Core of air-cooled fuel cell stack, and stack and thermal management design method therefor

Abstract

The present invention relates to the technical field of fuel cells. Disclosed are a core of an air-cooled fuel cell stack, and a stack and a thermal management design method therefor. The core of the air-cooled fuel cell stack comprises a plurality of bipolar plates and a plurality of membrane electrodes stacked in sequence, wherein each bipolar plate is formed by combining an anode plate and a cathode plate, a hydrogen flow channel is provided on the anode surface of the anode plate distant from the cathode plate, an air flow channel is provided on the cathode surface of the cathode plate distant from the anode plate, and an air-cooling flow channel is provided between the anode plate and the cathode plate. The air-cooled fuel cell stack comprises the described core, and the opening direction of the air-cooling flow channel on the core is opposite to the air supply direction of air-cooling fans. The air-cooled fuel cell stack of the present invention can solve the problems of difficulties in balancing the oxygen content and the membrane water content, sensitivity to the environment, and unstable performance in the bipolar plate structure of an open-cathode air-cooled fuel cell, thereby improving the performance of the stack and prolonging the service life.

Description

A design method for the core, stack, and thermal management of an air-cooled fuel cell stack. Technical Field

[0001] This invention belongs to the field of fuel cell technology, and particularly relates to a core, stack, and thermal management design method for an air-cooled fuel cell stack. Background Technology

[0002] An air-cooled fuel cell (PEMFC) is a proton exchange membrane fuel cell that uses air as a cooling medium. It has attracted attention due to its simple structure and good applicability. Its working principle involves the electrochemical reaction of hydrogen (as fuel) with oxygen (from air) to produce electricity, water, and heat. The core components of the cell include the anode and cathode, which consist of bipolar plates, a gas diffusion layer, and a catalyst, as well as the proton exchange membrane. Hydrogen is oxidized at the anode, releasing electrons and generating protons; the electrons generate an electric current through an external circuit, while the protons pass through the proton exchange membrane to the cathode and react with oxygen to produce water.

[0003] Air-cooled fuel cells offer several advantages, making them highly attractive for applications such as portable and small mobile power sources. First, their relatively simple structure eliminates the need for complex water-cooling piping and related systems, resulting in lower system complexity, higher reliability, and reduced manufacturing and maintenance costs. Second, the absence of a dedicated cooling system makes them lighter, facilitating portability and installation. Furthermore, air-cooled fuel cells can start up quickly, making them suitable for applications requiring immediate power. Moreover, their flexible design adapts to various environmental conditions, making them excellent for portable electronic devices, electric vehicles, and outdoor power generation. Finally, their lower operating costs and good energy density make them a popular choice for clean energy solutions.

[0004] Currently, the mainstream development direction of air-cooled fuel cells is the traditional open cathode reaction region, where the cathode flow channel is in direct contact with the ambient atmosphere, and air directly purges the diffusion layer on the cathode side of the membrane electrode assembly (MEA). However, the water content carried by the air is unlikely to meet the humidity requirements of the MEA. In addition, the open cathode structure often requires a large air stoichiometry. Therefore, in low humidity and high flow rate scenarios, the liquid water content in the cathode-side MEA is low, and the proton exchange membrane is in a water-deficient state, which affects the stack performance and service life. On the other hand, the open cathode structure increases the sensitivity of the electrochemical reaction to ambient air quality and airflow, resulting in poor performance in extreme environments and unstable battery output power. Summary of the Invention

[0005] This invention provides a core, stack, and thermal management design method for an air-cooled fuel cell stack, aiming to solve problems such as difficulty in balancing oxygen and membrane water content, environmental sensitivity, and performance instability in existing open-cathode air-cooled fuel cell stacks. The air-cooled fuel cell stack of this invention is a closed-cathode air-cooled fuel cell stack. Through electrode structure design and corresponding thermal management technology, it solves the problems of difficulty in balancing oxygen and membrane water content, environmental sensitivity, and performance instability in open-cathode air-cooled fuel cell stacks, thereby improving stack performance and extending stack lifespan.

[0006] The technical solution of this invention is implemented as follows:

[0007] A core of an air-cooled fuel cell stack includes several bipolar plates and several membrane electrode assemblies stacked sequentially; each bipolar plate is composed of an anode plate and a cathode plate, wherein a hydrogen flow channel is provided on the anode surface of the anode plate away from the cathode plate, and an air flow channel is provided on the cathode surface of the cathode plate away from the anode plate; an air-cooling flow channel is provided between the anode plate and the cathode plate.

