Fuel cell system having two-phase cooling with ejector

Abstract

To provide a fuel cell system having two-phase cooling with an ejector.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); a condenser (26) designed to condense and to supercool a coolant (20); a pump (28) designed to pump the supercooled coolant (20); and at least one ejector (30). The ejector (30) is fluidically connected to the coolant outlet (16), the pump (28), the condenser (26) and the fuel cell (12), and designed to supply the coolant to the fuel cell (12).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present description relates generally to the technical field of aeronautical mobility, and in particular to a fuel cell system having two-phase cooling using an ejector and an aircraft having such a fuel cell system. [Background technology]

[0002] Fuel cells are one possible solution to generate power in aircraft drive systems or emission-free on-board power supplies (APU = auxiliary power unit) without unwanted emissions. Polymer electrolyte membrane fuel cells (PEMFC) generate energy and power through the electrochemical reaction of hydrogen and oxygen, which produces water. This reaction generates heat, which must be released. In commercial fuel cell stacks, this is done by liquid cooling.

[0003] One possible alternative with a large potential for reducing the weight of the system is to replace the liquid cooling by two-phase cooling. In two-phase cooling, the latent heat of vaporization is used to remove a large amount of heat from the fuel cell. Furthermore, a high 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 surrounding environment. It is necessary that the coolant is supercooled, i.e. in a liquid state (avoiding cavitation of the pump), so that it can be pumped to the fuel cell. In this document, supercooling refers to the temperature range below the boiling point of the coolant. The supercooled coolant is then sent to the fuel cell, where the temperature of the coolant is increased and the coolant starts to boil. The presence of such a steep temperature gradient in the intake area can damage the fuel cell. Too low a temperature in this region can lead to the condensation of water in the gas channels (flooding). To overcome this and other risks, a preheater or recuperator is usually inserted upstream of the evaporator (fuel cell). However, this preheater / recuperator can be large and can reduce the weight advantage of two-phase cooling. Summary of the Invention [Problem to be solved by the invention]

[0004] It may 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 can be found in the dependent claims and the following description.

[0006] According to one embodiment, the fuel cell system includes a two-phase cooling system.Further, the fuel cell system includes at least one fuel cell having a coolant inlet and a coolant outlet.

[0007] According to one embodiment, the fuel cell system also includes an accumulator, where the phase separation into gas and liquid phases occurs, the accumulator being fluidly connected to the fuel cell and designed to receive the coolant exiting the fuel cell in liquid phase in a first portion and in gas phase in a second portion, and a condenser is also included, where the condenser is fluidly connected to the accumulator and designed to condense and subcool the coolant.

[0008] The fuel cell system also has a pump, which is designed to pump the subcooled refrigerant. The fuel cell system also has an ejector. The ejector inlet (propulsion jet) can be connected to the condenser via the pump. The ejector inlet (suction side) can be connected either to the refrigerant outlet of the fuel cell or to the first part of the accumulator. The ejector inlet can also be connected to the second part of the accumulator.

[0009] In the sense of the present invention, a fuel cell system is a technological unit consisting of several components and serving to convert chemical energy into electrical energy by electrochemical reactions. A fuel cell system generally comprises one or more fuel cells, which function as electrochemical cells and are the main components of the system. Furthermore, the system comprises further components such as a fuel supply mechanism, an oxidant supply mechanism, an electrolyte, electrodes, catalysts and electrical connections.

[0010] The fuel cell system uses a chemical reaction of a fuel and an oxidant (typically hydrogen and oxygen) to generate electrochemical power, where water is produced as the only product, making the fuel cell system considered an environmentally friendly energy source. The generated electrical energy can then be used to power electrical devices, vehicles, or generate power for a variety of applications.

[0011] In the sense of the present invention, a two-phase cooling system is a cooling solution that aims to efficiently dissipate large amounts of heat by using a phase transition from liquid to vapor. Two-phase cooling systems are often used in situations where traditional single-phase cooling systems reach their limits and are unable to dissipate heat adequately.

