FR2891404A1 - Fuel cell for use as electric source, has inlet collector whose effective fluid passage section varies progressively along longitudinal flow of fluid and with partition walls inclined for increasing and reducing fluid passage section - Google Patents

Abstract

The cell has an inlet collector (20) whose effective fluid passage section varies progressively along a longitudinal flow of a fluid from a main orifice (22) till its opposite end. The collector has a partition wall (26) dividing a case (21) into an isolated volume and a useful volume. The wall is inclined for reducing the fluid passage section along the fluid flow in the collector. A partition wall (36) is placed in an outlet collector (30) and inclined in a direction inverse to that of the wall (26) for increasing the passage section along the fluid flow in the collector (30).

Description

Fuel cell powered by a distribution system

  The invention relates to a fuel cell, in particular used as an electrical source on board a motor vehicle.

  The invention more particularly relates to a fluid distribution system supplying this fuel cell with reagents.

  Such a fuel cell 10, an example of which is represented in FIG. 1, is generally formed of a stack of cells 11 each of which is composed of a planar cathode 12 and of a planar anode 14, separated by an electrolytic membrane 16 , of polymer material in the case of PEMFC (Polymer Electrolyte Membrane Fuel Cell) and ceramic in the case of SOFC (Solid Oxyd Fuel Cell). The cells 11 of the stack are separated by plates 18 intended to supply the electrodes with reagents. The flat cathodes 12 are thus supplied with oxidant, which may be atmospheric air or any other source of oxygen while the flat anodes 14 are supplied with fuel, which is hydrogen H 2.

  The hydrogen and oxygen supply of this cell 10 is ensured by a system which allows for each reagent to distribute, from a single source, a fluid to plates supplying electrodes. Such a system comprises: parallel bundles of conduits 19 arranged in plates 18 also parallel to each other and providing at least one fluid to the electrodes; at least one collector 20 which extends longitudinally and which comprises a main inlet orifice 22 and a series of lateral secondary orifices 24 connected to the plates 18 for distributing at least one fluid in the conduits 19; and means for homogenizing the distribution of the fluid in all the plates.

  The system is generally equipped with an outlet manifold (not shown in FIG. 1) of the same type as the inlet manifold 20 and which collects the unreacted fluid, mixed with the fluids produced by the reaction, for the point to a single escape point.

  There are two possibilities for supplying the stack according to the direction of flow of the fluid in such a distribution system.

  According to the first possibility, the main orifices 22 in the inlet and outlet manifolds 30 are situated on the same side of the stack, so that if the fluid flows longitudinally from left to right in the collector input 20 then it flows in the opposite direction, from right to left, into the output collector. This possibility is commonly referred to as "U stack".

  According to the second possibility, the main orifices in the inlet and outlet manifolds 20 are situated on either side of the stack, so that the fluid flows longitudinally from left to right in the collector input and also in the output collector. This possibility is commonly called stacking in "Z" ("Z stack").

  There are also fuel cells operating in so-called "dead-end" mode at the anode 12. In such a stack, the anodic distribution system then comprises an inlet manifold of the type described above by which the fuel feeds the various anodes, but it does not have a fuel outlet manifold.

  Advantageously with respect to a traditional mode of operation at the anode, the mode of operation in "dead end" at the anode allows to consume substantially all the fuel. Thus, it is not necessary to provide a treatment of the fuel not consumed.

  All the cells 11 of such a cell 10 are, in general, electrically connected in series but the distribution of the reactive fluids is carried out in parallel between the cells 11. The electric power produced by the cell 10 is proportional to the flow rates of oxidizer and fuel. It is therefore necessary for all the cells 11 to be fed as homogeneously as possible in order to ensure overall good operation of the cell 10.

  In such a fluid distribution system in the fuel cells, the inlet and outlet manifolds have constant sections along the stack. However, the systematic pressure losses "slow down" the flow, which gradually decreases the flow along the flow in the collector. Thus all the cells 11 are not powered in the same way and this has the effect of greatly reducing the overall efficiency of the stack.

