DE202022106979U1 - Energy conduction plate for a heat exchanger or for a fuel cell stack - Google Patents

Abstract

Energy conducting plate for a heat exchanger or for a fuel cell stack,
- with a first outer metal layer (4),
- with a second outer metal layer (6) and
- with a third middle metal layer (8),
- wherein the metal layers (4, 6, 8) are plated together,
- wherein the first metal layer (4) and the second metal layer (6) consist of a metal with increased rigidity, corrosion resistance and/or pressure resistance compared to the third metal layer (8),
- wherein the third metal layer (8) consists of a metal with an increased energy conductivity compared to the first metal layer (4) and compared to the second metal layer (6),
- wherein the thickness of the first metal layer (4) is greater than the thickness of the second metal layer (6),
- wherein the first metal layer (4) has an outwardly open deep structure (10) for receiving a fluid and
- wherein the volume of the thicker first metal layer (4) with the recessed sections of the deep structure (10) is substantially equal to the volume of the second layer (6).

Description

The invention relates to an energy conducting plate for a heat exchanger or for a fuel cell stack.

Heat exchangers of the type of interest here are in particular heat exchangers for electronic components that produce heat during use and must be cooled passively or actively. For this purpose, the heat exchanger can have an energy conduction plate that is connected to the component to be cooled on one side, with the opposite side being provided with a deep structure to form an enlarged cooling surface and, if necessary, to conduct a fluid to absorb thermal energy. The fluid used is usually water or a combination of water and glycol. Gases can also be used for cooling.

For this purpose, the side of the energy conduction plate with the deep structure is usually connected to another plate in order to form a laterally open structure of channels for conducting the fluid from the deep structure.

The energy conduction plate for heat exchangers is therefore intended for conducting thermal energy.

Bipolar plates and end plates, also known as current collectors or cover plates, are components for use in fuel cell stacks which, when layered, form important components of a fuel cell system. The fuel cell has a membrane electrode unit, whereby the electrical outputs of several membrane electrode units arranged in the stack are added together. A bipolar plate is arranged between two membrane electrode units of a fuel cell stack. The end plates mentioned are then arranged at the outer ends of the fuel cell stack and are connected on one side to the respective outer fuel cell.

The main task of the bipolar plate in a fuel cell stack is to physically and electrically connect the anode of one cell to the cathode of the neighboring cell. The bipolar plate is also responsible for guiding the reaction gases into the reaction zone. For this purpose, flow profiles are milled or pressed into the plates on both sides as depth profiles, through which hydrogen flows on one side and air on the other. A bipolar plate therefore consists of the two poles, hence the name bipolar, i.e. the hydrogen-carrying negatively charged anode plate and the positively charged cathode plate for the supply of the reaction air. The plates also regulate the removal of water vapor and the conduction of thermal and electrical energy. The end plates at the ends of the fuel cell stack perform the same tasks.

Bipolar plates and end plates are therefore not only responsible for the electrical connection of the fuel cells and the distribution of gases across the plate surface, but also for gas separation between adjacent cells, cooling and sealing to the outside.

The bipolar plate and the end plate can also be understood as the energy conducting plates mentioned at the beginning, the energy conducting plate being intended for conducting both thermal energy and electrical energy.

The previously described energy conducting plates for a heat exchanger or for a fuel cell stack are usually made of stainless steel to ensure sufficient rigidity, corrosion resistance and pressure resistance.

The stainless steel material can be connected to other components, for example in the case of a fuel cell stack with the other components of the stack. The deep structures of the energy conducting plate are impressed by forming such as deep drawing or created using chemical etching.

However, the use of stainless steel has the disadvantage of lower energy conductivity compared to other materials such as copper or aluminum, which in turn have lower stability properties than stainless steel.

Therefore, the present invention is based on the technical problem of further improving the energy conducting plate mentioned at the beginning.

