SEALING DEVICE CONFIGURED FOR INSTALLATION IN FLUID FLOW PATHS OF A FUEL CELL STACK AND SEALING METHOD - Patent application

Abstract

The present invention relates to an insulating device (9) configured to be mounted in a fluid flow path of a fuel cell comprising a stack including a plurality of cells aligned along a stack axis X and a plurality of fluid flow paths in the stack, the insulating device (9) comprising a circumferential belt (90) configured to prevent fluid communication between the flow paths and at least one flow opening of a cell to be isolated in the stack, the belt (90) being deformable between a first configuration, referred to as an idle configuration, and a second configuration, referred to as a contracted configuration, the cross-section of the belt (90) being smaller than its cross-section in the first configuration.

Description

[Technical field]

[0001] The invention particularly relates to the field of servicing fuel cells that are installed on board aircraft to provide propulsive and non-propulsive energy. [Background technology]

[0002] Fuel cells allow the production of electrical energy from electrochemical reactions between different fluids. Conventionally, fuel cells are supplied with hydrogen and oxygen, which react in the fuel cell to produce electrical energy. Fuel cells comprise a stack comprising a number of cells aligned along a stack axis. The stack of cells allows the electrochemical reactions from the fluids.

[0003] Each cell consists of an ion-conducting electrolyte surrounded by two electrodes, which are in turn surrounded by interconnecting plates. As an example, in the case of a proton exchange membrane type fuel cell, known by its abbreviation PEMFC for "Proton Exchange Membrane Fuel Cell", the electrolyte takes the form of a proton-conducting polymer membrane and the electrodes take the form of a porous medium carrying a catalyst such as platinum. The assembly of electrolyte and electrodes is called a membrane electrode assembly, known by its abbreviation MEA. Each MEA is brought into contact with reactant gases (e.g. hydrogen and oxygen, which may be present in air) on the two opposite sides of the MEA through the interconnecting plates to form a cell.

[0004] In a known manner, an assembly of two interconnected plates belonging to two adjacent cells is called a bipolar plate. The bipolar plate is therefore inserted between the cathode of an MEA and the anode of the adjacent MEA. On the one hand, the bipolar plate supplies the fuel (hydrogen) to the first MEA on the anode side and, on the other hand, the oxidant (oxygen) to the second MEA on the cathode side. Generally, each bipolar plate is equipped with an internal cooling circuit in which a heat transfer fluid circulates to provide heat or to extract heat created by exothermic reactions.

[0005] The current generated by the cells is collected by so-called collector conductor plates at both ends of the stack. The power delivered by a fuel cell depends on the number of cells (delivered voltage capacity), the active surface area of ​​the cells (delivered current capacity), and the flow rate of the reactant fluids (the importance of the electrochemical reactions that create the current).

[0006] The entire stack of cells is kept compressed between two so-called end plates, connected by tie rods that hold the assembly and ensure the sealing of the stack. This sealing is provided by seals inserted between the bipolar plates and the MEAs of the cells. The end plates are conventionally solid, since they must apply a uniform pressure on the surfaces of the cells and be dimensionally stable under the influence of the internal pressure and temperature fluctuations of the stack.

[0007] The reaction and heat transfer fluids are introduced and discharged at the end plates, which distribute the reaction and heat transfer fluids in flow paths through the stack. These flow paths result from stacks of openings formed in the cells. As an example, three channels introduce fluids (two reaction fluids and one heat transfer fluid, if desired) from one side of the stack and move them into the cell, while the other three channels discharge the fluids from the other side of the stack.

[0008] In a known manner, a fuel cell comprises a stack comprising a plurality of cells aligned along a stack axis, tie rods connecting outer portions of end plates around the periphery so as to apply a constant compressive force to the stack, the end plates comprising flow lines leading into the flow passages of the stack.

[0009] During the electrochemical reactions in the fuel cell, the reacting fluids become charged with traces of acid that are part of the composition of the MEA. These traces of phosphoric acid are present in the flow paths corresponding to the outlets of the two fuel fluid circuits, especially in the form of water vapor in the case of high-temperature fuel cells. This acid can crystallize, especially during the start-up / stop steps of the fuel cell, during which the temperature is below the normal operating temperature, and this crystallization can block the flow paths. Such a blockage can cause damage that can lead to hot spots with the risk of perforation of the MEA. In addition to efficiency losses of the fuel cell, the possibility of fire and leakage risks increases.