[0008] Preferably, the bipolar plate is provided with a hydrogen inlet, a hydrogen outlet, an air inlet, and an air outlet.

[0009] More preferably, one end of the bipolar plate is provided with the hydrogen inlet and the air outlet, and the other end of the bipolar plate is provided with the air inlet and the hydrogen outlet.

[0010] More preferably, the air-cooled flow channel is provided at one end of the anode plate near the cathode plate, and the cathode plate covers the air-cooled flow channel to achieve a sealed air-cooled flow channel that does not contact the membrane electrode, for heat dissipation of the fuel cell stack.

[0011] Preferably, the opening direction of the air-cooled flow channel is opposite to the air delivery direction of the air-cooled fan.

[0012] The core of the air-cooled fuel cell stack of this invention, after the bipolar plates and membrane electrode assembly are bonded together, has a closed cathode cavity and an anode cavity, resulting in good stability of the electrochemical reaction. The air-cooling channel is located in the middle of the bipolar plates, avoiding direct contact with the membrane electrode assembly and preventing the membrane drying problem of open-cathode air-cooled stacks. At the same time, it reduces sensitivity to environmental humidity and temperature, making it more adaptable.

[0013] An air-cooled fuel cell stack includes the aforementioned stack core.

[0014] Preferably, the air-cooled fuel cell stack includes a core, a draft shroud, and an air-cooling fan. The draft shroud is disposed on the outer side of the core, and the air-cooling fan is disposed on the draft shroud. More preferably, the opening direction of the air-cooling channel on the core is opposite to the airflow direction of the air-cooling fan.

[0015] Preferably, the air-cooled fuel cell stack includes an air guide shroud, an air-cooling fan, and an upper end plate, an upper insulating plate, an upper current collector, a stack core, a lower current collector, a lower insulating plate, and a lower end plate stacked sequentially; the upper end plate and the lower end plate are respectively connected to the two end faces of the air guide shroud. More preferably, the upper end plate, the lower end plate, and the air guide shroud are fixedly connected by fasteners.

[0016] Preferably, the air guide shroud has a U-shaped frame structure, and the air-cooled fan is located at the bottom of the U-shaped frame structure. After the fuel cell stack is assembled, the bottom of the U-shaped frame structure with the air-cooled fan is positioned opposite to the opening direction of the air-cooling channel on the fuel cell core.

[0017] Preferably, the air-cooled fuel cell stack is a cathode-enclosed air-cooled fuel cell stack.

[0018] Preferably, the air-cooled fan is an axial flow fan.

[0019] A thermal management design method for an air-cooled fuel cell stack is proposed. Based on the structure of the air-cooled fuel cell stack described above, the thermal management design of the air-cooled fuel cell stack is achieved by calculating the heat generation of the stack and matching the specifications of the cooling fan, optimizing the opening size of the air-cooling flow channel and the specifications of the matching cooling fan.

[0020] The above-mentioned thermal management design method for air-cooled fuel cell stacks uses theoretical calculations to analyze the heat generation of the stack, thereby optimizing the actual design dimensions of the air-cooling channel. After determining the dimensions of the air-cooling channel, the fan is matched and selected again based on the fan PQ curve, thus realizing the thermal management design of the stack.

[0021] The above-mentioned thermal management design method for air-cooled fuel cell stacks specifically includes the following steps:

[0022] S01. Initial parameters of the air-cooled flow channel are given, including the height d, width w, length l, and N of the air-cooled flow channel. ch N represents the number of air-cooled flow channels. cell This refers to the number of individual cells;

[0023] S02. Calculate the heat generation and dissipation of the air-cooled fuel cell stack:

[0024] The heat Q generated during the operation of the fuel cell stack h for: P = VI

[0025] Among them, Q h V is the heat generated during the operation of the fuel cell stack, I is the rated operating voltage of the fuel cell stack, P is the rated operating power of the fuel cell stack, Er is the Nernst reversible electromotive force considering temperature correction, and P is the rated current generated during operation. a P is the anode inlet gas pressure. c R is the cathode inlet gas pressure, R is the universal gas constant (8.314 J / (mol·K)), and F is the Faraday constant (96485 C / mol).

[0026] S03. Perform fan selection calculations for air-cooled channel heat dissipation:

[0027] Select an axial fan with a suitable diameter based on the fuel cell stack size. The fan's technical specifications are: air inlet area A. fan This makes the static pressure P that the fan needs to provide... S With the fan's air intake area A fan The following relationship applies between them:

[0028] Where Ps is the static pressure that the fan needs to provide, and A fan The fan's intake area, ρ is the density of the incoming air, u is the average velocity in the air-cooled channel, and A is the air intake area. ch Let ΔP be the cross-sectional area of ​​the channel in the direction perpendicular to the airflow, and let ΔP be the minimum pressure drop in the channel when the heat dissipation requirement is met.

