fuel cell stack

Abstract

The present invention relates to a fuel cell stack. A cooling medium flow path (68) of a fuel cell stack (10) comprises: a power generation section cooling flow path (70) including a portion overlapping with the power generation section of an electrolyte membrane electrode assembly (28a); a bypass flow path (80) provided on the outer periphery of a separator (30, 32); a main supply flow path (82) extending from a cooling medium supply connecting hole (44a) through the bypass flow path 80 and communicating with the power generation section cooling flow path (70); and a bubble exhaust flow path (90) extending from above the cooling medium supply connecting hole (44a) in the direction of gravity toward the bypass flow path (80) to communicate with the bypass flow path (80), wherein the bubble exhaust flow path (90) extends above the cooling medium supply connecting hole (44a) in the direction of gravity.

Description

Technical Field

[0001] The present invention relates to a fuel cell stack in which a cooling medium flow path is provided inside a pair of separators joined to each other. Background Art

[0002] Generally, solid polymer fuel cells use a solid polymer electrolyte membrane formed of a polymer ion exchange membrane. The fuel cell comprises an electrolyte membrane electrode assembly (MEA). The MEA has an anode electrode on one side of the solid polymer electrolyte membrane and a cathode electrode on the other side of the solid polymer electrolyte membrane.

[0003] The MEA is sandwiched between separators (also called bipolar plates) to form a power generation cell (fuel cell). A predetermined number of power generation cells are stacked to form a fuel cell stack, which is used as a power source for a vehicle, for example.

[0004] In a fuel cell, a fuel gas flow path is provided between the MEA and one separator, serving as one reactant gas flow path. Furthermore, an oxidant gas flow path is provided between the MEA and the other separator, serving as the other reactant gas flow path. Furthermore, a coolant flow path is provided between one separator and the other separator, allowing a coolant to flow.

[0005] The coolant flows through the coolant flow path, absorbing heat generated in the fuel cell's power generation section and preventing overheating of the MEA. The coolant flow path is very narrow, at approximately 200 μm thick, so bubbles of coolant may remain in the path. These trapped bubbles can reduce local cooling efficiency, causing localized high temperatures in the MEA and potentially degrading the electrolyte membrane that constitutes the MEA.

[0006] Therefore, Patent Document 1 discloses a technique of providing a bypass flow path above the power generation unit in the direction of gravity. A cooling medium containing many bubbles and having a low specific gravity flows in the upper bypass flow path, preventing it from flowing into the power generation unit.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2019-160560 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] However, in the conventional technology, some of the bubbles may return to the power generation unit along with the flow of the coolant, and there is room for improvement in preventing the bubbles from flowing into the power generation unit.

[0012] Therefore, an object of one embodiment is to provide a fuel cell stack capable of directing more bubbles of a cooling medium toward a bypass flow path.

[0013] Solutions for solving problems

[0014] The following disclosed viewpoint relates to a fuel cell stack, which is formed by stacking a plurality of power generation cells, wherein the power generation cells include an electrolyte membrane electrode structure and a pair of separators that clamp the electrolyte membrane electrode structure. In the fuel cell stack, there are: a cooling medium flow path formed between bulging portions of adjacent separators; a cooling medium supply connecting hole that supplies cooling medium to the cooling medium flow path; a cooling medium discharge connecting hole that discharges the cooling medium from the cooling medium flow path, and the cooling medium flow path includes: a power generation section cooling flow path that includes a portion overlapping with the power generation section of the electrolyte membrane electrode structure; a bypass flow path formed in a flow path sealing portion The flow path sealing portion is provided on the outer periphery of the partition and seals the reaction gas flow path formed between the partition and the electrolyte membrane electrode structure; a main supply flow path, which passes through the bypass flow path from the portion of the cooling medium supply connecting hole facing the power generation part cooling flow path and extends toward the power generation part cooling flow path, connecting the cooling medium supply connecting hole with the power generation part cooling flow path; and a bubble exhaust flow path, which extends from above the cooling medium supply connecting hole in the direction of gravity toward the bypass flow path and is connected to the bypass flow path, and the bubble exhaust flow path extends above the cooling medium supply connecting hole in the direction of gravity.

[0015] Effects of the Invention

[0016] The fuel cell stack of the above-described aspect can cause more bubbles in the cooling medium to flow toward the bypass flow path.

[0017] The above-mentioned objects, features, and advantages will be easily understood by referring to the following description of the embodiments with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a perspective view of a fuel cell stack according to an embodiment.

[0019] Figure 2 yes Figure 1 An exploded perspective view of a fuel cell (power generation cell).

[0020] Figure 3 yes Figure 2 A partial enlarged top view of the partition.

[0021] Figure 4 Graph showing the relationship between the fluid force of the coolant in the coolant supply passage and the buoyancy of the bubbles.

[0022] Figure 5 It is an explanatory diagram showing a separator according to a comparative example and the flow of bubbles therein.

[0023] Figure 6 It is an explanatory diagram showing a bubble mixing region in a separator according to a comparative example.