The previously listed technical problem is solved according to the invention by an energy conduction plate for a heat exchanger or for a fuel cell stack with a first external metal layer, with a second external metal layer and with a third middle metal layer, the metal layers being plated together, the first metal layer and the second metal layer consists of a metal with an increased stiffness, corrosion resistance and / or pressure resistance compared to the third metal layer, wherein the third metal layer consists of a metal with an increased energy conductivity compared to the first metal layer and compared to the second metal layer, wherein the thickness of the first metal layer is greater than the thickness of the second metal layer, the first metal layer has an outwardly open deep structure for receiving a fluid and wherein the volume of the thicker first metal layer with the recessed sections of the deep structure is essentially the same size as the volume of the second layer.

The volume of the first metal layer is calculated from the volume of the existing material without the introduced deep structure. The free volume of the deep structure is therefore not added to the volume of the thicker first metal layer.

The plated composite of the three metal layers of the energy conducting plate according to the invention has a higher conductive portion of the third metal layer compared to the prior art described. The energy conductivity, i.e. the thermal conductivity and/or the electrical conductivity, of the third metal layer leads to an improved energy conductivity of the entire composite of the energy conducting plate.

The energy conducting plate is characterized by an asymmetrical distribution of the layer thicknesses. This asymmetry serves on the one hand to enable the first metal layer to be designed with a sufficiently voluminous deep structure and on the other hand to ensure a low thickness of the entire composite while simultaneously forming the more conductive middle metal layer through a lower thickness of the second metal layer.

However, since the metal layers have different thermal expansion coefficients, the asymmetrical distribution of the layer thicknesses can lead to a deformation of the energy conducting plate under varying thermal loads. This effect is solved according to the invention by the further measure of the essentially equal volumes of the first metal layer and the second metal layer. The equal volumes result in essentially equal thermal volume changes of the first metal layer and the second metal layer.

Essentially equal volumes and essentially equal volume changes mean that small deviations in the volumes are also included, which can be adequately compensated by the rigidity of the entire plated composite. In particular, the volume of the first layer and the volume of the second layer can differ from each other by less than 10%, in particular less than 5%. The deviations are preferably in a range of 2 to 10%.

The first metal layer and the second metal layer preferably consist of steel, stainless steel, 1.4404 or 1.4760, titanium or a titanium alloy, niobium, tantalum or aluminum (with or without anodization layer).

Especially when the energy conducting plate is used as a heat exchanger, the outer layer can consist of aluminum oxide, for example, since the outer layer represents a corrosion-resistant but conductive component in heat exchangers.

It is also preferred that the third metal layer consists of copper, a copper alloy, aluminum or an aluminum alloy.

For example, if the third metal layer is made of copper, the first metal layer and possibly the second metal layer can be made of aluminum.

A further preferred embodiment of the energy conducting plate is that the deep structure of the first metal layer represents a first deep structure, that the second metal layer has a second deep structure that is open to the outside for receiving a fluid and that the volume of the thicker first metal layer with the recessed sections of the first Deep structure is essentially the same size as the volume of the second layer with the excluded second deep structure. The energy conducting plate therefore also has a deep structure on the outside of the second metal layer. This is designed to be less extensive and leads to a smaller volume reduction than the first deep structure of the first metal layer.

Such an energy conducting plate is particularly suitable for use as part of a bipolar plate by connecting two identical energy conducting plates with their second metal layers, so that channels for a coolant are formed by the mutually aligned second deep structures, while the first deep structures of the respective first metal layers Form channels for the supply of hydrogen gas or air. The connection of two energy conducting plates at their second metal layers can be done by sintering, diffusion bonding, pressing, screwing or welding.

In a further preferred manner, the first deep structure and/or possibly the second deep structure are produced by means of an etching process. For this purpose, known etching techniques are used to create a to enable precise and burr-free formation of the deep structure.

The advantages of etching the deep structure are a greater number of degrees of freedom in terms of geometry. In addition to straight-line structures, curved or meandering depressions can also be created by etching. Wavy structures are also possible to increase the surface area.