[0029] Then, the operating point of the fan is determined by the intersection of the air-cooled flow field impedance curve and the fan characteristic curve. The flow rate provided by the fan at the operating point is then used to determine whether the design requirements are met.

[0030] S04. Thermal simulation verification of cathode-sealed air-cooled fuel cell stack:

[0031] After giving the structural parameters of the initial air-cooled channel and performing theoretical calculations on heat generation and dissipation, a suitable heat dissipation air-cooled fan is matched. Then, numerical simulation technology is used to confirm whether the selected fan can meet the heat dissipation target of the fuel cell stack.

[0032] S05. Calculation of cross-sectional dimensions for air-cooled aisles:

[0033] Based on the heat parameter Q generated during the operation of the fuel cell stack h and inlet / outlet temperature difference (T) out -T in To optimize the actual design dimensions of the air cooling channel, after determining the dimensions of the air cooling channel, the fan is matched and selected again based on the fan PQ curve, thus completing the thermal management design of the cathode-enclosed air-cooled fuel cell stack.

[0034] Preferably, in step S05, the optimization of the actual design dimensions of the air cooling channel involves the following steps: Based on the cross-sectional dimensions of the air cooling channel to obtain the optimal heat dissipation effect of the fuel cell stack, the reference design dimensions of the air cooling channel are optimized by combining heat generation theory calculations, fan selection calculations, and fuel cell stack thermal simulation verification processes; the inlet cross-sectional area of ​​the air cooling channel is determined by the channel height d and width w. After satisfying the electrode plate support strength and ease of processing factors, the specific calculation method is as follows:

[0035] Among them, Q h T is the heat generated during the operation of the fuel cell stack. out T is the outlet temperature of the fuel cell stack. in ρ is the air temperature drawn into the fuel cell under standard conditions, d is the height of the air-cooled channel, w is the width of the air-cooled channel, ρ is the density of the incoming air, C is the specific heat of the gas, and u is the average flow velocity in the air-cooled channel.

[0036] Preferably, in this invention, the fuel cell is considered as a heat exchanger with an internal heat source, and the overall thermal balance relationship of the stack during stable operation is: Q h =Q water +Q gas +Q rad

[0037] In the formula Q h Q is the heat generated during the operation of the fuel cell stack. water Q gas Q rad These represent the heat dissipation power of the cooling water, the heat loss power of the exhaust gas, and the heat carried away by radiation, respectively. In air-cooled reactors, there is no cooling water; the heat inside the reactor is mainly carried away by the forced convection of the inlet gas. Meanwhile, the heat carried away by the natural convection heat exchange and radiation between the outer surface of the battery and the ambient atmosphere is limited and can be ignored.

[0038] The heat Q carried away by the exhaust gas heat loss power gas It equals the difference between the heat carried by the gases exiting the reactor and the heat carried by the gases entering the reactor: Q gas =CωΔT

[0039] Where C is the specific heat of the gas, ω is the mass flow rate of the gas, and ΔT is the temperature difference between the inlet and outlet;

[0040] The heat Q carried away by the radiation rad The calculation is given by the blackbody radiation law:

[0041] Where δ is the emissivity, σ is the blackbody radiation constant, and A stack T is the surface area of ​​the fuel cell stack, T is the battery operating temperature, and T0 is the ambient temperature.

[0042] Preferably, in step S03,

[0043] Based on the parameters given in step S01 for the initial air-cooled channel, including the height d, width w, length l, and N of the air-cooled channel. ch N represents the number of air-cooled flow channels. cell This refers to the number of individual batteries;

[0044] The total convective heat transfer area A of the internal cold flow channel of the fuel cell stack con For: A con =2dwlN ch N cell

[0045] The cross-sectional area A of the channel in the direction perpendicular to the airflow direction ch For: A ch =dwN ch N cell

[0046] Qualitative temperature T of the gas in the air-cooled channel m for:

[0047] The convective heat transfer coefficient h of the inner surface of the air-cooled flow channel f for:

[0048] Equivalent diameter d of air-cooled flow channel e for:

[0049] Nusselt number N corresponding to forced convection heat transfer in air-cooled flow channels u for:

[0050] Where, k air The forced convection heat transfer coefficient of air;

[0051] Qualitative temperature T m If the dimensionless Prandtl number of the air below is given, then the dimensionless Reynolds number Re for the gas flow inside the pile is:

[0052] The average flow velocity u in the air-cooled channel is:

[0053] Air volume flow rate required from the fan for:

[0054] The minimum pressure drop ΔP in the flow channel to meet heat dissipation requirements is:

[0055] In step S04, during the thermal simulation of the fuel cell stack, the membrane electrode is used as the heat source, the flow domain of the anode and cathode reaction gases is ignored, and a fan model is used to simulate the temperature field distribution effect inside the fuel cell stack under different duty cycles.

