BIPOLAR PLATE WITH PREHEATING CHANNEL

Abstract

A bipolar plate (10) for a fuel cell with a two-phase cooling system and a fuel cell system (100) are specified, comprising: a coolant inlet (12), a coolant outlet (14), a large number of coolant channels (16), and an active area (18) wherein heat is induced in the active area by an electrochemical reaction of the fuel cell, wherein the coolant inlet (12) is in fluid contact with the active surface (18), wherein the active area (18) is in fluid communication with the coolant outlet (14) via the plurality of coolant channels (16), wherein the active area (18) comprises at least one preheating channel (20), and the preheating channel (20) is configured to redirect the flow direction of a coolant located in the preheating channel (20) such that a temperature gradient of the coolant along the preheating channel (20) is reduced.

Description

Field of the invention

[0001] This description generally relates to the technical field of aviation. In particular, the description relates to a bipolar plate with a preheating channel and a fuel cell system with such a bipolar plate. Background of the invention

[0002] Fuel cells represent a potential solution for emission-free propulsion or emission-free on-board power supply (APU = Auxiliary Power Unit), for example, in aircraft. Polymer electrolyte fuel cell stacks (PEMFCs) generate power and electricity through the electrochemical reaction of hydrogen and oxygen to form water. This reaction generates heat that must be dissipated. In commercial fuel cell stacks, this is achieved through liquid cooling. A potential alternative with significant weight savings potential at the system level is to replace the liquid cooling with a two-phase cooling circuit. This utilizes the latent heat of vaporization to remove large amounts of heat from the fuel cells. Furthermore, the high heat transfer coefficient improves the performance of the thermal management system compared to single-phase cooling.The change of the flow regime in the fuel cell stack from liquid to two-phase cooling requires a special thermal design of the flow fields. Summary of the invention

[0003] It can be considered the object of the invention to improve the thermal design of the flow fields of a fuel cell.

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

[0005] According to one aspect, the bipolar plate for a fuel cell with a two-phase cooling system has various components. These include a coolant inlet, a coolant outlet, and a plurality of coolant channels. In addition, there is an active area that is connected from the coolant inlet to the coolant outlet via a plurality of coolant channels. In the active area, there is at least one preheating channel, which serves to redirect the flow direction of the coolant before it enters the plurality of coolant channels. Furthermore, the active area is defined by the fact that heat is induced in the active area by an electrochemical reaction of the fuel cell. This reduces a temperature gradient along the preheating channel and transports heat in a direction from the coolant outlet to the coolant inlet.In a specific embodiment, the preheating channel in the active surface has at least one region in which the coolant flows counter to the usual flow direction.

[0006] The advantage of the two-phase cooling system in such a bipolar plate of a fuel cell is that the flow direction of the coolant is redirected by the preheating channel in the active area, and thereby heat is transported from the area of ​​the bipolar plate near the coolant outlet to the coolant inlet.

[0007] A fuel cell system with a bipolar plate, as defined by the invention, is a technological unit consisting of several components and used to convert chemical energy into electrical energy through electrochemical reactions. It typically comprises one or more fuel cells, which function as electrochemical cells and represent the main component of the system.

[0008] The fuel cell system uses a chemical reaction between a fuel and an oxidizer, typically hydrogen and oxygen, to generate electricity. Water is the only waste product, making the fuel cell system an environmentally friendly energy source. The generated electrical energy can then be used to power electrical devices, vehicles, or to generate electricity in various applications.

[0009] A two-phase cooling system is a cooling solution that aims to efficiently dissipate large amounts of heat by utilizing the phase transition from liquid to vapor. It is often used in situations where conventional single-phase cooling systems reach their limits and cannot provide sufficient heat dissipation.

[0010] A two-phase cooling system uses a coolant that, at suitable temperatures and pressures, can exist in both liquid and gaseous form. The coolant absorbs heat from the source to be cooled and evaporates, transforming from a liquid to a gaseous state. The resulting vapor absorbs large amounts of heat.

[0011] The phase change from liquid to vapor enables effective heat transfer. This leads to improved cooling performance and more efficient heat dissipation.

[0012] A two-phase cooling system typically consists of an evaporator, where the refrigerant absorbs heat and evaporates, and a condenser, where the vapor condenses and releases the heat. The condensate is then returned to the evaporator to continue the cooling cycle.

[0013] A coolant inlet is an opening or port in a fuel cell through which the coolant is introduced into the system. The coolant inlet allows the controlled entry of the coolant into the specific area or component that requires cooling.

