JP2005135814A - Fuel cell simulator, simulation method, simulation program, and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell simulator for surely obtaining a convergent solution without divergence of numerical operation when carrying out a simulation operation of gas-liquid two-phase flow analysis of reaction gas. <P>SOLUTION: Water drops contained in the reaction gas is handled as spherical bodies, and behavior of the water drops is analyzed in a Lagrangian method. On the gas-liquid two-phase flow analysis of the reaction gas, calculation is simplified and a convergent solution can be surely obtained by focusing on the fact that a flowing state of the reaction gas is a mist flow or a rather large water drop, and carrying out a simulation analysis of the Lagrangian method on the assumption that every water drop is spherical. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel cell simulation technique, and more particularly to an improved technique suitable for gas-liquid two-phase flow analysis of a reaction gas.

A fuel cell is known as a device that directly converts chemical energy of fuel gas into electrical energy. The fuel cell has a structure in which a plurality of single cells each having a pair of electrodes (anode electrode and cathode electrode) disposed therebetween with a polymer electrolyte membrane interposed therebetween, an anode gas channel for guiding fuel gas to the anode electrode, A cathode gas channel for introducing an oxidizing gas to the cathode electrode is provided. Since the gas channel contains water generated by battery reaction, water generated by condensation, water leaked from the polymer electrolyte membrane, etc., the power generation of each cell is not uniform and some variation occurs. In analyzing the power generation distribution of a fuel cell, gas-liquid two-phase flow analysis of the reaction gas (fuel gas, oxidizing gas) flowing through the gas channel occupies an important position. In numerical fluid dynamics such as gas-liquid two-phase flow analysis, analysis is generally performed using a simulation model suitable for simulation analysis. For example, JP-A-6-188020 proposes a simulation model suitable for dynamic analysis of a fuel cell system. As a conventional gas-liquid two-phase flow model for fuel cell power generation distribution analysis, a general gas-liquid two-phase flow analysis model is used, for example, a flow state such as a bubble flow or a slag flow based on a void ratio or the like. The simulation model with extremely strong nonlinearity was adopted considering the frictional force between phases.
JP-A-6-188020

  However, if gas-liquid two-phase flow analysis is performed using such a highly nonlinear simulation model, the number of nonlinear equations handled increases, so the calculation tends to be unstable, and the calculation results diverge and converge. May not be obtained.

  Therefore, the present invention proposes a fuel cell simulator, a simulation method, a simulation program, and a recording medium for reliably obtaining a convergent solution without causing numerical calculations to diverge when performing a simulation calculation of a gas-liquid two-phase flow analysis of a reaction gas. The task is to do.

  In order to solve the above problems, a fuel cell simulator (10) of the present invention is a simulator for analyzing a gas-liquid two-phase flow of a reaction gas flowing through a gas channel of a fuel cell, and drops water contained in the reaction gas. Water drop behavior analysis means (23) for handling as a sphere and analyzing the behavior of water drops in a Lagrangian manner is provided. When performing a gas-liquid two-phase flow analysis of the reaction gas, paying attention to the fact that the flow state of the reaction gas is a mist flow or a slightly larger droplet, the water droplet is handled as a sphere and a Lagrangian simulation analysis is performed. The simulation calculation can be performed more quickly without divergence.

  In the fuel cell simulator of the present invention, when the water droplet behavior analyzing means (23) determines that the position coordinates of the plurality of water droplets coincide (S25; YES), the plurality of water droplets are extinguished and one water droplet is newly added. It is desirable to analyze the behavior of water droplets on the condition that they are generated (S26, S27). By setting such conditions, it is possible to reduce the calculation load of water droplet behavior analysis.

  In the fuel cell simulator of the present invention, when the water droplet behavior analysis means (23) determines that the position coordinate of the water droplet matches the position coordinate of the wall surface of the gas channel (S23; YES), the water droplet causes a complete elastic collision on the wall surface. It is desirable to analyze the behavior of water droplets assuming that it is performed (S24). By setting such conditions, it is possible to reduce the calculation load of water droplet behavior analysis.

  The simulation method of the present invention is a simulation method for gas-liquid two-phase flow analysis of a reaction gas flowing through a gas channel of a fuel cell, and treats the water droplets contained in the reaction gas as a sphere to make the behavior of the water droplets in a Lagrangian manner. Analyzing steps (S21 to S29) are provided. When performing a gas-liquid two-phase flow analysis of the reaction gas, paying attention to the fact that the flow state of the reaction gas is a mist flow or a slightly larger droplet, the water droplet is handled as a sphere and a Lagrangian simulation analysis is performed. The simulation calculation can be performed more quickly without divergence.