[0056] In step S05, the heat Q generated when the fuel cell stack is operating... h The derivation process is as follows: Q h =Cω(T) out -T in )

[0057] Where ω is the inlet mass flow rate of the air-cooled channel, C is the specific heat of the gas, and T is the mass flow rate of the air-cooled channel. out T is the outlet temperature of the fuel cell stack. in The temperature of the air drawn into the fuel cell stack under standard conditions;

[0058] The inlet mass flow rate ω of the air-cooled channel is calculated as follows: ω = A ch u=dwu

[0059] Assuming the airflow into the air-cooled channel is laminar, and taking the dimensionless Reynolds number Re = 2000, the design reference for the heat generation of the fuel cell stack and the cross-sectional dimensions of the air-cooled channel can be derived as follows:

[0060] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0061] Existing air-cooling methods are typically used in low-power fuel cell systems. A fan pumps ambient air directly into the cathode channel, integrating the cathode air supply system and cooling system. The air flowing in the cathode field provides the oxygen required for the electrochemical reaction and also acts as a cooling medium. Since there is no air intake humidification device, the fuel cell system structure is greatly simplified. However, the high-velocity airflow carries away a large amount of water from the stack, drying the proton exchange membrane and causing significant ohmic losses, thus reducing stack performance. Therefore, the closed-cathode air-cooled fuel cell stack of this invention can solve the problems of difficulty in balancing oxygen and membrane water content, environmental sensitivity, and performance instability inherent in open-cathode air-cooled fuel cell plate structures, improving stack performance and extending service life.

[0062] Furthermore, this invention provides a thermal management design method for an air-cooled fuel cell stack. Based on the aforementioned structure of a cathode-enclosed air-cooled fuel cell stack, the method optimizes the opening size of the air-cooled flow channel and the matching specifications of the cooling fan by performing calculations on the heat generated by the stack and matching the specifications of the cooling fan, thereby realizing a thermal management design method for a cathode-enclosed air-cooled fuel cell stack. Attached Figure Description

[0063] Figure 1 is a structural diagram of the air-cooled fuel cell stack electrode plate in an embodiment of the present invention;

[0064] Figure 2 is a schematic diagram of the assembly of the electrode plates and membrane electrode of the air-cooled fuel cell stack in an embodiment of the present invention.

[0065] Figure 3 is an exploded view of the air-cooled fuel cell stack in an embodiment of the present invention;

[0066] Figure 4 is a roadmap of thermal management design technology for air-cooled fuel cell stacks in an embodiment of the present invention;

[0067] Figure 5 shows the system impedance and PQ curves of the air-cooled fuel cell stack and the selected fan in the embodiment of the present invention.

[0068] Figure 6 shows the temperature field distribution of the air-cooled fuel cell stack in an embodiment of the present invention; wherein, a is the temperature field distribution effect of the stack core when the fan has a 50% duty cycle, and b is the temperature field distribution effect of the stack core when the fan has a 100% duty cycle.

[0069] Figure 7 is a polarization performance diagram of the air-cooled fuel cell stack in an embodiment of the present invention;

[0070] Figure 8 shows the results of the average temperature and temperature difference of the inlet and outlet stacks under the corresponding polarization performance in the embodiment of the present invention. Detailed Implementation

[0071] 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 a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0072] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, top, bottom, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0073] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0074] It should be noted that when a component is described as "fixed to" or "set on" another component, it can be directly on the other component or there may be an intervening component. When a component is described as "connected to" another component, it can be directly connected to the other component or there may be an intervening component.

[0075] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0076] Currently, existing open-cathode air-cooled fuel cell stacks suffer from problems such as difficulty in balancing oxygen and membrane water content, environmental sensitivity, and performance instability. To address these technical issues, this invention proposes a core, stack, and thermal management design method for an air-cooled fuel cell stack. The air-cooled fuel cell stack of this invention is a closed-cathode air-cooled fuel cell stack. Through electrode structure design and corresponding thermal management technology, it solves the problems of difficulty in balancing oxygen and membrane water content, environmental sensitivity, and performance instability inherent in open-cathode air-cooled fuel cell stacks, thereby improving stack performance and extending stack lifespan.

