Air duct structure for cathode open type air-cooled fuel cell stack

Abstract

The invention belongs to the technical field of fuel cells, and particularly relates to an air duct structure for a cathode open type air-cooled fuel cell stack. Comprising a fuel cell stack and an axial flow fan, a variable cross-section flow guide air duct is coaxially arranged between the fuel cell stack and the axial flow fan, the variable cross-section flow guide air duct comprises a rectangular stable section, a contraction section and a circular stable section, and one end of the rectangular stable section is connected with the butt joint end of the fuel cell stack; the contraction section is located between the rectangular stabilizing section and the circular stabilizing section, and the diameter of the contraction section is in a gradually-changed contraction shape in the airflow flowing direction; one end of the circular stabilizing section is connected with the butt joint end of the axial flow fan, and a plurality of radial guide vanes are arranged in the circumferential direction of the circular stabilizing section. Through the combined design of the variable cross-section diversion air duct and the central airflow enhancement structure, the airflow of the axial-flow fan is secondarily distributed, the uniform distribution of air in the stack is realized, and the global temperature difference and voltage difference of the stack are reduced, so that the performance of the fuel cell is improved, and the service life of the fuel cell is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell technology, specifically relating to a duct structure for an open-cathode air-cooled fuel cell stack. Background Technology

[0002] Open-cathode air-cooled fuel cell stacks are widely used in portable power supplies, small backup power supplies, and hydrogen-powered drones due to their compact structure, low cost, and the elimination of the need for an additional liquid cooling system. During operation, the cathode reaction requires a continuous supply of air. This air not only provides oxygen for the reaction but also removes the heat generated during stack operation. Therefore, the uniformity of air distribution within the stack directly determines the accuracy of temperature control, current density stability, and voltage output performance. Currently, mainstream open-cathode air-cooled fuel cell stacks generally use axial-flow fans as the air source. Due to the presence of the central fan hub, the airflow characteristics of axial-flow fans are weak in the central area (fan hub region) and strong at the edges (fan blade region), meaning the air velocity in the fan center is significantly lower than in the edge region. This characteristic directly results in sufficient airflow and efficient heat dissipation at the edges of the stack, while airflow is obstructed and heat accumulates in the central region, creating a temperature gradient of low temperature at the edges and high temperature in the center. This uneven temperature distribution within the stack leads to poor voltage consistency among the individual cell units, thus affecting the overall output performance of the stack.

[0003] In practical applications, the fan in an open-cathode air-cooled fuel cell stack typically uses an intake mode. The stack is placed in front of the fan, and air enters the stack first under the fan's suction force, then enters the fan. Since the size of the stack's air outlet often differs from the size of the axial fan's inlet, a dedicated air duct becomes necessary. Its core function is to achieve size matching. The opening size at one end of the duct matches the fan inlet, and the opening size at the other end matches the stack's outlet. The inner wall of the duct is usually a smooth, tapered structure, used solely to connect the fan and the stack and complete the size-matched airflow conduction.

[0004] However, existing dedicated air ducts only focus on size transition functions and are not optimized for the inherent airflow characteristics of axial fans, which are weak at the center and strong at the edges. When airflow passes through the duct, the low-velocity airflow in the central region is not enhanced, and the high-velocity airflow in the edge region is not properly guided, resulting in the airflow entering the fuel cell stack maintaining the original distribution of low velocity at the center and high velocity at the edges. This directly causes insufficient heat dissipation in the central region of the fuel cell stack due to low airflow, resulting in a temperature 15°C to 25°C higher than the edge region, and a voltage 0.05V to 0.1V lower in the central region than in the edge region, seriously affecting the operating efficiency, output stability, and service life of the fuel cell stack. Summary of the Invention

[0005] The purpose of this invention is to provide a duct structure for an open-cathode air-cooled fuel cell stack, in order to solve the problems of poor voltage consistency, uneven current density and temperature distribution caused by uneven air flow in existing open-cathode air-cooled fuel cells. By combining the design of a variable cross-section guide duct and a central airflow enhancement structure, the airflow of the axial fan is secondary distributed to achieve uniform air distribution inside the stack, thereby improving the performance and lifespan of the fuel cell.

