HEAT SINK FOR COOLING POWER ELECTRONICS
Cross-Reference to Related Application
[0001] Reference is made to and this application claims priority from and the
benefit of U.S. Provisional Application Serial No. 61/487,068, filed May 17, 2011, and
entitled HEAT SINK FOR COOLING POWER ELECTRONICS, which application is
incorporated herein in its entirety by reference.
Background of the Invention
[0002] This invention relates generally to cooling electronics components, for
example isolated-gate bipolar transistors (IGBT), semiconductor devices, capacitors and
other components of an electronic device, such as, for example a power electronics
module of a variable speed drive.
[0003] Power electronic devices are commonly used for controlling and/or
manipulating the characteristics, for example the frequency and/or the voltage, of the
electric power being supplied to a variety of electrically powered devices. For example,
variable speed drives are commonly used in connection with variable speed motors for
controlling the speed of the motor. Variable speed motors are used in connection with
compressors, water pumps, fans and other devices. For example, refrigerant vapor
compressors, such as, but not limited to, scroll compressors, reciprocating compressors
and screw compressors, to enable driving the compression mechanism of the
compressor at various operating speeds. As the operating speed of the compression
mechanism is decreased, the output capacity of the compressor is decreased, and
conversely as the operating speed of the compressor is increased, the output capacity of
the compressor is increased. The variable speed drive is operative to vary the frequency
of the electric power supplied to drive motor of the compressor, thereby varying the
operating speed of the motor, and consequently the operating speed and output capacity
of the compressor.
[0004] In operation, adequate cooling the power electronics devices, such as but
not limited to variable speed drives, must be ensured by removing heat generated by the
power electronics so as to maintain the reliability and the functionally of the power
electronics devices.
Summary of the Invention
[0005] In an aspect, a heat sink device is provided that is useful for cooling a
power electronics module at a temperature below a specified operating threshold
temperature.
[0006] In an aspect, a heat sink device is provided that is useful for cooling the
power electronics of a variable speed drive housed in a sealed enclosure through which
a flow of cooling air is directed over and across the heat sink device.
[0007] A heat sink device for cooling a power electronics module includes a
base platform having a first surface and a second surface on opposite sides of the base
platform, a plurality of upright members extending outwardly from the first surface of
the base platform and defining a cavity wherein the power electronics module is
disposed in conductive heat exchange relationship with the first surface of the base
platform, and a plurality of heat transfer fins extending outwardly from the second
surface of the base platform and defining a plurality of cooling air flow channels. In an
embodiment, the plurality of heat transfer fins may be disposed in parallel spaced
relationship at a uniform spacing side-to-side. A fan may be disposed in operative
association with the plurality of cooling air flow channels for passing a flow of cooling
air through the plurality of cooling air flow channels in convective heat exchange
relationship with the plurality of heat transfer fins. The ratio of the fin spacing to a
thickness of a base portion of each fin of the plurality of heat transfer fins may be in the
range from 2 to 3 inclusive. In an embodiment, the plurality of heat transfer fins may
comprise flat plate fins having a uniform thickness. In an embodiment, the plurality of
heat transfer fins may comprise a plurality of tapered fins, each tapered fin having a
base portion and a tip portion with the base portion having a thickness greater then a
thickness of the tip portion. The tapered fins may have the fin slope as measured from
the fin centerline in the range from 1.0 to 1.5 degrees.
Brief Description of the Drawings
[0008] For a further understanding of the disclosure, reference will be made to
the following detailed description which is to be read in connection with the
accompanying drawing, where:
[0009] FIG. 1 is a perspective view of an exemplary embodiment of a hest sink
device as disclosed herein;
[0010] FIG. 2 is a cross-sectional elevation view of the exemplary embodiment
of the heat sink device depicted in FIG. 1 taken along line 2-2 of FIG. 1;
[0011] FIG. 3 is a cross-sectional elevation view of another exemplary
embodiment of the heat sink device disclosed herein showing a different configuration
of heat transfer fins;
[0012] FIG. 4 is a plan view of the heat sink device depicted in FIG. 2 taken
along line 4-4 of FIG. 2;
[0013] FIG. 5 is a perspective view of the heat sink device as disclosed herein
housed in a cooling air duct;
[0014] FIG. 6 is a cross-sectional elevation view taken along line 6-6 of FIG. 5;
[0015] FIGs. 7A and 7B are side elevation views showing various dimensional
parameters with respect to a uniform thickness heat transfer fin and a tapered heat
transfer fin, respectively; and
[0016] FIGs. 8A, 8B, 8C and 8D are side elevation views showing various
dimensional parameters with respect to fins, respectively, having bumps/risers, having
fin cut-offs, having a wave-like configuration, and having an arcuate configuration.