[0024] Figure 7 It is an explanatory diagram showing a separator according to an embodiment and the flow of bubbles therein.

[0025] Figure 8 It is an explanatory diagram showing a separator and its bubble mixing region according to an embodiment.

[0026] Figure 9 It is a graph showing the measurement results of the air mixing rate in the cooling medium and the flow path blockage rate of the separator according to the comparative example and the embodiment. DETAILED DESCRIPTION

[0027] The fuel cell stack will be described in detail below by listing appropriate embodiments and referring to the accompanying drawings.

[0028] like Figure 1 As shown, a fuel cell stack 10 according to one embodiment of the present invention includes a stack 14 formed by stacking a plurality of power generation cells 12 (fuel cells) in a horizontal direction (direction indicated by arrow A). The fuel cell stack 10 is mounted on a fuel cell vehicle, such as a fuel cell electric vehicle (not shown), for example.

[0029] At the end in the direction of arrow A1, i.e., one end in the stacking direction of the stacked body 14, a terminal plate 16a, an insulating member 18a, and an end plate 20a are arranged outward in this order. At the end in the direction of arrow A2, i.e., the other end in the stacking direction of the stacked body 14, a terminal plate 16b, an insulating member 18b, and an end plate 20b are arranged outward in this order.

[0030] The end panels 20a and 20b have a horizontally (or vertically) long rectangular shape and have connecting rods 24 between their sides. The ends of each connecting rod 24 are fixed to the inner side surfaces of the end panels 20a and 20b, applying a compressive load (fastening load) in the stacking direction (direction of arrow A) to the plurality of stacked power generation cells 12. Furthermore, the fuel cell stack 10 may include a housing in which the end panels 20a and 20b serve as end plates, and the stack 14 may be housed within the housing.

[0031] The power generation cell 12 has a horizontally long rectangular shape. Figure 2As shown, the power generation cell 12 includes a resin-framed MEA 28, a first separator 30, and a second separator 32 that sandwich the resin-framed MEA 28 from the direction of arrow A. The first separator 30 and the second separator 32 are formed by stamping a corrugated cross section of a thin metal plate, such as a steel plate, a stainless steel plate, an aluminum plate, a plated steel plate, or a thin metal plate having a surface treatment for corrosion prevention.

[0032] The first separator 30 and the second separator 32 are joined together along a predetermined joint line to form a joint separator 33. Furthermore, the joint separator 33 includes a plurality of joints that join the outermost periphery of the first separator 30 to the outermost periphery of the second separator 32. The joints are spaced apart along the outer periphery of the joint separator 33. The joint line is, for example, a linear weld portion formed by laser welding. Alternatively, the joint line may be a joint formed by MIG (metal inert gas welding), TIG (metal inert gas welding), seam welding, brazing, caulking, or the like.

[0033] exist Figure 2 In the embodiment, the resin-framed MEA 28 includes an electrolyte membrane electrode assembly 28a (hereinafter referred to as "MEA 28a") and a resin frame member 34 (resin frame portion, resin film). The resin frame member 34 is bonded to and surrounds the outer periphery of the MEA 28a. The MEA 28a includes an electrolyte membrane 36, a cathode electrode 38, and an anode electrode 40. The cathode electrode 38 is provided on one surface of the electrolyte membrane 36, and the anode electrode 40 is provided on the other surface of the electrolyte membrane 36.

[0034] Electrolyte membrane 36 is, for example, a solid polymer electrolyte membrane (cation exchange membrane). For example, the solid polymer electrolyte membrane is a thin film of perfluorosulfonic acid containing water. Electrolyte membrane 36 is sandwiched between cathode electrode 38 and anode electrode 40. Electrolyte membrane 36 can use a fluorine-based electrolyte or an HC (hydrocarbon) electrolyte.

[0035] Although not shown in detail, the cathode electrode 38 includes a first electrode catalyst layer bonded to one surface of the electrolyte membrane 36 and a first gas diffusion layer stacked on the first electrode catalyst layer. The anode electrode 40 includes a second electrode catalyst layer bonded to the other surface of the electrolyte membrane 36 and a second gas diffusion layer stacked on the second electrode catalyst layer.

[0036] Instead of using the resin frame member 34, the electrolyte membrane 36 may be made to protrude outward from the cathode electrode 38 and the anode electrode 40 to form a resin frame portion of the resin-framed MEA 28. In this case, frame-shaped films may be provided on both sides of the portion of the electrolyte membrane 36 that protrudes outward from the cathode electrode 38 and the anode electrode 40.

[0037] At one end edge portion in the longitudinal direction of each power generation cell 12 (the end edge portion in the direction of arrow symbol B1), there are provided a fuel gas supply passage 46a, a plurality of (for example, two) cooling medium discharge passages 44b, a first oxidizing gas discharge passage 42b1, and a second oxidizing gas discharge passage 42b2. Figure 1 as well as Figure 2 As shown, the fuel gas supply connecting hole 46a, multiple cooling medium exhaust connecting holes 44b, the first oxidant gas exhaust connecting hole 42b1 and the second oxidant gas exhaust connecting hole 42b2 respectively penetrate the stacked body 14, the insulating member 18a and the end panel 20a along the stacking direction (the terminal plate 16a can also be penetrated).

