JP2006216442A - Separator for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the ununiformity of gas flow rate in a unit cell. <P>SOLUTION: In a separator for a fuel cell equipped with two or more parallel passage group inverting gas flow direction and a passage inverting part (length L, width W), when the number of parallel grooves on the upstream side (downstream side) of a gas flow joining point is represented by N (M), the width of the groove by W<SB>1</SB>-W<SB>N</SB>(W'<SB>1</SB>-W'<SB>M</SB>), the width of a crest by w<SB>1</SB>-w<SB>N</SB>(w'<SB>1</SB>-w'<SB>M-1</SB>), the length L and the width H satisfy the formula (wherein Re is Reynolds number of gas measured in a flow passage). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell (gas) separator. More specifically, the present invention is an improvement of the flow path configuration in which fuel gas and oxidant gas flow in a separator of a fuel cell such as a solid polymer fuel cell.

The fuel cell, hydrogen _{H 2} → ^2H + + 2e that occurs at the anode electrode side is supplied ^- as occurs at oxygen supplying cathode side ^{_{(1/2) O 2 + 2H +}} + 2e - → of _H 2 O It is a device that takes out electric power using an electrochemical reaction. 2. Description of the Related Art A polymer electrolyte fuel cell using a solid polymer as an electrolyte of a fuel cell is attracting attention because it operates at a low temperature and can realize a high output density with a simple system.

  A single cell, which is the basic structure of a fuel cell, will be described with reference to FIG. The single cell comprises a MEA (Membrane Electrode Assembly) constructed by sandwiching both surfaces of a cation-conductive polymer electrolyte membrane 1 such as a perfluorocarbon sulfonic acid membrane with a carbon fiber membrane 2 carrying a catalyst such as platinum. The center. Porous electrodes 3 (cathode electrode and anode electrode) are arranged so as to sandwich the MEA from both sides. These electrodes have not only a role of collecting electrons generated by an electrochemical reaction but also a role of diffusing fuel gas or oxidant gas to the catalyst layer. Therefore, the electrode is also called a diffusion layer, and carbon paper or carbon cloth is used. On the outside of the electrode, separators 4 are arranged on both sides in order to prevent gas from flowing to adjacent cells.

  In general, the separator is made of a metal or a carbon material, and a flow path 5 for flowing fuel or oxidant gas is formed in a groove shape on the surface of the separator in contact with the electrode. The flow path 5 formed on the separator 4 is composed of a number of independent straight flow paths as shown in FIG. 2A, and a straight flow path system in which gas flows in the same direction in all flow paths. As shown in FIG. 2B, there is a serpentine channel method in which a single channel is meandered and the gas flow is alternately inverted by 180 °.

  In the straight channel method, the pressure loss in the channel is small compared to the serpentine channel method even when operating at high current density where the gas flow rate increases, so the pressure difference between the anode side channel and the cathode side channel This is advantageous in terms of protection of single cells and battery efficiency. However, in the operation at a low current density, the flow rate of each flow path is reduced, so that it is difficult to reliably remove water generated due to the electrochemical reaction.

  On the other hand, with the serpentine channel method, the flow rate of each channel can be maintained even during operation at a low current density at which the gas flow rate is reduced, so that the generated water can be removed reliably and the internal flow rate can be reduced. Since it becomes faster, internal diffusion is promoted, and excellent battery characteristics can be realized. However, when operating at a high current density, the flow rate increases, so the pressure loss increases and the pressure difference between the anode-side channel and the cathode-side channel increases, which causes problems in terms of MEA protection and gas supply. It will be held.

  As described above, it is difficult to realize excellent battery characteristics in a wide battery operation range by using any one of the straight type and the serpentine type. Therefore, in order to incorporate the advantages of both the above-mentioned methods, as shown in Fig. 2 (C), a plurality of straight channels repeat branching and merging, and a channel method that mixes a straight method and a serpentine method (hereinafter, mixed channel) Has also been proposed. In this mixed channel method, the gas introduced into one end of the separator branches into a plurality of channels and flows to the other end of the separator (this is the same as the straight method). Inverted 180 °, and branched into multiple flows and repeated. A group consisting of a plurality of flow paths branching from one flow and flowing across the separator in the same direction and joining at the other end of the separator is referred to as a parallel flow path group in the present invention. Therefore, it can be said that the mixed flow channel method is a method in which the flow is reversed and the meandering is repeated in units of parallel flow channel groups.

