FUEL CELL SYSTEM WITH TWO-PHASE COOLING AND ONE EJECTOR

Abstract

A fuel cell system (10) with a two-phase cooling system is specified, comprising: at least one fuel cell (12) with a coolant inlet (14) and a coolant outlet (16), a condenser (26), wherein the condenser (26) is configured to condense and subcool the coolant (20), a pump (28), wherein the pump (28) is configured to pump the subcooled coolant (20), at least one ejector (30), wherein the ejector (30) is in fluid communication with the coolant outlet (16), the pump (28), the condenser (26) and the fuel cell (12) and is configured to supply the coolant to the fuel cell (12).

Description

Field of invention

[0001] The present description relates generally to the technical field of aviation. In particular, the description relates to a fuel cell system with two-phase cooling and an ejector, and to an aircraft comprising such a fuel cell system. Background of the invention

[0002] Fuel cells are a potential solution for generating electricity in aircraft propulsion systems or for emission-free onboard power supply (APU = Auxiliary Power Unit) without unwanted emissions. Polymer electrolyte fuel cells (PEMFCs) generate energy and electricity through the electrochemical reaction of hydrogen and oxygen to form water. This reaction produces heat, which must be dissipated. In commercial fuel cell stacks, this is achieved through liquid cooling.

[0003] A potential alternative with significant weight reduction potential at the system level is replacing liquid cooling with two-phase cooling. This utilizes the latent heat of vaporization to dissipate large amounts of heat from the fuel cells. Additionally, the high heat transfer coefficient compared to single-phase cooling improves the performance of the thermal management system. Two-phase cooling relies on phase transitions in the evaporator (fuel cells) and in the heat exchanger with the environment (condenser). To pump the coolant to the fuel cell, it is necessary for the coolant to be supercooled, i.e., in a liquid state (to prevent pump cavitation). Supercooling refers to the temperature range below the coolant's boiling point. The supercooled coolant then enters the fuel cell, where its temperature is raised, and the coolant begins to boil.The presence of this steep temperature gradient in the inlet zone can be detrimental to the fuel cell. Temperatures that are too low in this area can lead to condensation of water in the gas channels (flooding). To mitigate this and other risks, a preheater or recuperator is typically used upstream of the evaporator (fuel cell). However, this preheater / recuperator can be large and reduce the weight advantages of two-phase cooling. Summary of the invention

[0004] The object of the invention can be considered to be to provide a fuel cell system with reduced weight.

[0005] This problem is solved by the subject matter of the independent claims. Further embodiments are described in the dependent claims and in the following description.

[0006] According to one aspect, a fuel cell system has a two-phase cooling system. The fuel cell system also has at least one fuel cell with a coolant inlet and a coolant outlet.

[0007] According to one embodiment, a fuel cell system further comprises a collector in which phase separation into gas and liquid phases takes place, the collector being in fluid communication with the fuel cell and configured to contain coolant flowing from the fuel cell in a liquid phase in a first section and a gas phase in a second section. The system also comprises a condenser, the condenser being in fluid communication with the collector and configured to condense and supercool the coolant.

[0008] The fuel cell system further includes a pump configured to circulate the subcooled coolant. The fuel cell system also includes an ejector. The ejector inlet (drive jet) can be connected to the condenser via the pump. The ejector inlet (suction side) can be connected either to the coolant outlet of the fuel cell or to the first section of the manifold. Furthermore, the ejector inlet can be connected to the second section of the manifold.

[0009] A fuel cell system according to the invention is a technological unit consisting of several components and used to convert chemical energy into electrical energy by means of electrochemical reactions. It typically comprises one or more fuel cells, which function as electrochemical cells and constitute the main component of the system. The system also includes further components such as a fuel supply mechanism, an oxidant supply mechanism, an electrolyte solution, electrodes, a catalyst, and an electrical connection.

[0010] The fuel cell system uses a chemical reaction between a fuel and an oxidant, typically hydrogen and oxygen, to generate electrochemical electricity. Water is the only byproduct, making the fuel cell system an environmentally friendly energy source. The generated electrical energy can then be used to power electrical devices, vehicles, or for power generation in various applications.

