ENERGY CONTROL PLATE FOR A HEAT EXCHANGER OR FOR A FUEL CELL STACK

Description

[0001] The invention relates to an energy conduction plate for a heat exchanger or for a fuel cell stack. US 2022 / 246950 A1, for example, discloses an energy conduction plate with multiple layers.

[0002] Heat exchangers of the type of heat exchanger of interest here are primarily used for electronic components that generate heat during operation and require passive or active cooling. For this purpose, the heat exchanger may have an energy transfer plate that is connected to the component to be cooled on one side, while the opposite side has a recessed structure to create a larger cooling surface and, if necessary, to conduct a fluid for absorbing heat energy. The fluid used is typically water or a combination of water and glycol. Gases can also be used for cooling.

[0003] 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 guiding the fluid from the deep structure.

[0004] The energy conduction plate for heat exchangers is therefore designed to conduct thermal energy.

[0005] Bipolar plates and end plates, also known as current collectors or cover plates, are components used in fuel cell stacks, forming essential parts of a fuel cell system when stacked. The fuel cell has a membrane electrode assembly (MEA), and the electrical output of several MEA arranged in the stack is additive. A bipolar plate is positioned between each pair of MEA in a fuel cell stack. The end plates are located at the outer ends of the fuel cell stack and are connected on one side to the outermost fuel cell.

[0006] In a fuel cell stack, the primary function of the bipolar plate is to connect the anode of one cell to the cathode of the adjacent cell, creating a physical and electrical conductive connection. Additionally, the bipolar plate directs the reaction gases into the reaction zone. To achieve this, flow profiles are milled or pressed into both sides of the plates, allowing hydrogen to flow through one side and air through the other. A bipolar plate thus consists of two poles—hence the name "bipolar"—namely, the negatively charged anode plate carrying hydrogen and the positively charged cathode plate for supplying the reaction gas. 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 functions.

[0007] Thus, bipolar plates and end plates are responsible not only 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.

[0008] The bipolar plate and the end plate can also be understood as the aforementioned energy conducting plates, with the energy conducting plate being intended for conducting both thermal energy and electrical energy.

[0009] The previously described energy conduction 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.

[0010] The stainless steel material can be bonded to other components, for example, in a fuel cell stack, to the other components of the stack. The deep structures of the energy conductor plate are embossed by forming processes such as deep drawing or created by chemical etching.

[0011] 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.

[0012] Therefore, the present invention is based on the technical problem of further improving the aforementioned energy conducting plate.

[0013] The aforementioned technical problem is solved according to the invention by an energy conduction plate for a heat exchanger or for a fuel cell stack, comprising a first outer metal layer, a second outer metal layer, and a third middle metal layer, wherein the metal layers are plated together, wherein the first metal layer and the second metal layer consist of a metal with increased stiffness, corrosion resistance, and / or pressure resistance compared to the third metal layer, wherein the third metal layer consists of a metal with increased energy conductivity compared to both the first and second metal layers, and wherein the thickness of the first metal layer is greater than the thickness of the second metal layer.wherein 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 excluded sections of the deep structure is essentially the same as the volume of the second layer.

[0014] 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 included in the volume of the thicker first metal layer.

[0015] The clad composite of the three metal layers of the energy conducting plate according to the invention exhibits a higher conductivity of the third metal layer compared to the prior art described. The energy conductivity, i.e., the thermal conductivity and / or electrical conductivity, of the third metal layer leads to an improved energy conductivity of the entire composite of the energy conducting plate.

[0016] The energy conductor plate is characterized by an asymmetrical distribution of layer thicknesses. This asymmetry serves, on the one hand, to allow the first metal layer to be designed with a sufficiently voluminous depth structure, and on the other hand, to achieve a low overall thickness of the composite while simultaneously forming the more conductive middle metal layer through a reduced thickness of the second metal layer.

[0017] However, since the metal layers have different coefficients of thermal expansion, the asymmetrical distribution of layer thicknesses can lead to deformation of the energy conducting plate under varying thermal loads. According to the invention, this effect is solved by ensuring that the first and second metal layers have essentially the same volume. This equal volume results in essentially equal thermal volume changes in the first and second metal layers.

