Flow field for improving peak power density of fuel cell and application

Abstract

The invention provides a parallel flow field with a gas flow distribution function, which can effectively improve the peak power density of a fuel cell, and mainly comprises a flow field gas inlet, a parallel flow field and a flow field gas outlet, a plurality of parallel flow channels are respectively connected with the gas inlet of the parallel flow field, the plurality of parallel flow channels are connected with the gas outlet of the parallel flow field after converging, and the gas flow distribution function is realized. The heights of the air inlet and the air outlet of the flow field and the tops of the plurality of flow channels are equal, the air inlet of the parallel flow field is provided with a width gradual change contraction section and / or a width fold line contraction section, and the widths of the gradual change contraction section and the fold line contraction section are gradually reduced along the flowing direction of the air inlet. According to the parallel flow field structure provided by the invention, the problems of non-uniform fluid distribution and easiness in water logging of a traditional parallel flow field are solved, the mass transfer characteristic of the parallel flow field is improved, and the peak power density of the fuel cell is further improved.

Description

Technical Field

[0001] The present invention belongs to the field of fuel cells, and particularly relates to a method for improving the uneven fluid distribution and easy flooding problems of traditional parallel flow fields by fine-tuning the fuel cell flow field structure, enhancing the mass transfer characteristics of parallel flow fields and the peak power density of fuel cells. Background Art

[0002] In order to achieve "carbon peak and carbon neutrality" at an early date, China has been vigorously promoting the development of fuel cell technology. Proton exchange membrane fuel cells have the advantages of high power generation efficiency, compact structure, and environmental friendliness, so they are widely used in fuel cell vehicles and power generation equipment. A single cell of a proton exchange membrane fuel cell mainly consists of a bipolar plate, a gas diffusion layer, a catalytic layer, and a proton exchange membrane. The flow field engraved on the bipolar plate serves as a channel for gas-liquid transmission, and its structure affects the transmission efficiency of reaction gases, the uniformity of gas distribution, water and heat management performance, etc., and also plays an important role in the peak power density of fuel cells.

[0003] Due to the consumption of reaction gases and the accumulation of generated water, significant changes occur in the water-gas distribution along the flow direction in the flow field of proton exchange membrane fuel cells. The most common flow fields in proton exchange membrane fuel cells are parallel flow fields and serpentine flow fields. The serpentine flow field has good drainage performance, but its flow path is long, pressure drop is large, energy consumption is high, and the gas mainly undergoes electrochemical reactions in the front section of the flow channel, while there is insufficient reaction gas in the rear section of the flow channel, affecting the performance of fuel cells. The parallel flow field is easy to process, has low gas flow resistance, small pressure drop, and low power consumption, but has poor mass transfer ability, uneven distribution of reaction gases, and poor drainage performance. Therefore, it is of great significance to improve the fluid mass transfer characteristics and uneven distribution of reaction gases in traditional parallel flow fields in order to enhance the battery performance of proton exchange membrane fuel cells with parallel flow fields (LIU, H., YANG, W., TAN, J., et al. Numericalanalysis of parallel flow fields improved by micro-distributor in protonexchange membrane fuel cells [J]. Energy Conversion and Management. 2018,176: 99-109.). Summary of the Invention

[0004] In view of this, in order to improve the uneven fluid distribution and easy flooding problems of traditional parallel flow fields, the object of the present invention is to propose a parallel flow field with a gas flow distribution function. The object of the present invention is achieved by the following technical solutions: A flow field for improving the peak power density of a fuel cell, characterized in that it includes a fuel cell flow field plate. Flow field inlets, parallel flow fields, and flow field outlets are respectively provided at both ends of the fuel cell flow field plate. The top heights of the flow field inlets, outlets, and multiple flow channels are equal. The multiple flow channels are respectively connected to the flow channel inlets and outlets at both ends to form a complete flow field structure, which has the function of gas flow distribution. Different flow channel positions are set at the positions of the cross-sections of the multiple flow channels in the fuel cell flow field in the flow direction. The contact surface between the flow field inlet and the multiple flow channels is set as the flow channel inlet, the middle cross-section of the multiple flow channels is set as the flow channel middle, and the contact surface between the multiple flow channels and the flow field outlet is set as the flow channel outlet.

[0005] Further, the flow channel inlet is provided with a width gradually changing contraction section and / or a width broken line contraction section. The widths of both the gradually changing contraction section and the broken line contraction section gradually decrease along the flow direction of the gas at the flow channel inlet. The planar projection of the flow channel inlet is a trapezoid or a right trapezoid, and the width ratio of the start end to the end of the flow channel inlet is 1-8.

[0006] Further, the width of the start end of the flow channel inlet of the fuel cell flow field is 0.8-1.2 mm.

[0007] Further, the width of the end of the flow channel inlet of the fuel cell flow field is 0.1-0.8 mm.

[0008] Further, the ridge width, groove width, and ridge-groove ratio of the multiple flow channels of the fuel cell flow field remain unchanged along the flow direction. The ridge width is equal to the groove width and is 0.8-1.2 mm.

