U.S. patent application number 09/876227 was filed with the patent office on 2002-03-21 for use of pcms in heat sinks for electronic components.
This patent application is currently assigned to Merck Patent GmbH. Invention is credited to Glausch, Ralf, Neuschutz, Mark.
Application Number | 20020033247 09/876227 |
Document ID | / |
Family ID | 26005968 |
Filed Date | 2002-03-21 |
United States Patent
Application |
20020033247 |
Kind Code |
A1 |
Neuschutz, Mark ; et
al. |
March 21, 2002 |
Use of PCMs in heat sinks for electronic components
Abstract
The present invention relates to the use of phase change
materials in devices for cooling electrical and electronic
components.
Inventors: |
Neuschutz, Mark; (Darmstadt,
DE) ; Glausch, Ralf; (Muhltal, DE) |
Correspondence
Address: |
MILLEN, WHITE, ZELANO & BRANIGAN, P.C.
2200 CLARENDON BLVD.
SUITE 1400
ARLINGTON
VA
22201
US
|
Assignee: |
Merck Patent GmbH
Darmstadt
DE
|
Family ID: |
26005968 |
Appl. No.: |
09/876227 |
Filed: |
June 8, 2001 |
Current U.S.
Class: |
165/10 ;
165/80.3; 257/E23.089 |
Current CPC
Class: |
F28D 20/02 20130101;
Y02E 60/145 20130101; Y02E 60/14 20130101; H01L 2924/0002 20130101;
F28D 15/02 20130101; H01L 23/4275 20130101; H01L 2924/0002
20130101; H01L 2924/00 20130101 |
Class at
Publication: |
165/10 ;
165/80.3 |
International
Class: |
F28D 017/00; F28D
019/00; F28F 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 8, 2000 |
DE |
100 27 803.5 |
Mar 26, 2001 |
DE |
101 14 998.0 |
Claims
1. A device for cooling heat-generating electrical or electronic
components having a non-uniform output profile, comprising a
heat-conducting unit (1) and a heat-absorbing unit which contains a
phase change material (4), wherein the phase change material is
arranged in such a way that heat flow from the electrical or
electronic component to the heat-conducting unit (1) is not
interrupted and a significant heat flow to the phase change
material only occurs if the temperature of the heat-conducting unit
(1) exceeds phase change temperature T.sub.PC of the phase change
material.
2. The device according to claim 1, wherein the phase change
material-containing unit (4) contains at least one cavity (6) into
which the phase change material has been introduced, where the
cavities (6) are formed by the heat-absorbing unit (4).
3. The device according to claim 1, wherein the phase change
material-containing unit (4) additionally contains a liquid/gaseous
heat transfer medium (5).
4. The device according to claim 3, wherein the liquid/gaseous heat
transfer medium (5) is a halogenated hydrocarbon.
5. The device according to claim 1, wherein a solid-solid phase
change material is employed.
6. The device according to claim 1, wherein the phase change
material is encapsulated.
7. The device according to claim 1, wherein the heat-conducting
unit (1) has surface area-increasing structures.
8. The device according to claim 1, wherein the heat-conducting
unit (1) has cooling fins.
9. A component (Z), comprising a cooling device according to claim
1, a heat-generating electronic component (2), wherein units (1),
(4) and component (2) are arranged in such a way that the heat flow
between the heat-generating electronic component (2) and the
heat-conducting unit (1) takes place in direct contact.
10. A component (Z) according to claim 9, wherein the electronic
component (2) is a computer CPU or memory chip.
11. A computer containing a component (Z) according to claim 9.
12. An electronic data processing system containing a device
according to claim 1.
13. A mobile communication power switch or power circuit, a mobile
telephone or fixed transmitter transmission circuit, an
electromechanical actuator control circuit, a satellite
communication or radar application high frequency circuit, or a
domestic appliance or industrial electronic actuator or control
unit, comprising a device according to claim 1.
