Fractal flow field structure of cell and proton exchange membrane fuel cell

Abstract

The invention belongs to the field of fuel cell structures, and provides a cell fractal flow field structure and a proton exchange membrane fuel cell, and a flow field is arranged between an inlet and an outlet of the cell fractal flow field structure; the flow dividing units are arranged side by side, and the flow converging units are arranged between the adjacent flow dividing unit groups; each group of flow dividing units comprises a plurality of flow dividing units, the flow dividing units are arranged at intervals, and each flow dividing unit comprises a fractal main body and a flow guide structure used for connecting the fractal main body and the corresponding confluence unit; from the inlet to the outlet, the number of different groups of shunting units is gradually increased, and the area of the fractal main body of each group of shunting units is sequentially reduced, thereby shortening the path of confluence of the reaction gas, being beneficial to enhancing the mixing effect of the reaction gas and enhancing the disturbance, and being beneficial to improving the speed of the reaction gas far away from the inlet area.

Description

Technical Field

[0001] The invention belongs to the field of fuel cell structures, and in particular relates to a battery fractal flow field structure and a proton exchange membrane fuel cell. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Proton exchange membrane fuel cell (PEMFC) is a highly efficient energy conversion device that can directly convert chemical energy into electrical energy. It has the advantages of high power density, high power generation efficiency, low operating temperature, fast startup, clean and environmentally friendly, etc. It is widely used in transportation, portable power supply and combined heat and power generation, and is of great significance to solving energy shortages and environmental pollution. Optimizing the PEMFC flow field structure can improve the heat and mass transfer capacity of the reaction gas and liquid water, thereby improving battery performance and reducing costs.

[0004] Conventional flow field arrangements include parallel flow field, serpentine flow field, point flow field and interdigital flow field. In the parallel flow field, the distance between the inlet main channel and the outlet main channel is relatively far, and due to the different distances between each sub-channel and the inlet, there will be uneven distribution of the reaction gas, and liquid water may gather in the middle flow field area; in the serpentine flow field, the reaction gas undergoes multiple turns from the inlet to the outlet. In a larger flow field, there will be a very serious pressure drop problem, and only one passage will cause liquid water blockage, thereby deteriorating battery performance; in the interdigital flow field, forced convection will occur in the process of the reaction gas flowing from the inlet flow channel to the outlet flow channel. The forced convection process will bring about a serious pressure drop and may cause impact on the diffusion layer, resulting in serious mechanical damage; in the point flow field, the flow channel is divided into many rectangular areas by ribs. Since the reaction gas will preferentially choose the path with the least resistance, there are more paths in this flow field, which is more likely to cause local reaction gas shortage and liquid water accumulation problems. The enhanced disturbance of the reaction gas may also cause secondary flow problems. Summary of the invention

[0005] In order to solve the above problems, the present invention proposes a battery fractal flow field structure and a proton exchange membrane fuel cell. The fractal flow field of the present invention is composed of a plurality of diversion units and confluence units arranged alternately. The number of diversion units increases continuously from the flow field inlet to the outlet, and the volume decreases continuously, which shortens the path of the reaction gas confluence, is beneficial to enhancing the mixing effect of the reaction gas, enhancing the disturbance, and is beneficial to increasing the reaction gas velocity away from the inlet area.

[0006] According to some embodiments, the present invention adopts the following technical solutions:

[0007] A battery fractal flow field structure, comprising an inlet, an outlet, a flow splitting unit and a flow converging unit, wherein the inlet and the outlet are located at different sides of the battery, and a flow field is between the inlet and the outlet;

[0008] The diversion units include multiple groups, each group is arranged side by side, and the confluence unit is arranged between adjacent diversion unit groups;

[0009] Each group of diversion units includes a plurality of diversion units, each of which is arranged at intervals, and each diversion unit includes a fractal body and a guide structure for connecting the fractal body and the corresponding confluence unit;

[0010] From the inlet to the outlet, the number of different groups of diversion units increases gradually, and the area of ​​the fractal body of each group of diversion units decreases successively.

[0011] As an optional implementation, the fractal body is a regular polygonal structure, such as a quadrilateral, a hexagon, an octagon, and the like.

[0012] As an optional implementation, the flow-guiding structure is a hexahedral structure.

[0013] As a further limitation, the length of the side connecting the guide structure and the fractal body is equal to the length of the side of the fractal body.