[0010] If one or more cells are damaged, they must be isolated from the reactant fluid flow so that they no longer produce electricity or allow fluid communication between the reactants. From an electrical standpoint, these cells must be shunted so as not to interrupt the power generation within the stack.

[0011] To reach the defective cell, it is necessary to go down along each of the channels and intervene individually on each of the flow openings of the defective cell. This intervention depends on the channel height (up to 300 mm) and the cross section of the flow path (from 300 to 1000 mm). 2 ) is complicated.

[0012] A method for repairing defective cells is known in the prior art in which an electric shock is applied to the defective cell in order to puncture the membrane during repair. The flow openings are individually sealed by depositing a resin. Summary of the Invention [Problem to be solved by the invention]

[0013] This solution is attractive in theory but complex to implement. It is an object of the present invention to enable defective cells to be practically and quickly isolated from the stack. [Means for solving the problem]

[0014] The present invention relates to an isolation device configured to be installed within a fluid flow path of a fuel cell comprising a stack including a plurality of cells aligned along a stack axis and a plurality of fluid flow paths within the stack.

[0015] The isolation device is notable in that it comprises a peripheral belt configured to interrupt fluid communication between the flow path and at least one flow opening of a cell to be isolated from the stack, the belt being deformable between a first configuration, referred to as the idle configuration, and a second configuration, referred to as the contracted configuration, the cross-section of the belt being smaller than its cross-section in the first configuration.

[0016] Preferably, such an insulating device can be conveniently positioned at a desired location in the flow path to isolate the cell from the stack. The peripheral belt provides a localized seal while allowing fluid to circulate through the belt to supply other cells. The deformable nature of the belt allows for convenient and rapid positioning without risk of damaging the inner surface of the flow path. The belt allows for convenient and simultaneous sealing of multiple flow openings of the cell.

[0017] Preferably, in the first configuration, the cross section of the belt is substantially similar to the cross section of the flow passage and is configured to accommodate the insulating device, so that the belt naturally conforms to the inner surface of the flow passage without undue stress and deformation, thereby allowing the cells to be sealed conveniently and nearby without risk of damage.

[0018] According to one embodiment, the isolation device comprises a spring member configured to constrain the belt in a first configuration. Thus, the belt is automatically deployed when the operator does not constrain the belt. This is particularly advantageous when the cell to be isolated is away from the access opening of the flow path and when easy handling of the isolation device is desired.

[0019] Preferably, the spring members take the form of spring leaves which are simple in design and can be positioned on the inner surface of the belt so as to avoid contact with the inner surface of the channel.

[0020] Preferably, the isolation device comprises an indexing member configured to ensure precise positioning of the isolation device in the flow path, in particular opposite the flow opening or openings of the cell to be isolated. Preferably, the cell comprises two seals on either side of the opening, the indexing member being configured to cooperate with the seals.

[0021] This is particularly advantageous for providing precise positioning when the cell to be isolated is away from the access opening of the flow path. Preferably, the indexing member takes the form of a peripheral tongue extending protruding from the outer surface of the belt, so that it fits snugly with the seal to enable cooperation.

[0022] Preferably, the insulating device comprises a plurality of guide members configured to cooperate with an inner surface of the flow channel. Preferably, the flow channel has a cross-section defining a plurality of corners, and the guide members are configured to cooperate with the corners of the flow channel, such that the belt is precisely angularly positioned within the channel to ensure optimal sealing.

[0023] The present invention also relates to a fuel cell assembly comprising a stack with a plurality of cells aligned along a stack axis and a plurality of fluid flow paths within the stack, and an isolation device as presented above positioned within the flow paths (20) so as to interrupt fluid communication between the flow paths and at least one cell that is to be isolated from the stack.

[0024] Preferably, the stack comprises alternating bipolar plates and membrane electrode assemblies that define the cells of the stack. The insulating device is positioned in the flow path so as to interrupt fluid communication between the flow path and the bipolar plate to be isolated. Thus, the supply of fluid to the bipolar plate is stopped.

[0025] Preferably, the insulating device has a thickness defined according to the stack axis at the mounting position, which thickness is greater than the thickness of the bipolar plate so as to prevent any flow of fluid at the mounting position.