  However, in this mixed channel method, there is a high possibility that the flow rate will vary at the position where the channel branches and / or merges (the part indicated by a in FIG. 2C), which may affect the battery performance. There is. As a countermeasure, for example, Japanese Patent Laid-Open No. 2003-77497 has a shape in which dense protrusions are provided at a portion where flow paths merge and branch, and Japanese Patent Laid-Open No. 2000-100458 has an end portion that connects straight flow paths. Each type has been proposed in which a large reservoir portion is provided by penetrating the entire space in the stacking direction. However, the former requires a large number of protrusions, and the pressure loss at this portion increases, and the drainage of the generated water is reduced. In the latter case, if one part of the straight flow path (flow path constituting the parallel flow path group) sandwiched between the manifolds (reservoir parts) is blocked by the generated water, the gas is easily bypassed to other flow paths. In other words, the pressure increase in the closed linear flow path is small, and the closed flow path is extremely difficult to regenerate.

JP 2003-77497 A JP 2000-100458 A

  An object of the present invention is to provide a separator that solves the above-described problems of the separator for a fuel cell and prevents the battery performance from deteriorating due to the non-uniform flow rate of gas passing through the single cell. .

  According to the present invention, in the mixed flow path type fuel cell separator, a plurality of flow paths from the parallel flow path group merge, the flow is reversed, and the flow path is branched into the multiple flow paths (the present invention) (Referred to as the channel reversal section), the width of the grooves and peaks of the parallel flow path group, the number of downstream parallel flow path groups, and the Reynolds number of the gas flowing through the flow path The above-mentioned problem can be solved by determining by a function having a variable.

The present invention relates to a fuel cell separator having a plurality of gas flow paths for flowing a fuel or oxidant gas, which are composed of a groove part through which gas flows and a peak part in contact with an electrode. And two or more parallel flow path groups in which the gas flow directions are alternately reversed, and a flow path inversion portion connected to each flow path of two adjacent parallel flow path groups. The separator for a fuel cell of the present invention has N number of grooves in the upstream parallel flow path group where the gas flows merge at the flow path inversion part, the width of the groove part is W _{1 to} W _N , and the width of the peak part. W ₁ to w _N , the number of grooves in the downstream parallel flow path group from which the gas flow branches from the flow reversal part is M, the width of the groove part is W ′ _{1 to} W ′ _M , The width is w ′ ₁ to w ′ _M−1 , and the length L and the width H of the flow path inversion portion satisfy the following expressions.

Here, H> max (Wmean, f (M, Re) × Wmean) means that H is larger than Wmean or (M, Re) × Wmean, whichever is larger. That means
If f (M, Re)> 1.0, then H> f (M, Re) × Wmean,
When f (M, Re) <1.0, H> Wmean.

When the width H of the channel reversal part varies in the length L direction (for example, different between the upstream side and the downstream side), the maximum value of H only needs to satisfy the above equation.
The width H of the channel inversion part preferably satisfies the following equation.

In the formula, A, B, C, and D are constants, respectively, preferably A = 1.7, B = 0.0194, C = 7.621 × 10 ⁻⁴ , and D = −5.321 × 10 ⁻⁷ . That is, the value of f (M, Re) depends on M (the number of parallel flow path groups on the downstream side). Therefore, when M is large and f (M, Re)> 1.0, the lower limit of H is f (M, Re) × Wmean, and when M is small and f (M, Re) <1.0 , H is the lower limit Wmean (that is, the average value of the channel width). In this way, the width H of the channel inversion portion is set according to the value of M, but it is set to be at least larger than the average value of the channel width.

The width _HA of the upstream flow channel reversal portion that is the flow channel reversal portion of the portion connected to the upstream parallel flow channel group and the downstream flow that is the flow channel reversal portion of the portion connected to the downstream parallel flow channel group It is preferable that the width H _B of the path reversal part satisfies the following formula.

  In order to make the variation in the flow rate more uniform, 1 is provided on the downstream side of the flow channel inversion portion (that is, the portion of the flow before branching to the parallel flow channel group on the downstream side, referred to as the downstream flow channel reversal portion in the present invention). Alternatively, two or more protrusions may be provided. Moreover, you may chamfer the at least 1 corner part of a flow path inversion part by a curved surface and / or a plane.

The material of the separator of the present invention can be metal or carbon as in the conventional case.
In the present invention, each parallel flow path group is composed of two or more straight flow paths having the same gas flow direction and having a common branching and merging point. It is also possible to configure from a flow path.