In addition, the deep structures can be formed as tapering and widening structures. When flowing through the deep structures, the Venturi effect can cause turbulence in the medium flowing through and improve heat absorption. The turbulence creates smaller diffusion boundary layers and smaller flow resistances.

Furthermore, passages can be created through the energy conducting plate by etching, so that a three-dimensional passage through the energy conducting plate can connect the deep structures on both sides of the energy conducting plate. This reduces the inflow and outflow structures on both sides, which reduces the technical effort.

The deep structures can additionally or alternatively be designed three-dimensionally by electroforming or laser structuring.

The deep structures explained above are used to conduct fluids, which, depending on the application, can be liquids such as water or water/glycol or gases.

The technical problem shown above is also solved by a heat exchanger with a previously described energy conducting plate, wherein the second metal layer is suitable for being connected to a component to be cooled, in particular an electronic component to be cooled, and wherein the energy conducting plate conducts heat energy away from the component to be cooled .

The advantageous design of the energy conduction plate described above can therefore be used particularly in the field of electronics. In addition to the good stability properties, the improved thermal conductivity of the third metal layer can be exploited.

The technical problem outlined above is also solved by a fuel cell stack with two end plates, with at least two membrane electrode units each consisting of an anode, a membrane and a cathode, with at least one bipolar plate arranged between two membrane electrode units, wherein at least one of the end plates has an energy conducting plate as described above and/or wherein the at least one bipolar plate has an energy conducting plate as described above.

The advantageous design of the energy conduction plate described above can therefore be used particularly in the area of fuel cell stacks. In addition to the good stability properties, the improved thermal conductivity of the third metal layer can be exploited.

Advantageously, at least one bipolar plate can be composed of two energy conducting plates, which are connected to one another with their second metal layers, in particular by sintering, diffusion bonding or welding. This results in an improved, stable and better energy-conducting structure of the fuel cell stack.

For the purposes of this entire description and the claims, plating is understood to mean a connection through adhesive bonding with atomic diffusion, i.e. a bond between two bonding partners in which a transition layer is formed as a bonding zone through atomic diffusion of the materials of the bonding partners, over which a continuous adjustment of the material properties takes place. The adhesive bond with atomic diffusion is therefore created by the formation of the transition layer between the layers.

In the transition layer, the atoms of the bonding partners are gradually mixed; the formation of a bond occurs through exchange processes (diffusion) in the transition layer, also called the bonding zone. This transition layer reduces internal stresses. The extent of the transition zone depends on the bonding partners used, in particular the diffusion properties of the materials involved.

To characterize the adhesive bond with atomic diffusion, i.e. the bonding zone of the adhesive bond in the transition layer, and the properties, analyzes can be used using various methods. These methods include optical light microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), secondary ion mass spectrometry (SIMS) and microhardness analyses.

Such a composite is also referred to as a cladding composite. The two binding partners are preferably metallic materials and the plating composite represents a metallic connection of the two binding partners or plating partners. The bonding partners in the plating composite can be connected by means of the aforementioned plating. For this purpose, the plating can be carried out by cold roll plating or hot plating.

• 1 eine Energieleitplatte nach dem Plattieren von drei Metallschichten,
• 2 eine Energieleitplatte nach 1 mit einer Tiefenstruktur in der oberen Metallschicht,
• 3 die Energieleitplatte nach 2 mit einer weiteren Tiefenstruktur in der unteren Metallschicht,
• 4 eine Bipolarplatte für einen Brennstoffzellenstapel bestehend aus zwei Energieleitplatten nach 3 und
• 5 ein erstes Ausführungsbeispiel eines Brennstoffzellenstapels mit erfindungsgemäßen Energieleitplatten als Endplatten.

The invention is explained below using exemplary embodiments with reference to the drawing. Show in the drawing

• 1 an energy conducting plate after plating three metal layers,
• 2 an energy conducting plate 1 with a deep structure in the upper metal layer,
• 3 the energy conduction plate 2 with a further deep structure in the lower metal layer,
• 4 a bipolar plate for a fuel cell stack consisting of two energy conducting plates 3 and
• 5 a first exemplary embodiment of a fuel cell stack with energy conducting plates according to the invention as end plates.