[0011] A two-phase cooling system according to the invention is a cooling solution designed to efficiently dissipate large amounts of heat by utilizing the phase transition from liquid to vapor. It is frequently used in situations where conventional single-phase cooling systems reach their limits and cannot provide sufficient heat dissipation.

[0012] In a two-phase cooling system, a refrigerant is used that can exist in both liquid and gaseous forms at suitable temperatures and pressures. The refrigerant absorbs heat from the source being cooled and evaporates, thus changing from a liquid to a gaseous state. The resulting vapor absorbs large amounts of heat in the process.

[0013] The phase change from liquid to vapor enables effective heat transfer. This leads to improved cooling performance and more efficient heat dissipation.

[0014] A two-phase refrigeration system typically consists of an evaporator, where the refrigerant absorbs heat and evaporates, and a condenser, where the vapor condenses back into water and releases the heat. The condensate is then returned to the evaporator to continue the refrigeration cycle.

[0015] A coolant inlet according to the invention is an opening or connection in a fuel cell cooling system through which the cooling medium, in this case the coolant, is introduced into the system. The coolant inlet enables the controlled entry of the coolant into the relevant area or components that require cooling.

[0016] A coolant outlet according to the invention is an opening or connection in a cooling system through which the cooling medium, in this case the coolant, is discharged from the system. The coolant outlet enables the controlled discharge of the heated coolant from the relevant area or components in order to cool them and ensure heat exchange.

[0017] A collector within the meaning of the invention is a component or device that serves to carry out a phase separation between the gas and liquid phases, for example due to gravity.

[0018] In a collector, one or more flows containing gas and liquid are combined or fed into it. Gravity exerts a separating force on the phases, which have different densities. This causes the heavier medium (usually the liquid) to accumulate at the bottom of the collector, while the lighter medium (usually the gas) remains in the upper region.

[0019] One possible accumulator is a heat-controlled accumulator (HCA): Such an accumulator comprises a volume filled with vapor and liquid of a single working fluid, without a membrane. The pressure in an HCA is controlled by a heater.

[0020] Another possible accumulator is a pressure-controlled accumulator (PCA): Such an accumulator comprises a volume that is pressurized mechanically by a piston or by gaseous pressure (with a bladder or diaphragm).

[0021] The collector is designed to enable efficient separation and collection of the two phases. This can be achieved through the use of gravity separators, partitions, hoppers, or other specialized structures. The goal is to ensure that the gas and liquid are separated and collected in separate areas for effective utilization or further processing.

[0022] A condenser within the meaning of the invention is a component or device that serves to condense vapor or gas into a liquid phase. The condenser is in fluid communication with the collector, which means that the coolant can circulate between the two components.

[0023] The main function of the condenser is to condense the refrigerant by releasing heat and thus changing it from a gaseous to a liquid state. This process typically occurs by cooling the vapor or gas through the condenser, bringing it into contact with a lower-temperature medium. This cooling causes the vapor or gas molecules to contract and condense, collecting them in liquid form.

[0024] Furthermore, the condenser is designed to subcool the coolant. Subcooling means that the temperature of the condensed coolant is below its saturation point, i.e., below the temperature at which it would normally condense. This allows the coolant to absorb more heat before it evaporates again or is circulated. Subcooling is important to prevent cavitation at the pump.

[0025] A pump within the meaning of the invention is a device or apparatus used to convey or move liquids or gases from one place to another. In the present case, the pump is specifically designed to convey the subcooled coolant.

[0026] The primary function of a pump is to apply mechanical energy to the coolant to move it along a pipe or through a system. The pump creates a pressure or flow gradient that moves the coolant from a lower pressure area to a higher pressure area. This is achieved by transferring kinetic energy or by changing the pump's volume to draw in the coolant and then push it in the desired direction.

[0027] In the specific case of a subcooled coolant, the pump is configured to draw in the liquid phase of the coolant and transport it through the system. The pump must be able to handle the low pressure of the subcooled coolant and generate sufficient pressure to circulate it through the system. This ensures continuous circulation of the subcooled coolant to maintain the desired cooling effect.