Moreover, when there are two or more flow path inversion parts, it is sufficient that at least one flow path inversion part conforms to the present invention. Of course, it is preferable that all the channel reversal sections follow the present invention.
The separator of the present invention is particularly suitable for a separator of a polymer electrolyte fuel cell. However, application to separators for other types of fuel cells is also within the scope of the present invention.

  In the fuel cell separator of the mixed flow channel system, the flow rate in the flow channel inversion portion is varied by widening the width H of the flow channel inversion portion, which is a portion where a plurality of flow channels merge and branch, in accordance with the present invention. Even if the flow rate of any of the straight flow paths constituting the parallel flow path group is minimized and the generated water stays therewith, the water is pushed out by the pressure increase in this part, Blockage of the flow path is avoided. Therefore, the fuel cell separator of the present invention can efficiently supply gas to the catalyst layer even under conditions where the amount of power generation is large, and can suppress deterioration in battery performance over time.

Next, the present invention will be described more specifically with reference to the accompanying drawings.
The fuel cell separator of the present invention is a mixed channel system. Therefore, as shown in FIG. 2 (C), it is a flow system that repeats reversal in units of parallel flow channel groups, and in each flow channel reversal unit, after the gas flowing from the upstream parallel flow channel groups merges The flow direction is reversed, and the flow is branched into the parallel flow path group on the downstream side.

FIG. 3 is an explanatory view of the vicinity of one flow path inversion portion. Groove W _1, W ₂ ··· W _N diffusion layer crests w ₁ in contact with the (electrode), w ₂ each flow path · · · w _N and the upstream side of the parallel flow path group consisting of 6 (i.e. The gas (gas) flowing in the groove portion) as shown by the arrows joins at the flow path merging portion 7 and flows while mixing in the flow path reversing portion 10 at the end of the separator, and then again as indicated by the arrows. , through the flow path branching portion 9, the groove portions _{W '1, W' 2 ···} W M and ridges w in contact with the diffusion layer _'1, w' downstream consists ₂ · · · w _M-1 Metropolitan The parallel flow path group 8 branches into each flow path and flows.

  In the present invention, the width H of the entire flow channel inversion section 10 including the portion connected to the upstream parallel flow channel group 6 and the portion connected to the downstream parallel flow channel group 8 is expressed by the above (Equation 4). As shown, the Reynolds number (Re) of the gas passing through the flow path, the number of flow paths (grooves) in the downstream parallel flow path group 8 (M), and the average value (Wmean) of the flow path width (groove width) Expand beyond a certain minimum value derived as a function. Further, the length L of the flow path inversion portion is set to be equal to or larger than the sum of the widths of the groove portion and the peak portion as shown in the above (Equation 4).

  Thereby, an excessive increase in flow velocity in this region can be suppressed, and the pressure drop in the flow path merging portion 7 can be maintained at an appropriate value. As a result, the gas from the upstream parallel flow channel group 6 to the flow channel reversing unit 10 via the flow channel merge unit 7 reaches the flow channel branching unit 9 with significant drift generated by the merge. Instead, the gas from the plurality of upstream parallel flow path groups 6 is once mixed and then distributed to the plurality of downstream parallel flow path groups 8. For this reason, generation | occurrence | production of deviation will be suppressed about the gas distributed to the some downstream parallel flow path group 8 about both the component and flow volume. In this way, mixing of gas components in the flow path reversal part is promoted, and the battery performance is improved, and the flow speed in the downstream parallel flow path group 8 after branching is kept uniform to prevent the occurrence of a low flow speed flow path. This makes it possible to prevent the product water from staying in the low flow channel and blocking the channel.

  However, although the expansion of the width H of the channel reversing part 10 leads to improvement of the flow characteristics, if it is excessively enlarged, the contact area between the separator peak and the diffusion layer (electrode) is decreased, and excessive generation of water is caused. It causes the low flow velocity region. In the present invention, as a function of the Reynolds number in the flow path, the number of flow paths in the downstream parallel flow path group 8 and the average flow path width, the width H of the flow channel reversing unit 10 required for flow equalization after branching is obtained. Although the minimum value is derived, the width H of the flow path inversion unit 10 is preferably within 3 times the minimum value thus derived, and more preferably within 1.5 times.

  Note that the width H of the channel inversion portion need not be the same over the entire length L thereof. When the width H of the flow path inversion portion varies in the length direction, the value of H is the minimum value, that is, the value of H of the portion where the width is minimum. However, the width of the chamfered portion when the corner of the flow path inversion portion is chamfered is excluded from this minimum value.

