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Title:
HEAT EXCHANGER FOR CONDUCTING ELSEWHERE HEAT ENERGY GENERATED BY HEAT SOURCE
Document Type and Number:
WIPO Patent Application WO/2000/011423
Kind Code:
A1
Abstract:
The invention relates to a heat exchanger (10) for conducting elsewhere heat energy generated by a heat source (11) by means of heat energy bound to working fluid in phase transition. The heat exchanger (10) comprises a heat exchanger element (13), which has at least two separate condenser portions (15), and an evaporator portion (14), which is between said at least two separate condenser portions (15). The heat exchanger element (13) and/or heat exchanger (10) has a portion (19) which is broader and/or flatter than the other portions.

Inventors:
LEHTINIEMI REIJO (FI)
Application Number:
PCT/FI1999/000683
Publication Date:
March 02, 2000
Filing Date:
August 17, 1999
Export Citation:
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Assignee:
NOKIA NETWORKS OY (FI)
LEHTINIEMI REIJO (FI)
International Classes:
F28D15/02; H01L23/427; (IPC1-7): F28D15/02
Domestic Patent References:
WO1997008483A21997-03-06
Foreign References:
US5198889A1993-03-30
NL9400082A1995-09-01
EP0177660A11986-04-16
Other References:
DATABASE WPI Week 8834, Derwent World Patents Index; AN 1988-241518/34
PATENT ABSTRACTS OF JAPAN vol. 14, no. 365 (E - 961)
Attorney, Agent or Firm:
KOLSTER OY AB (Iso Roobertinkatu 23 P.O. Box 148 Helsinki, FI)
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Claims:
CLAIMS
1. A heat exchanger (10) for conducting elsewhere heat energy generated by a heat source (11) by means of heat energy bound to working fluid in phase transition, which heat exchanger (10) comprises a heat exchanger element (13) containing working fluid, which heat exchanger element (13) comprises an evaporator portion (14) in which working fluid in liquid phase is adapted to receive heat energy generated by the heat source (11) and to vaporize, and a condenser portion (15) in which the temperature is lower than in the evaporator portion (14) and in which vaporized working fluid is adapted to emit its latent heat and to condense back to liquid phase, whereby the evaporation of working fluid in the evaporator portion (14) is adapted to produce a pressure difference between the evaporator portion (14) and the condenser portion (15), which pressure difference is adapted to transfer vaporized working fluid from the evaporator portion (14) to the condenser portion (15) in the heat exchanger element (13), whereby the heat exchanger element (13) is adapted to transfer working fluid in liquid phase from the condenser portion (15) to the evaporator portion (14), whereby the heat exchanger element (13) has at least two separate condenser portions (15), and the evaporator portion (14) is between said at least two separate condenser portions (15), characterized in that the heat exchanger element (13) and/or heat exchanger (10) has a portion (19) which is broader and/or flatter than the other portions.
2. A heat exchanger as claimed in claim 1, c h a r a c t e r i z e d in that the condenser portions (15) are substantially at the ends of the heat exchanger element (13).
3. A heat exchanger as claimed in claim 1, c h a r a c t e r i z e d in that it comprises heat exchanger members (16) adapted to cool the condenser portions (15) of the heat exchanger element (13).
4. A heat exchanger as claimed in claim 1, c h a r a c t e r i z e d in that the heat exchanger element (13) is at least partly integrated into a heat conducting material (12).
5. A heat exchanger as claimed in claim 4, c h a r a c t e r i z e d in that the heatconducting material (12) is a metal composite.
6. A heat exchanger as claimed in claim 1, c h a r a c t e r i z e d in that the heat exchanger (10) has at least substantially a rectangular cross profile.
7. A heat exchanger as claimed in claim 1, c h a r a c t e r i z e d in that the area of said broader and/or flatter portion (19) includes mounting members to fasten the heat source (11).
Description:
HEAT EXCHANGER FOR CONDUCTING ELSEWHERE HEAT ENERGY GENERATED BY HEAT SOURCE BACKGROUND OF THE INVENTION The invention relates to a heat exchanger disclosed in the preamble of claim 1 for conducting elsewhere heat energy generated by a heat source by means of heat energy bound to working fluid in phase transition.

