PEM fuel cell bipolar plate runner embedded gradient guide block

Abstract

The invention discloses a PEM fuel cell bipolar plate runner embedded gradient guide block, and relates to the field of fuel cells, a fuel cell comprises a polar plate and a diffusion layer located on one side of the polar plate, a runner is arranged on one side, facing the diffusion layer, of the polar plate, and the guide block is arranged at the bottom of the runner. The direction perpendicular to the diffusion layer is the height direction of the flow channel and the guide block, and the height of the guide block is lower than that of the flow channel; the side, facing the reaction gas inflow direction, of the guide block is an inlet side, the inlet side is an arc-shaped face, and the upper edge, facing the diffusion layer, of the inlet side is located behind the bottom edge, connected with the bottom of the flow channel, of the inlet side in the flowing direction of the reaction gas in the flow channel. The effect of guiding reaction gas to be transmitted to the diffusion layer is achieved, and the problem that mass transfer of an electrochemical reaction area is insufficient is solved.

Description

Technical Field

[0001] The invention relates to the technical field of fuel cells, and in particular to a fuel cell polar plate flow channel embedded gradient guide block. Background Art

[0002] Fuel cells are an important innovation in the contemporary energy field. They are devices that convert the chemical energy of fuel and oxidant directly into electrical energy through electrochemical reactions. This power generation technology is not limited by the Carnot cycle effect, so it is highly efficient and emits very few harmful gases. Proton exchange membrane fuel cells are considered one of the most promising power sources due to their high energy density and rapid start-up. The flow field structure of the bipolar plate is crucial to the performance and life of proton exchange membrane fuel cells. Many factors need to be considered in the design of the flow channel, including mass transfer, water blockage, uniformity, etc. The reaction gas in the conventional direct flow channel continuously undergoes electrochemical reactions along the direction of fluid flow, and the concentration of the reaction gas continues to decrease, resulting in a low concentration of the reaction gas on the rear side of the electrochemical reaction zone, which will make the current density distribution before and after the flow field uneven, and easily form local hot spots, thereby accelerating the reduction of the service life of the fuel cell. At the same time, because the reaction gas is transmitted in the porous diffusion layer and the catalyst layer in the form of diffusion, the gas flow velocity is low, and the generated liquid water remains in the gap and cannot be discharged, which reduces the transmission efficiency of the reaction gas. In practical applications, uniformly arranged guide blocks are added to the flow field to cause flow disturbances to achieve the purpose of enhancing mass transfer. However, such a design significantly reduces the concentration of the reaction gas at the rear side of the flow channel, which in turn exacerbates the problem of uneven distribution of the reaction gas in the flow field plate. Therefore, further research on the structural design of the embedded guide blocks in the flow field and the layout relationship design between the guide blocks is very important for improving the uniformity and performance of the proton exchange membrane fuel cell. Summary of the invention

[0003] The technical problem solved by this application is: to overcome the shortcomings of the prior art and provide a PEM fuel cell bipolar plate flow channel embedded gradient guide block, when the reaction gas enters the flow field, the flow channel embedded guide block can play a role in guiding the gas flow to transmit upward, solving the problem of insufficient mass transfer in the electrochemical reaction zone. At the same time, the reaction gas flows in the flow channel due to continuous reaction consumption, resulting in low uniformity of current density, and it is necessary to match the angle of each guide block to meet the demand for high uniformity of current density in the fuel cell flow field.

[0004] The technical solutions provided by this application are as follows:

[0005] A PEM fuel cell bipolar plate flow channel embedded with a gradient guide block comprises a guide block, the fuel cell comprises a polar plate and a diffusion layer located on one side of the polar plate, a flow channel is arranged on the side of the polar plate facing the diffusion layer, the guide block is arranged at the bottom of the flow channel, a direction perpendicular to the diffusion layer is the height direction of the flow channel and the guide block, and the height of the guide block is lower than the height of the flow channel; a side of the guide block facing the inflow direction of the reaction gas is the inlet side, the inlet side is an arcuate surface, along the flow direction of the reaction gas in the flow channel, the upper edge of the inlet side facing the diffusion layer is located behind the bottom edge where the inlet side is connected to the bottom of the flow channel.