[0038] exist Figure 2 In the embodiment, the fuel gas supply manifold 46a, the plurality of coolant discharge manifolds 44b, the first oxidant gas discharge manifold 42b1, and the second oxidant gas discharge manifold 42b2 are arranged in the direction of arrow C (along the short side of the power generation cell 12). The first oxidant gas discharge manifold 42b1 and the second oxidant gas discharge manifold 42b2 each discharge an oxidant gas, such as air, as one reactant gas, in the direction of arrow A. The fuel gas supply manifold 46a supplies a fuel gas, such as hydrogen-containing gas, as the other reactant gas, in the direction of arrow A. The coolant discharge manifold 44b discharges the coolant in the direction of arrow A.

[0039] The fuel gas supply passage 46a is located between two coolant discharge passages 44b spaced apart in the vertical direction. The first oxidizing gas discharge passage 42b1 is located above the upper coolant discharge passage 44b (in the direction of arrow C1). The second oxidizing gas discharge passage 42b2 is located below the lower coolant discharge passage 44b (in the direction of arrow C2).

[0040] At the other end edge portion in the longitudinal direction of each power generation cell 12 (the end edge portion in the direction of arrow symbol B2), there are oxidant gas supply passages 42a, a plurality of (for example, two) cooling medium supply passages 44a, a first fuel gas discharge passage 46b1, and a second fuel gas discharge passage 46b2. Figure 1 as well as Figure 2 As shown, the oxidant gas supply connecting hole 42a, multiple cooling medium supply connecting holes 44a, the first fuel gas exhaust connecting hole 46b1 and the second fuel gas exhaust connecting hole 46b2 respectively penetrate the stacked body 14, the insulating member 18a and the end panel 20a along the stacking direction (the terminal plate 16a can also be penetrated).

[0041] exist Figure 2In the embodiment, the oxidant gas supply passage 42a, the plurality of coolant supply passages 44a, the first fuel gas discharge passage 46b1, and the second fuel gas discharge passage 46b2 are arranged in the direction of arrow C (along the short side of the power generation cell 12). The oxidant gas supply passage 42a supplies oxidant gas in the direction of arrow A. The first fuel gas discharge passage 46b1 and the second fuel gas discharge passage 46b2 each discharge fuel gas in the direction of arrow A. The coolant supply passage 44a supplies coolant in the direction of arrow A.

[0042] The oxidant gas supply passage 42a is located between two coolant supply passages 44a spaced apart in the vertical direction. The first fuel gas discharge passage 46b1 is located above the upper coolant supply passage 44a (in the direction of arrow C1). The second fuel gas discharge passage 46b2 is located below the lower coolant supply passage 44a (in the direction of arrow C2).

[0043] Each power generating cell 12 has a first drain communication hole 48a and a second drain communication hole 48b. Figure 1 as well as Figure 2 As shown, the first drain communication hole 48a and the second drain communication hole 48b respectively penetrate the stacked body 14, the insulating member 18a, and the end plate 20a in the stacking direction (and may also penetrate the terminal plate 16a).

[0044] exist Figure 2 In the embodiment, the first drain passage 48a is located at the end (lower end) of the power generating cell 12 in the direction of arrow C2. The first drain passage 48a is located between the center of the longitudinal direction of the power generating cell 12 and one end (end in the direction of arrow B1) of the power generating cell 12. The first drain passage 48a is located further (below) the lower end of the second oxidizing gas discharge passage 42b2 in the direction of arrow C2.

[0045] The first drain passage 48a communicates with the first oxidizing gas discharge passage 42b1 and the second oxidizing gas discharge passage 42b2 via a communication path (not shown) provided in the insulating member 18b or the end plate 20b. Specifically, the first drain passage 48a discharges the portion of generated water produced during operation (power generation) of the power generating cell 12 that is directed to the first oxidizing gas discharge passage 42b1 and the second oxidizing gas discharge passage 42b2 to the outside.

[0046] The second drain passage 48b is located at the end (lower end) of the power generating cell 12 in the direction of arrow C2. The second drain passage 48b is located between the center of the longitudinal direction of the power generating cell 12 and the other end (end in the direction of arrow B2) of the power generating cell 12. The second drain passage 48b is located further (below) the lower end of the second fuel gas discharge passage 46b2 in the direction of arrow C2.

[0047] Second drain manifold 48b communicates with first fuel gas discharge manifold 46b1 and second fuel gas discharge manifold 46b2 via a communication path (not shown) provided in insulating member 18b or end plate 20b. Specifically, second drain manifold 48b discharges the portion of generated water produced during operation (power generation) of power generating cell 12 that is directed to first fuel gas discharge manifold 46b1 and second fuel gas discharge manifold 46b2 to the outside.

