Bipolar plate including surface-treated flow channel

Abstract

To provide a bipolar plate including surface-treated flow channels.SOLUTION: There are presented a bipolar plate (10) for a fuel cell having a two-phase cooling system and a fuel cell system (100). The bipolar plate (10) includes a coolant inlet (12), a coolant outlet (14), and a plurality of coolant channels (16). The coolant inlet (12) is fluidically connected to the coolant outlet (14) via the coolant channels (16). At least one inner surface of the coolant inlet (12), the coolant outlet (14) and at least one of the coolant channels (16) has surface treatment to influence a flow regime of a cooling fluid along the at least one inner surface and / or a phase transition of the cooling fluid.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates generally to the aeronautical technical field. In particular, the present disclosure relates to a bipolar plate including surface-treated flow channels and a fuel cell system including such a bipolar plate. [Background technology]

[0002] Fuel cells are one possible solution for emission-free propulsion, for example, in aircraft. Polymer electrolyte membrane fuel cell stacks (PEMFC) generate power and electricity through the electrochemical reaction of hydrogen and oxygen producing water. This reaction is accompanied by the generation of heat, which must be dissipated. In commercial fuel cell stacks, this is achieved by liquid cooling. A possible alternative that would offer significant weight savings at the system level is to replace the liquid cooling by a two-phase cooling circuit. A two-phase cooling circuit uses the latent heat of vaporization to dissipate a large amount of heat from the fuel cell. Furthermore, the performance of the thermal management system is improved due to the higher heat transfer coefficient compared to single-phase cooling. Changing the flow regime in the fuel cell stack from liquid to two-phase cooling requires a specific thermal design of the flow fields. Summary of the Invention [Problem to be solved by the invention]

[0003] The objective of the present invention can be seen as improving the hydrodynamic design of flow fields. [Means for solving the problem]

[0004] This object is achieved by the subject matter of the independent claims. Further embodiments will become apparent from the dependent claims and the following description.

[0005] According to one embodiment, a bipolar plate for a fuel cell has a two-phase cooling system having the following features: a coolant inlet, a coolant outlet, and a plurality of coolant channels. The coolant inlet is in fluid communication with the coolant outlet via the plurality of coolant channels. Further, at least one inner surface of the coolant inlet, the coolant outlet, and at least one of the plurality of coolant channels has a surface treatment to affect a flow regime of the cooling fluid and / or a phase transition of the cooling fluid along the at least one inner surface.

[0006] In the context of the present invention, a fuel cell system including a bipolar plate is a technological unit consisting of several components and used to convert chemical energy into electrical energy by electrochemical reactions. A fuel cell system generally includes one or more fuel cells, which function as electrochemical cells and are the main components of the system. Furthermore, the system includes further components such as a fuel supply, an oxidant supply, an electrolyte, catalyzed electrodes, electrical connections, etc.

[0007] Fuel cell systems generate electrical power using a chemical reaction of a fuel and an oxidant (usually hydrogen and oxygen). The chemical reaction produces water as a reaction product in addition to thermal and electrical energy, making the fuel cell system an environmentally friendly source of energy. The generated electrical energy can then be used to power an electrical device or vehicle or to generate electrical power for a variety of applications.

[0008] In the context of the present invention, a two-phase cooling system is a cooling solution intended to efficiently dissipate large amounts of heat by utilizing a phase transition from liquid to vapor, which is often used in situations where traditional single-phase cooling systems reach their limits and are unable to provide sufficient heat dissipation or where a particularly lightweight, particularly weight-optimized, cooling system would be beneficial.

[0009] Two-phase cooling systems use a refrigerant that can exist in both liquid and gas forms at the appropriate temperature and pressure. The refrigerant absorbs heat from the source to be cooled and evaporates, thereby transitioning from a liquid state to a gas state. The vapor produced absorbs large amounts of heat.

[0010] A two-phase cooling system typically consists of an evaporator where the refrigerant absorbs heat and vaporizes, and a condenser where the vapor re-condenses and releases heat. The condensate is then returned to the evaporator to continue the cooling circuit.

