DE102021115601A1 - Flow element, bipolar plate and fuel cell device - Google Patents

Abstract

The invention relates to a flow element for a bipolar plate of an electrochemical device, comprising a plate-shaped base body extending in two main directions of extension aligned at an angle to one another, the base body comprising a channel structure with a plurality of channels for forming an active area of the flow element, with an inflow opening in the base body and an outflow opening for a fluid are formed, which are flow-connected to the channel structure via an inflow area with an inflow channel structure or via an outflow area with an outflow channel structure, wherein a pressure loss of the fluid flowing from the inflow opening to the outflow opening is greater over the outflow area than over it the inflow area and/or over the active area. The invention also relates to a bipolar plate and a fuel cell device.

Description

The present invention relates to a flow element for a bipolar plate of an electrochemical device, in particular a fuel cell device, wherein the flow element comprises a plate-shaped base body with a channel structure extending in two main directions of extension aligned at an angle to one another.

Plate-shaped flow elements with a channel structure can be assembled in pairs to form a bipolar plate. A fuel cell device includes fuel cells with an active layer positioned between adjacent bipolar plates. In the example of a PEM fuel cell device (PEM, polymer electrode membrane), the active layer comprises in particular gas diffusion layers (GDL, gas diffusion layer) and a membrane electrode assembly (MEA). The invention is described below in particular using the example of a PEM fuel cell device with hydrogen and atmospheric oxygen as reactants (educts) and water as the reaction product, in which case cooling can be provided in particular. However, the invention is not limited to this fuel cell device used, for example, in the field of automotive engineering.

In the fuel cell stack, the fluidic media can be supplied to the individual flow elements in particular via distribution channels running in the direction of the stack. Collecting channels enable the media to be discharged from the flow elements. The distribution channels and collecting channels can in particular be referred to as so-called “manifolds”. A respective flow element can comprise an inflow opening and an outflow opening for at least one fluid, which are flow-connected to a channel structure of the flow element, the channel structure adjoining the active layer in order to enable a fluid exchange for the reaction. The flow element can also include passage openings for other fluids, such as coolants, which are fed to another side of the flow element or to another flow element within the stack. It goes without saying that the necessary sealing elements for sealing distribution channels, collecting channels and active layers are present within the fuel cell stack.

It is known that there are pressure differences in the direction of flow of the inflowing medium within the distribution channels. Within a respective fuel cell, there is also a pressure difference between the inflow side and the outflow side, as desired. In the present case, these pressure differences are referred to in particular as “pressure loss”. A pressure loss over the fuel cells is desirable in order to ensure the most homogeneous possible distribution of the respective fluid over the fuel cells with their channel structures and the respective active layers. This applies to the educts from the point of view of a performance that is as homogeneous as possible, for the cooling fluid, for example, from the point of view of improved, for example homogeneous, cooling. It is known that a pressure loss across the channel structure of a flow element bordering the active layer should preferably be kept as low as possible in order to avoid a drop in the partial pressure from the inflow to the outflow side in the case of gaseous educts. Nevertheless, a sufficiently large pressure drop is desirable to achieve a homogeneous distribution over the stack.

The object of the present invention is to provide a flow element for a bipolar plate of an electrochemical device which has improved flow properties with regard to improved performance when the flow element is used in an electrochemical device.

This object is achieved by a flow element according to the invention for a bipolar plate of an electrochemical device, comprising a plate-shaped base body extending in two main directions of extension aligned at an angle to one another, the base body comprising a channel structure with a plurality of channels for forming an active area of the flow element, wherein in Base body an inflow opening and an outflow opening for a fluid are formed, which are flow-connected to the channel structure via an inflow area with an inflow channel structure or via an outflow area with an outflow channel structure, with a pressure loss of the fluid flowing from the inflow opening to the outflow opening being greater over the outflow area than across the inflow region and/or across the active region.

According to one aspect of the invention, the fluid in the flow element according to the invention can flow from the inflow opening through the inflow channel structure, the channel structure for the active region which borders the active layer of the fuel cell, and the outflow channel structure to the outflow opening. In this case, a pressure loss occurs which, according to the invention, is greater over the outflow area than over the inflow area. Alternatively or additionally, the pressure drop across the outflow area can be greater than across the active area. With such a configuration tion is preferably avoided that the pressure loss over the inflow is too high and the concentration of the reactant in the active layer drops too much (in hydrogen-oxygen fuel cells, for example, this can also lead to the problem of a shift in the water balance). Due to the higher pressure loss in the outflow area, there is in particular the possibility of achieving a high pressure loss via the flow element and thus the individual fuel cell when used as intended, which can be relatively low up to the end of the channel structure at the active area. This can preferably prove to be advantageous for the homogeneity of the distribution of the fluid over the individual fuel cells with their respective channel structure on the one hand and/or advantageous for the highest possible absolute pressure to achieve a high yield on the other.

The channel structure on the active area forms in particular what is known as a flow field.

The channel structure in the active area can be designed in different ways. For example, a channel structure with channels running parallel to one another along one of the main directions of extension is provided, a meandering channel structure, a small foot channel structure, an interdigital channel structure, a fractal channel structure or combinations of the aforementioned channel structures are possible.

In particular, the absolute pressure loss over the outflow area is greater than over the inflow area and/or over the active area.

In particular, it can prove to be advantageous if a pressure loss per length of the flow element through which flow occurs over the outflow area is greater than over the inflow area and/or over the active area. For example, the shortest flow path in each case through the inflow channel structure, the channel structure in the active area and the outflow channel structure can be regarded as the “through-flow length”.

It can be advantageous if a pressure loss across the duct structure, in absolute terms and/or per length of the flow element through which flow occurs, is lower than a pressure loss across the inflow duct structure.