[0048] In the following description, the oxidant gas supply connecting hole 42a, the first oxidant gas exhaust connecting hole 42b1, the second oxidant gas exhaust connecting hole 42b2, the cooling medium supply connecting hole 44a, the cooling medium exhaust connecting hole 44b, the fuel gas supply connecting hole 46a, the first fuel gas exhaust connecting hole 46b1, the second fuel gas exhaust connecting hole 46b2, the first drain connecting hole 48a and the second drain connecting hole 48b are simply collectively referred to as the connecting hole 50.

[0049] The arrangement, shape, and size of the communicating holes 50 are not limited to those in this embodiment, and can be appropriately set according to the required specifications.

[0050] like Figure 2 As shown, the first separator 30 of the power generating cell 12 is stacked on the second separator 32 of another power generating cell 12 adjacent to the power generating cell 12. The stacked first separator 30 and second separator 32 are joined by welding, caulking, or the like to form a joined separator 33.

[0051] The surface of the first separator 30 facing the electrolyte membrane electrode assembly 28a is hereinafter referred to as the "surface 30b". The surface 30b has a first connecting hole sealing portion 54, a first flow path sealing portion 56, and a flow path protrusion 52. The first connecting hole sealing portion 54, the first flow path sealing portion 56, and the flow path protrusion 52 are formed by bulging from the surface 30b. The first connecting hole sealing portion 54 surrounds the connecting hole 50 individually. The first flow path sealing portion 56 is arranged along the outer periphery of the first separator 30. The flow path protrusion 52 allows the fuel gas to flow in the reaction part. A fuel gas flow path 64 through which the fuel gas flows is formed between the first separator 30 and the electrolyte membrane electrode assembly 28a. The fuel gas flow path 64 is sealed by the flow path sealing portion provided on the outer periphery of the first separator 30.

[0052] In addition, the surface of the second separator 32 facing the electrolyte membrane electrode assembly 28a is referred to as the "surface 32b" below. The surface 32b has a second connecting hole sealing portion 60, a second flow path sealing portion 62, and a plurality of flow path protrusions 58. The second connecting hole sealing portion 60 is individually surrounded by the connecting hole 50. The second flow path sealing portion 62 is arranged along the outer periphery of the second separator 32. The plurality of flow path protrusions 58 extend along the flow direction of the oxidant gas in the reaction section. An oxidant gas flow path for circulating the oxidant gas is formed between the second separator 32 and the electrolyte membrane electrode assembly 28a. The oxidant gas flow path is sealed by the second flow path sealing portion 62 provided on the outer periphery of the second separator 32.

[0053] In the joined partition 33, the first communication hole sealing portion 54 of the first partition 30 and the second communication hole sealing portion 60 of the second partition 32 are arranged to face each other. Furthermore, the first flow path sealing portion 56 of the first partition 30 and the second flow path sealing portion 62 of the second partition 32 are arranged to face each other. Furthermore, the flow path protrusion 52 of the first partition 30 and the flow path protrusion 58 of the second partition 32 are arranged to face each other with an offset. In the joined partition 33, a coolant flow path 68 is provided between the bulged portion of the first partition 30 and the bulged portion of the second partition 32, through which the coolant flows.

[0054] The cooling medium flow path 68 will be further described below.

[0055] like Figure 3 As shown, the surface of the first separator 30 facing the second separator 32 is hereinafter referred to as the "inner surface 30a." In the inner surface 30a, a portion corresponding to the bulging portion of the surface 30b is recessed. A portion of the recessed portion of the inner surface 30a constitutes the cooling medium flow path 68. The cooling medium flow path 68 includes a power generation section cooling flow path 70 provided at a position overlapping with the power generation section of the electrolyte membrane 36. In the power generation section cooling flow path 70, a plurality of flow path grooves 74 provided on the inner side of the flow path protrusion 52 are provided, extending in the direction of arrow symbol B.

[0056] The first separator 30 includes a flat portion 76 between adjacent flow grooves 74. The flat portion 76 abuts against the flat portion 76 of the opposing second separator 32, closing the side of the flow groove 74. The flow grooves 74 and the flat portion 76 constitute the power generation unit corresponding region 72 of the power generation unit cooling flow path 70. The power generation unit corresponding region 72 includes a buffer portion 78 at the end in the direction of arrow symbol B2. The buffer portion 78 has a concave shape. The buffer portion 78 includes a plurality of protrusions 78a that distribute the cooling medium to the flow grooves 74. The buffer portion 78 is also provided at the end in the direction of arrow symbol B1 of the power generation unit corresponding region 72.

