Reactor core of air-cooled fuel cell stack, stack and thermal management design method thereof

Abstract

The invention discloses a reactor core of an air-cooled fuel cell stack, the stack and a thermal management design method of the stack, and belongs to the technical field of fuel cells. The reactor core of the air-cooled fuel cell stack comprises a plurality of bipolar plates and a plurality of membrane electrodes which are sequentially stacked, the bipolar plate is formed by combining an anode plate and a cathode plate, a hydrogen runner is arranged on the anode surface, far away from the cathode plate, of the anode plate, and an air runner is arranged on the cathode surface, far away from the anode plate, of the cathode plate; and an air cooling runner is arranged between the anode plate and the cathode plate. The air-cooling fuel cell stack comprises the stack core, and the opening direction of the air-cooling flow channel on the stack core is opposite to the air supply direction of an air-cooling fan. By adopting the air-cooled fuel cell stack, the problems of difficulty in balancing oxygen and membrane water content, environmental sensitivity, unstable performance and the like of a cathode open type air-cooled fuel cell polar plate structure can be solved, the stack performance is improved, and the service life is prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel cells, and particularly relates to a core of an air-cooled fuel cell stack, a fuel cell stack, and a thermal management design method thereof. Background Art

[0002] An air-cooled fuel cell is a proton exchange membrane fuel cell (PEMFC) that uses air as a cooling medium and has attracted attention due to its simple structure and good applicability. Its working principle is to generate electric energy, water, and heat through the electrochemical reaction of hydrogen (as fuel) and oxygen (from air). The core components of the fuel cell include the anode and cathode composed of bipolar plates, gas diffusion layers, and catalysts, and a 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 reach the cathode through the proton exchange membrane and react with oxygen to form water.

[0003] Air-cooled fuel cells have many advantages, making them attractive in application scenarios such as portable and small mobile power sources. First, its structure is relatively simple, eliminating complex water-cooling pipelines and supporting systems, with a low system complexity and high reliability, while also being able to reduce manufacturing and maintenance costs. Second, due to the absence of a supporting cooling system, the overall weight is lighter, making it convenient for carrying and installation. In addition, air-cooled fuel cells can start quickly and are suitable for application scenarios that require instant power. Moreover, its flexible design is applicable to a variety of environmental conditions, making it perform well in fields such as portable electronic devices, electric vehicles, and outdoor power generation. Finally, its low operating cost and good energy density make it a popular choice in clean energy solutions.

[0004] Currently, the mainstream development direction of air-cooled fuel cells is the traditional open cathode reaction area, that is, the cathode flow channel is directly in contact with the ambient atmosphere, and air directly sweeps the diffusion layer on the cathode side of the membrane electrode. However, the water content carried by the air in the atmosphere is difficult to meet the humidity requirements of the membrane electrode. In addition, the open cathode structure often requires a large air stoichiometric ratio. Therefore, in scenarios with low humidity and large flow rates, the liquid water content in the cathode side membrane electrode of the fuel cell stack is low, and the proton exchange membrane is in a water-deficient state, thus affecting the performance and service life of the fuel cell stack. On the other hand, the open cathode structure increases the sensitivity of the electrochemical reaction to the quality of the ambient atmosphere and air flow, and its performance is poor in extreme environments, resulting in unstable battery output power. Summary of the Invention

[0005] An embodiment of the present invention provides a core of an air-cooled fuel cell stack, a fuel cell stack, and a thermal management design method thereof, aiming to solve the problems existing in the existing cathode open-type air-cooled fuel cell stack, such as the difficulty in balancing oxygen and membrane water content, sensitivity to the environment, and unstable performance. The air-cooled fuel cell stack of the present invention is a cathode closed-type air-cooled fuel cell stack. Through the design of the plate structure and the supporting thermal management technology, the problems existing in the cathode open-type air-cooled fuel cell stack, such as the difficulty in balancing oxygen and membrane water content, sensitivity to the environment, and unstable performance, are solved, the performance of the fuel cell stack is improved, and the service life of the fuel cell stack is prolonged.