  In addition, as shown in FIG. 1, the wall and the ridge that constitute the straight flow path in each parallel flow path group may have a wall surface that divides both of them perpendicular to the electrode, or the wall surface is inclined. May be. When the wall surface is inclined or curved, the widths W, W ′, w, w ′ of the grooves and peaks are all intermediate values between the minimum and maximum widths (usually half the width of the grooves or peaks). Equal to the width measured in depth or height).

  More specifically, the Reynolds number of the gas in the flow channel for deriving the minimum width H of the flow channel reversing unit 10 required for equalizing the flow rate after branching, the flow channel number M of the parallel flow channel group 8 on the downstream side. The function of the average flow path width W ′ is as shown in the above (Equation 5).

  By using this function form, the channel inversion unit can optimize the flow status of each channel after branching regardless of the position of the channel inversion unit in the separator, the number of channels after branching, and the channel width. A minimum width H of 10 can be determined.

Deriving the minimum width H of the flow channel inversion unit 10 required for flow equalization after branching, the Reynolds number in the flow channel defined by (Equation 5), the number of parallel flow channel groups on the downstream side, and the average flow By setting constants in the function of the path width as A = 1.7, B = 0.0194, C = 7.621 × 10 ⁻⁴ , D = −5.321 × 10 ⁻⁷ , the flow rate deviation of the downstream parallel flow path group 8 can be reduced. It can be suppressed to ± 20% or less.

As shown in FIG. 4, the width _HA of the upstream-side channel reversing unit 10 </ b> _A , which is the channel-inverting unit of the portion connected to the upstream parallel channel group 6, and the downstream parallel channel group 8 are connected. It is preferable that the width H _B of the downstream flow channel inversion unit 10B, which is the partial flow channel inversion unit, satisfies H _A <H _B. As a result, the width of the flow path inversion portion 10 changes in a stepped manner at the boundary between the upstream side and the downstream side, and the gas flow is once collected at the flow path merging portion 7 having a small cross-sectional area on the upstream side. By enlarging the cross-sectional area before reaching 9, it is possible to avoid the influence of the drift generated at the joining portion from affecting the flow path branching portion 9. In addition, it is possible to suppress a decrease in the contact area between the separator / diffusion layer (electrode) while maintaining a uniform flow rate as compared with the case where the length is extended over the entire width of the flow path inversion unit 10. .

In this way, the flow path reversal is performed such that the width H _{B of the} downstream flow path reversing part 10B following the flow path branching part 9 is larger than the width _HA of the upstream flow reversing part 10A following the flow path joining part 7. When the width of the portion is changed in the length direction, one or two or more protrusions having a rectifying action may be provided in the downstream-side channel reversing portion 10B. The location of the protrusion is preferably a portion through which the main flow 11 of the gas flow indicated by an arrow in FIG. The protrusions may be one protrusion 12 as shown in FIG. 5 (b), or two or more protrusion rows 13 arranged at an appropriate interval as shown in FIG. 5 (c).

  By installing this protrusion, it is possible to suppress the occurrence of a flow deviation between the flow paths after branching even in a region with a high Reynolds number where the influence of drift increases. Furthermore, when the top portion of the installed protrusion is brought into contact with the diffusion layer, an increase in the contact area between the separator / diffusion layer can be realized and the diffusion layer facing the flow path and the MEA can be held.

  When the number of protrusions is further increased and installed in two or more rows, as shown in FIG. 5 (d), it is preferable that the protrusion rows 13 provided in the downstream-side flow path inversion portion 10B are arranged in a staggered manner. . When the protrusion rows 13 are arranged in a staggered manner in this way, it is possible to further enhance the rectification effect due to the protrusions under a high Reynolds number condition.

  The shape of each protrusion of the protrusion 12 or the protrusion row 13 may be a shape selected from a cylinder, a cone, a truncated cone, a polygonal column, a polygonal pyramid, a polygonal frustum, and a part of a sphere (eg, a hemisphere). When forming the protrusion, various restrictions are imposed on the shape of the protrusion due to the material of the separator and the processing method. In any of the above-described shapes, it is possible to obtain the same effect of uniform flow rate. The protrusion is preferably the same as the material of the separator, but may be a different material.