[0006] Five trapezoidal guide blocks are arranged in a single flow channel, and the spacing between the guide blocks is kept consistent. The pressure difference formed by the flow of fluid in the two guide blocks can enhance convection. In the flow field plate with parallel flow channels, the convection effect under the ridge between the two flow channels is enhanced. The circulation of the reaction gas between the two flow channels helps to improve the liquid water discharge efficiency of the pores of the catalyst layer above the ridge.

[0007] The height of the trapezoidal guide block occupies between 1 / 2 and 9 / 10 of the overall height of the flow channel, and the rest of the flow channel is empty, ensuring that water generated by the reaction of the catalyst layer can be discharged in time through the empty spaces in the flow channel.

[0008] A plurality of evenly distributed guide blocks are arranged at the bottom of the flow channel.

[0009] The angle between the upper edge of the inlet side facing the diffusion layer and the plane where the bottom edge connected to the bottom of the flow channel is located and the bottom of the flow channel is the airflow inclination angle. Along the flow direction of the reaction gas, the airflow inclination angle of the guide block gradually increases. Along the flow direction of the fluid, the guide block is set to have different airflow inclination angles. When the reaction gas passes through the guide block, the arc surface structure forces the airflow to change from radial flow to oblique flow, and a part of the reaction gas convects along the normal direction, so that the electrochemical reaction zone is enhanced in mass transfer, which greatly reduces the concentration polarization loss in the reaction zone.

[0010] The variation trend of the gradient airflow inclination angle is y=ax 2 +b, 1≤x≤n, where x is the serial number of the guide block, the serial number of the guide block increases gradually along the flow direction of the reaction gas, and x is an integer; an 2 +b=90°, a+b=30°.

[0011] Along the airflow direction, the airflow inclination angle of different trapezoidal guide blocks increases exponentially. The angle design is defined by the parabola formula: y = 2.5x 2 +27.5. Each trapezoidal guide block has a different effect on the normal enhanced mass transfer. The gradient airflow inclination angle structure can increase the normal material transfer of the reaction gas exponentially, ensuring that the electrochemical reaction zone at the rear end of the flow channel will not be reduced in concentration due to the consumption of the reaction gas in the front section of the flow channel, thereby improving the uniformity of the current density distribution in the active area of ​​the flow channel.

[0012] Along the flow direction of the reaction gas, the bottom lengths of the guide blocks in the same flow channel are the same, and the arc surface is tangent to the bottom of the flow channel.

[0013] The side of the guide block facing away from the inflow direction of the reaction gas is the outlet side, and the outlet side and the bottom of the flow channel are rounded.

[0014] The fillet radius is 1 / 2 of the guide block height.

[0015] The airflow inclination angle on the inlet side of the trapezoidal guide block adopts a transition arc design, and the arcs are tangent to the inclined waist and the lower bottom edge of the flow channel respectively, ensuring that each trapezoidal guide block can adapt to the corresponding arc structure, maximizing the reduction of the angle deviation of the reaction airflow at the end of the guide block entering the reaction zone, while reducing turbulent pressure drop losses.

[0016] In summary, this application at least includes the following beneficial technical effects:

[0017] 1. The design of the trapezoidal guide block structure embedded in the flow channel can guide the reaction fluid to flow along the membrane electrode direction. When the reaction gas passes through the trapezoidal guide block, the inclined waist structure on the trapezoidal guide block forces the airflow to change from radial flow to oblique flow. Part of the reactants enter the reaction zone in the form of normal convection transmission to undergo electrochemical reactions, reducing the concentration polarization loss of the fuel cell. At the same time, the higher airflow velocity effectively reduces the occurrence of flooding.