[0014] As an optional implementation, the areas of the fractal bodies of the respective groups of diversion units vary in proportion to each other, and the proportion is the value of the optimal scaling factor.

[0015] As a further limitation, the value of the optimal scaling factor is calculated according to Murray's law.

[0016] As a further limitation, each group of diversion units is of the same level, and the diversion units of adjacent groups differ by one level. The area of ​​the fractal body of the first-level diversion unit is A 1 , the area of ​​the fractal body of the second-level flow-dividing unit is w×A 1 , the area of ​​the fractal body of the nth level flow splitter is w n-1 ×A 1 .

[0017] As an optional embodiment, the sizes of the combined flow units are the same.

[0018] As an optional implementation, the number of the diversion units and the number of the merging units are determined by calculation based on the size of the battery.

[0019] A proton exchange membrane fuel cell, comprising a cathode component, an anode component and a proton exchange membrane, wherein the anode component comprises a current collector, a flow channel, a diffusion layer and a catalyst layer arranged in sequence, and the cathode component comprises a current collector, a flow channel, a diffusion layer and a catalyst layer arranged in sequence, wherein the cathode component and the anode component are symmetrically arranged with the proton exchange membrane as the center;

[0020] The flow channel of the anode component and the flow channel of the cathode component are both the above-mentioned fractal flow field structures.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention provides a novel fractal flow field structure, which is composed of a plurality of flow diversion units and flow confluence units arranged alternately, shortening the path of reaction gas confluence, facilitating enhanced mixing of reaction gases and disturbance enhancement.

[0023] The fractal flow field structure of the present invention has an increasing number of diversion units and a decreasing volume from the flow field inlet to the outlet, which is beneficial to increasing the velocity of the reaction gas away from the inlet area; the fractal body with a variable cross-section is beneficial to enhancing the lateral disturbance in the flow field; and the application of the extension of Murray's law is also beneficial to reducing flow losses.

[0024] The fractal flow field structure of the present invention can effectively improve the mass transfer efficiency, make the reaction gas evenly distributed and have good water removal performance, and reduce the pressure drop loss as much as possible while increasing the output power of PEMFC.

[0025] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0027] Figure 1 is a structural diagram of a proton exchange membrane fuel cell according to an embodiment of the present invention;

[0028] FIG. 2( a ) is a three-dimensional diagram of a novel fractal flow field structure of a proton exchange membrane fuel cell according to an embodiment of the present invention;

[0029] FIG2( b ) is a top view of a novel fractal flow field structure of a proton exchange membrane fuel cell according to an embodiment of the present invention;

[0030] Figure 3 It is a three-dimensional diagram of the geometric structure of a new fractal flow field diversion unit of a proton exchange membrane fuel cell according to an embodiment of the present invention;

[0031] Figure 4It is a three-dimensional diagram of the geometric structure of the new fractal flow field flow unit of the proton exchange membrane fuel cell according to an embodiment of the present invention;

[0032] Figure 5 is a polarization curve of a proton exchange membrane fuel cell according to an embodiment of the present invention;

[0033] Figure 6 is an output power density curve of a proton exchange membrane fuel cell according to an embodiment of the present invention;

[0034] Figure 7 It is the flow field pressure drop curve of the proton exchange membrane fuel cell of the embodiment of the present invention. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0036] It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0037] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0038] In the absence of conflict, the embodiments in this application and the features in the embodiments may be combined with each other.

[0039] Embodiment 1

[0040] A battery fractal flow field structure, comprising an inlet, an outlet, a flow diversion unit and a flow confluence unit, wherein the inlet and the outlet are respectively located on different sides of the battery. In this embodiment, the inlet and the outlet are arranged opposite to each other, that is, the inlet and the outlet are arranged on opposite sides of the battery;

[0041] Between the inlet and the outlet is the flow field;

[0042] The diversion units include multiple groups, each group is arranged side by side, and the confluence unit is arranged between adjacent diversion unit groups;

[0043] By alternately arranging the splitter unit and the converging unit, sufficient heat and mass transfer can be achieved.

[0044] Each group of diversion units includes a plurality of diversion units, each of which is arranged at intervals, and each diversion unit includes a fractal body and a guide structure for connecting the fractal body and the corresponding confluence unit;

[0045] From the inlet to the outlet, the number of different groups of diversion units increases gradually, and the area of ​​the fractal body of each group of diversion units decreases successively.

