Patent Description:
In order to reduce the fuel consumption of an aircraft, it is known practice to use fuel cells, in which each generates an electrical current used to power an electric motor turning one or more propellers.

The fuel cell makes it possible to convert chemical energy deriving from an oxidoreduction reaction of dihydrogen and of dioxygen into electrical energy, into heat and into water.

In order to control the temperature of the fuel cell, such an installation comprises a cooling system.

<FIG> is a schematic representation of such an installation <NUM> in an aircraft, which comprises a fuel cell <NUM>, and a cooling system <NUM> which comprises a line <NUM> which takes a heat-transfer fluid at an output of the fuel cell <NUM> and which introduces this heat-transfer fluid at an input of the fuel cell <NUM>.

The cooling system <NUM> also comprises a pumping system comprising at least one pump <NUM> which is arranged on the line <NUM> to drive the heat-transfer fluid in the line <NUM> between the output and the input of the fuel cell <NUM>.

The cooling system <NUM> also comprises a heat exchanger <NUM> which is arranged on the line <NUM> and which ensures the transfer of calories from the heat-transfer fluid to a cold fluid, conventionally the air outside the aircraft. Thus, the outside air passes through the heat exchanger <NUM> then is rejected outside. At the same time, the heat-transfer fluid passes through the heat exchanger <NUM> and the calories of the heat-transfer fluid are transferred to the outside air.

Because of the large quantity of calories to be discharged, the heat exchanger <NUM> has a relatively large size, which is detrimental in terms of weight and of drag.

It is therefore desirable to find an installation which makes it possible to discharge the calories while having smaller dimensions.

Document <CIT> discloses an installation for the evacuation of calories from a fuel cell on board an aircraft, the fuel cell system comprising a single circulation loop for a single heat transfer fluid, from a pump or a tank, to cooling channels, to a condenser, to return to the pump or to the tank.

Document <CIT> discloses a de-icing system comprising a heat source/fuel cell, an air heating device/heat exchanger and an air conditioning system. Heat transfer between the fuel cell and the air conditioning system cools the fuel cell, while heating the air of the air conditioning system.

Document <CIT> discloses an improved icing protection system of an aircraft comprising a single circulation loop for a single heat transfer fluid, from a tank, to a pump, to cooling conduits, to a condenser, to return to the tank.

Document <CIT> discloses an aircraft comprising a fuel cell, as well as a water transport conduit connected between the fuel cells and the cabin of the aircraft, and a heat transport conduit connected between the fuel cells and the cabin of the aircraft, in order to supply energy to the aircraft without weighing it down.

Document <CIT> discloses an aircraft comprising a fuel tank, a fuel cell system comprising at least a fuel cell and a cooling system for cooling said fuel cell by heating the fuel of the fuel tank.

One object of the present invention is to propose an aircraft comprising at least one fuel cell and a structure having a tank allowing the storage of a two-phase heat-transfer fluid ensuring the cooling of said fuel cell.

To this end, an aircraft is proposed comprising:.

Thus, the use of a first, two-phase heat-transfer fluid allows for a better transfer of the calories from the second heat-transfer fluid to the first heat-transfer fluid and the storage of the first heat-transfer fluid in a tank of the structure of the aircraft in contact with the outside air ensures the cooling of the first heat-transfer fluid at lower cost in terms of bulk and drag.

Advantageously, the structure comprises a fuselage with an inner wall and an outer wall, and the leakproof tank is delimited between the inner wall and the outer wall.

Advantageously, the structure comprises at least one wing with a lower surface wall and an upper surface wall, and the leakproof tank is delimited between the lower surface wall and the upper surface wall.

Advantageously, the first heat-transfer fluid is water.

Advantageously, the line is divided into a plurality of sublines in the leakproof tank.

Advantageously, the aircraft comprises a heat exchanger arranged on the line and ensuring the transfer of calories from the second heat-transfer fluid to the outside air.

Advantageously, the aircraft comprises an overpressure system arranged at the leakproof tank.

The features of the invention mentioned above, and others, will become more clearly apparent on reading the following description of an exemplary embodiment, said description being given in relation to the attached drawings, in which:.