[0077] Example

[0078] Referring to Figures 1 to 3, embodiments of the present invention provide a core and a stack of an air-cooled fuel cell stack.

[0079] As shown in Figures 1 and 2, a core 10 of an air-cooled fuel cell stack includes several bipolar plates 11 and several membrane electrode 12 stacked sequentially. The bipolar plates 11 are composed of an anode plate 111 and a cathode plate 112. A hydrogen flow channel 113 is provided on the anode surface of the anode plate 111 away from the cathode plate 112, and an air flow channel 114 is provided on the cathode surface of the cathode plate 112 away from the anode plate 111. An air-cooling channel 115 is provided between the anode plate 111 and the cathode plate 112.

[0080] Preferably, the bipolar plate 11 is provided with a hydrogen inlet 116, a hydrogen outlet 117, an air inlet 118, and an air outlet 119. More preferably, one end of the bipolar plate 11 is provided with the hydrogen inlet 116 and the air outlet 119, and the other end of the bipolar plate 11 is provided with the air inlet 118 and the hydrogen outlet 117.

[0081] More preferably, the air-cooled flow channel 115 is provided at one end of the anode plate 111 near the cathode plate 112, and the cathode plate 112 covers the air-cooled flow channel 115, so that the air-cooled flow channel 115 is a sealed air-cooled flow channel that does not contact the membrane electrode 12, and is used for heat dissipation of the fuel cell stack.

[0082] Preferably, the opening direction of the air-cooled flow channel 115 is opposite to the air delivery direction of the air-cooled fan 20.

[0083] In the cathode-enclosed air-cooled fuel cell stack of the present invention, after the bipolar plates 11 and membrane electrode 12 are bonded together, the cathode cavity and anode cavity are closed cavities, resulting in good stability of the electrochemical reaction. The air-cooling channel 115 is located in the middle of the bipolar plates 11, avoiding direct contact with the membrane electrode 12, thus avoiding the membrane drying problem of open-cathode air-cooled stacks. At the same time, it reduces the sensitivity to environmental humidity and temperature, making it more adaptable.

[0084] As shown in Figure 3, an air-cooled fuel cell stack includes the aforementioned stack core 10.

[0085] Preferably, the air-cooled fuel cell stack includes a core 10, an air guide shroud 30, and an air-cooling fan 20. The air guide shroud 30 is disposed on the outer side of the core 10, and the air-cooling fan 20 is disposed on the air guide shroud 30. More preferably, the opening direction of the air-cooling flow channel 115 on the core 10 is opposite to the air delivery direction of the air-cooling fan 20.

[0086] Preferably, the air-cooled fuel cell stack includes an air guide shroud 30, an air-cooling fan 20, and an upper end plate 40, an upper insulating plate 50, an upper current collector 60, a core 10, a lower current collector 70, a lower insulating plate 80, and a lower end plate 90, which are stacked sequentially. The upper end plate 40 and the lower end plate 90 are respectively connected to the two end faces of the air guide shroud 30. More preferably, the upper end plate 40, the lower end plate 90, and the air guide shroud 30 are fixedly connected by fasteners 31.

[0087] Preferably, the air guide shroud 30 has a U-shaped frame structure, and the air-cooled fan 20 is disposed at the bottom of the U-shaped frame structure. After the fuel cell stack is assembled, the bottom of the U-shaped frame structure with the air-cooled fan 20 is positioned opposite to the opening direction of the air-cooled flow channel 115 on the core 10.

[0088] Preferably, the air-cooled fan 20 is an axial flow fan.

[0089] As shown in Figure 4, the above-mentioned thermal management design method for air-cooled fuel cell stacks, which involves calculating the heat generation of the stack and matching the specifications of the cooling fan, includes the following steps:

[0090] First, based on the input requirements for the fuel cell stack, input the stack's rated operating voltage, rated operating current density, and the number of individual cells in the stack;

[0091] S01. Initial parameter setting and evaluation of the air-cooled flow channel, including the height d, width w, length l, and N of the air-cooled flow channel. ch N represents the number of air-cooled flow channels. cell This refers to the number of individual cells;

[0092] S02. Calculate the heat generation and dissipation of the air-cooled fuel cell stack:

[0093] The heat Q generated during the operation of the fuel cell stack h for: P = VI Q gas =CωΔT