[0012] 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 gaseous state. The resulting vapor then absorbs a large amount of heat.

[0013] The phase change from liquid to vapor allows for more efficient heat transfer, which improves cooling performance and makes heat dissipation more efficient.

[0014] A two-phase cooling system typically consists of an evaporator where the refrigerant absorbs heat and vaporizes, and a condenser where the vapor is condensed again, releasing heat. The condensate is then returned to the evaporator to continue the cooling circuit.

[0015] A coolant inlet in the sense of the present invention is an opening or connection of the fuel cell of the cooling system through which a cooling medium, in this case a cooling liquid, is introduced into the system. The coolant inlet allows the cooling liquid to flow in a controlled manner into the corresponding area or component that must be cooled.

[0016] In the sense of the present invention, a coolant outlet is an opening or connection in a cooling system through which a cooling medium, in this case a coolant, leaves the system. The coolant outlet allows the controlled exit of heated coolant from the corresponding area or component, cooling said area or component and ensuring heat exchange.

[0017] In the sense of the present invention, an accumulator is a component or device used to effect phase separation between a gas phase and a liquid phase, for example by gravity.

[0018] In an 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) collects at the bottom of the accumulator and the lighter medium (usually gas) remains in the upper region of the accumulator.

[0019] One possible accumulator is the thermally controlled accumulator (HCA). Such an accumulator contains a volume filled with vapor and liquid of a single working fluid without a diaphragm. The pressure in the HCA is controlled by a heater.

[0020] A further possible accumulator is the Pressure Controlled Accumulator (PCA). Such an accumulator contains a volume that is mechanically pressurized by a piston or gas pressure (using a bladder or diaphragm).

[0021] The accumulator is constructed to allow for efficient separation and accumulation of the two phases. This may be achieved through the use of gravity separators, partitions, funnels or other specialized structures. The objective is to ensure that the gas and liquid are separated and accumulate in separate areas for effective use or further processing.

[0022] In the sense of the present invention, a condenser is a component or device used to condense a vapor or gas into a liquid phase. The condenser is fluidly connected to an accumulator, which means that a refrigerant can circulate between these two components.

[0023] The primary function of a condenser is to condense the refrigerant by causing it to give up heat, thereby transitioning 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. As a result of this cooling, the vapor or gas molecules contract and condense, accumulating in liquid form.

[0024] Furthermore, the condenser is designed to be able to subcool the refrigerant, meaning that the temperature of the condensed refrigerant is lower than its saturation point, i.e. the temperature at which it would normally condense. This allows the refrigerant to absorb more heat before evaporating or being transported again. Subcooling is important to avoid cavitation of the pump.

[0025] In the sense of the present invention, a pump is an equipment or device used to pump or move a liquid or gas from one place to another. In this case, the pump is specifically designed for pumping subcooled refrigerant.

[0026] 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 gradient or flow gradient to force the refrigerant from an area of ​​lower pressure to an area of ​​higher pressure. This is done by transferring kinetic energy or changing the volume of the pump to draw in and force the refrigerant in the desired direction.

[0027] In the specific case of sub-cooled 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 sub-cooled refrigerant and generate sufficient pressure to pump the refrigerant throughout the system. This allows for continuous circulation of the sub-cooled refrigerant to maintain the desired cooling action.

[0028] There are different types of pumps suitable for different applications and fluids, e.g., centrifugal pumps, piston pumps or screw pumps. The selection of an appropriate pump depends on the specific requirements of the system, such as flow volume, pressure range and type of refrigerant.

[0029] In the sense of the present invention, an ejector is a device used to mix and transport liquids or gases by using the pressure difference between two fluids, where the ejector is fluidly connected to various components of the system, including the first part of the accumulator, the second part of the accumulator, the pump, the condenser, and the fuel cell.

