A method and apparatus for carbon paper fiber bundling simulation for fuel cells

Abstract

The application relates to a carbon paper fiber bundling simulation method and device for fuel cells, which comprises the following steps: inputting initial value parameters for constructing a carbon paper model, constructing an initial carbon paper model; randomly selecting a unit direction vector in the initial carbon paper model and randomly selecting a fiber axis passing point on a reference surface, generating fibers passing through a construction space according to the unit direction vector and the fiber axis passing point; judging whether the generated fibers are bundled; generating the fibers into a bundle fiber structure according to a bundle number setting; calculating the porosity of the current model; judging whether the porosity reaches a given value; and obtaining a completed carbon paper model. Compared with the prior art, the application has the advantages of high practicability and high accuracy.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a method and apparatus for simulating the bundling of carbon paper fibers for fuel cells. Background Technology

[0002] As one of the core key materials of the proton exchange membrane in fuel cells, the gas diffusion layer plays a crucial role in providing a mass transport channel. The most widely used materials for this layer are carbon paper substrates and microporous layers.

[0003] Currently, there are two methods for constructing carbon paper simulation structural models: one is to randomly distribute single carbon fibers in three-dimensional space, and the other is to first randomly distribute single carbon fibers on a horizontal plane and then stack multiple layers. The former method considers the case where the fibers have a longitudinal orientation angle in the thickness direction, while the latter method does not. Furthermore, both methods construct single fibers, which results in a significant error compared to the bundled fibers in actual manufactured carbon paper.

[0004] In the actual production of carbon paper, it is necessary to break up the fiber bundles. During this process, it is difficult to avoid situations where there are two, three, or even more fibers. Since simulation models are generally used for structural design or water transport simulation, these situations are ignored. However, when it is necessary to use simulation structures to study the effects of fiber bundles on physical properties and single-cell performance, the above-mentioned single-fiber model is no longer applicable. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology, which has large errors, and to provide a method and apparatus for simulating the bundling of carbon paper fibers for fuel cells.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A simulation method for carbon paper fiber bundling for fuel cells includes the following steps:

[0008] S1: Input the initial parameters for building the carbon paper model and build the initial carbon paper model;

[0009] S2: Randomly select a unit direction vector in the initial carbon paper model, randomly select a point through which the fiber axis passes on the reference plane, and generate fibers that pass through the construction space based on the unit direction vector and the point through which the fiber axis passes.

[0010] S3: Determine whether the fibers generated in S2 are bundled. If they are bundled, continue to S4; otherwise, skip S4.

[0011] S4: Based on the number of bundles set, move the fibers generated by S2 to form a bundled fiber structure;

[0012] S5: Calculate the porosity of the current model;

[0013] S6: Determine if the porosity has reached the given value. If it has, continue to S7; otherwise, return to S2.

[0014] S7: Obtain the completed carbon paper model.

[0015] Furthermore, the initial parameters include side length, thickness, porosity, carbon fiber diameter, fiber orientation isotropic coefficient, fiber bundle ratio coefficient, and number of fiber bundles.

[0016] Furthermore, when the number of fiber bundles is greater than 1, other fibers in the same bundle are constructed by translating the fibers, and all fibers in the same bundle are located in the same plane.

[0017] Furthermore, the expression for the unit direction vector is:

[0018]

[0019] In the formula, It is a unit direction vector. θ is the azimuth angle, with a value range of [0, 2π], and θ is the polar angle, with a value range of [0, π / 2].

[0020] Furthermore, the reference plane is the normal plane passing through the body center of the three-dimensional structure.

[0021] Furthermore, the carbon paper model can be a three-dimensional image model or a three-dimensional digital model.

[0022] Furthermore, the fiber construction process of the three-dimensional image model is as follows: first, the isosurface function in the MATLAB function library is used to obtain the side surface of the hollow cylinder, and then the isocaps function is used to generate the upper and lower surfaces of the cylinder to obtain the hollow cylinder representing the fiber.

[0023] Furthermore, the three-dimensional digital model is: a three-dimensional array composed of a set of integer points in three-dimensional space assigned fourth coordinate values, wherein the expression for the fourth coordinate value is:

[0024]

[0025] In the formula, M ix,iy,iz For point (i) x i y i z The fourth coordinate value of ).

[0026] Furthermore, the porosity calculation expression for the three-dimensional digital model is as follows:

[0027]

[0028] In the formula, ε1 is the porosity, M is the number of all elements in the three-dimensional digital model, and N is the number of elements labeled as fibers.