[0094] Among them, Q h V is the heat generated during the operation of the fuel cell stack, I is the rated operating voltage of the fuel cell stack, P is the rated operating power of the fuel cell stack, Er is the Nernst reversible electromotive force considering temperature correction, and P is the rated current generated during operation. a P is the anode inlet gas pressure. c Where is the cathode inlet gas pressure, R is the universal gas constant (8.314 J / (mol·K)), and F is the Faraday constant (96485 C / mol); Q gasω represents the heat lost through exhaust gas; C is the specific heat of the gas; ω is the mass flow rate of the gas; ΔT is the inlet and outlet temperature difference; Q rad Let δ be the heat carried away by radiation, σ be the emissivity, and A be the blackbody radiation constant. stack T is the surface area of ​​the fuel cell stack, T is the battery operating temperature, and T0 is the ambient temperature.

[0095] The rated operating condition of a single cell in this air-cooled fuel cell stack is 0.76V@1.3A / cm. 2 A total of 10 pieces were used. The key parameters involved in the theoretical calculation of heat dissipation and heat generation are shown in Table 1.

[0096] Table 1 Key parameters involved in the theoretical calculations of heat dissipation and heat generation.

[0097] S03. Perform fan selection calculations for air-cooled channel heat dissipation:

[0098] Based on the parameters given in step S01 for the initial air-cooled channel, including the height d, width w, length l, and N of the air-cooled channel. ch N represents the number of air-cooled flow channels. cell This refers to the number of individual cells;

[0099] The total convective heat transfer area A of the internal cold flow channel of the fuel cell stack con For: A con =2dwlN ch N cell ;

[0100] Channel cross-sectional area A in the direction of vertical airflow ch For: A ch =dwN ch N cell ;

[0101] Taking the convective heat transfer temperature difference as ΔT = 10K, then the qualitative temperature T of the gas in the air-cooled channel is... m for:

[0102] The convective heat transfer coefficient (i.e., the forced convection heat transfer coefficient) h of the inner surface of the air-cooled flow channel f for:

[0103] Equivalent diameter d of air-cooled flow channel e for:

[0104] Nusselt number N corresponding to forced convection heat transfer in air-cooled flow channels u for:

[0105] Assuming the flow is laminar, the Reynolds number Re can be derived from the dimensionless Prandtl number Pr (which is determined by the characteristic temperature T). m The determination (that is, a constant value at a given temperature) is as follows:

[0106] Qualitative temperature T m The density ρ and dynamic viscosity μ of the air are constants and can be obtained by acquiring the physical properties of the air at the corresponding temperature. Therefore, the average flow velocity (i.e., the flow rate provided by the fan) u in the air-cooled channel is:

[0107] The required air volumetric flow rate (i.e., the air volume required to meet the minimum pressure drop) must be provided by the fan. for:

[0108] The minimum pressure drop ΔP in the flow channel to meet heat dissipation requirements is:

[0109] Based on the fuel cell stack size, select an axial fan with a suitable diameter. Calculate the static pressure Ps that the fan needs to provide:

[0110] Table 2 Fan Selection Calculation Results

[0111] Table 2 shows the fan selection calculation results corresponding to the air-cooled flow channel structure designed in Example 1. As shown in Figure 5, the intersection of the air-cooled flow field impedance curve and the fan characteristic curve is the operating point of the fan. When the fan duty cycle is 100%, the air flow rate supplied by the fan to the fuel cell stack is 3.1 m³ / s. 3 / min, greater than the stack requirement of 2.542m 3 / min, the selected fan meets the design requirements.

[0112] S04. Thermal simulation verification of cathode-sealed air-cooled fuel cell stack:

[0113] After giving the structural parameters of the initial air-cooled channel and performing theoretical calculations on heat generation and dissipation, a suitable heat dissipation air-cooled fan is matched. Then, numerical simulation technology is used to confirm whether the selected fan can meet the heat dissipation target of the fuel cell stack. In the thermal simulation of the fuel cell stack, the membrane electrode is used as the heat source, the flow domain of the anode and cathode reaction gases is ignored, and the fan model is used to simulate the effect of the fan on the temperature field distribution inside the fuel cell stack under different duty cycles.

[0114] Table 3 shows the battery heat source obtained after simulation post-processing.

[0115] Table 3 shows the heat sources inside each component of a single cell obtained after post-simulation processing, which are the heat sources given when using the fan model in thermal simulation. During thermal simulation, the temperature field distribution of the core is compared at 50% and 100% duty cycles of the selected fan. Figure 6(a) shows the temperature field distribution of the core at 50% fan duty cycle, and Figure 6(b) shows the temperature field distribution of the core at 100% fan duty cycle.