  As shown in FIG. 6, at least one of corner portions that are corners of the channel inversion portion 10, preferably both, are straight and / or curved on the plane of the separator (the bottom surface of the groove or the top surface of the crest). May be chamfered. FIG. 6A shows an example of chamfering with a curved line (arc) and FIG. 6B with a straight line. The chamfering may be a vertical surface in the thickness direction of the separator (the depth direction of the groove or the height direction of the crest). However, the upper and lower ends in the thickness direction can be slightly rounded. Similarly, the upper end and the lower end in the thickness direction of the end portion of the separator (that is, the end portion of the flow path inversion portion) may be slightly rounded.

  In this way, when the corner portion of the flow channel reversing unit 10 is chamfered and a portion where the low flow velocity region 14 shown in FIG. 6C is expected to be generated is excluded from the flow channel, the corner portion of the flow channel is generated. The low flow rate region becomes small, and the retention of water generated in the flow path can be suppressed, so that the battery performance can be prevented from deteriorating.

  The material for the fuel cell separator of the present invention is preferably either a metal or a carbon material. Examples of suitable metals include stainless steel, titanium, aluminum and the like. The carbon material is preferably graphite (graphite) in terms of conductivity. If the material is different, the processing method for forming the flow path is different, but an appropriate processing method can be easily determined by those skilled in the art. For example, in the case of a carbon material, processing is generally performed by cutting. In the case of a metal, press molding can be used in addition to cutting. Regardless of the processing method, the battery performance improvement effect by the separator according to the present invention can be obtained.

  The solid polymer membrane is a perfluorocarbon sulfonic acid 50 μm thick membrane (Dupont, Nafion), and the diffusion layer is 300 μm thick carbon paper. A single cell was produced. The electrode area of the single cell used in this example was 70 mm × 100 mm, and separators having various flow path configurations shown in Table 1 and FIGS. 7A and 7B were compared.

  Among the separators used for evaluation, Examples A to E are flow paths based on the present invention, and Examples F to H are flow paths of comparative examples. Examples F and G are comparative examples in which the width H of the channel reversal part does not satisfy the requirements defined in the present invention. In Example H, the width H of the channel reversal part satisfies the requirements defined in the present invention. However, this is a comparative example whose length L does not satisfy the requirements defined in the present invention. In order to simplify the channel configuration, the number of channels (grooves) in each parallel channel group has been unified to three in all examples, but the number of channels may be varied for each parallel channel group. It is natural.

  In Examples A to D, F, and H, the separator material is a graphite plate provided with a flow path by cutting. In Examples E and G, after press forming a stainless steel plate, the contact resistance is reduced. It was gold plated.

  In Example E, protrusions were formed on the downstream-side channel inversion part of the separator. The protrusions had a hemispherical shape formed simultaneously with the grooves in press forming when the grooves of the separator were formed, and the size and arrangement were 0.8 mm in diameter and 2.5 mm apart. In any of the separators, chamfering of the corner portion of the flow path inversion portion was not performed.

In the flow path of each separator, 99.9999% hydrogen gas is used as the anode-side fuel gas, air is used as the cathode-side oxidant gas, and the flow rate is 3.5 × 10 ⁻⁴ mol / s for hydrogen gas. The air was a constant value of 10.0 × 10 ⁻³ mol / s. Separators having the same flow path configuration were used on the anode side and the cathode side.

Table 1 shows the sum of the widths of the grooves and the peaks, the Reynolds number (Re) of the gas measured in the straight channel (measured with air), and f (M, Re) × Wmean (in Table 1, f × The value of Wmean is also shown.
During the evaluation, the temperature of the battery body was maintained at 78 ± 2 ° C., humidity control was performed at the cell inlet, the anode side was humidified to saturation, and the pressure inside the battery was 1 atm. FIG. 8 shows changes in cell voltage when the current density is changed. As can be seen from this figure, in the separator having the flow path of the present invention, the flow rate deviation at the flow path branching portion hardly occurs, so the consumption of fuel and oxidant increases, and the influence of the flow rate deviation appears greatly. There is no performance degradation in the current region, and a high battery voltage is maintained. On the other hand, in the flow path shown as a comparative example, the flow rate deviation generated in the flow path branching part leads to the occurrence of local current density deviation due to the increase in consumption of fuel and oxidant accompanying the increase in current density. As expected, significant performance degradation has emerged.

As another performance test, battery performance was evaluated for deterioration over time for separators having flow paths having the shapes shown in Table 1. The configuration of the single cell used for the evaluation is the same as above, and by adjusting the consumption rate of fuel and oxidant in the single cell state, the initial power generation state of the battery is 0.5 A / cm ² , 0.62 V, and the current Voltage drop rate after 50 hours,
The voltage drop rate was evaluated by the cell voltage after 1-50 hours / the initial voltage.