Heat control, i. e. cooling and heating, of heat sources, such as electronic components, is an old problem known per se, which has become more and more pronounced with increasing integration intensities and power.

However, this invention is not restricted only to the temperature control of electronic components, but here a heat source refers to any object requiring temperature control.

New methods, such as heat pipes, have lately emerged along with conventional convection cooling.

The operation of heat pipes is based on phase transition of a liquid working fluid in an evaporator, and on vapour moving to a condenser where it condenses back to liquid. The condensed liquid working fluid is driven by capillary force back to the evaporator by means of a particular porous wick.

Another alternative to bring the condensed working fluid back to the evaporator is to use gravity. Evaporation occurs by utilizing the heat energy generated by the heat source, and condensation is accomplished in such a manner that the condenser end of the heat pipe is in a colder state, which is why the vapour releases its latent heat obtained by evaporation and condenses to liquid. By means of evaporation, the vapour moves from the evaporator end to the condenser end through the pressure difference created in the heat pipe. Since the latent heat bound to evaporation is particularly high and the mass transfer is rapid, the heat pipes provide heat exchange powers of a totally different category than the exchangers based on heat conduction.

Up till now, heat pipes have traditionally been installed in such a manner that each heat source has had its own separate heat pipe which has transferred heat energy from the heat source in one direction only. Especially in electronic applications, one circuit board usually has several electronic components requiring temperature control and, therefore, it is difficult to place the heat pipes effectively, the installation requires space and is awkward.

BRIEF DESCRIPTION OF THE INVENTION It is thus an object of the invention to create a heat exchanger which solves the above-mentioned problems.

The heat exchanger of the invention is characterized by what is disclosed in the characterizing part of the independent claim 1.

The preferred embodiments of the heat exchanger of the invention are set forth in the dependent claims.

The heat exchanger of the invention provides the advantage that because its heat exchanger element and/or heat exchanger has a broader and/or flatter portion than the other portions, which is adapted to operate as an evaporator portion, the transfer of heat energy to the working fluid is efficient.

This is based on the fact that there is more contact surface between the evaporator portion and the heat source.

The heat exchanger of the invention provides the advantage that heat transfer from a heat source is more efficient, because it transfers vaporized working fluid, to which heat energy generated by the heat source is bound, into at least two directions in the heat exchanger element, and conducts the latent heat energy from the vaporized working fluid to at least two separate condenser portions.

By means of the invention, the cooling of heat sources can be considerably improved. This improved cooling makes possible more powerful electronic systems, for instance, and/or reduces the costs caused by conventional cooling methods.

The heat exchanger of the invention provides the further advantage that the vaporized working fluid is automatically transferred to the condenser portion which has more cooling capacity, because there the pressure is lower.

The heat exchanger of the invention provides the yet further advantage that it allows a freer placement of the heat source in relation to the heat exchanger, because the heat source need not be placed in the immediate proximity of the second end of the heat exchanger element.

A preferred embodiment of the heat exchanger of the invention provides the advantage that because the condenser portions are preferably at the ends of its heat exchanger element, it is possible to use a broad evaporator portion, which makes it possible to freely place the heat source in relation to the heat exchanger element.

A preferred embodiment of the heat exchanger of the invention provides the further advantage that thanks to the heat exchanger elements adapted to cool the condenser portions, the condensation of the vaporized working fluid back to its liquid phase is accelerated, which then improves the operation of the heat exchanger of the invention.

A preferred embodiment of the heat exchanger of the invention provides the yet further advantage that because its heat exchanger element is at least partly integrated into a heat-conducting material, preferably a metal composite, the conduction of heat energy to the working liquid in the evaporator portion and from the working liquid in the condenser portion is improved.

