Heat sinks with carbon nanostructure-based fibers

Description

[0001] The invention relates to a heat sink comprising a base body and a plurality of carbon nanostructure-based fibers (CNB), in particular carbon nanotubes or carbon nanotubes (CNT) or graphene fibers, some of which are initially attached to the base body for heat transfer. State of the art

[0002] A heat sink of the type mentioned above is known from US 2007158584.

[0003] The known heat sink has a base body from which carbon nanostructure-based fibers extend in a parallel arrangement. The heat sink serves to cool an object connected to the base body, with a cooling medium flowing through the carbon nanostructure-based fibers. The object's heat thus travels to the base body, from there to the carbon nanostructure-based fibers, and then to the cooling medium.

[0004] JP2014-220280 A refers to a sheet-like structure used as heat radiation sheet for electronic apparatus, having a carbon nanotube element with linear structures, where a deformation of the first portion of the element is larger than that of the second portion of the element.

[0005] US2007 / 053168 A1 refers to a thermal management assembly, comprising a heat sink including a graphite layer obtained by cleaving a graphene layer from a graphite sheet, and a support layer.

[0006] US2013 / 163205 A1 refers to a heat-dissipation structure including a first carbon nanotube layer and a metal mesh layer. The first carbon nanotube layer and the metal mesh layer are stacked on each other. The first carbon nanotube layer includes at least one first carbon nanotube paper.

[0007] Such heat sinks can be used in electrical engineering, particularly in power electronics, for example, to dissipate heat generated by power semiconductors. Especially in the field of power electronics, especially in modern inverters, heat sinks with high efficiency and a compact design are required. The invention relates to a heat sink that, while being simple to manufacture and compact in size, still provides a structure with a very large surface area, allowing large amounts of heat to be dissipated without any problems. Disclosure of the invention

[0008] The heat sink according to the invention comprises a base body and a plurality of carbon nanostructure-based fibers (CNB), in particular carbon nanotubes (CNT) or graphene fibers, at least some of which are attached to the base body for heat dissipation. Due to adhesion or support among each other, the fibers form a volume structure, in particular in the manner of cotton wool, felt, or a woven fabric, or wherein the fibers form loops or a three-dimensional fabric. Furthermore, at least one support structure is provided, in particular made of metal and / or preferably further carbon nanostructure-based fibers (CNB), in particular carbon nanotubes (CNT) or graphene fibers, which supports the fibers.The support structure is therefore, in particular, a metal structure or a fiber structure, wherein this fiber structure in turn consists of (in particular other) carbon nanostructure-based fibers or carbon nanotubes. The at least one support structure is lattice-shaped and serves for attachment to the base body and / or the counterbody. It can be provided, in particular, that the support structure is cast into the base body and / or the counterbody.

[0009] The invention exploits the specific properties of carbon nanostructure-based fibers (CNB), in particular carbon nanotubes (CNTs) or graphene fibers, which consist of very good thermal conductivity. Due to the volume structure of the fibers, the loops of the fibers, or the three-dimensional weave, a very large surface area is created, allowing the fibers to very effectively transfer heat to a preferably flowing cooling medium, with the cooling medium surrounding or flowing through the fibers. In particular, the cooling medium can be a cooling liquid.The volume structure, in which the fibers touch each other, thus creating a kind of adhesion or support, or the loop structure of the fibers, or the weave structure of the three-dimensional fabric, not only creates the aforementioned large surface area but also produces a relatively rigid mechanical structure, so that even a flowing cooling medium does not deform the fibers, or only slightly deforms them. Rather, the aforementioned structures create a very good turbulence in the flow of the cooling medium, which leads to better heat dissipation. The aforementioned "adhesion" of the fibers to each other does not generally mean adhesion or the like, but rather a kind of frictional resistance that exists, for example, between two touching fibers.Nevertheless, according to another embodiment, the aforementioned adhesion also encompasses the bonding of two touching fibers, for example, by means of an additional substance, such as a type of adhesive or the like. Solder joints are also conceivable. The base body is thermally connected to an object to be cooled, preferably at least one power semiconductor.

[0010] According to a further development of the invention, the fibers form an ordered and / or at least partially a disordered structure. A cotton-like volume structure represents a disordered structure. The same applies to felt or woven fabric. Loop-shaped fibers are more likely to be assumed to have an ordered structure. The same applies to the aforementioned fabric, since certain stitch patterns are constantly repeated there.

