JP2006216441A - Method of designing passage of separator for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simply predict an internal gas flow state in a passage without actually installing the passage in a separator and design a passage shape capable of enhancing the uniformity of flow and distribution of gas in the passage shape of the separator for the fuel cell having a plurality of parallel passages through which fuel or oxidant gas flows. <P>SOLUTION: The variation range of Reynolds number of gas in the passage varying by consumption of fuel or oxidant gas flowing through the passage and production of water during the operation of the fuel cell is decided, and by using the variation range as a boundary condition, formula of conservation of mass, formula of conservation of momentum, and formula of conservation of energy are compounded and analyzed, deviation of indexes indicating the gas flow state in the passage is found every passage, and the passage shape is designed so that the deviation becomes a constant value or lower. As the index indicating the gas flow state, flow rate, flux, flow velocity, and the amount of pressure drop of gas flowing through parallel passages after branching can be used. For example, by using the flow velocity in the vicinity of a passage wall as the index, the passage is designed so as to delete a region decreasing the flow velocity. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a (gas) separator for a fuel cell such as a polymer electrolyte fuel cell. More specifically, the present invention relates to a method for optimally designing a flow path in a separator through which a fuel or oxidant gas flows, and the method. It is related with the separator for fuel cells designed based on this.

The fuel cell is H ₂ → 2H ⁺ + 2e ⁻ generated on the anode electrode side supplying hydrogen and (1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O generated on the cathode electrode side supplying oxygen. 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 is an 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 large 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 system 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 for each flow path is reduced, so that it is difficult to reliably remove water generated by the electrochemical reaction by the gas pressure.

  On the other hand, in 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 reliably removed and the internal flow rate is 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 from the point of view 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, a channel method that mixes the straight method and the serpentine method (hereinafter, mixed channel) Was also proposed). In this mixed channel method, the gas introduced into one end of the separator is branched 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 plurality of flow paths that branch from one flow, flow across the separator in the same direction, and merge at the other end of the separator are referred to as parallel flow paths in the present invention.

  In any of the above-described flow channel systems, when designing the flow channel of the separator, it is necessary to take into account variations in the flow rate in the straight flow channel that occupies the main part of the flow channel, the elimination of water generated by the reaction, and the like. Conventionally, a method has been used in which a flow path is actually constructed in a separator based on a design that takes these into consideration, and a fluid is allowed to flow through the separator.

  This method includes a method in which a separator having a flow path is configured so that it can actually generate electricity as a battery, and a flow state (predicted Reynolds predicted for a battery as it is in a separator having a flow path). There is a method of examining the flow form by flowing a fluid in several regions. The former method can take into account the influence of water generated in the battery and has an advantage of directly capturing the battery performance, but requires a huge amount of money to perform trial and error. The latter method has an advantage that the outline of the flow form can be grasped with a simple apparatus configuration, but the influence of water generated inside cannot be considered at all.

  In addition, for any method, the flow rate, pressure, flow rate, etc. can be considered as indicators for capturing the internal flow pattern and indirectly predicting battery performance, but the flow path configured on the separator is fine. Therefore, it is very difficult to measure these with high accuracy.

  The present invention solves the above-mentioned problems, easily predicts the gas flow situation inside the flow path including the influence of generated water without actually constructing the flow path in the separator, and predicts the flow path of the separator. Design of shape, especially gas distribution state to each flow path and flow rate non-uniformity easily occur, flow path branching section where parallel flow paths branch, flow path merge section where the flow paths merge, or parallel flow path end in the vicinity It is an object to provide a means that can be reflected in the design of.

The above problems can be solved by the present invention described below.
(A) A method for designing a flow path shape of a separator for a fuel cell having a plurality of parallel flow paths through which fuel or oxidant gas flows, and during fuel cell operation of fuel or oxidant gas flowing in the flow path The fluctuation range of the Reynolds number of the gas in the flow path, which fluctuates due to the consumption of water and the generation of water, is determined, and with this fluctuation range as the boundary condition, the mass conservation equation, momentum conservation equation, and energy conservation are defined for the flow channel shape By combining and analyzing the above formula, the deviation of each index indicating the gas flow state in the flow path is obtained for each flow path, and the flow path shape is designed so that this deviation is a certain value or less. A fuel cell separator channel design method.

(B) In the above (A), in the design of the flow path shape of the branch part to the plurality of parallel flow paths, the flow rate of the gas flowing through the parallel flow paths after branching is used as an index indicating the gas flow status in the flow paths. .
(C) In (B) above, as the index, a value obtained by dividing the flux (flow rate per unit cross-sectional area) of each flow path of the parallel flow paths after branching by the average flux is used.

(D) In (C) above, the flow path is designed to have a deviation of ± 0.2 or less.
(E) In the above (A), when designing the flow path shape of the merge / branch section and / or the straight flow path section of a plurality of parallel flow paths, The amount of gas pressure drop is used.

(F) In (A) above, the gas flow rate in the flow path is used as an index indicating the state of gas flow in the flow path.
(G) In the above (A), when designing the flow path shape of the merging / branching section and / or the straight flow path section of the plurality of parallel flow paths, the flow path wall is used as an index indicating the gas flow status in the flow path. Using the flow velocity in the vicinity, the flow path design of the merging / branching portion and / or the straight flow passage portion is performed so as to delete the region where the flow velocity is low from the flow passage shape.