  In the current state of the art and in the case of fuel cells used in the automobile, the solution adopted to avoid the gradual decrease of the fluid flow and thus to homogenize its distribution is to oversize the collectors so as to make the negligible losses. However, compactness and lightness are key factors that must be respected for automotive applications.

  Another solution, proposed in document US-A-2003/0104265, is to "regulate" the flow entering the plates by introducing a cylindrical "obstacle" into the inlet manifold upstream of the secondary distribution orifices. This element causes a local narrowing of the flow passage section. The dispersion and the distribution of the flow, due to the passage by this narrowing, cause a more homogeneous distribution of the gas at the entrance of the beams.

  However, the incorporation of such a cylindrical obstacle has the disadvantage of considerably increasing the pressure drops and decreasing the overall efficiency of the system.

  To remedy these problems, the present invention proposes a fuel cell powered by a fluid distribution system of the type described above equipped with means for homogenizing the distribution of the fluid in all the plates, characterized in that the cross section of the Fluid passage in the manifold evolves longitudinally from the inlet port to its opposite end.

  According to other characteristics of the invention: the collector is a constant section housing in which is arranged a partition gradually varying the passage section of the collector; the collector is a duct formed longitudinally in the stack of cells; the fuel cell comprises at least one inlet manifold and an outlet manifold, made in accordance with the teachings of the invention, which are connected to the bundle plates, and which are arranged longitudinally on either side of the stack; the main orifices of the two inlet and outlet manifolds are situated on the same side of the stack and the passage section is progressively decreasing from upstream to downstream according to the direction of flow of the fluid in the inlet manifold, and the fluid passage section is progressively increasing from upstream to downstream depending on the flow direction of the fluid in the outlet manifold; the main orifices of the two inlet and outlet manifolds are situated on either side of the stack and the section of passage of the fluid in the two manifolds is progressively increasing from upstream to downstream in the direction of flow fluid up to mid-length of the stack then gradually decreasing; the roughness of the internal walls of the collectors is determined as a function of the losses of charges.

  Other features and advantages will become apparent upon reading the detailed description which follows for the understanding of which reference will be made to the appended drawings in which: FIG. 1 is a diagrammatic sectional view of a stack; According to the prior art; FIG. 2A is a perspective view of the distribution system according to the prior art and FIG. 2B is a schematic perspective view of the stack with a collector comprising a partition according to a first embodiment of the invention; - Figure 3 is a sectional view of a stack of a battery according to the first embodiment of the invention for the so-called "U" distribution; FIGS. 4A and 4B show sections of a stack of a stack whose distribution is called "Z" according to the first embodiment of the invention; FIGS. 5A and 5B illustrate the embodiment procedure according to the second embodiment of the invention.

  In the following description, identical, like or like elements will be designated by the same reference numerals.

  In the description and in the claims, the vertical, longitudinal and transverse terminology will be adopted in a nonlimiting manner with reference to the trihedron (L, V, T) of the figures and the upstream to downstream orientation according to the direction of flow of the flow with reference to the arrows indicating the direction of flow in the manifolds.

  The dispensing system, represented in FIG. 2A, comprises an inlet manifold 20, which is a casing 21 of generally tubular shape of longitudinal orientation whose length is substantially equal to the thickness of the stack of the fuel cell 10 The manifold 20 comprises at its upstream end a main orifice 22 through which a fluid is injected at a certain speed and lateral orifices 24, distributed regularly along the manifold 20, through which the fluid flows out of the manifold 20. Each these lateral orifices 24 is connected to a plate 18 having a bundle of parallel ducts 19 (not visible in FIG. 2). Thus, the fluid flowing in the manifold 20 flows into the duct bundles 19 of the plates 18. The fluid said to be unreacted, mixed with the fluids produced by the reaction, is collected in an outlet manifold 30 of the It is the same type as the inlet manifold 20 and which directs the fluid to a single exhaust point. The inlet manifolds 20 and outlet 30 are here arranged symmetrically with respect to the axis passing through the centers of the cells 11 of the stack for a better distribution of the fluid in the fuel cell 10. Each manifold has a rectangular section substantially constant throughout its length.

