FR3028097B1 - FUEL CELL HAVING AN IMPROVED COOLING SYSTEM - Google Patents

Abstract

Fuel cell comprising a stack of superimposed bipolar plates (1, 2) and proton exchange membranes (3) arranged between two successive plates, the fuel cell comprising a cooling system, characterized in that the cooling system comprises two disrupted coolant flow circuits (4, 5) in the fuel cell, each bipolar plate (1, 2) being connected to one or the other of said coolant flow circuits (4, 5), thereby defining - a first type of bipolar plates (1), each connected to the first coolant flow circuit (4), - a second type of bipolar plates (2), each connected to the second flow circuit coolant fluid (5), said coolant flow circuits (4, 5) defining coolant flows having distinct flow directions.

Description

GENERAL TECHNICAL FIELD

The present invention relates to the field of fuel cells, and more particularly to fuel cells for applications in the field of aeronautics.

STATE OF THE ART

High temperature fuel cells emit a significant amount of heat that must be removed during operation to ensure proper operation under nominal conditions.

Current solutions consist essentially of cooling by means of a heat transfer fluid flow perpendicular to the flow of the reagents, or a stream of coolant having a serpentine-like shape.

These solutions, however, lead to the formation of a temperature gradient in the fuel cell along the plates forming the stack of the fuel cell, which generates thermomechanical stresses on the surfaces of the plates, and thus adversely affects the operation of the fuel cells while affecting their life.

PRESENTATION OF THE INVENTION

The present invention thus aims at remedying at least partially these problems, and proposes a fuel cell comprising a stack of superimposed bipolar plates, and proton exchange membranes arranged between two successive plates, characterized in that the bipolar plates are configured from in order to define two disjoint heat transfer fluid circuits in the fuel cell, each bipolar plate being connected to one or the other of said heat transfer fluid flow circuits, thus defining - a first type of bipolar plates, each connected to the first coolant flow circuit; - a second type of bipolar plates, each connected to the second coolant flow circuit, said coolant flow circuits (4, 5) defining fluid flows. coolant having distinct flow directions.

The first and second types of bipolar plates are advantageously configured so that the coolant flow in two successive bipolar plates is made in two opposite directions. The stack is for example made in a longitudinal direction of the fuel cell, the stack having first and second opposite ends in a transverse direction of the fuel cell, perpendicular to the longitudinal direction, the bipolar plates being configured from in such a way that the coolant flow in the bipolar plates of the first type is from the first to the second end of the stack, and that the coolant flow in the bipolar plates of the second type is second towards the first end of the stack.

The bipolar plates typically comprise each of the channels defining two separate coolant flow circuits, each bipolar plate having a single one of said conduits connected to the first coolant flow circuit or the coolant flow circuit.

The fuel cell is typically of the proton exchange membrane fuel cell type.

PRESENTATION OF THE FIGURES Other features, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, and which should be read with reference to the accompanying drawings, in which: FIG. schematic diagram showing the structure of a fuel cell according to one aspect of the invention; - Figure 2 schematically illustrates a fuel cell stack according to one aspect of the invention.

In all the figures, the elements in common are identified by identical reference numerals.

DETAILED DESCRIPTION

Fig. 1 is a block diagram showing the structure of a fuel cell according to one aspect of the invention.

This figure shows schematically two bipolar plates 1 and 2, forming for example an anode and a cathode of a fuel cell, between which is disposed a proton exchange membrane 3, commonly referred to as "Proton Exchange Membrane" or "PEM". The assembly thus formed has an operation well known to those skilled in the art of proton exchange membrane fuel cell, in which the two bipolar plates 1 and 2 perform a proton exchange through the membrane 3, to generate an electric current.

The operation of such a fuel cell is well known to those skilled in the art, and will not be described in more detail here.

The fuel cell thus formed is provided with a cooling system, for capturing and evacuating the calories generated in particular by the exothermic reaction at the membrane 3 during operation of the fuel cell.

As shown in FIG. 1, the fuel cell cooling system comprises two disjoint heat transfer fluid circuits 4 and 5, respectively connected to the bipolar plates 1 and 2.

The two bipolar plates 1 and 2 are thus cooled by heat transfer fluid flow circuits 4 and 5 separate and disjoint.

These heat transfer fluid flow circuits 4 and 5 typically comprise heat sinks, so as to evacuate the heat captured by the heat transfer fluid during its passage in the bipolar plates 1 and 2. In the embodiment shown, there are shown heat exchangers, respectively 41 and 51 for the coolant flow circuits 4 and 5.

The fuel cell thus comprises two disjoint flow circuits of heat transfer fluid 4 and 5, thus defining two cooling circuits for the fuel cell. Such a structure thus offers multiple possibilities for the cooling of the fuel cell, including cross-cooling as presented below, in contrast to conventional structures which are limited in terms of the cooling circuit possibilities.

