U.S. patent application number 10/284030 was filed with the patent office on 2003-05-01 for cooling element.
This patent application is currently assigned to SIEMENS AKTIENGESELLSCHAFT. Invention is credited to Hoffmann, Ingolf, Schinn, Volker.
Application Number | 20030079860 10/284030 |
Document ID | / |
Family ID | 7704199 |
Filed Date | 2003-05-01 |
United States Patent
Application |
20030079860 |
Kind Code |
A1 |
Hoffmann, Ingolf ; et
al. |
May 1, 2003 |
Cooling element
Abstract
A cooling element includes a base plate and several spaced-apart
cooling fins which are arranged on a flat side of the base plate.
The end faces of the cooling fins together with the formed cooling
channels form an inflow side and an outflow side for cooling air.
The end face of the cooling fins on the inflow side and the outflow
side are configured to produce a low flow resistance. This
substantially reduces the counterpressure exerted on the cooling
air flow and thereby obviates the need for high-power fans, without
a reduction in the removed heat per unit time {dot over (Q)}.
Inventors: |
Hoffmann, Ingolf;
(Herzogenaurach, DE) ; Schinn, Volker; (Erlangen,
DE) |
Correspondence
Address: |
Henry M. Feiereisen
Suite 3220
350 Fifth Avenue
New York
NY
10118
US
|
Assignee: |
SIEMENS AKTIENGESELLSCHAFT
Munchen
DE
|
Family ID: |
7704199 |
Appl. No.: |
10/284030 |
Filed: |
October 30, 2002 |
Current U.S.
Class: |
165/80.3 ;
257/E23.099 |
Current CPC
Class: |
H01L 2924/0002 20130101;
H01L 23/467 20130101; H01L 2924/00 20130101; F28F 3/048 20130101;
H01L 2924/0002 20130101 |
Class at
Publication: |
165/80.3 |
International
Class: |
F28F 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 30, 2001 |
DE |
101 53 512.0 |
Claims
What is claimed is:
1. A cooling element, comprising: a base plate; and a plurality of
cooling fins spaced apart transversely to a flow direction and
arranged on a flat side of the base plate so as to form cooling
channels, each of the cooling fins having an end face on an inflow
side and an end face on an outflow side for flow of cooling air in
the flow direction from the inflow side to the outflow side,
wherein the end faces of the cooling fins are constructed to
enhance flow dynamics.
2. The cooling element of claim 1, wherein the spaced-apart cooling
fins are disposed in offset relationship in the flow direction so
that the end faces of the cooling fins on the inflow and outflow
sides form a wave-shaped pattern transversely to the flow
direction.
3. The cooling element of claim 1, wherein the end face on the
inflow side of each of the cooling fins has a convex shape and the
end face on the outflow side of each of the cooling fins has a
wedge shape.
4. The cooling element of claim 1, wherein the end faces on the
inflow and outflow sides of the cooling fins are inclined with
respect to the flow direction.
5. The cooling element of claim 1, wherein the spaced-apart cooling
fins are placed in offset relationship in the flow direction so
that both the inflow side and the outflow side form a zigzag
pattern.
6. The cooling element of claim 1, wherein the cooling fins
includes transverse ribs extending in the flow direction.
7. The cooling element of claim 1, wherein the cooling fins have
free ends with narrow sides located opposite the base plate, and
further comprising a second base plate having a flat major surface
disposed on the narrow sides of the free ends of the cooling
fins.
8. The cooling element of claim 1, wherein the base plate has a
plurality of spaced-apart grooves substantially aligned in the flow
direction of the cooling air, with the cooling fins being pressed
into corresponding ones of the spaced-apart grooves.
9. The cooling element of claim 7, wherein the second base plate
has a plurality of spaced-apart grooves substantially aligned in
the flow direction of the cooling air, with the free ends of the
cooling fins being pressed into corresponding ones of the
spaced-apart second grooves.
10. The cooling element of claim 1, wherein the base plate and the
cooling fins are made of extruded aluminum.
11. The cooling element of claim 7, wherein the second base plate
is made of extruded aluminum.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims the priority of German Patent
Application, Serial No. 101 53 512.0, filed Oct. 30, 2001, pursuant
to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a cooling element with a
base plate and several spaced-apart cooling fins which are arranged
on a flat side of the base plate. The end faces of the cooling fins
together with the formed cooling channels form an inflow and
outflow side for cooling air.
[0003] A cooling element of this type is commercially available and
illustrated in greater detail in FIG. 1. The cooling element
includes a base plate 2 having a flat side 4 and cooling fins 6,
end faces 8 and 10 formed by the cooling fins as well as cooling
channels 16 having an inflow side 12 and an outflow side 14.