The inflow opening and the outflow opening can have the same or essentially the same opening cross section, based on the direction of the fuel cell stack.

The inflow channel structure and the outflow channel structure are preferably configured differently.

In particular, it can be provided that the higher pressure loss across the outflow area compared to the inflow area can be achieved by the difference between the inflow channel structure and the outflow channel structure. This is simple in terms of manufacturing technology and can therefore be carried out inexpensively. The quality of the channel structures at the inflow and outflow areas can differ from one another, so that ideally optimized channel structures are provided there in each case with regard to the best possible properties, for example pressure loss characteristics.

• - Gesamtströmungsquerschnitt der Einström-Kanalstruktur und der Ausström-Kanalstruktur;
• - Querschnitt von Kanälen;
• - Länge von Kanälen;
• - Breite von Kanälen;
• - Höhe von Kanälen;
• - Anzahl von Kanälen;
• - Vorsehen von Verzweigungen und/oder Vereinigungen von Kanälen;
• - Verlaufsrichtung von Kanälen, insbesondere Umlenkungen von Fluid in Kanälen mit dem Ziel der Steigerung des Strömungswiderstandes beispielsweise durch Verwirbelung.

In a preferred embodiment of the invention, the pressure loss across the outflow area compared to the inflow area can be achieved, for example, by a difference in at least one of the following:

• - Total flow cross section of the inflow channel structure and the outflow channel structure;
• - cross-section of channels;
• - length of channels;
• - width of channels;
• - height of channels;
• - number of channels;
• - provision of branching and/or merging of channels;
• - Direction of channels, in particular deflections of fluid in channels with the aim of increasing the flow resistance, for example by turbulence.

Alternatively or additionally, in a preferred embodiment of the invention it can be provided that the pressure loss across the outflow area in relation to the inflow area and/or to the active area can be achieved by at least one resistance element arranged in the outflow channel structure. The resistance element can, for example, be used in a targeted manner to shape the fluid flow in order to increase the pressure loss.

The flow element can, for example, be designed symmetrically, at least with regard to an outer contour, with respect to an axis of symmetry that is aligned transversely and, in particular, perpendicularly to a plane defined by the base body. Complete symmetry with respect to the axis is preferably provided. In order to take any manufacturing tolerances into account, this can be done Flow element rotates about the axis of symmetry and are thus installed in different orientations in the fuel cell stack.

Alternatively or additionally, it is advantageous if the inflow opening and the outflow opening are arranged diametrically opposite one another with respect to an axis which is aligned transversely and in particular perpendicularly to a plane defined by the base body. This also proves to be advantageous in order to arrange the flow element in a different orientation in the fuel cell stack after rotation about the axis.

In the case of bipolar plates with two flow elements, it can be provided that a respective side of a flow element, which faces away from the other flow element, can serve to conduct fluid for a reactant. On the sides facing one another, the flow elements can have, for example, a respective channel structure for a cooling medium. As already mentioned, in addition to the inflow opening and the outflow opening of the flow element, at least one further passage opening can be provided for a further distribution channel or a further collecting channel for the transport of a cooling fluid or a reactant.

According to what has been said, it can be provided that the flow element comprises a further inflow opening which is adjacent to the outflow opening or the inflow opening, and that the flow element comprises a further outflow opening which is adjacent to the inflow opening or the outflow opening. The respective openings are positioned side by side, for example.

The flow element can, for example, comprise a first side and a second side facing away from it, the channel structure, the inflow channel structure and the outflow channel structure being arranged on the first side. A further channel structure, a further inflow area with a further inflow channel structure and a further outflow area with a further outflow channel structure can be arranged on the second side. There is a fluid connection from the additional inflow opening to the additional outflow opening via the additional inflow area, the additional channel structure and the additional outflow area.

For example, the first side of an active layer faces the fuel cell and is used to conduct fluid for a reactant. The second side faces a further flow element of the bipolar plate, for example, and is used to conduct a cooling medium.

Based on a projection of the flow element transverse to the plane of the base body, the inflow area or the outflow area can be arranged, for example, laterally and in particular directly laterally next to the further outflow area. Alternatively or additionally, the outflow area or the inflow area can be arranged laterally and in particular directly laterally next to the further inflow area. If, for example, size changes are made in the inflow area and/or in the outflow area compared to a conventional flow element with regard to a desired pressure loss, a corresponding adjustment can be made to the further inflow area or the further outflow area, for example without additional installation space. This provides the ability to make adjustments to the sizes of inflow areas and outflow areas to achieve the benefits of the invention with two or more fluids without requiring additional area compared to conventional flow elements.

In a preferred embodiment of the invention, it can be provided that the flow element comprises a first edge region and a second edge region on opposite sides in one of the main directions of extension, with the inflow opening and at least one further through opening of the flow element being arranged on the first edge region and the Outflow opening and at least one further through-opening of the flow element, wherein in the second main direction of extension, which is aligned transversely to the first main direction of extension, the inflow area and the outflow area are only partially extended. In this case, in particular, the active area is arranged, for example, completely between the first and the second edge area, along the first main extension direction. Along the second main direction of extension, the extension of the channel structure of the inflow area and/or the outflow area is limited to a section of the flow element.

The inflow opening and the outflow opening for the medium are arranged, for example, on opposite edge regions of the base body. Correspondingly, if present, a through-opening and a further through-opening associated therewith for a further medium are arranged on mutually opposite edge regions of the base body.

The inflow opening and at least one further through-opening of the flow element, in particular two further through-openings, are connected to one another, for example arranged near edge region of the body. The outflow opening and at least one further through-opening of the flow element, in particular two further through-openings, are arranged in a corresponding manner, for example on a continuous edge area of the base body. The openings (inflow or outflow opening and at least one through-opening) lie side by side, for example, at the respective edge area.