14. A device for absorbing heat, comprising a heat sink and a heat
absorbing component containing a phase change material, wherein
heat flows from the heat sink to the heat absorbing component when
the heat sink temperature exceeds the phase change temperature of
the phase change material.
15. A device for absorbing heat, comprising a heat sink means and a
heat absorbing means containing a phase change material, wherein
heat flows from the heat sink means to the heat absorbing means
when the heat sink temperature exceeds the phase change temperature
of the phase change material.
16. A device for absorbing heat, comprising, in contact with a
heat-generating electric or electronic component, a heat sink and a
heat absorbing component containing a phase change material,
wherein heat flows from the heat sink to the heat absorbing
component when the heat sink temperature exceeds the phase change
temperature of the phase change material.
Description
[0001] The present invention relates to the use of phase change
materials in cooling devices for electrical and electronic
components.
[0002] In industrial processes, heat peaks or deficits often have
to be avoided, i.e. temperature control must be provided. This is
usually achieved using heat exchangers. In the simplest case, they
may consist merely of a heat conduction plate, which dissipates the
heat and releases it to the ambient air, or alternatively contain
heat transfer media, which firstly transport the heat from one
location or medium to another.
[0003] The state of the art (FIG. 1) for the cooling of electronic
components, such as, for example, microprocessors (central
processing units=CPUs) (2), are heat sinks made from extruded
aluminium, which absorb the heat from the electronic component,
which is mounted on support (3), and release it to the environment
via cooling fins (1). The convection at the cooling fins is almost
always supported by fans.
[0004] Heat sinks of this type must always be designed for the most
unfavorable case of high outside temperatures and full load of the
component in order to avoid overheating, which would reduce the
service life and reliability of the components. The maximum working
temperature for CPUs is between 60 and 90.degree. C., depending on
the design.
[0005] As the clock speed of CPUs becomes ever faster, the amount
of heat they emit jumps with each new generation. While hitherto
peak outputs of a maximum of 30 watts had to be dissipated, it is
expected that cooling capacities of up to 90 watts will be
necessary. These outputs can no longer be dissipated using
conventional cooling systems.
[0006] For extreme ambient conditions, as occur, for example, in
remote-controlled missiles, heat sinks, in which the heat emitted
by electronic components is absorbed in phase change materials, for
example in the form of heat of melting, have been described (U.S.
Pat. No. 4,673,030, EP 1 16503A, U.S. Pat. No. 4,446,916). These
PCM heat sinks serve for short-term replacement of dissipation of
the energy into the environment and cannot (and must not) be
re-used.
[0007] Known storage media for the storage of sensible heat are,
for example, water or stones/concrete or phase change materials
(PCMs), such as salts, salt hydrates or mixtures thereof, or
organic compounds (for example paraffin) for the storage of heat in
the form of heat of melting (latent heat).
[0008] It is known that when a substance melts, i.e. is converted
from the solid phase into the liquid phase, heat is consumed, i.e.
absorbed, and is stored as latent heat so long as the substance
remains in the liquid state, and that this latent heat is liberated
again on solidification, i.e. on conversion from the liquid phase
into the solid phase.
[0009] The charging of a heat storage system basically requires a
higher temperature than can be obtained during discharging, since a
temperature difference is necessary for the transport/flow of heat.
The quality of the heat is dependent on the temperature at which it
is available: the higher the temperature, the better the heat can
be dissipated. For this reason, it is desirable for the temperature
level during storage to drop as little as possible.
[0010] In the case of storage of sensible heat (for example by
heating water), the input of heat is associated with constant
heating of the storage material (and the opposite during
discharging), while latent heat is stored and discharged at the
melting point of the PCM. Latent heat storage therefore has the
advantage over sensible heat storage that the temperature loss is
restricted to the loss during heat transport from and to the
storage system.
[0011] The storage media employed hitherto in latent heat storage
systems are usually substances which have a solid-liquid phase
transition in the temperature range which is essential for the use,
i.e. substances which melt during use.
