Thermal management air duct for airborne fuel cell systems

Abstract

The present invention relates to an aircraft comprising a cooling system integrated into the fuselage (2), and at least one propeller (16) driven by an electric motor suitable for propelling the aircraft, the cooling system comprising: - at least one cooling duct (13, 17) (or air duct (13, 17)), installed within the fuselage (2) of the aircraft and provided with an air inlet and outlet, the cooling duct (13) being designed to allow air to circulate between the air inlet and the air outlet; - at least one heat exchanger (12) positioned within the cooling duct (13), the heat exchanger being designed to transfer thermal energy to the air circulating in the cooling duct (13); wherein the air inlet is positioned in an overpressure zone generated by the air accelerated by the rotation of the propeller, and the air outlet is strategically positioned on an outer surface of the fuselage (2) over which the air flow accelerated by the rotation of the propeller passes, creating a zone of lower pressure facilitating the circulation of the air through the cooling duct (13), thus allowing heat to be efficiently dissipated through the heat exchanger.

Description

Description Title of the invention: Thermal management air duct for airborne fuel cell systems TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to an aircraft, more particularly an aircraft powered by electric motors powered by hydrogen fuel cells. The invention finds application in particular with electric aircraft and in particular airplanes implementing the invention described. STATE OF THE ART

[0002] Current aircraft, and more specifically airplanes, are powered by energy produced by burning kerosene. Civil aviation is a very large emitter of greenhouse gases, including carbon dioxide. It is imperative to develop alternative solutions that produce little or no greenhouse gases. Electrically powered aircraft are one solution to reduce greenhouse gases emitted by civil aviation. The use of batteries is not optimal given their weight. Electric propulsion powered by a hydrogen fuel cell is a possible solution to replace batteries.

[0003] Thermal management of the hydrogen fuel cell plays a key role in the proper functioning of the fuel cell. One of the challenges of electric propulsion powered by hydrogen fuel cells lies in the cooling of the fuel cell. Indeed, the efficiency of a fuel cell is higher than that of the internal combustion engine, but the heat generated by a fuel cell, for example a PEM (Proton Exchange Membrane) type, is significant. Fifty to 60% of the energy produced by the fuel cell is in the form of thermal energy and therefore in the form of heat to be evacuated. In addition, to operate efficiently, LT (Low Temperature) type fuel cells must be maintained at low temperatures, around 80°C.

[0004] Therefore, proper cooling of the fuel cell is crucial to ensure its proper use and to avoid reducing its lifespan.

[0005] Cooling systems are already planned for aviation. A heat transfer fluid (liquid or vapor) circulating between the device to be cooled and a heat exchanger can be provided. The heat exchanger is arranged in a cooling duct with an air inlet, also called a scoop, and an air outlet. Due to the movement of the aircraft, the scoop draws outside air which circulates in the duct. cooling, then passes through the heat exchanger. The heat exchanger transfers thermal energy from the heat transfer fluid to the air, which, once heated, is then discharged through the air outlet.

[0006] These cooling systems are designed in particular to cool the electronics on board aircraft.

[0007] However, to evacuate the thermal energy produced by a fuel cell used to power the electric motors enabling the propulsion of an aircraft, the dimensions of these heat exchange systems must be large. Indeed, the greater the quantity of heat to be evacuated, the greater the air flow rate to be provided. In order to have greater air flows, it is generally necessary to provide larger air inlets and air ducts sized for this purpose, which has negative consequences on aerodynamics, and more specifically on the aircraft drag and the mass of the aircraft to be moved.

[0008] Thus, current solutions for removing large quantities of heat, particularly from fuel cells, from an aircraft have significant disadvantages for aerodynamics, in terms of increased drag, aerodynamics and the weight of the aircraft.

[0009] The present invention aims to resolve, at least in part, these drawbacks. Summary of the invention

[0010] The present invention relates to an aircraft comprising a cooling system integrated into the fuselage, and at least one propeller driven by an electric motor adapted to propel the aircraft, the cooling system comprising - at least one cooling duct (or air duct), located within the fuselage of the aircraft, provided with an air inlet and an air outlet, the cooling duct being designed to allow the circulation of air between the air inlet and the air outlet; - at least one heat exchanger positioned within the cooling duct, the heat exchanger being adapted to transfer thermal energy to the air circulating in the cooling duct; wherein, the air inlet is positioned in an overpressure zone generated by the air accelerated by the rotation of the propeller, and the air outlet is strategically positioned on an external surface of the fuselage swept by the air flow accelerated by the rotation of the propeller, causing an area of ​​lower pressure facilitating the circulation of air through the cooling duct, thus allowing efficient dissipation of heat through the heat exchanger.