Detailed Description of the Invention
[0017] Referring initially to FIGs. 1 - 4, there are depicted exemplary
embodiments of a heat sink device 20 for cooling electronics components, for example
isolated-gate bipolar transistors, semiconductor devices, capacitors and other electronics
components that generate heat during operation. The heat sink device 20 will be
described herein in application for cooling a power electronics module 22 of a variable
frequency drive. In the depicted embodiments, the power electronics module 22
includes an isolated-gate bipolar transistor (IGBT) 24 and may include other
semiconductor devices (not shown), capacitors (not shown), or other heat generating
components. Variable speed drives are used, for example, in connection with variable
speed drive motors (not shown) for driving refrigerant vapor compressors, air moving
devices and/or water pumps on refrigerant vapor compression systems of transport
refrigeration units for controlling a temperature within the cargo box of a refrigerated
container for shipping perishable cargo by sea, by road, by rail or intermodally.
[0018] The heat sink device 20 includes a base platform 26, a plurality of
upright members 28, and a plurality of heat transfer fins 30. The base platform 26, the
upright members 28 and the heat transfer fins 30 may be formed by extrusion, by
casting, or by machining to form an integral one-piece heat sink device 20. The heat
sink device 20 may be formed of aluminum, aluminum alloys, copper, copper alloys, or
other materials having a high thermal conductivity.
[0019] In the depicted embodiment, the base platform 26 has a middle span 32,
a right-hand span 34 (to the right of the middle span 32 as viewed in FIGs. 2 and 3) and
a left hand span 36 (to the left of the middle span 32 as viewed in FIGs. 2 and 3). Link
member 42 connects the right-hand span 34 of the base platform 26 to the right end of
the middle span 32 and link member 44 connects the left-hand span 36 of the base
platform 26 to the left end of the middle span 36. In the depicted embodiments, the link
member 42 extends perpendicularly to the right-hand span 34 and to the middle span 32
and the link member 44 extends perpendicularly to the left-hand span 36 and to the
middle span 32. It is to be understood, however, that the base platform 26 may take
other forms, including a flat plate, a plate having one or more recessed spans, a plate
having one or more raised sections, a plate having a combination of one or more
recessed spans and one or more raised sections.
[0020] The base platform 26 has a first surface 38 on one side thereof and a
second surface 40 on the opposite side thereof. Upright members 28-1, 28-2, 28-3, 28-4
extend outwardly from the first surface 38 of the base platform 26, which in the
embodiments depicted in FIGs. 2- 4 is on the lower side of the base platform 26. A
cavity 46 is defined on the lower side of the base platform 26 bounded by the wall 25
formed by the outboard upright members 28-1 and 28-2 and the laterally extending
upright members interconnecting members 28-1 and 28-3. The power electronics
module 22 is housed within the cavity 46. In the depicted embodiment, the IGBT 24 is
mounted in a central portion of the cavity 46 between the inboard uprights 2-3 and 28-4
and disposed in conductive heat transfer relationship with the middle span 32 of the
base platform 26. Although not shown, it is to be understood that other heat generating
components of the power electronics module may be disposed in the two side portions
of the cavity 46 in conduction heat transfer relationship with the respective right-hand
and left-hand spans 34, 36 of the base platform 26. Further, it is to be understood that
the configuration of cavity 46 and the arrangement and type of the power electronics
housed therein is exemplary and other arrangements are permissible.
