Bipolar plate
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-05-02
- Publication Date
- 2026-03-25
AI Technical Summary
Existing bipolar plates in electrochemical systems face challenges in optimizing fluid flow and space utilization, as designs that enhance flow technology often result in high space requirements and increased pressure losses, particularly when dealing with different fluid properties like gaseous and liquid media.
A bipolar plate design with elongated rectangular and pentagonal port cross-sections, where the coolant port is aligned parallel to the narrow side and resource ports are aligned with the long sides, allowing for linear channels and a distribution field to minimize pressure losses and maximize space efficiency, with a specific ratio of port dimensions that balances flow resistance and space utilization.
This design achieves low pressure losses and efficient fluid distribution across the active field, optimizing space usage and material savings while maintaining high power density, by aligning coolant and resource flow paths to minimize deflections and utilizing mirror-symmetrical port arrangements for uniform cooling and resource distribution.
Smart Images
Figure DE2024100394_21112024_PF_FP_ABST
Abstract
Description
[0001] Bipolar plate
[0002] The invention relates to a bipolar plate according to the preamble of claim 1, which is intended for use in an electrochemical system and through which a coolant can flow.
[0003] A bipolar plate is known, for example, from WO 2022 / 253384 A1. The known bipolar plate is constructed from two rectangular half-sheets, with three ports arranged side by side on their narrow sides. These are two ports for the passage of operating media and one port arranged between these ports for the passage of a coolant.
[0004] Another bipolar plate with a rectangular basic shape, with three ports for different fluids arranged on each of its narrow sides, is described in WO 2006 / 054399 A1. In this case, as in WO 2022 / 253384 A1, the middle of the three adjacent ports is rectangular, whereas the two outer ports have a pentagonal cross-sectional shape.
[0005] Bipolar plates intended for use in fuel cell systems, through which ports with a triangular cross-sectional shape are provided, are known, for example, from the documents DE 10 2018 128 593 A1 and WO 2014 / 102534 A1.
[0006] A bipolar plate disclosed in DE 10 2008 056 900 A1, which is also a component of a fuel cell, has an arrangement of three ports, which in one case have a triangular shape, in another case a modified rectangular shape, and in another case a pentagonal shape. The ports are not arranged next to one another in a row. Rather, the arrangement of the three ports describes an L-shape, with two ports located next to the narrow side of the bipolar plate, while the third port, separated from the narrow side by one of the first two ports, is arranged next to a long side of the bipolar plate.
[0007] Various design options for bipolar plates forming ports with a circular cross-section are described in detail, for example, in the documents DE 10 2021 212 053 A1 and DE 10 2021 207 304 A1.
[0008] The invention is based on the object of specifying a fuel cell for use in an electrochemical system, in particular a fuel cell system, which is further developed compared to the cited prior art, in particular with regard to fluidic aspects and space utilization.
[0009] This object is achieved according to the invention by a bipolar plate having the features of claim 1. The bipolar plate, in a basic concept known per se, has a rectangular basic shape, with three ports, namely two operating medium ports and one cooling water port, arranged next to one another on each of its narrow sides. The cooling water port is located between the two operating medium ports. The cooling water port has a port long side which is aligned parallel to the narrow side of the plate, whereas each operating medium port has a port long side aligned parallel to a long side of the plate. A rectangular active field is arranged between the three ports on one narrow side of the plate and the three ports on the opposite narrow side of the plate, with the active field having two active field long sides, each of which is arranged parallel to the long sides of the plate.The active field has linear channels for fluid flow control and coolant flow control parallel to the active field long sides.
[0010] According to claim 1, the product of the length of the long side of the coolant port and the length of the long side of one of the two operating fluid ports is at least six times, in particular at least eight times, the product of the length of a narrow side of the coolant port and the length of a narrow side of the operating fluid port. Said narrow side of the operating fluid port is aligned parallel to the long side of the coolant port. Each of the long sides of two operating fluid ports is aligned, and these are aligned with an active field long side.