  In the simulation method of the present invention, the step (S25) of determining whether or not the position coordinates of a plurality of water droplets match, and if it is determined that the coordinate positions of the plurality of water droplets match (S25; YES), a plurality of It is desirable to provide a step (S26, S27) of eliminating one water droplet and generating one new water droplet. By setting such conditions, it is possible to reduce the calculation load of water droplet behavior analysis.

  In the simulation method of the present invention, the step of determining whether or not the position coordinates of the water droplet match the coordinates of the wall surface of the gas channel (S23), and the position coordinate of the water drop is determined to match the position coordinates of the wall surface of the gas channel. (S23; YES), it is desirable to provide a step (S24) for calculating the behavior of the water droplet on the assumption that the water droplet performs a complete elastic collision on the wall surface. By setting such conditions, it is possible to reduce the calculation load of water droplet behavior analysis.

  The simulation program (34) of the present invention is a computer program for causing a computer system to execute the simulation method of the present invention. According to the simulation program of the present invention, a complicated gas-liquid two-phase flow analysis can be stably executed by a computer system without diverging.

  The recording medium of the present invention is a computer-readable recording medium that records the above-described simulation program of the present invention. As such a recording medium, for example, a semiconductor memory element (ROM, RAM, EEPROM, etc.), a magnetic recording medium (a recording medium capable of magnetically reading data such as a flexible disk, a magnetic card, etc.), an optical recording medium (CD -RAM, CD-ROM, DVD-RAM, DVD-ROM, DVD-R, PD disk, MD disk, MO disk, and other recording media capable of optically reading data) are preferable. The recording format of data on these recording media is not particularly limited.

  According to the present invention, in performing a gas-liquid two-phase flow analysis of the reaction gas, focusing on the fact that the flow state of the reaction gas is a mist flow or a slightly larger droplet, the water droplet is handled as a sphere, and a Lagrangian simulation analysis is performed. By performing the above, it is possible to perform the simulation operation faster without causing the calculation to diverge.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a functional block diagram of a fuel cell simulator according to the present embodiment. As shown in the figure, the fuel cell simulator 10 includes a processor 20 that executes a simulation calculation, a memory 30 that stores various physical models and programs necessary for the simulation calculation, and a display device 40 that displays a simulation result. Configured. The processor 20 reads the simulation program 34 stored in the memory 30, interprets and executes the simulation program 34, thereby performing the gas flow analysis means 21 for executing the gas flow analysis (S 11) and the phase for executing the phase change analysis (S 12). It functions as the change analysis means 22 and the water drop behavior analysis means 23 for executing the water drop behavior analysis (S13). The memory 30 stores a gas flow analysis model 31, a phase change analysis model 32, and a water droplet behavior analysis model 33 necessary for gas-liquid two-phase flow analysis. In gas-liquid two-phase flow analysis, it is difficult to describe all the dynamics with a single model because multiple physical phenomena are interrelated. For these reasons, a simulation model is prepared in the memory 30 for each certain physical phenomenon that governs the gas-liquid two-phase flow.

  The gas flow analysis model 31 is a model for calculating the gas flow by regarding the reaction gas as a gas single phase. In actual battery operation, the reaction gas is consumed as the battery reaction progresses. However, if the reaction gas flow is calculated in consideration of the consumption of the reaction gas, the calculation becomes very complicated. Gas consumption is ignored. The gas flow analysis model 31 is a physical model derived from various physical laws such as Reynolds' transport theorem, equation of motion, and energy conservation law. For example, the velocity distribution, temperature distribution, gas density distribution, It is described so that dynamic characteristics such as vorticity distribution and gas flow direction can be analyzed. The phase change model 32 is a model for calculating the phase change of the reaction gas. In actual battery operation, water produced by battery reaction, water produced by condensation, water leaked from the polymer electrolyte membrane, and the like are contained in the reaction gas. By calculating the phase change, the reaction gas can be handled as a gas-liquid two-phase flow.

  The water droplet behavior analysis model 33 is a model for analyzing the behavior of water droplets contained in the reaction gas. In order to numerically solve a differential equation describing a physical phenomenon represented by the Navier-Stokes equation describing a fluid flow phenomenon on a computer, it is necessary to discretize it spatially and temporally. There are two known approaches to discretize differential equations: an Euler system model for continuum and a Lagrange model for fluid particles. . The former is a technique for tracking how the physical quantities (velocity, density, pressure, temperature, etc.) in each part of the fluid are spatially distributed and how they vary over time. The latter is a technique that temporally tracks the behavior of the individual particles that make up the fluid, and extends the dynamics of the mass system to a continuum. In the present embodiment, focusing on the fact that the flow state of the gas-liquid two-phase flow in the fuel cell is limited to a mist flow or a slightly larger droplet, the flow state such as a bubble flow or a slag flow based on a void ratio as in the conventional case The simulation model with strong non-linearity that takes into account the classification and frictional force between phases is stopped, and all water droplets contained in the gas-liquid two-phase flow are handled as a sphere with a volume corresponding to the mass, and a Lagrangian simulation is performed. Perform analysis.