[0006] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0007] The purpose of this invention is to provide a duct structure for an open-cathode air-cooled fuel cell stack, comprising a fuel cell stack and an axial flow fan, wherein a variable cross-section guide duct is coaxially arranged between the fuel cell stack and the axial flow fan, the variable cross-section guide duct comprising a rectangular stabilizing section, a contracting section, and a circular stabilizing section, wherein: A rectangular stabilizing section, one end of which is connected to the docking end of the fuel cell stack, forms a stable and uniform airflow; The contraction section, located between the rectangular and circular stable sections, has a diameter that gradually narrows along the airflow direction, and is used to guide the edge airflow toward the central axis. The circular stabilizing section is connected at one end to the docking end of the axial flow fan. Multiple radial guide vanes are provided along the circumference of the circular stabilizing section to form a central airflow enhancement structure. This structure is used to accelerate and guide the airflow from the edge to the central region and integrate the airflow from the edge to form a uniform airflow field with enhanced central airflow and smooth edge airflow.

[0008] Furthermore, the length ratio of the rectangular stable segment, the contracting segment, and the circular stable segment is 1:1 to 4:0.5 to 2.

[0009] Furthermore, 10 to 16 radial guide vanes are provided along the circumference of the circular stable section.

[0010] Furthermore, one end of each radial guide vane is fixed to the inner wall of the circular stabilizing section, while the other end is not fixed and faces the central axis of the circular stabilizing section.

[0011] Furthermore, each radial guide vane has a centripetally curved arc-shaped protrusion structure, wherein the concave surface faces the surrounding airflow, the convex surface faces the central region, the protrusion direction is consistent with the airflow direction, and the radius of curvature of the arc-shaped protrusion is 5mm to 15mm.

[0012] Furthermore, the radial angle between the other end of the radial guide vane and the radial direction of the circular stabilizing section is 30° to 60°.

[0013] Furthermore, the thickness of the radial guide vanes is 1.5 mm to 2.5 mm.

[0014] Furthermore, the variable cross-section air duct is integrally molded using injection molding or 3D printing processes, and is made of plastic.

[0015] Compared with the prior art, the present invention has the following advantages: The air duct structure provided by this invention features a fuel cell stack, an axial fan, and a variable cross-section guide air duct with their central axes aligned, ensuring stable airflow along the central axis. Along the airflow direction, the variable cross-section guide air duct consists of a rectangular stabilizing section, a contracting section, and a circular stabilizing section. The rectangular stabilizing section creates a stable and relatively uniform airflow. The contracting section's diameter gradually narrows along the airflow direction, guiding some airflow from the fan's edge towards the central axis, gradually directing the strong edge airflow to the central region and compensating for insufficient airflow in the central area. The circular stabilizing section has radially distributed guide vanes along its inner circumference, forming a central airflow enhancement structure. This accelerates the airflow from the duct's edge towards the central region and further integrates the airflow from the edge, creating a uniform airflow field with enhanced central airflow and smooth edge airflow. This combined design of the variable cross-section guide air duct and the central airflow enhancement structure corrects the airflow distribution pattern, guiding the strong edge airflow towards the center, enhancing the central airflow, and achieving secondary airflow distribution. Ultimately, this solves the problems of poor voltage consistency, uneven current density, and uneven temperature distribution caused by uneven airflow within the fuel cell stack.