  Also during this evaluation, the temperature of the battery body was maintained at 78 ± 2 ° C., humidity control was performed at the cell inlet, the anode side was humidified to saturation, and the pressure inside the battery was 1 atm. Further, 99.9999% hydrogen gas was used as the anode-side fuel gas, and air was used as the cathode-side oxidant gas. The results are also shown in Table 1.

  As shown in Table 1, in Examples A to E which are invention examples, the voltage drop rate was 0.03 or less, and no battery performance deterioration was observed over time. On the other hand, in Examples F to H, which are comparative examples because the value of the width H or the length L of the channel reversal part is outside the range of the present invention, the remarkable performance that seems to be caused by the retention of the generated water is considered. Deterioration was observed, and the voltage drop rate was 0.1 or more.

It is a schematic explanatory drawing which shows the structure of the single cell of a polymer electrolyte membrane type fuel cell. FIGS. 2A to 2C are diagrams for explaining the structure of a typical gas flow path in the fuel cell (separator). It is channel explanatory drawing which shows the flow-path structure of the flow-path inversion part vicinity of 1 aspect of the separator for fuel cells of this invention. It is flow path explanatory drawing similar to the top of another aspect of the separator for fuel cells of this invention. FIGS. 5A to 5D are flow charts similar to those in the case where there are no protrusions and no protrusions in the flow path inversion part on the downstream side. 6 (a) to 6 (c) are channel explanatory views similar to the above, showing an aspect in which the corner portion of the channel inversion portion is chamfered. It is explanatory drawing which shows the structure of the flow path of the separator employ | adopted in the Example. It is a figure which shows the comparison of the battery performance in an Example.

Explanation of symbols

1. 1. polymer electrolyte membrane; 2. catalyst-supported carbon fiber membrane; 3. porous electrode (diffusion layer); Separator, 5. Flow path, 6. 6. upstream parallel flow path group; Flow path confluence, 8. 8. downstream parallel flow path group; Flow path branch, 10. Channel inversion section, 10A. Upstream channel inversion section, 10B. 10. downstream channel inversion section; 11. The main flow part of the gas flow in the channel inversion part, Protrusion, 13. Protrusion row, 14. Low flow area

Claims (9)

A separator for a fuel cell having a plurality of gas passages for flowing a fuel or oxidant gas, which is composed of a groove portion through which a gas flows and a peak portion in contact with an electrode, Two or more parallel flow path groups whose flow directions are alternately reversed, and a flow path reversal portion connected to each flow path of two adjacent parallel flow path groups, in which the gas flow is The number of grooves in the upstream parallel flow path group to be merged is N, the width of the groove is W _{1 to} W _N , and the width of the peak is w ₁ to w _N, and the gas flow branches from the flow path inversion part The number of grooves in the downstream parallel flow path group is M, the width of the groove is W ′ _{1 to} W ′ _M , and the width of the peak is w ′ ₁ to w ′ _M−1. The fuel cell separator is characterized in that the length L and the width H of the fuel cell satisfy the following formula.

The fuel cell separator according to claim 1, wherein the width H of the flow path inversion portion satisfies the following expression.

In the formula, A, B, C, and D are constants. The fuel cell separator according to claim 2, wherein A = 1.7, B = 0.0194, C = 7.621 × 10 ⁻⁴ , and D = −5.321 × 10 ⁻⁷ . The width _HA of the upstream flow channel reversal portion that is the flow channel reversal portion of the portion connected to the upstream parallel flow channel group and the downstream flow that is the flow channel reversal portion of the portion connected to the downstream parallel flow channel group the width H _B of the road-inverting portion satisfies the following equation, the fuel cell separator according to claim 1.

  The fuel cell separator according to claim 4, wherein the downstream channel inversion portion has one or more protrusions.   The fuel cell separator according to claim 5, wherein the protrusions form a plurality of rows arranged in a staggered manner.   The fuel cell separator according to claim 5 or 6, wherein the protrusion has a shape selected from the group consisting of a cylinder, a cone, a truncated cone, a polygonal column, a polygonal pyramid, a polygonal truncated cone, and a part of a sphere.   The fuel cell separator according to any one of claims 1 to 7, wherein at least one corner portion of the flow path reversing portion is chamfered by a curved surface and / or a flat surface.   The fuel cell separator according to any one of claims 1 to 8, wherein the material is metal or carbon.

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