[0018] 2. The pressure difference formed by the flow of fluid between two adjacent guide blocks can promote the circulation and transfer of the reaction gas between the electrochemical reaction zone and the flow channel. At the same time, the sub-ridge convection effect between the two flow channels is enhanced, which helps to reduce the liquid water content in the pores of the catalyst layer and play a role in enhancing mass transfer.

[0019] 3. The design concept of the gradual airflow inclination angle of the trapezoidal guide block can ensure that the concentration of the electrochemical reaction zone at the rear end of the flow channel will not decrease due to the consumption of reaction gas in the front area of ​​the flow channel, thereby improving the uniformity of current density distribution in the active area of ​​the flow channel and helping to increase the service life of the fuel cell.

[0020] 4. The arc design of the airflow inclination angle transition and the rounded corner design on the rear side of the guide block can improve the influence of the internal structure of the flow field on the airflow disturbance, reduce the generation of vortices and reduce the turbulence intensity, which has an important influence on reducing the energy loss caused by pressure drop. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a proton exchange membrane fuel cell structure;

[0022] Figure 2 It is a single flow channel structure of a proton exchange membrane fuel cell;

[0023] Figure 3It is the position relationship diagram of the guide block cross section;

[0024] Figure 4 It is the principle diagram of convection under the parallel flow channel ridge;

[0025] Figure 5 The schematic diagram of the mass transfer enhancement with guide blocks embedded in the flow channel;

[0026] Figure 6 This is a cross-sectional view of a single direct current gradient guide block.

[0027] Description of the accompanying drawings: 1. Plate; 2. Diffusion layer; 3. Guide block;

[0028] 11. Flow channel inlet; 12. Reaction gas flow area; 13. Flow channel outlet; 14. Spine;

[0029] 31. Inlet side; 32. Outlet side; DETAILED DESCRIPTION

[0030] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments disclosed in the present invention will be further described in detail below with reference to the accompanying drawings.

[0031] The embodiment of the present application discloses a PEM fuel cell bipolar plate flow channel embedded gradient guide block, which can be applied to both fuel cell graphite bipolar plates and metal bipolar plates. The fuel cell includes a polar plate 1, a diffusion layer 2 and a membrane electrode 4, the polar plate includes an anode plate and a cathode plate, and the diffusion layer includes an anode diffusion layer and a cathode diffusion layer; the specific fuel cell includes an anode flow field plate 1-1, an anode diffusion layer 2-1, a membrane electrode, a cathode diffusion layer 2-2 and a cathode flow field plate 1-2 arranged in sequence, and the anode flow field plate and the cathode flow field plate are provided with a flow channel on the side facing the membrane electrode, Figure 1 The flow channel is a straight flow channel, including a flow channel inlet 11, a reaction gas flow area 12, and a flow channel outlet 13. The geometric structure of the single straight flow channel is as follows: Figure 2 As shown. The guide block 3 is a convex block arranged in the flow channel, the guide block is connected to the bottom and two side walls of the flow channel, the lower bottom edge of the guide block is connected to the lower bottom edge of the flow channel, and one side of the upper bottom edge of the guide block is adjacent to the diffusion layer. The guide blocks are arranged in sequence along the flow channel inlet until the flow channel outlet. The trapezoidal guide block can guide the reaction fluid to flow normally in a direction perpendicular to the plane where the catalyst layer is located (wherein the catalyst layer is attached to the membrane electrode), and the reaction gas is converted from diffusion transmission to convection transmission in the diffusion layer and the catalyst layer, which can play a role in enhancing mass transfer.