[0011] The aim of these arrangements is to ensure sufficient flow for cooling- dissement, while minimizing the impact of the exchanger on drag, via the reduction of the induced pressure drop. To achieve this, it is crucial that the available pressure difference is greater than the pressure drop generated by the heat exchanger and the cooling duct pressure drop itself. The greater this pressure difference, the less the exchanger pressure drop affects drag. The heat load is then removed with less impact on the aircraft's aerodynamics.

[0012] Aircraft means any vehicle capable of moving in the air, including an airplane, a helicopter, etc.

[0013] Fuselage refers to any type of main structure of an aircraft. For example, the fuselage can be composed of a monocoque or semi-monocoque structure, or a frame-and-spar structure. The fuselage can be of various shapes and sizes, suitable for different types of aircraft, including airliners, business jets, small propeller planes, military aircraft, drones, and helicopters, but is not limited to these categories.

[0014] A cooling system is any system that allows thermal energy to be evacuated by means of a heat exchanger.

[0015] Cooling duct or cooling pipe is a duct or pipe that allows fresh air from outside to circulate. Fresh air is taken in through a scoop, also called an air inlet, and is discharged through an air outlet. The cooling duct can be of any shape used in aeronautics for cooling ducts, but is not limited to existing shapes. The cooling duct can be made of carbon, metallic material, such as aluminum and its alloys, or any type of composite material (such as carbon fiber, fiberglass), technical plastics, polymers, technical ceramics.

[0016] The duct may have branches called splitters, these are separations in the duct allowing the flow to separate into two or more sub-flows upstream or downstream of the heat exchanger. These can be vertical, horizontal or in any other geometric configuration.

[0017] A heat exchanger is a device that allows the transfer of heat between two or more fluids of any kind, having different temperatures. The fluids may be separated by a solid wall to prevent them from mixing or coming into direct contact. One of the fluids, usually at a higher temperature, transfers heat to the other, thus causing the fluid in question to cool or heat up.

[0018] A two-phase heat exchanger (evaporator and condenser) is also a heat exchanger option. In the latter, one of the fluids gives off heat latent by changing phase (condensation or evaporation) while the other fluid heats up or cools down.

[0019] Heat exchangers can come in various shapes, sizes and materials.

[0020] The heat exchanger can, for example, cool a heat transfer fluid, liquid, vapor or gas, with the air circulating in the sheath. The heat exchanger can also directly extract thermal energy from the device to be cooled by pure thermal conduction or by using any passive device with capillary pumping or not such as heat pipes or vapor chambers. The heat exchanger can transfer thermal energy to the air in the sheath by any means, in particular by means of fins, pins, cones, broken fins, perforated fins, etc. and any section such as triangular, cylindrical, rectangular, etc.

[0021] By heat energy transfer to air, it is meant that heat is transferred to the air through contact with the heat exchanger.

[0022] A propeller, propeller, fan, or ducted blower suitable for propelling an aircraft means a propeller that allows the aircraft to move forward. This may be a traction or propulsion propeller. The propeller includes blades, otherwise known as vanes. This propeller may be powered by an electric motor.

[0023] An electric motor is any type of device that converts electrical energy into rotating mechanical energy. In this case, this electric motor is suitable for the propulsion of an aircraft.

[0024] By operating thruster, it is meant that the propeller produces sufficient force to impact the movement of the aircraft.

[0025] In the case of a propeller being a propeller, the pressure zones are distributed as follows: - Low pressure zone in front of the propeller: When the propeller turns, it creates a low pressure zone or low pressure zone in front of it. It is this low pressure that draws air towards the propeller. - Overpressure zone behind the propeller: As air is pushed backward by the propeller, its pressure increases. This creates a high pressure or overpressure zone behind the propeller. It is this expulsion of high-pressure air that generates the thrust that propels the aircraft forward.

[0026] In the case of a propeller being a shrouded electric fan, the pressure zones are distributed as follows: - Inlet depression zone: When air is drawn into the nacelle fairing, a low pressure or depression zone forms at the inlet of the duct. It is this depression that draws air into the system. - Overpressure zone in the duct: As the air is accelerated by the fan blades, its pressure increases. This creates a high pressure or overpressure zone in the duct. - Depression zone behind the fan: Just behind the fan blades, another depression zone forms. This is due to the acceleration of the air by the fan, which "pulls" the air behind it. - Overpressure zone at the outlet: The high pressure air in the duct is finally expelled at the rear of the EDF, creating another overpressure zone

[0027] Air inlet means any type of air inlet used in aeronautics for cooling systems, but is not limited to these types. For example, the air inlet may consist of several openings leading into the cooling duct.