Cooling air produced by a fan 18 is blown through the cooling
channels 16. The fan 18 is directly attached to the inflow side 12
of the cooling element. Each of the cooling channels 16 is formed
by two adjacent cooling fins 16 and a section of the flat side 4 of
the base plate 2. The outflow side 14 is arranged in opposition to
the inflow side 12 and is formed by the end faces 10 of the cooling
fins 6 and the cooling channels 16. FIG. 1 does not show the end
faces 8 of cooling fins 6 which together with a cooling channels 16
form the inflow side 12, since these are covered by the fan 18.
Several semiconductor components 22 are mounted with a
heat-conducting mounting plate 24 on the flat side 20 of the base
plate 2 that faces away from the cooling fins 6.
[0004] Modern high-efficiency semiconductor devices have a heat
flux density of approximately 10.sup.5 W/cm.sup.2. These devices
can be cooled efficiently only by using a cooling element with a
high fin ratio R.sub.V, which is defined as the quotient of the
cooling fin width or thickness R.sub.B to the fin spacing R.sub.A.
The efficiency of the cooling element is limited by the achievable
temperature increase .DELTA.T of the cooling air. This temperature
increase .DELTA.T depends on the geometry of the cooling element
and, more particularly, is proportional to the rib ratio R.sub.V. A
cooling element with a rib ratio R.sub.V=1 has an upper limit value
for the increase in the cooling air temperature of approximately
24K as determined by the flow conditions. This increase in cooling
air temperature is capable to remove an average heat current {dot
over (Q)}.
[0005] The increase of the air temperature in the cooling element
is a result of a momentum transfer between the cooling air and the
cooled surface at the boundary between the cooling fin 6 and
cooling channel 16, whereby the momentum transfer depends on the
degree of turbulence in the flow and increases with increasing
degree of turbulence. The degree of turbulence, on the other hand,
depends on the surface characteristic of the rib 6, the physical
properties of the cooling air as well as the inherent momentum of
the cooling air (airspeed).
[0006] For a given temperature increase and rib characteristic,
such as geometry and roughness, the removable heat current {dot
over (Q)} can only be increased by increasing the degree of
turbulence. This can be achieved, for example, by increasing the
airspeed. To achieve this, either the mass flow of the air has to
be increased or the cross-section of the flow channel has to be
reduced. Both measures necessitate an increase in the required fan
power.
[0007] With a constant air mass flow {dot over (m)}, the flow
velocity increases with decreasing cross-sectional A of the flow
channel, which is equal to the product of fin spacing R.sub.A and
height of the cooling fins R.sub.H. Increasing the flow velocity
causes an increased counterpressure in the flow channel. The
pressure drop of a flow channel can be expressed by the following
equation using Bernoulli's law: 1 P = * 2 * ( s t ) 2 = * 2 * ( m .
* R H * R A ) 2
[0008] As seen from this equation, decreasing the fin spacing
R.sub.A cause an increase .DELTA.P in the pressure. The form factor
.zeta. describes herein the flow resistance of the flow channel.
This form factor .zeta. is essentially composed of three
components, which are:
[0009] a) the surface properties along the flow channel
(roughness),
[0010] b) the conditions at the inflow end of the flow channel
(geometry), and
[0011] c) the conditions at the outflow end of the flow channel
(geometry).
[0012] While for the momentum transfer the form factor .zeta. along
the flow channel should be as large as possible, the components b)
and c) listed above and also relating to the form factor .zeta. are
undesirable and detrimental, since they tend to increase the system
cost.
[0013] The effect of the form factor .zeta. in particular of the
components b) and c) above, is typically neglected in conventional
embodiments of cooling elements. If the heat flow {dot over (Q)} to
be removed by the cooling element is to be increased, the pressure
drop increases quadratically with the flow velocity and linearly
with the form factor .zeta.. This is a reason why commercially
available cooling elements require heavy-duty fans to produce the
mechanical power to move the cooling air. However, such fans are
large and expensive.
[0014] It would therefore be desirable and advantageous to provide
an improved cooling element which obviates prior art shortcomings
and which is so configure that a fan requiring less power can be
used.
SUMMARY OF THE INVENTION
[0015] According to one aspect of the present invention, a cooling
element cooled with cooling air having a flow direction includes a
base plate and a plurality of spaced-apart cooling fins spaced
apart transversely to the flow direction and arranged on a flat
side of the base plate so as to form cooling channels. The cooling
fins have end faces which cooperate to form an inflow side and an
outflow side for the cooling air. The end faces of the cooling fins
on the inflow side and the outflow side are configured so as to
provide a low flow resistance. As a result, the fan power can be
reduced due to the reduced pressure drop. This advantageous effect
increases with decreasing spacing between the cooling fins of a
cooling element. The fin density is considered to be high when the
fin spacing is approximately equal to the fin width.