  As can be seen in FIG. 2B, the inlet manifold 20 comprises a partition 26 and the outlet manifold 30 comprises a partition 36.

  The partition 26 located in the inlet manifold 20 divides the housing 21 into two volumes. FIG. 3 shows an isolated or "dead" volume 28 in which the fluid does not circulate, and a working volume 29 in which the fluid flows. For the case of the flow called "U" and in accordance with the teachings of the invention, the partition 26 located in the inlet manifold 20 is inclined so as to gradually reduce the passage section along the flow of the fluid in the inlet manifold 20. Symmetrically, the partition 36 located in the outlet manifold 30 is inclined in the opposite direction to that of the partition 26, as shown in Figure 3, to gradually increase the passage section along the flow of fluid in the outlet manifold 30.

  Thus, the fluid injected into the inlet manifold 20 is subjected to losses of loads all the higher as the cross section in the inlet manifold 20 decreases. The flow rate of the fluid in the manifold decreases along the flow while the flow rate in the plates is uniform. This loss of speed is compensated by the arrangement of the partition 36 in the outlet manifold 30. In fact, the fluid collected in the outlet manifold 30 then undergoes losses of loads that are lower than the passage section. increases. The fluid is thus gradually "braked" in the inlet manifold 20, and is then "accelerated" gradually in the outlet manifold 30, so that, after a transient start-up regime, the circulation of the fluid in the system is more homogeneous than in the case of constant section collectors according to the state of the art.

  In the case of the so-called "Z" flow, represented in FIG. 4A, the inlet manifold 20, the partitions 26 and 36 located in the inlet and outlet manifolds 30 are inclined in the same direction, so as to obtain as previously, a progressive reduction of the effective section of the housing 21 along the flow in the inlet manifold 20 and a gradual increase of this section in the outlet manifold 30.

  For this type of stack, it is possible to use partitions 46 and 56, shown in FIG. 4B, which comprise two slopes of opposite inclinations so as to progressively reduce the passage section along the flow of the fluid up to mid-length of the housing 21, then increase gradually. The fluid thus undergoes variable losses of charge throughout its flow throughout the distribution system so as to homogenize globally its diffusion in the plates 18 of the stack.

  In the case of "dead-end" batteries in which there is no outlet manifold, an inclined partition can be fixed in the inlet manifold 20 oriented such that the fluid passage section in the housing 21 increases along the flow, so as to compensate for loss of charge and to make more homogeneous circulation of the fluid in the various plates 18.

  For the partitions, it is possible to choose flat or solid elements introduced into the collector having profiles of linear or parabolic evolution, or else other profiles of more specific evolution or of more or less important inclination, so as to obtain the desired variation of the passage section. Furthermore, all the partitions can be equipped with seals on their edges to ensure the tightness of the volume 28.

  It is also possible to implement the invention without using separating partitions but using other techniques for manufacturing commutators with an evolutionary section.

  A second embodiment of the present invention relates more particularly to so-called internal collector distribution systems, frequently used in fuel cells so as to increase their compactness.

  As can be seen in FIG. 5A, the housing 21 of the collector 20 is formed in the stack of cells 11, each pierced by an opening 38. Once the cells 11 have been stacked, as shown in FIG. 5B, the collector internal inlet 20 comprises, as for the external collector described above, the main orifice 22 through which the fluid is injected and the remaining fluid is collected in the internal outlet manifold 30. Interstices between the cells 11 which have the function lateral orifices 24 (not visible in FIG. 5B) are arranged in such a way as to feed only the electrodes of the same electrical nature of the cells 11.