[0028] The air intake is positioned at a location of high air pressure as the aircraft moves forward, for example at the nose of the aircraft or on one side, below or above the fuselage, or on a wing, on the wing root or at the base of the stabilizer, or on a pylon holding a nacelle, etc.

[0029] The air inlet can be arranged in an area downstream of the thruster, so that a portion of the air accelerated by the latter is directed into the cooling duct or more generally so that it benefits from an overpressure zone. This air inlet can be located directly in the air flow or on an overpressure zone, or so that part of the air flow is diverted by a dedicated device. In other words, the propeller makes it possible to blow air into the duct to accelerate its circulation.

[0030] In the case of the propeller being a ducted fan, then the air inlet can be located in the nacelle, downstream of the propeller.

[0031] An air outlet is understood to mean any type of air outlet used in aeronautics for cooling systems, but is not limited to these types. For example, the air outlet may consist of several openings from the cooling duct. In addition, there may be several air outlets, each corresponding to a branch of the cooling duct. The duct may have one or more outlets, and thus several ducts may have a single common outlet.

[0032] The air outlet can be placed in a low pressure area generated by the propeller, either upstream (when the air is sucked in), or downstream (just behind the fan blades, following the acceleration of the air by the propeller, which "sucks in" the air behind it) or, via a suction venturi effect, on areas of the fuselage or nacelle where the air flow speed increases due to the action of the propeller. In other words, the propeller allows the air contained in the duct to be sucked in to accelerate its circulation.

[0033] Positioning the air outlet in a low-pressure area of ​​the fuselage or nacelle increases the available pressure differential.

[0034] Positioning the air inlet in an overpressure zone of the fuselage or nacelle increases the available pressure differential.

[0035] For example, increasing the available pressure differential can overcome a potentially higher pressure drop. This pressure drop may be due to the geometry of the duct or a heat exchanger with a larger contact surface with the air. As a result, this can improve the removal of thermal energy, thereby increasing the efficiency of the cooling system.

[0036] The greater the heat to be dissipated, the greater the airflow required to dissipate it, and the greater the pressure drop caused by the heat exchanger. This situation results in a significant reduction in the difference between the available pressure jump and the pressure drop introduced, resulting in aerodynamic drag that is detrimental to the aircraft.

[0037] The air inlet is positioned at a location of greater air pressure as the aircraft moves forward relative to the air outlet, for example in the front part of the aircraft.

[0038] The air outlet is positioned at a location of lower air pressure as the aircraft moves forward relative to the air inlet, for example in the rear part of the aircraft.

[0039] The air inlet may include a movable part that moves depending on the airflow required to cool the exchanger. For example, the air inlet may include a damper or modulation flaps or one or more deflectors that open more or less depending on the airflow required.

[0040] The air outlet may include a movable part that moves depending on the airflow required to cool the exchanger. For example, the air outlet may include a damper or modulation flaps or one or more deflectors that open more or less depending on the airflow required.

[0041] In front of or upstream of the propeller, it is understood in front of a plane attached to the aircraft's reference frame and in which the propeller moves. In front of this plane it is understood on the side where the airflow passing through the propeller arrives when the propeller is in operation. In the context of an airplane, in front of the propeller means positioned on the side of the plane which is located on the nose side of the airplane.

[0042] Behind or downstream of the propeller, it is understood in front of a plane attached to the aircraft's reference frame and in which the propeller moves. Behind this plane is understood to be the side where the airflow passing through the propeller is accelerated when the propeller is in operation. In the context of an aircraft, behind the propeller means positioned on the side of the plane which is located on the side of the aircraft's tail cone.

[0043] By circle circumscribed to the propeller, we mean the circle, in a fixed frame of reference relative to the aircraft, formed by a series of small outlets positioned on the internal wall of the nacelle in correspondence with the tips of the blades. It is also the circle passing through all the tips of the propeller and having as its center, the center of the propeller.

[0044] By positioned in an area in front of the propeller such that the air leaving the air outlet passes at least partly within a circle circumscribed to the propeller or in a plane parallel to this circumscribed circle upstream of the propeller when the propeller is in operation, it is understood that the outlet is positioned so as to be in an area in which the propeller produces a depression during its operation. Thus, when the propeller is in operation, the air flow leaving the cooling duct exits into a depression zone created by the propeller, which generates a depression at the outlet of the cooling duct. In other words, the area is defined as an area in which the air pressure is lower when the propeller is in operation.

