Fuel cell system including heat pipe

Abstract

To provide a fuel cell system including a heat pipe.SOLUTION: There is presented a fuel cell system (10) having a two-phase cooling system. The fuel cell system (10) includes: at least one fuel cell (12) with a coolant inlet (14) and a coolant outlet (16); an accumulator (18) that is in fluid connection with the fuel cell (12) and that is adapted to contain a coolant (20) which flows out of the fuel cell in a liquid phase in a first portion (22) and in a gas phase in a second portion (24); a condenser (26) that is in fluid connection with the accumulator(18) and that is adapted to condense and supercool the coolant; and a thermally conductive element (28) that is provided between the coolant inlet (14) and the coolant outlet (16), the thermally conductive element (28) being adapted to transfer heat from the coolant outlet to the coolant inlet.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present description relates generally to the technical field of aviation, and in particular to a fuel cell system having two-phase cooling with a thermal element, 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 presented. The fuel cell system comprises at least one fuel cell having a coolant inlet and a coolant outlet. According to one embodiment, a thermally conductive element is provided between the coolant inlet and the coolant outlet, the thermally conductive element being adapted to transfer heat from the coolant outlet to the coolant inlet.

[0007] 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 includes further components such as a fuel supply, an oxidant supply, an electrolyte, electrodes, a catalyst, and electrical connections.

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

[0009] Two-phase cooling systems are cooling solutions intended to efficiently dissipate large amounts of heat by utilizing a liquid-to-vapor phase transition. They are 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 efficient heat transfer, which results 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 electronics, processors, fuel cells, engines, and other thermally demanding systems where efficient heat dissipation is critical.

[0014] In the context of this invention, 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.

[0015] 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.

[0016] Furthermore, the condenser is adapted to be able to subcool the refrigerant. Subcooling means that the temperature of the condensed refrigerant is below its saturation point, i.e., lower than the temperature at which it would normally condense. This allows the refrigerant to absorb more heat before it is evaporated or pumped away again. Subcooling is important to avoid cavitation and ensure that the refrigerant maintains its condensed form.

[0017] The thermally conductive element between the coolant inlet and the coolant outlet is a component used to transfer heat from a hotter point to a colder point in the cooling circuit. This configuration is defined below and its advantages are presented.

[0018] The thermally conductive element is a connection or structure placed between the coolant inlet and the coolant outlet that has good thermal conductivity, and may be made of materials such as metal or thermally conductive plastic.

[0019] 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.

[0020] Another advantage is the reduction of heat loss: the use of thermally conductive elements means that heat is transferred directly from one point to another, rather than being lost unnecessarily. This improves the efficiency of the cooling circuit and reduces energy consumption.

[0021] Another positive effect of this configuration is an improved temperature distribution within the system: efficient heat transfer between the coolant inlet and outlet provides a more uniform temperature distribution within the cooling circuit, which avoids hot spots and ensures better cooling of the relevant components.

[0022] Furthermore, the thermally conductive element between the coolant inlet and the coolant outlet allows for more precise control of the system temperature. The specific heat transfer allows for control and optimization of the temperature at the desired location due to the properties of the thermally conductive element itself as a passive element. This is particularly advantageous in situations where precise temperature control is required to optimize the operation of the system.

[0023] In summary, the use of thermally conductive elements between the coolant inlet and outlet allows for efficient heat transfer, reduced heat loss, improved temperature distribution, and precise passive temperature control, which can improve the performance and reliability of the cooling circuit, resulting in a stable operating environment and extending the useful life of the associated components.

[0024] According to one embodiment, the thermally conductive element comprises copper.

[0025] One advantage of using copper as the thermally conductive element between the refrigerant inlet and the refrigerant outlet is its high thermal conductivity. Copper is an excellent thermal conductor, thus allowing for the efficient transfer of thermal energy from one point to another. This allows the thermally conductive element to improve heat dissipation and help ensure the thermal stability of the system. Furthermore, copper is a robust and durable material suitable for use in cooling systems. Copper is corrosion resistant, which increases the useful life of the thermally conductive element. Thus, the use of copper can improve the efficiency and reliability of the cooling system and contribute to effective heat dissipation.

[0026] According to one embodiment, the thermally conductive element comprises aluminum.