[0028] There are various types of pumps suitable for different applications and fluids, such as centrifugal pumps, piston pumps, or screw pumps. Selecting the right pump depends on the specific requirements of the system, including flow rate, pressure range, and type of coolant.

[0029] An ejector within the meaning of the invention is a device used to mix and convey liquids or gases by utilizing the pressure difference between the two fluids. In the present case, the ejector is in fluid communication with various components of the system, including the first section of the collector, the second section of the collector, the pump, the condenser, and the fuel cell.

[0030] The ejector's main function is to mix the coolant in the gas phase from the first section of the collector with the supercooled coolant from the condenser and then supply it to the fuel cell. The ejector uses the pressure difference between the two fluids to draw in the coolant in the gas phase and mix it with the supercooled coolant.

[0031] The ejector operates on the principle of the jet effect. The supercooled coolant is forced into the ejector by the pump and accelerated in a nozzle. This creates a low-pressure zone in the ejector, which draws in the coolant in its gaseous phase from the first section of the collector. The two streams are then mixed together in the ejector, forming a homogeneous mixture of gas and supercooled coolant.

[0032] This mixture is then pumped to the fuel cell to provide cooling. Mixing the coolant in the gas phase with the supercooled coolant preheats the coolant and compensates for the supercooling of the coolant at the fuel cell's coolant inlet.

[0033] The ejector plays a crucial role in mixing and supplying the coolant in the gas phase with the supercooled coolant in the system. It enables efficient use of the existing pressure differential and ensures a uniform distribution of the coolant for cooling the fuel cell.

[0034] Another advantage lies in the introduction of gas bubbles in the coolant inlet of the fuel cell, which are beneficial in counteracting boiling delay of the coolant. They help to reduce the surface tension, leading to more effective heat exchange at higher temperatures.

[0035] According to one embodiment, the ejector comprises a Venturi tube.

[0036] A Venturi tube is a special section of pipe with a narrowed cross-sectional area in the middle. It consists of a wider inlet, a narrowed neck, and a wider outlet.

[0037] The operation of a Venturi-type ejector is based on Bernoulli's principle and the pressure difference created by the change in velocity of the fluid within the Venturi tube. When a fluid, such as a gas or liquid, flows through the ejector's inlet, it passes through the constricted neck of the Venturi tube. In this narrow section, the fluid's velocity increases while the pressure decreases.

[0038] The pressure difference between the inlet and the neck of the ejector creates a suction effect. This draws a second fluid, located in a different pipe or container, into the ejector. The second fluid then mixes with the first fluid at the ejector's outlet and can be conveyed or used together.

[0039] According to one embodiment, the fuel cell is a fuel cell stack with at least one base plate, and the base plate includes the ejector.

[0040] Combining these two components results in a weight reduction, as separate ejectors and additional connecting lines can be eliminated. A conventional system typically requires separate ejectors that are externally connected to the fuel cell stack. These additional components increase the overall weight and space requirements of the system.

[0041] Integrating the ejector into the base plate of the fuel cell stack reduces weight, as no additional external components are required. The base plate serves both as a structural element of the fuel cell stack and as the ejector. This saves weight and space, which is particularly advantageous in applications with limited installation space, such as in aerospace or mobile applications.

[0042] The weight savings achieved by integrating the ejector into the base plate of the fuel cell stack contribute to the system's efficiency by reducing the overall weight while enabling a compact design. This advantage can lead to improved performance, increased energy efficiency, and greater range for the fuel cell system.

[0043] According to one embodiment, the coolant comprises methanol and / or ethanol.

[0044] Methanol and ethanol offer several advantages as refrigerants. They have a lower boiling point, allowing them to evaporate at higher temperatures and thus enabling better cooling. A key advantage of alcohols is their low freezing point and high enthalpy of vaporization.

[0045] Another advantage lies in the low viscosity of methanol compared to water. This facilitates flow and reduces the pump's energy consumption.

[0046] Furthermore, methanol and ethanol have a high enthalpy of vaporization. This allows for very small mass flow rates in the system, thereby reducing pressure loss. As a result, pipes and pumps can be smaller than with liquid cooling, leading to weight savings in the system.

[0047] According to one embodiment, the at least one fuel cell is a fuel cell stack with a media module, wherein the media module comprises the ejector.