[0045] By positioned in an area behind the propeller such that air entering the air inlet passes at least partly within a circle circumscribed by the propeller when the propeller is in operation, it is understood that the inlet is positioned so as to be in an area in which the propeller produces overpressure during its operation. Thus, when the propeller is in operation, the airflow enters the cooling duct from an overpressure area created by the propeller, which generates overpressure at the inlet of the cooling duct. In other words, the area is defined as an area in which the air pressure is higher when the propeller is in operation.

[0046] An electric fan is any type of electrically powered mechanical device designed to move air.

[0047] The fan is powered by the aircraft's electrical generation system, which it helps cool. This means that some of the electrical energy produced by the system is used to operate the fan. However, this energy consumption is offset by the increased efficiency of the cooling system, which helps maintain a safe and efficient operating temperature for the aircraft's entire propulsion system.

[0048] A duct fan is a mechanical device integrated inside the cooling duct. This fan, which can consist of a propeller or several blades, is specifically designed to accelerate the movement of air through the duct. Its main role is to promote heat exchange by increasing the airflow through the heat exchanger, thus optimizing the efficiency of the cooling system.

[0049] The fan can be positioned at different points along the duct. For example, it can be placed upstream of the heat exchanger, i.e. before the exchanger in the direction of the airflow. This helps push air through the exchanger, increasing the amount of thermal energy that can be transferred from the exchanger to the air.

[0050] Alternatively, the fan can be positioned downstream of the heat exchanger, i.e. after the exchanger in the direction of airflow. In this case, the fan draws air through the exchanger, which can be particularly useful for maintaining airflow in situations where the air pressure at the duct outlet is low.

[0051] If the system includes multiple heat exchangers, one or more fans can be installed between them. This configuration optimizes the pressure jump across each exchanger, thus increasing the overall efficiency of the cooling system. This type of fan configuration is therefore defined as “in series.”

[0052] Several smaller fans can be installed next to each other to ensure the correct airflow through the heat exchanger. This type of fan configuration is therefore called “parallel”.

[0053] The fan may have a moving part that moves according to the airflow required to cool the exchanger. For example, the fan speed can be modulated according to the required airflow, or the fan blades can be oriented to optimize the fan's performance according to needs. A combination of these two approaches is also possible.

[0054] In terms of positioning, the fan can be mounted axially, i.e. aligned with the airflow circulating in the duct, or radially, i.e. perpendicular to the airflow. Each of these configurations offers specific advantages. For example, an axial mounting (axial inlet, axial outlet) ensures a greater airflow and a homogeneous distribution of the airflow, promoting a regular heat exchange throughout the exchanger. This type of fan favors the flow rate over the pressure jump and is used when the airflow to be supplied is high and the pressure jump to be provided is lower. Conversely, a radial mounting (axial inlet, radial outlet) is useful when the pressure jump to be provided is greater compared to the required airflow.

[0055] The size and shape of the fan can also vary depending on the specifics of the cooling duct and heat exchanger. For example, in a small diameter duct, a fan with short, angled blades may be preferred to maximize airflow. Conversely, in a larger duct, a fan with long, straight blades may be used to generate a more powerful airflow.

[0056] Finally, the fan can be equipped with regulation and control devices, allowing its operation to be adjusted in real time based on flight conditions, electric thruster performance, and cooling requirements. These devices can include temperature and pressure sensors, rotational speed controllers, and blade control systems. This technological sophistication helps optimize the performance of the cooling system while minimizing the impact on the aircraft's energy efficiency and aerodynamics.

[0057] According to one embodiment, the cooling system is used to cool a fuel cell.

[0058] LT (Low Temperature) fuel cells generate a lot of heat and need to be kept at controlled temperatures. This makes such a cooling system particularly suitable for cooling hydrogen fuel cells.

[0059] According to one embodiment, the cooling duct is positioned in the fuselage of the aircraft.

[0060] This helps to improve the aerodynamics of the aircraft.

[0061] According to one embodiment, the aircraft further comprises a fairing (a nacelle) in which the propeller and the air outlet are positioned.

[0062] A nacelle fairing for an electric ducted fan improves the efficiency of the propeller and ensures that the air outlet is fully and stably positioned in a vacuum zone. Indeed, the nacelle fairing ensures stability of the vacuum zone located in front of the propeller, by placing the air outlet in the nacelle fairing, in front of the propeller, this ensures that the air outlet is permanently positioned in the vacuum zone.

[0063] The nacelle of a ducted fan refers to the part surrounding the propeller and improving its efficiency. The fairing is a component of the nacelle (also called a "duct" in English). The propeller is attached to the nacelle and the propeller engine is located inside the nacelle. The air outlet is positioned on the inner wall of the fairing.