FIG. 1 shows the direction of fluid flow in the coolant flow circuits 4 and 5.

An arbitrary proximal end and a distal end of the stack formed of the two bipolar plates 1 and 2 and the membrane 3 are arbitrarily defined.

Thus, a proximal end 11 of the first bipolar plate 1 and a distal end 12 of the first bipolar plate 1 are defined.

Likewise, a proximal end 21 of the second bipolar plate 2 and a distal end 22 of the second bipolar plate 2 are defined. The proximal ends 11 and 21 of the two bipolar plates 1 and 2 are superimposed in the stack, likewise that the distal ends 12 and 22 of the two bipolar plates 1 and 2 are superimposed in the stack.

The heat transfer fluid flow circuits 4 and 5 are advantageously configured to flow in opposite directions. By opposite, it is meant that the flow direction of the fluid in these two coolant flow circuits 4 and 5 is such that a first of said heat transfer fluid flow circuits defines a circulation of heat transfer fluid generally ranging from a first end of the stack at a second end of the stack, while a second of said heat transfer fluid flow circuits defines a coolant flow generally from a second end of the stack to a first end stacking.

In the schematic representation of FIG. 1, the heat transfer fluid flow circuit 4 of the bipolar plate 1 establishes a circulation of heat transfer fluid from the proximal end 11 towards the distal end 12 of the bipolar plate 1. The heat transfer fluid is cooled by arriving at the proximal end 11, and calorie loaded spring by the distal end 12. In contrast, the coolant flow circuit 5 of the bipolar plate 2 establishes a heat transfer fluid circulation of the distal end 22 towards the proximal end 21 of the bipolar plate 2. The coolant is cooled by arriving at the distal end 22, and calorically loaded spring by the proximal end 21.

There is therefore a cross flow of heat transfer fluids of the disjoint heat transfer fluid circuits 4 and 5; the two heat transfer fluid flow circuits 4 and 5 provide a heat transfer fluid inlet in the bipolar plates 1 and 2 at opposite ends of these bipolar plates 1 and 2.

Thus, the stack formed by the bipolar plates 1 and 2 and the membrane 3 is cooled by two opposite ends, and not by a single end as in conventional systems.

This fuel cell cooling system is advantageous in that it avoids the formation of a temperature gradient along the fuel cell.

Indeed, the coolant flow circuits 4 and 5 intersect; there is therefore an average temperature balance between the proximal end and the distal end of the stack, and not a gradual increase in temperature as would have been the case with uncrossed circuits.

Indeed, near the proximal end of the stack, the heat transfer fluid of the first circulation circuit 4 is still cooled and not loaded with calories, whereas, on the contrary, the heat transfer fluid of the second circulation circuit 5 is charged in calories after having passed through the entire bipolar plate 5. On the other hand, near the distal end of the stack, the coolant of the first circulation circuit 4 is loaded with calories after passing through the entire bipolar plate 1 whereas, on the other hand, the coolant of the second circulation circuit 5 is cooled.

Between the proximal end and the distal end of the stack, the change in the temperature of the heat transfer fluid is inversely proportional between the heat transfer fluid of the first circulation circuit 4 and the heat transfer fluid of the second circulation circuit 5.

The heat flows between the first circulation circuit 4 and the second heat transfer fluid circulation circuit 5 are therefore crossed, which balances the temperature on the surface of the fuel cell and thus prevents the formation of hot spots and thermomechanical stresses on the fuel cell. the surface of bipolar plates 1 and 2.

The coolant circulation circuits 4 and 5 may have several patterns that the bipolar plates 1 and 2. In the embodiment shown in Figure 1, there is shown serpentine circuits on the bipolar plates 1 and 2. It is understood although other reasons may be used, since they allow a circulation of coolant on the surfaces of the bipolar plates 1 and 2 to cool.

More generally, the invention defines two crossed cooling circuits arranged in the bipolar plates 2 and 3 of a fuel cell defining heat transfer fluid flows having distinct flow directions.

One can for example have flows in two parallel directions but in opposite directions, as illustrated in the figures, or for example flows in two perpendicular directions.

As indicated above, thus having heat transfer fluid streams having distinct flow directions within the fuel cell makes it possible to avoid or at least greatly attenuate the formation of a temperature gradient along the plates. bipolar.

FIG. 2 is a partially exploded view of a fuel cell stack comprising a plurality of bipolar plates and proton exchange membranes and having a cooling system as hereinbefore defined. The stack consists of bipolar plates and exchange membranes, arranged alternately, and further comprises end plates 6 on either side of the stack. The stack is further equipped with a cooling system comprising two coolant flow circuits 4 and 5 arranged in the bipolar plates 1 and 2, as previously described.

Two sets of bipolar plates are defined, depending on whether they are connected to the first coolant flow circuit 4 or to the second heat transfer fluid flow circuit 5.