[0006] The technical solution of the present invention is realized as follows:

[0007] A core of an air-cooled fuel cell stack includes several bipolar plates and several membrane electrodes stacked in sequence; the bipolar plate is composed of an anode plate and a cathode plate, a hydrogen gas flow channel is arranged on the anode surface of the anode plate far away from the cathode plate, and an air flow channel is arranged on the cathode surface of the cathode plate far away from the anode plate; an air-cooled flow channel is arranged between the anode plate and the cathode plate.

[0008] Preferably, a hydrogen gas inlet, a hydrogen gas outlet, an air inlet, and an air outlet are arranged on the bipolar plate.

[0009] Further preferably, the hydrogen gas inlet and the air outlet are arranged at one end of the bipolar plate, and the air inlet and the hydrogen gas outlet are arranged at the other end of the bipolar plate.

[0010] Further preferably, the air-cooled flow channel is arranged at one end of the anode plate close to the cathode plate, and the cathode plate covers the air-cooled flow channel to form a sealed air-cooled flow channel that does not contact the membrane electrode, which is used for heat dissipation of the fuel cell stack.

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

[0012] In the core of the air-cooled fuel cell stack of the present invention, after the bipolar plate and the membrane electrode are attached, the cathode cavity and the anode cavity are closed cavities, and the stability of the electrochemical reaction is good. The air-cooled flow channel is located in the middle of the bipolar plate, avoiding direct contact with the membrane electrode, and there will be no membrane drying problem in the cathode open-type air-cooled stack. At the same time, the sensitivity to environmental humidity and temperature is reduced, and the adaptability is stronger.

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

[0014] Preferably, the air-cooled fuel cell stack includes a stack core, a wind guide cover, and an air-cooling fan. The wind guide cover is disposed outside the stack core, and the air-cooling fan is disposed in the wind guide cover. Further preferably, the opening direction of the air-cooling flow channel on the stack core is opposite to the air supply direction of the air-cooling fan.

[0015] Preferably, the air-cooled fuel cell stack includes a wind guide cover, an air-cooling fan, and an upper end plate, an upper insulating plate, an upper current collector plate, a stack core, a lower current collector plate, a lower insulating plate, and a lower end plate that are sequentially arranged and stacked; the upper end plate and the lower end plate are respectively connected to both end faces of the wind guide cover. Further preferably, the connection between the upper end plate, the lower end plate and the wind guide cover is fixedly connected by fasteners.

[0016] Preferably, the wind guide cover is a U-shaped frame structure, and the air-cooling fan is disposed at the bottom of the U-shaped frame structure. After the stack is assembled, the bottom of the U-shaped frame structure provided with the air-cooling fan is arranged opposite to the opening direction of the air-cooling flow channel on the stack core.

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

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

[0019] A thermal management design method for an air-cooled fuel cell stack, based on the structure of the above-mentioned air-cooled fuel cell stack, optimizes the opening size of the air-cooling flow channel and the specifications of the matching cooling fan by calculating the heat generation of the stack and matching the specifications of the cooling fan, so as to realize the thermal management design of the air-cooled fuel cell stack.

[0020] The above-mentioned thermal management design method for an air-cooled fuel cell stack analyzes the heat generation of the stack through theoretical calculation, so as to optimize the actual design size of the air-cooling channel. After determining the size of the air-cooling channel, the fan is matched and selected again in combination with the fan P-Q curve to realize the heat management design of the stack.