  (H) In (G) above, after grasping and deleting the low-velocity region by analysis, repeating the grasping and deleting of the low-velocity region by analyzing the flow path shape updated by the deletion, the merge / branch part and / or Alternatively, the flow path shape of the straight flow path portion is a shape along the streamline.

(I) A fuel cell separator having a plurality of parallel flow paths designed by the method according to any one of (A) to (H).
(J) A recording medium on which a flow path design program for a fuel cell separator including a calculation formula using the flow path design method for a fuel cell separator according to any one of (A) to (H) is recorded.

  In the present invention, the “parallel flow path” means a flow path that flows in the same direction and branches from the same place and joins at the same place.

  According to the present invention, in the fuel cell separator having the above-described mixed flow path type flow path, which particularly involves branching / merging of a plurality of parallel flow paths (that is, parallel flow path groups), It is possible to suppress the non-uniformity and the blockage of the flow path accompanying the retention of the generated water. As a result, gas can be efficiently supplied to the catalyst layer even under conditions with a large amount of power generation, and deterioration of battery performance over time can be suppressed.

Hereinafter, the present invention will be described more specifically with reference to the accompanying drawings. The meaning of each symbol in the mathematical expressions in the following description is as follows.
A: Current-carrying area (m ² ) of 1 cell,
E: Internal energy (J / Kg),
F: Faraday constant (C / mol),
I: Cell current (A),
K _N2 : nitrogen mole fraction in the feed gas,
K _O2 : oxygen mole fraction in the feed gas,

_MH2 : fuel (hydrogen) supply per cell (mol / sec),
M ′ _H2 : Amount of fuel remaining at the anode outlet per cell (mol / sec),
M _N2 : amount of nitrogen (mol / sec) supplied when the cathode side gas is air.
M _O2 : _Oxidant (oxygen) supply amount per cell (mol / sec),
_M'O2 : residual amount of oxidant at the cathode outlet per cell (mol / sec),
_MH2O : anode inlet, flow rate of water vapor supplied in condition 2 (mol / sec),
M ′ _{H 2 O} : anode outlet, flow rate of water vapor discharged under condition 2 (mol / sec),
M ″ _{H 2 O} : cathode outlet, water vapor flow rate (mol / sec) discharged under condition 1,
M ′ ″ _{H 2 O} : cathode outlet, water vapor flow rate (mol / sec) discharged under condition 2,

_NH2 : molecular weight of hydrogen (Kg / mol),
_NH2O : molecular weight of water (Kg / mol),
N _N2 : Molecular weight of nitrogen (Kg / mol),
N _O2 : Molecular weight of oxygen (Kg / mol),

P: Pressure (Pa)
P _SAT : Saturated vapor pressure at temperature T (Pa)
R: Gas constant (8.314 J / K · mol),
T: temperature (K),

Re _Alin : anode inlet, Reynolds number under condition 1,
Re _A2in : anode inlet, Reynolds number under condition 2,
Re _Alout : Anode outlet, Reynolds number under condition 1,
Re _A2out : Anode outlet, Reynolds number under condition 2,
Re _C1in : cathode inlet, Reynolds number under condition 1,
Re _C2in : cathode inlet, Reynolds number under condition 2,
Re _C1out : cathode exit, Reynolds number under condition 1,
Re _C2out : cathode exit, Reynolds number under condition 2,
Re _Ain : Reynolds number at the anode entrance,
Re _Aout : Reynolds number at the anode exit,
Re _Cin : Reynolds number at the cathode entrance,
Re _Cout : Reynolds number at cathode exit,

V _A1in : anode inlet, volumetric flow rate under condition 1 (m ³ / sec),
V _A2in : anode inlet, volumetric flow rate under condition 2 (m ³ / sec),
V _A1out : anode outlet, volumetric flow rate under condition 1 (m ³ / sec),
V _A2out : anode outlet, volumetric flow rate under condition 2 (m ³ / sec),
V _C1in : cathode inlet, volumetric flow rate under condition 1 (m ³ / sec),
V _C2in : cathode inlet, volumetric flow rate under condition 2 (m ³ / sec),
V _C1out : cathode outlet, volumetric flow rate under condition 1 (m ³ / sec),
V _C2out : cathode outlet, volumetric flow rate under condition 2 (m ³ / sec),

a: Channel cross-sectional area (total cross-sectional area when branching / merging into multiple channels) (m ² ),
i: current density (A / m ² ),
d: representative length (m),
g _i : Gravitational acceleration (m / sec ² ),
k: thermal conductivity (J / m · sec · K),
m _H2 : fuel (hydrogen) consumption per cell (mol / sec),
_mO2 : oxidant (oxygen) consumption per cell (mol / sec),
t: Time (sec)

u _A1in : anode inlet, average flow velocity in the channel under condition 1 (m / sec),
u _A2in : anode inlet, average flow velocity in the channel under condition 2 (m / sec),
u _A1out : anode outlet, average flow velocity in the channel under condition 1 (m / sec),
u _A2out : anode outlet, average flow velocity in the channel under condition 2 (m / sec),
u _C1in : cathode inlet, average flow velocity in the channel under condition 1 (m / sec),
u _C2in : cathode inlet, average flow velocity in the channel under condition 2 (m / sec),
u _C1out : cathode outlet, average flow velocity in the channel under condition 1 (m / sec),
u _C2out : cathode outlet, average flow velocity in the channel under condition 2 (m / sec),

u _i , u _j , u _l : velocity in i, j, l direction (m / sec),
x _i , x _j , x _l : coordinates in the i, j, l direction (m),
δ _ij : δ of Kronecker
η _H2 : fuel (hydrogen) consumption rate (-),
η _O : oxidant (oxygen) consumption rate (−),