A preferred embodiment of the heat exchanger of the invention provides the yet further advantage that because its cross-profile is substantially rectangular, it is easy to combine such heat exchangers of the invention to produce a heat exchanger module. Heat exchangers of the invention with a rectangular cross-profile can advantageously be produced by integrating the heat exchanger element into a heat-conducting material and processing or shaping the heat-conducting material so as to produce a heat exchanger with a rectangular cross-profile. An individual heat exchanger of the invention having several heat exchanger elements can also form such a heat exchanger module. With such heat exchanger modules, it is possible to advantageously control the temperature of an entire circuit board, for instance, which, as is well known, absorbs a great deal of the heat generated by electronic components, i. e. as much as 70% of it.

Because in the heat exchanger of the invention the heat generated by the heat sources is conducted away in at least two directions and in an above-mentioned heat exchanger module as a combined effect of the several heat exchanger elements, individual circuit board components requiring heat control can freely be placed on the circuit board. Heat conducts automatically away from where it is generated. Due to the operating principle of a heat pipe, the area of the entire circuit board is not unnecessarily cooled, but only the hot areas. This also produces the most homogeneous heat distribution, which extends the service life of individual components.

A heat exchanger module of this kind is also simple to install, handle, service, change, test, etc.

The area of the broader and/or flatter portion also advantageously includes mounting members to fasten the heat source. An electronic component, for instance, is typically a board of approximately 10 x 10 mm, and it is difficult to fasten such a component to a tubular heat exchanger. It is easier to fasten the component to a broader and/or flatter portion.

BRIEF DESCRIPTION OF THE DRAWINGS In the following the invention will be described in greater detail in connection with preferred embodiments with reference to the accompanying drawings, in which Figure 1 shows the operation of the heat exchanger elements of a heat exchanger of the invention, Figure 2 shows a heat exchanger module formed by several heat exchangers of the invention, Figure 3 shows a heat exchanger of the invention arranged in a circuit board and comprising three condenser portions, Figure 4 shows from above a heat exchanger of the invention comprising a broader and flatter portion, and Figure 5 shows from the side a heat exchanger of the invention comprising a broader and flatter portion.

DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows a heat exchanger 10 of the invention for conducting elsewhere heat energy generated by a heat source 11 by means of heat energy bound to working fluid in phase transition. The heat exchanger 10 comprises a heat exchanger element 13 containing working fluid (not shown in the figure). A heat exchanger 10 of the invention can, of course, comprise more than one heat exchanger element 13. There can also be more than one heat sources 11.

The heat exchanger element 13 comprises an evaporator portion 14 in which working fluid in liquid phase is adapted to receive heat energy generated by a heat source 11 and to vaporize. In evaporation, evaporation heat is bound to working fluid, i. e. heat energy transfers from the heat source 11 to the working fluid.

The heat exchanger element 13 also comprises a condenser portion 15 in which the temperature is lower than in the evaporator portion 14 and in which the vaporized working fluid is adapted to emit its latent heat, i. e.

evaporation heat, and to condense back to liquid phase. In the condenser portion 15, heat energy transfers from working fluid to the colder condenser portion 15.

The evaporation of working fluid in the evaporator portion 14 is adapted to produce a pressure difference, i. e. pressure gradient, between the evaporator portion 14 and the condenser portion 15, which pressure difference is adapted to move vaporized working fluid and the heat energy bound to it from the evaporator portion 14 to the condenser portion 15 in the heat exchanger element 13. Since the latent heat, i. e. evaporation heat, bound to evaporation is high, large quantities of heat energy move thus away from the heat source 11.

The heat exchanger element 13 is correspondingly adapted to move working fluid in liquid phase from the condenser portion 15 to the evaporator portion 14.

Working fluid can advantageously move from the condenser portion 15 back to the evaporator portion 14 either by gravity or by capillary force directed by the heat exchanger element 13 to the working fluid. Other possibilities also exist.

The operating principe of such a heat exchanger is known per se and is, therefore, not disclosed in greater detail in this context.