[0011] In the context of the present invention, a coolant inlet is an opening or port in a cooling system through which a cooling medium, in this case a coolant, is introduced into the system. The coolant inlet allows the cooling fluid to flow in a controlled manner to the relevant area or component that must be cooled.

[0012] In the context of the present invention, a coolant outlet is an opening or port in a cooling system through which a cooling medium, in this case a coolant, leaves the system. The coolant outlet allows the controlled exit of heated cooling fluid from the relevant area or component in order to cool them and ensure heat exchange.

[0013] In the context of the present invention, multiple coolant channels are multiple channels or passages within a component or structure through which a coolant flows to dissipate heat. The coolant channels serve to efficiently distribute the coolant to the area or component to be cooled and allow for heat exchange. Multiple cooling channels create a relatively large surface area for the heat transfer process, resulting in effective cooling.

[0014] Surface treatment of the inner surface of the coolant inlet, coolant outlet, coolant channel or combination thereof refers to the specific modification or processing of the surface in contact with the coolant. Said treatment may include various methods and techniques aimed at influencing the flow regime of the coolant or improving the phase transition of the coolant.

[0015] According to one embodiment, at least part of the surface treatment comprises the introduction of macrostructures, such as grooves, meshes or sintering, on at least one inner surface.

[0016] An advantage of such an embodiment is that the macrostructure of the inner surface of the bipolar plate can increase the surface area and improve the flow regime of the cooling fluid. The grooves, mesh or sintering create an enlarged contact surface between the cooling fluid and the bipolar plate, thereby ensuring efficient heat transfer. This results in improved cooling performance and reduced risk of hot spots in the fuel cell. Furthermore, the specific flow regime provides a uniform distribution of the cooling fluid over the entire inner surface of the bipolar plate, resulting in improved cooling and increased performance of the fuel cell.

[0017] According to a further embodiment, at least a portion of the surface treatment comprises the introduction of porous microparticles and / or nanoparticles. These porous particles may be selected from materials such as metals, ceramics, carbon, plastics or combinations thereof.

[0018] The advantage of this embodiment is that the porous micro- and / or nanoparticles provide increased surface area and improved heat transfer efficiency. The introduction of these porous particles into the surface structure of the bipolar plate significantly increases the contact area between the cooling fluid and the plate. Furthermore, the porous particles allow for a more uniform distribution of the coolant through capillary transport. This allows for more effective absorption and evacuation of thermal energy, resulting in improved cooling performance and reduced thermal stress on the fuel cell.

[0019] Additionally, the porous micro- and / or nanoparticles also help filter or trap impurities or contaminants in the cooling fluid, which helps maintain the operational performance and lifespan of the fuel cell by removing potentially damaging particles from the cooling system.

[0020] The choice of material for the porous particles, such as metal, ceramic, carbon or plastic, further allows adaptation to specific requirements regarding thermal stability, corrosion resistance and mechanical strength, allowing the use of bipolar plates containing the porous particles in a wide variety of environments and operating conditions without affecting performance.

[0021] According to a further embodiment, at least part of the surface treatment comprises the introduction of hydrophobic and / or hydrophilic layers, which may be selected from metals, triels, pnictogens, chalcogens, halogens or combinations thereof.

[0022] An advantage of this embodiment is that the hydrophobic and / or hydrophilic layers allow for control of the wetting characteristics of the bipolar plate. The introduction of these layers on the inner surfaces of the coolant inlets, coolant outlets and coolant channels allows for precise control of the flow and distribution of the cooling fluid.

[0023] The use of a hydrophobic layer makes the bipolar plates water repellent, which prevents water or other liquid components of the cooling fluid from accumulating on the surfaces of the plates and causing undesirable flow blockages or erosion. The hydrophobic layer may also contribute to uniform and efficient flow of coolant through the coolant channels by reducing wettability.