[0030] The main function of the ejector is to mix the vapor refrigerant from the first part of the accumulator with the subcooled refrigerant from the condenser and then feed it to the fuel cell. The ejector uses the pressure difference between the two fluids to draw in the vapor refrigerant and mix it with the subcooled refrigerant.

[0031] The ejector works according to the principle of the propulsive jet effect. The subcooled refrigerant is forced by a pump into the ejector, where it is accelerated in a nozzle. This creates a low-pressure area in the ejector, which draws in the refrigerant in gas phase from the first part of the accumulator. The two flows then mix with each other in the ejector, creating a homogeneous mixture of gas and subcooled refrigerant.

[0032] This mixture is delivered to the fuel cell and ensures its cooling there. By mixing the refrigerant in the gas phase with the subcooled refrigerant, a preheating of the refrigerant is achieved, compensating for the subcooling of the refrigerant at the refrigerant inlet of the fuel cell.

[0033] The ejector plays a key role in supplying the gas phase coolant to mix with the subcooled coolant in the system, allowing efficient use of the existing pressure differential and ensuring uniform distribution of the coolant to cool the fuel cells.

[0034] A further advantage is the provision of gas bubbles at the entrance to the fuel cell coolant inlet, which are advantageous for countering the boiling retardation of the coolant. The gas bubbles help reduce surface tension, resulting in more effective heat exchange at higher temperatures.

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

[0036] A Venturi tube is a special type of tube section that has a cross-sectional surface that narrows in the middle: a wider entrance, a narrowed neck, and a wider exit.

[0037] The mode of operation of an ejector in the form of a Venturi tube is based on Bernoulli's principle and the pressure difference created by the change in the velocity of a fluid in the Venturi tube. When a fluid, e.g. a gas or liquid, flows through the inlet of the ejector, it passes through the narrowed neck of the Venturi tube. In this narrowed region, the velocity of the fluid increases and the pressure decreases.

[0038] The pressure difference between the inlet and the neck of the ejector creates a suction effect, which causes a second fluid, either in a different line or in another container, to be drawn into the ejector. The second fluid then mixes with the first fluid at the outlet of the ejector and can be transported or used together.

[0039] According to one embodiment, the fuel cell is a fuel cell stack having at least one base plate, the base plate including an ejector.

[0040] The combination of these two components provides weight savings since a separate ejector and additional connection lines may be eliminated. Conventional systems typically require a separate ejector that is externally connected to the fuel cell stack. These additional components increase the overall weight and space requirements of the system.

[0041] The integration of the ejector into the base plate of the fuel cell stack reduces weight by eliminating the need for additional external components. The base plate serves as a structural element of the fuel cell stack and as an ejector. This results in weight and space savings, which is particularly advantageous in applications where installation space is limited, such as in aeronautical and space travel or mobile object applications.

[0042] The weight savings from incorporating the ejector into the base plate of the fuel cell stack contributes to the efficiency of the system by reducing the overall weight while enabling a compact design. This benefit can lead to improved performance, greater energy efficiency and a wider range of use of the fuel cell system.

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

[0044] Methanol and ethanol offer different advantages as refrigerants: they have relatively low boiling points, which allow them to evaporate at high temperatures, thus enabling enhanced cooling. The essential advantages of alcohols are their low freezing points and high enthalpies of vaporization.

[0045] A further advantage is the lower viscosity of methanol compared to water, which results in improved flow and reduced pump energy consumption.

[0046] Furthermore, methanol and ethanol have high enthalpies of vaporization. As a result, very low mass flows can be achieved in the system, which reduces pressure losses. As a result, lines and pumps can be smaller in size than in the case of liquid cooling, which results in a reduction in the weight of the system.

[0047] According to one embodiment, the at least one fuel cell is a fuel cell stack having a media module, the media module including an ejector.

[0048] According to one embodiment, the fuel cell system also includes a bypass line having a pitot tube insert.