[0011] The invention is based on the consideration that, when designing fluid-conducting contours in fuel cell stacks or stacks of other electrochemical cells, competing objectives must be considered. For example, a fluidically favorable design may require a large amount of space. For example, if one considers only the flow resistance in a channel, a circular channel cross-section is considered optimal.
[0012] However, not only the flow of a gaseous or liquid fluid within the channel must be considered, but also the conduction of the fluid flowing out of the channel, if, for example, the fluid needs to be distributed as evenly as possible within a flat area, such as the active field of an electrochemical cell, such as a fuel cell. The same applies in cases where a fluid located within a flat area needs to be collected and fed into a channel. Furthermore, it may be important whether the fluid is in liquid and / or gaseous form.
[0013] With regard to the flow of coolant through the active field or the linear channels within the active field, it is advantageous if the port is exactly as wide as the active field. However, in such a design, the operating fluid ports must be arranged 100% to the side of the active field. Space savings are possible here by approximating the operating fluid port cross-sections to a circle, as this provides the largest surface area for a given size.
[0014] An active field through which the operating fluids and the coolant flow linearly is of great advantage in view of the resulting particularly low pressure losses. The flow paths of the operating fluids and the coolant are diverted at as few deflection points as possible in order to further minimize pressure losses. Due to the very different properties of liquid media, in particular coolants, on the one hand, and gaseous media such as hydrogen, air or oxygen, on the other, media-specific characteristics must also be taken into account when designing fluid-carrying components. This applies, for example, to the design of a distribution field, which is placed between the arrangement of the various ports and the active field. In the distribution field, the various media must be distributed transversely of the bipolar plate, i.e. orthogonally to the main flow direction of the media.Since the transverse distribution of the gaseous operating media is easier than the transverse distribution of the liquid coolant, a longitudinal orientation of the operating media ports relative to the longitudinal direction of the bipolar plate, which coincides with the main flow direction of the operating media, combined with a transverse orientation of the coolant port, appears to be sensible in principle. This approach is generally known from the prior art, including the aforementioned documents WO 2022 / 253384 A1 and WO 2006 / 054399 A1.
[0015] The inventive solution goes beyond this approach by providing more extreme cross-sectional shapes for the ports, which deviate more significantly from a compact, for example, approximately square or circular shape. Increased flow resistances within the ports and within a channel formed by the entirety of similar ports, which runs through a cell stack comprising a plurality of bipolar plates, are accepted.
[0016] The fraction, whose numerator is given by the product of the length of the long side of the coolant port and the length of the long side of one of the two operating fluid ports, and whose denominator corresponds to the product of the length of one narrow side of the coolant port and the length of one narrow side of the operating fluid port, lies in the range between six and 30, in particular in the range between eight and 18, according to various possible embodiments. The length of the long side of the coolant port, measured in the transverse direction of the rectangular, not square, bipolar plate and parallel to the narrow side of the entire bipolar plate, corresponds, according to various possible designs, to at least 40%, in particular at least half, of the width of the bipolar plate. At the same time, the said long side of the port extends, for example, over less than 80% of the length of the narrow side of the bipolar plate.
[0017] The coolant port can be centered between the two long sides of the bipolar plate. Alternatively, an off-center arrangement of the coolant port is also possible. This is especially true in cases where the two adjacent fluid ports are of unequal size.
[0018] The pronouncedly elongated, not necessarily strictly rectangular cross-sectional shape of the coolant port compared to older solutions can be expressed, among other things, by the fact that the long side of the coolant port aligned in the transverse direction of the bipolar plate is longer than the long side of the operating fluid port aligned orthogonally to it and parallel to the long sides of the bipolar plate.
[0019] The rectangular or modified rectangular shape of the coolant port can be combined within the bipolar plate with a pentagonal cross-sectional shape of a component port. In particular, both component ports of one and the same three-port arrangement can be pentagonal. Optionally, the two component ports arranged next to the coolant port are mirror-symmetrical to each other. The length of the long sides of the component ports included in the aforementioned quotient, which lies in the range between 6 and 30, is to be measured on the side of the component port that is closest to the nearest long side of the bipolar plate.