[0014] A coolant outlet is an opening or connection in a cooling system through which the coolant, in this case the refrigerant, is removed from the system. The coolant outlet allows the controlled escape of heated coolant from the corresponding area or components to cool them and ensure heat exchange.

[0015] Heat is induced in the active area by an electrochemical reaction in the fuel cell. An active area is also a specific region or section within the bipolar plate that serves to preheat the coolant, in this case the cooling medium, to the evaporation temperature. The goal is to heat the coolant in or in front of the active area evenly to the evaporation temperature in order to avoid a temperature gradient in the active area. This prevents so-called subcooling (coolant temperature below the evaporation temperature) in the active area. For this purpose, the coolant inlet is in fluid communication with the active area, which means that the coolant flows from the coolant inlet towards the active area. The active area is in turn also connected to the coolant outlet via the numerous coolant channels.This allows for a continuous flow of coolant from the active surface to the coolant channels and ultimately to the coolant outlet. This fluid connection ensures that the coolant circulates efficiently along the active surface and the coolant channels, absorbing heat and transporting it from the area near the coolant outlet to the area near the coolant inlet.

[0016] A plurality of coolant channels is a set of passages or channels in a component or structure through which the coolant flows to dissipate heat. These coolant channels serve to efficiently distribute the coolant across the areas or components to be cooled and facilitate heat exchange. The multitude of coolant channels creates a larger surface area for the heat transfer process, resulting in effective cooling.

[0017] The active surface includes at least one preheating channel. This channel is designed to redirect the flow direction of the coolant located in the preheating channel before it enters the coolant channels. The goal is to mitigate the gradient in the active surface, or to minimize areas within the active surface that are affected by subcooling. This means that the coolant is heated more evenly, achieving a more uniform temperature along the channel. This redirection ensures better heat distribution and dissipation, ultimately leading to more efficient cooling of the components.

[0018] According to one embodiment, the bipolar plate has a preheating channel in the active area, which has at least one region with a counter-flow direction of the coolant. This leads to improved heat transfer and cooling.

[0019] According to a further embodiment, the preheating channel in the active area is designed in a serpentine shape to enable efficient use of the available space and optimized heat transfer.

[0020] The serpentine design of the channel allows for a greater length and surface area available for heat transfer. The coolant is guided along this longer path, allowing more time for heat exchange between sections of the preheating channel and the bipolar plate. This results in improved heat transfer efficiency.

[0021] Furthermore, the serpentine design allows for compact space utilization. By winding the duct several times, a longer duct length can be accommodated in a small space. This is particularly advantageous in applications with limited installation space, such as aircraft or fuel cell-powered vehicles. The optimized space utilization enables efficient integration of the preheating duct into the overall system.

[0022] According to an additional embodiment, the preheating channel has a plurality of bends and straight sections.

[0023] According to a further embodiment, the distance between the straight sections in the plurality of straight sections varies in order to optimally control the heat flow and the cooling performance.

[0024] According to an additional embodiment, the preheating channel has a cross-sectional area that influences the speed and efficiency of the coolant flow as well as the heat transfer properties.

[0025] The design of the cross-sectional area allows for control of the coolant's velocity. A smaller cross-sectional area allows for a higher coolant flow velocity. Conversely, a larger cross-sectional area can slow the coolant flow and increase the coolant's residence time in the preheating channel, which can lead to improved heat transfer.

[0026] Furthermore, the cross-sectional area can also influence the heat transfer properties. A smaller cross-sectional area allows for a larger contact area between the coolant and the bipolar plate, which can lead to improved heat transfer along the preheating channel. Optimizing the cross-sectional area in terms of shape and size can ensure efficient heat transfer and minimize unwanted heat losses.

[0027] According to a further embodiment, the preheating channel has a cross-sectional area of ​​at most 5 mm 2 , preferably no more than 1 mm 2 , particularly preferably not more than 0.5 mm 2 amounts.

[0028] According to a further embodiment, the preheating channel has a cross-section selected from the group of semicircle, rectangle, trapezoid, triangle and embossed channel structure in order to adapt the channel to the specific requirements of the heat transfer and the cooling system.

[0029] An advantage of this design is that the preheating channel has a cross-section that can be adapted to the specific heat transfer and cooling system requirements. This enables optimized cooling system performance and efficiency.