[0064] According to one embodiment, the air outlet has several openings distributed around the entire inner circumference of the nacelle.

[0065] According to one embodiment, the air outlet could be positioned at the rear of the nacelle, in a depression zone created by the acceleration of the air. This configuration would make it possible to exploit this depression to facilitate the evacuation of hot air from the cooling system, while minimizing the impact on the aircraft's drag.

[0066] This prevents periodic imbalance of the mechanical load on the propeller, i.e. having greater force applied to the propeller in some places. These dis- twists reduce engine efficiency.

[0067] By openings distributed around the entire inner circumference of the nacelle, it is understood that the openings are arranged substantially symmetrically with respect to the center of the propeller, i.e., arranged with axial symmetry from center to center of the propeller. For example, the openings may be arranged substantially continuously along the inner circumference of the fairing. Not all openings may have the same diameter depending on the balancing of the airflow in each opening.

[0068] According to one embodiment, the cooling duct comprises a second air outlet and the aircraft further comprises a second propeller positioned in a second fairing, and wherein the second air outlet is positioned in front of the second propeller in a second fairing.

[0069] Thus, two air outlets are provided to evacuate the air entering the cooling duct. These two air outlets are both arranged respectively in the depression zones generated by the propeller and the second propeller. Thus, the air contained in the duct is sucked in by two propellers which further accelerates the circulation of air in the cooling duct.

[0070] According to one embodiment, the reaction products from the fuel cell are injected under pressure into the cooling sheath upstream of the heat exchanger and towards the air outlet.

[0071] This accelerates the ejection of the air contained in the duct and thus improves the efficiency of the evacuation of the thermal energy provided by the heat exchanger.

[0072] Reaction products are the elements produced by the oxidation reaction when the fuel cell produces electricity. In the case of a hydrogen combustion cell, the products of the reaction producing electricity are mainly water vapor.

[0073] According to one embodiment, the air inlet may be equipped with an adjustable flap system, making it possible to modulate the quantity of air entering according to the cooling requirements. These flaps, by opening and closing, can control the flow of air entering the cooling duct and thus optimize the cooling efficiency and the resulting aerodynamic drag according to the flight conditions and the thermal load of the system.

[0074] In yet another embodiment, the air inlet may include a system of internal ducts designed to optimally direct air to the heat exchanger. These ducts may be designed to minimize pressure drop and maximize heat exchange efficiency.

[0075] According to one embodiment, the air inlet could be configured to collect air not only from the front, but also from the sides, using ducts auxiliaries. This configuration could increase the airflow available for cooling, while allowing greater flexibility in the positioning of the air intake on the fuselage.

[0076] According to one embodiment, the air outlet may be equipped with an adjustable flap system, allowing the quantity of incoming air to be modulated according to the cooling requirements. These flaps would make it possible to control the flow of air leaving the cooling duct, thus optimizing the cooling efficiency and aerodynamic drag according to the flight conditions and the thermal load of the system.

[0077] According to one embodiment, the air outlet could include several openings strategically placed along the fuselage to optimize air distribution and minimize disruption of airflow around the aircraft.

[0078] In one embodiment, the air outlet could be designed to direct the exiting air in a manner that minimizes the impact on the aerodynamics of the aircraft. For example, the air could be directed to optimally mix with the airflow around the aircraft, thereby minimizing drag.

[0079] In one embodiment, the air outlet could be designed to direct the exiting air in a manner that contributes to the propulsion of the aircraft. Although this effect would likely be minimal, it could nevertheless contribute to the overall efficiency of the aircraft.

[0080] According to one embodiment, the fan in the duct can be associated with an electronic or mechanical speed controller. The latter allows the rotation speed of the fan to be finely regulated according to the cooling requirements, thus minimizing power consumption while ensuring adequate cooling of the system.

[0081] According to one embodiment, the fan in the duct may be equipped with variable pitch blades. This allows the blade angle to be dynamically adjusted depending on flight conditions and cooling requirements. Thus, the fan can provide optimal airflow regardless of flight conditions.

[0082] According to one embodiment, the fan in the duct may be configured to operate in a reversible mode. In other words, it may reverse the direction of its airflow, which may be useful for quickly dissipating heat accumulated in the duct in the event of overheating, or for reducing energy consumption under low heat load conditions.

[0083] In one embodiment, multiple fans could be arranged along the cooling duct. This series or parallel configuration could allow for finer modulation of the airflow through the heat exchanger and a more uniform temperature distribution within the duct.

[0084] According to one embodiment, the fan in the duct could be designed to operate in conjunction with a heat recovery system. By recovering some of the heat released by the electrical system and reusing it for cabin heating or wing de-icing, for example, the overall energy efficiency of the aircraft could be improved.