The following are defined: a first type of bipolar plates, designated by the reference numeral 1, each connected to the first coolant flow circuit 4, a second type of bipolar plates, which is designated by 2, each connected to the second coolant flow circuit 5.

The plates of the first and second types 1 and 2 are arranged alternately in the stack. The stack is thus arranged as follows: - Bipolar plate of the first type 1; Proton exchange membrane; - Bipolar plate of the second type 2; Proton exchange membrane; - Bipolar plate of the first type 1; Proton exchange membrane; - Bipolar plate of the second type 2; Proton exchange membrane;

As already explained with reference to FIG. 1, the stack 10 comprises two disjoint heat transfer fluid flow circuits 4 and 5 defined by ducts arranged on the bipolar plates 1 and 2, thus making it possible to define several cooling circuit structures. for the fuel cell by virtue of these two disjoint heat transfer fluid flow circuits 4 and 5 integrated into the structure of the fuel cell.

In addition, as already explained with reference to FIG. 1, the two heat transfer fluid flow circuits 4 and 5 of the cooling system are advantageously configured so as to produce a cross flow of heat transfer fluid. The general flow directions of the heat transfer fluid on the bipolar plates of the first and second types 1 and 2 are shown schematically by arrows in FIG.

Thus, by defining a proximal end and a distal end of the stack, and therefore a proximal end 11 and a distal end 12 of the first type 1 bipolar plates, and a proximal end 21 and a distal end 22 of the bipolar plates of the first type 1, second type 2, the flow of the coolant of the first heat transfer fluid flow circuit 4 is substantially from the proximal end 11 to the distal end 12 of the stack, while the flow of heat transfer fluid of the second circuit heat transfer fluid flow 5 is substantially from the distal end 22 to the proximal end 21 of the stack. The stack therefore has a succession of cross flows of heat transfer fluid.

As already explained with reference to FIG. 1, these successive cross flows of heat transfer fluid cause a substantially uniform distribution of the temperature of the different bipolar plates 1 and 2 of the stack, and not a temperature gradient from one end to one other of the stacking. The bipolar plates are indeed cooled by opposite ends, and the heat transfer fluid cross flows distribute the heat on the surface of the plates, instead of creating a temperature gradient along the length of the bipolar plates 1 and 2.

More generally, as indicated previously, having heat transfer fluid streams having distinct flow directions within the fuel cell makes it possible to avoid or at least greatly attenuate the formation of a temperature gradient along the fuel cell. bipolar plates.

In the embodiment shown, the bipolar plates of the first and second type 1 and 2 have similar architectures, and each have six orifices forming two sets of conduits on the surface of the plate, each set of ducts typically having an inlet and two fluid outlets, and defining a fluid flow substantially from one end to another of the bipolar plate in question.

For each bipolar plate, only one of these sets of conduits is connected to one or the other of the coolant flow circuits 4 or 5 arranged in the bipolar plates 1 and 2 of the fuel cell, depending on whether the bipolar plate is first or second type 1 or 2.

Such a similar structure for the different bipolar plates 1 and 2 and for the membranes 3 is particularly advantageous in terms of manufacture and assembly.

Claims (5)

claims A fuel cell comprising a stack of superimposed bipolar plates (1, 2) and proton exchange membranes (3) arranged between two successive bipolar plates, characterized in that the bipolar plates (1, 2) are configured defining two disordered heat transfer fluid flow circuits (4, 5) in the fuel cell, each bipolar plate (1, 2) being connected to one or the other of said coolant flow circuits (4); , 5), thereby defining - a first type of bipolar plates (1), each connected to the first coolant flow circuit (4), - a second type of bipolar plates (2), each connected to the second circuit of heat transfer fluid flow (5), said coolant flow circuits (4, 5) defining coolant flows having distinct flow directions. The fuel cell of claim 1, wherein the first and second types of bipolar plates (1, 2) are configured such that the coolant flow in two successive bipolar plates is made in two opposite directions. The fuel cell of claim 2, wherein the stack is made in a longitudinal direction of the fuel cell, the stack having first and second opposite ends in a transverse direction of the fuel cell, perpendicular to the fuel cell. the longitudinal direction, the bipolar plates (1, 2) being configured so that the coolant flow in the bipolar plates of the first type (1) is from the first to the second end of the stack, and the coolant flow in the bipolar plates of the second type (2) is from the second to the first end of the stack. 4. Fuel cell according to one of claims 1 to 3, wherein the bipolar plates (1, 2) each comprise channels defining two separate heat transfer fluid flow circuits, each bipolar plate (1, 2) having a one of said conduits connected to the first coolant flow circuit (4) or the coolant flow circuit (5). 5. Fuel cell according to one of claims 1 to 4, wherein the fuel cell is of the proton exchange membrane fuel cell type.