The respective edge area can, for example, extend along a main extension direction along the entire base body.

The respective edge region can, for example, extend “around the corner” on the base body, in sections along a first main direction of extension and in sections along a second main direction of extension.

In another advantageous embodiment of the invention, it can be provided that the outflow area comprises a collecting section and an outlet section, the channel structure opening into the collecting section, this into the outlet section and the outlet section into the outflow opening. It is provided here, for example, that the outflow opening and at least one further through-opening of the base body are arranged on an edge region of the flow element on a side of the collecting section facing away from the channel structure.

In a corresponding manner, it can be provided that the inflow area comprises an inlet section and a distributor section, the inflow opening opening into the inlet section, this opening into the distributor section and the distributor section opening into the channel structure. It can be provided here, for example, that the inflow opening and at least one further through-opening of the base body are arranged on an edge region of the flow element on a side of the distributor section facing away from the channel structure.

The distributor section allows inflowing fluid to be distributed to the channels of the channel structure on the active area. Correspondingly, the collection section allows fluid to be collected from the channels of the channel structure. The distributor section and the collector section are not, for example, in the area of the active layer of the fuel cell. This configuration is used, for example, in structures in which a sealing element (for example an edge reinforcement or a subgasket) or a film covers the distribution section or the collection section.

The collection section and/or the distribution section preferably border the channel structure along the entire extent of the base body in one of the main directions of extent, in particular on opposite sides of the channel structure. For example, the collection section and/or the distributor section extend completely along the flow element in the above-mentioned main direction of movement.

It can be provided, for example, that a pressure loss at the collecting section and/or at the distributor section per length of the flow element through which flow occurs is greater than a pressure loss at the channel structure.

Favorably, a pressure loss per flow element length through which flow occurs is smaller at the outlet section than at the collecting section.

A pressure loss per length of the flow element through which flow occurs is preferably greater at the inlet section than at the distributor section.

The flow element can be a formed part, for example, and can be produced specifically by embossing.

The flow element can be made at least partially from a metal, for example.

The flow element can be formed at least partially graphitic, for example.

The flow element can, for example, be made at least partially from a plastic material, for example in the inflow area and/or in the outflow area.

The flow element can be manufactured by means of an additive method, for example.

The flow element can, for example, be made at least partially from a composite material, for example a carbon composite material.

As mentioned, the fluid conveyed by means of the flow plate can be a reactant, in particular hydrogen or atmospheric oxygen. Alternatively, it can be a cooling fluid, in particular water.

As mentioned above, the present invention also relates to a bipolar plate.

A bipolar plate according to the invention for an electrochemical device comprises a first flow element and a second flow element, wherein at least one flow element is formed a flow element according to the type mentioned above.

As already mentioned, the invention also relates to a fuel cell device.

A fuel cell device according to the invention comprises a fuel cell stack comprising two or more bipolar plates of the type described above and an active layer between adjacent bipolar plates, channels for transporting a fluid in the fuel cell stack being formed via the inflow openings and outflow openings of the flow elements.

The advantages that have already been mentioned in connection with the explanation of the flow element according to the invention can also be achieved with the bipolar plate according to the invention and the fuel cell device according to the invention. Advantageous embodiments of the bipolar plate and the fuel cell device result from advantageous embodiments of the flow element according to the invention. In this regard, reference can be made to the above statements.

In conventional fuel cell devices, a throttle is often used on the cathode side in the air exhaust system in order to achieve a high operating pressure at the load point. The present invention allows a part of the choke to be functionally assigned to the output side of the bipolar plate.

• Druckdifferenz von Verteilerkanal zu Sammelkanal (Manifold zu Manifold) vorzugsweise kleiner ungefähr 1,5 bar, bevorzugt kleiner ungefähr 1 bar, noch bevorzugter kleiner ungefähr 400 bis 500 mbar.
• Druckverlust für gasförmige Reaktanden beispielsweise ungefähr 50 bis 700 mbar für die Kathodenseite am Volllastpunkt, vorzugsweise ungefähr 80 bis 400 mbar.
• Druckverlust für gasförmige Reaktanden beispielsweise ungefähr 20 bis 300 mbar für die Anodenseite am Volllastpunkt, vorzugsweise ungefähr 50 bis 200 mbar.

In an exemplary implementation of the invention in practice for a fuel cell device in the automotive sector (in particular a PEM fuel cell device in the passenger car sector), the following pressure ratios can be provided, for example:

• Pressure difference from distribution channel to collecting channel (manifold to manifold) preferably less than about 1.5 bar, preferably less than about 1 bar, even more preferably less than about 400 to 500 mbar.
• Pressure loss for gaseous reactants, for example, about 50 to 700 mbar for the cathode side at the full load point, preferably about 80 to 400 mbar.
• Pressure loss for gaseous reactants, for example, about 20 to 300 mbar for the anode side at the full load point, preferably about 50 to 200 mbar.

In the above cases, there are different pressure losses at the partial load point.

In the above application, the pressure loss on the cathode side can be, for example, approximately 100 mbar or more at the active region and approximately 120 mbar or more at the outflow region. On the anode side, the pressure loss can be, for example, 40 mbar or more in the active area, and approximately 30 mbar or more in the outflow area. This information relates to the full load point.

With a total pressure drop across the fuel cell of 100%, the active area accounts for, for example, approximately 40% or more, and the outflow area, for example, approximately 20% or more, for example 40%.

