Fuel cell system having two-phase cooling system including bypass line

Abstract

To provide a fuel cell system having a two-phase cooling including a bypass line.SOLUTION: There is presented a fuel cell system (10) having a two-phase cooling system. The fuel cell system includes: at least one fuel cell (12) with a coolant inlet (14) and a coolant outlet (16); a condenser (26) that is in fluid connection with the accumulator (18) and that is adapted to condense and supercool a coolant; and a bypass line (28) including a pump (30). The bypass line (28) is in fluid connection with the coolant outlet (16) and the coolant inlet (14) and is adapted to return the coolant to the fuel cell (12) by the pump (30).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates generally to the technical field of aviation, and in particular to a fuel cell system having two-phase cooling with a bypass line, and to an aircraft equipped with such a fuel cell system. [Background technology]

[0002] Fuel cells are one possible solution to generate power in aircraft propulsion systems or emission-free auxiliary power units (APUs) without unwanted emissions. Polymer electrolyte membrane fuel cells (PEMFCs) generate energy and power through the electrochemical reaction of hydrogen and oxygen, which produces water. This reaction inevitably results in the generation of heat, which must be dissipated. In commercial fuel cell stacks, this is achieved by liquid cooling.

[0003] A possible alternative that would offer significant weight savings at the system level is to replace liquid cooling by two-phase cooling. Two-phase cooling utilizes the latent heat of vaporization to dissipate a large amount of heat from the fuel cell. Furthermore, a higher heat transfer coefficient improves the performance of the thermal management system compared to single-phase cooling. Two-phase cooling is based on a phase transition in the heat exchanger (condenser) with the evaporator (fuel cell) and the environment. To be able to pump the coolant to the fuel cell, it must be subcooled, i.e. in liquid state (avoiding cavitation of the pump). Subcooling refers to the temperature range below the boiling point of the coolant. The subcooled coolant then reaches the fuel cell, where the temperature of the coolant is increased and it starts to boil. The presence of such a sharp temperature gradient in the inlet area can cause the destruction of the fuel cell. An extremely low temperature in this area can lead to the condensation of water in the gas ducts (flooding). To overcome this and other risks, a preheater or recuperator is usually used upstream of the evaporator (fuel cell). However, such preheater / recuperators can be quite large, reducing the weight benefits of two-phase cooling. Summary of the Invention [Problem to be solved by the invention]

[0004] SUMMARY OF THE PRESENT DISCLOSURE It can be seen as an object of the present invention to provide a fuel cell system that is lightweight. [Means for solving the problem]

[0005] 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.

[0006] According to one aspect, a fuel cell system having a two-phase cooling system is provided. The fuel cell system comprises at least one fuel cell having a coolant inlet and a coolant outlet. The fuel cell system further comprises an accumulator, the accumulator in fluid communication with the fuel cell and adapted to contain a coolant exiting the fuel cell in a first portion in a gas phase and in a second portion in a liquid phase. The fuel cell system further comprises a condenser, the condenser in fluid communication with the accumulator and adapted to condense and subcool the coolant. The fuel cell system further comprises a bypass line comprising a pump, the coolant inlet in fluid communication with the coolant outlet via the bypass line.

[0007] In the context of the present invention, a fuel cell system 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 comprises one or more fuel cells, which act as electrochemical cells and are the main components of the system. Furthermore, the system comprises further components such as a fuel supply, an oxidant supply, an electrolyte, electrodes, a catalyst and electrical connections.

[0008] Fuel cell systems use a chemical reaction between a fuel and an oxidant, typically hydrogen and oxygen, to generate electrochemical power. This chemical reaction produces water as the only waste product, making the fuel cell system an environmentally friendly source of energy. The generated electrical energy can then be used to power electrical devices, power vehicles, or generate electricity for a variety of applications.

[0009] 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.

[0010] 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.