[0018] Essentially equal volumes and essentially equal volume changes mean that even small volume deviations are included, which can be adequately compensated for by the stiffness of the entire clad 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%, and preferably by less than 5%. Preferably, the deviations are in the range of 2 to 10%.

[0019] Preferably, the first metal layer and the second metal layer consist of steel, stainless steel, 1.4404 or 1.4760, titanium or a titanium alloy, niobium, tantalum or aluminium (with or without an anodized layer).

[0020] Particularly when using the energy conducting plate as a heat exchanger, the outer layer can consist of, for example, aluminum oxide, since the outer layer represents a corrosion-resistant but conductive component in heat exchangers.

[0021] It is also preferred that the third metal layer consists of copper, a copper alloy, aluminum, or an aluminum alloy.

[0022] 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.

[0023] Another preferred embodiment of the energy carrier plate consists in the first metal layer having a first deep structure, the second metal layer having an outwardly open second deep structure for fluid absorption, and the volume of the thicker first metal layer, including the sections of the first deep structure, being essentially the same as the volume of the second layer including the second deep structure. Thus, the energy carrier plate also has a deep structure on the outside of the second metal layer. This structure is less extensive and results in a smaller volume reduction than the first deep structure of the first metal layer.

[0024] Such an energy carrier plate is particularly suitable for use as part of a bipolar plate, where two identical energy carrier plates are joined together at their second metal layers. The aligned second layer structures then form channels for a coolant, while the first layer structures of the respective first metal layers form channels for supplying hydrogen gas or air. Joining two energy carrier plates at their second metal layers can be achieved by sintering, diffusion bonding, pressing, screwing, or welding.

[0025] In a further preferred configuration, the first deep structure and / or, if applicable, the second deep structure are produced by means of an etching process. Established etching techniques are used to ensure precise and burr-free formation of the deep structure.

[0026] The advantages of etching deep structures lie in the greater number of degrees of freedom in the geometry. Etching allows for the creation of not only straight structures but also curved or meandering depressions. Wavy structures for increasing surface area are also possible.

[0027] Furthermore, the deep structures can be designed as tapered and widening structures. Thus, when fluid flows through these deep structures, the Venturi effect can create turbulence in the flowing medium, resulting in improved heat absorption. This is because the turbulence creates smaller diffusion boundary layers and lower flow resistance.

[0028] Furthermore, etching can also create passages through the energy carrier plate, allowing three-dimensional connections between the deep structures on both sides of the plate. This reduces the number of inflow and outflow structures on both sides, thereby decreasing the technical complexity. The deep structures can also be designed three-dimensionally using electroforming or laser structuring, either additionally or alternatively.

[0029] The previously explained deep structures serve to guide fluids, which, depending on the application, can be liquids such as water or water / glycol, or gases.

[0030] The technical problem outlined above is also solved by a heat exchanger with a previously described energy conduction 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 conduction plate conducts heat energy away from the component to be cooled.

[0031] Therefore, the advantageous design of the previously described energy conductor plate can be used, particularly in the field of electronics. In addition to its good stability properties, the improved thermal conductivity of the third metal layer can be utilized.

[0032] 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 a previously described energy conducting plate and / or wherein the at least one bipolar plate has a previously described energy conducting plate.

[0033] Therefore, the advantageous design of the previously described energy conduction plate can be used, particularly in the area of ​​fuel cell stacks. In addition to its good stability properties, the improved thermal conductivity of the third metal layer can be utilized.

[0034] Advantageously, at least one bipolar plate can be composed of two energy-conducting plates, which are joined together, in particular by sintering, diffusion bonding, or welding, with their second metal layers. This results in an improved, stable, and better energy-conducting structure of the fuel cell stack.

[0035] Within the context of this entire description and the claims, cladding is understood to mean a bond formed by adhesion with atomic diffusion, i.e., a bond between two bonding partners in which a transition layer forms as a bonding zone through atomic diffusion of the materials of the bonding partners, across which a continuous adaptation of the material properties takes place. The adhesion bond with atomic diffusion thus arises from the formation of the transition layer between the layers.