The heat exchanger 10 of the invention is characterized in that it comprises at least two separate condenser portions 15, and the evaporator portion 14 is between said at least two separate condenser portions 15.

A tubular heat exchanger element 13 can thus have two separate condenser portions 15 (ends of the tube), and a Y-shaped heat exchanger element 13 can thus have three separate condenser portions 15, and a cross- shaped heat exchanger element 13 can have four separate condenser portions 15, etc.

In Figures 4 and 5, the heat exchanger element 13 and/or heat exchanger 10 advantageously has a portion 19 which is broader and/or flatter than the other portions. Such a portion 19 can advantageously be adapted to function as an evaporator portion 14 in a manner that the heat source is arranged in the proximity of this broader and/or flatter portion 19. The transfer of heat energy is efficient between such a broader and/or flatter evaporator portion and the heat source, because there is more contact surface between the evaporator portion and the heat source. Such a broader and/or flatter

portion 19 can be achieved by for instance pressing flat a standard heat exchanger element 13 with a round cross-profile. A broader and/or flatter evaporator portion 14 can also be created in a heat exchanger element 13, which has more than two condenser portions 15, by pressing it flat in the area of the evaporator portion 14.

Said broader and/or flatter portion 19 also advantageously includes mounting members (not shown in the figure), such as mounting slots for screws, to fasten the heat source 11.

Figure 3 shows a heat exchanger 10 of the invention with three condenser portions 15. The condenser portions 15 are advantageously located in areas with cooling capacity. The heat exchanger element 13 in Figure 3 is also advantageously bent to follow the route determined by the available space from the evaporator portion 14 to the condenser portions 15.

For clarity's sake, other components 17 located on the circuit board 18 are also shown in the figure.

Advantageously, the condenser portions 15 are substantially at the ends of the heat exchanger element 13 to make a broad evaporator portion 14 available. Placing the condenser portions 15 at the ends of the heat exchanger element 13 also makes possible a freer placement of the heat source 11 in relation to the heat exchanger element 13. However, it is important in this context that the heat source 11 emits heat energy to the working fluid in the heat exchanger element 13 between two condenser portions 15.

When necessary, additional cooling can be arranged to the condenser portions 15 of the heat exchanger 10 of the invention. For this, the heat exchanger 10 of the invention advantageously has heat exchanger members 16 adapted to cool the condenser portions 15. This improves the conducting of heat energy away from vaporized working fluid making the condensation of the working fluid more efficient, i. e. making it condense faster back to its liquid phase.

The heat exchanger 10 of the invention is preferably at least partly integrated into a heat-conducting material 12. The heat-conducting material 12 is preferably a metal composite. This heat-conducting material 12 efficiently conducts heat energy from the heat source 11 to the working fluid in the evaporator portion 14 and from the working fluid in the condenser portion 15.

In Figure 1, fins acting as heat exchanger members 16 are advantageously integrated into the heat-conducting material and they are adapted to emit the heat energy conducted to the heat-conducting material 12 on to the environment. This way, it is possible to achieve between the heat- conducting material 12 and the environment more boundary through which the heat-conducting material 12 emits the heat energy conducted to it to the environment thus improving the heat transfer capability of the heat exchanger of the invention.

Heat exchangers 10 of the invention can advantageously be combined together to form heat exchanger modules, for instance.

For instance, heat exchangers 10 with rectangular cross-profiles can easily be combined together to form a heat exchanger module shown in Figure 2. Such a heat exchanger module can advantageously control the temperature or temperatures of an entire circuit board, for instance.

Alternatively, an individual heat exchanger 10 of the invention can be made to hold several heat exchanger elements 13, in which case it alone forms a heat exchanger module. The evaporator portion 14 of such a heat exchanger module can advantageously be made equal to the size of a circuit board 18, for instance.

It is obvious to a person skilled in the art that while technology advances, the basic idea of the invention can be implemented in many different ways. The invention and its embodiments are thus not restricted to the examples described above, but can vary within the scope of the claims.