[0085] According to one embodiment, the air inlet is located in a zone of high natural pressure of the fuselage of the aircraft without direct impact from the propeller while the air outlet is positioned in a zone of low pressure generated by the propeller.

[0086] According to one embodiment, the air inlet is located in an overpressure zone generated by the propeller while the air outlet is positioned in a natural low pressure zone of the aircraft fuselage without direct impact from the propeller.

[0087] According to one embodiment, there is no fan in the cooling duct.

[0088] According to one embodiment, the air inlet includes an air filter to prevent the entry of debris. BRIEF DESCRIPTION OF THE FIGURES

[0089] [Fig.1] represents an aircraft according to an embodiment of the state of the art.

[0090] [Fig.2] represents the cooling system according to one embodiment of the invention.

[0091] [Fig.3] represents a diagram corresponding to the operation of the cooling system according to one embodiment of the invention.

[0092] [Fig.4] represents a three-dimensional view of the cooling sheath according to one embodiment of the invention.

[0093] [Fig.5] shows several types of air outlets in a nacelle according to the invention.

[0094] [Fig.6] represents several types of sheaths according to the invention.

[0095] [Fig.7] represents the configuration of the cooling duct and its internal elements considering a fan upstream of the heat exchanger according to an embodiment of the invention.

[0096] [Fig.8] represents the configuration of the cooling duct and its internal elements considering several fans installed in parallel according to an embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0097] [Fig.l] represents an airplane 1.

[0098] The aircraft comprises a fuselage 2, wings 3. It is an aircraft powered by electric motors 4 supplied via cable 11 by electricity produced by a hydrogen fuel cell 5 supplied by hydrogen stored in a tank 6.

[0099] The fuel cell 6 is cooled by a cooling system comprising a fuel cell cooling circuit 7, a cooling unit (heat exchanger) 8 and two pipes 9 and 10 for transporting a heat transfer fluid between the unit 8 and the cooling circuit of the fuel cell 7. Thus, the first pipe 9 makes it possible to transport the heat transfer fluid from the cooling circuit of the fuel cell 7 to the cooling unit 8. Conversely, the second pipe 10 makes it possible to transport the heat transfer fluid from the cooling unit 8 to the cooling circuit of the fuel cell 7.

[0100] The cooling circuit of the fuel cell 7 is not described in detail. However, any fuel cell cooling circuit can be used. For example, it is possible to provide for the heat transfer fluid to circulate in the bipolar plates of the fuel cell. The contact between the heat transfer fluid and the cells allows the transfer of the thermal energy produced by the cells of the fuel cell 5.

[0101] The cooling unit 8 comprises a heat exchanger and a cooling jacket. These elements will be described in more detail in the following figures.

[0102] [Fig.2] represents the cooling system according to one embodiment of the invention.

[0103] The cooling unit 8 comprises an air / liquid heat exchanger 12 positioned in a cooling duct 13. The cooling duct 13 has an air inlet 14 and an air outlet 15.

[0104] The air inlet 14 is positioned so as to allow outside air to enter the duct 13. The air inlet 14 is therefore positioned at a high pressure location when the aircraft is moving forward, for example at the nose of the aircraft or on a side, underside or top of the fuselage, or on a wing, on a pylon holding a nacelle, etc. In the case of the embodiment described in Figures 1 and 2, the air inlet 14 is positioned above the fuselage at the base of the fin, and overpressure generated by the propeller 16.

[0105] The air inlet 14 is positioned in an overpressure zone generated by the propeller 16.

[0106] The air outlet 15 is positioned so as to allow the air present in the duct 13 to be evacuated. The air outlet 15 is therefore positioned at a location of lower pressure when the aircraft is moving forward and in particular of lower pressure compared to the pressure at the air inlet 14. For example, the air outlet 15 can be arranged in the rear part of the aircraft. In the case of the embodiment described in FIGS. 1 and 2, the air outlet 15 is positioned in the air flow generated by the propeller 16 so as to benefit from a venturi-type suction effect. More precisely, the air outlet 15 is positioned on the face of the fuselage in contact with the air flow generated by the propeller 16.

[0107] [Fig.5] describes in more detail the position of the air outlet 15 when it is po- CORRECTED SHEET (RULE 91) ISA / EP located at the level of the nacelle 20. The nacelle 20 is an embodiment of the invention but not necessary.