[0020] In the case of an at least approximately rectangular cross-section of the coolant port, in particular cooling water port, the ratio between the length of the port long side and the length of the port narrow side of the corresponding port can be more than three, in particular in the range of four to ten.
[0021] The two port arrangements, each comprising three ports, can be formed as a mirror image of a plane located centrally between the two narrow sides of the bipolar plate.
[0022] In a preferred embodiment, the long sides of two device ports are aligned with each other and aligned with one of the long sides of the active field. This has the advantage that the footprint of the bipolar plate can be optimally utilized, which, due to the arrangement of the active field and the ports on the plate, leads to material savings and a high power density per plate.
[0023] It has proven advantageous to arrange a distribution array between each port arrangement and the active array, and to arrange several parallel channel sections between each cooling water port and the adjacent distribution array, aligned in a flow direction ST that extends along the longitudinal sides of the plates. Preferably, each distribution array fans out from the respective channel sections toward the active array.
[0024] Preferably, the equipment ports are arranged on their side adjacent to the respective distribution panel (here the sloping side) parallel to the course of the distribution panel.
[0025] Alternatively, the designs of the port arrangements located on both sides of the aforementioned plane can differ from one another. For example, the cooling water port arranged first in the flow direction ST, i.e. on the inflow side, has a length-to-width ratio that is at least 50% greater than the cooling water port arranged next in the flow direction ST, i.e. on the outflow side. The higher cooling water pressure on the inflow side allows the use of a particularly narrow, elongated port to supply the cooling water to the active field. The only small transverse components of the cooling water flow ensure uniform cooling across the entire width of the active field. At the outflow end of the coolant channels traversing the bipolar plate, the coolant port with a less extreme length-to-width ratio ensures that the coolant is discharged with low flow resistance.
[0026] The bipolar plate can be composed of two half-plates, in particular half-sheets, using manufacturing technologies known in principle. In these cases, the coolant channels are formed between the half-plates. The electrochemical system comprising a plurality of bipolar plates of the type according to the application is, for example, a stationary or mobile fuel cell system, a redox flow battery, or an electrolyzer for hydrogen production.
[0027] An embodiment of the invention and a comparative example (not claimed) are explained in more detail below with reference to a drawing. Herein:
[0028] Fig. 1 shows a bipolar plate intended for use in an electrochemical system, namely a fuel cell system,
[0029] Fig. 2 shows a non-claimed comparative example in a view analogous to Fig. 1 .
[0030] In the following text, the same reference numerals are used, where applicable, both for the embodiment according to Fig. 1 and for the comparative example according to Fig. 2, which serves only for explanation.
[0031] A bipolar plate, designated overall by reference numeral 1, is used in a stack of electrochemical cells, namely fuel cells, and separates a half-cell of a first electrochemical cell from a half-cell of another electrochemical cell. Regarding the basic function of the electrochemical system, which comprises a plurality of bipolar plates 1 arranged in a stack, reference is made to the prior art cited above.
[0032] The bipolar plate 1 is constructed, in a manner known in principle, from two half-plates between which a coolant flows. In this case, the half-plates are made of sheet metal, i.e., they are designed as half-sheets. Alternatively, the half-plates can be manufactured from an electrically conductive composite material containing graphite and bonded by a polymer.
[0033] The operating media flow along the outer surfaces of the bipolar plates 1 in a cell stack, also referred to as a "stack." A rectangular active field, designated 10, in which the desired electrochemical reactions take place, occupies the largest part of the surface of the bipolar plate 1.
[0034] The bipolar plate 1 has an elongated rectangular shape, with the long sides designated 2, 3 and the narrow sides 4, 5. The length of the bipolar plate 1 is designated L1, and the significantly smaller width of the bipolar plate is designated B1. A first port arrangement 6 is located next to the first narrow side 4, and a second port arrangement 7 is located next to the second narrow side 5. The first port arrangement 6, arranged on the left in the arrangements according to Figures 1 and 2, comprises three adjacent ports 11, 12, 13, namely two operating fluid ports 11, 13 for conducting operating fluids of the electrochemical system, and a cooling water port 12, generally referred to as a coolant port, for supplying cooling water to the bipolar plate 1.