[0036] In the transition layer, the atoms of the bonding partners are gradually mixed. The formation of a bond occurs through diffusion processes within the transition layer, also known as the bonding zone. This transition layer reduces internal stresses. The extent of the transition zone depends on the specific bonding partners used, particularly the diffusion properties of the materials involved.

[0037] Various methods can be used to characterize the adhesion bond with atomic diffusion, i.e., the bonding zone of the adhesion bond in the transition layer, and its properties. 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 analyses of microhardness profiles.

[0038] Such a composite is also referred to as a cladding composite. Preferably, the two bonding partners are metallic materials, and the cladding composite represents a metallic connection between the two bonding or cladding partners. The bonding partners in the cladding composite can be joined by the aforementioned cladding process. This cladding can be carried out by cold roll cladding or hot cladding.

[0039] The invention will now be explained using exemplary embodiments with reference to the drawing. The drawing shows... Fig. 1: An energy conducting plate after plating with three metal layers; Fig. 2: An energy conducting plate after Fig. 1 with a deep structure in the upper metal layer, Fig. 3 the energy conducting plate according to Fig. 2 with a further deep structure in the lower metal layer, Fig. 4 a bipolar plate for a fuel cell stack consisting of two energy conducting plates according to Fig. 3 and Fig. 5 a first embodiment of a fuel cell stack with energy conducting plates according to the invention as end plates.

[0040] In In the following description of the various embodiments according to the invention, components and elements with the same function and mode of operation are provided with the same reference numerals, even if the components and elements may differ in their dimensions or shape in the various embodiments.

[0041] Fig. 1 shows an energy conduction plate 2 for a heat exchanger or for a fuel cell stack.

[0042] The energy conductor plate 2 has a first outer metal layer 4, a second outer metal layer 6, and a third middle metal layer 8. The metal layers 4 to 8 are plated together, whereby cold rolling plating, hot plating, or other plating processes such as explosive plating may have been used.

[0043] The first metal layer 4 and the second metal layer 6 consist of a metal with increased stiffness, 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 increased energy conductivity compared to the first metal layer 4 and the second metal layer 6.

[0044] Furthermore, the thickness of the first metal layer 4 is greater than the thickness of the second metal layer 6.

[0045] Thus, the energy conducting plate 2 demonstrates Fig. 1 The structure is asymmetrical with respect to the layer thicknesses. Therefore, changes in shape and deflection can occur during heating and cooling due to differing expansion behavior. To compensate for this expected effect, the energy conducting plate 2 is further designed as follows: Fig. 2 schematically shown.

[0046] The first metal layer 4 has an outwardly open deep structure 10 for receiving a fluid. The deep structure 10 has a plurality of upwardly open depressions 12, which are designed to guide a fluid and are closed from above by another component in one application.

[0047] To compensate for thermal deformations due to a bimetallic effect, the volume of the thicker first metal layer 4, including the excluded sections of the recesses 12 of the depth structure 10, is essentially the same as the volume of the second layer 6. Volume deviations of up to 10% or up to 5% are permissible without these deviations of equal magnitude having any technical effect of deformation on the energy conductor plate 2.

[0048] The first metal layer 4 and the second metal layer 6 consist of steel, stainless steel, titanium, or a titanium alloy; preferably, both metal layers 4 and 6 consist of the same metal. Other metals have been mentioned above.

[0049] In contrast, the third metal layer 8 consists of copper, a copper alloy, aluminum or an aluminum alloy.

[0050] Thus, the two metal layers 4 and 6 exhibit increased stiffness (measured as modulus of elasticity), corrosion resistance and / or pressure resistance compared to the third metal layer.

[0051] Fig. 3 schematically shows a further development of the energy conducting plate according to Fig. 2 . The already in Fig. 2 The depth structure 10 shown in the first metal layer 4 represents a first depth structure. Furthermore, the second metal layer 6 also has a second depth structure 14, 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, including the excluded sections of the first depth structure 10, can be essentially the same as the volume of the second layer 6, including the excluded second depth structure 14.