ρ: Density (Kg / m ³ ),
ρH ₂ : density of hydrogen at temperature T and pressure P (Kg / m ³ ),
ρN ₂ : density of nitrogen at temperature T and pressure P (Kg / m ³ ),
ρO ₂ : density of oxygen at temperature T and pressure P (Kg / m ³ ),
ρH ₂ O: density of water vapor at temperature T and pressure P (Kg / m ³ ),
ρ _mA2in : anode inlet, density of mixed gas in condition 2 (Kg / m ³ ),
ρ _mA2out : anode outlet, mixed gas density in condition 2 (Kg / m ³ ),
ρ _mC2in : cathode entrance, density of mixed gas in condition 2 (Kg / m ³ ),
ρ _mC1out : cathode outlet, density of mixed gas in condition 1 (Kg / m ³ ),
ρ _mC2out : cathode outlet, density of mixed gas in condition 2 (Kg / m ³ ),

μ: Viscosity coefficient (Pa · sec),
μH ₂ : Viscosity coefficient of hydrogen at temperature T (Pa · sec),
μN ₂ : Viscosity coefficient of nitrogen at temperature T (Pa · sec),
μO ₂ : Viscosity coefficient of oxygen at temperature T (Pa · sec),
μH ₂ O: Viscosity coefficient of water vapor at temperature T (Pa · sec)

μ _mA2in : Anode inlet, viscosity coefficient of gas mixture in condition 2 (Pa · sec),
μ _mA2out : Anode outlet, viscosity coefficient (Pa · sec) of gas mixture in condition 2
μ _mC2in : Cathode inlet, viscosity coefficient of mixed gas in condition 2 (Pa · sec),
μ _mC1out : Cathode outlet, viscosity coefficient of gas mixture in condition 1 (Pa · sec),
μ _mC2out : Cathode outlet, viscosity coefficient of gas mixture in condition 1 (Pa · sec),
τij: Shear stress (Pa).

  In the flow path design method according to the present invention described in the above (A), in order to grasp the flow state of the gas flowing in the plurality of parallel flow paths provided in the fuel cell separator, both are well known,

-Mass conservation formula for internal fluid:

・ Momentum conservation formula:

・ Energy conservation formula:

To analyze. In order to simplify the analysis, it is preferable to set analysis conditions by the following method.
The consumption of fuel (assuming hydrogen) and oxidant (oxygen) in one fuel cell is

It becomes.
Usually, in a fuel cell, both the fuel and the oxidant are supplied more than the amount actually consumed. If the consumption rates at this time are ηH ₂ and ηO ₂ , the amount of fuel and oxidant supplied per cell is

It becomes.
Based on the consumption and supply amount of the fuel and oxidant described above, the gas in the flow path for the cathode side, anode side inlet and outlet of each unit cell (fuel gas on the anode side, oxidant gas on the cathode side) The flow situation regarding the Reynolds number can be estimated as follows.

  First, when pure hydrogen is used as the fuel at the anode-side inlet, the condition of supplying the fuel in a dry state without being humidified is the condition where the Reynolds number is minimum at the anode inlet (referred to as condition 1 at the anode-side inlet). Become. On the other hand, a state in which the fuel humidified to a saturated state in order to improve the water distribution state of the electrolyte membrane in the cell is a condition in which the Reynolds number is maximum at the anode inlet (referred to as condition 2 at the anode side inlet). Become.

  Next, at the anode outlet, even when fuel is consumed, both the moisture supplied from the inlet and the moisture moved from the cathode by back diffusion are transported to the cathode side by electroosmosis, resulting in zero moisture. However, this is a condition where the Reynolds number that can be assumed is minimum (referred to as condition 1 at the outlet on the anode side). On the other hand, the situation in which the fuel is consumed and the water is contained up to the saturation state is the condition where the Reynolds number is the maximum (referred to as the outlet condition 2 on the anode side).

  At the cathode side inlet, when pure oxygen is used as the oxidant, the Reynolds number is minimum (referred to as cathode side inlet condition 1). On the other hand, in the case where air is supplied from the cathode inlet in order to use oxygen contained in the air as an oxidant, the Reynolds number is substantially maximum at the cathode side inlet (referred to as cathode side inlet condition 2). It becomes.

  Next, at the cathode side outlet, oxygen is consumed in a situation where pure oxygen is used, and a situation where the state is saturated by water produced by the reaction is a condition where the Reynolds number is minimum (referred to as cathode side outlet condition 1). ) On the other hand, a condition in which air is supplied as an oxidant and the remaining gas is humidified to a saturated state (referred to as cathode-side outlet condition 2) is a condition in which the Reynolds number is substantially maximum.