[0029] In a second aspect, a carbon paper fiber bundling simulation device for fuel cells includes a memory, a processor, and a program stored in the memory. When the processor executes the program, it implements any of the above-mentioned carbon paper fiber bundling simulation methods for fuel cells.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1) This invention takes into account the possibility of fiber bundles in carbon paper fibers in practical applications, allowing fibers to bundle in two, three or more strands according to a set ratio. It also allows fibers to overlap and cross each other. The direction of the fiber or fiber bundle is determined by the unit direction vector and the points selected on the reference plane. The porosity is used as the termination condition of the model to simulate the growth process of carbon paper fibers, which is more in line with reality and has better practicality.

[0032] 2) This invention can simultaneously obtain a three-dimensional digital model and a three-dimensional image model. The three-dimensional digital model helps to calculate porosity and improves the accuracy of the model, while the three-dimensional image model is easy for researchers to observe and understand intuitively. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the process of the present invention.

[0034] Figure 2 A model diagram showing the condition where two fibers are allowed to bundle together with a 50% probability.

[0035] Figure 3 A model diagram showing the structure where three fibers are allowed to bundle together with a 50% probability.

[0036] Figure 4 This is a model diagram of a single fiber structure. Detailed Implementation

[0037] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0038] This invention relates to a method and apparatus for simulating the bundling of carbon paper fibers for fuel cells, such as... Figure 1 As shown, the method includes the following steps:

[0039] S1: Input the initial parameters for building the carbon paper model and build the initial carbon paper model;

[0040] S2: Randomly select a unit direction vector in the initial carbon paper model, randomly select a point through which the fiber axis passes on the reference plane, and generate fibers that pass through the construction space based on the unit direction vector and the point through which the fiber axis passes.

[0041] S3: Determine whether the fibers generated in S2 are bundled. If they are bundled, continue to S4; otherwise, skip S4.

[0042] S4: Based on the number of bundles set, move the fibers generated by S2 to form a bundled fiber structure;

[0043] S5: Calculate the porosity of the current model;

[0044] S6: Determine if the porosity has reached the given value. If it has, continue to S7; otherwise, return to S2.

[0045] S7: Obtain the completed carbon paper model.

[0046] Before building the model, the following assumptions need to be made about the structural model:

[0047] (1) Each fiber is an absolutely straight cylinder with no infinite length;

[0048] (2) The diameter of each fiber in the model is the same;

[0049] (3) Fibers can cross and overlap;

[0050] Based on the assumptions, the carbon paper model is simplified to a structure composed of randomly distributed, non-overlapping, and non-intersecting infinitely long cylinders stacked together. When this model is represented by a three-dimensional array, any cylindrical fiber can be represented by a set of points, where the distance from all points in the set to the cylinder's axis is less than or equal to the cylinder's radius. The cylinder's axis can be uniquely defined by its direction vector and a point it passes through. The angle between the fiber and the material plane ensures that each fiber is randomly distributed in the reconstructed three-dimensional space of the model, that is, uniquely determining the unit direction vector of the cylinder's axis. The value of any point P0(x0,y0,z0) passing through the axis is generated by a pseudo-random generator. The distance s from any point P(x,y,z) in three-dimensional space to the axis is:

[0051]

[0052] In three-dimensional space, the set of points that satisfy s≤R (fiber radius) forms the fiber solid region, while the set of points that satisfy s>R (fiber radius) forms the pore region. Multiple fibers are randomly generated in three-dimensional space until the set porosity is reached to obtain the carbon paper model.

[0053] The steps to reconstruct the carbon paper model are as follows:

[0054] (1) Given initial values: Before randomly generating the model, it is necessary to obtain the actual carbon paper through X-Ray CT technology to determine the side length L (μm), thickness s (μm), porosity ε, carbon fiber diameter d (μm), fiber orientation isotropic coefficient, bundle fiber ratio coefficient Bu and bundle fiber number BR of the required carbon paper structure model. The ratio of fiber diameter d to the program input diameter (grid unit) is the resolution of the model.

[0055] (2) Select the unit direction vector

[0056]

[0057] Where angle θ is a vector The angle between the projection onto the xy-plane and the x-axis, angle For vectors The angles between the vector and the z-axis, which reflect the relationship between the direction vector and the spatial coordinate axes, are called the polar angle θ and the azimuth angle. It can perform bijective description of the direction in which the fiber is located.

[0058] When azimuth angle When the polar angle θ is randomly selected within the interval [0, 2π] and within the interval [0, π / 2], it can be guaranteed that fibers appearing in any direction can be selected, meaning that the resulting structural model is homogeneous. The anisotropy of the actual fiber structure can be represented by the parameter fiber orientation angle. When different fiber orientation angles are input, the random selection range of the polar angle will change accordingly. The maximum value of the polar angle can be calculated from the fiber orientation angle α.