[0026] According to a preferred embodiment, seals are inserted between the bipolar plates and extend protrudingly into the flow passages so as to participate in tight sealing of the bipolar plates.

[0027] Preferably, the indexing member cooperates with the seal to provide tight insulation, so that the positioning of the insulating device is precise to tightly insulate the bipolar plates.

[0028] The present invention also relates to a method of insulating a cell from a fuel cell comprising a stack comprising a plurality of cells aligned along a stack axis and a plurality of fluid flow paths within the stack, the method comprising: - transforming an insulating device as presented above from a first configuration to a second configuration, so as to reduce a cross-section of the insulating device such that the cross-section is smaller than a cross-section of the flow path; - moving the insulating device in a second configuration within the flow path so as to align said insulating device with at least one flow opening of a cell to be isolated; - releasing the constraint to deform the insulating device from the second configuration to the first configuration such that the belt is pressed against an inner surface of the flow channel to interrupt fluid communication between the flow channel and the flow opening of the defective cell; The method includes the steps of:

[0029] Preferably, the isolation method comprises the step of electrically connecting the cell to be isolated to another cell of the stack, preferably an adjacent cell, so that the defective cell is electrically isolated to enable the stack to supply voltage.

[0030] The invention will be better understood on reading the following description, given by way of example, and by referring to the following figures, given by way of non-limiting example, in which the same reference numbers have been given to similar objects: [Brief description of the drawings]

[0031] [Figure 1] 1 is a schematic diagram of a fuel cell according to the present invention; [Diagram 2] FIG. 2 is a first schematic cross-sectional view of a fluid flow path having an insulating device. [Diagram 3] FIG. 2 is a second schematic cross-sectional view of a fluid flow path having an insulating device. [Figure 4] FIG. 13 is a third schematic cross-sectional view of a fluid flow path having an insulating device. [Diagram 5] FIG. 2 is a first schematic diagram of an isolation device. [Figure 6] FIG. 2 is a second schematic diagram of an isolation device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] It should be noted that the figures present the invention in detail for implementing the invention, and said figures can of course be used to better define the invention as needed.

[0033] The present invention relates to the field of fuel cells of the proton exchange membrane type, known by its abbreviation PEMFC for "Proton Exchange Membrane Fuel Cell". Preferably, the fuel cells are installed on board aircraft to power their propulsion equipment.

[0034] 1, there is shown a fuel cell 1 comprising a stack 2 comprising a plurality of cells aligned along a stack axis X. Each cell comprises a plurality of fluid flow openings aligned parallel to the stack axis X to form a plurality of fluid flow paths 20 within the stack 2.

[0035] The stack 2 of cells allows electrochemical reactions from fluids, in particular hydrogen and oxygen. In this example, each cell comprises a membrane electrode assembly, known by its abbreviation MEA. Each MEA is brought into contact with reactant gases (for example hydrogen and oxygen that may be present in the air) on the two opposite sides of that MEA through interconnecting plates to form a cell. In a known manner, an assembly of two interconnecting plates, belonging to two adjacent cells, is called a bipolar plate. The bipolar plate is thus inserted between the cathode of the MEA and the anode of the adjacent MEA. The bipolar plate thus supplies, on the one hand, fuel (hydrogen) to the first MEA on the anode side and, on the other hand, oxidant (oxygen) to the second MEA on the cathode side. Generally, each bipolar plate comprises an internal cooling circuit in which a heat transfer fluid circulates to provide heat or to extract heat created by exothermic reactions. Such stacks 2 formed of alternating MEAs and bipolar plates are known in the prior art and will not be presented in further detail.

[0036] In this example, with reference to Figure 1, the fuel cell 1 further comprises a collector plate 4 positioned at the end of the stack 2 so as to collect the current generated by the cells. In a known manner, the power delivered by the fuel cell 1 depends on the number of cells (delivered voltage capacity) and the flow rate of the reactant fluids (the importance of the electrochemical reactions producing the current).

[0037] Referring to FIG. 1 , the fuel cell 1 further comprises two end plates 3 arranged at the ends of the stack 2 along the stack axis X, and a number of traction members connecting the end plates 3 to each other for compressing the stack 2.