  In the water drop behavior analysis model 33, when analyzing the behavior of a water drop modeled on a sphere in a Lagrangian manner, each water drop has independent position coordinates (X, Y, Z) in a three-dimensional space and time t. Given as a variable. The volume of each water droplet is not necessarily uniform, and has a volume corresponding to the mass. It is assumed that the mass dynamics, the momentum conservation, and the kinetic energy conservation law are established by applying the kinematics of the mass system to the water droplet behavior analysis. Furthermore, it is assumed that the disappearance / generation of water droplets in the water droplet behavior analysis is caused only by collision between water droplets. That is, it is assumed that the disappearance of the water droplets occurs only by the collision of the water droplets, and the water droplets do not disappear even if they collide with the wall surface such as the gas channel. In addition, the generation of new water droplets occurs only when the water droplets collide with each other. Under such an assumption, when a plurality of water droplets collide, all of the collided water droplets disappear together and one new water droplet is generated. It is assumed that the above three laws are also established in the collision coalescence of water droplets.

  FIG. 4 shows a process of generating new water droplets by the collision coalescence of a plurality of water droplets. With reference to the figure, the case where water droplet n and water droplet m collide and the water droplet k is newly produced | generated is considered. If the velocity (scalar amount) of water droplet n, water droplet m, and water droplet k is Vn, Vm, and Vk, respectively, and mass is Mn, Mm, and Mk, respectively, equation (1) is established by the law of conservation of mass, and the momentum is stored. Equations (2) to (3) are established according to the above law. Also, equation (4) is established by the law of kinetic energy conservation. Θn and θm are the incident angles of the water droplet n and the water droplet m, respectively, based on the velocity Vk. The initial values of the velocities Vn, Vm, and Vk are values corresponding to the momentum of water droplets received from the gas flow.

Mn + Mm = Mk (1)
Mn * Vn * cos (θn) + Mm * Vm * cos (θm) = Mk * Vk (2)
Mn * Vn * sin (θn) = Mm * Vm * sin (θm) (3)
(1/2) Mn * Vn ² + (1/2) Mm * Vm ² = (1/2) Mk * Vk ² (4)

  FIG. 5 shows a collision process between a water droplet and a gas channel. In the water droplet behavior analysis using the water droplet behavior analysis model 33, in order to simplify the calculation, the water droplet and the gas channel are assumed to perform a completely elastic collision in any case, and the law of conservation of momentum is established in the collision process. Assume. When a water droplet collides with a gas channel, it actually causes a phenomenon such as a water droplet adhering to the wall surface of the gas channel or splitting into smaller water droplets, but it is very complicated to analyze such a phenomenon. Since the calculation is required, the above assumption is set. As shown in the figure, when the water droplet n collides with the wall surface of the gas channel 50 at the incident angle θ1, the water droplet n does not cause division, deformation, adhesion, etc., and performs a complete elastic collision while maintaining the shape of the sphere, Rebounds at the reflection angle θ2. The collision determination between the water droplet n and the wall surface of the gas channel 50 is determined as “collision” when the position coordinates of the two coincide. If the incident angle of the water droplet n is θ1, the reflection angle is θ2, the incident velocity is V1, and the reflection velocity is V2, equations (5) to (6) are established according to the law of conservation of momentum.

θ1 = θ2 (5)
V1 = V2 (6)

  FIG. 2 is a flowchart describing a main routine for analyzing a gas-liquid two-phase flow of a reaction gas. This routine is described in the simulation program 34 and is interpreted and executed by the processor 20. The processor 20 performs the gas flow analysis of the reaction gas based on the gas flow analysis model 31, and calculates the gas flow in the gas single phase (S11). Next, after calculating the phase change based on the phase change model 32 (S12), the behavior of the water droplet is analyzed by simulation based on the water droplet behavior model 33 (S13).