[0011] The phase change from liquid to vapor allows for more efficient heat transfer since evaporation has a higher heat transfer capacity than convection liquid cooling, resulting in 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 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.

[0013] Cooling systems of this type are used in a variety of applications, including cooling high performance electronic devices, processors, fuel cells, engines, and other thermally demanding systems where efficient heat dissipation is critical.

[0014] In the context of the present invention, an accumulator is a component or device used to effect phase separation between gas and liquid phases based on gravity.

[0015] In the accumulator, one or more streams containing gas and liquid are combined or fed. Gravity exerts a separating force on the phases having different densities. Thus, the heavier medium (usually liquid) accumulates at the bottom of the accumulator, while the lighter medium (usually gas) remains in the upper region of the accumulator.

[0016] One possible accumulator is the thermally controlled accumulator (HCA). Such an accumulator has no diaphragm and consists of a volume filled with the vapor and liquid of a single working fluid. The pressure in the HCA is controlled by a heater.

[0017] Another possible accumulator is the Pressure Controlled Accumulator (PCA). Such an accumulator comprises a volume that is mechanically pressurized by a piston or gas pressure (using a bladder or diaphragm).

[0018] Accumulators are designed to allow for efficient separation and accumulation of the two phases. This can be accomplished through the use of gravity separators, partitions, funnels, or other specialized structures. The goal is to ensure that the gas and liquid are separated and collected in separate areas for effective use or further processing.

[0019] A condenser is a component or device used to condense a vapor or gas into a liquid phase. The condenser is in fluid communication with the accumulator, which means that a refrigerant can circulate between these two components.

[0020] The primary function of a condenser is to condense a refrigerant by releasing heat, thereby transitioning it from a gaseous state to a liquid state. This process is generally accomplished by cooling the vapor or gas by contacting it with a cooler medium through the condenser. This cooling causes the vapor or gas molecules to come together and condense, so that they can be collected in liquid form.

[0021] Furthermore, the condenser is adapted to be able to subcool the refrigerant, meaning that the temperature of the condensed refrigerant is below its saturation point, i.e. below the temperature at which it would normally condense. This allows the refrigerant to absorb more heat before it is evaporated or pumped again. Subcooling is important to avoid cavitation of the pump.

[0022] A pump is a unit or device used to convey or move a liquid or gas from one place to another. In this case, the pump is specifically adapted for conveying a sub-cooled refrigerant.

[0023] The primary function of a pump is to apply mechanical energy to the refrigerant to move it along a line or through a system. The pump creates a pressure or flow gradient to transport the refrigerant from an area of ​​lower pressure to an area of ​​higher pressure. This is done by the transfer of kinetic energy or by changing the volume of the pump to draw in and force the refrigerant in the desired direction.

[0024] In the particular case of a subcooled refrigerant, the pump is configured to receive the liquid phase of the refrigerant and transport it along the system. The pump must be able to handle the low pressure of the subcooled refrigerant and generate sufficient pressure to transport the refrigerant throughout the system. This allows for continuous circulation of the subcooled refrigerant to maintain the desired cooling action.

[0025] There are different types of pumps suitable for different applications and fluids, such as centrifugal, piston, or screw pumps. Choosing the appropriate pump depends on the specific requirements of the system, including flow volume, pressure range, and type of refrigerant.

[0026] A bypass line is a line or pipe that is in fluid communication with the refrigerant inlet and the refrigerant outlet and is used to direct warm refrigerant directly to cold refrigerant without the refrigerant having to flow through the main path of the cooling circuit. The bypass line allows for a specific diversion of the normal cooling circuit, directing the warm cooling medium directly to the cold cooling medium.

[0027] This allows for rapid and efficient heat transfer to effectively raise the temperature of the cooling medium. Bypass lines can be used in a variety of applications to allow for specific cooling or specific temperature control, eliminating the need for a preheater / recuperator.

[0028] According to one embodiment, the bypass line comprises a control valve, in particular a thermostatic valve.