In summary,
The Reynolds number at the anode entrance is roughly
Condition 1 (Supply only hydrogen) <Re _Ain <Condition 2 (Supply of hydrogen humidified to saturation)
It becomes the range of
The Reynolds number at the anode outlet is roughly
Condition 1 (only residual hydrogen is discharged) <Re _Aout <Condition 2 (discharge of residual hydrogen saturated with product water)
It becomes.

On the other hand, the Reynolds number at the cathode entrance is roughly
Condition 1 (supplying only oxygen) <Re _Cin <condition 2 (supplying air (oxygen + nitrogen))
It becomes the range of
The Reynolds number at the cathode exit is roughly
Condition 1 (residual oxygen saturated with product water) <Re _Cout <Condition 2 (residual oxygen and nitrogen saturated with product water)
It becomes the range.

The Reynolds number is considered to fall within these ranges in the entire flow path, and if the flow state can be grasped in the fluctuation range of the Reynolds number, the state in the flow path can be easily grasped.
Furthermore, the Reynolds number fluctuation range shown here can be derived as follows.

(i) Anode inlet
(i-1) Condition 1 (Situation where Reynolds number is minimized)
Under this condition, only pure hydrogen is supplied to the anode inlet, and the flow rate is an amount represented by equation (7). At this time, the density of the supply gas is

となる。また、粘性係数は温度の関数、

It becomes. The viscosity coefficient is a function of temperature,

であり、例えば、

For example,

により導出される。流路内での流速は、体積流量、

Is derived by The flow velocity in the flow path is the volume flow rate,

を流路部断面積で割ることにより導出される。

Is divided by the cross-sectional area of the flow path.

これらの値を用いれば、アノード入口における条件１のレイノルズ数は、

Using these values, the Reynolds number of condition 1 at the anode inlet is

より得られる。

More obtained.

(i-2) Condition 2 (Situation where the Reynolds number is maximized)
This condition assumes a situation where the supplied fuel is humidified to a saturated state. Saturated vapor pressure is expressed as a function of temperature, for example

により導出され、これより、アノード入口において燃料と伴に供給される水蒸気の量は、

From this, the amount of water vapor supplied with fuel at the anode inlet is

として得られる。ここで水蒸気の粘性係数は温度の関数であるとし、例えば、

As obtained. Here, the viscosity coefficient of water vapor is a function of temperature.

で導出される。また、密度は状態方程式、

Is derived by The density is the equation of state,

より導出され、供給される気体の粘性係数及び密度は、それぞれ

The viscosity coefficient and density of the gas derived and supplied are respectively

から導出できる。この混合気体の体積流量は、

Can be derived from The volume flow rate of this gas mixture is

で求められ、流路での平均流速は、

The average flow velocity in the flow path is

となり、アノ−ド入口の条件２に対するレイノルズ数は、

And the Reynolds number for condition 2 at the anode entrance is

で与えられる。

Given in.

(ii) Anode outlet
(ii-1) Condition 1 (Situation where Reynolds number is minimized)
Under this condition, the outflowing gas is only residual hydrogen after hydrogen is consumed by the reaction.

で求められ、体積流量は、

And the volume flow rate is

となる。流速は、

It becomes. The flow rate is

となり、粘性係数を式（11）より、密度を式（９）よりそれぞれ導けば、アノード出口の条件１に対するレイノルズ数は、

If the viscosity coefficient is derived from equation (11) and the density is derived from equation (9), the Reynolds number for condition 1 at the anode outlet is

より求められる。

More demanded.

(ii-2) Condition 2 (Situation in which the Reynolds number is maximized)
The gas component under this condition is the same as the anode inlet condition 2 (saturated hydrogen), and only the flow rate is reduced. The flow rate of hydrogen is derived from equation (24), and the amount of water vapor contained here assumes a saturated state.

となり、これらの混合気体の体積流量は、

The volume flow rate of these gas mixtures is

となり、これより導出されるアノード出口流速は、

The anode outlet flow velocity derived from this is

となる。ここでの密度及び粘性係数は気体成分が入口条件２と同じであるので、

It becomes. Since the density and viscosity coefficient here are the same as those in the inlet condition 2 for the gas component,

である。よって、アノード入口、条件２のレイノルズ数は、

It is. Therefore, the Reynolds number of the anode inlet and condition 2 is

で定義される。

Defined by

(iii) Cathode side inlet
(iii-1) Condition 1 (Condition that minimizes the Reynolds number)
This condition is a situation in which pure oxygen is used as the oxidizing agent, and the flow rate is an amount represented by the equation (8). At this time, the density of the supply gas is

となる。また、粘性係数は温度の関数であり、例えば、

It becomes. The viscosity coefficient is a function of temperature, for example,

で導出される。ここでの体積流量は、

Is derived by The volume flow here is

であり、これより流速は、

From this, the flow rate is

で求められる。これらより、カソード入口、条件１のレイノルズ数は、

Is required. From these, the Reynolds number of the cathode inlet and condition 1 is

で求めることができる。

Can be obtained.