• 1: eine schematische Darstellung einer erfindungsgemäßen Brennstoffzelleneinrichtung umfassend erfindungsgemäße Bipolarplatten, die aus erfindungsgemäßen Strömungselementen bestehen, in einer Explosionsdarstellung;
• 2: eine schematische Draufsicht auf ein herkömmliches Strömungselement;
• 3: eine schematische Draufsicht auf eine herkömmliche Bipolarplatte in einer funktionellen Darstellung;
• 4: eine perspektivische Ansicht der Bipolarplatte aus 3, wobei deren zwei Strömungselemente im Abstand zueinander angeordnet und gezeigt sind, in Blickrichtung von oben;
• 5: eine weitere Darstellung der Bipolarplatte mit den beiden Strömungselementen im Abstand zueinander, mit der Blickrichtung von unten;
• 6: eine Draufsicht auf ein erfindungsgemäßes Strömungselement der Brennstoffzelleneinrichtung aus 1;
• 7: schematisch den Druckverlauf für einen Reaktanden einer Brennstoffzelle der Brennstoffzelleneinrichtung aus 1 als Funktion der durchströmten Länge für eine herkömmliche Brennstoffzelleneinrichtung (gestrichelte Darstellung, für das Strömungselement in 2) und die Brennstoffzelleneinrichtung aus 1 (durchgezogene Linie, für das erfindungsgemäße Strömungselement in 6);
• 8 bis 11: alternative Ausgestaltungen eines Ausströmbereiches bei erfindungsgemäßen Strömungselementen anstelle des Details A in 6;
• 12: eine Draufsicht auf eine erfindungsgemäße Bipolarplatte mit erfindungsgemäßem Strömungselement in einer funktionalen Darstellung;
• 13: eine Draufsicht auf ein erfindungsgemäßes Strömungselement; und
• 14: eine Darstellung entsprechend 7 bei Einsatz des erfindungsgemäßen Strömungselementes gemäß 13 in einer Brennstoffzelleneinrichtung (durchgezogene Linie) im Vergleich zu einem herkömmlichen Strömungselement (gestrichelte Darstellung).

The following description of preferred embodiments of the invention is used in connection with the drawing to explain the invention in more detail. Show it:

• 1 1: a schematic representation of a fuel cell device according to the invention comprising bipolar plates according to the invention, which consist of flow elements according to the invention, in an exploded view;
• 2 1: a schematic plan view of a conventional flow element;
• 3 1: a schematic plan view of a conventional bipolar plate in a functional representation;
• 4 : a perspective view of the bipolar plate 3 12 with the two flow elements thereof spaced apart and shown as viewed from above;
• 5 : another representation of the bipolar plate with the two flow elements at a distance from one another, viewed from below;
• 6 : a plan view of a flow element according to the invention of the fuel cell device 1 ;
• 7 : schematically shows the pressure curve for a reactant of a fuel cell of the fuel cell device 1 as a function of the flow-through length for a conventional fuel cell device (dashed representation, for the flow element in 2 ) and the fuel cell device 1 (solid line, for the flow element according to the invention in 6 );
• 8th until 11 : alternative configurations of an outflow area in flow elements according to the invention instead of detail A in 6 ;
• 12 : a plan view of a bipolar plate according to the invention with the invention flow element in a functional representation;
• 13 : a plan view of a flow element according to the invention; and
• 14 : a representation accordingly 7 when using the flow element according to the invention 13 in a fuel cell device (solid line) compared to a conventional flow element (dashed line).

1 FIG. 1 shows a schematic representation of a preferred embodiment of a fuel cell device according to the invention, which is given the overall reference number 10 . The fuel cell device 10 comprises a fuel cell stack 12 (stack) of a plurality of fuel cells 14. In the present example, these are, for example, PEM fuel cells for the automotive sector, with hydrogen and atmospheric oxygen being used as reactants. A cooling medium is provided, in particular water.

1 shows a schematic two-dimensional exploded view of the fuel cell device 10, with sealing elements being hidden for the sake of clarity.

In a stacking direction 30, the fuel cell device 10 comprises a plurality of bipolar plates 16 stacked one on top of the other, which in the present case are preferred embodiments of the bipolar plate according to the invention. A respective bipolar plate 16 consists of two flow elements 18. At least one of the flow elements 18, preferably both flow elements 18, are preferred embodiments of the flow element according to the invention.

The flow element 18 can, for example, be a formed part produced by embossing, in particular made of metal, or produced in another of the ways described above.

The flow elements 18 of a respective fuel cell 14 accommodate between them a schematically illustrated active layer 20, which in the present case comprises gas diffusion layers (GDL) and a membrane electrode assembly (MEA). An active area 22 of the respective flow element borders on the active layer 20.

Such as from 6 shows that the flow elements 18 are flat with a plate-shaped base body 24. The base body 24 extends along a first main extension direction 26 and along a second main extension direction 28 oriented transversely and in particular perpendicularly thereto. The plane of the flow elements 18 is aligned transversely and in particular perpendicularly to the stacking direction 30 of the fuel cell stack 12 .

Each flow element 18 comprises a first edge region 32 and a second edge region 34. The edge regions 32, 34 are arranged at opposite ends of the flow element 18 in relation to the first main direction of extent 26. Both edge regions 32, 34 extend along the entire width in the second main direction of extent 28 of the flow element 18.

The edge regions 32, 34 protrude laterally in the main extension direction 26 beyond the active layer 20. Distribution channels 36 for supplying media and collecting channels 38 for discharging media are formed in the fuel cell stack 12 via the passage openings of the flow elements 18 (also referred to as “manifolds”).

In a conventional manner, the fuel cell device 10 comprises holding elements 40 at the end, which are braced relative to one another by means of a tensioning device 42 .

Before explaining the flow element according to the invention and the bipolar plate according to the invention, the configuration of a conventional flow element will first be discussed. This in 2 The flow element shown with the reference number 44 comprises an inflow opening 46 for a medium, for example a reactant, at the edge region 32 . The flow element 44 conforms to the conventional bipolar plate 3 for use.