In the following description of the various exemplary embodiments according to the invention, components and elements with the same function and the same mode of operation are given the same reference numbers, even if the components and elements in the various exemplary embodiments may have differences in their dimensions or shape.

1 shows an energy conducting plate 2 for a heat exchanger or for a fuel cell stack.

The energy conducting plate 2 has a first external metal layer 4, a second external metal layer 6 and a third middle metal layer 8. The metal layers 4 to 8 are plated together using cold roll plating, hot plating and other plating methods such as explosive plating.

The first metal layer 4 and the second metal layer 6 also consist of a metal with increased rigidity, corrosion resistance and/or pressure resistance compared to the third metal layer 8. In contrast, the third metal layer 8 consists of a metal with an increased energy conductivity compared to the first metal layer 4 and compared to the second metal layer 6.

Furthermore, the thickness of the first metal layer 4 is greater than the thickness of the second metal layer 6.

The energy conducting plate 2 thus points 1 an asymmetrical structure based on the layer thickness. When heating and cooling, changes in shape and bending can occur due to different expansion behavior. In order to compensate for this expected effect, the energy conducting plate 2 is further designed, as 2 shows schematically.

The first metal layer 4 has a deep structure 10 that is open to the outside for receiving a fluid. The deep structure 10 has a plurality of upwardly open depressions 12 that are designed to conduct a fluid and are closed from above by another component in one application.

In order to compensate for thermal changes in shape due to a bimetallic effect, the volume of the thicker first metal layer 4 with the recessed sections of the depressions 12 of the deep structure 10 is essentially the same size as the volume of the second layer 6. Deviations in the volumes can be in the range of a maximum of 10% or A maximum of 5% occurs without these deviations in volumes from the same size having a technical effect of deformation of the energy conducting plate 2.

The first metal layer 4 and the second metal layer 6 consist of steel, stainless steel, titanium or a titanium alloy, preferably the two metal layers 4 and 6 consist of the same metal. Other metals have been mentioned above.

In contrast, the third metal layer 8 consists of copper, a copper alloy, aluminum or an aluminum alloy.

The two metal layers 4 and 6 thus have increased rigidity (measured as modulus of elasticity), corrosion resistance and/or pressure resistance compared to the third metal layer.

3 shows schematically a further development of the energy conducting plate according to 2 . The already in 2 The depth structure 10 of the first metal layer 4 shown represents a first depth structure. Furthermore, the second metal layer 6 has a second depth structure 14 that is also open to the outside for receiving a fluid. This depth structure 14 is smaller in volume than the first depth structure 10 and is taken into account in the thickness ratios and the requirement for equal volumes. Thus the volume of the thicker first metal layer 4 with the recessed sections of the first deep structure 10 can be substantially equal to the volume of the second layer 6 with the recessed second deep structure 14.

The previously described first deep structure 10 and second deep structure 14 are preferably produced by means of an etching process after plating the metal layers 4, 6 and 8.

In principle, the deep structures 10 and 14 can also be produced by deep drawing like most bipolar plates and heat exchanger plates. Furthermore, electrochemical milling (ECM process) is also available for bipolar plates.

4 shows schematically a bipolar plate 20 for a fuel cell stack, which in 5 The bipolar plate 20 also consists of two energy conducting plates 2 according to 3 , which are connected to each other with their respective second metal layers 6. The connection between the second metal layers 6 is made by means of sintering, diffusion bonding or welding.

The connection between the two energy conducting plates 2 creates a channel 22 from the deep structures 14, which can be used in the fuel cell stack 20 to conduct a cooling liquid.

5 shows a first exemplary embodiment of a fuel cell stack 100 with two end plates 102 and 104, with two membrane-electrode units 106, each having an anode 108, a membrane 110 and a cathode 112. A bipolar plate 114 is arranged between the two membrane electrode units 106.