[0016] According to an advantageous embodiment of the cooling
element of the invention, the spaced-apart cooling fins are offset
in the flow direction of the cooling air in such a way that the
inflow and outflow sides have a wave-like shape. This measure
further decreases the pressure drop and simultaneously reduces the
fan power requirement.
[0017] According to another advantageous embodiment of the cooling
element of the invention, each end face of each cooling fin on the
inflow side is formed convex and each end face of each cooling fin
on the outflow side is wedge-shaped. These different configurations
of the end faces of each cooling fin gives the cooling fin the
shape of an elongated drop that is oriented opposite the flow
direction. This produces an ideal form of the cooling fins by
reducing the counterpressure, and thereby also the mechanical power
requirements of the fan. However, this disadvantageously makes the
fabrication process for the cooling element quite complex.
[0018] According to another embodiment of the cooling element of
the invention, each end face of each cooling fin on the inflow and
outflow side is inclined and/or the spaced-apart cooling fins are
mutually offset in the flow direction of the cooling air in such a
way that the inflow and outflow side each form a zigzag pattern.
The two zigzag surfaces in this embodiment are in phase. This
arrangement produces a particularly economical solution for a
cooling element according to the invention. By inclining each fin
end with the aforedescribed arrangement, a mini-region (each fin)
and a macro-region (arrangement of the fins) results, each of which
contributes to the reduction in the counterpressure.
[0019] According to yet another advantageous embodiment, each
cooling fin can include transverse ribs oriented in the flow
direction of the cooling air. In addition, a second base plate can
be arranged so that its flat side contacts the narrow sides of the
free ends of the cooling fins. At least one the base plate can
include spaced-apart grooves oriented in the flow direction of the
cooling air, into which grooves a cooling rib can be pressed. For
improved heat conduction, the base plate(s) and the cooling fins
can be made of extruded aluminum or another metal with a high
thermal conductivity.
BRIEF DESCRIPTION OF THE DRAWING
[0020] Other features and advantages of the present invention will
be more readily apparent upon reading the following description of
currently preferred exemplified embodiments of the invention with
reference to the accompanying drawing, in which:
[0021] FIG. 1 is a perspective view of a conventional cooling
element;
[0022] FIG. 2 shows a flow pattern on the cooling fins of the
cooling element according to FIG. 1
[0023] FIG. 3 shows a flow pattern on the cooling fins of a first
embodiment of a cooling element according to the present
invention;
[0024] FIG. 4 shows a flow pattern on the cooling fins of a second
embodiment of a cooling element according to the present invention;
and
[0025] FIG. 5 is a perspective view of a third embodiment of a
cooling element according to the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0026] Throughout all the Figures, same or corresponding elements
are generally indicated by same reference numerals.
[0027] Turning now to the drawing, and in particular to FIG. 2,
there is shown a flow pattern of cooling air on cooling fins of a
commercially available cooling element according to FIG. 1. The
cooling air produced by the fan 18 is depicted in FIG. 2 by arrows
A. Also seen in FIG. 1 are on the inflow side 12 turbulent zones B
which generate the undesirable counterpressure. This effect
increases with increasing width R.sub.B of the fins. This effect is
particularly pronounced in extruded cooling fins. Turbulent zones C
also form on the outflow side 14 of the flow channels 16 due to the
movement of the cooling air at the edges of the fin ends. The
turbulent zones C can even experience a flow reversal. The flow
distribution is a result of the geometry at the inflow and outflow
sides of the flow channels 16. These two components substantially
affect the form factor .zeta. of the cooling element which is
responsible for the generation and the magnitude of the pressure
drop on the cooling element.
[0028] FIG. 3 shows the flow pattern on the cooling fins of a
cooling element according to a first embodiment of the invention.
The sake of clarity, only a few individual cooling fins 6 are
shown. The cooling air produced by the fan 18 is also depicted by
arrows A. In this first embodiment of the cooling element, the end
faces 8 of the cooling fins 6 are convex and the end faces 10 are
formed as wedges. The convex form of the end faces 8 of the cooling
fins 6 of a cooling element prevent the formation of turbulent
zones B at the inflow end of the flow channels 16, since the
cooling air A no longer impinges on a rebounding surface. The
cooling ribs 6 are offset in the flow direction of the cooling air
A at the inflow side 12 in a wavy pattern. As a result, the convex
end faces 8 divert the cooling air A in the region between the end
faces 8 into adjacent flow channels 16. The end faces 8 of the
different cooling fins 6 of the cooling element at the inflow side
12 are located on a concave curvature with respect to the flow in
cooling air A. The curvature of the concave end faces 8 required
for efficiently preventing turbulence depends on the airspeed of
the supplied cooling air A. The air mass flow in each flow channel
16 of the fin arrangement of the cooling element can be increased
by suitably shaping the end faces 8 on the inflow side 12. As a
result, the airspeed in the flow channels 16 of the cooling element
also increases.