[0029] Bypass lines in conjunction with control valves provide a variety of benefits to cooling systems. The control valve acts as a control valve, allowing precise control of the cooling circuit based on temperature. This ensures effective temperature control.

[0030] A big advantage is the precise temperature control: the control valve allows precise setting of the coolant temperature by controlling the flow rate of the cooling medium in the bypass line. This ensures an optimum operating temperature and increases the efficiency of the system.

[0031] Another advantage is the fast response time of the control valve, which can respond quickly to temperature changes and adjust the flow rate of the cooling medium accordingly, allowing the system to respond quickly to changing operating conditions and avoid overheating or overcooling.

[0032] The use of a bypass line in conjunction with a control valve can also lead to energy savings. The control valve controls the cooling circuit in a specific manner, directing the cooling medium from the refrigerant outlet directly to the refrigerant inlet. This reduces flow through the rest of the system, leading to more efficient cooling and energy savings.

[0033] Additionally, the use of a control valve can extend the service life of components in the cooling circuit: precise temperature control and avoidance of overheating or overcooling protects components, improving their reliability and extending their service life.

[0034] The use of bypass lines in conjunction with control valves makes the cooling system more versatile and adaptable. The control valves allow for different temperature ranges and cooling levels to be set to meet different operating conditions.

[0035] Another benefit is that gas bubbles are provided at the inlet to the fuel cell coolant, which has many benefits for countering overheating of the coolant: the gas bubbles help reduce surface tension, resulting in more effective heat exchange at higher temperatures.

[0036] Overall, the use of bypass lines in conjunction with control valves provides precise and efficient cooling, improving control of operating temperatures, which translates into improved performance, reduced mass, and extended system life.

[0037] According to one embodiment, the bypass line comprises a pre-heating module.

[0038] A bypass line with a pre-heat module is a cooling system configuration that offers additional advantages: the pre-heat module is a component that is integrated into the bypass line and used to pre-heat the cooling medium before it is returned to the main cooling circuit. This configuration is defined below and its advantages are presented.

[0039] The bypass line is a connection between the refrigerant outlet and the refrigerant inlet that runs parallel to the main cooling circuit. The preheat module is a unit in the bypass line specially developed to preheat the cooling medium.

[0040] Another advantage is that condensation problems are reduced. In certain situations, especially at lower temperatures or high air humidity, condensation can occur in the cooling circuit. The pre-heating module brings the cooling medium to a high temperature, thereby reducing the risk of condensation and stabilizing the performance of the system.

[0041] The use of a preheat module in the bypass line also allows for faster heat-up times for the cooling circuit. Because the media is already preheated before entering the main cooling circuit, the system reaches the desired operating temperature more quickly. This is particularly advantageous when starting the system cold or when recovering after a shutdown.

[0042] Another advantage is the possibility of temperature control: the pre-heating module can be equipped with a control valve that controls the flow rate or temperature of the pre-heated cooling medium, allowing the operating temperature of the system to be precisely controlled and adapted to specific requirements.

[0043] In summary, the bypass line with pre-heat module provides increased thermal efficiency, reduced condensation issues, faster heat up times, and precise temperature control. This configuration can result in optimized performance and mass efficiency of the cooling system, ensuring a more stable operating environment.

[0044] According to one embodiment, the fuel cell comprises a fuel cell stack having a media module, said media module comprising a bypass line and a pump.

[0045] According to one embodiment, the fuel cell is a fuel cell stack having at least one base plate, the base plate comprising a bypass line and a pump.

[0046] According to one embodiment, the refrigerant comprises methanol and / or ethanol.

[0047] Methanol and ethanol have various advantages as refrigerants: these two substances have relatively low boiling points, which means that they can evaporate at relatively high temperatures, thus allowing for better cooling.

[0048] Another advantage is the lower viscosity of methanol compared to water, which promotes flow and reduces pump energy consumption.