[0021] Heat transfer fins 30 extend outwardly from the second surface 40 of the
base platform 26, which in the embodiments depicted in FIGs 1-3 is on the upper side
of the base platform 26. The plurality of heat transfer fins 30 extending outwardly from
the base platform 26 of the heat sink device 20 may be arrayed in laterally spaced,
parallel relationship and extend generally longitudinally along the second surface 40 of
the base platform 26 to form a plurality of cooling air flow channels 48, including a
cooling air flow channel 48 between each of the various sets of neighboring heat
transfer fins 30. As will be discussed further hereinafter, a flow of cooling air may be
passed through the channels 48 in heat exchange relationship with the heat transfer fins
30 to remove heat from the heat transfer fins 30. As the heat transfer fins 30 are
disposed in conductive heat transfer relationship through the base platform 26 of the
heat sink device 20 with the cavity 36 and the power electronics module 22 housed
therein, heat generated by the power electronics module 22 is effectively transferred to
and removed by the cooling air flow passing through the channels 48 without the
cooling air flow directly contacting the power electronics module 22 housed within
cavity 46.
[0022] In the embodiment depicted in FIG. 2, the heat transfer fins 30 comprise
flat plate fins having a rectangular cross section profile of uniform thickness from base
to tip. In the embodiment depicted in FIG. 3, the heat transfer fins 30 comprise flat
plate fins having a tapered cross section profile of tapering thickness, being tapered
inwardly from base to tip. In the uniform thickness embodiment for example, the heat
transfer fins 30 may have a thickness in the range of from 3 to 4 millimeters (0.12 to
0.157 inches) and spaced side-to-side at spacing in the range of 10 to 11 millimeters
(0.39 to 0.43 inches). In the uniform thickness embodiment, the base platform 26, the
upright members 28 and heat transfer fins 30 may be formed by extrusion as an integral,
one-piece heat sink device 20. In the tapered fin embodiment for example, the heat
transfer fins may have a thickness at the fin base in the range of 3 to 4 millimeters (0.12
to 0.157 inches) and inwardly sloping sides having a slope greater than 1 degree and
less than 1.5 degrees. In the tapered thickness fin embodiment, the base platform 26,
the upright members 28 and heat transfer fins 30 may be formed by casting as an
integral, one-piece heat sink device 20. Further, the fin density and fin parameters, such
as cross-section thickness, height and form factor, may be selectively varied along the
base platform 26 to provide the most optimal heat exchange pattern and temperature
distribution across the longitudinal and lateral expanse of the base platform 26 to
maintain the power electronics housed within the cavity 46 below the desired
operational threshold temperature. For instance, higher fin density and increased crosssection
thickness may be desired in the area surrounding the higher power generation
electronics.
[0023] It is to be understood that in other embodiments, the heat transfer fins 40
may be curved plate fins or wave-like fins extending longitudinally in parallel spaced
relationship. The heat transfer fins 30 may have a cross-section form that is rectangular
or tapered, as shown in the depicted embodiments, but may instead have a cross-section
form that is triangular, trapezoidal, hyperbolic, parabolic, elliptical or other desired
cross-section shape. The heat transfer fins 30 may include heat transfer enhancements
such as, but not limited to surface roughness, beads, surface bumps or risers, louvers,
off-sets, and cut-offs between fins. Any combination of the abovementioned heat
transfer enhancement features may be used on the heat sink device 20 disclosed herein.
[0024] Referring now to FIGs. 5 and 6, the heat sink device 20 is shown
disposed within a housing 50 defining a chamber 52 wherein the heat sink device 20 is
disposed and also defining a cooling air flow duct 54. The housing 50 further includes
a cooling air inlet opening 56 at a first end of the housing 50 and a cooling air outlet
opening 58 at a second end of the housing 32 longitudinally opposite the first end of the
housing 50. A cooling air fan 60 is provided in operative association with the housing
50 for passing cooling air through the flow duct 54. The cooling air fan 60 may be
mounted in the cooling air inlet opening 56 for blowing cooling air through the flow
duct 54 or may be mounted in the cooling air outlet opening 42 for drawing cooling air
through the flow duct 54. In either arrangement, the cooling air fan 50 is operative to
pass a flow of cooling air, typically, but not limited to, ambient air, through the
channels 48 formed between the various sets of neighboring pairs of heat transfer fins
30.