[0035] The cooling water flows through the bipolar plate 1 in the flow direction ST, i.e., essentially in the longitudinal direction of the bipolar plate 1, in the cases outlined from left to right. This does not imply any statement about the actual orientation of the bipolar plates 1. In particular, the bipolar plates 1 can be aligned vertically within a cell stack.
[0036] On the second narrow side 5, there are three additional ports 14, 15, 16 belonging to the second port arrangement 7. In this case, operating media, in particular hydrogen and atmospheric oxygen, are conducted through the two outer ports 14, 16, i.e., those located next to the two long sides 2, 3, while cooling water is discharged from the bipolar plate 1 through the central port 15. All ports 11, 12, 13, 14, 15, 16 extend through the fuel cell stack in the stacking direction.
[0037] The rectangular active field 10 is arranged between the three ports 11, 12, 13 on the plate narrow side 4 and the three ports 14, 15, 16 on the opposite plate narrow side 5. The active field 10 has two active field longitudinal sides 22, 22', which in the embodiment shown here are each arranged parallel to the plate longitudinal sides 2, 3. The active field 10 has linear channels 10a for a fluid flow guide, i.e., hydrogen and oxygen, and a coolant flow guide, i.e., the cooling water, parallel to the active field longitudinal sides 22, 22'.
[0038] In particular, in an embodiment of a bipolar plate 1 made of two interconnected, three-dimensionally embossed thin half-sheets, the linear channels 10a in the active field 10 are formed through each half-sheet and are thus present on one side of a half-sheet in a positive form and on the back of the half-sheet in an inverse negative form.
[0039] Between the port arrangements 6, 7 and the active field 10, there is a distribution field 8, 9 in each case, in which the various material flows intersect, based on the plan view according to Figures 1 and 2, while the different materials remain separate from each other. Between the cooling water ports 12, 15 and the distribution fields 8, 9, several parallel channel sections 17 can be seen, aligned in the flow direction ST.
[0040] The extent of the flat area in which the short channel sections 17 are located already shows a clear difference between the embodiment according to Fig. 1 and the comparison example according to Fig. 2:
[0041] According to Fig. 1, cooling water, which is supplied to the distribution field 8 through the channel sections 17, flows largely in a straight direction, namely in the longitudinal direction of the bipolar plate 1, through the distribution field 8 to the active field 10. Only in relatively narrow edge regions of the distribution field 8 does the cooling water flow need to be significantly spread out in order to reach the active field 10 across its entire width. Comparable conditions exist in the region of the second distribution field 7 and the second port arrangement 7, i.e., on the outflow side of the cooling water, whereby in this case the cooling water flow needs to be concentrated.
[0042] In relation to the embodiment according to Fig. 1, in the unclaimed comparative example according to Fig. 2, a much more pronounced fanning out of the cooling water flow in the first distribution field 7 and a likewise much more pronounced constriction of the cooling water flow in the second distribution field 8 are present. This results in a significantly higher flow resistance in the case of Fig. 2. A continuously straight flow through the bipolar plate 1 occurs only in a central, very narrow region, as indicated in Fig. 2 in an idealized manner by a single long arrow oriented in the flow direction ST.
[0043] The largely rectilinear, low-resistance flow through the bipolar plate 1 according to Fig. 1 is achieved primarily by the design of the port arrangements 6, 7. The cooling water ports 12, 15 each have an elongated rectangular shape, with a long side 18 of the respective port 12, 15 lying parallel to the nearest plate narrow side 4, 5. The narrow sides of the cooling water ports 12, 15 are designated 19. The port long side 18 of each cooling water port 12, 15 has a length L18, which is more than three times the length of the port narrow side 19 of the same cooling water port 12, 15, designated L19.