[0016] This invention, based on a central airflow enhancement structure formed by a variable cross-section guide duct and radial guide vanes, offers the following advantages: 1. Optimized airflow distribution and improved power generation efficiency: It effectively enhances the uniformity of airflow velocity at the fuel cell inlet and inside the fuel cell, reducing the velocity difference between the central and edge regions. Improved airflow uniformity leads to a more even temperature distribution within the fuel cell, effectively reducing current density distribution differences and improving overall fuel cell output performance. 2. Balanced fuel cell temperature and extended service life: Enhanced airflow in the central region significantly improves heat dissipation efficiency, reducing the overall temperature difference across the fuel cell from 15℃~25℃ in existing technologies to 5℃~8℃, avoiding high-temperature aging issues in the central region. The fuel cell using this solution can reduce the aging rate of the proton exchange membrane and extend the fuel cell's service life. 3. Stable output voltage and improved power supply performance: The uniformity of temperature and current density eliminates local overpotentials, reducing the fuel cell output voltage fluctuation range from ±0.05V in existing technologies to ±0.01V, and narrowing the voltage difference between the central and edge regions to within 0.02V, significantly improving voltage stability. 4. The structure is simple and easy to implement, with strong compatibility. The fan connection end of the air duct can be adapted to different models of axial flow fans, and the rectangular stabilizing section size of the fuel cell stack docking end can be adjusted according to the size of the fuel cell stack inlet, ensuring good compatibility. The air duct can be processed using injection molding or 3D printing, resulting in low cost and convenient assembly. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the air duct structure of the present invention.

[0018] Figure 2 This is a schematic diagram of the cross-sectional structure of the air duct structure of the present invention.

[0019] Illustration: 1. Fuel cell stack; 2. Variable cross-section air duct; 3. Axial flow fan; 4. Circular stabilizing section; 5. Converging section; 6. Rectangular stabilizing section; 7. Radial guide vanes. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0022] It should be noted that the technical terms used in this invention are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this invention. Certain terms are used in this invention to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component.

[0023] Existing open-cathode air-cooled fuel cell stacks utilize dedicated air ducts that focus solely on size transitions, failing to optimize for the inherent airflow characteristics of axial fans, which are weaker at the center and stronger at the edges. When airflow passes through the duct, the low-velocity airflow in the central region is not enhanced, while the high-velocity airflow at the edges is not properly guided, resulting in the airflow entering the stack maintaining its original distribution of low velocity at the center and high velocity at the edges. This directly leads to insufficient heat dissipation in the central region of the stack due to lower airflow, resulting in a temperature 15°C to 25°C higher than the edge regions. The voltage in the central region is also 0.05V to 0.1V lower than the edge regions, severely impacting the stack's operating efficiency, output stability, and lifespan. Furthermore, in some scenarios, simplified design omits dedicated air ducts, directly fixing the fan and stack to a bracket. However, this leads to airflow diffusion and the intrusion of external impurities, further exacerbating uneven airflow distribution and stack contamination problems. Such solutions are inferior in performance to the aforementioned dedicated air duct solutions.

[0024] Based on this, the present invention employs a combined design of a variable cross-section guiding air duct and a central airflow enhancement structure. By modifying the airflow distribution pattern through structural design, it guides strong airflow from the edges towards the center, enhancing the central airflow and achieving secondary airflow distribution. This ultimately solves the problems of poor voltage consistency, uneven current density, and uneven temperature distribution caused by uneven airflow within the fuel cell stack. Furthermore, it does not require altering the overall shape of the fuel cell stack or introducing additional impeller power components, thus avoiding increased system complexity. Specifically:

[0025] A duct structure for an open-type air-cooled fuel cell stack, such as Figure 1 As shown, the system includes a fuel cell stack 1 and an axial fan 3. A variable cross-section guide duct 2 is coaxially arranged between the fuel cell stack 1 and the axial fan 3. The variable cross-section guide duct includes a rectangular stabilizing section 6, a contracting section 5, and a circular stabilizing section 4. Specifically: the rectangular stabilizing section 6 is connected at one end to the docking end of the fuel cell stack 1 to form a stable and uniform airflow; the contracting section 5 is located between the rectangular stabilizing section 6 and the circular stabilizing section 4, and the diameter of the contracting section 5 gradually contracts along the airflow direction to guide the edge airflow towards the central axis; the circular stabilizing section 4 is connected at one end to the docking end of the axial fan 3, and multiple radial guide blades 7 are arranged along the circumference of the circular stabilizing section 4 to form a central airflow enhancement structure, which is used to accelerate and guide the edge airflow to the central region and integrate the airflow guided from the edge to form a uniform airflow field with enhanced central airflow and smooth edge airflow.