[0057] The cooling medium flow path 68 further includes a bypass flow path 80, a bypass flow path 86, a main supply flow path 82, a bubble exhaust flow path 90, and a main exhaust flow path 88 (see Figure 2 The bulging portion of the first separator 30 constituting the first flow path sealing portion 56 and the bulging portion of the second separator 32 constituting the second flow path sealing portion 62 (see Figure 2 ) between the bulging parts to form a bypass flow path 80. Figure 3 As shown, the bypass flow path 80 is provided along the outer periphery of the first separator 30 (and the second separator 32). The bypass flow path 80 is configured to bypass the power generation unit. However, the end of the bypass flow path 80 in the direction of arrow symbol B2 passes through the outside of the oxidant gas supply through hole 42a, which allows the reaction gas to pass through, the first fuel gas exhaust through hole 46b1, and the second fuel gas exhaust through hole 46b2 in the through hole 50, and passes through the inside of the two cooling medium supply through holes 44a (between the cooling medium supply through holes 44a and the power generation unit). Therefore, the end of the bypass flow path 80 in the direction of arrow symbol B2 meanders in a manner that passes between the two cooling medium supply through holes 44a and the other through holes 50.

[0058] In addition, if Figure 2 As shown, the end of the bypass flow path 80 in the direction of arrow B1 is arranged to pass through the outside of the fuel gas supply passage 46a, the first oxidant gas discharge passage 42b1, and the second oxidant gas discharge passage 42b2 in the communication hole 50, and pass through the inside of the two coolant discharge passages 44b. Therefore, the end of the bypass flow path 80 on the side of arrow B1 meanders so as to pass between the two coolant discharge passages 44b and the other communication holes 50.

[0059] like Figure 3 As shown, in this embodiment, two cooling medium supply holes 44a are provided at the end of the power generation cell 12 in the direction of the arrow symbol B2. The cooling medium supply holes 44a are respectively arranged between the three reaction gas holes 50 arranged in the vertical direction. Therefore, the bypass flow path 80 has a hole bypass portion 94 that bypasses the hole 50 adjacent to the cooling medium supply hole 44a from the outside. Figure 2 As shown, two cooling medium discharge passages 44b are provided at the end of the power generation cell 12 in the direction of arrow B1. The bypass flow path 80 also has a passage bypass portion 94 near the cooling medium discharge passage 44b, which bypasses the reaction gas passage 50 adjacent in the vertical direction.

[0060] like Figure 3As shown, the surrounding flow path 86 is a flow path that surrounds the two cooling medium supply communication holes 44a. The surrounding flow path 86 is formed in the first separator 30 and constitutes the first communication hole sealing portion 54 (see Figure 2 The inner side of the bulging portion of the second separator 32 constitutes the second communication hole sealing portion 60 (see Figure 2 ) is formed on the inner side of the bulging portion. The surrounding flow path 86 is also provided on Figure 2 The surrounding flow path 86 is arranged at a position closer to the cooling medium supply flow path 44a or the cooling medium discharge flow path 44b than the bypass flow path 80. The surrounding flow path 86 passes through the main supply flow path 82 and the main discharge flow path 88 (see Figure 2 ) to communicate with the power generation unit cooling flow path 70 and the bypass flow path 80.

[0061] like Figure 3 As shown, the main supply flow path 82 extends from the portion of the cooling medium supply passage 44a near the power generation unit toward the power generation unit cooling flow path 70. The main supply flow path 82 extends in the direction of arrow B. In this embodiment, a plurality of main supply flow paths 82 are spaced apart in the vertical direction. The plurality of main supply flow paths 82 constitute a main supply flow path group 84. The main supply flow path 82 extends through the bypass flow path 80 in the direction of arrow B. The main supply flow path 82 connects the cooling medium supply passage 44a, the bypass flow path 80, and the power generation unit cooling flow path 70 to allow fluid flow.

[0062] like Figure 2 As shown, the main discharge flow path 88 extends from the side of the cooling medium discharge passage 44b facing the power generation unit toward the power generation unit. A plurality of main discharge flow paths 88 are provided. The plurality of main discharge flow paths 88 constitute a main discharge flow path group 89.

[0063] like Figure 3 As shown, the bubble exhaust flow path 90 extends from above the cooling medium supply passage 44a in the direction of gravity toward the bypass flow path 80, connecting the cooling medium supply passage 44a with the bypass flow path 80. The bubble exhaust flow path 90 is provided at a portion of the cooling medium supply passage 44a that is away from the side facing the power generation section. The bubble exhaust flow path 90 is inclined upward by more than 30° relative to the main supply passage 82. The closer the inclination angle of the bubble exhaust flow path 90 is to the direction of gravity, the smaller the flow velocity v of the cooling medium inside the bubble exhaust flow path 90 in the direction of the arrow symbol B1. In addition, the distance L between the bubble exhaust flow path 90 and the main supply passage 82 can be increased, and the backflow of bubbles through the bypass flow path 80 can be prevented, which is preferable.

[0064] The bubble exhaust passage 90 extends toward the communication hole 50 (first fuel gas exhaust communication hole 46b1) located above and adjacent to the coolant supply communication hole 44a. The bubble exhaust passage 90 merges with the bypass passage 80 at the first confluence 92a of the communication hole bypass portion 94 of the bypass passage 80. The bypass passage 80 directs the coolant from the main supply passage 82 toward the main exhaust passage 88. The communication hole bypass portion 94 of the bypass passage 80, where the first confluence 92a is located, is the portion where the coolant flows in the direction indicated by arrow B2, which is opposite to the direction indicated by arrow B1, which is the direction of the coolant flow in the main supply passage 82. Since bubbles are exhausted along with the fluid in the communication hole bypass portion 94, the bypass passage 80 can prevent bubbles from flowing into the power generation unit cooling passage 70.