<FIG> is a schematic representation of an installation <NUM> implemented in an aircraft according to the invention and represented schematically in <FIG>.

The installation <NUM> comprises a fuel cell <NUM> which converts the chemical energy deriving from an oxidoreduction of dihydrogen and of dioxygen into electrical energy, into heat and into water. To this end, the aircraft <NUM> comprises a tank of dihydrogen and a line circuit ensuring that the fuel cell <NUM> is supplied with the dihydrogen. Likewise, the fuel cell <NUM> is supplied with dioxygen, either from a tank of dioxygen of the aircraft <NUM>, or by the outside air. Such an architecture is conventional and is not described further.

<FIG> is a schematic representation of the aircraft <NUM> which comprises a structure <NUM> and engines <NUM>.

The structure <NUM> conventionally comprises a fuselage <NUM> and a wing <NUM> on either side of the fuselage <NUM>. The aircraft <NUM> here comprises two engines <NUM> under each wing <NUM>. Obviously, the aircraft can comprise just one or more than two engines <NUM> under each wing <NUM>. The fuel cells <NUM> electrically power the engines <NUM> which are, for example, propeller engines.

In order to control the temperature of the fuel cell <NUM>, the latter is passed through by a heat-transfer fluid, called second heat-transfer fluid. The second heat-transfer fluid is generally in liquid phase. The second heat-transfer fluid can also be a two-phase heat-transfer fluid having a gaseous phase and a liquid phase. The second heat-transfer fluid can be water, or a mixture of water and additives, such as glycol water. The installation <NUM> also comprises a cooling system <NUM> which ensures the cooling of the second heat-transfer fluid.

The cooling system <NUM> comprises at least one line <NUM> which takes the second heat-transfer fluid at an output of the fuel cell <NUM> and which reintroduces this second heat-transfer fluid at an input of the fuel cell <NUM>. The line <NUM> and the fuel cell <NUM> thus form a closed loop of circulation of the second heat-transfer fluid.

The cooling system <NUM> also comprises a pumping system comprising at least one pump <NUM> which is arranged on the line <NUM> to drive the second heat-transfer fluid in the line <NUM> between the output and the input of the fuel cell <NUM>.

The structure <NUM> comprises at least one leakproof tank <NUM>.

The leakproof tank <NUM> can be a part of the wing <NUM> and/or a part of the fuselage <NUM>. For example, if the fuel cell <NUM> is in the engine <NUM> on the wing <NUM>, it is preferable to provide the leakproof tank <NUM> in the wing <NUM>, and if the fuel cell <NUM> is in the fuselage <NUM>, it is preferable to provide the leakproof tank <NUM> in the fuselage <NUM> to reduce the length of the line <NUM>. However, other layouts are possible.

The leakproof tank <NUM> is delimited by walls of the aircraft <NUM> of which at least one is in contact with the air outside the aircraft <NUM>. In the case where the leakproof tank <NUM> is in the wing <NUM>, the leakproof tank <NUM> is delimited between the lower surface wall and the upper surface wall of the wing <NUM>, and the two walls are in contact with the outside air. In the case where the leakproof tank <NUM> is in the fuselage <NUM> which has an inner wall and an outer wall, the leakproof tank <NUM> is delimited between the inner wall and the outer wall which is the wall in contact with the outside air.

The leakproof tank <NUM> is filled partly with a heat-transfer fluid, called first heat-transfer fluid, which has two phases, namely a liquid phase <NUM> and a gaseous phase <NUM>, within the temperature ranges considered, that is to say according to the temperature of the heat-transfer fluid coming from the fuel cell <NUM>. The leakproof tank <NUM> forms a closed loop of circulation of the first heat-transfer fluid.

The first heat-transfer fluid is distinct from the second heat-transfer fluid.

According to a preferred embodiment, the first heat-transfer fluid is water which all evaporates at approximately <NUM> at ground level (in conventional atmospheric conditions) and at approximately <NUM> at an altitude of <NUM><NUM> feet. Because of this, it is possible to cool this first heat-transfer fluid to a lower temperature at altitude than at ground level. The first heat-transfer fluid can also be a mixture of water and of additives, such as glycol water.