[0049] Furthermore, methanol and ethanol have a high enthalpy of vaporization, which allows for very low mass flows in the system, thereby reducing pressure losses, which means that lines and pumps can be smaller in size than for liquid cooling, resulting in a reduction in the weight of the system.

[0050] According to one aspect, an aircraft is provided with a fuel cell system of the above-described configuration.

[0051] According to one embodiment, the fuel cell system further comprises an ejector in fluid communication with the first portion of the accumulator, the second portion of the accumulator, the pump, the condenser, and the fuel cell, and adapted to mix the refrigerant in the gas phase from the accumulator with the subcooled refrigerant from the condenser, and supply the refrigerant to the fuel cell.

[0052] The main function of the ejector is to mix the refrigerant in the vapor phase from the first part of the accumulator with the subcooled refrigerant from the condenser and then supply the refrigerant to the fuel cell. The ejector uses the pressure difference between the two fluids to draw in the refrigerant in the vapor phase and mix it with the subcooled refrigerant.

[0053] The ejector plays a key role in delivering the gas phase refrigerant mixed with the sub-cooled refrigerant in the system, allowing for efficient use of the available pressure differential and ensuring uniform distribution of the refrigerant to cool the fuel cells.

[0054] Another benefit is the creation of gas bubbles within the refrigerant system, which are beneficial for countering superheating of the refrigerant: the gas bubbles help reduce surface tension, resulting in more effective heat exchange at higher temperatures.

[0055] According to one embodiment, the fuel cell system further comprises a thermally conductive element between the coolant inlet and the coolant outlet, the thermally conductive element adapted to transfer heat from the coolant outlet to the coolant inlet.

[0056] The main advantage of the thermally conductive element between the coolant inlet and the coolant outlet is the efficient heat transfer. The use of the thermally conductive element allows the heat present at the coolant outlet to be effectively transferred to the coolant inlet, thereby improving the heat dissipation and stabilizing the temperature in the cooling circuit by pre-heating the cooling fluid.

[0057] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings, in which the illustrations are schematic and not drawn to scale, and in which the same reference signs represent the same or similar elements, in which: [Brief description of the drawings]

[0058] [Figure 1] FIG. 1 illustrates a fuel cell system. [Diagram 2] FIG. 1 shows another fuel cell system. [Diagram 3] FIG. 1 shows another fuel cell system. [Figure 4] FIG. 1 illustrates an aircraft. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0059] 1 shows a fuel cell system 10 with a two-phase cooling system. The system comprises at least one fuel cell 12 having a coolant inlet 14 and a coolant outlet 16. A bypass connection 28 between the coolant inlet and the coolant outlet allows for the flow of coolant.

[0060] The system 10 also includes an accumulator 18 in fluid communication with the fuel cell 12. The accumulator is designed to receive the coolant exiting the fuel cell and to provide pressure to the cooling system.

[0061] Additionally, the system 10 includes a condenser 26 in fluid communication with the accumulator 18. The condenser condenses and sub-cools the refrigerant to ensure efficient cooling.

[0062] The system also has a bypass line 28 equipped with a pump 30. The refrigerant inlet 14 is connected to the refrigerant outlet 16 via said bypass line.

[0063] Additionally, the illustrated example includes a condensate pump 32 adapted to transport the refrigerant 20 .

[0064] The bypass line 28 allows for a specific diversion of the normal cooling circuit, allowing the warm cooling medium to be led directly to the cold cooling medium.

[0065] This allows for rapid and efficient heat transfer to effectively reduce the temperature of the cooling medium. The bypass line 28 can be used in various applications to allow for specific cooling or specific temperature control, eliminating the need for a preheater / recuperator.

[0066] 2 shows another embodiment of a fuel cell system 10 with an efficient two-phase cooling system. The system includes at least one fuel cell 12 having a coolant inlet 14 and a coolant outlet 16. The connection between the coolant inlet and the coolant outlet allows for the flow of coolant.