(iii-2) Condition 2 (Conditions that maximize the Reynolds number)
This condition is a situation where oxygen in the air is used as the oxidant. For this reason, in addition to oxygen, gases such as nitrogen also flow into the flow path. Assuming that the amount of gas other than nitrogen is very small, the amount of gas supplied in addition to oxygen can be calculated as follows: If the mole fraction of oxygen and nitrogen in the supply air is K _O2 and K _N2 , the amount of nitrogen flowing in is ,

で導出され、これより入口における体積流量は、

From this, the volume flow rate at the inlet is

となる。窒素の粘性係数は、温度の関数であり、例えば、

It becomes. The viscosity coefficient of nitrogen is a function of temperature, for example

から導出される。密度は、状態方程式、

Is derived from Density is the equation of state,

から求める。これらを用いて供給気体の粘性係数及び密度は、混合成分のモル分率から決まるとして、それぞれ

Ask from. Using these, the viscosity coefficient and density of the supply gas are determined from the mole fraction of the mixed components,

となる。流速は式（38）で示される体積流量より次のように導出する。

It becomes. The flow velocity is derived as follows from the volume flow rate represented by equation (38).

これらを用いると、カソード入口、条件２の場合のレイノルズ数は、

When these are used, the Reynolds number for the cathode inlet and condition 2 is

となる。

It becomes.

(iv) Cathode side outlet
(iv-1) Condition 1 (Condition that minimizes the Reynolds number)
This condition is a condition in which pure oxygen is supplied as an oxidizing agent at the inlet, and what is discharged is residual oxygen that has been humidified to a saturated state with water produced by the reaction. The flow rate of oxygen in this case is the remaining amount after consumption due to the reaction,

で求められる。ここに含まれる水蒸気の量は、

Is required. The amount of water vapor contained here is

で得られ、出口気体の体積流量は、

And the volume flow rate of the outlet gas is

となり、これより導出されるアノード出口流速は、

The anode outlet flow velocity derived from this is

で求められる。また、飽和状態の気体の粘性係数と密度は、

Is required. The viscosity coefficient and density of the saturated gas are

で求められ、これに基づけば、カソード出口の条件１でのレイノルズ数は、

Based on this, the Reynolds number under condition 1 at the cathode outlet is

となる。

It becomes.

(iv-2) Condition 2 (Condition that maximizes the Reynolds number)
This condition is that oxygen in the taken-in air is used as an oxidant and is humidified to a saturated state by water produced by the reaction, and the oxygen discharged from the cathode side outlet is contained in the residual oxygen and air. Nitrogen and water vapor. The amount of water vapor contained

とすれば、混合気体の体積流量は、

Then, the volume flow rate of the mixed gas is

となり、流速は、

And the flow rate is

で得られる。また、混合された流体の物性はそのモル分率より導出できるとすれば、次式

It is obtained with. If the physical properties of the mixed fluid can be derived from its molar fraction,

で得られ、カソード出口の条件２でのレイノルズ数は、

And the Reynolds number in condition 2 at the cathode exit is

で求められる。

Is required.

  From the minimum and maximum Reynolds numbers at the inlet and outlet of the anode and cathode determined as described above, the fluctuation range of the Reynolds number in the flow path of the separator used on the anode side or the cathode side is determined. Then, assuming the variation range determined in this way as a boundary condition, it is assumed as a base by the analysis that combines the mass conservation formula, the momentum conservation formula, and the energy conservation formula shown in the above formulas (1) to (4). For each of the plurality of flow paths, an index value (for example, a flow rate, a flow rate, a pressure drop amount, etc.) indicating a gas flow state in the flow path is derived. And the deviation for every flow path is calculated | required and a flow path shape is designed so that this deviation may become below a fixed value. In this way, the flow path shape of the fuel cell separator can be designed only by calculating the flow path shape with less variation in the gas flow situation in the plurality of parallel flow paths.

Specific examples thereof will be exemplified below. However, other modes are possible, and the present invention is not limited to the modes described below.
In the flow path design method according to the present invention described in the above (B), as shown in FIG. 3, the balance of the gas flow rate in each flow path is obtained at the branching portion where the flow path of the fuel cell separator branches into a plurality. In order to search for the channel shape to be maintained, the Reynolds number derived from the target channel shape (FIG. 3), for example,

As described in (A) above, the fluctuation range of the Reynolds number at the entrance or exit of the cathode or anode is obtained, the boundary condition is set for the fluctuation range, and the above formulas (1) to (4) are coupled. Thus, flow rates Q _{1 to} Q _N (or flux: flow rates q _{1 to} q _N per channel cross-sectional area) for each of the channels 1 to _N are derived. Then, according to the flowchart shown in FIG. 4 (for example, the flow shape) until the flow rate or flux balance is sufficiently secured (that is, until the flow rate or flux deviation of each flow channel becomes a certain value or less). The cross-sectional shape of the road, the size of the branching portion, the curvature of the corner portion, etc.) are changed to determine the optimum flow path shape. In this way, a flow path shape with a well-balanced flow rate is designed.