The line <NUM> passes through the leakproof tank <NUM> at a height where the line <NUM> is immersed in the first heat-transfer fluid in liquid phase <NUM>, that is to say more in the lower part of the leakproof tank <NUM>.

Thus, when the second heat-transfer fluid coming from the output of the fuel cell <NUM> passes through the leakproof tank <NUM>, the first heat-transfer fluid which surrounds the line <NUM> picks up the calories from the second heat-transfer fluid and evaporates, then, in contact with the wall in contact with the outside air, the vapour thus given off condenses to drop back into the liquid phase <NUM>. The outside air (arrows <NUM> along the lower surface and the upper surface) cools the wall of the leakproof tank <NUM> and thus makes it possible to lower the temperature of the first heat-transfer fluid and condense it. Since the first heat-transfer fluid reverts to its liquid state, and the first heat-transfer fluid considered has a significant latent heat, there is no need to install a very significant volume and mass of said first heat-transfer fluid.

The second heat-transfer fluid can be in liquid phase and/or in gaseous phase in the line <NUM> between the output of the fuel cell <NUM> and the leakproof tank <NUM>, and in liquid phase in the line <NUM> between the leakproof tank <NUM> and the input of the fuel cell <NUM>.

The quantity of calories thus discharged is then relatively great without it being necessary to put in place one or more imposing heat exchangers in terms of weight and drag.

To enhance the transfer of calories, the line <NUM> can be divided into a plurality of sublines in the leakproof tank <NUM> as is represented in <FIG>.

<FIG> shows the wing <NUM> with the plurality of sublines immersed in the first heat-transfer fluid in liquid phase <NUM>.

In the case where the discharge of the calories by the first heat-transfer fluid would not be sufficient, it is possible to arrange one or more heat exchangers <NUM> on the line <NUM>. Depending on the surface of the tank in contact with the outside air, this heat exchanger <NUM> can be of very much smaller size than that of the state of the art, because it serves only to discharge a small part of the calories. This heat exchanger <NUM> ensures the transfer of calories from the heat-transfer fluid to a cold fluid, for example the air outside the aircraft <NUM>. Thus, the outside air passes through the heat exchanger <NUM> then is rejected outside. At the same time, the second heat-transfer fluid passes through the heat exchanger <NUM> and the calories from the second heat-transfer fluid are transferred to the outside air. This heat exchanger <NUM> is preferentially installed downstream of the leakproof tank <NUM> with respect to the direction of flow of the second heat-transfer fluid. Obviously, this heat exchanger <NUM> can be installed upstream of the leakproof tank <NUM> with respect to the direction of flow of the heat-transfer fluid.

Claim 1:
Aircraft (<NUM>) comprising:
- a structure (<NUM>) comprising a leakproof tank (<NUM>) delimited by walls of which at least one is in contact with the air outside the aircraft (<NUM>), and filled partly with a first, two-phase heat-transfer fluid, the first heat-transfer fluid having a liquid phase and a gaseous phase,
- a fuel cell (<NUM>) passed through by a second heat-transfer fluid, and
- at least one line (<NUM>) which takes the second heat-transfer fluid at the output of the fuel cell (<NUM>),
characterized in that said second heat transfer fluid is distinct from said first heat-transfer fluid,
in that the at least one line (<NUM>) reintroduces this second heat-transfer fluid at an input of the fuel cell (<NUM>), the at least one line (<NUM>) and the fuel cell (<NUM>) forming a closed loop of circulation of the second heat-transfer fluid,
and in that the line (<NUM>) passes through the leakproof tank (<NUM>) immersed in the first heat-transfer fluid in liquid phase, the first heat-transfer fluid surrounding the line (<NUM>) being configured to pick up the calories from the second heat-transfer fluid and to evaporate, and to condense to drop back into the liquid phase in contact with the wall in contact with the outside air,
and in that the leakproof tank (<NUM>) forms a closed loop of circulation of the first heat-transfer fluid.