[0030] By selecting the appropriate cross-section, such as a semicircle, rectangle, trapezoid, triangle, or embossed channel structure, the channel can be tailored to specific heat transfer requirements. Each cross-section offers different flow characteristics and heat transfer efficiency. For example, a semicircular cross-section can enable good flow guidance and improved heat transfer, while a rectangular cross-section can provide a larger contact area for heat transfer. By selecting the appropriate cross-section, the performance of the cooling system can be optimized.

[0031] Furthermore, adjusting the cross-section of the preheating channel allows for better control over the coolant flow. By selecting a specific cross-section, the fluid flow can be accelerated, decelerated, or evenly distributed depending on the cooling system's requirements. This contributes to improving the cooling system's efficiency and ensuring effective cooling of the bipolar plate.

[0032] According to an additional embodiment, the bipolar plate consists of a material such as iron-based materials, titanium, carbon, carbon composite, flake graphite material (Grafoil) or conductive plastic composite materials to ensure optimized thermal conductivity and mechanical stability.

[0033] An advantage of this embodiment is that the bipolar plate is made of a suitable material that ensures optimized thermal conductivity and mechanical stability.

[0034] High thermal conductivity can be achieved through the use of materials such as iron-based materials, titanium, carbon, carbon composites, flake graphite (Grafoil), or conductive plastic composites. Efficient heat dissipation is crucial to maintaining optimal operating temperatures. The selected material enables effective heat distribution across the bipolar plate and helps prevent hot spots and temperature gradients.

[0035] In addition, these materials also offer good mechanical stability and strength. This is important to withstand the demands of the fuel cell system, especially under operating conditions with pressure fluctuations and vibrations. The bipolar plate must have sufficient structural integrity to fulfill its function as a fuel cell component. The use of materials with high mechanical stability ensures reliable and long-lasting performance of the bipolar plate.

[0036] According to a further embodiment, the active surface has a geometry selected from the group consisting of semicircle, rectangle, triangle, trapezoid, and embossed channel structure to enable efficient heat distribution and dissipation in the bipolar plate. The active surface can be arranged in the region of the coolant inlet and / or in the region of the coolant outlet.

[0037] According to a further embodiment, the active surface comprises the plurality of coolant channels. The active surface can encompass at least 20%, in particular 50%, of the plurality of coolant channels, preferably completely. The coolant is thus redirected over the region of the plurality of coolant channels in such a way that a temperature gradient of the coolant along the plurality of coolant channels is reduced. For this purpose, the plurality of coolant channels are preferably connected to one another and particularly preferably form a single, connected coolant channel, wherein the connected coolant channel thus corresponds to the preheating channel and the plurality of coolant channels.

[0038] According to one embodiment, the coolant may comprise methanol and / or ethanol. This type of coolant offers the advantage of high thermal conductivity and efficient cooling.

[0039] Furthermore, methanol and ethanol have low boiling points. This is advantageous because they can evaporate quickly as they flow through the coolant channels. Evaporation absorbs heat from the components, leading to effective cooling. The combination of boiling temperature and saturation pressure, which is appropriate for fuel cell operation, is particularly advantageous.

[0040] Furthermore, methanol and ethanol have a high enthalpy of vaporization. This allows for very small mass flows in the system, reducing pressure loss. This allows smaller pipes and pumps to be dimensioned than with liquid cooling, resulting in a reduction in system weight.

[0041] According to another aspect, a fuel cell system comprises at least one fuel cell, a two-phase cooling system, a heat exchanger, and a bipolar plate having a plurality of coolant channels. The bipolar plate is designed to preheat the coolant before it enters the coolant channels.

[0042] An advantage of this fuel cell system is that the bipolar plate is designed to preheat the coolant before it enters the coolant channels.

[0043] Preheating the coolant ensures efficient and even heat distribution throughout the cooling system. This helps prevent cold spots and temperature gradients that can impair fuel cell performance and service life. Preheating ensures that the coolant is already at a certain temperature before entering the coolant channels, allowing the fuel cell to reach its optimal operating temperature more quickly.

[0044] Furthermore, preheating the coolant enables improved efficiency of the fuel cell system, as less energy is required to heat the coolant during operation. This can lead to an overall higher energy yield of the system.

[0045] Preheating increases the temperature of the bipolar plate, reducing the risk of condensation and related problems such as corrosion and channel blockage.