[0029] The end faces 10 of the cooling fins on the outflow side 14
of the fin arrangement are wedge-shaped. It should be noted that
the wedge-like shape of the end faces 10 should optimally be free
of any edges. Advantageously, if the inclined surfaces of the
wedge-shaped end faces 10 should be concave. In this way, the
cooling air A can exit from the flow channels 16 without
experiencing turbulence in spite of the increased airspeed.
[0030] The two end faces 8 and 10 of each cooling fin 6 of the
cooling element are formed in the shape of a drop oriented opposite
the flow direction. More particularly, the wedge-like shape of the
end faces 10 on the outflow side 14 of each fin 6 of the fin
arrangement significantly reduced the counterpressure.
[0031] FIG. 4 shows a flow pattern on the cooling fins 6 of another
cooling element according to the invention. The cooling air
produced by the fan 18 is also indicated by the arrows A. In this
particularly advantageous embodiment, the cooling fins 6 have
inclined end faces 8 and 10. The inclined end faces 8 and 10 of
each cooling fin 6 are beveled so as to extend in parallel in
space. Moreover, the cooling fins 6 in this embodiment are mutually
offset in the flow direction of the cooling air A on the flat side
10 of the base plate 2 so that (the envelopes of) both the inflow
side 12 and the outflow side 14 form a zigzag pattern. Since each
cooling fin has an identical angle of inclination, the
zigzag-shaped inflow and outflow sides 12 and 14 have the same
phase. The base plate 2 is made substantially longer (overhang)
than that of the cooling element depicted in FIG. 1 so that the
flow channels 16 in the inflow and outflow region of the fin
arrangement are not entirely open. The angle of inclination (bevel
angle) of the inclined end faces 8 and 10 determines the overhang
of the base plate 2. The length of the base plate 2 of the cooling
element increases with increasing bevel angle of the end faces 8
and 10 of each cooling fin 6.
[0032] The aforedescribed advantageous shape of the end faces 8 and
10 of the cooling fins 6 of a fin arrangement of a cooling element
produces an embodiment with a substantially reduced
counterpressure. Each cooling fin 6 thereby forms a mini-region in
the region of the inflow and outflow side 12 and 14, whereby the
arrangement of the fins according to the invention forms a
macro-region, which separately contribute to a reduction in the
counterpressure.
[0033] FIG. 5 shows in a perspective view an advantageous cooling
element according to the invention. This advantageous cooling
element has cooling fins 6 which according to FIG. 4 are arranged
on the base plate 2 and have inclined end faces 8 and 10. The
cooling fins 6 are pressed into grooves 26 provided in the base
plate 2. In addition, this cooling element has a second base plate
28, which is placed with a flat surface on the narrow side of the
free ends of the cooling fins 6. The flat side of the second base
plate 28 also has grooves into which the cooling fins 6 can be
pressed. The flow channels 16 are closed off by the second base
plate 28, except for the inflow and outflow side 12 and 14. In
addition, high-power semiconductors can be releaseably secured on
the flat surfaces 20 and 30 of the two base plates 2 and 28
opposite the grooved surfaces. To increase the surface area of the
cooling fin 6, the cooling fins are provided with transverse ribs
extending in the flow direction of the cooling air A.
[0034] By forming the cooling fins 6 in the inflow and outflow
region of a fin arrangement of the cooling body according to the
invention, the components b) and c) of the form factor .zeta. can
be significantly reduced or even eliminated. This reduces
substantially the counterpressure exerted on the cooling air flow,
obviating the need for high-power fans 18, while removing the same
heat per unit time {dot over (Q)}. This not only reduces the system
cost, but also maintenance expenses.
[0035] While the invention has been illustrated and described in
connection with currently preferred embodiments shown and described
in detail, it is not intended to be limited to the details shown
since various modifications and structural changes may be made
without departing in any way from the spirit of the present
invention. The embodiments were chosen and described in order to
best explain the principles of the invention and practical
application to thereby enable a person skilled in the art to best
utilize the invention and various embodiments with various
modifications as are suited to the particular use contemplated.
[0036] What is claimed as new and desired to be protected by
Letters Patent is set forth in the appended claims and their
equivalents:
* * * * *