[0009] Further, the heights of the flow field inlet, parallel flow field, and flow field outlet of the fuel cell flow field are equal and are 0.8-1.6 mm.

[0010] On the other hand, an evaluation method for the fluid distribution uniformity of a fuel cell flow field provided by the present invention includes the following steps:

[0011] The first step is to obtain the comprehensive performance data of the flow field, including performance parameters such as the i-V curve, peak power density, oxygen molar concentration distribution at the inlets of multiple flow channels, oxygen molar concentration distribution in the middle of multiple flow channels, and oxygen molar concentration at the outlets of multiple flow channels.

[0012] The second step is to normalize the oxygen molar concentrations at the flow channel positions such as the flow channel inlet, flow channel middle, and flow channel outlet of each flow channel according to formula (1).

[0013] (1)

[0014] The third step is to normalize the oxygen molar concentrations at the flow channel positions such as the flow channel inlet, flow channel middle, and flow channel outlet according to formula (2).

[0015] (2)

[0016] Step 4: Calculate the fluid distribution uniformity of the overall flow field according to formula (3).

[0017] (3)

[0018] Among them, i represents a certain flow channel, j represents the flow field position, and m represents the number of flow field positions evaluated. represents the oxygen molar concentration of a certain flow channel at a certain flow field position. represents the average value of the oxygen molar concentrations of n flow channels at a certain flow field position. represents the oxygen concentration uniformity performance parameter of multiple flow channels at a certain flow field position after normalization. represents the oxygen concentration uniformity performance parameter of a certain position in the flow field after normalization. represents the oxygen concentration uniformity performance index of the overall flow field. The smaller the value of, the better the oxygen concentration uniformity of the flow field.

[0019] In a preferred embodiment of the present invention, through a flow field for improving the peak power density of a fuel cell, the peak power density of the fuel cell can be increased by 11.8%, and the oxygen uniformity index is reduced to 11.2% of that of the traditional parallel flow field, indicating that the flow field for improving the peak power density of the fuel cell in the present invention has a significant effect on improving the performance of the fuel cell.

[0020] On the basis of conforming to the common knowledge in the field, the preferred parameter conditions of the proton exchange membrane fuel cell can be arbitrarily combined to obtain various preferred embodiments of the present invention.

[0021] The membrane electrode and other fuel cell components used in the present invention are all commercially available.

[0022] The positive and progressive effects of the present invention are as follows: By finely adjusting the structure of the air inlet of the parallel flow field, the parallel flow field structure proposed in the present invention improves the problems of uneven fluid distribution and easy flooding in the traditional parallel flow field, enhances the mass transfer characteristics of the parallel flow field, and further enhances the peak power density of the fuel cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic structural diagram of a traditional parallel flow field.

[0024] Figure 2 is a schematic structural diagram of the parallel flow field proposed in Embodiment 1 of the present invention.

[0025] Figure 3 is the oxygen concentration distribution diagram of the parallel flow field proposed in Embodiment 1 of the present invention.

[0026] Figure 4 are the polarization curves and power density curves of the fuel cell with a parallel flow field and a traditional parallel flow field proposed in Embodiment 1 of the present invention.

[0027] Figure 5 is a schematic structural diagram of the parallel flow field proposed in Embodiment 2 of the present invention.

[0028] Figure 6 is the oxygen concentration distribution diagram of the parallel flow field proposed in Embodiment 2 of the present invention.

[0029] Figure 7 are the polarization curves and power density curves of the fuel cell with a parallel flow field and a traditional parallel flow field proposed in Embodiment 2 of the present invention. Detailed implementation manners

[0030] The present invention will be further described below by way of embodiments, but the present invention is not limited to the scope of the described embodiments. For the experimental methods without specific conditions in the following embodiments, they are carried out according to conventional methods and conditions, or selected according to the product specifications. Embodiment 1

[0031] As Figure 2 shown, a flow field for improving the peak power density of a fuel cell includes a flow field air inlet, a parallel flow field, and a flow field air outlet. The heights of the air inlet, air outlet, and each flow channel are the same, which is 0.8 mm. The air inlet part of the flow channel is a width broken line contraction section, and the width of the flow channel air inlet gradually decreases along the fluid flow direction. The width ratio of the start end to the end end of the flow channel air inlet is 8. The width of the start end of the flow channel air inlet is 0.8 mm, and the width of the end end of the flow channel air inlet is 0.1 mm. Moreover, the ridge width, groove width, and ridge-groove ratio of multiple flow channels of the fuel cell flow field remain unchanged along the flow direction, and the ridge width is equal to the groove width, which is 0.9 mm.

[0032] Through the conventional fuel cell assembly method, the traditional parallel flow field is used for the anode in this embodiment, and the parallel flow field proposed in Embodiment 1 of the present invention is used for the cathode. The conditions of the embodiment are a battery pressure of 100 kPa, a battery temperature of 70 °C, 100% humidification of the anode and cathode, an anode stoichiometric ratio of 1.5, and a cathode stoichiometric ratio of 2.5.