[0027] One advantage of using aluminum as a thermally conductive element between the coolant inlet and outlet is its excellent thermal conductivity. Aluminum is an efficient conductor of heat, allowing for the efficient transfer of thermal energy from one point to another. This allows the thermally conductive element to improve heat dissipation and help maintain the system's optimal operating temperature.

[0028] Another advantage of aluminium is its lower density compared to copper, which means that its use as a thermally conductive element contributes to a lighter overall system weight, which can be particularly advantageous in applications requiring high mobility or low weight, for example in aerospace and vehicle manufacturing.

[0029] Additionally, aluminum is corrosion resistant, which extends the useful life of the thermally conductive elements, and is cheaper than copper, providing a cost-effective solution.

[0030] The use of aluminum as a thermally conductive element can therefore improve the efficiency of the cooling system, allow for weight reduction and contribute to reliable heat dissipation.

[0031] According to one embodiment, the thermally conductive element comprises a metal fiber composite.

[0032] One advantage of using metal fiber composites as the thermally conductive element between the coolant inlet and outlet is that they combine high strength with good thermal conductivity. Metal fiber composites consist of a metal matrix reinforced with embedded fibers, which increases the mechanical stability and stiffness of the thermally conductive element.

[0033] The use of metal fiber composites allows for efficient heat transfer between the coolant outlet and the coolant inlet. The fibers of the composite act as heat conduction channels, allowing for rapid and uniform distribution of thermal energy. At the same time, the metal in the matrix provides high thermal conductivity, dissipating heat effectively.

[0034] Another advantage of metal fiber composites is their low density compared to pure metals, which means that their use contributes to a lighter system, which is particularly advantageous in applications that require high maneuverability or low weight.

[0035] Metal fiber composites can also be highly corrosion resistant and have high mechanical strength, which increases the service life of the thermally conductive element.

[0036] The use of metal fiber composites as thermally conductive elements allows for efficient heat transfer, reduced weight, and improved mechanical stability of the system.

[0037] According to one embodiment, the thermally conductive element includes fins. One advantage of using a thermally conductive element with fins between the coolant inlet and the coolant outlet is that the surface area available for heat transfer is increased. The fins serve to increase the contact area between the element and the cooling medium, resulting in more efficient heat dissipation.

[0038] The placement of fins on a thermally conductive element allows for a more efficient transfer of thermal energy from one side (coolant outlet) to the other (coolant inlet). The fins increase the thermal conductivity of the element, improving heat exchange with the surrounding medium, be it air or liquid.

[0039] Another advantage of the fins of the thermally conductive element is that they improve the hydrodynamic behavior of the cooling medium: the fins create channels or vortices, which improve the mixing of the coolant and therefore make the heat transfer more efficient.

[0040] The use of fins on thermally conductive elements provides better cooling performance and more effective heat dissipation, allowing for better control of the system temperature and improving the performance and life of components.

[0041] Additionally, the fins on the thermally conductive element allow for a more compact design of the system, as they increase the surface area for heat transfer without the need for additional external heat sinks or heat exchangers.

[0042] Overall, the fins on the thermally conductive element provide improved heat transfer, more efficient cooling performance, a more compact design, and better temperature control of the system.

[0043] According to one embodiment, the thermally conductive element is a heat pipe.

[0044] One advantage of using a thermally conductive element in the form of a heat pipe between the coolant inlet and outlet is efficient heat transfer and improved temperature control.

[0045] A heat pipe consists of a closed pipe that contains a specific heat transfer fluid inside. When heat is applied to one end of the heat pipe, the liquid evaporates to produce steam. Due to the temperature difference, the steam travels through the pipe to a cooler location where it condenses. The condensed steam releases heat and turns back into a liquid, which is carried back to the hot end by the capillary forces of the inner wall of the heat pipe.

[0046] The use of heat pipes as the thermally conductive element allows for very efficient heat transfer due to the phase change of the heat transfer fluid, which allows for quick and efficient transfer of heat from the hottest location (coolant outlet) to the coldest location (coolant inlet).

[0047] Additionally, heat pipes provide uniform heat distribution over their entire length, which ensures uniform cooling of components within the system and avoids hot spots.