[0025] When disposed within the housing 50, the tips of the heat transfer fins 30
are juxtaposed in substantially abutting relationship with one interior wall of the
housing 50, while the end faces of the upright members forming the bounding wall 25
are juxtaposed in substantially abutting relationship with the opposite interior wall of
the housing 50. The cooling air flow passes through the channels 48 across and over,
and in convective heat exchange relationship with, the heat transfer surface of the heat
transfer fins 30. In this manner, heat generated by the power electronics module 22
housed in the chamber 46 is removed by the cooling air flow by means of conductive
heat exchange from the cavity 46 and the power electronics module 22 through the base
platform 26 to the heat transfer fins 30 and by means of convective heat exchange from
the heat transfer fins 30 to the cooling air flow passing through the channels 48.
However, the power electronics module 22, being disposed in the cavity 46, remains
isolated from the cooling air flow and therefore not exposed to moisture or corrosive
elements that might be present in the cooling air flow.
[0026] In the depicted embodiment, the cooling air fan 60 is mounted in the
cooling air inlet opening 56 and operates to blow ambient air into and through the
cooling air flow duct 54 to pass across and over the surfaces of the heat transfer fins 30
and the base platform 26 of the heat sink device 20. To achieve sufficient convective
heat transfer between the cooling air flow and the heat transfer fins 30 and the base
platform 26 of the heat sink device 20 to ensure cooling of the power electronics
module 24 to a temperature below a threshold temperature of 85°C (185°F) in accord
with the method disclosed herein, the cooling air flow may be passed through the flow
channel at an air flow velocity in the range of from 4 to 20 millimeters per second per
Watt of heat rejection by the power electronics module 24.
[0027] By way of example, tests of a prototype of the heat sink device 20
housing a 300 Watt IGBT and disposed in a cooling air flow duct at or within a distance
of one-half the width of the heat sink device downstream of the outlet of the cooling air
fan 60. Additionally, the heat transfer fins 30 were tapered fins having a height of 45
millimeters (1.77 inches), a base width of 3 millimeters (0.118 inches) and a tip width
of 1.43 millimeters (0.056 inches) on the right-hand and left-hand sections 34, 36 of the
base platform 26 and having a height of 70 millimeters (2.76 inches), a base width of 4
millimeters (0.157 inches) and a tip width of 0.56 millimeters (0.022 inches) on the
middle section 32 of the base platform 26. The base platform 26 of the tested heat sink
device 20 had a thickness of 8 millimeters (0.315 inches) in the middle section 32 and a
thickness of 4 millimeters (0.157 inches) in each of the right-hand side and left-hand
side sections 34, 36 of the base platform 26. The heat sink device was cast as an
integral one-piece heat sink device 20 using an AlSil2 aluminum silicon alloy. The
temperature of the 300 W IGBT was maintained below a threshold maximum
temperature of 85°C (185°F) using a cooling air flow having at inlet temperature of
39°C (100°F) passing through the cooling air flow channels at an air flow velocity of in
the range of at least 3.0 meters/second (9.8 feet per second) to 8.0 meters per second (26
feet per second) at a fan output cooling air flow rate in the range from 70 to 90 CFM
(cubic feet per minute) (2.0 to 2.5 cubic meters per minute).
[0028] Various specific non-dimensional geometric ratios have been identified
and quantified for facilitating manufacturing and enhancing heat transfer performance
of the heat sink device 20 disclosed herein, while achieving a reduction in footprint
area, a reduction in material content, and a reduction in cost. The various dimensional
parameters referred to in the following paragraphs are shown in FIG. 7A with respect to
a heat transfer fin having uniform thickness and in FIG. 7B with respect to a tapered
heat transfer fin.
[0029] The ratio of the height of the heat transfer fins 30 to the thickness of the
base platform 26 from which the fins 30 extend should lie in the range of 2 to 30,
inclusive, to facilitate manufacturing.
[0030] The ratio of the thickness tp of the base platform 26 from which the fins
30 extend to the nominal fin thickness, which for a fin having a uniform thickness tf and
for a fin having a non-uniform thickness is an average thickness - tt)/2, should be in
the range from 0.5 to 1.0, inclusive, to ensure adequate conductive heat transfer
between the fins 30 and the base platform 26.