[0012] Thus, the literature discloses the use of paraffins as
storage medium in latent heat storage systems. International patent
application WO 93/15625 describes shoe soles which contain
PCM-containing microcapsules. The PCMs proposed here are either
paraffins or crystalline 2,2-dimethyl-1,3-propanediol or
2-hydroxymethyl-2-methyl-1,3-propanediol. The application WO
93/24241 describes fabrics having a coating comprising
microcapsules of this type and binders. Preference is given here to
paraffinic hydrocarbons having from 13 to 28 carbon atoms. European
Patent EP-B-306 202 describes fibers having heat-storage properties
in which the storage medium is a paraffinic hydrocarbon or a
crystalline plastic, and the storage material is integrated into
the basic fiber material in the form of microcapsules.
[0013] U.S. Pat. No. 5,728,316 recommends salt mixtures based on
magnesium nitrate and lithium nitrate for the storage and
utilization of thermal energy. The heat storage here is carried out
in the melt at above the melting point of 75.degree. C.
[0014] In the said storage media in latent heat storage systems, a
transition into the liquid state takes place during use. This is
accompanied by problems in the case of industrial use of storage
media in latent heat storage systems since sealing or encapsulation
is always necessary in order to prevent leakage of liquid resulting
in loss of substance or contamination of the environment.
Especially in the case of use in or on flexible structures, such
as, for example, fibers, fabrics or foams, this generally requires
microencapsulation of the heat storage materials.
[0015] In addition, the vapor pressure of many potentially suitable
compounds increases greatly during melting, and consequently the
volatility of the melts often stands in the way of long-term use of
the storage materials. On industrial use of melting PCMs, problems
frequently arise due to considerable volume changes during melting
of many substances.
[0016] A new area of phase change materials is therefore provided
with a particular focus. These are solid-solid phase change
materials. Since these substances remain solid during the entire
use, there is no longer a requirement for encapsulation. Loss of
the storage medium or contamination of the environment by the melt
of the storage medium in latent heat storage systems can thus be
excluded. This group of phase change materials is finding many new
areas of application.
[0017] U.S. Pat. No. 5,831,831, JP 10135381 A and SU 570131A
describe the use of similar PCM heat sinks in non-military
applications. A common feature of the inventions is the omission of
conventional heat sinks (for example with cooling fins and
fans).
[0018] The PCM heat sinks described above are not suitable for
absorbing the peak output of components having an irregular output
profile since they do not ensure optimized discharge of the PCM or
also absorb the base load.
[0019] The present invention enables cooling electronic and
electrical components effectively and absorbing temperature
peaks.
[0020] The invention provides devices for cooling heat-generating
electrical and electronic components having an irregular output
profile, comprising a heat-conducting unit and a heat-absorbing
unit which contains a phase change material (PCM).
[0021] This invention relates to devices for cooling electrical and
electronic components (e.g., microprocessors in desktop and laptop
computers both on the motherboard and on the graphics card,
power-supply parts and other components which emit heat during
operation) which have a non-uniform output profile.
[0022] Cooling devices are, for example, heat sinks. Conventional
heat sinks can be improved by the use of PCMs if the heat flow from
the electronic component to the heat sink is not interrupted. An
interruption in this sense exists if the PCM, owing to the design
of the heat sink, firstly has to absorb the heat before the heat
can be dissipated via the cooling fins--which results in an
impairment of the performance of the heat sink for a given
design.
[0023] There are various ways of ensuring that the PCM only absorbs
the output peaks.
[0024] Electrical and electronic components are usually cooled
using heat sinks (FIG. 1) having cooling fins.
[0025] It has been found that it is advantageous to arrange the PCM
in or on the heat sink in such a way that a significant heat flow
to the PCM only occurs if the heat sink exceeds the phase change
temperature T.sub.PC of the PCM (FIG. 2, FIG. 3, FIG. 4 and FIG.
5).