[0011] A further development of the invention provides a counter body that is spaced apart from the base body and to which at least some of the fibers are attached. By attaching fibers to the base body and the counter body, the entire fiber structure is mechanically held particularly well, so that no undesirable deformations can occur due to a flowing cooling medium. The cooling medium then flows between the base body and the counter body, dissipating heat from the fibers in between. Preferably, the counter body can also dissipate heat.

[0012] Preferably, the attachment to the base body and / or the counter body is provided as soldering points, adhesive points, and / or casting points. The base body and / or counter body can, for example, be plate-shaped, with the aforementioned attachment of the fibers taking place on these plates, or with sections of the fibers being cast in during the manufacture of the base body and / or counter body through a casting process.

[0013] In particular, it can be provided that the loops have end regions and that at least some of the end regions of the loops are attached to / in the base body and / or the counter body. The end regions can be the beginning and / or end of a loop or a reversal region of the loop.

[0014] Preferably, the fibers are compressed against each other, at least in some areas. During production, for example, a cotton-like structure of the fibers is created and then compressed to create a more rigid structure. However, the compression is not carried out so strongly that the flow paths for the cooling medium are closed too much.

[0015] In order to create a special resistance against the flowing cooling medium, it may be provided to provide at least some of the fibers with a mechanically stabilizing coating.

[0016] Preferably, the three-dimensional fabric is mechanically stabilized by the type of mesh and / or the mesh size of the fabric. This stabilization resulting from the mesh also mechanically protects the carbon nanostructure-based fibers, in particular carbon nanotubes, against deformation.

[0017] It can be provided that at least some of the fibers originate from a fiber base, in particular a planar one, formed by the fibers and / or other carbon nanostructure-based fibers (CNB), in particular carbon nanotubes (CNTs) or graphene fibers. This fiber base can in particular be attached to the base body and / or the counter body or cast into the base body and / or the counter body.

[0018] In particular, it is possible that the mentioned fiber base is formed as a fabric.

[0019] A further development of the invention provides that at least some of the fibers run from the base body to the counter body at an angle other than 90° to achieve the greatest possible fiber length between these two bodies and / or at an angle of 90°. The greater the fiber length between the base body and the counter body, the more heat the individual fiber can dissipate.

[0020] The invention is defined in the following claims.

[0021] The drawings illustrate the invention using exemplary embodiments, namely: Figure 1 shows a region of a heat sink with loop-shaped carbon nanostructure-based fibers, Figure 2 shows the region of the heat sink of the Figure 1with a region of a counter body, Figure 3 shows a region of a heat sink with carbon nanostructure-based fibers in the form of individual filaments and in the form of loops, Figure 4 shows a region of a heat sink with a fiber base and carbon nanostructure-based fibers in the form of a volume structure, for example in the manner of cotton wool or felt or a spun fabric, Figure 5 shows regions of two variants of a heat sink with filaments running essentially at right angles to the fiber base or obliquely to the fiber base, and Figure 6 shows a region of a heat sink with lattice-shaped support structures and loop-shaped fibers.

[0022] The Figure 1shows a heat sink 1 comprising a base body 2 and carbon nanostructure-based fibers 3, in particular carbon nanotubes 4, which are also referred to as carbon nanotubes or tubelets, or alternatively graphene fibers. A power electronics component (not shown) that requires cooling during operation is thermally connected to the heat sink 1. A cooling medium, indicated by arrows 5, for example a cooling liquid, flows along the heat sink 1, in particular transversely to the course of the carbon nanotubes 4. Heat from the power electronics component is transferred to the base body 2, from where it is conducted to the carbon nanotubes 4, and dissipated by the cooling medium. The carbon nanotubes 4 extend as loops 6, forming an approximately meandering structure, with end regions 7 of the loops 6 being embedded in the base body 2. Embedding is preferably carried out by pouring when creating the base body 2.The base body 2 is preferably made of a material with good thermal conductivity, particularly metal. The looped structure of the carbon nanotubes 4 provides them with good mechanical stability against the flowing coolant, preventing them from being deformed by the flow. Furthermore, the looped shape leads to very good heat transfer, as a large surface area is created.