  In the flow path design method according to the present invention described in (C) above, the gas shown in FIG. 5 is used as an index for determining the flow rate balance shown in (B) (condition 1 in the flowchart of FIG. 4). Flux of each flow path after branching in the flow state (ie, flow rate per unit cross-sectional area)

を、分岐した全流路の平均流束、

The average flux of all branched flow paths,

で除した値、即ち、

The value divided by

を用いる。それにより、簡便に流量バランスを把握でき、セパレータ上の流路設計へ反映させることができる。

Is used. Thereby, the flow rate balance can be easily grasped and reflected in the flow path design on the separator.

In the flow path design method according to the present invention described in (D) above, the inlet and outlet on the anode side and cathode side described in (A) above are used using the flow rate index q ′ _i shown in Formula (61). The flow path shape according to the method described in (B) above (flow chart in FIG. 3) so that the deviation between the maximum value and the minimum value of each of the flow paths in the Reynolds number fluctuation range is ± 0.2 or less. Repeat the improvement. Thereby, the flow path shape of the separator excellent in the flow rate balance in the flow path can be designed, and high battery performance can be maintained.

  In the flow path design method according to the present invention described in (E) above, an analysis for grasping the flow inside the flow path is performed with the fluctuation range of the Reynolds number shown in (A) as a boundary condition. By deriving the pressure drop deviation at the confluence / branch section or straight flow path section and using this as an index to select a flow path shape that can minimize the pressure drop volume, a flow with low pressure loss across the entire fuel cell is selected. The road can be designed.

  In the flow path design method according to the present invention described in (F) above, an analysis for grasping the flow inside the flow path is performed with the Reynolds number range shown in (A) as a boundary condition, and Derive the flow velocity distribution (deviation between the maximum and minimum values) at the bifurcation. Using this flow velocity distribution as an index, it is possible to suppress the occurrence of MEA damage and the retention of condensed product water by adopting a flow channel shape that suppresses the generation of a high flow velocity region and a low flow velocity region in the flow channel. Become.

  In the flow path design method according to the present invention described in (G) above, in the method for searching the flow path shape using the flow velocity shown in (F) as an index, in particular, the flow velocity in the vicinity of the wall is used as a design index, and FIG. As shown in a), the low flow velocity region generated in the flow path is deleted from the flow path. Specifically, as shown in the figure, the low flow velocity region occurs because the gas flow from the upstream parallel flow path merges and the direction reverses and branches to the downstream parallel flow path (flow The corner is mainly at the road junction / branch. Further, a low flow velocity region is also generated in the vicinity of the front end of the branched straight flow path on the downstream side, particularly in the vicinity of the end of the flow path closest to the upstream side.

  In the flow channel designed to eliminate such a low flow velocity region according to the present invention, as shown in FIG. 6B, the generation area of the low flow velocity region in the flow channel is remarkably reduced. Therefore, it is easy to eliminate the generated water staying in such a region, and high battery performance can be realized.

  In the flow path design method according to the present invention described in (H) above, the generation of a low flow velocity area that causes retention of product water by deleting the low speed area obtained by the analysis from the flow path shown in (G) above. As shown in the flowchart of FIG. 7, the new method has been improved based on the analysis result [FIG. 8 (a), the black portion in the figure indicates the low speed region]. Re-analyze the flow path (updated flow path) and grasp the occurrence of the low flow velocity region [Fig. 8 (b)]. The flow path is improved again (removal of the low flow velocity region) based on the newly grasped flow characteristics, and the analysis is performed in the same manner [FIG. 8 (c)]. As described above, by repeatedly grasping the low flow velocity generation region and improving the flow path, it is possible to minimize the existence of the low flow velocity region that causes the generation of accumulated water, and it is possible to realize higher power generation performance. .

  The present invention also includes a separator for a fuel cell having a plurality of parallel flow paths designed by using the above flow path design method, particularly for a polymer electrolyte fuel cell. The parallel flow path is preferably a mixed flow path system in which a straight system and a serpentine system are mixed.

  The present invention also includes a recording medium on which a flow path design program for a fuel cell separator including a calculation formula necessary for the design in the flow path design method for a fuel cell separator described above is recorded.

  The material of the fuel cell separator is generally a metal or a carbon material. 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. Any processing method can be used to form the flow path designed according to the present invention.

  In the merging / branching part of the channel, which is the part of the channel where the gas flows from the plurality of parallel flow channels, the flow direction is reversed, and the gas flows through the reverse parallel flow channel, For example, as shown in FIGS. 6 (a) and 6 (b), the flow path in the downstream portion (branch section) where the flow path branches from the flow path width of the upstream section (merging section) where the flow paths merge. The width may be increased. As a result, the gas flow is once collected at the confluence portion with a small cross-sectional area on the upstream side, and the cross-sectional area is enlarged before reaching the branch portion, and the influence of the drift generated at the confluence portion affects the branch portion. Can be avoided.

  It has been conventionally known that a projection having a gas flow rectifying action is provided at a junction / branch portion of a flow path. It is preferable that the protrusion is installed at a location where the main flow of the gas flow at the flow path branching portion whose flow path width is enlarged as described above passes. The number of the protrusions may be one, or the protrusions may be arranged in a single row or a plurality of rows. In the case of a plurality of rows, a staggered arrangement is preferable.