[0031] For tapered fins, the ratio of the difference between the thickness of the
fin base and the thickness of the fin tip - tt) to the fin height hf should be such as to
provide a fin slope 0 ,as measured from the fin centerline, in the range from 1.0 to 1.5
degrees, inclusive, to facilitate casting of the heat sink device 20.
[0032] The ratio of the spacing S between the side walls of neighboring fins 30
at the base of the fins to the thickness of the fins ¾at the fin base should be in the range
from 2 to 3, inclusive, to facilitate manufacturing.
[0033] As noted previously, the heat transfer fins 30 may include heat transfer
enhancements such as surface roughness, surface bumps, which includes risers, and fin
cutoffs. With respect to surface roughness, the surface roughness enhancement may
have a height in the range of 0.38 to 1.52 millimeters (0.015 to 0.06 inches). With
respect to fins 30 having surface bumps or risers, see FIG. 8A, the ratio of enhancement
height he to enhancement spacing Se may have a value in the range of 0.01 to 0.10 and
more narrowly in the range of 0.02 to 0.05. With respect to fins 30 having fin cutoffs,
see FIG. 8B, the ratio of the cutoff width wc to the spacing Sc between cutoffs may have
a value in the range of 0.25 to 0.75, and more narrowly in the range of 0.4 to 0.6, and
the ratio of the cutoff height h to fin spacing may have a value in the range of 0.1 to
0.5.
[0034] For wave-like heat transfer fins, see FIG. 8C, the ratio of wave height hw
to wave length lw may have a value in the range of 0.06 to 0.56, and more narrowly in
the range of 0.12 to 0.28. The heat transfer fins may be arcuate in longitudinal expanse
having a nominal curvature radius and a curvature length. For example, in an
embodiment, the arcuate fins may have a curvature that has an upwardly convex profile
in the vertical so that water/condensate would drain off rather than collect in the curve
of the arcuate fin. For such a curved fin, see FIG. 8D, the ratio of the nominal curvature
radius of the fin to the channel length Lc of the fin may have a value in the range of 0.5
to 3, and more narrowly in the range of 0.8 to 1.5.
[0035] With the heat sink device 20 as disclosed herein, heat may be removed
from the cavity 36 and the power electronics module 24 disclosed within the cavity 36
through primarily conductive heat exchange to the base platform 26 and therethrough to
the heat transfer fins 30 and thence by primary convective heat exchange trough the
heat transfer fins 30 to the cooling air flow passing through the channels 48 of the heat
sink device 20. In this manner, the power electronics module 24 may be cooled without
being in direct contact with the cooling air. Thus, the power electronics module 24 will
not be exposed to moisture or corrosive elements within the cooling air, typically
ambient air, and the potential corrosive effects attendant with such exposure.
[0036] The terminology used herein is for the purpose of description, not
limitation. Specific structural and functional details disclosed herein are not to be
interpreted as limiting, but merely as basis for teaching one skilled in the art to employ
the present invention. Those skilled in the art will also recognize the equivalents that
may be substituted for elements described with reference to the exemplary
embodiments disclosed herein without departing from the scope of the present
invention.
[0037] While the present invention has been particularly shown and described
with reference to the exemplary embodiments as illustrated in the drawing, it will be
recognized by those skilled in the art that various modifications may be made without
departing from the spirit and scope of the invention. Therefore, it is intended that the
present disclosure not be limited to the particular embodiment(s) disclosed as, but that
the disclosure will include all embodiments falling within the scope of the appended
claims.
We Claim:
1. A heat sink device for cooling a power electronics module
comprising:
a base platform having a first surface and a second surface on opposite sides
of the base platform;
a plurality of upright members extending outwardly from the first surface of
the base platform and defining a cavity wherein the power electronics module is
disposed in conductive heat exchange relationship with the first surface of the base
platform;
a plurality of heat transfer fins extending outwardly from the second surface
of the base platform and defining a plurality of cooling air flow channels.