[0116] When the fan duty cycle is 50%, the average core temperature is 69.7℃, the maximum temperature is 94.9℃, the average outlet static pressure is 393Pa, the average exhaust velocity is 16.32m / s, and the fan heat decomposition is 351W.

[0117] When the fan duty cycle is 100%, the average core temperature is 47.6℃, the maximum temperature is 61.7℃, the average outlet static pressure is 433Pa, the average exhaust velocity is 17.69m / s, and the fan heat decomposition is 570W.

[0118] Simulation results verify that the temperature field distribution of the core of the closed-cathode air-cooled battery stack is reasonable and the overall heat dissipation performance meets the standards when the fan duty cycle is 50% and 100%, and the proposed solution can be output.

[0119] Actual performance of closed-loop air-cooled fuel cell stack prototype

[0120] Figures 7 and 8 illustrate the measured polarization and temperature performance of the enclosed air-cooled fuel cell stack prototype. Polarization 1 was conducted at a reactant gas inlet temperature of 70°C, anode relative humidity of 40% (RH), cathode relative humidity of 60%, anode inlet pressure of 140 kPa, cathode inlet pressure of 130 kPa, cathode stoichiometry of 1.6, anode stoichiometry of 3.7, and room temperature of 25°C. Polarization 2 was conducted at 65°C, 40 / 60 RH, 140 / 130 kPa, and a stoichiometry of 1.6 / 2.2. Polarization 3 was conducted at 65°C, 40 / 60 RH, 95 / 75 kPa, and a stoichiometry of 1.6 / 2.2. Performance-wise, the stack exhibited similar performance under the three polarization test conditions, with an output voltage of approximately 0.7 V at a current density of 1.2. The entire stack comprises 10 membrane electrodes with an active area of ​​300 cm². 2 The stack output power is 2.52kW. Based on the temperature performance obtained from Figure 8, the inlet and outlet temperatures are greatly affected by the test conditions. The highest outlet temperature is about 81℃ under polarization 1 conditions. At this time, the temperature difference between the inlet and outlet is about 13℃. The performance and temperature characteristics are consistent with the structure and thermal management design method of this closed air-cooled stack.

[0121] Existing air-cooling methods are typically used in low-power fuel cell systems. A fan pumps ambient air directly into the cathode channel, integrating the cathode air supply system and cooling system. The air flowing in the cathode field provides the oxygen required for the electrochemical reaction and also acts as a cooling medium. Since there is no air intake humidification device, the fuel cell system structure is greatly simplified. However, the high-velocity airflow carries away a large amount of water from the stack, drying the proton exchange membrane and causing significant ohmic losses, thus reducing stack performance. Therefore, the closed-cathode air-cooled fuel cell stack of this invention can solve the problems of difficulty in balancing oxygen and membrane water content, environmental sensitivity, and performance instability inherent in open-cathode air-cooled fuel cell plate structures, improving stack performance and extending service life.

[0122] Furthermore, this invention provides a thermal management design method for an air-cooled fuel cell stack. Based on the aforementioned structure of a cathode-enclosed air-cooled fuel cell stack, the method optimizes the opening size of the air-cooled flow channel and the matching specifications of the cooling fan by performing calculations on the heat generated by the stack and matching the specifications of the cooling fan, thereby realizing a thermal management design method for a cathode-enclosed air-cooled fuel cell stack.

[0123] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A core of an air-cooled fuel cell stack, characterized in that: It includes several bipolar plates and several membrane electrodes stacked in sequence; the bipolar plates are composed of an anode plate and a cathode plate, the anode plate has a hydrogen flow channel on the anode surface away from the cathode plate, and the cathode plate has an air flow channel on the cathode surface away from the anode plate; an air cooling channel is provided between the anode plate and the cathode plate.

2. The core of the air-cooled fuel cell stack according to claim 1, characterized in that: The bipolar plate is provided with a hydrogen inlet, a hydrogen outlet, an air inlet, and an air outlet.

3. The core of the air-cooled fuel cell stack according to claim 2, characterized in that: One end of the bipolar plate is provided with a hydrogen inlet and an air outlet, and the other end of the bipolar plate is provided with an air inlet and a hydrogen outlet.

4. The core of the air-cooled fuel cell stack according to claim 1, characterized in that: The air-cooled flow channel is provided at one end of the anode plate near the cathode plate, and the cathode plate covers the air-cooled flow channel.