  This embodiment of the invention results from the fact that several or all the cells 11 each comprise an opening 38 of different section of the cell 11 which precedes it so that the inlet or outlet manifold thus formed, has a passage section of the fluid which varies progressively along the stack.

  This embodiment allows a gain in compactness because, as shown in FIGS. 5A and 5B, the two distribution systems, anodic and cathodic, can be arranged, that is to say, "drill" four head-tail collectors. ", two symmetrically opposite collectors for the anodic distribution and the two others for the cathodic distribution.

  For fuel cells, it is common to circulate three fluids, two reactive fluids and a coolant. The present invention can be applied to each of the three distribution circuits depending on which embodiment is best suited.

  According to another embodiment of the invention (not shown), the inner walls of inlet and outlet manifolds 20 and 30 comprise foreign elements which disturb the flow and increase the characteristic resistance of the housings. By progressively increasing the characteristic coefficient of friction along the pipe, the pressure drops are progressively increased and the speed of the flow is changed.

  This can be achieved, as in US-A-4,809,744, by adding a metal grid on the inner wall of the housing 21, but also by the introduction of pins, grains or other rough elements intended to increase the roughness internal walls, while restricting the diameter of the pipe. io

  Depending on the intended application, these elements are easy to size and introduce. These elements can also be introduced or embedded directly on the separating partitions 26, 36 described in the previous embodiments or they may be added independently thereafter. he

Claims (8)

  A fuel cell (10), powered by a fluid distribution system (fuel, oxidizer or coolant), comprising: s - parallel bundles of conduits (19) arranged in the form of plates (18) beams parallel to each other and which provide at least one fluid electrodes of the same electrical nature; at least one longitudinally extending manifold (20) which has a main port (22) and a series of lateral side ports (24) connected to the beam plates (18) for distributing at least one fluid in the conduits (19) beams; and means for homogenizing the distribution of the fluid is in the entire system characterized in that the effective cross section of the fluid in the manifold (20) varies gradually along the longitudinal flow of the fluid from the main orifice input (22) to its opposite end.   2. Fuel cell (10) fed by a fluid distribution system according to claim 1, characterized in that the collector (20) is a housing (21) of constant section in which is arranged a partition (26) which the divides into a "dead" volume (28), in which the fluid does not circulate and a working volume (29) in which the fluid circulates, and whose passage section varies gradually.   3. fuel cell (10) fed by a fluid distribution system according to claim 1, characterized in that it comprises a solid element introduced into the manifold so as to gradually vary the effective cross section of the fluid.   4. fuel cell (10) fed by a fluid distribution system according to claim 1, characterized in that the collector (20) is a duct formed longitudinally in the stack of cells (11).   Fuel cell (10) fed by a fluid distribution system according to any one of the preceding claims, characterized in that it comprises at least one inlet manifold (20) and one outlet manifold (30), realized in accordance with the teachings of the invention, which are connected to the plates (18) of beams, and which arranged longitudinally on either side of the stack.   io Fuel cell (10) fed by a fluid distribution system according to claim 5, characterized in that the main orifices (22) and (32) of the two inlet (20) and outlet (30) manifolds are located on the same side of the stack and in that the passage section is progressively decreasing from upstream to downstream according to the flow direction of the fluid in the inlet manifold (20) and the fluid passage section is progressively increasing from upstream to downstream according to the flow direction of the fluid in the outlet manifold (30).   Fuel cell (10) fed by a fluid distribution system according to claim 5, characterized in that the main orifices (22) and (32) of the two inlet (20) and outlet (30) manifolds are located on either side of the stack and in that the fluid passage section in the two collectors is progressively increasing from upstream to downstream depending on the direction of flow of the fluid to the half-length of the 'stacking then gradually decreasing.   8. Fuel cell (10) fed by a fluid distribution system according to any one of the preceding claims, characterized in that the roughness of the internal walls of the collectors (20, 30) is determined as a function of the losses of charges.