[0044] In contrast to the cooling water ports 12, 15, the operating fluid ports 11, 13, 14, 16 each have a pentagonal cross-sectional shape. A longitudinal side 20, 20', which represents the longest of the five sides of the operating fluid port 11, 13, 14, 16, is closest to the longitudinal side 2, 3 of the bipolar plate 1 adjacent to the respective operating fluid port 11, 13, 14, 16. The longitudinal sides 20, 20' of all operating fluid ports 11, 13, 14, 16 are thus aligned orthogonally to the longitudinal sides 18 of the cooling water ports 12, 15. Parallel to the long sides 18 of the cooling water ports 11, 15 are the narrow sides, designated 21, of the operating fluid ports 11, 13, 14, 16. The narrow side 21 is the side of the operating fluid port 11, 13, 14, 16 that has the shortest distance from the adjacent narrow side 4, 5 of the bipolar plate 1. The length of each port narrow side 21 is designated L21.
[0045] The following relationship exists between the different lengths L18, L19, L20, L21 of the different ports 11, 12, 13, 14, 15, 16:
[0046] 6 < (L18 x L20) / (L19 x L21 ) < 30
[0047] The fraction given in this relation, i.e. the quotient of the product of the lengths L18, L20 of the two long sides 18, 20 and 20' as numerator and the product of the lengths L19, L21 of the two narrow sides 19, 21 as denominator, is a dimensionless value, so that the validity of the relation does not depend on the chosen units.
[0048] List of reference symbols
[0049] 1 bipolar plate
[0050] 2 Long side of the bipolar plate, plate long side
[0051] 3 Long side of the bipolar plate, plate long side
[0052] 4 Narrow side of the bipolar plate, plate narrow side
[0053] 5 Narrow side of the bipolar plate, plate narrow side
[0054] 6 Port arrangement, inlet side of the cooling water
[0055] 7 Port arrangement, cooling water outlet side
[0056] 8 Distribution panel
[0057] 9 Distribution panel
[0058] 10 Active field
[0059] 10a linear channels
[0060] 11 Equipment port
[0061] 12 Cooling water port
[0062] 13 Equipment port
[0063] 14 Equipment port
[0064] 15 Cooling water port
[0065] 16 Equipment port
[0066] 17 Canal section
[0067] 18 Long side of the cooling water port, port long side
[0068] 19 Narrow side of the cooling water port, port narrow side
[0069] 20, 20' Long side of the equipment port, Long side of the port
[0070] 21 Narrow side of the equipment port, port narrow side
[0071] 22, 22' active field long side
[0072] B1 Width of the bipolar plate
[0073] L1 Length of the bipolar plate
[0074] L18 Length of the port long side of the cooling water port
[0075] L19 Length of the port narrow side of the cooling water port
[0076] L20 Length of the port long side of the equipment port
[0077] L21 Length of the narrow side of the equipment port
[0078] ST flow direction
Claims
Patent claims 1 . Bipolar plate for an electrochemical system, having a rectangular basic shape, wherein on the narrow plate sides (4, 5) of which three ports (11, 12, 13, 14, 15, 16), namely two operating medium ports (11, 13, 14, 16) and one coolant port (12, 15), are arranged next to one another, wherein the coolant port (12, 15) is located between the operating medium ports (11, 13, 14, 16) and has a port longitudinal side (18) which is aligned parallel to the narrow plate side (4, 5), whereas each operating medium port (11, 13, 14, 16) has a port longitudinal side (20) aligned parallel to a plate longitudinal side (2, 3), wherein a rectangular active field (10) is arranged between the three ports (11, 12, 13) is arranged on one narrow side of the plate (4) and the three ports (14, 15, 16) on the opposite narrow side of the plate (5), wherein the active field (10) has two active field longitudinal sides (22, 22'), each of which is arranged parallel to the longitudinal sides (2, 3) of the plate,and wherein the active field (10) has linear channels (10a) for directing operating medium flow and coolant flow parallel to the active field longitudinal sides (22, 22'), characterized in that the product of the length (L18) of the port longitudinal side (18) of the coolant port (12, 15) and the length (L20) of the port longitudinal side (20) of one of the two operating medium ports (11, 13, 14, 16) adjacent to the coolant port (12, 15) is at least six times the product of the length (L19) of a port narrow side (19) of the coolant port (12, 15) and the length (L21) of a port narrow side (21) of the operating medium port (11, 13, 14, 16).