[0046] Preferably, the fractal body is a regular polygonal structure, such as a quadrilateral, hexagon, octagon, etc. This shape can simplify the production process and reduce the difficulty of preparing the structure or mold. On the other hand, it is also easy to calculate the area of ​​the fractal body and calculate and design the size of the diversion unit and the confluence unit.

[0047] In some embodiments, the flow guiding structure is a hexahedral structure, and the length of the side connecting the flow guiding structure and the fractal body is equal to the side length of the fractal body. Such a design can also reduce the difficulty of preparation and ensure a smooth process.

[0048] In this embodiment, the areas of the fractal bodies of the diversion units of each group vary in proportion, and the proportion is the value of the optimal scaling factor. The value of the optimal scaling factor is calculated according to Murray's law, with w being the optimal scaling factor.

[0049] The diversion units in the same group are of the same level, and the diversion units in adjacent groups differ by one level. The area of ​​the fractal body of the first-level diversion unit is A. 1 , the area of ​​the fractal body of the second-level flow-dividing unit is w×A 1 , the area of ​​the fractal body of the nth level flow splitter is w n-1 ×A 1 , n is an integer greater than 1.

[0050] In this embodiment, the sizes of the combined flow units are the same. Such a design can simplify the calculation process. Of course, in other embodiments, the sizes of the combined flow units may also be different.

[0051] The number of shunt units and merging units is determined by calculation based on the total size of the battery.

[0052] Embodiment 2

[0053] A fractal flow field structure of a battery is shown in FIG2(a) and FIG2(b). This embodiment is specifically described by taking the application scenario where there are five groups (ie, five levels) of flow diversion units as an example. However, it does not mean that the solution provided by the present invention can only be used in this scenario.

[0054] The flow distribution unit is divided into five levels. This embodiment adopts a regular octagonal fractal body, and A is 118.91mm 2, W and L are 13.5 mm and 13 mm respectively. w is 0.62996, and the calculated dimensions of the flow distribution units at each level are shown in Table 1. The structures of the flow distribution units at each level are shown in Figure 3 shown.

[0055] The m of the confluence unit is 6, the values ​​of e and f are 1 mm and 13 mm respectively, and the geometric structure is as follows Figure 4 shown.

[0056] The structural characteristic dimensions of the fractal body are the side length of the regular polygon (a i ), the length of the diversion structure (b i ) and width (c i ), the area of ​​the first-level fractal body is A 1 .

[0057] This embodiment generalizes Murray's law and proposes a geometric relationship applicable to polygonal flow channels. It is believed that there is an optimal scaling factor (w) between the surface areas of fractal units. The area of ​​the second-level fractal body is w×A 1 , the area of ​​the third-level fractal body is w 2 ×A 1 , the area of ​​the fourth-level fractal body is w 3 ×A 1 , the area of ​​the fifth-level fractal body is w 4 ×A 1 .

[0058] The dimensions of each confluence unit remain unchanged, including width (e) and length (f). The number of diversion units (n) can be set according to the size requirements of the battery. i ) and the number of confluence units (m), the distance between the diversion units is W i , the length of the shunt unit is L i The area of ​​the splitter unit (A s ) including the area of ​​the diversion structure (A spoiler ) and the area of ​​the regular polygonal fractal body (A i ), which is calculated as follows:

[0059] A s =A spoiler +A i ;

[0060] A spoiler =2×b i ×c i ;

[0061]

[0062] Here, k is the number of sides of the regular polygon.

[0063] The area of ​​the confluence unit (A c ) is calculated as follows:

[0064] A c =e×f;

[0065] The total area (A) and total length (L) of the flow channel are calculated as follows:

[0066] A=(n 1 +n 2 w+n 3 w 2 +n 4 w 3 +n 5 w 4 )×A 1 +(n 1 +n 2 +n 3 +n 4 +n 5 )×A spoiler ;

[0067] +m×A c +2×e×(f+0.5)

[0068] L = 6 × e + L 1 +L 2 +L 3 +L 4 +L 5 ;

[0069] The geometric parameters of the diversion unit structures at each level are shown in Table 1.