[0108] Thus, the cold outside air enters through the air inlet 14, passes through the upstream part 17 of the duct 13 and then passes through the heat exchanger 12. The cold air in contact with the heat exchanger 12 is charged with thermal energy, that is to say the air heats up. Then the hot air passes through the downstream part 18 of the duct 13 to finally exit through the air outlet 15. The propeller 16 in operation creates an overpressure at the air inlet 14 and therefore the air enters the duct 13 more quickly which accelerates the circulation of the air in the duct 13. The propeller 16 in operation creates a depression at the air outlet 15. The air at the outlet of the air outlet 15 is therefore sucked in by the air accelerated by the propeller 16, thus, the air is evacuated more quickly outside the duct 13 which accelerates the circulation of the air in the duct 13.

[0109] The reaction products from the fuel cell can be injected under pressure into the downstream part 18 of the sheath 13. These products are conveyed by a pipe 5 to an injection device 19 arranged in the downstream part 18 of the sheath 13. The injection of the combustion products is carried out in the direction of circulation of the air in the cooling sheath 13, namely from the air inlet 14 to the air outlet 15.

[0110] The cooling system described in Figures 1 and 2 is a cooling system based on a heat transfer fluid that does not change phase. The cooling system can also rely on a phase change fluid, in which case the cooling system comprises an evaporator placed at the fuel cell so as to transfer the thermal energy from the fuel cell to the heat transfer fluid. Then the fluid in the vapor state passes into a condenser placed in the sheath 13 in place of the air / liquid heat exchanger 12. The cooling system can also also comprise an expander to expand the fluid or a turbine to extract mechanical power from a pump to allow the circulation of the heat transfer fluid. Then the expanded gas passes again into the evaporator.

[0111] [Fig.3] shows a diagram corresponding to the cooling system.

[0112] In step S21, the heat transfer liquid passes through the cooling circuit of the fuel cell 7. The liquid rises in temperature and thus stores thermal energy produced by the cells of the fuel cell 5.

[0113] In step S22, the hot heat transfer fluid is transmitted via the pipe 9 to the heat exchanger 12 included in the cooling unit 8.

[0114] In step S23, the hot heat transfer fluid is cooled in the heat exchanger 12 by means of the air circulating in the sheath.

[0115] In step S24, the cold heat transfer fluid is transmitted via the pipe 10 to the cooling circuit of the fuel cell 7.

[0116] Steps S21 to S24 are then repeated in a loop.

[0117] [Fig.4] represents a three-dimensional view of an embodiment of the cooling unit 8.

[0118] We find the same elements as those described in [Fig.2], namely, a duct 13 with an air inlet 14 and an air outlet 15. The heat exchanger 12 is positioned in the duct 13. The air outlet 15 is via the inner face of the nacelle 20 upstream of the propeller 16.

[0119] The air flow passing through the cooling duct 13 is represented by white wires. The air flow enters the duct 13 through the air inlet 14 and then passes through the upstream portion 17 of the duct 13. Then the air flow passes through the heat exchanger 12 where it discharges the heat exchanger with thermal energy. The hot air flow then passes through the downstream portion 18 of the duct 13 to exit through the air outlet 15 which opens into the nacelle 20 in front of the propeller.

[0120] [Fig.5] shows several types of air outlets in the nacelle 20 according to the invention.

[0121] In [Fig. 5], the air outlet 15 in the internal face of the nacelle 20 is shown more precisely, which can take several shapes and dimensions and have several openings. The description of the previous figures applies here.

[0122] In all three representations, the nacelle 20 surrounds the propeller 16, more precisely the fairing of the nacelle 20. The area in the nacelle 20 present in front of the propeller 16 represents a depression area when the propeller 16 is in operation. In all three examples, the openings 21, 22.1, 22.2 and 23 of each air outlet 15 (15, 15.1, 15.2, 15.3) are located in this depression area.

[0123] In the representation of the nacelle on the left in [Fig.5], the air outlet 15 takes the form of a single opening 21 in the internal face of the nacelle 20. This is simpler to design, but has the disadvantage of making the propeller 16 work asymmetrically and therefore of applying a stress on the axis of rotation of the propeller.

[0124] In the representation of the nacelle in the center in [Fig. 5], the air outlet 15 takes the form of two openings 22.1 and 22.2 located symmetrically to each other with respect to the axis of the propeller 16. This has the advantage of balancing the pressure experienced by the propeller 16 and therefore of applying lower stresses on the axis of rotation of the propeller than in the case on the left. However, although the pressure is balanced with respect to the axis of rotation of the propeller 16, the propeller 16 experiences variable pressures at iso distance from the center of the propeller 16. This causes load distortions on the propeller 16.

[0125] In the representation of the nacelle on the right in [Fig.5], the air outlet 15 takes the form of a ring 23 located on the internal wall of the nacelle 20. This reduces the dis- load twists on propeller 16.