5. The core of the air-cooled fuel cell stack according to claim 1, characterized in that: The opening direction of the air-cooled flow channel is opposite to the air delivery direction of the air-cooled fan.

6. An air-cooled fuel cell stack, characterized in that: Includes the reactor core as described in any one of claims 1-5.

7. The air-cooled fuel cell stack according to claim 6, characterized in that: The reactor includes a reactor core, a wind deflector, and an air-cooled fan. The wind deflector is located on the outer side of the reactor core, and the air-cooled fan is located on the wind deflector. The opening direction of the air-cooled flow channel on the reactor core is opposite to the air delivery direction of the air-cooled fan.

8. The air-cooled fuel cell stack according to claim 6, characterized in that: The air-cooled fuel cell stack includes an air guide shroud, an air-cooling fan, and an upper end plate, an upper insulating plate, an upper current collector, a stack core, a lower current collector, a lower insulating plate, and a lower end plate stacked sequentially. The upper end plate and the lower end plate are respectively connected to the two end faces of the air guide shroud. More preferably, the upper end plate, the lower end plate, and the air guide shroud are fixedly connected by fasteners.

9. A thermal management design method for an air-cooled fuel cell stack, characterized in that: Specifically, the following steps are included: S01. Initial parameters of the air-cooled flow channel are given, including the height d, width w, length l, and N of the air-cooled flow channel. ch N represents the number of air-cooled flow channels. cell This refers to the number of individual batteries; S02. Calculate the heat generation and dissipation of the air-cooled fuel cell stack: The heat Q generated during the operation of the fuel cell stack h for: P=VI Among them, Q h V is the heat generated during the operation of the fuel cell stack, I is the rated operating voltage of the fuel cell stack, P is the rated operating power of the fuel cell stack, Er is the Nernst reversible electromotive force considering temperature correction, and P is the rated current generated during operation. a P is the anode inlet gas pressure. c Where is the cathode inlet gas pressure, R is the universal gas constant, and F is the Faraday constant; S03. Perform fan selection calculations for air-cooled channel heat dissipation: Select an axial fan with a suitable diameter based on the fuel cell stack size. The fan's technical specifications are: air inlet area A. fan This makes the static pressure P that the fan needs to provide... S With the fan's air intake area A fan The following relationship applies between them: Where Ps is the static pressure that the fan needs to provide, and A fan The fan's intake area, ρ is the density of the incoming air, u is the average velocity in the air-cooled channel, and A is the air intake area. ch Let ΔP be the cross-sectional area of ​​the channel in the direction perpendicular to the airflow, and let ΔP be the minimum pressure drop in the channel when the heat dissipation requirement is met. Then, the operating point of the fan is determined by the intersection of the air-cooled flow field impedance curve and the fan characteristic curve. The flow rate provided by the fan at the operating point is then used to determine whether the design requirements are met. S04. Thermal simulation verification of cathode-sealed air-cooled fuel cell stack: After giving the structural parameters of the initial air-cooled channel and performing theoretical calculations on heat generation and dissipation, a suitable heat dissipation air-cooled fan is matched. Then, numerical simulation technology is used to confirm whether the selected fan can meet the heat dissipation target of the fuel cell stack. S05. Calculation of cross-sectional dimensions for air-cooled aisles: Based on the heat parameter Q generated during the operation of the fuel cell stack h and inlet / outlet temperature difference (T) out -T in To optimize the actual design dimensions of the air cooling channel, after determining the dimensions of the air cooling channel, the fan is matched and selected again based on the fan PQ curve, thus completing the thermal management design of the cathode-enclosed air-cooled fuel cell stack.

10. The thermal management design method for an air-cooled fuel cell stack according to claim 9, characterized in that: In step S05, the specific steps for optimizing the actual design dimensions of the air cooling channel are as follows: Based on the cross-sectional dimensions of the air cooling channel to obtain the best heat dissipation effect of the fuel cell stack, the reference design dimensions of the air cooling channel are optimized by combining heat generation theory calculations, fan selection calculations, and fuel cell stack thermal simulation verification processes; the inlet cross-sectional area of ​​the air cooling channel is determined by the channel height d and width w. After satisfying the electrode plate support strength and ease of processing factors, the specific calculation method is as follows: Among them, Q h T is the heat generated during the operation of the fuel cell stack. out T is the outlet temperature of the fuel cell stack. in ρ is the air temperature drawn into the fuel cell under standard conditions, d is the height of the air-cooled channel, w is the width of the air-cooled channel, ρ is the density of the incoming air, C is the specific heat of the gas, and u is the average flow velocity in the air-cooled channel.

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