[0046] According to another aspect, an aircraft has a fuel cell system comprising at least one fuel cell, a two-phase cooling system, and a bipolar plate with a plurality of coolant channels. The bipolar plate is designed to preheat the coolant before it enters the coolant channels. The system can also be explicitly used in other systems, such as motor vehicles, watercraft, aerospace, or other fuel cell-powered units.

[0047] An advantage of this aircraft with the described fuel cell system is that the bipolar plate preheats the coolant before it enters the coolant channels.

[0048] 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 a coolant along the channels and / or the backflow of the coolant.

[0049] The advantage of this bipolar plate with an efficient two-phase cooling system is that it offers improved cooling performance. The variable cross-section of at least one, and especially all, coolant channels reduces the coolant pressure gradient along the channels. This enables a more even distribution of the cooling medium and prevents unwanted coolant backflow.

[0050] According to a further embodiment, at least one inner surface of the coolant inlet, coolant outlet and at least one of the plurality of coolant channels has a surface treatment in order to influence the flow pattern of a cooling liquid along at least one inner surface and / or a phase transition of the cooling liquid.

[0051] Surface treatment of the inside of a coolant inlet, coolant outlet, coolant channel, or a combination thereof refers to the targeted modification or processing of the surface in contact with the coolant. This treatment can include various processes and techniques aimed at influencing the flow pattern of the coolant or enhancing the phase transition of the coolant.

[0052] Embodiments with coolant channels having a variable cross-section and at least one inner surface of the coolant inlet, coolant outlet and at least one of the plurality of coolant channels having a surface treatment are advantageous for cooling in a two-phase cooling system since they are advantageous, for example, for forming boiling initiators of the coolant. Short description of the characters

[0053] The following describes embodiments of the invention in more detail with reference to the accompanying drawings. The illustrations are schematic and not to scale. Like reference numerals refer to like or similar elements. They show: Fig. 1 a bipolar plate for a fuel cell; Fig. 2 a bipolar plate for a fuel cell with a plurality of preheating channels; Fig. 3 a bipolar plate for a fuel cell with a plurality of regions with individual preheating channels; Fig. 4 an aircraft with a fuel cell system. Detailed description of implementation examples

[0054] Fig. Figure 1 shows a bipolar plate 10 for a fuel cell equipped with an efficient two-phase cooling system. On the left side of the bipolar plate is the coolant inlet 12, through which the coolant is introduced into the system. The coolant inlet 12 is marked as a square-shaped opening (only the center opening is the cooling channel). The other openings are the anode and cathode channels, respectively. On the right side of the bipolar plate is the coolant outlet 14, which removes the coolant from the system. Both components are fluidly connected to the corresponding areas of the bipolar plate 10.

[0055] The bipolar plate 10 has a plurality of coolant channels 16 extending through the bipolar plate 10. These channels enable the efficient flow of coolant through the bipolar plate 10 and contribute to the cooling of the fuel cell.

[0056] The bipolar plate 10 further comprises an active area 18. The active area 18 is preferably not the preheating region. The active area 18 is preferably the region where heat occurs due to the electrochemical reaction. The cooling channels should preferably be located wherever the active area 18 is. This active area 18 is characterized by the preheating channel 20, which extends in a serpentine shape in the area near the coolant inlet 12. The preheating channel 20 is designed to redirect the flow direction of the coolant before it enters the plurality of coolant channels 16. This reduces a temperature gradient along the preheating channel 20, and the coolant enters the plurality of coolant channels 16 preheated. The formation of gas bubbles in the active area 18 also prevents boiling delay of the coolant.

[0057] Fig. Figure 1 illustrates the various components of the bipolar plate and the coolant paths within the two-phase cooling system. It clarifies the functions and fluid connections between the individual components to ensure preheating of the coolant.

[0058] Fig. Figure 2 shows a bipolar plate 10 for a fuel cell, wherein the active surface 18 extends over almost the entire bipolar plate 10. The plurality of coolant channels 16 are configured as a plurality of meander-shaped preheating channels 20. The coolant is thus deflected over the entire area of ​​the plurality of coolant channels 16, in this embodiment the meander-shaped preheating channels 20, such that a temperature gradient of the coolant is reduced. The active surface 18 thus extends over the area that in the Fig. 1 is formed by the plurality of coolant channels.

[0059] Fig. 3 shows an example of a bipolar plate for a fuel cell, where, in contrast to the Fig. 2, the serpentine-shaped regions are limited to a sub-region. In the illustrated embodiment, only one serpentine is shown, although it is evident that eleven additional such regions exist in the 3x4 matrix. The number and dimensions of these regions can vary. Furthermore, the number of bends and the cross-section of the respective preheating channels can vary.