The inflow opening 46 opens into an inflow area 48 with channels which open into a channel structure 50 . The channel structure 50 forms the active region 22 and is covered by the active layer 20 in the stacking direction 30 .

The channel structure 50 opens into an outflow area 54 with channels. The outflow area 54 is flow-connected to the outflow opening 58 .

Webs 59 separate the adjacent channels of the channel structure 50, the inflow area 48 and the outflow area 54 from one another.

In the main extension direction 28 , two further passage openings 60 for the passage of media are arranged laterally next to the inflow opening 46 and the outflow opening 58 one after the other.

The bipolar plate 62 in 3 is of conventional type and shown in plan view in a so-called functional representation. The channel structure 50 is an example for channel structures of the bipolar plate 62 as a whole. In addition to the openings 46, 58, two further inflow openings 64, 68 and outflow openings 66 and 70 assigned to them are formed for the supply and discharge of a respective fluid.

The bipolar plate 62 is connected to the flow element 44 and a further flow element 45, which is also designed conventionally, in the 4 and 5 shown in exploded perspective view. 4 shows the flow elements 44, 45 from above and 5 the flow elements 44, 45 from below.

The flow element 44 has on a first side 441 (top side), which in 2 is shown in plan view, the inflow area 48, the channel structure 50 and the outflow area 54. On a second page 442 (underside, 5 ), the flow element 44 has an inflow area 48, a channel structure 50 and an outflow area 54. In this case, the inflow takes place via the inflow opening 68 and the outflow via the outflow opening 70.

The second page 442 corresponds to a first page 451 (top, 4 ) of the flow element 45, with the inflow also taking place via a corresponding inflow opening 68 and the outflow via a corresponding outflow opening 70 in this case.

The flow element 45 has a second side 452 which faces away from the first side 451 (underside, 5 ). While the first side 441 of the flow element 44 forms the upper side of the bipolar plate 62, the second side 452 of the flow element 45 forms the underside of the bipolar plate 62.

The flow element 45 has an inflow area 48 , a channel structure 50 and an outflow area 54 on the second side 452 . The inflow takes place via the inflow opening 64 and the outflow via the outflow opening 70.

For example, in the 62 bipolar plate, the reactants are routed on sides 441 and 452 and the coolant between sides 442 and 451.

If flow elements of the present disclosure have channel structures on opposite sides, these can be inverted relative to one another, for example in the case of flow elements formed by reshaping, in deviation from the schematic illustration in the drawing.

7 FIG. 7 schematically shows the pressure curve over the conventional flow element 44 in FIG 2 as a function of the flow length. A first section 72 represents the pressure loss over the inflow area 48, a second section 73 the pressure loss over the active area 22 and a third section 74 the pressure loss over the outflow area 54.

6 shows in one of the 2 a corresponding plan view of the flow element 18 according to the invention.

In contrast to the conventional flow element 44 , the flow element 18 is provided with an inflow channel structure 76 on the inflow side. On the outflow side, an outflow channel structure 78 is provided in the outflow area 54 .

According to the present invention, the outflow channel structure 78 is designed in such a way that the pressure loss of the medium over the outflow area 54 is greater than the pressure loss over the inflow area 48. In the present case, the pressure loss is also greater than over the active area 22.

The above statement for the pressure loss applies in absolute terms in the present example, based on the absolute pressure loss and also per length of the flow element 18 through which flow occurs.

The course of the pressure loss for the flow element 18 according to 6 is in 7 shown with solid line 80 as an example. In this case, the lengths of the flow-through areas were chosen to be the same length for a better comparison with the flow element 44 . Sections 72, 73 and 74 also indicate the pressure curve over the inflow area 48, the active area 22 and the outflow area 54 in the case of the solid line 80.

Due to the increased pressure loss at the outflow area 54, a high pressure loss can be achieved overall via the fuel cell 14 comprising the flow element 18. This proves to be advantageous for a homogeneous concentration of the reactant in the active region 22 and thus in the active layer 20.

In addition, it is preferably ensured that the pressure loss across the active area 22 is as small as possible in order to ensure the smallest possible drop in the partial pressure of the reactant in the active area 22 .

In the flow element 18 according to the invention 6 there is also the advantage that the pressure loss across the outflow area 54 in relation to the pressure loss across the outflow area 54 in the conventional flow element 44 according to 2 is enlarged ( 7 ).

The increased pressure loss across the outflow area 54 compared to the inflow area 48 is achieved in particular by the design of the outflow channel structure 78 ( 6 ). Here, in particular, the free cross-sectional area of the outflow channel structure 78 is reduced. In particular, it is conceivable to reduce the cross-sectional area of channels, the length of channels, the width of channels, the height of channels and/or the number of channels. Branches and/or junctions of channels can be provided to increase the pressure difference. As an alternative or in addition, for example, deflections of the fluid can be used by the direction in which the channels run in the outflow channel structure 78 in order to increase the pressure loss.

The local pressure loss at or in the outflow area 54 of the multiple bipolar plates in the stack preferably makes it possible to avoid pressure-dependent differences in the flow velocities in the channel structure 50, combined with inhomogeneous flows and, as a result, different performance.

In addition, there is the advantage that in the flow element 18 according to the invention 6 the pressure drop across the inflow area 48 in relation to the pressure drop across the inflow area 48 in the conventional flow element 44 according to FIG 2 is reduced ( 7 ).

This offers the advantage of providing an overall higher total pressure of the reactant within the active region 22 than in the case of the conventional flow element 44. In this way, better performance can be achieved with the fuel cell 14 using the flow element 18.