[0067] The system 10 also includes an accumulator 18 in fluid communication with the fuel cell 12. The accumulator is designed to receive the coolant exiting the fuel cell. The coolant is maintained in a gas phase in a first portion 22 of the accumulator and in a liquid phase in a second portion 24.

[0068] Additionally, the system 10 includes a condenser 26 in fluid communication with the accumulator 18. The condenser condenses and sub-cools the refrigerant to ensure efficient cooling.

[0069] The system also has a bypass line 28 equipped with a pump 30. The refrigerant inlet 14 is connected to the refrigerant outlet 16 via said bypass line.

[0070] Additionally, the illustrated example includes a condensate pump 32 adapted to transport the refrigerant 20 .

[0071] The bypass line 28 allows for a specific diversion of the normal cooling circuit, allowing the warm cooling medium to be led directly to the cold cooling medium.

[0072] This allows for rapid and efficient heat transfer to effectively reduce the temperature of the cooling medium. The bypass line 28 can be used in various applications to allow for specific cooling or specific temperature control, eliminating the need for a preheater / recuperator.

[0073] The main difference compared to the embodiment of FIG. 1 is that an accumulator is connected to the return line, so that the gas phase can mix with the liquid phase.

[0074] 3 illustrates another embodiment of a fuel cell system 10 with an efficient two-phase cooling system. The fuel cell system 10 also includes at least one fuel cell 12 having a coolant inlet 14 and a coolant outlet 16.

[0075] The main differences compared to the embodiment according to figures 1 and 2 are the phase separation in the accumulator and the specific injection of the vapour phase at the inlet of the fuel cell by means of an ejector.

[0076] FIG. 4 shows an aircraft 100 equipped with the fuel cell system 10 described above.

[0077] It should further be noted that "comprising" or "having" does not exclude other elements or steps, and that the singular forms "a", "an", and "one" do 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]

[0078] 10. Fuel Cell System 12 Fuel Cell 14 Refrigerant inlet 16 Refrigerant outlet 18 Accumulator 20 Refrigerants 22 First Part 24 Second Part 26 Condenser 28 Bypass Line 30 Pump 32 Condensate Pump 100 aircraft

Claims

1. A fuel cell system (10) having a two-phase cooling system, comprising: at least one fuel cell (12) having a coolant inlet (14) and a coolant outlet (16); a condenser (26) adapted to condense and subcool the refrigerant (20); a condensate pump (32) adapted to transport the subcooled refrigerant (20); Bypass line (28) and Equipped with the bypass line (28) is in fluid communication with the coolant outlet (16) and the coolant inlet (14) and is adapted to return the coolant to the fuel cell (12) by a pump (30); A fuel cell system (10).

2. and an accumulator (18) in which phase separation into a gas phase and a liquid phase occurs, the accumulator (18) being in fluid communication with the fuel cell (12) and adapted to contain a coolant (20) exiting the fuel cell in a first portion (22) in gas phase and in a second portion (24) in liquid phase. The fuel cell system (10) of claim 1.

3. The fuel cell system (10) of claim 1 or 2, wherein the bypass line (28) comprises a control valve.

4. The fuel cell system (10) of any one of claims 1 to 3, wherein the bypass line (28) comprises a pre-heating module.

5. The fuel cell system (10) of any one of claims 1 to 4, wherein the fuel cell (12) comprises a fuel cell stack having a media module, the media module comprising the bypass line (28) and the pump (30).

6. The fuel cell system (10) of any one of claims 1 to 5, wherein the fuel cell (12) is a fuel cell stack having at least one base plate, the base plate comprising the bypass line (28) and the pump (30).

7. The fuel cell system (10) of any one of claims 1 to 6, wherein the coolant (20) comprises methanol and / or ethanol.

8. An aircraft (100) comprising a fuel cell system (10) according to any one of the preceding claims.

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