[0026] In this invention, the variable cross-section airflow duct 2 is a hollow cavity with openings at both ends. It can be integrally molded using injection molding or 3D printing processes. Made of engineering plastic, it is low-cost and easy to assemble. One end of the variable cross-section airflow duct 2 is sealed to the air inlet (i.e., the docking end) of the axial flow fan 3, and the other end is sealed to the air outlet (i.e., the docking end) of the fuel cell stack 1. The rectangular stabilizing section 6 has the same cross-sectional dimensions as the docking end of the fuel cell stack 1, and its inner wall is planar. The circular stabilizing section 4 has the same cross-sectional dimensions as the docking end of the axial flow fan 3. The two ends of the contraction section 5 correspond to the connecting ends of the rectangular stabilizing section 6 and the circular stabilizing section 4, respectively, and the connecting ends have the same cross-sectional dimensions. The central axes of the fuel cell stack 1, the axial flow fan 3, and the variable cross-section airflow duct 2 coincide, ensuring stable airflow along the central axis. Specifically, along the airflow direction, the variable cross-section airflow duct 2 consists of the rectangular stabilizing section 6, the contraction section 5, and the circular stabilizing section 4 in sequence. The inner wall of the rectangular stabilizing section 6 is planar, and its cross-sectional dimensions are consistent with the fuel cell stack's air outlet. Under the influence of the airflow in the contraction section 5, a stable and relatively uniform airflow is formed at various locations in this region. The diameter of the contraction section 5 gradually contracts along the direction of airflow, that is, the inner wall of the contraction section 5 gradually contracts from the docking end of the fuel cell stack 1 to the docking end of the axial fan 3. This can guide some of the airflow in the edge area of ​​the axial fan 3 towards the central axis, gradually guiding the strong airflow at the edge to the middle area, and initially compensating for the insufficient airflow in the middle area. The inner wall of the circular stabilization section 4 is uniformly equipped with radial guide vanes in the circumferential direction, forming a central airflow enhancement structure design. This can accelerate and guide the airflow at the edge of the duct to the middle area, and further integrate the airflow guided from the edge, forming a uniform airflow field with enhanced central airflow and smooth edge airflow. This is achieved through the combined design of the variable cross-section guide duct and the central airflow enhancement structure.

[0027] In this invention, a central airflow enhancement structure based on a variable cross-section guide duct and radial guide vanes 7 achieves the following: 1. Optimized airflow distribution and improved power generation efficiency: It effectively improves the uniformity of airflow velocity at the fuel cell inlet and inside the fuel cell, reducing the velocity difference between the central and edge regions. Improved airflow uniformity leads to a more uniform temperature distribution inside the fuel cell, effectively reducing current density distribution differences and improving the overall output performance of the fuel cell. 2. Balanced fuel cell temperature and extended service life: Enhanced airflow in the central region improves heat dissipation efficiency, reducing the overall temperature difference of the fuel cell from 15℃~25℃ in the prior art to 5℃~8℃, avoiding high-temperature aging problems in the central region. The fuel cell using this solution can reduce the aging rate of the proton exchange membrane and extend the service life of the fuel cell. 3. The uniformity of temperature and current density eliminates local overpotentials, reducing the output voltage fluctuation range of the fuel cell from ±0.05V in the prior art to ±0.01V, and reducing the voltage difference between the central and edge regions to within 0.02V, significantly improving voltage stability. 4. The structure is simple and easy to implement, with strong compatibility. The fan connection end of the air duct can be adapted to different models of axial flow fans, and the rectangular stabilizing section size of the fuel cell stack docking end can be adjusted according to the fuel cell stack air inlet size, with good compatibility.