[Example 1]
For the solid polymer membrane, a 50 μm thick membrane made of perfluorocarbon sulfonic acid (Dupont, Nafion) is used, and 300 μm carbon paper is used for the diffusion layer (electrode). A cell was built. The electrode area of the single cell used in the example is 70 mm × 100 mm, and the various flow paths shown in FIGS. 9A to 9H are formed at the branching / merging portion of the flow path indicated by a in FIG. With respect to the separator to which is applied, the flow path design method of the present invention was evaluated. In any cell, the flow path shape of the separator was the same on the anode side and the cathode side. Circles having a diameter of 0.8 mm seen in FIGS. 9 (g) and (h) indicate rectifying hemispherical protrusions provided in a portion where the flow at the branching portion of the branching / merging portion is large.

  The flow path of the separator used for evaluation has been studied in advance by flow analysis based on the present invention. The analysis conditions are: pure hydrogen gas as the fuel gas on the anode side, air as the oxidant gas on the cathode side, the internal fluid temperature is 78 ° C., and the anode side is humidified to saturation at the cell inlet, and the battery The internal pressure was 1 atm.

  The Reynolds number in the straight channel assumed under these conditions is about 50 to 500, and a flow analysis was performed assuming a laminar flow condition within this Reynolds number range (reynolds number conditions used in the analysis are shown). 1). The results are shown in FIG. Here, the flow rate deviation of each flow path after merging and branching from the straight flow path at the flow path bending portion is shown. According to this, the flow rate deviation of each flow path tends to be suppressed in the order of flow paths 1 → 2 → 4 → 5 → 3 → 6 → 7 → 8.

In the evaluation of actual power generation under the same conditions (99.999% hydrogen gas is used as the fuel gas), the same type of fuel gas (hydrogen) and oxidant gas (air) as above are used, and the flow rate is 3.5 respectively. The constant values were × 10 ⁻⁴ mol / s and 10.0 × 10 ⁻⁴ mol / s. 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. 11 shows changes in cell voltage when the current density is changed. According to this, in the flow path evaluated by the present invention and the flow deviation at the merging / branching part is suppressed by changing the flow path shape, the flow deviation at the flow branching part is unlikely to occur. Even in the high current region where the consumption of the agent increases and the influence of the flow rate deviation appears greatly, the performance is not deteriorated and a high battery voltage is maintained. That is, the analysis result according to the present invention shown in FIG. 10 and the result shown in FIG. 11 tested under actual power generation conditions correspond well, and it can be seen that the flow path design method according to the present invention is effective. .

[Example 2]
Using the same solid polymer membrane and diffusion layer as in Example 1, evaluation of battery performance over time was performed. The separator channel shapes used in the evaluation are shown in FIGS. 12 (a) to (c) and FIGS. 13 (a) to (c).

  The flow path shape used for the evaluation here is the flow according to the present invention under the same conditions as in Example 1 (Reynolds number conditions shown in Table 1) for the flow paths shown in FIGS. 12 (a) to 12 (c). Evaluation by analysis was performed. In the analysis, the analysis was performed again on the channel shapes of FIGS. 13 (a) to (c) obtained by deleting the region where the vicinity of the wall surface has a low flow velocity. Low flow velocity region generated in the analysis of the flow path shapes in Fig. 12 (a) to (c) and Fig. 13 (a) to (c) (region where the flow velocity at a position of 0.1 mm from the wall is 0.25 m / s or less) Are shown in FIGS. 14 (a) to (c) and FIGS. 15 (a) to (c), respectively.

  In the analysis in the flow path shown in FIGS. 12 (a) to (c) that do not delete the low flow velocity region of the branching / merging portion according to the present invention, as shown in FIGS. 14 (a) to (c), A large low flow velocity region is generated at the corner of the merging / branching portion of the flow path and at the end of the flow path peak. On the other hand, in the flow path analysis shown in FIGS. 13 (a) to 13 (c) in which the flow path shape is changed so as to delete the low flow velocity region based on the evaluation method according to the present invention, FIG. ) To (c), the generation of the low flow velocity region seen in FIGS. 14 (a) to (c) is greatly suppressed.

In each of the flow paths 1 to 6 shown in FIGS. 12 (a) to 12 (c) and FIGS. 13 (a) to 13 (c), evaluation was performed in actual power generation under the same conditions as in Example 1. The same type of fuel and oxidant as in Example 1 were used, and the flow rates were constant values of 3.5 × 10 ⁻⁴ mol / s and 10.0 × 10 ⁻⁴ mol / s, respectively. 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. 16 shows changes in cell voltage when the current density is changed. From this figure, in the flow paths 4 to 6 in which the low flow velocity region is deleted according to the present invention, compared with the flow paths 1 to 3 that were not deleted under the high current density condition in which the amount of water generated by the reaction is large, It can be seen that the battery performance is slightly improved.

[Example 3]
Using the same separator flow path shape as in Example 2, by adjusting the fuel and oxidant consumption rates in the single cell state, the initial battery power generation state was set to 0.5 A / cm ² , 0.62 V, and the current Voltage drop rate after 50 hours,
Voltage drop rate = 1 Cell voltage after 1-50 hours / initial voltage was evaluated. 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 shown in Table 2. From this table, in the flow paths 1 to 3 in which the low flow velocity regions as shown in FIGS. 14 (a) to (c) exist, battery performance deterioration due to relatively large time passage is observed. This is considered to be due to the fact that water generated by power generation stays in the low flow rate region with time, and the supply of fuel and oxidant to the catalyst layer is likely to be hindered. On the other hand, as shown in FIGS. 15 (a) to 15 (c) in accordance with the present invention, in the separator having the flow path shape in which the generation of the low flow velocity region is reduced, no significant performance deterioration was observed over time.