[0048] According to one embodiment, the fuel cell system further comprises a bypass line with a pitot tube insert.

[0049] The advantage of using a Pitot tube lies in the ability to selectively extract the gas phase during an annular flow. The gas phase has a higher enthalpy than the liquid phase near the wall, thus reducing subcooling at the fuel cell inlet.

[0050] According to one aspect, an aircraft includes a fuel cell system of the aforementioned type.

[0051] According to one embodiment, the fuel cell system further comprises a bypass line and a pump, wherein the coolant inlet is in fluid communication with the coolant outlet via the bypass line.

[0052] The bypass line makes it possible to deliberately bypass the normal cooling circuit and direct the warm cooling medium directly to the cold cooling medium.

[0053] This enables rapid and efficient heat transfer to effectively increase the temperature of the cooling medium. The bypass line can be used in various applications to allow targeted cooling or specific temperature control, eliminating the need for a preheater / recuperator.

[0054] According to one embodiment, the fuel cell system further comprises a thermally conductive element between the coolant inlet and the coolant outlet, wherein the thermally conductive element is configured to transfer heat from the coolant outlet to the coolant inlet.

[0055] The main advantage of a thermally conductive element between the coolant inlet and outlet is efficient heat transfer. By using a thermally conductive element, the heat accumulated at the coolant outlet can be effectively transferred to the coolant inlet. This improves heat dissipation and stabilizes the temperature in the cooling circuit by preheating the coolant. Short description of the characters

[0056] The following section describes exemplary embodiments of the invention with reference to the accompanying drawings. The illustrations are schematic and not to scale. Identical reference numerals refer to identical or similar elements. The drawings show: Fig. 1 a fuel cell system; Fig. 2 another fuel cell system; Fig. 3 another fuel cell system; Fig. 4 a pitot tube insertion; Fig. 5 another fuel cell system with a pitot tube insert; Fig. 6 an aircraft. Detailed description of implementation examples

[0057] Fig. Figure 1 shows a fuel cell system 10 equipped with an efficient two-phase cooling system. The fuel cell system 10 comprises at least one fuel cell 12, which has a coolant inlet 14 and a coolant outlet 16.

[0058] The central component of the cooling system is the collector 18, which serves as compensation for the expansion of the coolant and for printing the cooling system.

[0059] To further treat the coolant, a condenser 26 is integrated into the system 10. The condenser 26 is in fluid communication with the collector 18 and is designed to condense and subcool the coolant 20. This allows the heat to be efficiently removed from the coolant.

[0060] To ensure the flow of the subcooled coolant 20, a pump 28 is used. The pump 28 is designed to circulate the subcooled coolant 20 and maintain the cycle.

[0061] Another crucial element of the two-phase cooling system is the ejector 30. The ejector 30 is in fluid communication with the inlet 14 and the outlet 16 of the fuel cell 12. Its function is to mix the coolant in the gas phase from the outlet 16 with the supercooled coolant from the condenser 26 and then supply it to the fuel cell 12 via the inlet 14.

[0062] Through the interaction of these components, the two-phase cooling system enables efficient cooling of the fuel cell 12. It ensures optimal temperature control by reducing subcooling at the inlet 14 and thus contributes to the performance and longevity of the fuel cell system.

[0063] Fig. Figure 2 shows a further embodiment of a fuel cell system 10 equipped with an efficient two-phase cooling system. The fuel cell system 10 also comprises at least one fuel cell 12 having a coolant inlet 14 and a coolant outlet 16.

[0064] The essential difference to the embodiment of Fig. Point 1 is that the collector is connected to the return line, allowing the gas phase to mix with the liquid phase. Furthermore, the collector is connected to the return line, allowing the gas phase and liquid phase to be separated.

[0065] Fig. Figure 3 shows a fuel cell system 10 equipped with an efficient two-phase cooling system. The fuel cell system 10 comprises at least one fuel cell 12, which has a coolant inlet 14 and a coolant outlet 16.