[0126] The invention is not limited to these three types of air outlets 15.

[0127] [Fig.6] shows two different sheath shapes from that shown in [Fig.2],

[0128] The ducts shown in [Fig.6] have an air inlet 14 as previously described. This air inlet 14 can take any shape. The air inlet 14 is connected to the upstream part of the duct 17. On the other hand, the ducts have two air outlets 15.1 and 15.2 formed by a bifurcation in two of the duct.

[0129] More precisely, in the duct shown on the left in [Fig.6], a single heat exchanger 12 is provided. The air leaving the heat exchanger 12 is distributed in the two downstream parts 18.1 and 18.2 of the duct, each of these branches has its own air outlet 15.1 and 15.2.

[0130] In the duct shown on the right in [Fig.6], two independent heat exchangers 12.1 and 12.2 are provided, one exchanger for each downstream part 18.1 or 18.2 of the duct. At the outlet of the heat exchanger 12.1, the air passes into the downstream part 18.1. At the outlet of the heat exchanger 12.2, the air passes into the downstream part 18.2.

[0131] When the duct provides two air outlets 12.1 and 12.2, as described with [Fig.6], each outlet can be positioned on a different nacelle in the case of aircraft with two or more engines.

[0132] [Fig.7] shows a diagram corresponding to a configuration of the cooling duct to supply a heat exchanger with a fan.

[0133] At step S25 fresh air enters the cooling duct from outside through the air inlet.

[0134] At step S26 fresh air flows into the air duct

[0135] At step S27 the fan pushes air into the heat exchanger

[0136] At step S28 the air passes through the exchanger and by exchanging heat with the heat transfer fluid the air heats up.

[0137] At step S29 the hot air flows through the cooling duct to the outlet.

[0138] At step S30 the air is expelled out of the aircraft through the air outlet.

[0139] Steps S25 to S30 are done through an open circuit.

[0140] [Fig.8] shows a diagram corresponding to a configuration of the cooling duct to supply a heat exchanger using two fans installed in parallel. CORRECTED SHEET (RULE 91) ISA / EP

[0141] At step S31 the air sucked in by fans S33 and S34 enters the cooling duct through the air inlet.

[0142] At step S32 the air passes through the cooling duct.

[0143] At steps S33 and S34 the air is pushed by the fans.

[0144] At step S35 the air passes through the exchanger and by exchanging heat with the heat transfer fluid the air heats up.

[0145] At step S36 the hot air flows through the cooling duct to the outlet.

[0146] At step S337 the air is expelled out of the aircraft through the air outlet. Steps from S231 to S37 are done through an open circuit. CORRECTED SHEET (RULE 91) ISA / EP

Claims

Claims

1. An aircraft comprising a cooling system integrated into the fuselage, and at least one propeller driven by an electric motor adapted to propel the aircraft, the cooling system comprising: - at least one cooling duct (or air duct), located within the fuselage of the aircraft, provided with an air inlet and an air outlet, the cooling duct being designed to allow the circulation of air between the air inlet and the air outlet; at least one heat exchanger positioned within the cooling duct, the heat exchanger being designed to transfer thermal energy to the air circulating in the cooling duct; wherein, the air inlet is positioned in an overpressure zone generated by the air accelerated by the rotation of the propeller, and the air outlet is strategically positioned on an external surface of the fuselage swept by the air flow accelerated by the rotation of the propeller, causing a zone of lower pressure facilitating the circulation of air through the cooling duct, thus allowing efficient dissipation of heat through the heat exchanger.

2. An aircraft according to claim 1, wherein the cooling system is for cooling a fuel cell system.

3. An aircraft according to any preceding claim, wherein at least one fan is located within the duct to facilitate airflow.

4. Aircraft according to one of the preceding claims, in which the cooling system comprises several heat exchangers placed at different locations in the cooling duct.

5. Aircraft according to one of the preceding claims, in which the air outlet is located in a natural low pressure zone of the fuselage of the aircraft in flight, without direct impact of the air accelerated by the propeller.

6. Aircraft according to one of the preceding claims in which the air intake is located in a zone of high natural pressure of the fuselage of the aircraft without direct impact from the propeller.

7. An aircraft according to any preceding claim further comprising a nacelle fairing in which the propeller and the air inlet are positioned, the air inlet positioned in an overpressure zone generated by the propeller in said nacelle fairing.

8. An aircraft according to claim 1, wherein at least one cooling duct has multiple air inlets or multiple air outlets.

9. An aircraft according to any preceding claim, wherein the air inlets and outlets are controlled to control the flow of air circulating in the duct.

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