In order to achieve the pressure loss at the inflow area 48 compared to the conventional flow element 44, the channels of the inflow channel structure 76 can be designed in such a way that, compared to the conventional case, an enlarged cross-sectional area is provided for the flowing fluid. this is in 6 exemplified by widened channels in relation to the representation according to FIG 2 shown.

the 8th until 11 provide excerpts according to detail A in 6 Embodiments of the flow element 18 according to the invention. A section of the base body 24 at the outflow area 54 with the outflow channel structure 78 and the outflow opening 58 is shown here.

To increase the pressure loss compared to the conventional outflow area 54, the channel length, the channel cross-sectional area, the channel width and/or the channel height are changed, for example, as shown by way of example. In particular, extended channels have proven to be advantageous.

The variants of 10 and 11 show how additional diversions can be used to lengthen the channels and thus achieve a higher pressure loss. In the variant according to 11 unions of channels are also provided. Two or more channels are combined here to form one channel in the direction of the outflow opening 58 .

It is advantageous, for example as in the variant according to FIG 11 , if constrictions to fewer channels and/or channels with a smaller cross section are only arranged inside the outflow area 54 . This avoids local pressure losses within the channel structure 50, but still ensures the increased pressure loss in the outflow to the outflow opening. Locally high flow velocities in the channel structure 50 are also avoided, which lead to inhomogeneous flows or can lead to high pressure losses and/or disadvantages in water management in some sections.

As already explained above, the basic idea of the invention can be implemented within a flow element 18 on both sides of the base body 24 .

Alternatively or additionally, the basic idea of the invention can be implemented with two flow elements 18 of a bipolar plate 16 according to the invention.

The following is in relation to 12 referenced, which shows a top view of a bipolar plate 82 according to the invention with a flow element 84 according to the invention, with the bipolar plate 82 corresponding 3 shown in the functional representation.

The embodiment according to 12 can be used, for example, in a counterflow design with three media.

The inflow area 48 and the outflow area 54 with the relevant inflow channel structures 76 and outflow channel structures 78 are also shown here.

The functional representation of the bipolar plate 82 corresponds to the functional representation of the bipolar plate 62 according to FIG 3 , explained there using the 4 and 5 with the flow elements 44, 45.

A further outflow opening 86 and a further inflow opening 88 are provided in the bipolar plate 82 . The inflow opening 88 and the outflow opening 86 are associated with one another in the same way as the inflow opening 46 and the outflow opening 48 are. A channel structure 50 also runs between the inflow opening 88 and the outflow opening 86. As in the example of FIG 3 until 5 As explained, for example, a reactant flows in through the inflow opening 46 and out through the outflow opening 58 . The respective other reactant flows in via the inflow opening 88 and out via the outflow opening 86 . The respective channel structures are arranged, for example, on opposite sides of the bipolar plate 82, as can be seen from FIG 4 and 5 was explained using the example of the conventional bipolar plate 62.

In the present example, the inflow opening 46 and the outflow opening 86 are arranged on the edge region 32 and lie side by side, but in this example not directly side by side. A through-opening 60 is formed on the base body 24 between the openings 46 , 86 . A cooling medium, for example, flows through this passage opening 60 .

The outflow opening 58 and the inflow opening 88 are arranged in the edge region 34 in a corresponding manner. In the present example, the openings 58, 88 lie side by side, but in the present case not directly next to each other. Between the openings 58, 88, a through-opening 60 is formed on the base body, through which, for example, the cooling medium can flow.

The passage openings 60 allow in particular the inflow and outflow of the cooling medium between the two flow elements of the bipolar plate 82 and through a respective channel structure 50, as described above with reference to FIG 4 and 5 was explained using the example of the conventional bipolar plate 62.

It could be different from what is shown 12 be provided that, for example, the inflow opening 46 and the outflow opening 86 are arranged directly next to each other. Alternatively or additionally, for example, the outflow opening 58 and the inflow opening 88 could be arranged directly next to one another.

The reference number 90 designates the further inflow area for the medium flowing in via the inflow opening 88 . The relevant inflow channel structure is identified by reference number 91 .

In a corresponding manner, the reference number 92 designates the outflow area via the medium flowing out through the outflow opening 86 . The relevant outflow channel structure is identified by reference number 93 .

Just as the pressure losses at the inflow area and at the outflow area 54 can be designed through the differences between the inflow channel structure 76 and the outflow channel structure 78, the pressure losses at the inflow area 90 can be adjusted via the inflow channel structure 91 and at the outflow area 92 via the outflow channel structure 93 to be designed.

The flow element 84 and the bipolar plate 82 also have the advantage that an increased space requirement or a reduced space requirement due to the channel structures 76 and 78 for a medium can be used to vary the space required by the channel structures 91 and 93 for the further medium, and vice versa.

In this case, the increased space requirement for the outflow channel structure 76 is provided by the reduced space requirement for the outflow channel structure 93 . A necessary adjustment with regard to the space requirement for the outflow channel structure 78 and the inflow channel structure 91 can be carried out in a corresponding manner.

12 shows this as an example in the functional representation of the bipolar plate 82. The increased space requirement for the inflow area 48 and the outflow area 54 can be achieved by reducing the further inflow area 90 and the further outflow area 93. The additional adjustment of the additional inflow channel structure 91 and the additional outflow channel structure 93 can also achieve the pressure losses for the additional medium as described above.

In the case of the bipolar plate 82, provision can be made in particular for the pressure loss for the additional medium to be greater across the additional outflow area 92 than across the additional inflow area 90 and an additional active area 22.

Enlarging the further outflow opening 86 ensures in the present example that the required volume flow can flow through the manifold of the fuel cell stack 12 over the multiple bipolar plates while maintaining the desired pressure loss and preferably without disturbing inhomogeneities ing example through the collecting channel 38, in which the outflow opening 86 opens.