[0065] A distance L between a first merging portion 92 a where the bubble exhaust flow path 90 and the bypass flow path 80 merge and a second merging portion 92 b where the main supply flow path 82 and the bypass flow path 80 merge at the upper end of the main supply flow path group 84 is greater than the intervals between the main supply flow paths 82 included in the main supply flow path group 84 .

[0066] In this embodiment, the bubble exhaust flow path 90 is composed of a first path 90a connecting the coolant supply passage 44a and the surrounding flow path 86, and a second path 90b connecting the surrounding flow path 86 and the bypass flow path 80. The second path 90b is arranged on the arrow B2 side (outer side) farther from the power generation unit than the first path 90a.

[0067] exist Figure 3 In the illustrated example, the bubble exhaust flow path 90 is provided only in the upper cooling medium supply passage 44 a , but the present embodiment is not limited thereto, and the bubble exhaust flow path 90 may be provided in the lower cooling medium supply passage 44 a .

[0068] From the perspective of preventing bubbles from flowing into the power generation unit cooling flow path 70, the fluid force (jet force) of the coolant from the coolant supply passage 44a to the main supply flow path 82 is smaller than the buoyancy of the bubbles, which promotes the upward separation of the bubbles. The fluid force of the coolant is calculated by the product of the density ρ of the coolant, the cross-sectional area S of the main supply flow path 82, and the square of the flow velocity v of the coolant. Figure 4 As shown, as the flow velocity v increases, the fluid force of the coolant increases. A pressure loss is generated in the main supply flow path 82 so that the fluid force is smaller than the buoyancy of the bubbles. To achieve this pressure loss and keep the fluid force smaller than the buoyancy of the coolant bubbles, it is preferable to reduce the cross-sectional area S of the main supply flow path 82 and increase its length.

[0069] The fuel cell stack 10 of the present embodiment is configured as described above, and its operation will be described below.

[0070] Before describing the fuel cell stack 10 according to the embodiment, a comparative example will be described. Figure 5 In the coolant flow path 68 connected to the separator 33 according to the comparative example shown, the bubble exhaust flow path 90A is provided near the main supply flow path 82. In the bubble exhaust flow path 90A according to the comparative example, as indicated by the arrows, some of the bubbles that flow into the bypass flow path 80 flow into the main supply flow path 82 and enter the power generation unit cooling flow path 70, causing the bubbles to clog the flow path grooves 74.

[0071] like Figure 6 As shown, in the case of the comparative example, air bubbles enter a wide area of ​​the power generation unit cooling flow path 70 .

[0072] On the other hand, Figure 7 In the joint partition 33 involved in the present embodiment shown, the bubble exhaust flow path 90 extends toward the adjacent communicating hole 50 above, and the distance L between the bubble exhaust flow path 90 and the main supply flow path 82 is greater than that in the comparative example. In addition, the bubble exhaust flow path 90 is connected to the bypass flow path 80 in a direction in which the flow velocity component in the direction of the arrow symbol B1 decreases. Therefore, the bubbles flowing from the bubble exhaust flow path 90 into the bypass flow path 80 flow upward due to buoyancy along with the fluid in the bypass flow path 80, as shown by the arrow symbol. In addition, the distance L between the bubble exhaust flow path 90 and the main supply flow path 82 is large, and the flow velocity in the direction of the arrow symbol B1 is small, thereby preventing backflow in the bypass flow path 80 and suppressing the flow of bubbles into the main supply flow path 82.

[0073] Therefore, the fuel cell stack 10 can prevent the coolant flowing into the power generation section cooling flow path 70 through the main supply flow path 82 from being mixed with air bubbles, thereby preventing the flow path grooves 74 from being clogged.

[0074] like Figure 8 As shown, according to this embodiment, bubbles are mixed only in a limited portion near the upper end of the power generation unit cooling flow path 70 , and the bubble mixing area can be significantly reduced compared to the comparative example.

[0075] Regarding the bonding spacers 33 of the comparative example and the present embodiment, Figure 9 The results show measurements of the blockage rate of flow channel grooves 74 due to air bubbles when a coolant mixed with air is allowed to flow. As shown, in the comparative example and the bonding separator 33 of the embodiment, the blockage rate increases as the air mixing rate in the coolant increases. The bonding separator 33 of this embodiment can achieve a result that suppresses the blockage rate compared to the comparative example, even when the air mixing rate increases.

[0076] The fuel cell stack 10 of this embodiment achieves the following effects.