[0024] On the other hand, the hydrophilic layer improves the wetting of the bipolar plate by the coolant, which may result in better distribution of the fluid along the inner surface, improving heat transfer efficiency. The hydrophilic layer may also help reduce the formation of air bubbles in the cooling fluid, which further improves cooling performance.

[0025] The choice of materials for the hydrophobic and / or hydrophilic layers from metals, triels, pnictogens, chalcogens, halogens, or combinations thereof allows adaptation to the specific requirements of the fuel cell and cooling system. Depending on the operating conditions and type of cooling fluid, the layers can be selected to ensure optimal performance and stability.

[0026] Ideally, the coating also improves electrical conductivity between the subplates of the bipolar plate.

[0027] According to one embodiment, the hydrophobic and / or hydrophilic layers are designed to reduce overheating. Furthermore, the hydrophobic and / or hydrophilic layers or the porous layers may be designed to allow better distribution of the refrigerant.

[0028] According to a further embodiment, a hydrophobic layer is provided in the region of the coolant inlet, while porous micro- and / or nano-particles are used in the region of the multiple coolant channels.

[0029] The advantage of this embodiment is that the specific application of the hydrophobic layer in the coolant inlet region and the porous micro- and / or nano-particles in the coolant channel region provides different effects, each of which can be highly beneficial.

[0030] The use of a hydrophobic layer in the coolant inlet region causes the cooling fluid to be repelled by the surface of the bipolar plate. This prevents the fluid from accumulating at the inlet site and impeding the flow. The hydrophobic layer provides for rapid and uniform flow of the coolant across the entire surface of the bipolar plate, thereby ensuring efficient heat exchange.

[0031] Porous micro- and / or nano-particles are used in the region of the cooling channels. These particles serve to increase the surface area of ​​the coolant channels and improve wettability. This allows for better distribution of the cooling fluid along the channels, resulting in more efficient cooling of the bipolar plates. The porous particles can also help promote turbulence in the cooling fluid and eliminate air bubbles, which improves the performance and reliability of the cooling system.

[0032] Therefore, the specific use of a hydrophobic layer in the coolant inlet region and porous particles in the coolant channels provides an optimal combination of benefits, resulting in improved heat dissipation, more efficient cooling and improved overall performance of the fuel cell.

[0033] According to further embodiments, the coolant in the bipolar plates may include methanol and / or ethanol.

[0034] One advantage is that methanol and ethanol as cooling fluids have high thermal conductivity, which allows for efficient dissipation of heat from the bipolar plates, resulting in better cooling and lower operating temperatures. Lower operating temperatures can improve the performance and service life of the fuel cell.

[0035] Another advantage of methanol and ethanol is their excellent fluidity and low viscosity. These properties allow for smooth flow of the cooling fluid through the refrigerant channels of the bipolar plates. Efficient flow ensures uniform distribution of the cooling fluid along the surfaces of the bipolar plates and effective heat dissipation.

[0036] According to further embodiments, the coolant in the bipolar plates may contain dissolved inert gas, such as nitrogen, which for example results in the creation of boiling nuclei within the pores of the porous micro- and / or nanoparticles, thereby reducing superheating.

[0037] According to another aspect, a fuel cell system includes at least one fuel cell, a two-phase cooling system, and a bipolar plate configured such that at least one inner surface of the coolant inlet, the coolant outlet, and at least one of the plurality of coolant channels has a surface treatment to affect a flow regime of a cooling fluid and / or a phase transition of the cooling fluid along the at least one inner surface.

[0038] The use of bipolar plates having surface treatments along the inner surfaces of the coolant inlets, coolant outlets, and coolant channels affects both the flow regime of the cooling fluid and the phase transitions of the fluid.

[0039] One advantage is the enhanced heat transfer between the bipolar plates and the cooling fluid. The optimized flow of the cooling fluid along the inner surface allows efficient heat removal, resulting in effective cooling of the fuel cell. This stabilizes the operating temperature of the fuel cell and optimizes the performance of the fuel cell.