In a different advantageous embodiment, it can be advantageously provided that an enlargement of the outflow opening 86 for the further medium is not necessary. This may provide the benefit, for example, of preserving the overall size of flow element 84 and bipolar plate 82 relative to flow element 18 and bipolar plate 62 . 12 FIG. 12 shows this schematically using a dashed line 94 which characterizes the wall of the outflow opening 86 for such an embodiment. the inside 12 The section of the outflow opening 86 located to the right of this wall would be omitted in this case.

13 shows a flow element according to the invention, denoted by reference numeral 96, in one of 6 appropriate way. The flow element 96 can be part of a bipolar plate according to the invention.

The inflow area 48 and the outflow area 54 are also provided for the flow element 96 . The inflow area 48 comprises an inlet section 98 and a distributor section 100. The outflow area 54 comprises a collection section 102 and an outlet section 104.

There is a flow connection for the fluid from the inflow opening 46 via the inlet section 98, the distributor section 100, the channel structure 50, the collecting section 102 and the outlet section 104 to the outflow opening 58. The inlet section 98 serves to distribute the fluid to the channel structure 50, and the Collection section 102 for bringing together the fluid from the channel structure 50.

In the present example, the distributor section 100 extends over the entire width of the flow element 96 in the main direction of extension 28. In a corresponding manner, the collecting section 102 in the present example extends over the entire width of the flow element 96 in the main direction of extension 28. The distributor section 100 and the collecting section 102 adjoin the channel structure 50 on opposite sides.

The inlet section 98 extends in the main direction of extent 28 only over a section of the flow element 96. In a corresponding manner, the outlet section 104 extends along the main direction of extent 28 only over the section of the flow element 96.

If the flow element 96 is used in the fuel cell 14, the distributor section 100 and the collector section 102 are in particular covered by a separate sealing element (subgasket) or covered with a film. The active layer 20 only covers the active region 22.

14 shows in one of the 7 corresponding manner with the dashed line 71 and the solid line 80 pressure curves depending on the flow path of the flow element 96. Here, the dashed line 71 refers to the same as in FIG 7 to a conventional comparison variant (not shown in the drawing) with an inlet section 98 and a collecting section 102. The solid line 80 relates to the solution according to the invention of the flow element 96 according to FIG 11 .

The respective lines 71, 80 are divided into five sections 106 to 110 starting from the inlet section 98 to the outlet section 104. The first section 106 refers to the inlet section 98, the second section 107 to the distributor section 100, the third section 108 to the active area 22, the fourth section 109 to the collection section 102 and the fifth section 110 to the outlet section 104.

In the case of the flow element 96, too, provision is made in particular for the pressure loss over the outflow area 54 to be greater than over the inflow area 48 and over the channel structure 50. In addition, the pressure loss over the inflow area 48 is lower than in the conventional comparison variant. The advantages described above can thus also be achieved with the flow element 96 .

In particular, it can be seen that the pressure loss across the outlet section 104 is greater than across the collection section 102, in absolute terms and per length of the flow element 96 through which flow occurs.

A pressure loss in absolute terms and per flow length is greater at the inlet section 98 than at the distributor section 100.

A respective pressure loss at the collecting section 102 in absolute terms and per length through which flows is greater than a pressure loss at channel structure 50. A pressure loss at the inlet section per length through which flows is greater than a pressure loss at channel structure 50.

The drawing shows channels running parallel for the channel structure 50 and a so-called “feet” structure on the distributor section 100 and on the collector section 102 . It goes without saying that the invention is not limited to this channel shape.

Reference List

10

fuel cell device

12

fuel cell stack

14

fuel cell

16

bipolar plate

18

flow element

20

active layer

22

active area

24

body

26, 28

main extension direction

30

stacking direction

32, 34

edge area

36

distribution channel

38

collection channel

40

holding element

42

clamping device

44

flow element (conventional)

441

first page

442

second page

45

flow element (conventional)

451

first page

452

second page

46

inflow opening

48

inflow area

50

channel structure

54

outflow area

58

outflow opening

59

web

60

passage opening

62

bipolar plate (conventional)

64

inflow opening

66

outflow opening

68

inflow opening

70

outflow opening

71

dashed line

72, 73, 74

section

76

Inflow channel structure

78

outflow channel structure

80

solid line

82

bipolar plate

84

flow element

86

further outflow opening

88

further inflow opening

90

further inflow area

91

further inflow channel structure

92

further outflow area

93

further outflow channel structure

94

dashed line

96

flow element

98

inlet section

100

distribution section

102

collecting section

104

outlet section

106, 107, 108, 109, 110

section

Claims (20)