[0059]

[0060] (3) Select the point through which the cylindrical fiber axis passes or the reference point:

[0061] Once the direction vector is determined, the generated carbon fiber cylinders will be distributed along this vector direction, meaning the fiber will pass through... The normal plane of the vector. To ensure that the fibers have the same probability of distribution in three-dimensional space, a point or reference point P0(x0,y0,z0) passing through the fiber axis is selected on the normal plane, rather than the entire three-dimensional space. To facilitate point selection and ensure that the area of ​​the reference point selection surface is maximized, the normal plane passing through the body center of the three-dimensional structure is selected as the reference plane (hereinafter referred to as the reference plane), and two orthonormal bases are established on the reference plane. and The Cartesian coordinate system is formed, where each line should be parallel to the xy plane, combined with the unit vector. It can be deduced that:

[0062]

[0063] When the construction space is a cube and The maximum value is:

[0064]

[0065] According to the above formula, on the reference plane, The boundary value is half the length of the body diagonal of the cube. The boundary value is half the length of the face diagonal. This is to ensure that all fibers passing through the construction space with a direction vector perpendicular to the reference plane are possible. However, this will cause the fibers generated at the selected point to not pass through the construction volume. However, even if the fibers generated at the selected point do not pass through the construction space, it only means that the current fiber does not affect the sample. Since the generation of each fiber is independent, it will not affect the establishment of the overall model.

[0066] (4) Set the number of fiber bundles and the probability. Determine whether the current fiber needs to be bundled based on the probability. When bundled and the number of fiber bundles BR is greater than 1, after generating a fiber on the initial center line, the center line needs to be moved parallel to the positive x-axis by a distance of (BR-1) times the diameter based on the number of bundles.

[0067] (5) Verify whether the porosity has reached the given value: By traversing each element in the three-dimensional digital model and counting the number of 0s or 1s, the actual porosity ε1 of the current structure can be quickly calculated.

[0068]

[0069] Where N is the number of element 1 (fiber entity) and M is the total number of all elements.

[0070] Determine if ε1 is equal to ε. If not, continue generating the next fiber. If it is greater than or equal to ε, output the 3D visual model and the 3D digital model.

[0071] The resulting model has two representations: First, a three-dimensional visual model. Each fiber is generated using MATLAB functions to create a cylindrical surface. Although not a solid entity, this does not affect the visual model's presentation. The isosurface function is used to obtain the side surface of the hollow cylinder, which is a reconstructed isosurface in three-dimensional space at a distance from the axis equal to the fiber radius. The isocaps function is then used to generate the top and bottom surfaces of the cylinder, resulting in a hollow cylinder representing a specific fiber. This process is repeated until the porosity requirement is met, yielding a three-dimensional visual model of carbon paper composed of a multi-layered fiber system. Second, a three-dimensional digital model. This model can be directly used for simulation calculations of the porosity and fluid transport characteristics of the carbon paper structure. It is a three-dimensional array composed of a set of integer points in three-dimensional space assigned fourth coordinate values. The expression for the fourth coordinate value is:

[0072]

[0073] In the formula, M ix,iy,iz For point (i) x i y i z The fourth coordinate value of ).

[0074] The process described above in this invention can be translated into a programming language, and parameter input, model construction, and output can be implemented using Matlab.

[0075] Example 1

[0076] The carbon paper structure model is configured with the following parameters: xy-plane side length L = 400 μm, thickness s = 200 μm, porosity ε = 80%, carbon fiber diameter d = 8 μm, isotropy coefficient = 0 (indicating complete anisotropy, with completely different fiber distribution patterns in the horizontal and thickness directions), fiber bundle ratio Bu = 50%, and fiber bundle number BR = 2. The ratio of the model's resolution fiber diameter d to the program input diameter (grid unit) is 2. Inputting these parameters into the program yields the following result: Figure 2 The diagram shows a structure that allows two fibers to be bundled with a 50% probability.

[0077] Example 2

[0078] The carbon paper structure model is configured with the following parameters: xy-plane side length L = 400 μm, thickness s = 200 μm, porosity ε = 80%, carbon fiber diameter d = 8 μm, isotropy coefficient = 0 (indicating complete anisotropy, with completely different fiber distribution patterns in the horizontal and thickness directions), fiber bundle ratio Bu = 50%, and fiber bundle number BR = 2. The ratio of the model's resolution fiber diameter d to the program input diameter (grid unit) is 2. Inputting these parameters into the program yields the following result: Figure 3 As shown, the structure allows three fibers to bundle together with a 50% probability.