[0077] The present embodiment relates to a fuel cell stack, which is formed by stacking a plurality of power generation cells 12, wherein the power generation cells 12 include an electrolyte membrane electrode structure 28a and a pair of separators 30 and 32 that clamp the electrolyte membrane electrode structure 28a. In the fuel cell stack 10, there are: a cooling medium flow path 68 formed between the bulging portions of adjacent separators 30 and 32; a cooling medium supply connecting hole 44a that supplies cooling medium to the cooling medium flow path 68; and a cooling medium discharge connecting hole 44b that discharges the cooling medium from the cooling medium flow path 68. The cooling medium flow path 68 includes: a power generation section cooling flow path 70 that includes a portion overlapping with the power generation section of the electrolyte membrane electrode structure 28a; a bulging portion formed in the flow path sealing portion; and a cooling medium discharge connecting hole 44b that discharges the cooling medium from the cooling medium flow path 68. A bypass flow path 80 between the outflow parts, the flow path sealing portion is provided on the outer periphery of the partitions 30, 32 and seals the reaction gas flow path formed between the partitions 30, 32 and the electrolyte membrane electrode assembly 28a; a main supply flow path 82, which penetrates the bypass flow path 80 from the portion of the cooling medium supply connecting hole 44a facing the power generation part cooling flow path 70 and extends toward the power generation part cooling flow path 70 to connect the cooling medium supply connecting hole 44a with the power generation part cooling flow path 70; and a bubble exhaust flow path 90, which extends from the upper side of the cooling medium supply connecting hole 44a in the direction of gravity toward the bypass flow path 80 to connect with the bypass flow path 80, and the bubble exhaust flow path 90 extends toward the upper side of the cooling medium supply connecting hole 44a in the direction of gravity.

[0078] In the fuel cell stack 10 having the above-described structure, the bubble exhaust flow path 90 faces upward, thereby allowing bubbles in the coolant to flow toward the bypass flow path 80 due to their buoyancy. In the bypass flow path 80, the pressure difference between the coolant supply passage 44a and the coolant discharge passage 44b allows the coolant, which has bypassed the power generation unit and has been mixed with bubbles, to flow toward the coolant discharge passage 44b. Furthermore, since the bubble exhaust flow path 90 faces the upward-facing passage 50, the distance L along the bypass flow path 80 to the main supply flow path 82 is increased. This prevents backflow of coolant flowing from the bubble exhaust flow path 90 into the bypass flow path 80, and more effectively prevents the mixing of bubbles that have passed through the main supply flow path 82.

[0079] In the above-described fuel cell stack 10, a plurality of main supply flow paths 82 are provided to form a main supply flow path group 84. The distance L between a first merging portion 92a where the bubble exhaust flow path 90 and the bypass flow path 80 merge and a second merging portion 92b at the upper end of the main supply flow path group 84 where the main supply flow path 82 and the bypass flow path 80 merge is greater than the spacing between the main supply flow paths 82 included in the main supply flow path group 84. In the fuel cell stack 10 with this structure, the distance L between the main supply flow paths 82 and the bubble exhaust flow paths 90 along the bypass flow path 80 is increased, thereby preventing bubbles from flowing back into the bypass flow path 80 and returning to the main supply flow path 82, thereby suppressing the mixing of bubbles into the power generation unit cooling flow path 70.

[0080] In the above-described fuel cell stack 10, the bubble exhaust passage 90 may be inclined upward in the direction of gravity by at least 30° relative to the direction of the main supply passage 82. The fuel cell stack 10 with this structure can efficiently flow the coolant mixed with bubbles through the bubble exhaust passage 90 by utilizing the buoyancy of the bubbles.

[0081] In the above-described fuel cell stack 10 , the bubble exhaust flow path 90 may extend toward the communication hole 50 adjacent to and located above the coolant supply communication hole 44 a in the direction of gravity.

[0082] In the above-described fuel cell stack 10, the bypass flow path 80 may include a communication hole bypass portion 94 that bypasses the adjacent communication hole 50 located above the coolant supply communication hole 44a in the direction of gravity from the outside, and the bubble exhaust flow path 90 may be connected to a portion of the communication hole bypass portion 94 that flows in the opposite direction to the flow direction of the coolant in the power generation section cooling flow path 70. The fuel cell stack 10 with this structure can prevent bubbles in the bypass flow path 80 from flowing back, thereby preventing bubbles from entering the main supply flow path 82.

[0083] The fuel cell stack 10 described above also includes a surrounding flow path 86, which is disposed between the bypass flow path 80 and the coolant supply manifold 44a and formed between the bulged portions of the manifold seals 54 and 60 surrounding the coolant supply manifold 44a. A bubble exhaust flow path 90 includes a first path 90a connecting the coolant supply manifold 44a with the surrounding flow path 86 and a second path 90b connecting the surrounding flow path 86 with the bypass flow path 80. The second path 90b is positioned further outward (away from the power generation unit) than the first path 90a. The fuel cell stack 10 with this structure has an actual inclination angle of the bubble exhaust flow path 90 close to vertically upward, thereby utilizing the buoyancy of the bubbles to more efficiently exhaust the bubbles. Furthermore, the distance L between the bubble exhaust flow path 90 and the main supply flow path 82 is increased, thereby preventing the incorporation of bubbles due to backflow.