[0049] Here, the advantage of the pitot tube insert can be seen in the targeted extraction of the gas phase by the annular flow: near the wall, the gas phase has a higher enthalpy than the liquid phase, which can more effectively reduce the subcooling at the inlet of the fuel cell.

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

[0051] According to one embodiment, the fuel cell system also includes a bypass line having a pump, and the coolant inlet is fluidly connected to the coolant outlet via the bypass line, allowing the warm coolant to be conducted directly to the cold coolant, selectively providing a diversion from the normal cooling circuit.

[0052] Thus, rapid and efficient heat transfer can be enabled, effectively increasing the temperature of the cooling medium. The bypass line can be used in various applications to enable targeted cooling or specific temperature control, and to eliminate the need for a preheater / recuperator.

[0053] According to one embodiment, the fuel cell system also has a thermally conductive element between the coolant inlet and the coolant outlet, the thermally conductive element designed to transfer heat from the coolant outlet to the coolant inlet.

[0054] The main advantage of placing a thermally conductive element between the coolant inlet and the coolant outlet is the efficient heat transfer. The use of a thermally conductive element can effectively transfer the heat accumulated at the coolant outlet to the coolant inlet. As a result, the coolant is pre-heated, improving heat dissipation and stabilizing the temperature in the cooling circuit.

[0055] In the following, exemplary embodiments of the invention will be described in more detail with reference to the accompanying drawings, in which the figures are schematic and not drawn to scale, and in which the same reference signs represent the same or similar elements. [Brief description of the drawings]

[0056] [Figure 1] 1 shows a fuel cell system. [Diagram 2] 1 shows a further fuel cell system; [Diagram 3] 1 shows a further fuel cell system; [Figure 4] The pitot tube insert is shown. [Diagram 5] 1 shows a further fuel cell system having a pitot tube insert. [Figure 6] Shows aircraft. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] 1 shows a fuel cell system 10 with an efficient two-phase cooling system. The fuel cell system 10 includes at least one fuel cell 12 having a coolant inlet 14 and a coolant outlet 16.

[0058] The central component of the refrigeration system is the accumulator 18, which acts as a means to counteract the expansion of the refrigerant and provides pressurization to the refrigeration system.

[0059] To further process the refrigerant, a condenser 26 is incorporated into the system 10. The condenser 26 is fluidly connected to the accumulator 18 and is designed to condense and sub-cool the refrigerant 20, thereby efficiently removing heat from the refrigerant.

[0060] To ensure the flow of the sub-cooled refrigerant 20, a pump 28 is used. The pump 28 is designed to pump the sub-cooled refrigerant 20 and maintain the circuit.

[0061] A further important element of the two-phase cooling system is the ejector 30. The ejector 30 is fluidly connected to the inlet 14 and outlet 16 of the fuel cell 12. The purpose of the ejector is to mix the refrigerant in the vapor phase from the outlet 16 with the subcooled refrigerant from the condenser 26 and then supply it to the fuel cell 12 through the inlet 14.

[0062] With these components working together, the two-phase cooling system provides efficient cooling of the fuel cell 12. Reduced sub-cooling at the inlet 14 ensures optimal temperature control, thus contributing to the performance and durability of the fuel cell system.

[0063] 2 shows a further 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.

[0064] The essential difference with respect to the embodiment of figure 1 is that an accumulator is connected to the return line, which allows the gas and liquid phases to be mixed, and also that an accumulator is connected to the return line, which allows the gas and liquid phases to be separated from each other.

[0065] 3 shows a fuel cell system 10 with an efficient two-phase cooling system. The fuel cell system 10 includes at least one fuel cell 12 having a coolant inlet 14 and a coolant outlet 16.

[0066] The central component of the cooling system is an accumulator 18, which allows phase separation between gas and liquid phases by gravity. The accumulator 18 is directly fluidly connected to the fuel cell 12 and ensures that the coolant 20 from the fuel cell is split into two parts, where the coolant 20 is in liquid phase in a first part 22 of the accumulator 18 and in gas phase in a second part 24.