[0026] It has been found that on reaching this temperature, the
cooling capacity of the cooling fins is supplemented by the heat
absorption by the PCM. This causes a jump in the efficiency of the
heat sink. It is thus achieved that the electrical or electronic
component is not overheated.
[0027] The use of PCMs in the manner according to the invention
allows the use of heat sinks of lower capacity since extreme heat
peaks do not have to be dissipated.
[0028] It has been found that particularly suitable phase change
materials are those whose phase change temperature T.sub.PC is
suitably below the critical maximum temperature for the
component.
[0029] Depending on the desired maximum temperature, all known PCMs
are suitable. Suitable for use of the PCMs in a heat transfer
medium are encapsulated materials or solid-solid PCMs which are
insoluble in the heat transfer medium.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 represents a conventional heat sink.
[0031] FIGS. 2-5 represent various embodiments of the
heat-dissipating devices according to the invention.
[0032] A general example of the invention is explained in greater
detail below.
[0033] The devices according to the invention are described with
reference to an example of the cooling of CPUs (central processing
units) for computers.
[0034] In the device according to the invention (FIG. 2), the PCM
(4) is arranged in or on the heat sink (1) in such a way that
significant heat flow from the CPU (2) on the support (3) to the
PCM (4) only occurs if the heat sink exceeds the phase change
temperature T.sub.PC of the PCM. It is thus ensured that the PCM
only absorbs the output peaks.
[0035] In principle, all known PCMs are suitable for this
application. For example, it is possible to use PCMs whose phase
change temperature is between about -100.degree. C. and 150.degree.
C. For use in electrical and electronic components, PCMs in the
range of about 40.degree. C. to 95.degree. C. are preferred. In
this case, the materials can be selected from paraffins
(C.sub.20-C.sub.45), inorganic salts, salt hydrates and mixtures
thereof, carboxylic acids and/or sugar alcohols. A non-limiting
selection is shown in Table 1.
1TABLE 1 Melting point Melting Material [.degree. C.] enthalpy
[J/g] Group Heneicosane 40 213 Paraffins Docosane 44 252 Paraffins
Tricosane 48 234 Paraffins Sodium thiosulfate 48 210 Salt hydrates
pentahydrate Myristic acid 52 190 Carboxylic acids Tetracosane 53
255 Paraffins Hexacosane 56 250 Paraffins Sodium acetate 58 265
Salt hydrates trihydrate Nonacosane 63 239 Paraffins Sodium
hydroxide 64 272 Salt hydrates monohydrate Stearic acid 69 200
Carboxylic acids Mixture of lithium 75 180 Salt hydrates nitrate
and magnesium nitrate hexahydrate Trisodium 75 216 Salt hydrates
phosphate dodecahydrate Magnesium nitrate 89 160 Salt hydrates
hexahydrate Xylitol 93-95 270 Sugar alcohols
[0036] Also suitable are solid-solid PCMs such as diethylammonium
chloride, dipropylammonium chloride, dibutylammonium chloride,
dipentylammonium chloride, dihexylammonium chloride,
dioctylammonium chloride, didecylammonium chloride,
didodecylammonium chloride, dioctadecylammonium chloride,
diethylammonium bromide, dipropylammonium bromide, dibutylammonium
bromide, dipentylammonium bromide, dihexylammonium bromide,
dioctylammonium bromide, didecylammonium bromide, didodecylammonium
bromide, dioctadecylammonium bromide, diethylammonium nitrate,
dipropylammonium nitrate, dibutylammonium nitrate, dipentylammonium
nitrate, dihexylammonium nitrate, dioctylammonium nitrate,
didecylammonium nitrate, dioctylammonium chlorate, dioctylammonium
acetate, dioctylammonium formate, didecylammonium chlorate,
didecylammonium acetate, didecylammonium formate, didodecylammonium
chlorate, didodecylammonium formate, didodecylammonium
hydrogensulfate, didodecylammonium propionate, dibutylammonium
2-nitrobenzoate, diundecylammonium nitrate and didodecylammonium
nitrate.