[0084] In the above-mentioned fuel cell stack 10, the cross-sectional area S of the main supply flow path 82 may be limited to a range that maintains the following flow velocity v, which makes the buoyancy of the bubbles inside the cooling medium supply connecting hole 44a greater than the fluid force from the cooling medium supply connecting hole 44a toward the main supply flow path 82. Here, the buoyancy of the bubbles is the buoyancy of bubbles larger than a predetermined size. There is a possibility that bubbles of this predetermined size will clog the flow path groove 74 of the power generation unit cooling flow path 70. Based on Figure 4 The flow velocity v from the coolant supply manifold 44a toward the main supply flow path 82 can be set to, for example, 0.17 m / s or less. In the fuel cell stack 10 with this structure, bubble separation is enhanced within the coolant supply manifold 44a, allowing efficient bubble removal through the bubble exhaust flow path 90. As a result, the fuel cell stack 10 can reduce the intrusion of bubbles into the power generation unit cooling flow path 70.

[0085] In the above-described fuel cell stack 10, a plurality of cooling medium supply manifolds 44a may be provided at intervals in the vertical direction relative to the direction of gravity, and at least the uppermost cooling medium supply manifold 44a may be provided with a bubble exhaust passage 90. The fuel cell stack 10 with this structure can efficiently separate and remove bubbles from the uppermost cooling medium supply manifold 44a, where relatively many bubbles are mixed.

[0086] In the above description, the present invention has been described by way of preferred embodiments. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention.

Claims

1. A fuel cell stack comprising a plurality of stacked power generation cells, each of which comprises an electrolyte membrane electrode assembly and a pair of separators sandwiching the electrolyte membrane electrode assembly, wherein: a cooling medium flow path formed between the bulged portions of the adjacent partition plates; a cooling medium supply communication hole for supplying cooling medium to the cooling medium flow path; and a cooling medium discharge communication hole for discharging the cooling medium from the cooling medium flow path; The cooling medium flow path has: a power generation section cooling flow path including a portion overlapping with the power generation section of the electrolyte membrane electrode assembly; a bypass flow path formed between bulging portions of a flow path sealing portion provided on an outer periphery of the separator and sealing a reaction gas flow path formed between the separator and the membrane electrode assembly; a main supply flow path extending from a portion of the cooling medium supply passageway facing the power generation unit cooling flow path through the bypass flow path and toward the power generation unit cooling flow path, thereby connecting the cooling medium supply passageway with the power generation unit cooling flow path; a bubble exhaust flow path extending from vertically above the cooling medium supply communication hole toward the bypass flow path and communicating with the bypass flow path; as well as a main discharge flow path extending from a side of the cooling medium discharge passage facing the power generation unit toward the power generation unit, The bypass flow path allows the cooling medium to flow from the main supply flow path toward the main discharge flow path. The bubble exhaust flow path extends upward in the direction of gravity relative to the cooling medium supply passage.

2. The fuel cell stack according to claim 1, wherein: A plurality of the main supply flow paths are provided to form a main supply flow path group, A distance between a first merging portion where the bubble exhaust flow path and the bypass flow path merge and a second merging portion where the main supply flow path and the bypass flow path merge at the upper end of the main supply flow path group is greater than intervals between the main supply flow paths included in the main supply flow path group.

3. The fuel cell stack according to claim 1 or 2, characterized in that: The bubble exhaust flow path is inclined upward by 30° or more in the direction of gravity relative to the direction of the main supply flow path.

4. The fuel cell stack according to claim 1 or 2, characterized in that: The bubble exhaust flow path extends toward a communication hole adjacent to the cooling medium supply communication hole vertically above.

5. The fuel cell stack according to claim 1 or 2, characterized in that: The bypass flow path includes a communication hole bypass portion that bypasses the adjacent communication hole vertically above the cooling medium supply communication hole from the outside. The bubble exhaust flow path is connected to a reverse portion of the communication hole bypass portion that is reverse to the flow direction of the cooling medium in the power generation unit cooling flow path.

6. The fuel cell stack according to claim 5, characterized in that The cooling medium supply passage is provided between the bypass passage and the cooling medium supply passage and formed between bulging portions of the passage seal portion surrounding the cooling medium supply passage. The bubble exhaust flow path includes a first path connecting the coolant supply passage and the surrounding flow path, and a second path connecting the surrounding flow path and the bypass flow path, wherein the second path is arranged outside the first path.

7. The fuel cell stack according to claim 2, wherein: The cross-sectional area of ​​the main supply flow path is limited to a range that maintains a flow velocity at which the buoyancy of bubbles in the coolant supply passage becomes greater than the fluid force from the coolant supply passage toward the main supply flow path.

8. The fuel cell stack according to any one of claims 1, 2 and 7, wherein: The plurality of cooling medium supply passages are provided at intervals in the vertical direction relative to the direction of gravity, and the bubble exhaust passage is provided in at least the uppermost cooling medium supply passage.

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