[0040] Furthermore, specific influences on the flow regime and phase transitions help to achieve uniform distribution of the cooling fluid within the bipolar plate, which prevents the creation of hot spots, i.e. areas of elevated temperature, and ensures homogeneous cooling across the entire surface of the fuel cell, which ensures uniform operation of the fuel cell and contributes to improved performance and extended service life.

[0041] Furthermore, the generation of air bubbles due to the surface treatment of the inner surface prevents the refrigerant from overheating.

[0042] According to another aspect, the aircraft is an aircraft comprising a fuel cell system as described above, which may also be expressly used in other systems such as automobiles, ships, spaceflights or other units powered by fuel cells.

[0043] Aircraft including said fuel cell system have the advantage of being an environmentally friendly and efficient energy source. Fuel cell systems have a low emission profile, making aircraft operation more sustainable. The integration of the above-mentioned bipolar plates with the surface treatment improves the performance of the cooling system, contributing to the reliability and efficiency of the aircraft, which ultimately contributes to greener and more advanced aviation.

[0044] According to a further embodiment, the bipolar plate has a preheating area connected from the coolant inlet to the coolant outlet via a plurality of coolant channels. At least one preheating channel is present in the preheating area and serves to change the flow direction of the coolant before it enters the plurality of coolant channels. This reduces the temperature gradient along the preheating channel. In a particular embodiment, the preheating channel in the preheating area has at least one area where the coolant flows in a direction opposite to the normal flow direction.

[0045] The advantage here is that the preheat channels in the preheat region redirect the coolant flow, thereby reducing the temperature gradient along the channels.

[0046] According to a further embodiment, at least one of the coolant channels has a variable cross section which serves to reduce the pressure gradient of the coolant along the channel and / or the backflow of the coolant.

[0047] The advantage of this bipolar plate with an efficient two-phase cooling system is that it provides improved cooling performance. The variable cross-sectional area of ​​at least one coolant channel, and in particular all coolant channels, reduces the pressure gradient of the coolant along the channel. This allows for a more uniform distribution of the cooling medium and prevents undesirable backflow of the coolant.

[0048] In some embodiments, cooling channels with preheat channels present in the preheat region and cooling channels with variable cross sections are advantageous for cooling in two-phase cooling systems, for example, to facilitate the creation of boiling initiation action of the refrigerant.

[0049] In the following, exemplary embodiments of the invention will be discussed in more detail with reference to the accompanying drawings, in which the illustrations are schematic and not to scale, and in which the same reference signs indicate identical or similar elements. [Brief description of the drawings]

[0050] [Figure 1] 1 shows a bipolar plate. [Diagram 2] 13 illustrates various embodiments of surface treatments for the inner surfaces of the coolant channels. [Diagram 3] 1 shows a fuel cell system. [Figure 4] 1 illustrates an aircraft including a fuel cell system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0051] 1 shows a bipolar plate 10 for a fuel cell having a two-phase cooling system. The bipolar plate includes a coolant inlet 12, a coolant outlet 14, and a number of coolant channels 16. The coolant inlet 12 is fluidly connected to the coolant outlet 14 via the number of coolant channels 16. It is noted that at least one inner surface of the coolant inlet 12, the coolant outlet 14, and at least one of the coolant channels 16 has a surface treatment to affect the flow regime of the cooling fluid and / or the phase transition of the cooling fluid along at least one inner surface.

[0052] Figure 2 shows that various options are available for the surface treatment of the inner surface of the coolant channels. One option is to use a grooved surface. This method has been found to work well, especially with gravity.

[0053] Another popular option is to use wire mesh. This technique also offers good performance. Note that wire mesh works well against the effects of gravity and is therefore effective.

[0054] A third surface treatment option is sintering. Sintered surfaces are particularly effective at resisting gravity and achieve the best results in this regard.

[0055] FIG. 3 shows a multi-component fuel cell system 100 including a fuel cell 110, which may also be configured as a fuel cell stack, a two-phase cooling system 120, and a heat exchanger .