[0066] A central component of the cooling system is the collector 18, which enables phase separation between the gas and liquid phases due to gravity. The collector 18 is in direct fluid communication with the fuel cell 12 and ensures that the coolant 20 from the fuel cell is divided into two sections. The coolant 20 is in liquid phase in the first section 22 of the collector 18 and in gaseous phase in the second section 24.

[0067] To further treat the coolant, a condenser 26 is integrated into the system 10. The condenser 26 is in fluid communication with the collector 18 and is designed to condense and subcool the coolant 20. This allows the heat to be efficiently removed from the coolant.

[0068] To ensure the flow of the subcooled coolant 20, a pump 28 is used. The pump 28 is designed to circulate the subcooled coolant 20 and maintain the cycle.

[0069] Another crucial element of the two-phase cooling system is the ejector 30. The ejector 30 is in fluid communication with the first section 22 of the collector 18, the second section 24 of the collector 18, the pump 28, the condenser 26, and the fuel cell 12. Its function is to mix the coolant 20 in the gas phase from the collector 18 with the supercooled coolant from the condenser 26 and then supply it to the fuel cell 12.

[0070] Through the interaction of these components, the two-phase cooling system enables efficient cooling of the fuel cell 12. It ensures optimal temperature control and thus contributes to the performance and longevity of the fuel cell system 10.

[0071] The essential difference to the embodiment to Fig. 1 and Fig. 2 is a phase separation in the collector and the targeted injection of the vapor phase via the ejector towards the inlet of the fuel cell.

[0072] Fig. Figure 4 shows a Pitot tube insert 32 inside a coolant line. This allows the gas phase to be selectively tapped during an annular flow. The gas phase has a higher enthalpy than the liquid phase near the wall, thus reducing subcooling at the fuel cell inlet.

[0073] Fig. Figure 5 shows another embodiment of a fuel cell system 10 with a pitot insert 32 inside a coolant line.

[0074] Fig. Figure 6 shows an aircraft 100 with a described fuel cell system 10. This eliminates the need for a preheater / recuperator, resulting in advantageous weight savings.

[0075] It should also be noted that "comprehensive" or "comprising" 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 numerals in the claims are not to be considered as limitations. List of reference symbols 10 Fuel cell system 12 Fuel cell 14 Coolant inlet 16 Coolant outlet 18 collectors 20 Coolant 22 first section 24 second section 26 Capacitor 28 Pump 30 ejector 32 Pitot tube insertions 100 aircraft

Claims

[1] Fuel cell system (10) with a two-phase cooling system, comprising: at least one fuel cell (12) with a coolant inlet (14) and a coolant outlet (16), a condenser (26), wherein the condenser (26) is arranged to condense and subcool the coolant (20), a pump (28), wherein the pump (28) is arranged to convey the subcooled coolant (20), at least one ejector (30), wherein the ejector (30) is in fluid communication with the coolant outlet (16), the pump (28), the condenser (26) and the fuel cell (12) and is configured to supply the coolant to the fuel cell (12). [2] Fuel cell system (10) according to claim 1, further comprising: a collector (18), wherein a phase separation into gas and liquid phases takes place in the collector (18), wherein the collector (18) is in fluid communication with the fuel cell (12) and is designed to contain coolant (20) flowing from the fuel cell in a liquid phase in a first section (22) and a gas phase in a second section (24), wherein the ejector (30) is designed to mix the coolant (20) in the gas phase from the collector (18) with the subcooled coolant from the condenser (26) and to supply it to the fuel cell (12). [3] Fuel cell system (10) according to one of the preceding claims, wherein the ejector (30) comprises a Venturi tube. [4] Fuel cell system (10) according to one of the preceding claims, wherein the at least one fuel cell (12) is a fuel cell stack with at least one base plate, and the base plate comprises the ejector (30). [5] Fuel cell system (10) according to one of the preceding claims, wherein the coolant (20) comprises methanol and / or ethanol. [6] Fuel cell system (10) according to one of the preceding claims, wherein the at least one fuel cell (12) is a fuel cell stack with a media module, wherein the media module comprises the ejector (30). [7] Fuel cell system (10) according to one of the preceding claims, wherein the fuel cell system (10) further comprises a bypass line with a Pitot insert (32). [8] Aircraft (100) with a fuel cell system (10) according to one of the preceding claims.

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