2. The heat sink device as recited in claim 1 further including a fan
disposed in operative association with the plurality of cooling air flow channels for
passing a cooling air flow through the plurality of cooling air flow channels in
convective heat exchange relationship with the plurality of heat transfer fins.
3. The heat sink device as recited in claim 1 wherein the plurality of
heat transfer fins are disposed in parallel spaced relationship at a uniform spacing
side-to-side.
4. The heat sink device as recited in claim 3 wherein the ratio of the fin
spacing to a thickness of a base portion of each fin of the plurality of heat transfer
fins is in the range from 2 to 3 inclusive.
5. The heat sink device as recited in claim 1 wherein the plurality of
heat transfer fins comprise flat plate fins having a uniform thickness.
6. The heat sink assembly as recited in claim 1 wherein the plurality of
heat transfer fins comprise a plurality of tapered fins, each tapered fin a base portion
and a tip portion, the base portion having a thickness greater then a thickness of the
tip portion.
7. The heat sink device as recited in claim 6 wherein the fin slope as
measured from the fin centerline is in the range from 1.0 to 1.5 degrees.
8. The heat sink device as recited in claim 1 wherein the base platform
has a right span, a middle span and a left span, the right span and the left span being
connected to the opposite respective ends of the middle span.
9. The heat sink device as recited in claim 8 wherein the middle span of
the base platform has a first thickness, the right span has a second thickness and the
left span has a third thickness.
10. The heat sink device as recited in claim 9 wherein each fin of the
plurality of fins has a fin base at the base platform having at thickness and the ratio
of the base thickness of each fin to the thickness of the respective span of the base
platform from which the fin extends is in the range of 0.5 to 1.0 inclusive.
11. The heat sink device as recited in claim 9 wherein each fin of the
plurality of fins has a fin height and the ratio of the fin height to the thickness of the
respective span of the base platform from which the fin extends in the range of 2 to
30 inclusive.
12. The heat sink device as recited in claim 9 wherein the first thickness
of the middle span is in the range of 8 to 10 millimeters and each of the second
thickness of right span and the third thickness of the left span is the range of 4 to 8
millimeters.
13. The heat sink device as recited in claim 1 wherein the heat transfer
fins are disposed at a non-uniform fin density.
14. The heat sink device as recited in claim 1 wherein each of the
plurality of fins has a cross-section profile selected from the group of cross-section
profiles including rectangular, tapered, triangular, trapezoidal, hyperbolic, parabolic
and elliptical.
15. The heat sink device as recited in claim 1 wherein the plurality of fins
comprises wave-like plate fins, each wave-like plate fin having a wave height and a
wave length, and a ratio of the wave height to wave length having a value in the
range of 0.3 to 0.8.
16. The heat sink device as recited in claim 1 wherein the plurality of fins
comprises at least one fin having a heat transfer enhancement in the form of a
plurality of surface roughness enhancements having an enhancement height up to
0.060 inches.
17. The heat sink device as recited in claim 1 wherein the plurality of fins
comprises at least one fin having a heat transfer enhancement in the form of a
plurality of raised bumps having an enhancement height and disposed in spaced
relation on a fin heat exchange surface at an enhancement spacing, a ratio of the
enhancement height to the enhancement spacing having a value in the range of 0.01
to 0.10.
18. The heat sink device as recited in claim 1 wherein the plurality of fins
comprises a plurality of fins having at least one fin cutoff, the fin cutoff having a
ratio of a cutoff width to a cutoff spacing in the range of 0.25 to 0.75 and a ratio of a
cutoff height to a cutoff spacing in the range of 0.1 to 0.5.
19. The heat sink device as recited in claim 1 wherein the plurality of fins
comprises a plurality of arcuate fins having an upwardly convex curvature in a
vertical plane.
20. The hat sink device as recited in claim 19 wherein the plurality of
arcuate fins have a curvature having a nominal curvature radius and a curvature
length, a ratio of the nominal curvature radius to the curvature length having a value
in the range of 0.5 to 3.0.
21. The heat sink device as recited in claim 1 wherein the plurality of
heat transfer fins comprises fins of at least two different heights.
22. The heat sink device as recited in claim 1 wherein the plurality of
heat transfer fins comprises fins of at least two different cross-sections.