Note: Descriptions are shown in the official language in which they were submitted.
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Heat sink comprising a tube through which cooling medium flows
Description
The invention relates to a heat sink comprising at least one
tube through which cooling medium flows and which is surrounded
by a heat-conducting material.
Heat sinks of said kind are used for example for cooling heat-
generating components for whose operation an increase in the
temperature of the ambient air is not desirable. Examples of
such components are snubber resistors, power semiconductors or
electrolytic capacitors in power electronics. In such cases the
heat sink typically serves as a mount on which the electronic
components are placed. The components are mounted onto the heat
sink surface-to-surface with good thermal contact such that a
transfer of heat takes place from the components onto the heat
sink. At the same time this leads to the requirement for the
heat to be dissipated as directly as possible to the cooling
medium. If that is the case, the components exhibit very good
thermal resistance and only a slight heating of the respective
component environment takes place in the heat sink.
In the heat sink, heat is released to the cooling medium
flowing in tubes. In such an arrangement a closed circuit is
usually provided in which the cooling medium is circulated by
means of a pump and cooled down by way of a heat exchanger. At
the same time the aim is to keep the amount of cooling medium
small in order to ensure a maximum ratio of cooling performance
to device volume.
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According to the prior art, embodiment variants are known in
which welded high-grade steel tubes are cast in aluminum, as
manufactured for example by the company Ehtwicklung und
Fertigung Volker EEbach, D-09600 Berthelsdorf, Germany
(www.efe-essbach.de).
Effort is directed at achieving good heat transfer between heat
sink and cooling medium in order to optimize cooling
performance. According to the prior art turbulating elements
are for that reason arranged inside the tubes in order to
ensure a turbulent flow. A laminar flow is disadvantageous due
to the low heat transfer coefficient.
Turbulating elements of the aforesaid kind often result in the
formation inside the tubes of zones within which small amounts
of cooling medium circulate or within which low flow velocities
arise. This leads over time to the accumulation of waste
products and residues which are precipitated from the cooling
medium and adhere to the tube inner wall and the turbulating
elements. The consequence of this is deterioration in heat
transfer efficiency together with an increase in flow
resistance which may ultimately lead to a complete blockage of
the tube.
Without turbulating elements the flow velocity must be chosen
high enough to ensure that a transition from laminar to
turbulent flow takes place. Due to the necessary increase in
the pump delivery rate this, however, leads to a drop in the
overall efficiency of the cooling system and an undesirable
increase in noise emission results.
The object underlying the present invention is to specify an
improvement over the prior art for a heat sink of the type
cited in the introduction.
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This object is achieved according to the invention by means of
a heat sink comprising at least one tube through which cooling
medium flows and which is surrounded by a heat-conducting
material, wherein the tube wall of the at least one tube is
corrugated in the flow direction and the heat sink has an
essentially plate-shaped geometry.
The corrugated embodiment has the advantage that the transition
from laminar to turbulent flow takes place at a lower flow
velocity compared to a straight-walled tube. Turbulating
elements are then no longer necessary. Furthermore the heat
transfer area is greater for the same tube length compared to a
straight-walled tube, as a result of which more heat is
dissipated to the cooling medium. Owing to the essentially
plate-shaped geometry the heat sink is easy to manufacture and
has a flat mounting surface for affixing heat-dissipating
components.
In an advantageous embodiment of the invention it is provided
that the at least one tube is embodied as a corrugated tube
with parallel corrugations. Corrugated tubes of said kind are
available in different materials at affordable cost.
Furthermore the parallel corrugation has the advantage that a
tube can easily be bent.
A further advantageous embodiment is provided if the at least
one tube is embodied as a spiral tube with spiral corrugations.
A tube of said kind combines the advantages of a corrugated
tube with a simple means of connecting to connector fittings
which have suitable internal threads and are screwed onto the
ends of the spiral tube without additional preparatory work.
Furthermore a better purging effect for evacuating possible
cooling medium waste products is achieved in a spiral tube.
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It is also advantageous if the at least one tube is manufactured
from corrosion-resistant high-grade steel or copper. With high-
grade steel, a long useful life of the heat sink is assured even
if the cooling medium contains corrosion-promoting substances.
When a cooling medium whose corrosive effect is known to be
minor is employed, the use of copper is also advantageous, since
its thermal conductivity is superior to high-grade steel.
It is favorable therein to provide aluminum or copper or brass
or zinc as the surrounding material. These materials are well
suited to casting and possess high thermal conductivity, with
the result that the waste heat of the components mounted on the
heat sink is dissipated directly to the cooling medium.
Another favorable embodiment variant of the invention provides
that the at least one tube is formed from the heat-conducting
material as a tubular cavity. In this case no separate tube is
used, but instead, during a casting process, a casting core
having the shape of the corrugated tube inner wall is placed in
a casting mold. A cavity having the shape of the casting core is
then embodied in the cast body made of heat-conducting material.
A further possibility consists in embodying the heat sink in two
parts with a mold seam defined by the central axis of the tube.