[0028] In some embodiments, the length ratio of the rectangular stabilizing section 6, the contracting section 5, and the circular stabilizing section 4 is 1:1 to 4:1 to 2. This invention, through the length ratio of the rectangular stabilizing section 6, the contracting section 5, and the circular stabilizing section 4, can achieve a smooth transition of airflow from the rectangular stabilizing section to the circular stabilizing section, effectively avoiding turbulence problems caused by sudden airflow changes, and can also control the overall axial dimension of the duct, avoiding increased system volume redundancy due to excessive duct length.

[0029] In some embodiments, 10 to 16 radial guide vanes 7 are provided along the circumference of the circular stabilizing section 4. The thickness of the radial guide vanes is 1.5 mm to 2.5 mm. One end of each radial guide vane 7 is fixed to the inner wall of the circular stabilizing section 4, while the other end is not fixed and faces the central axis of the circular stabilizing section 4. In this invention, based on the airflow rate and the target guide flow rate, the number of radial guide vanes is rationally designed to control the spacing between them, thus avoiding airflow turbulence caused by too few vanes and preventing increased wind resistance due to too many vanes. The thickness of the radial guide vanes can minimize airflow obstruction while ensuring the structural strength of the vanes.

[0030] In some embodiments, one end of each radial guide vane 7 is fixed to the inner wall of the wall, while the other end is not fixed and is oriented toward the central axis of the circular stable section 4. Each radial guide vane 7 has a centripetally curved arc-shaped protrusion structure, wherein the concave surface faces the surrounding airflow and the convex surface faces the central region, and the protrusion direction is consistent with the airflow direction. In this way, when the surrounding air impacts the radial guide vane, it will be smoothly guided toward the center along the curved surface of the radial guide vane, reducing airflow separation and resistance. It can accelerate and guide the airflow at the edge of the duct to the middle region, and further integrate the airflow guided from the edge to form a uniform airflow field with enhanced central airflow and smooth edge airflow.

[0031] In some embodiments, the angle between the other end of the radial guide vane 7 and the radial direction of the circular stabilizing section 4 is 30° to 60°. In this invention, the radial guide vane 7 needs to form a certain angle with the radial direction (the straight line from the center to the outer periphery) of the circular stabilizing section 4, which can convert the circumferential velocity component of the airflow into a centripetal velocity component, thereby enhancing the airflow intensity in the central region. Simply put, the extension direction of the vane should point towards the center and have an inclination with the airflow, so that the airflow is guided to the central region when it flows through the vane.

[0032] The following specific examples will provide further explanation.

[0033] Example 1 Taking a 1kW cathode open-type air-cooled fuel cell stack as an example, the air duct structure of the present invention will be described in detail.

[0034] The fuel cell stack outlet dimensions are 144mm x 120mm. The circular stabilizing section has an inner diameter of 120mm (matching the fan inlet) and a length of 20mm. The rectangular stabilizing section also measures 144mm x 120mm (matching the fuel cell stack outlet). The contraction section is 40mm long, and the rectangular stabilizing section is 20mm long. There are 12 radial guide vanes, each 2mm thick, and the angle between the radial guide vanes and the radial direction (the straight line from the center to the outer circumference) of the circular stabilizing section must be 30°.

[0035] The main body of the air duct (rectangular stabilizing section + contraction section + circular stabilizing section) is 3D printed. The fuel cell stack assembled with the air duct of this invention was tested, and the results are as follows:

[0036] Airflow uniformity: The flow velocity across the entire outlet of the fuel cell stack is 2.8 m / s to 3.0 m / s, with a uniformity of 93%.