[0037] Particularly suitable PCMs for use in electrical and
electronic components are those whose T.sub.PC is between
40.degree. C. and 95.degree. C., such as, for example,
didecylammonium chloride, didodecylammonium chloride,
dioctadecylammonium chloride, diethylammonium bromide,
didecylammonium bromide, didodecylammonium bromide,
dioctadecylammonium bromide, diethylammonium nitrate,
dioctylammonium nitrate, didecylammonium nitrate and
didodecylammonium nitrate.
[0038] Besides the actual heat storage material, the PCMs
preferably comprise at least one auxiliary. The at least one
auxiliary is preferably a substance or composition having good
thermal conductivity, in particular a metal powder, metal granules
or graphite. The heat storage material is preferably in the form of
an intimate mixture with the auxiliary, the entire composition
preferably being in the form of either a loose bed or moldings. The
term moldings here is taken to mean, in particular, all structures
which can be produced by compaction methods, such as pelleting,
tabletting, roll compaction or extrusion. The moldings here can
adopt a very wide variety of spatial shapes, such as, for example,
spherical, cubic or cuboid shapes. In addition, the mixtures or
moldings described here may comprise paraffin as an additional
auxiliary. Paraffin is employed in particular if intimate contact
between the heat storage composition and a component is to be
established during use. For example, latent heat storage systems
can be installed with a precise fit in this way for the cooling of
electronic components. During installation of the heat storage
system, the handling of, in particular, a molding described above
is simple; the paraffin melts during use, expels air at the contact
surfaces and so ensures close contact between the heat storage
material and the component. Compositions of this type are therefore
preferably used in devices for cooling electronic components.
[0039] In addition, binders, preferably a polymeric binder, may be
present as auxiliaries. In this case, the crystallites of the heat
storage material are preferably in finely divided form in the
binder. The preferably polymeric binders which may be present can
be the polymers which are suitable as binder in accordance with the
application. The polymeric binder is preferably selected from
curable polymers or polymer precursors, which in turn are
preferably selected from the group consisting of polyurethanes,
nitrile rubber, chloroprene, polyvinyl chloride, silicones,
ethylene-vinyl acetate copolymers and polyacrylates. The suitable
methods for incorporation of the heat storage materials into these
polymeric binders are well known to the person skilled in the art
in this area. One of ordinary skill has no difficulties in finding,
where appropriate, the requisite additives, such as, for example,
emulsifiers, which stabilize a mixture of this type.
[0040] For liquid-solid PCMs, nucleating agents, such as, for
example, borax or various metal oxides, are preferably employed in
addition.
[0041] Besides ensuring good heat transfer through metals
(aluminium, copper, etc.) or other heat conduction structures
(metal powders, graphite, etc.), the heat transfer in the heat sink
may also be implemented in the form of a heat pipe (for example
U.S. Pat. No. 5,770,903 for motor cooling incl. PCM).
[0042] In a heat sink with heat pipe (FIG. 3), the interior of the
heat sink (1) then has, for example, a cavity (6), which is
partially filled with a liquid and/or gaseous medium. The
liquid/gaseous heat transfer medium (5) is selected from the group
consisting of the halogenated hydrocarbons (for example ethyl
bromide, trichloroethylene or freons) and their equivalents. The
design of a heat pipe and the choice of a suitable medium presents
no problems to the person skilled in the art.
[0043] Besides this medium, the cavity also contains PCM particles
(4), which absorb heat as soon as the internal temperature in the
heat pipe reaches the phase change temperature T.sub.PC.
[0044] It has been found that encapsulated or microencapsulated
PCMs and solid-solid PCMs which are insoluble in the medium are
particularly suitable. All known PCMs can be used.
[0045] Surprisingly, it has been found that, due to the good mixing
of the PCM/medium suspension, the dynamics of the heat sink are
particularly great.