Flow element for a bipolar plate (16) of an electrochemical device, comprising a plate-shaped base body (24) extending in two main directions of extent (26, 28) oriented at an angle to one another, the base body (24) having a channel structure (50) with a plurality of channels for Forming an active area (22) of the flow element (18; 84; 96), an inflow opening (46) and an outflow opening (58) for a fluid being formed in the base body (24), which are connected to the channel structure (50) via a The inflow area (48) is flow-connected to the inflow channel structure (76) and via an outflow area (54) to the outflow channel structure (78), with a pressure loss in the fluid flowing from the inflow opening (46) to the outflow opening (58) via the outflow area ( 54) is greater than over the inflow area (48) and/or over the active area (22). flow element after claim 1 , characterized in that a pressure loss per flow length of the flow element (18; 84; 96) over the outflow area (54) is greater than over the inflow area (48) and/or over the active area (22). flow element after claim 1 or 2 , characterized in that a pressure drop across the channel structure (50) is less than a pressure drop across the inflow channel structure (76). Flow element according to one of the preceding claims, characterized in that the inflow opening (46) and the outflow opening (58) have the same or substantially the same opening cross section. Flow element according to one of the preceding claims, characterized in that the inflow channel structure (76) and the outflow channel structure (78) are designed differently, in particular that the higher pressure loss over the outflow area (54) compared to the inflow area (48) through the Difference of inflow channel structure (76) from outflow channel structure (78). Flow element according to one of the preceding claims, characterized in that the pressure loss over the outflow area (54) compared to the inflow area (48) can be achieved by a difference in at least one of the following: - Total flow cross section of the inflow channel structure (76) and the outflow channel structure (78); - cross-section of channels; - length of channels; - width of channels; - height of channels; - number of channels; - provision of branching and/or merging of channels; - Direction of channels, especially deflections of fluid in channels. Flow element according to one of the preceding claims, characterized in that the pressure loss across the outflow area (54) compared to the inflow area (48) and/or to the active area (22) can be achieved by at least one resistance element arranged in the outflow channel structure (78). . Flow element according to one of the preceding claims, characterized in that the flow element (18; 84; 96), at least with regard to an outer contour, is symmetrical in itself with respect to an axis of symmetry which is aligned transversely and in particular perpendicularly to a plane defined by the base body (24) and /or that the inflow opening (46) and the outflow opening (58) are arranged diametrically opposite one another with respect to an axis which is aligned transversely and in particular perpendicularly to a plane defined by the base body (24). Flow element according to one of the preceding claims, characterized in that the flow element (18; 84; 96) comprises a further inflow opening (88) which is adjacent to the outflow opening (58) or the inflow opening (46), and in that the flow element (18; 84; 96) comprises a further outflow opening (86) which is adjacent to the inflow opening (46) or the outflow opening (58). flow element after claim 9 , characterized in that the flow element (18; 84; 96) comprises a first side and a second side facing away therefrom, wherein the channel structure (50), the inflow channel structure (76) and the outflow channel structure (78) on the first are arranged on the second side, and that a further channel structure, a further inflow area (90) with a further inflow channel structure (91) and a further outflow area (92) with a further outflow channel structure (93) are arranged on the second side, via which a fluid connection from the further inflow opening (88) to the further outflow opening (86). flow element after claim 9 or 10 , characterized in that, based on a projection of the flow element (18; 84; 96) transverse to a plane of the base body (24), the inflow area (48) is arranged laterally next to the further outflow area (92) and/or the outflow area ( 54) is arranged laterally next to the further inflow area (88). Flow element according to one of the preceding claims, characterized in that the flow element (18; 84; 96) comprises a first edge region (32) and a second edge region (34) on opposite sides in one of the main directions of extension (26, 28), wherein at The inflow opening (48) and at least one further passage opening (60) of the flow element (18; 84; 96) are arranged in the first edge region (32) and the outflow opening (58) and at least one further through opening (60) of the flow element (18; 84; 96) are arranged in the second edge region (34). Flow element (18; 84; 96), and in that the inflow area (48) and/or the outflow area (54) are only partially extended in the second main extension direction (28) oriented transversely to the first main extension direction (26). Flow element according to one of Claims 1 until 11 , characterized in that the outflow area (54) comprises a collection section (102) and an outlet section (104), the channel structure (50) in the collection section (102), this in the outlet section (104) and the outlet section (104) in the outflow opening (58) opens out, in particular that the outflow opening (58) and at least one further through-opening (60) of the base body (24) in an edge area (32, 34) of the flow element (96) on a side of the channel structure (50) facing away from the Collection section (102) are arranged. Flow element according to one of Claims 1 until 12 or 13 , characterized in that the inflow area (48) comprises an inlet section (98) and a distributor section (100), the inflow opening (46) in the inlet section (98), this in the distributor section (100) and the distributor section (100) in the channel structure (50) opens out, in particular that the inflow opening (46) and at least one further through opening (60) of the base body (24) are arranged in an edge area of the flow element (96) on a side of the distributor section (100) facing away from the channel structure (50). are. flow element after Claim 13 or 14 , characterized in that the collecting section (102) and/or the distributor section (100) along the entire extent of the base body (24) in one of the main directions of extent (26, 28) adjoin the channel structure (50), in particular on opposite sides of the Channel structure (50) and/or that the collecting section (102) and/or the distributor section (100) extend completely along the flow element (96) in this main direction of movement (26, 28). Flow element according to one of Claims 13 until 15 , characterized in that a pressure loss at the collecting section (102) and/or at the distributor section (100) per length of the flow element (96) through which flow occurs is greater than a pressure loss at the channel structure (50). Flow element according to one of Claims 13 until 16 , characterized in that a pressure loss per length of the flow element (96) through which flow occurs at the outlet section (104) is smaller than at the collecting section (102) and/or that a pressure loss per length of flow element (96) through which flow occurs at the inlet section (98) is greater than at the manifold section (100). Flow element according to one of the preceding claims , characterized in that at least one of the following applies: - the flow element (18; 84; 96) is a formed part; - The flow element (18; 84; 96) is at least partially made of a metal; - The flow element (18; 84; 96) is at least partially made of a plastic material; - The flow element (18; 84; 96) is manufactured by means of an additive process; - The flow element (18; 84; 96) is at least partially made of a composite material. Bipolar plate for an electrochemical device, comprising a first flow element (18; 84; 96) and a second flow element (18; 84; 96), wherein at least one flow element (18; 84; 96) is designed according to one of the preceding claims. Fuel cell device, with a fuel cell stack (12) comprising two or more bipolar plates (16, 82). claim 19 and an active layer (20) between adjacent bipolar plates (16, 82), channels (36, 38) for transporting a fluid in the fuel cell stack ( 12) are formed.

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