[0067] To further process the refrigerant, a condenser 26 is incorporated into the system 10. The condenser 26 is fluidly connected to the accumulator 18 and is designed to condense and sub-cool the refrigerant 20, thereby efficiently removing heat from the refrigerant.

[0068] To ensure the flow of the sub-cooled refrigerant 20, a pump 28 is used. The pump 28 is designed to pump the sub-cooled refrigerant 20 and maintain the circuit.

[0069] A further important element of the two-phase cooling system is the ejector 30. The ejector 30 is fluidly connected to the first portion 22 of the accumulator 18, the second portion 24 of the accumulator 18, the pump 28, the condenser 26 and the fuel cell 12. The purpose of the ejector is to mix the refrigerant 20 in the vapor phase from the accumulator 18 with the subcooled refrigerant from the condenser 26 and then supply it to the fuel cell 12.

[0070] Through the cooperation of these components, the two-phase cooling system provides efficient cooling of the fuel cell 12. Optimal temperature control is ensured, thus contributing to the performance and durability of the fuel cell system 10.

[0071] The essential difference with respect to the embodiment of figures 1 and 2 is the phase separation in the accumulator and the targeted injection of the vapour phase at the inlet of the fuel cell by means of an ejector.

[0072] Figure 4 shows a pitot tube insert 32 in the coolant line, which allows targeted extraction of the gas phase by annular flow. Close to the wall, the gas phase has a higher enthalpy than the liquid phase, which can more effectively reduce subcooling at the inlet of the fuel cell.

[0073] FIG. 5 shows a further embodiment of the fuel cell system 10 having a pitot tube insert 32 in the coolant line.

[0074] 6 shows an aircraft 100 having the fuel cell system 10 described above, which may eliminate the need for a preheater / recuperator, providing advantageous weight savings.

[0075] It should further be noted that "comprise" or "have" does not exclude other elements or steps, and "a" or "one" does not exclude a plurality. It should further be noted that features or steps described with reference to one of the above exemplary embodiments can also be used in combination with other features or steps of other exemplary embodiments described above. Reference signs in the claims should not be considered as limiting. [Explanation of symbols]

[0076] 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 Pump 30 Ejector 32 Pitot tube insert 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) designed to condense and subcool the refrigerant (20); a pump (28) designed to pump the subcooled refrigerant (20); At least one ejector (30); the ejector (30) is fluidly connected to the coolant outlet (16), the pump (28), the condenser (26) and the fuel cell (12), and is designed to supply the coolant to the fuel cell (12).

2. 2. The fuel cell system (10) of claim 1, further comprising an accumulator (18), wherein phase separation into gas and liquid phases occurs in the accumulator (18), the accumulator (18) is fluidly connected to the fuel cell (12) and designed to receive a refrigerant (20) exiting the fuel cell (12) in a liquid phase in a first portion (22) and in a gas phase in a second portion (24), and the ejector (30) is designed to mix the refrigerant (20) in the gas phase from the accumulator (18) with the subcooled refrigerant from the condenser (26) and supply it to the fuel cell (12).

3. The fuel cell system (10) of claim 1 or 2, wherein the ejector (30) comprises a Venturi tube.

4. The fuel cell system (10) of any one of claims 1 to 3, wherein the at least one fuel cell (12) is a fuel cell stack having at least one base plate, and the base plate includes the ejector (30).

5. The fuel cell system (10) of any one of claims 1 to 4, wherein the coolant (20) comprises methanol and / or ethanol.

6. The fuel cell system (10) of any one of claims 1 to 5, wherein the at least one fuel cell (12) is a fuel cell stack having a media module, the media module including the ejector (30).

7. The fuel cell system (10) of any one of claims 1 to 6, also including a bypass line having a pitot tube insert (32).

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

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