[0038] With reference to FIGS. 2 to 6, an isolation device 9 according to the invention is presented for isolating a defective cell from the stack 2.

[0039] As a reminder, as mentioned earlier, a cell comprises a membrane electrode assembly MEA and two interconnected plates. Two adjacent interconnected plates form a bipolar plate.

[0040] 2 to 4, the stack 2 comprises alternating bipolar plates 21 and membrane electrode assemblies MEA 22 for generating electrical energy. The stack 2 comprises several flow channels 20 extending along the stack axis X and placing each of the bipolar plates 21 in fluid communication, thus feeding the MEA 22. To provide a seal between the bipolar plates 21, seals 23 are provided between the bipolar plates 21. The seals 23 are elastic and contribute to the indexing of the insulating device 9 as presented below. Preferably, the seals 23 extend protrudingly into the flow channels 20, which facilitates the formation of a seal with the insulating device 9. Each bipolar plate 21 comprises a flow opening 210 leading into the flow channels 20 to allow the fluid circulating in the flow channels 20 to be fed to the bipolar plates 21.

[0041] In practice, a channel 20 supplies a reactant fluid to a single side of the bipolar plate 21 and its contacting MEA 22, while the other side is supplied by a different reactant fluid via another channel 20.

[0042] 2 to 4, the bipolar plate 21 is configured to supply an MEA 22 located above the bipolar plate 21 for this flow path 20. Of course, this can be different for different flow paths 20.

[0043] When an MEA 22d is defective, this defect can create hot spots and pose a risk to the fuel cell 1. It is therefore necessary to insulate the cell to which the defective MEA 22d belongs, and in particular the bipolar plate 21a that supplies it. In this example, the bipolar plate 21a that supplies the defective MEA 22d is located below the defective MEA 22d.

[0044] In this example, stopping the supply of a single reactant fluid from the defective MEA 22d is sufficient to isolate the defective MEA. Nevertheless, it goes without saying that the supply of all reactant fluids of the defective MEA 22d can be stopped by using an isolation device 9 in the other flow paths 20. Preferably, the isolation is performed in the flow path 20 conducting hydrogen.

[0045] According to the invention, and with reference to figures 2 to 4, an insulating device 9 according to an embodiment of the invention is used to seal all fluid flow openings 210 of at least one bipolar plate 21 adjacent to a defective MEA 22d. In this example, the bipolar plate 21 located below the defective MEA 22d will be isolated since it is the latter that feeds the defective MEA 22d. In the following, the bipolar plate to be isolated will be referred to as 21a.

[0046] 5 and 6, the isolation device 9 comprises a circumferential belt 90. The belt 90 has a thickness defined according to the stack axis X in the mounting position, which is greater than the thickness of the bipolar plate 21 so as to prevent any flow of fluid in the mounting position. In particular, the belt 90 allows to cooperate with the seal 23 adjacent to the bipolar plate 21 to be isolated, as shown in FIG. 4. The flow channels 20 are therefore no longer in fluid communication with the flow openings 210 of the bipolar plate 21a to be isolated. The bipolar plate 21 is no longer supplied with fluid and can no longer supply the defective MEA 22d. The belt 90, due to its circumferential shape, always allows the supply of fluid of the bipolar plates 21 located above and below the isolation device 9, so that the fluid can circulate in the center of the belt 90.

[0047] Preferably, the belt 90 is configured to be deformable between a first configuration, referred to as an idle configuration, and a second configuration, referred to as a contracted configuration, the cross-section of the second configuration being smaller than the cross-section of the first configuration. Preferably, the cross-section of the first configuration is substantially similar to the cross-section of the flow passage 20, and the insulating device 9 is configured to be mounted to closely conform to its contour. Preferably, the belt 90 is formed of a deformable elastic material, for example an elastomer or rubber, which further has good sealing properties.

[0048] Preferably, the insulating device 9 comprises a spring member 91 configured to constrain the belt 90 in the first configuration. In this example, the spring member 91 takes the form of a spring leaf, as shown in Figures 5 and 6. Preferably, the spring member 91 is mounted within the belt 90, in particular within a groove 94 formed within the inner surface so as not to contact the inner surface of the flow passage 20. The spring member 91 preferably comprises a protruding end 91a that allows an operator to conveniently constrain the spring member 91 to deform the belt 90 in the second configuration.