[0060] Fig.Figure 4 shows an aircraft 200 with a fuel cell system 100 and a bipolar plate 10. The fuel cell system 100 consists of several components, such as a fuel cell 110, a heat exchanger 130, and a two-phase cooling system 120, which work together to generate electrical energy from hydrogen. Preheating the coolant ensures effective cooling of the fuel cell system 100 and realizes the central idea of ​​transporting the coolant from the coolant outlet area to the coolant inlet.

[0061] Additionally, it should be noted that "comprising" or "having" does not exclude other elements or steps, and "a" or "an" does not exclude a plurality. Furthermore, it should be noted that features or steps described with reference to one of the above embodiments may also be used in combination with other features or steps of other embodiments described above. Reference signs in the claims are not to be considered as limitations. List of reference symbols 10 bipolar plate 12 Coolant inlet 14 Coolant outlet 16 variety of coolant channels 18 active area 20 Preheating channel 100 fuel cell system 110 fuel cell 120 Two-phase cooling system 130 heat exchangers 200 aircraft

Claims

[1] Bipolar plate (10) for a fuel cell (110) with a two-phase cooling system, comprising: a coolant inlet (12), a coolant outlet (14), a plurality of coolant channels (16), and an active surface (18), wherein heat is induced in the active surface by an electrochemical reaction of the fuel cell (110), wherein the coolant inlet (12) is in fluid communication with the active surface (18), wherein the active surface (18) is in fluid communication with the coolant outlet (14) via the plurality of coolant channels (16), wherein the active surface (18) comprises at least one preheating channel (20), and the at least one preheating channel (20) is configured to redirect the flow direction of a coolant located in the preheating channel (20) such that a temperature gradient of the coolant along the preheating channel (20) is reduced and heat is transported in a direction from the coolant outlet (14) to the coolant inlet (12). [2] Bipolar plate (10) according to claim 1, wherein the at least one preheating channel (20) in the active area (18) has at least one region with an opposite flow direction of the coolant. [3] Bipolar plate (10) according to claim 2, wherein the at least one preheating channel (20) is designed to run in a serpentine shape. [4] Bipolar plate (10) according to claim 3, wherein the at least one preheating channel (20) has a plurality of turns and a plurality of straight sections. [5] Bipolar plate (10) according to claim 4, wherein a respective distance between individual ones of the plurality of straight sections is 300 mm, preferably 100 mm, particularly preferably 30 mm. [6] Bipolar plate (10) according to claim 4, wherein the respective distances between individual ones of the plurality of straight sections differ. [7] Bipolar plate (10) according to one of the preceding claims, wherein the at least one preheating channel (20) has a cross-sectional area of ​​at most 5 mm 2 , preferably no more than 1 mm 2 , particularly preferably not more than 0.5 mm 2 amounts. [8] Bipolar plate (10) according to one of the preceding claims, wherein the at least one preheating channel (20) has a cross section selected from the group: semicircle, rectangle, trapezoid, triangle, embossed channel structure. [9] Bipolar plate (10) according to one of the preceding claims, wherein the bipolar plate (10) comprises a material selected from the group: Iron-based materials, titanium, carbon, carbon composites, flake graphite material (Grafoil) or conductive plastic composite materials. [10] Bipolar plate (10) according to one of the preceding claims, wherein the active area (18) has a geometry selected from the group: semicircle, rectangle, triangle, and trapezoid. [11] Bipolar plate (10) according to one of the preceding claims, wherein the active surface (18) comprises the plurality of coolant channels (16) which are at least partially formed by the at least one preheating channel (20). [12] Bipolar plate (10) according to one of the preceding claims, wherein the coolant comprises methanol and / or ethanol. [13] Fuel cell system (100), comprising: at least one fuel cell (110), a two-phase cooling system (120), a heat exchanger (130), a bipolar plate (10) having a plurality of coolant channels (16) according to one of claims 1 to 12, wherein the bipolar plate (10) has an active area, and wherein the active area (18) comprises at least one preheating channel (20), and the at least one preheating channel (20) is configured to redirect the flow direction of a coolant located in the preheating channel (20) such that a temperature gradient of the coolant along the preheating channel (20) is reduced and heat is transported in a direction from the coolant outlet (14) to the coolant inlet (12). [14] Aircraft (200) with a fuel cell system (100) according to claim 13.

Images