[0037] Temperature distribution: After the fuel cell stack has been running for 1 hour, the temperature range is 45℃~50℃, with a temperature difference of 5℃.

[0038] Voltage output: Under rated load, the output voltage is 36.2V~36.4V, with a voltage difference of 0.015V between the middle and edge areas.

[0039] In summary, this invention designs and develops an air duct structure for an open-cathode air-cooled fuel cell stack. Targeting the axial fan's suction mode, it employs an independent air duct structure design combining a variable cross-section guiding structure and central airflow enhancement blades. This structural design corrects the airflow distribution pattern, guiding strong edge airflow towards the center and enhancing the central airflow. This approach eliminates the need to alter the overall stack shape and introduce additional impeller power components, avoiding increased system complexity. It achieves uniform air distribution within the stack, solving the problems of poor voltage consistency, uneven current density, and uneven temperature distribution caused by uneven airflow in existing open-cathode air-cooled fuel cells, thereby improving fuel cell performance and lifespan.

[0040] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0041] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. An air duct structure for a cathode open air-cooled fuel cell stack, comprising a fuel cell stack and an axial flow fan, characterized by, The variable cross-section air guide channel coaxial with the fuel cell stack and the axial fan comprises a rectangular stabilizing section, a converging section and a circular stabilizing section, wherein: The rectangular stabilizing section is connected to the butt joint end of the fuel cell stack at one end, forming a stable and uniform air flow. The converging section is located between the rectangular stabilizing section and the circular stabilizing section, and the diameter of the converging section gradually shrinks along the direction of air flow, for guiding the edge air flow to the central axis direction. The circular stabilizing section is connected to the butt joint end of the axial fan at one end, and a plurality of radial air guide vanes are arranged along the circumferential direction of the circular stabilizing section, forming a central air flow strengthening structure, for accelerating and guiding the edge air flow to the middle area, and integrating the air flow from the edge, forming a uniform air flow field with strengthened central air flow and smooth edge air flow.

2. The air duct structure for a cathode open air-cooled fuel cell stack according to claim 1, characterized by, The length ratio of the rectangular stabilizing section, the converging section and the circular stabilizing section is 1:1-4:0.5-2.

3. The air duct structure for a cathode open air-cooled fuel cell stack according to claim 1, characterized by There are 10-16 radial air guide vanes along the circumferential direction of the circular stabilizing section.

4. The air duct structure for a cathode open air-cooled fuel cell stack according to claim 1, characterized by One end of each radial air guide vane is fixed to the inner wall of the circular stabilizing section, and the other end is not fixed and directed towards the central axis of the circular stabilizing section.

5. The air duct structure for a cathode open air-cooled fuel cell stack according to claim 4, characterized by Each radial air guide vane has a centripetal curved arc convex structure, wherein the concave surface faces the surrounding air flow, the convex surface faces the central area, the convex direction is consistent with the direction of air flow, and the curvature radius of the arc convex is 5-15mm.

6. The air duct structure for a cathode open air-cooled fuel cell stack according to claim 4, characterized by The other end of the radial air guide vane and the radial direction of the circular stabilizing section form an angle of 30-60°.

7. The air duct structure for a cathode open air-cooled fuel cell stack according to claim 4, characterized by The thickness of the radial air guide vane is 1.5-2.5mm.

8. The air duct structure for a cathode open air-cooled fuel cell stack according to claim 1, characterized by The cross-sectional size of the rectangular stabilizing section is the same as that of the butt joint end of the fuel cell stack.

9. The air duct structure for a cathode open air-cooled fuel cell stack according to claim 1, characterized by The cross-sectional size of the circular stabilizing section is the same as that of the butt joint end of the axial fan.

10. The air duct structure for a cathode open air-cooled fuel cell stack according to claim 1, characterized by The variable cross-section air guide channel is integrally formed by injection molding or 3D printing process, and the material is plastic.

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