[0049] Such a spring member 91 is not required, and the belt 90 can elastically deform the seal 23 when the insulating device 9 is installed.

[0050] Preferably, the insulating device 9 comprises an indexing member 92 configured to be received between two seals 23 so as to provide a precise positioning of the insulating device 9 in the flow passage 20, i.e. aligned with the flow openings 210 of the bipolar plate 21a to be insulated. In this example, the indexing member 92 takes the form of a peripheral tab extending protruding from the outer surface of the belt 90. Preferably, the indexing member 92 is drawn from the material of the belt 90, which makes it possible to reduce the manufacturing costs of the belt 90 and to maintain the sealing properties of the belt 90. Such an indexing member 92 advantageously makes it possible to index with respect to the seals 23 and to deform them. The tongue shape makes it possible to optimize the contact with the seals 23 to improve sealing.

[0051] With reference to Figures 5 and 6, the insulating device 9 comprises a number of guide members 93 configured to cooperate with the inner surface of the flow passage 20 but not completely block the flow openings 210 of the bipolar plate adjacent to the bipolar plate 21a to be insulated. In this example, the guide members 93 are simple and discontinuous to allow fluid flow between them. The guide members 93 are preferably positioned at each corner of the shape defined by the cross section of the flow passage 20. In this example, the flow passage 20 has a parallelogram cross section defining four corners. Also, as shown in Figures 5 and 6, the insulating device 9 comprises four guide members 93 to provide rigidity and improve the cooperation of the insulating device 9 with the recessed zones (corners) of the flow passage 20. The precise guiding and positioning substantially improves the sealing. As shown in Figures 5 and 6, the guide members 93 take the form of parts that protrude vertically from the upper wall of the belt 90 so that the guide members 93 can be conveniently manipulated by the operator. Preferably, the guide members 93 are derived from the material of the belt 90, thereby making it possible to reduce manufacturing costs.

[0052] An example of the implementation of the method for isolating the cells of the stack 2 is now presented. In this example, with reference to Fig. 4, a flow channel 20 contains a defective membrane electrode assembly (MEA) 22d that must be isolated. The flow channel 20 runs vertically and is accessible from an upper opening of the flow channel. Preferably, the isolation is performed in the flow channel 20 that conducts hydrogen.

[0053] The method comprises the step of deforming the insulating device 9 from a first configuration to a second configuration, such that a cross-section of the insulating device 9 is reduced such that the cross-section is smaller than a cross-section of the flow passage 20. The deformation is simply performed by an operator by acting on the spring member 91, in particular on the end 91a of the spring member 91.

[0054] The method includes moving the insulating device 9 in the flow channel 20 according to a second configuration such that the indexing member 92 is aligned with the bipolar plate 21a to be isolated that is located below the defective MEA 22d.

[0055] The method includes a step of releasing the constraints applied to the insulating device 9, so that in the idle position it regains the first configuration, having a substantially equal idle cross section of the flow channel 20. When the constraints are released, the belt 90 presses the seals 23 so as to impede any flow of fluid between the flow channel 20 and the bipolar plate 21a to be insulated located below the defective MEA 22d. The presence of the indexing members 92 allows a precise positioning and an optimal sealing cooperation between the seals 23. The guiding members 93 allow the expansion of the belt 90 to be guided in the first configuration, by positioning itself in the recessed zone of the flow channel 20, in particular in its four corners. This limits the risk of positioning defects of the insulating device 9, especially when the flow channel 20 has a large height and the defective MEA 22d is away from the access to the flow channel 20.

[0056] With the insulating device 9 in place, any fluid circulation between the flow paths 20 and the bipolar plate 21a located below the defective MEA 22d is stopped, which makes it possible to interrupt the supply to the MEA 22 located adjacent to the bipolar plate 21a. The defective MEA 22d is therefore no longer supplied, which prevents the formation of hot spots.

[0057] Preferably, the method includes the step of electrically connecting the adjacent bipolar plate 21a to the defective MEA 22d to provide electrical continuity within the fuel cell 1. Preferably, an electrical cable 10 is used to electrically connect the bipolar plates 21, as shown in Figure 4. In other words, the bipolar plate 21a is no longer fluidly supplied but is electrically shunted, which provides isolation of the defective cell, allowing the fuel cell 1 to operate with one less cell.