[0032] The cross-sectional height of the single flow channel is set to 1mm, the cross-sectional width is set to 1mm, the portion of the plate 1 between the two flow channels is the ridge 14, and the width of the ridge 14 is set to 1mm. Five trapezoidal guide blocks 3 are arranged in the single flow channel, and the spacing between the guide blocks is consistent. The vertical waist spacing of the guide blocks is 4mm, the spacing between the leftmost trapezoidal guide block and the flow channel inlet is 1.5mm, and the spacing between the rightmost trapezoidal guide block and the flow channel outlet is 1.5mm. The specific geometric position relationship is as follows: Figure 3 In the flow field plate with parallel flow channels, there is a large offset pressure difference between the two adjacent flow channels with trapezoidal guide blocks. Driven by the pressure difference, the reaction gas bypasses the ridge of the flow field plate for offset flow, thereby forcing the reaction gas to circulate between the diffusion layer and the flow channel, which helps to discharge the liquid water in the pores of the catalyst layer above the ridge, effectively preventing the occurrence of flooding. Figure 4 This is the schematic diagram of the convection under the ridge of the flow channel structure.

[0033] The height of the trapezoidal guide block occupies between 1 / 2 and 9 / 10 of the overall height of the flow channel, and the rest of the flow channel is gaps, ensuring that the water generated by the membrane electrode reaction can be discharged in time through the gaps in the flow channel.

[0034] In this embodiment, the length of the lower bottom side of the trapezoidal guide block is 1 mm, the length of the upper bottom side varies with the inclination angle, the height of the trapezoidal guide block is 0.6 mm, the height of the remaining gap in the flow channel is 0.4 mm, and the airflow of the guide block in the flow channel passes through the space to ensure that the water generated by the reaction of the catalyst layer can be discharged in time through the flow channel. The geometric structure of the trapezoidal guide block is as follows: Figure 3 a.

[0035] The side of the guide block facing the flow channel inlet is the inlet side 31, and the side away from the flow channel inlet is the outlet side 32. The inlet side 31 is designed as an inclined waist. The angle formed by the inclined waist and the lower bottom edge of the flow channel is the gas flow inclination angle. Each guide block for the reaction gas from the flow channel inlet to the outlet is sequentially set to a gas flow inclination angle of different angles. Figure 5 It can be seen that when the reaction gas passes through the trapezoidal guide block, the inclined waist structure forces the airflow to change from radial flow to oblique flow. Among them, the normal component reaction airflow strengthens mass transfer in the form of convection transmission, enters the diffusion layer for electrochemical reaction, and reduces the concentration polarization loss of the battery.

[0036] Figure 6 This is a cross-sectional view of a single straight channel gradient guide block. Along the airflow direction, the airflow inclination angles of different trapezoidal guide blocks increase exponentially. The gradient airflow inclination angle design is defined by the parabola formula: y = 2.5x 2+27.5[1≤x≤5, x is an integer, the dependent variable represents the guide block number, the guide block numbers from the inlet to the outlet in the single straight channel are 1, 2, 3, 4, 5, and the guide block airflow inclination angles according to this formula are: 30°, 37.5°, 50°, 67.5°, 90°. The concentration of the reaction gas in the conventional straight channel continues to decrease, resulting in a low concentration of the reaction gas at the rear side of the electrochemical reaction zone, while the gradient airflow inclination angle structure can ensure that the gas concentration in the front and rear electrochemical reaction zones remains consistent, thereby improving the uniformity of the reaction gas distribution in the active area of ​​the flow channel.

[0037] Each guide block has a different effect on the normal enhanced mass transfer. The gradient airflow inclination angle structure can increase the material transfer of the reaction gas exponentially along the normal direction, ensuring that the concentration of the electrochemical reaction zone at the rear end of the flow channel will not decrease due to the consumption of the reaction gas in the front section of the flow channel, thereby improving the uniformity of the current density distribution in the active area of ​​the flow channel.

[0038] The inclination angle of the airflow on the inlet side of the guide block adopts a transition arc design. Based on the initial structure, the arc is tangent to the inclined waist and the lower bottom edge of the flow channel. The tangent points are the upper vertex of the inclined waist and the intersection of the circle with the lower vertex of the inclined waist as the origin and the length of the inclined waist as the radius and the lower bottom edge. The specific tangent point confirmation process is as follows: Figure 3 As shown in b, the transition arc design ensures that each trapezoidal guide block can adapt to the corresponding arc structure, maximizing the reduction of the angle deviation of the reaction gas flow at the end of each guide block entering the reaction zone and reducing the energy caused by pressure drop.