The functionality of such a fuel cell stack 100 is known. By supplying hydrogen as a reaction gas on the side of the anode 108 and by supplying oxygen, usually obtained from air, as a reaction gas on the side of the cathode 112, the membrane-electrode units 106 result from the exchange of hydrogen ions through the membrane 110 an electrical voltage between the electrodes 108 and 112. The stack formation then creates a series connection of the individual layers and thus a sufficiently high voltage and performance for electrical applications.

The in 5 The structure shown has two end plates 102 and 104, which consist of an energy conducting plate 2 according to 2 consist. Accordingly, the end plates 102 and 104 each have metal layers 4, 6 and 8 and a deep structure 10, the depressions of which serve to conduct one of the gases.

The bipolar plate 114 of the fuel cell stack 100 after 5 is still in the same way as in 4 shown and consists of two energy conducting plates 2 connected to each other. The only difference is 4 is that the depressions 12 of the deep structures 10 of the two energy conducting plates 2 are not aligned parallel, but at right angles to one another.

Furthermore, the optional use of a bipolar plate 20 according to 4 in the fuel cell stack 100 (not shown), so that an additional channel 22 for conducting a cooling liquid is provided.

Claims (9)

Energy conduction plate for a heat exchanger or for a fuel cell stack, - with a first external metal layer (4), - with a second external metal layer (6) and - with a third middle metal layer (8), - wherein the metal layers (4, 6, 8) are plated together, - wherein the first metal layer (4) and the second metal layer (6) consist of a metal with increased rigidity, corrosion resistance and/or pressure resistance compared to the third metal layer (8), - wherein the third metal layer (8) consists of a metal with an increased energy conductivity compared to the first metal layer (4) and compared to the second metal layer (6), - wherein the thickness of the first metal layer (4) is greater than the thickness of the second metal layer (6), - wherein the first metal layer (4) has a deep structure (10) that is open to the outside for receiving a fluid and - Wherein the volume of the thicker first metal layer (4) with the recessed sections of the deep structure (10) is essentially the same size as the volume of the second layer (6). Energy conduction plate according to Claim 1 , characterized in that the volume of the first layer (4) and the volume of the second layer (6) differ from each other by less than 10%, in particular less than 5%. Energy conduction plate Claim 1 or 2 , characterized in that the first metal layer (4) and the second metal layer (6) consist of steel, stainless steel, 1.4404, 1.4760, titanium or a titanium alloy, niobium, tantalum or aluminum. Energy conducting plate according to one of the Claims 1 until 3 , characterized in that the third metal layer (8) consists of copper, a copper alloy, aluminium or an aluminium alloy. Energy conduction plate according to one of the Claims 1 until 4 , characterized in - that the deep structure (10) of the first metal layer (4) represents a first deep structure, - that the second metal layer (6) has an outwardly open second deep structure (14) for receiving a fluid and - that the volume the thicker first metal layer (4) with the recessed sections of the first deep structure (10) is essentially the same size as the volume of the second layer (6) with the recessed second deep structure (14). Energy conduction plate according to one of the Claims 1 until 5 , characterized in that the first deep structure (10) and/or possibly the second deep structure (14) are produced by means of an etching process. Heat exchanger - with an energy conducting plate (2) according to one of the Claims 1 until 6 , - wherein the second metal layer (6) is suitable for being connected to a component to be cooled, in particular an electronic component to be cooled, and - wherein the energy conducting plate conducts thermal energy away from the component to be cooled. Fuel cell stack - with two end plates (102, 104), - with at least two membrane-electrode units (106), each consisting of an anode (108), a membrane (110) and a cathode (112), - with at least one between two Membrane-electrode units (106) arranged bipolar plate (114), - at least one of the end plates (102, 104) being an energy conducting plate (2) according to one of the Claims 1 until 6 and/or - wherein the at least one bipolar plate (114) has an energy conducting plate (2) according to one of Claims 1 until 6 having. Fuel cell stack Claim 8 , characterized in that at least one bipolar plate (114) is composed of two energy conducting plates (2).

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