[0023] At the Figure 2 and all other following figures, the same reference numerals refer to the same parts as in the Figure 1 used, so that no further explanation is required. Rather, the same applies. The area of ​​the heat sink 1 of the Figure 2 is structured in the same way as in the Figure 1However, a counter-body 8 is additionally positioned opposite the base body 2 at a distance, such that end regions 9 of the loops 6 are attached to this counter-body 8, preferably cast into it. This holds the loops 6 at both ends, providing even better mechanical stability. The attachment of the carbon nanotubes 4 to the base body 2 and / or to the counter-body 8 can also be achieved in other ways, for example, in the form of soldered or glued joints.

[0024] The Figure 3 shows a region of a heat sink 1 that has both individual filaments 10 and loops 6 with respect to the carbon nanotubes 4. Alternatively, it is also possible to have a heat sink 1 that has only individual filaments 10 or only loops 6. The individual filaments 10 each have a kind of rod-shaped configuration. In the embodiment of the Figure 3The carbon nanotubes 4 originate from a fiber base 11, which is attached to the base body 2 or embedded therein (not shown). Preferably, the carbon nanotubes 4 form both the fiber base 11 and the individual filaments 10 or the loops 6. The fiber base 11 can preferably be formed in the form of intertwined or interwoven regions of the carbon nanotubes 4.

[0025] The Figure 4 shows a region of a heat sink 1, which also has a fiber base 11, which is preferably formed as a substantially sheet-like fabric. Just as in the embodiment of the Figure 3 The fiber base 11 is embedded in or attached to a base body 2 (not shown). The heat sink 1 of the Figure 4further comprises carbon nanostructure-based fibers 3, in particular carbon nanotubes 4 or graphene fibers, which in this exemplary embodiment form a volume structure 12, wherein the fibers are in contact with one another due to adhesion or support, so that in particular a volume structure 12 in the manner of cotton wool, felt, or a woven fabric is present. This volume structure 12 leads to a very large surface area of ​​the carbon nanotubes 4 and also to a stable mechanical structure. According to a special exemplary embodiment, it can be provided that the carbon nanostructure-based fibers 3 are compressed against one another at least in some regions in order to achieve an even more compact and thus stronger structure, which, however, leaves sufficient flow paths open for the cooling medium.

[0026] In the embodiment of the Figure 5 On the left side a structure is shown, as it is already shown on the left side of the Figure 3, i.e. a structure with individual filaments 10, which are preferably partially incorporated into the fiber base 11, but then lie with "free areas" in the flow path of the cooling medium, whereby the difference in Figure 5 to Figure 3 is that on the opposite side to the fiber base 11 there is another fiber base 13, which is formed by end regions of the carbon nanostructure-based fibers 3, so that the free fiber regions are supported at both ends and are therefore not deformed by the flow of the cooling medium. On the right side of the Figure 5 A corresponding example of a heat sink 1 is shown, as it appears from the left side of the Figure 5However, the difference between these two variants is that on the left side, the free fiber areas are particularly perpendicular to the flow of the cooling medium 5 and thus essentially at right angles to the two fiber bases 11 and 13 respectively; on the right side of the Figure 5 However, these free fiber areas run diagonally to the flow of the cooling medium, thus forming an angle other than 90° with the respective fiber base 11 or 13. This results in the right-hand side of the Figure 5 a longer free fiber length compared to the embodiment on the left, creating a larger surface area that lies in the flow of the cooling medium.

[0027] The Figure 6illustrates an embodiment of a region of a heat sink 1, in which a base body 2 and a counter body 8 are also present, although these two components are not shown, but rather only a grid-like support structure 14 and 15 is shown, wherein the support structures 14, 15 can preferably be formed from carbon nanostructure-based fibers 3, in particular carbon nanotubes 4. These two support structures 14, 15 are fastened to the base body 2 and / or counter body 8 or cast therein and accommodate end regions 7 and 9 of carbon nanostructure-based fibers 3, in particular carbon nanotubes 4, extending therebetween. The support structures 14 and 15 have a stabilizing effect. In particular, they improve the fastening or casting. The two support grids 14 and 15 can also be connected to one another. This is achieved by means of corresponding connections 16, of which Figure 6Only one example is shown. This keeps the two support structures 14 and 15 at a distance. The two support structures 14 and 15 can also be made of metal, i.e., metal grids.