[0056] The fuel cell 110 includes a plurality of bipolar plates 10 (not shown) that include a plurality of coolant channels 16. The surface treatment of the inner surfaces of the coolant inlet 12, the coolant outlet 14, and at least one of the plurality of coolant channels 16 positively influences the coolant flow regime and / or phase transition of the cooling fluid along at least one of the inner surfaces.

[0057] FIG. 4 shows an aircraft 200 including a fuel cell system 100 that includes a fuel cell 100 and a bipolar plate 10 residing therein.

[0058] It should further be noted that "comprise" or "have" does not exclude other elements or steps, and "a", "an" or "one" does not exclude a plurality. It should further be noted that features or steps described with reference to one of the above exemplary embodiments can also be used in combination with other features or steps of other exemplary embodiments described above. Reference signs in the claims should not be interpreted as limiting. [Explanation of symbols]

[0059] 10 Bipolar Plates 12 Refrigerant inlet 14 Refrigerant outlet 16 Multiple Coolant Channels 100 Fuel Cell System 110 Fuel Cell 120 Two-phase cooling system 130 Heat exchanger 200 aircraft

Claims

1. A bipolar plate (10) for a fuel cell having a two-phase cooling system, comprising: A refrigerant inlet (12); A refrigerant outlet (14); A plurality of coolant channels (16); Including, the refrigerant inlet (12) is in fluid communication with the refrigerant outlet (14) via the plurality of refrigerant channels (16); A bipolar plate (10) wherein at least one inner surface of a coolant inlet (12), a coolant outlet (14), and at least one of the plurality of coolant channels (16) has a surface treatment to affect a flow regime of a cooling fluid and / or a phase transition of the cooling fluid along the at least one inner surface.

2. 2. The bipolar plate (10) of claim 1, wherein at least a portion of said surface treatment comprises the introduction of macrostructures, preferably selected from the group consisting of grooves, meshes, sintering, on said at least one inner surface.

3. The bipolar plate (10) according to claim 1 or 2, wherein at least a portion of the surface treatment comprises the introduction of porous micro- and / or nano-particles.

4. The bipolar plate (10) of claim 3, wherein the porous micro- and / or nano-particles are selected from the group consisting of metal, ceramic, carbon, plastic or combinations thereof.

5. The bipolar plate (10) according to claim 3 or 4, wherein the porous micro- and / or nano-particles are adapted to reduce overheating of the cooling fluid.

6. The bipolar plate (10) according to any one of the preceding claims, wherein at least part of the surface treatment comprises the introduction of a hydrophobic and / or hydrophilic layer.

7. The bipolar plate (10) of claim 6, wherein the hydrophobic and / or hydrophilic layers are selected from the group consisting of metals, triels, pnictogens, chalcogens and halogens or combinations thereof.

8. The bipolar plate (10) according to claim 6 or 7, wherein the hydrophobic and / or hydrophilic and / or porous layers are adapted to reduce overheating of the cooling fluid.

9. The bipolar plate (10) according to any one of claims 3 to 8, wherein the hydrophobic layer is provided in the region of the coolant inlet (12) and / or porous micro- and / or nano-particles are provided in the region of the at least one of the plurality of coolant channels (16).

10. The bipolar plate (10) according to any one of the preceding claims, wherein the coolant comprises methanol and / or ethanol.

11. The bipolar plate (10) according to any one of the preceding claims, wherein the coolant comprises a dissolved inert gas.

12. At least one fuel cell (110); a two-phase cooling system (120); A heat exchanger (130); A bipolar plate (10) according to any one of claims 1 to 11, 1. A fuel cell system (100) comprising: at least one inner surface of a coolant inlet (12), a coolant outlet (14), and at least one of the plurality of coolant channels (16) having a surface treatment to affect a flow regime of a cooling fluid and / or a phase transition of the cooling fluid along the at least one inner surface.

13. An aircraft (200) comprising the fuel cell system (100) of claim 12.

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