complex cross section. The flow diverter 530 may
have any height above the base 510, though typically the height
will be less than or equal to the height of the fin 520. One flow
diverter 530 is illustrated, but other embodiments include multiple
flow diverters 530 between the fins 520. Multiple flow diverters
530 may be the same or different heights, or have the same or
different cross sectional profiles.
[0028] FIG. 5B illustrates plan and sectional views of the fins
520. The embodiment 500 has a single triangular flow diverter 530
with an air stream 540 impinging thereon. Air is forced to flow
between the flow diverter 530 and the fin 520, thereby increasing
its velocity. The greater air speed parallel to the fin 520 is
thought to cause the laminar flow region proximate the fin 520 to
thin, thus reducing the thermal resistance between the air stream
540 and the fin 520.
[0029] When a flow diverter 530 has an abrupt transition downstream
of the leading edge, such as for the illustrated triangular flow
diverter 530, vortexes 550 may be formed. In some cases, such
vortexes may be undesirable, such as when induced drag associated
with the vortexes 550 increases the pressure drop across the heat
sink.
[0030] An alternate embodiment is illustrated in FIG. 5B in which a
flow diverter 560 has an elliptical or streamlined cross section.
In one embodiment, the flow diverter is configured as an elliptical
airfoil. In each of these embodiments, the air stream 540 is forced
to flow faster between the flow diverter and the fins 520 as
before. However, the streamlined profile of the flow diverter 560
reduces the formation of vortexes at the downstream side, resulting
in lower drag. This lower drag is expected to reduce the pressure
drop across the heat sink 500, improving heat transfer relative to
the heat sink 500 using the triangular flow diverter 530.
[0031] FIG. 5C illustrates an embodiment in which the flow diverter
530 is positioned at a location 580 upstream of the fins 520 and
outside a volume 585 bounded by the fins 520. The volume 585 is
that volume between the fins 520 that does not extend beyond the
terminus of the fins 520. The flow diverter 530 is attached to the
fins 520 by, e.g., supports 590. The flow diverter 530 may be any
shape and may be placed in any position relative to the fins 520
that disturbs laminar flow of the air stream 540 adjacent to the
fins 520. In another embodiment, not shown, the flow diverter 530
is attached to a portion of the base, e.g., the base 510, that
extends beyond the terminus of the fins 520.
[0032] In each of the embodiments illustrated in FIG. 3, FIG. 4,
and FIG. 5, the flow diverters may optionally be placed at a
position downstream of the leading edge of the fin (e.g., fin 320,
420, 520) to reduce thermal resistance between the fin and the air
stream in the vicinity of a hot spot. A hot spot is a region of
relatively greater heat flux from an integrated circuit, e.g.,
relative to the surrounding areas of the circuit. By so placing the
flow diverter, thermal resistance may be reduced in a portion of
the heat sink where the lower resistance is particularly
beneficial, while minimizing the number of flow diverters to reduce
resulting pressure drop.
[0033] Returning briefly to FIG. 5B, an embodiment is illustrated
in which the flow diverter 530 is placed over a hot spot 570. It is
expected that the heat flux from the hot spot 570 will be partially
localized to the portion of the fins 520 immediately above the hot
spot 570. Therefore, reducing the thermal resistance between the
fins 520 and the air stream 540 by decreasing the thickness of the
laminar flow region in the vicinity of the hot spot 570 is expected
to be particularly beneficial.
[0034] In some cases, the flow diverter (e.g., flow diverter 330,
430 or 530) may be placed near the point where the boundary layers
between fins become fully developed. Referring to FIG. 2, this
point would be, e.g., about at the point 270. Placement of the flow
diverter near this point is thought to be particularly beneficial
in some cases in that the number of flow diverters in an air path
may be reduced. The effect of drag caused by the flow diverter may
be balanced against the benefit of disrupting laminar flow regions
by only placing the flow diverters at points of convergence of the
boundary layers. Depending on factors such as fin spacing and the
length of the path between the fins, two or more points of boundary
layer convergence may possible in the path of air flow between the
fins. In an embodiment, a flow diverter is placed at each
convergence point in an air path.