[0046] A further possibility has been found through a mixed form
(FIG. 4). The CPU (2) is again mounted on a support (3). In order
to improve the heat conduction, cooling fins (7) are run through
the cavity (6), which is in turn partially filled with a
liquid/gaseous heat transfer medium (5). Continuous cooling fins
are preferred. As in the previous variants, the cavity, besides the
liquid/gaseous heat transfer medium, here too contains PCM
particles (4), which absorb heat as soon as the internal
temperature in the heat pipe reaches the phase change temperature
T.sub.PC.
[0047] The PCM can be compression molded into any desired shapes.
The material can be compression molded in pure form, compression
molded after comminution (for example grinding), or compression
molded in mixtures with other binders and/or auxiliaries. The
moldings can be stored, transported and employed in a variety of
ways without problems. For example, the moldings can be inserted
directly into electronic components (FIG. 5). Here too, the CPU (2)
is mounted on a support (3). The moldings are installed between the
cooling fins in such a way that they are in intimate contact with
the surfaces of the cooling fins. The thickness of the moldings is
selected so that a frictional connection is formed between the fins
and the molding. The moldings can also be inserted between cooling
fins/heat exchangers before the latter are connected to form a
stack.
[0048] However, these types of cooling with the aid of PCMs for
absorbing heat peaks are not restricted to use in computers. These
systems can be used in power switches and power circuits for mobile
communications, transmission circuits for mobile telephones and
fixed transmitters, control circuits for electromechanical
actuators in industrial electronics and in motor vehicles,
high-frequency circuits for satellite communications and radar
applications, single-board computers, and for actuators and control
units for domestic appliances and industrial electronics.
[0049] These cooling devices can be applied to all applications in
which heat, e.g., heat peaks, are to be absorbed (for example
motors for elevators, in electrical substations and in
internal-combustion engines).
2TABLE 2 Explanation of the symbols in the figures Symbol
Explanation 1 Cooling ribs 2 Central processing unit (CPU) 3
Support 4 Phase change material (PCM) 5 Liquid/gaseous heat
exchange medium 6 Cavity 7 Cooling fins in cavity Z Entire
component
[0050] Without further elaboration, it is believed that one skilled
in the art can, using the preceding description, utilize the
present invention to its fullest extent. The following preferred
specific embodiments are, therefore, to be construed as merely
illustrative, and not limitative of the remainder of the disclosure
in any way whatsoever.
[0051] In the foregoing and in the following examples, all
temperatures are set forth uncorrected in degrees Celsius; and,
unless otherwise indicated, all parts and percentages are by
weight.
[0052] The entire disclosure of all applications, patents and
publications, cited above and below, and of corresponding German
application Nos. DE 100 27 803.5, filed Jun. 8, 2000, and DE 101 14
998.0, filed Mar. 26, 2001, are is hereby incorporated by
reference.
EXAMPLES
Example 1
[0053] A heat sink as shown in FIG. 2 is designed for a processor
whose maximum operating temperature is 75.degree. C. A phase change
material having a T.sub.PC of between 60.degree. C. and 65.degree.
C. is selected in the cavities in the heat sink. Sodium hydroxide
monohydrate having a T.sub.PC of 64.degree. C. is used.
Example 2
[0054] A heat sink as shown in FIG. 3 is designed for a processor
having a maximum operating temperature of 75.degree. C. The
cavities of the heat sink contain trichloroethylene as heat
transfer fluid. The PCM used is an encapsulated paraffin.
Nonacosane, which has a T.sub.PC of 63.degree. C., is used.
However, solid-solid PCMs are also suitable as phase change
material here. Didoceylammonium nitrate is suitable for this
processor as it has a T.sub.PC of 66.degree. C.
[0055] The preceding examples can be repeated with similar success
by substituting the generically or specifically described reactants
and/or operating conditions of this invention for those used in the
preceding examples.
[0056] From the foregoing description, one skilled in the art can
easily ascertain the essential characteristics of this invention
and, without departing from the spirit and scope thereof, can make
various changes and modifications of the invention to adapt it to
various usages and conditions.
* * * * *