[0058] When the fuel cell 1 is in use, fluid flows into the flow passages 20 to supply the uninsulated cells to produce electrical energy. The fluid pressure constrains the belt 90 radially outwardly, allowing the belt to press against the flow openings 210, which provides an optimal seal.

[0059] It goes without saying that, although the isolation of a cell whose MEA 22d is defective is presented, the invention also applies to one or more cells whose bipolar plate 21 is defective. The isolation device 9 advantageously makes it possible to cut off the fluid supply of said bipolar plate 21 and the associated cell.

[0060] When some adjacent MEAs 22 are defective, the insulating device 9 has a larger height and indexing members 92 for each bipolar plate to be isolated.

Claims

1. 1. An insulating device (9) configured to be mounted in a fluid flow path (20) of a fuel cell (1) comprising a stack (2) comprising a plurality of cells aligned along a stack axis (X) and a plurality of fluid flow paths (20) in the stack (2), the insulating device (9) comprising a belt (90) on its periphery and configured to interrupt fluid communication between the flow paths (20) and at least one flow opening of a cell to be isolated from the stack (2), the belt (90) having a cross-section defined as a surface bounded by the periphery of the belt (90), the belt (90) comprising: a first configuration, referred to as the idle configuration, in which the cross section of the belt (90) is substantially similar to the cross section of the flow path (20) and in which an insulating device (9) is configured to be attached; a second configuration, referred to as a contracted configuration, in which the cross-section of the belt (90) is smaller than its cross-section in the first configuration; an insulating device (9) that is deformable between

2. 2. The isolation device (9) of claim 1, wherein the isolation device (9) comprises a spring member (91) configured to constrain the belt (90) in the first configuration.

3. 10. The insulating device (9) of claim 1, wherein the insulating device (9) comprises an indexing member (92) configured to provide precise positioning of the insulating device (9) within the flow path (20).

4. The insulating device (9) of claim 1, wherein the insulating device (9) comprises a plurality of guide members (93) configured to cooperate with an inner surface of the flow passage (20).

5. 5. The isolation device (9) of claim 4, wherein the flow passage (20) has a cross section defining a plurality of corners, and the guide members (93) are configured to cooperate with the corners of the flow passage (20).

6. 6. A fuel cell assembly (1) comprising a stack (2) having a plurality of cells aligned along a stack axis (X) and a plurality of fluid flow paths (20) within the stack (2), and an isolation device (9) according to any one of claims 1 to 5 positioned within the flow paths (20) to seal fluid communication between the flow paths (20) and at least one cell to be isolated from the stack (2).

7. 7. The assembly of claim 6, wherein the stack (2) comprises alternating bipolar plates (21) and membrane electrode assemblies (22) that define cells of the stack (2), and wherein an insulating device (9) is positioned in the flow path (20) so as to block fluid communication between the flow path (20) and the bipolar plate (21 a) to be insulated.

8. 8. The assembly of claim 7, wherein a seal (23) is inserted between the bipolar plates (21), the seal (23) extending protruding into the flow path (20).

9. 9. The assembly of claim 8, wherein the insulating device (9) comprises an indexing member (92) configured to ensure precise positioning of the insulating device (9) within the flow path (20), the indexing member (92) cooperating with the seal (23) to provide tight insulation.

10. 1. A method for insulating cells from a fuel cell (1) comprising a stack (2) comprising a plurality of cells aligned along a stack axis (X) and a plurality of fluid flow paths (20) within the stack (2), comprising: transforming an insulating device (9) according to any one of claims 1 to 5 from a first configuration to a second configuration, so as to reduce the cross section of the insulating device (9) so that the cross section is smaller than the cross section of the flow path (20); moving the insulating device (9) in a second configuration within the flow path (20) so as to align said insulating device (9) with at least one flow opening of a cell to be isolated; Releasing the restraint and deforming the insulating device (9) from the second configuration to the first configuration so as to press the belt (90) against the inner surface of the flow channel (20) to interrupt fluid communication between the flow channel (20) and the flow opening of the defective cell; A method of insulating, comprising the steps of:

11. 11. A method of isolation according to claim 10, comprising the step of electrically connecting the cell to be isolated to another cell of the stack (2), preferably to an adjacent cell.

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