[0070] Table 1 Geometric parameters of octagonal flow distribution unit structure

[0071]

[0072] Embodiment 3

[0073] like Figure 1 As shown, a proton exchange membrane fuel cell includes an anode current collecting plate 1, an anode flow channel 2, an anode diffusion layer 3, an anode catalyst layer 4, a proton exchange membrane 5, a cathode catalyst layer 6, a cathode diffusion layer 7, a cathode flow channel 8 and a cathode current collecting plate 9 which are arranged in sequence from top to bottom.

[0074] The anode flow channel 2 and the cathode flow channel 8 both adopt the fractal flow field structure provided in the first embodiment, the second embodiment or a simple transformation of the first embodiment or the second embodiment.

[0075] The present invention is described in detail below through simulation. The working pressure of the battery is one standard atmospheric pressure, and the working temperature is 343.15K. The anode is fed with humidified hydrogen, and its relative humidity is 100% and the mass flow rate is 6.08×10 -7 kg / s; the cathode is fed with humidified air, the relative humidity is 100%, and the intake air mass flow rate is 2.65×10 -6 kg / s, and the results are obtained through CFD simulation.

[0076] The performance curve of PEMFC is as follows Figure 5 , Figure 6 As shown in the figure, the current density of the proton exchange membrane fuel cell in this embodiment increases as the voltage decreases. The output power density reaches the maximum when the voltage is 0.4V, and the maximum output power density is 0.694W / cm 2 , the corresponding current density is 1.734A / cm 2 At the same time, the overall pressure drop of the new fractal flow field does not change significantly with the increase of current density, such as Figure 7 As shown, they are all maintained at 66.785Pa-70.737Pa, indicating that the new fractal flow field helps the proton exchange membrane fuel cell to obtain a higher output power without causing a large flow resistance.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made by those skilled in the art within the spirit and principle of the present invention without creative labor shall be included in the protection scope of the present invention.

Claims

1. A battery fractal flow field structure, characterized in that: It includes an inlet, an outlet, a flow splitting unit and a flow converging unit, wherein the inlet and the outlet are located at different sides of the battery, and a flow field is between the inlet and the outlet; The diversion units include multiple groups, each group is arranged side by side, and the confluence unit is arranged between adjacent diversion unit groups; Each group of diversion units includes a plurality of diversion units, each of which is arranged at intervals, and each diversion unit includes a fractal body and a guide structure for connecting the fractal body and the corresponding confluence unit; From the inlet to the outlet, the number of different groups of diversion units increases gradually, and the area of ​​the fractal body of each group of diversion units decreases successively.

2. A battery fractal flow field structure as claimed in claim 1, characterized in that: The fractal body is a regular polygon structure.

3. A battery fractal flow field structure as claimed in claim 1, characterized in that: The flow-guiding structure is a hexahedral structure.

4. A battery fractal flow field structure as claimed in claim 3, characterized in that: The length of the side connecting the flow-guiding structure and the fractal body is equal to the length of the side of the fractal body.

5. A battery fractal flow field structure as claimed in claim 1, characterized in that: The areas of the fractal bodies of the diversion units of each group vary in proportion to each other, and the proportion is the value of the optimal scaling factor.

6. A battery fractal flow field structure as claimed in claim 5, characterized in that: The optimal scaling factor is calculated according to Murray's law.

7. A battery fractal flow field structure as claimed in claim 5 or 6, characterized in that: Each group of diversion units is of the same level, and the diversion units of adjacent groups differ by one level. The area of ​​the fractal body of the first-level diversion unit is A1, the area of ​​the fractal body of the second-level diversion unit is w×A1, and the area of ​​the fractal body of the n-th-level diversion unit is w n-1 ×A1.

8. A battery fractal flow field structure as claimed in claim 1, characterized in that: The dimensions of each combined flow unit are the same.

9. A battery fractal flow field structure as claimed in claim 1, 5 or 8, characterized in that: The number of the diversion units and the number of the merging units are determined by calculation according to the size of the battery.

10. A proton exchange membrane fuel cell, comprising a cathode component, an anode component and a proton exchange membrane, wherein the anode component comprises a current collector, a flow channel, a diffusion layer and a catalyst layer arranged in sequence, and the cathode component comprises a current collector, a flow channel, a diffusion layer and a catalyst layer arranged in sequence, wherein: The cathode component and the anode component are symmetrically arranged with the proton exchange membrane as the center; Its characteristic is that the flow channel of the anode component and the flow channel of the cathode component are both fractal flow field structures according to any one of claims 1-9.

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