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 a flow path schematic diagram near a flow path branching part of a separator for a fuel cell having parallel flow paths for explaining a flow path design according to one aspect of the present invention. It is a flowchart for implementing the flow-path design which concerns on 1 aspect of this invention. It is the schematic which shows the flow condition of the flow-path branch part vicinity of the separator for fuel cells which has a parallel flow path explaining the flow-path design which concerns on another aspect of this invention. 6 (a) and 6 (b) are schematic views showing a low flow velocity region generated in the merging / branching portion of the parallel flow path and its deletion. 4 is a flow chart for implementing a channel design that reduces the low flow velocity region of the channel in accordance with an aspect of the present invention. FIGS. 8A to 8C are schematic diagrams illustrating a flow channel design that repeats the reduction of the low flow velocity region of the flow channel according to one embodiment of the present invention. FIG. 3 is a schematic diagram showing a flow path shape of a separator employed in Example 1. It is the schematic which shows another channel shape of the separator employ | adopted in Example 1. FIG. It is a figure which shows the flow volume deviation of each flow path shape evaluated in Example 1. FIG. It is a graph which shows the relationship between the cell voltage at the time of generating electric power with a fuel cell, and current density about each flow path shape evaluated in Example 1. FIG. 12 (a) to 12 (c) are schematic views showing three types of separator channel shapes used for comparison in Example 2. FIG. FIGS. 13 (a) to (c) are schematic views showing separator channel shapes designed to reduce the low flow velocity region by the method according to the present invention in Example 2. FIG. 14 (a) to 14 (c) are schematic diagrams showing the occurrence of a low flow velocity region in the separator used for comparison in Example 2. FIG. FIGS. 15 (a) to 15 (c) are schematic views showing the state of occurrence of a low flow velocity region in the separator designed by the method according to the present invention in Example 2. FIG. In Example 2, it is a graph which shows the relationship between the battery voltage at the time of generating electric power with a fuel cell about each flow path, and current density.

Explanation of symbols

1. 1. polymer electrolyte membrane; 2. catalyst-supported carbon fiber membrane; 3. porous electrode (diffusion layer); Separator, 5. Flow path

Claims (10)

  A method for designing a flow path shape of a fuel cell separator having a plurality of parallel flow paths through which fuel or oxidant gas flows, and consumption of fuel or oxidant gas flowing in the flow path during fuel cell operation The fluctuation range of the Reynolds number of the gas in the flow path that fluctuates due to water generation is determined, and with this fluctuation range as the boundary condition, the mass conservation equation, the momentum conservation equation, and the energy conservation equation are defined for the channel shape. By analyzing coupled, the deviation of the maximum value and the minimum value of each index of the index indicating the gas flow status in the flow path is obtained, and the flow path shape is designed so that this deviation is a certain value or less. A method for designing a flow path of a separator for a fuel cell.   2. The fuel cell according to claim 1, wherein the flow rate of the gas flowing in the parallel flow path after branching is used as an index indicating a gas flow state in the flow path in the design of the flow path shape of the branch portion to the plurality of parallel flow paths. Separator flow path design method.   The flow path design of the separator for a fuel cell according to claim 2, wherein a value obtained by dividing the flux (flow rate per unit cross-sectional area) of the parallel flow paths after branching by the average flux is used as the index. Method.   The flow path design method for a fuel cell separator according to claim 3, wherein the flow path is designed so that the deviation of the flow path is ± 0.2 or less.   The gas pressure drop amount in the flow path is used as an index indicating the gas flow state in the flow path in the design of the flow path shape of the merge / branch section and / or the straight flow path section of the plurality of parallel flow paths. 2. A flow path design method for a separator for a fuel cell according to 1.   The method for designing a flow path of a separator for a fuel cell according to claim 1, wherein a gas flow rate in the flow path is used as an index indicating a gas flow state in the flow path.   In the design of the flow path shape of the confluence / branch section and / or the straight flow path section of a plurality of parallel flow paths, the flow velocity is reduced by using the flow velocity near the flow passage wall as an indicator of the gas flow status in the flow passage. 2. The flow path design method for a fuel cell separator according to claim 1, wherein the flow path design of the merging / branching section and / or the straight flow path section is performed so as to be removed from the flow path shape.   After grasping and deleting the low flow velocity region by analysis, by repeatedly grasping and deleting the low flow velocity region by analysis of the flow channel shape updated by deletion, the flow channel shape of the merge / branch part and / or the straight flow channel part The flow path designing method for a fuel cell separator according to claim 7, wherein the shape of the fuel cell separator is a shape along a streamline.   A fuel cell separator having a plurality of parallel flow paths designed by the method according to claim 1.   A recording medium in which a flow path design program for a fuel cell separator including a calculation formula used in the flow path design method for a fuel cell separator according to any one of claims 1 to 8 is recorded.

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