[0052] The first deep structure 10 and second deep structure 14 described above are preferably produced by means of an etching process after the plating of the metal layers 4, 6 and 8.

[0053] 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) is another suitable method for bipolar plates.

[0054] Fig. 4 schematically shows a bipolar plate 20 for a fuel cell stack, which is in Fig. 5 The bipolar plate 20 also consists of two energy conducting plates 2 according to Fig. 3 , which are connected to each other by their respective second metal layers 6. The connection between the second metal layers 6 is achieved by means of sintering, diffusion bonding or welding.

[0055] 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 for guiding a cooling fluid.

[0056] Fig. 5 Figure 1 shows a first embodiment of a fuel cell stack 100 with two end plates 102 and 104, with two membrane electrode units 106, each comprising an anode 108, a membrane 110 and a cathode 112. A bipolar plate 114 is arranged between the two membrane electrode units 106.

[0057] The operating principle of such a fuel cell stack 100 is known. By supplying hydrogen as a reaction gas to the side of the anode 108 and by supplying oxygen, usually obtained from air, as a reaction gas to the side of the cathode 112 of the membrane electrode assemblies 106, an electrical voltage is generated between the electrodes 108 and 112 via the exchange of hydrogen ions through the membrane 110. The stacking process then creates a series connection of the individual layers, resulting in a voltage and power output sufficiently high for electrical applications.

[0058] The in Fig. 5 The illustrated structure has two end plates 102 and 104, which consist of an energy conducting plate 2 according to Fig. 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.

[0059] The bipolar plate 114 of the fuel cell stack 100 after Fig. 5 is still in the same way as in Fig. 4 depicted as formed and consists of two interconnected energy conduction plates 2. The only difference to Fig. 4 The fact is that the recesses 12 of the deep structures 10 of the two energy conducting plates 2 are not parallel, but aligned at right angles to each other.

[0060] Furthermore, the optional use of a bipolar plate 20 is possible. Fig. 4 in the fuel cell stack 100 possible (not shown), so that an additional channel 22 exists for guiding a coolant.

Claims

1. Energy conduction plate (2) 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 clad together, - wherein the first metal layer (4) and the second metal layer (6) consist of a metal with increased stiffness, corrosion resistance and / or pressure resistance compared to the third metal layer (8), - wherein the third metal layer (8) consists of a metal with increased energy conductivity compared to the first metal layer (4) and 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 depth structure (10) for receiving a fluid, and - wherein the volume of the thicker first metal layer (4) with the recessed sections of the depth structure (10) is substantially equal to the volume of the second layer (6).

2. Energy conduction plate according to claim 1, characterised in that the volume of the first layer (4) and the volume of the second layer (6) differ by less than 10%, in particular less than 5%.

3. Energy conduction plate according to claim 1 or 2, characterised 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 aluminium.

4. Energy conduction plate according to one of claims 1 to 3, characterised in that the third metal layer (8) consists of copper, a copper alloy, aluminium or an aluminium alloy.

5. Energy conduction plate according to one of claims 1 to 4, characterised in - that the depth structure (10) of the first metal layer (4) represents a first depth structure, - that the second metal layer (6) has a second outwardly open depth structure (14) for receiving a fluid, and - that the volume of the thicker first metal layer (4) with the recessed sections of the first depth structure (10) is essentially the same as the volume of the second layer (6) with the recessed second depth structure (14).

6. Energy conduction plate according to one of claims 1 to 5, characterised in that the first depth structure (10) and / or, if applicable, the second depth structure (14) are produced by means of an etching process.

7. Heat exchanger - with an energy conduction plate (2) according to one of claims 1 to 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 conduction plate conducts heat energy away from the component to be cooled.

8. 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 bipolar plate (114) arranged between two membrane electrode units (106), - wherein at least one of the end plates (102, 104) has an energy conduction plate (2) according to one of claims 1 to 6 and / or - wherein the at least one bipolar plate (114) comprises an energy conduction plate (2) according to one of claims 1 to 6.

9. Fuel cell stack according to claim 8, characterised in that at least one bipolar plate (114) is composed of two energy conduction plates (2).