[0079] Example 3

[0080] The carbon paper structure model is configured with the following parameters: xy-plane side length L = 400 μm, thickness s = 200 μm, porosity ε = 80%, carbon fiber diameter d = 8 μm, isotropy coefficient = 0 (indicating complete anisotropy, with completely different fiber distribution patterns in the horizontal and thickness directions), fiber bundle ratio Bu = 0%, and fiber bundle number BR = 1. The model's resolution is set to a fiber diameter d ratio to the program input diameter (grid unit) of 2. Inputting these parameters into the program yields the following result: Figure 4 The single fiber structure shown.

[0081] This patent enables the construction of a three-dimensional simulation model of carbon paper that allows fiber bundles. All parameters in the embodiments can be adjusted according to actual needs. Based on this method, the influence of fiber bundle probability and number on the carbon paper structure and its physical properties can be studied, and thus the impact on battery performance can be calculated. This model reflects the possibility of fiber bundles in carbon paper during practical applications, resulting in simulation results that more closely match actual performance and are more practical and reliable.

[0082] The electronic device of this invention includes a central processing unit (CPU), which can perform various appropriate actions and processes according to computer program instructions stored in read-only memory (ROM) or loaded from a storage unit into random access memory (RAM). The RAM may also store various programs and data required for device operation. The CPU, ROM, and RAM are interconnected via a bus. Input / output (I / O) interfaces are also connected to the bus.

[0083] The program code used to implement the methods of the present invention can be written in any combination of one or more programming languages. This program code can be provided to a processor or controller of a general-purpose computer, special-purpose computer, or other programmable data processing device, such that when executed by the processor or controller, the program code causes the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code can be executed entirely on the machine, partially on the machine, as a standalone software package partially on the machine and partially on a remote machine, or entirely on a remote machine or server.

[0084] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A simulation method for carbon paper fiber bundling for fuel cells, characterized in that, Includes the following steps: S1: Input the initial parameters for building the carbon paper model and build the initial carbon paper model; The initial parameters include side length, thickness, porosity, carbon fiber diameter, fiber orientation isotropic coefficient, fiber bundle ratio coefficient, and number of fiber bundles. When the number of fiber bundles is greater than 1, other fibers in the same bundle are constructed by translating the fibers, and all fibers in the same bundle are located in the same plane. S2: Randomly select a unit direction vector in the initial carbon paper model, and randomly select a point through which the fiber axis passes on the reference plane. Generate fibers that pass through the construction space based on the unit direction vector and the point through which the fiber axis passes; the reference plane is the normal plane that passes through the body center of the three-dimensional structure. S3: Determine whether the fibers generated in S2 are bundled. If they are bundled, continue to S4; otherwise, skip S4. S4: Based on the number of bundles set, move the fibers generated by S2 to form a bundled fiber structure; S5: Calculate the porosity of the current model; S6: Determine if the porosity has reached the given value. If it has, continue to S7; otherwise, return to S2. S7: Obtain the completed carbon paper model.

2. The method for simulating carbon paper fiber bundling for fuel cells according to claim 1, characterized in that, The expression for the unit direction vector is: In the formula, It is a unit direction vector. The azimuth angle has a range of values ​​of [ ], The polar angle is [ ], and its range is [ ] ].

3. The method for simulating carbon paper fiber bundling for fuel cells according to claim 1, characterized in that, The carbon paper model is a three-dimensional image model or a three-dimensional digital model.

4. The method for simulating carbon paper fiber bundling for fuel cells according to claim 3, characterized in that, The fiber construction process of the three-dimensional image model is as follows: first, the isosurface function in the MATLAB function library is used to obtain the side surface of the hollow cylinder, and then the isocaps function is used to generate the upper and lower surfaces of the cylinder to obtain the hollow cylinder representing the fiber.

5. The method for simulating carbon paper fiber bundling for fuel cells according to claim 3, characterized in that, The three-dimensional digital model is a three-dimensional array composed of a set of integer points in three-dimensional space assigned fourth coordinate values, wherein the expression for the fourth coordinate value is: In the formula, For point The fourth coordinate value.

6. The method for simulating carbon paper fiber bundling for fuel cells according to claim 5, characterized in that, The porosity calculation expression for the three-dimensional digital model is as follows: In the formula, Porosity M The number of all elements in the three-dimensional digital model. N The element is labeled with the number of fibers.

7. A carbon paper fiber bundling simulation device for fuel cells, comprising a memory, a processor, and a program stored in the memory, characterized in that, When the processor executes the program, it implements a simulation method for carbon paper fiber bundling for fuel cells as described in any one of claims 1-6.

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