[0035] In each of the illustrated embodiments, the flow diverters
may or may not be integral to the structure of the heat sink. When
a flow diverter is not integral, it may be, e.g., a metal or
plastic portion affixed to the remaining portion of the heat sink.
The flow diverter may be affixed by adhesive, welding, or brazing,
e.g., or in some cases may simply be held in place by friction. In
some cases, it may be desirable to use a heat transfer agent such
as thermal grease to increase thermal coupling between the flow
diverter and the remaining portion of the heat sink.
[0036] When the flow diverter is integral to the heat sink, the
heat sink and the flow diverter may be formed as a monolithic
structure, e.g., by the method of three dimensional (3-D) printing
and investment casting. Such a method is disclosed in U.S. patent
application Ser. No. ______ (Hernon 3). Briefly described, the
method provides for using a 3-D printer to produce a sacrificial
form of a heat sink. The form is used to fashion a mold, and is
then melted or vaporized out of the mold. The mold is then used to
form the final heat sink. This method provides the ability to form
detailed 3-D patterns that might not be manufacturable by
conventional methods, such as machining, die casting, folding or
skiving. Moreover, the structural features are extensions of a
single physical entity, e.g., a polycrystalline metallic casting.
In addition to forming structural details not amendable to other
methods, a monolithic structure is expected to reduce thermal
resistance within the heat sink, making a greater surface area
available to transfer heat to the air stream.
[0037] Turning to FIG. 6A, illustrated is an embodiment of a ducted
heat sink 600 in a projection view. The heat sink 600 includes a
base 610 and fins 620 thereon. Air flow is diverted by one or more
ducts 630 between the fins 620. The ducts 630 may be formed by
planar segments 640, as illustrated, or any other desired shape,
such as smoothly curved surfaces.
[0038] As illustrated in FIG. 6B, in plan view, the ducts 630
divert an air stream 650 from a direction generally parallel to the
base 610 to a direction having a component normal to the base 610.
Thus, cooler, faster air from a portion of the heat sink 600
further from the base 610 may be diverted to a region of warmer,
slower air nearer to the base 610 at a hot spot 660. Moreover,
because the air diverted by the one or more ducts 630 joins the
flow of air near the base 610, a greater volume of air per unit
time may be caused to flow over the hot spot 660 than may otherwise
occur absent the ducts 630.
[0039] FIG. 6C illustrates a sacrificial form 670 of the heat sink
600 formed by 3-D printing. Ducts 680 may be seen through the
semi-transparent fins 690 of the form 670. As described previously,
the form 670 may be used to render the heat sink 600 in, e.g., a
metal to produce a monolithic heat sink with the ducts 680 in a
practical and efficient manner.
[0040] FIG. 7 illustrates an embodiment of a heat sink 700 having a
base 710 and fins 720 thereon. A flow diverter 730 directs air flow
from a lower level of the heat sink 700 to a higher level. The fin
720 also includes an optional opening 740 formed therein. The flow
diverter 730 and the opening 740 may be positioned to allow cooler
air from one portion of the heat sink 700 to flow through the fin
720 due to a pressure differential formed on the downstream side of
the flow diverter 730. The cooler air can then displace or mix with
warmer air in the vicinity of a hot spot, e.g., thereby increasing
the rate of heat removal from the hot spot. Optionally, another
flow diverter may be positioned on the side of the fin 720 opposite
the flow diverter 730 to direct air into the opening 740. Without
limitation, the investment casting method described above is
well-suited to economically forming such features at the scale of
heat sinks used to cool electronic components.
[0041] The various embodiments described herein may be combined in
any desired manner to result in a desired air flow characteristic
from a heat sink. Moreover, while the embodiments are described
with respect to parallel-fin heat sinks, the embodiments may be
practiced with heat sinks of other geometries where thermal
resistance may be reduced by disturbing laminar flow regimes near a
surface of the heat sink. Although the present invention has been
described in detail, those skilled in the art should understand
that they can make various changes, substitutions and alterations
herein without departing from the spirit and scope of the invention
in its broadest form.
* * * * *