  FIG. 3 is a flowchart describing a subroutine for water droplet behavior analysis. When this subroutine is called, first, 1 is assigned to the variable n (S21). The value of the variable n is incremented by 1 every time the loop of S22 to S29 is repeated once (S29). When the value of the variable n is determined, the processor 20 calculates the position coordinates (Xn, Yn, Zn) of the water droplet n (S22). Next, it is determined whether or not the water droplet n collides with the gas channel (S23). The collision determination is based on whether or not the position coordinate of the water droplet n matches the position coordinate of the gas channel. If it is determined that the water droplet n collides with the gas channel (S23; YES), the velocity and reflection angle after the complete elastic collision of the water droplet n are calculated based on the above-described equations (5) to (6). (S24). When the water droplet n does not collide with the gas channel (S23; NO), or when the calculation of the complete elastic collision is completed (S24), it is determined whether or not the water droplet n collides with another water droplet (S25). ). The determination of collision between water droplets is based on whether or not there is a water droplet having the same position coordinate. If the water droplet n does not collide with other water droplets (S25; NO), it is checked whether or not the calculation for all the water droplets has been completed (S28), and if the calculation has not been completed for all the water droplets. (S28; NO), the value of the variable n is incremented by 1 (S29), and the process returns to S22. On the other hand, if the water droplet n collides with other water droplets (S25; YES), the collision coalescence is calculated (S26). Here, assuming that the water droplet n collides with the water droplet m (another water droplet), the above-described equations (1) to (4) are calculated. Next, water droplets k and water droplets m are erased and water droplets k are newly generated (S27). When the above calculation steps are performed for all the water droplets (S28; YES), this subroutine ends.

  As described above, according to this embodiment, when performing a gas-liquid two-phase flow analysis of the reaction gas, focusing on the fact that the flow state of the reaction gas is a mist flow or a slightly larger droplet, all the water droplets are handled as a sphere. By conducting Lagrangian simulation analysis, it is possible to apply the kinematics of the mass system. Even if such an analysis method is adopted, it has been confirmed from the simulation results of the present inventors that the calculation accuracy is comparable to that of the conventional model. This analysis method does not diverge the calculation compared to the conventional model with strong nonlinearity, and it is possible to reduce the calculation load and perform the gas-liquid two-phase flow analysis more accurately in a shorter time. .

It is a functional block diagram of the fuel cell simulator of this embodiment. It is a flowchart which shows the main routine of a gas-liquid two-phase flow analysis. It is a flowchart which shows the subroutine of a water droplet behavior analysis. It is explanatory drawing which shows the collision coalescence of a water droplet. It is explanatory drawing which shows the perfect elastic collision of a water droplet.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell simulator 20 ... Processor 21 ... Gas flow analysis means 22 ... Phase change analysis means 23 ... Water drop behavior analysis means 30 ... Memory 31 ... Gas flow analysis model 32 ... Phase change analysis model 33 ... Water drop behavior analysis model 34 ... Simulation Program 40 ... Display device 50 ... Gas channel

Claims (8)

A fuel cell simulator for gas-liquid two-phase flow analysis of a reaction gas flowing through a gas channel of a fuel cell,
A fuel cell simulator comprising water droplet behavior analysis means for treating water droplets contained in the reaction gas as a sphere and analyzing the behavior of the water droplets in a Lagrangian manner. The fuel cell simulator according to claim 1,
When the water droplet behavior analysis means determines that the position coordinates of a plurality of water droplets coincide with each other, the water droplet behavior is analyzed on the condition that the plurality of water droplets are extinguished and one water droplet is newly generated. Fuel cell simulator. A fuel cell simulator according to claim 1 or 2, wherein
When the water droplet behavior analysis means determines that the position coordinates of the water droplet coincide with the coordinates of the wall surface of the gas channel, the water droplet behavior is analyzed on the assumption that the water droplet performs a complete elastic collision on the wall surface. A fuel cell simulator. A simulation method for gas-liquid two-phase flow analysis of a reaction gas flowing through a gas channel of a fuel cell,
A simulation method comprising a step of treating a water droplet contained in the reaction gas as a sphere and analyzing a behavior of the water droplet in a Lagrangian manner. The simulation method according to claim 4,
Determining whether or not the position coordinates of the plurality of water droplets match;
When it is determined that the coordinate positions of the plurality of water droplets coincide with each other, the simulation method includes a step of extinguishing the plurality of water droplets and newly generating one water droplet. The simulation method according to claim 4 or 5, wherein
Determining whether the position coordinates of the water droplets coincide with the position coordinates of the wall surface of the gas channel;
When it is determined that the position coordinates of the water droplet coincide with the position coordinates of the wall surface of the gas channel, the water drop comprises a step of calculating the behavior of the water drop on the assumption that the water droplet performs a complete elastic collision on the wall surface, Simulation method.   A simulation program for causing a computer system to execute the simulation method according to any one of claims 4 to 6.   A computer-readable recording medium on which the simulation program according to claim 7 is recorded.

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