[0033] Obtain the comprehensive performance data of the fuel cell, including performance parameters such as the i-V curve, peak power density, oxygen molar concentration distribution at the inlets of multiple flow channels, oxygen molar concentration distribution in the middle of multiple flow channels, and oxygen molar concentration distribution at the outlets of multiple flow channels.

[0034] As described in claim 7, obtain Figure 3 the oxygen concentration distribution diagram of the parallel flow field proposed in Embodiment 1 of the present invention shown inFigure 4 The polarization curves and power density curves of the fuel cell with a parallel flow field proposed in Embodiment 1 of the present invention and a traditional parallel flow field fuel cell are shown.

[0035] The inlet of the flow channel is provided with a gradually varying width contraction section and / or a stepped width contraction section, which can keep a certain gas flow velocity in the middle section of the flow channel, thereby improving the mass transfer characteristics of the traditional parallel flow channel, reducing the possibility of flooding, and further increasing the peak power density of the fuel cell. In addition, the gradually varying width contraction section or the stepped width contraction section has less stress concentration and can better maintain the mechanical strength of the bipolar plate. Embodiment 2

[0036] As Figure 5 shown, a flow field for increasing the peak power density of a fuel cell includes a flow field inlet, a parallel flow field, and a flow field outlet. The heights of the inlet, the outlet, and each flow channel are the same, which is 1.2 mm. The inlet part of the flow channel is a gradually varying width contraction section, and the width of the flow channel inlet gradually decreases along the fluid flow direction. The width ratio of the start end to the end end of the flow channel inlet is 2. The width of the start end of the flow channel inlet is 1 mm, and the width of the end end of the flow channel inlet is 0.5 mm. Moreover, the ridge width, the groove width, and the ridge-groove ratio of multiple flow channels of the fuel cell flow field remain unchanged along the flow direction, and the ridge width is equal to the groove width, which is 1 mm.

[0037] By means of the conventional fuel cell assembly method, in this embodiment, the anode uses a traditional parallel flow field, and the cathode uses the parallel flow field proposed in Embodiment 2 of the present invention. The conditions of the embodiment are a battery pressure of 50 kPa, a battery temperature of 80 °C, 100% humidification of both the anode and the cathode, an anode stoichiometric ratio of 1.5, and a cathode stoichiometric ratio of 2.5.

[0038] Obtain the comprehensive performance data of the fuel cell, including performance parameters such as the i-V curve, the peak power density, the oxygen molar concentration distribution at the inlets of multiple flow channels, the oxygen molar concentration distribution in the middle of multiple flow channels, and the oxygen molar concentration distribution at the outlets of multiple flow channels.

[0039] As described in Claim 7, obtain Figure 6 the oxygen concentration distribution diagram of the parallel flow field proposed in Embodiment 2 of the present invention as shown in Figure 7 the polarization curves and power density curves of the fuel cell with the parallel flow field proposed in Embodiment 2 of the present invention and a traditional parallel flow field fuel cell as shown in

Claims

1. A flow field for improving the peak power density of a fuel cell, characterized in that: It comprises a fuel cell flow field plate, wherein two ends of the fuel cell flow field plate are respectively provided with a flow field air inlet, a parallel flow field and a flow field air outlet, the flow field air inlet, the air outlet and the top heights of multiple flow channels are equal, and the multiple flow channels are respectively connected with the flow channel air inlet and the flow channel air outlet at the two ends to form a flow field structure with a gas flow distribution function.

2. The fuel cell flow field according to claim 1, characterized in that The positions of the cross-sections of the flow directions of the multiple flow channels of the fuel cell flow field are set as different flow channel positions, the contact surfaces between the flow field air inlet and the multiple flow channels are set as the flow channel inlet, the middle cross-sections of the multiple flow channels are set as the middle of the flow channels, the contact surfaces between the multiple flow channels and the flow channel air outlets are set as the flow channel outlets, and so on.

3. The fuel cell flow field according to claim 1, characterized in that The flow channel air inlet is provided with a gradually contracting section and / or a folded-line contracting section in width, the widths of the gradually contracting section and the folded-line contracting section gradually decrease along the flow direction of the gas at the flow channel air inlet, the plane projection of the flow field air inlet is a trapezoid or a right-angled trapezoid, and the width ratio of the start end to the end end of the flow channel air inlet is 1 to 8.

4. The fuel cell flow field according to claim 1, characterized in that The width of the start end of the air inlet of the flow channel of the fuel cell flow field is 0.8-1.2 mm.

5. The fuel cell flow field according to claim 1, characterized in that The width of the end of the flow channel air inlet of the fuel cell flow field is 0.1-0.8 mm.

6. The fuel cell flow field according to claim 1, characterized in that The ridge width, groove width and ridge-groove ratio of the multiple flow channels of the fuel cell flow field remain unchanged along the flow direction, and the ridge width is equal to the groove width, which is 0.8-1.2 mm.

7. The fuel cell flow field according to claim 1, characterized in that The heights of the flow field air inlet, the parallel flow field, and the flow field air outlet of the fuel cell flow field are equal, and are 0.8 to 1.6 mm.

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