2. Bipolar plate according to claim 1, characterized in that the port longitudinal sides (20, 20') of two operating medium ports (11, 14; 13, 16) are arranged in alignment and are arranged in alignment with one of the active field longitudinal sides (22, 22').
3. Bipolar plate according to claim 1 or claim 2, characterized in that the product of the length (L18) of the port longitudinal side (18) of the coolant port (12, 15) and the length (L20) of the port longitudinal side (20) of one of the two operating medium ports (11, 13, 14, 16) is not more than 30 times the product of the length (L19) of the port narrow side (19) of the coolant port (12, 15) and the length (L21) of the Port narrow side (21) of the equipment port (11, 13, 14, 16).
4. Bipolar plate according to claim 3, characterized in that the relations listed in claims 1 to 3 apply to both operating medium ports (11, 13, 14, 16) adjacent to the coolant port (12, 15).
5. Bipolar plate according to one of claims 1 to 4, characterized in that the length (L18) of the port longitudinal side (18) of the coolant port (12, 15) corresponds to at least half the width (B1) of the bipolar plate (1).
6. Bipolar plate according to one of claims 1 to 5, characterized in that the port longitudinal side (18) of the coolant port (12, 15) is longer than the port longitudinal side (20, 20') of the operating medium port (11, 13, 14, 16) aligned orthogonally thereto.
7. Bipolar plate according to one of claims 1 to 6, characterized in that at least one operating medium port (11, 13, 14, 16) has a pentagonal cross-sectional shape.
8. Bipolar plate according to claim 7, characterized in that each operating medium port (11, 13, 14, 16) has a pentagonal cross-sectional shape.
9. Bipolar plate according to one of claims 1 to 8, characterized in that the ratio between the length (L18) of the port longitudinal side (18) of the coolant port (12, 15) and the length (L19) of the port narrow side (19) of the coolant port (12, 15) is at least three.
10. Bipolar plate according to one of claims 1 to 9, characterized in that port arrangements (6, 7) comprising three ports (11, 12, 13; 14, 15, 16) each are formed as a mirror image of a plane which is located centrally between the two narrow sides (4, 5) of the bipolar plate.
11. Bipolar plate according to one of claims 1 to 10, characterized in that a first port arrangement (6), which comprises three ports (11, 12, 13) arranged next to one another and adjacent to the first narrow plate side (4), differs from a second port arrangement (7), which also comprises three ports (14, 15, 16) arranged next to one another and is arranged on the second narrow plate side (5).
12. Bipolar plate according to one of claims 10 or 11, characterized in that a distribution field (8, 9) is arranged between the port arrangements (6, 7) and the active field (10) and between each cooling water port (12, 15) and the respectively adjacent distribution field (8, 9) a plurality of channel sections (17) are arranged which are parallel to one another and aligned in a flow direction (ST) which extends along the longitudinal sides (2, 3) of the plate.
13. Bipolar plate according to claim 12, characterized in that each distribution field (8, 9) fans out from the respective channel sections (17) in the direction of the active field (10).
14. Bipolar plate according to claim 13, characterized in that the operating medium ports (11, 13, 14, 16) are arranged on their side adjacent to the respective distribution field (8, 9) running parallel to the course of the distribution field (8, 9). 15.. Bipolar plate according to one of claims 12 to 14, characterized in that the cooling water port (12) arranged first in the flow direction (ST) has a length-to-width ratio that is at least 50% greater than the cooling water port (15) arranged subsequently in the flow direction (ST).