[0028] Regarding all embodiments, it should be noted that often only one carbon nanostructure-based fiber 3 or only a few carbon nanostructure-based fibers 3 are shown. In the complete respective heat sink 1, a very large number of carbon nanostructure-based fibers 3 are naturally provided, particularly in a three-dimensional arrangement, to achieve a large surface area.

[0029] In the embodiment of the Figure 5 (both left and right) there is an ordered structure of the carbon nanostructure-based fibers 3, which in this case run essentially parallel to each other. In the embodiment of the Figure 4there is a completely different structure, namely a disordered structure.

[0030] Furthermore, in the various embodiments, it can be provided that at least some of the carbon nanostructure-based fibers 3 are provided with a mechanically stabilizing coating. This also results in the carbon nanostructure-based fibers 3 remaining relatively stable in the flow of the cooled medium and not bending excessively. For example, a coating made of copper or another metal can be provided.

[0031] In particular, in the embodiment of the Figure 4Instead of the volume structure 12 in the form of cotton wool, felt or a spun fabric, it can also be provided that a three-dimensional fabric is present, that is to say, the volume structure 12 is woven with the aid of carbon nanostructure-based fibers 3 and then embedded at least on one side in a base body 2 or fastened there, whereby alternatively this can also be done - as well as in Figure 4 shown - by means of a fiber base 11, which is preferably also created as a woven structure from carbon nanostructure-based fibers 3.

Claims

1. Heat sink (1) having a main body (2) and a plurality of carbon nanostructure-based fibres (CNB, 3), in particular carbon nanotubes (CNT, 4) or graphene fibres, at least some of which are secured to the main body (2) for heat transfer, wherein due to mutual adhesion or support the fibres (3, 4) form a volume structure (12), in particular in the form of a wadding, felt or a yarn, or wherein the fibres (3, 4) form loops (6) or a three-dimensional fabric, characterized by at least one support structure (14, 15), in particular made of metal and / or of preferably further carbon nanostructure-based fibres (CNB, 3), in particular carbon nanotubes (CNT, 4) or graphene fibres, which supports the fibres (3, 4), wherein the at least one support structure (14, 15) is grid-shaped and assists the securing to the main body (2) and / or counterbody (8), in particular is cast into the main body (2) and / or the counterbody (8).

2. Heat sink according to Claim 1, characterized in that the fibres (3, 4) at least in regions form an ordered structure and / or at least in regions form an unordered structure.

3. Heat sink according to any of the preceding claims, characterized by a counterbody (8) which is a distance away from the main body (2) and has at least some of the fibres (3, 4) secured to it.

4. Heat sink according to any of the preceding claims, characterized in that the securing to the main body (2) and / or to the counterbody (8) is in the form of soldering sites, adhesive bonding sites and / or casting sites.

5. Heat sink according to any of the preceding claims, characterized in that the loops (6) comprise end regions (7, 9) and in that at least some of the end regions (7, 9) of the loops (6) are secured to / in the main body (2) and / or the counterbody (8).

6. Heat sink according to any of the preceding claims, characterized in that the fibres (3, 4) are at least in regions compressed with one another.

7. Heat sink according to any of the preceding claims, characterized in that at least some of the fibres (3, 4) are provided with a mechanically stabilizing coating.

8. Heat sink according to any of the preceding claims, characterized in that the three-dimensional fabric is mechanically stabilized by the type of mesh of the fabric and / or the mesh size of the fabric.

9. Heat sink according to any one of the preceding claims, characterized in that at least some of the fibres (3, 4) extend from an especially sheetlike fibre basis (11, 13) formed by the fibres (3, 4) and / or further carbon nanostructure-based fibres (CNB, 3), in particular carbon nanotubes (CNT, 4) or graphene fibres.

10. Heat sink according to any of the preceding claims, characterized in that the fibre basis (11, 13) is secured to / in the main body (2) and / or counterbody (8).

11. Heat sink according to any of the preceding claims, characterized in that the fibre basis (11, 13) is in the form of a fabric.

12. Heat sink according to any of the preceding claims, characterized in that at least some of the fibres (3, 4) extend from the main body (2) to the counterbody (8) at an angle not equal to 90 degrees to achieve the greatest possible fibre length between these two bodies and / or at an angle of 90 degrees.