[0039] like Figure 3 As shown in b, the angle formed by the outlet side 32 of the guide block 3 and the lower bottom edge of the flow channel adopts a rounded corner design with a radius of 0.3 mm to reduce the generation of the eddy current zone at the rear side of the guide block.

[0040] The contents not described in detail in this application specification belong to the common knowledge of those skilled in the art.

[0041] The present application is described in detail above in conjunction with specific implementation methods and exemplary examples, but these descriptions cannot be understood as limiting the present application. Those skilled in the art understand that, without departing from the spirit and scope of the present application, a variety of equivalent replacements, modifications or improvements can be made to the technical solution of the present application and its implementation methods, all of which fall within the scope of the present application. The scope of protection of the present application shall be subject to the attached claims.

Claims

1. A PEM fuel cell bipolar plate flow channel embedded with a gradient guide block, characterized in that: The fuel cell comprises a guide block (3), wherein the fuel cell comprises an electrode plate (1) and a diffusion layer (2) located on one side of the electrode plate (1); a flow channel is arranged on the side of the electrode plate (1) facing the diffusion layer (2); the guide block (3) is arranged at the bottom of the flow channel; the direction perpendicular to the diffusion layer (2) is the height direction of the flow channel and the guide block (3); the height of the guide block (3) is lower than the height of the flow channel; the side of the guide block (3) facing the inflow direction of the reaction gas is the inlet side (31); the inlet side (31) is an arc-shaped surface; along the flow direction of the reaction gas in the flow channel, the upper edge of the inlet side (31) facing the diffusion layer (2) is located behind the bottom edge of the inlet side (31) connected to the bottom of the flow channel.

2. A PEM fuel cell bipolar plate flow channel embedded gradient guide block according to claim 1, characterized in that: The height of the guide block (3) occupies between 1 / 2 and 9 / 10 of the height of the flow channel.

3. A PEM fuel cell bipolar plate flow channel embedded gradient guide block according to claim 1, characterized in that: A plurality of evenly distributed guide blocks (3) are arranged at the bottom of the flow channel.

4. A PEM fuel cell bipolar plate flow channel embedded gradient guide block according to claim 1, characterized in that: The angle between the upper edge of the inlet side (31) facing the diffusion layer (2) and the plane where the bottom edge of the inlet side (31) connected to the bottom of the flow channel is located and the bottom of the flow channel is the gas flow inclination angle. Along the flow direction of the reaction gas, the gas flow inclination angle of the guide block (3) gradually increases.

5. A PEM fuel cell bipolar plate flow channel embedded gradient guide block according to claim 4, characterized in that: Along the flow direction of the reaction gas, the gas flow inclination angle of the guide block (3) increases exponentially.

6. A PEM fuel cell bipolar plate flow channel embedded gradient guide block according to claim 4, characterized in that: The variation trend of the gradient airflow inclination angle is y=ax 2 +b, 1≤x≤n, wherein x is the serial number of the guide block (3), the serial number of the guide block (3) gradually increases along the flow direction of the reaction gas, and x is an integer; an 2 +b=90°, a+b=30°.

7. A PEM fuel cell bipolar plate flow channel embedded gradient guide block according to claim 1, characterized in that: Along the flow direction of the reaction gas, the bottom lengths of the guide blocks (3) in the same flow channel are the same, and the arcuate surface is tangent to the bottom of the flow channel.

8. The PEM fuel cell bipolar plate flow channel embedded gradient guide block according to claim 1, characterized in that: The side of the guide block (3) facing away from the inflow direction of the reaction gas is an outlet side (32), and the outlet side (32) and the bottom of the flow channel are rounded.

9. A PEM fuel cell bipolar plate flow channel embedded gradient guide block according to claim 8, characterized in that: The radius of the fillet is 1 / 2 of the height of the guide block.

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