[0048] Heat pipes are also flexible and can be used in a variety of spatial configurations, allowing them to be adapted to the specific requirements of the fuel cell system, providing optimal heat transfer and temperature control.

[0049] Overall, the use of heat pipes as thermally conductive elements allows for efficient heat transfer, uniform cooling, and improved temperature control in fuel cell systems.

[0050] According to one embodiment, the refrigerant comprises at least one of methanol and ethanol.

[0051] Methanol and ethanol have various advantages as refrigerants: they have relatively low boiling points, which means that they can evaporate at relatively high temperatures, thus allowing for better cooling.

[0052] Another advantage is the lower viscosity of methanol compared to water, which promotes flow and reduces pump energy consumption.

[0053] 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.

[0054] According to one embodiment, the at least one fuel cell is a fuel cell stack having at least one base plate, the base plate comprising a thermally conductive element.

[0055] According to one aspect, an aircraft is provided with a fuel cell system of the above-described configuration.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] According to one embodiment, the fuel cell system further comprises a bypass line comprising a pump, the coolant inlet being in fluid communication with the coolant outlet via the bypass line.

[0061] The bypass line allows a specific diversion of the normal cooling circuit to be achieved and allows the hot cooling medium to be led directly to the cold cooling medium.

[0062] This allows for rapid and efficient heat transfer to effectively reduce 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.

[0063] 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]

[0064] [Figure 1] FIG. 1 illustrates a fuel cell system. [Diagram 2] FIG. 1 illustrates an aircraft. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] 1 shows a fuel cell system 10 with a two-phase cooling system. The system 10 includes at least one fuel cell 12 having a coolant inlet 14 and a coolant outlet 16. A connection between the coolant inlet and the coolant outlet allows for the flow of coolant.

[0066] 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 liquid phase in a first portion 22 of the accumulator 18 and in a gas phase in a second portion 24.

[0067] Additionally, there is a condenser 26 in fluid communication with the accumulator 18. The condenser 26 condenses and sub-cools the refrigerant to prevent cavitation in the refrigerant pump.

[0068] A thermally conductive element 28 is provided between the refrigerant inlet 14 and the refrigerant outlet 16 , the thermally conductive element 28 being adapted to transfer heat from the refrigerant outlet 16 to the refrigerant inlet 14 .

[0069] FIG. 2 shows an aircraft 100 equipped with the fuel cell system 10 described above.

[0070] A positive effect of this configuration is improved temperature distribution within the fuel cell system 10. Efficient heat transfer between the coolant inlet 14 and the coolant outlet 16 provides a more uniform temperature distribution within the cooling circuit. This reduces subcooling at the inlet due to heating of the cooling fluid 20 by the thermal element 28. As a result, a preheater / recuperator can be eliminated, resulting in an advantageous weight reduction.

[0071] 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]

[0072] 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 Thermal elements 32 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; a heat conductive element (28) provided between the coolant inlet (14) and the coolant outlet (16), the heat conductive element (28) adapted to transfer heat from the coolant outlet (16) to the coolant inlet (14); A fuel cell system (10) comprising:

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 liquid phase and in a second portion (24) in gas phase. The fuel cell system (10) of claim 1.

3. The fuel cell system (10) of claim 1 or 2, wherein the thermally conductive element (28) comprises copper.

4. The fuel cell system (10) of any one of claims 1 to 3, wherein the thermally conductive element (28) comprises aluminum.

5. The fuel cell system (10) of any one of claims 1 to 4, wherein the thermally conductive element (28) comprises a metal fiber composite.

6. The fuel cell system (10) of any one of claims 1 to 5, wherein the thermally conductive element (28) comprises a fin.

7. The fuel cell system (10) of any one of claims 1 to 6, wherein the thermally conductive element (28) is a heat pipe.

8. The fuel cell system (10) of any one of claims 1 to 7, wherein the fuel cell (12) is a fuel cell stack having at least one base plate, the base plate comprising the thermally conductive element (28).

9. The fuel cell system (10) according to any one of the preceding claims, wherein the at least one fuel cell (12) is a fuel cell stack having a media module, the media module comprising the thermally conductive element (28).

10. The fuel cell system (10) of any one of the preceding claims, wherein the coolant (20) comprises at least one of methanol and ethanol.

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

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