Chip-removing machining methods are then used to produce the
tubular cavity in such a way that a corrugated channel is
hollowed out in each half of the heat sink. When the heat sink
is assembled, these two channels form the tubular cavity.
It is favorable for the arrangement of the at least one tube if
said tube is arranged in a meander shape. The tube then forms a
plurality of cooling coils within the heat sink, thereby
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producing a more effective dissipation of heat to the cooling
medium. Furthermore, sufficient space for mounting holes
remains between the cooling coils.
Another favorable arrangement is given if the at least one tube
is arranged in a spiral shape. In such an arrangement the tube
is embodied e.g. in the center of the spiral with a
semicircular arc, such that two tube sections running in
parallel are brought out in a spiral shape and provided with
connector fittings at the edge of the heat sink. As in the case
of the meander-shaped arrangement, this provides a sufficient
tube length within the heat sink for good heat dissipation to
the cooling medium.
It is also favorable if a water/antifreeze mixture is provided
as the cooling medium. A mixture of said kind is not only
readily available but is also suitable for a frostproof
application of the heat sink.
The invention is explained below as an exemplary embodiment
with reference to the accompanying figures, which show in
schematic form:
Fig. 1: a front view and side view of a heat sink
Fig. 2: a longitudinal cross-section of a corrugated tube
Fig. 3: a longitudinal cross-section of a spiral tube
Figure 1 shows an exemplary embodiment of a heat sink
comprising a tube 2 arranged in a meander shape, wherein
according to the invention the tube wall is corrugated in the
flow direction. In this arrangement the tube has connector
fittings 3, 4 at its ends, with cooling medium that has been
cooled being pumped into the heat sink by way of a first
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connector fitting 3. Within the heat sink the tube 2 forms a
plurality of cooling coils with semicircles being arranged
between straight tube sections such that the straight
successive tube sections run parallel to one another. The
alignment of the tube sections running parallel to one another
can be changed here within the heat sink, resulting in an
adjustment to the position and heat dissipation of the
components arranged on the heat sink. Components exhibiting a
higher heat dissipation are therein arranged directly over one
or more tube sections, whereas components exhibiting lower heat
dissipation can also be placed in zones between two tube
sections.
When flowing through the tube 2 arranged within the heat sink,
the cooling medium absorbs heat and flows out of the heat sink
by way of a second connector fitting 4, usually via a pump to a
heat exchanger by means of which the cooling medium is cooled
down.
The tube 2 is embodied by way of example as a corrugated tube
made of corrosion-resistant high-grade steel. It is also
possible to equip a heat sink with a plurality of tubes 2 and
in this way provide a plurality of cooling circuits. In this
case each cooling circuit can have its own particular
temperature level and its own particular flow velocity, thereby
ensuring an optimal matching to the cooling requirements of the
components mounted on the heat sink.
The tube 2 is meander-shaped in one plane and cast in a heat-
conducting material (1), aluminum for example. Thus, only the
ends of the tube 2 with the connector fittings 4, 5 project
from the heat-conducting material (1).
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Drilled holes 5 are provided in the zones between the parallel
tube sections and serve as mounting holes for installing
components. The heat sink itself, however, can also be mounted
on an appropriate support by means of the drilled holes 5.
When the components are mounted on the heat sink, care should
be taken to ensure good heat transfer from the components to
the heat sink. Where appropriate a heat-conducting substance
should be provided in the gap between a component and the heat
sink.
In order to determine the optimal cooling conditions it makes
sense to carry out empirical tests with different tube
arrangements, wherein the heat sink is initially uniformly
heated in a test setup and then cooled down through circulation
of a cooling medium. During the cooling-down process the change
in temperature is measured as a function of time and the
position on the heat sink surface. The placement of the
individual components on the heat sink is subsequently carried
out on the basis of these measurement results.
In corrugated or spiral tubes through which cooling medium
flows, the pressure loss per tube length unit as a function of
the volume flow rate follows a parabolic profile, i.e. the
pressure loss per tube length unit increases continuously more
sharply as the volume flow rate increases. At the same time the
scale of this increase is magnified as the diameter of the tube
becomes smaller. The optimal tuning of the individual variables
(volume flow rate, tube diameter, tube length, pressure drop,
etc.) is performed either empirically using tests, through
simulation or by means of fluidic calculations. The optimum
balance is then attained when the maximum heat extraction of
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the heat sink is achieved with the minimum supply of energy
(for a circulating pump and other units).
Furthermore, the fluidic properties of corrugated and spiral
tubes are usually published by the manufacturers of such tubes
(e.g. Water Way Engineering GmbH, D-47441 Moers, Germany).
Figure 2 shows a tube 2 embodied as a corrugated tube in
longitudinal cross-section, with the individual corrugations
running axially symmetrically. In Figure 3, on the other hand,
a tube 2 embodied as a spiral tube is shown in longitudinal
cross-section. In this case the corrugations run in a helical
line around the central axis of the tube 2.