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

[0022] S01. Given the parameters of the initial air-cooling flow channel, including the height d, width w, length l of the air-cooling flow channel, and N ch is the number of air-cooling flow channels, and N cell is the number of single cells;

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

[0024] The heat Q generated when the stack is working h is:

[0025]

[0026] P = VI

[0027]

[0028] Among them, Q h is the heat generated during the operation of the stack, V is the rated voltage of the stack during operation, I is the rated current generated during operation, P is the rated power of the stack during operation, Er is the Nernst reversible electromotive force considering temperature correction, P a is the anode inlet gas pressure, P c 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);

[0029] S03. Perform the fan selection calculation for air-cooled channel heat dissipation:

[0030] Select an axial fan with a suitable diameter according to the stack size. The technical specification of the fan is the inlet area A fan such that the static pressure P S required to be provided by the fan and the inlet area A fan of the fan conform to the following relationship:

[0031]

[0032] Among them, Ps is the static pressure required to be provided by the fan, A fan is the inlet area of the fan, ρ is the density of the oncoming air, u is the average flow velocity in the air-cooled channel, A ch is the cross-sectional area of the channel in the direction perpendicular to the air flow, and ΔP is the minimum pressure drop in the channel to meet the heat dissipation requirement;

[0033] Then, determine the operating point of the fan through the intersection of the air-cooled flow field impedance curve and the fan characteristic curve, and determine whether it meets the design requirements according to the flow rate provided by the fan at the operating point;

[0034] S04. Thermal simulation verification of the cathode closed air-cooled fuel cell stack:

[0035] After specifying the structural parameters of the initial air-cooled channel and performing theoretical calculations of heat generation and heat dissipation, match a suitable air-cooled fan for heat dissipation, and then use numerical simulation technology to confirm whether the fan to be selected can meet the heat dissipation target of the stack;

[0036] S05. Selection calculation of the cross-sectional size of the air-cooled channel:

[0037] According to the heat parameter Q h generated during the operation of the stack and the temperature difference (T out - Tin ) Optimize the actual design dimensions of the air cooling channels. After determining the dimensions of the air cooling channels, reselect the fan in combination with the fan P-Q curve to complete the thermal management design of the cathode closed-air-cooled fuel cell stack.

[0038] Preferably, in step S05, the specific steps for optimizing the actual design dimensions of the air cooling channels are as follows: Based on the cross-sectional dimensions of the air cooling channels to obtain the best heat dissipation effect of the stack, optimize the reference design dimensions of the air cooling flow channels in combination with the heat generation theory calculation, fan selection calculation, and stack thermal simulation verification process; the inlet cross-sectional area of the air cooling flow channel is determined by the height d and width w of the flow channel. After considering the plate support strength and ease of processing factors, the specific calculation method is as follows:

[0039]

[0040] where Q h is the heat generated during the operation of the stack, T out is the outlet temperature of the stack, T in is the air temperature inhaled by the stack under standard conditions, d is the height of the air cooling flow channel, w is the width of the air cooling flow 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 cooling flow channel.

[0041] Preferably, in the present invention, by regarding the fuel cell as a heat exchanger with an internal heat source, the overall heat balance relationship of the stack during stable operation is:

[0042] Q h = Q water + Q gas + Q rad

[0043] In the formula, Q h is the heat generated during the operation of the stack, Q water , Q gas , Q rad respectively represent the heat dissipation power of the cooling water, the heat loss power of the tail gas, and the heat carried away by radiation; in the air-cooled stack, there is no cooling water, and the heat in the stack is mainly carried away by the forced convection of the inlet gas. At the same time, the heat carried away by the natural convection heat transfer and radiation heat dissipation between the outer surface of the battery and the ambient atmosphere is limited and can be ignored.

[0044] The heat Q gas carried away by the heat loss power of the tail gas is equal to the difference between the heat carried by the gas leaving the stack and the heat carried by the gas entering the stack:

[0045] Q gas = CωΔT

[0046] 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;

[0047] The heat Q carried away by the radiation rad The calculation is given by the blackbody radiation law:

[0048]

[0049] where δ is the emissivity, σ is the blackbody radiation constant, Q stack is the surface area of the stack, T is the battery operating temperature, and T0 is the ambient temperature.

[0050] Preferably, in step S03,

[0051] Based on the parameters given for the initial air-cooled flow channels in step S01, including the height d, width w, length l of the air-cooled flow channels, N ch is the number of air-cooled flow channels, and N cell is the number of single cells;

[0052] The total convective heat transfer area A of the internal air-cooled flow channels of the stack con is:

[0053] A con = 2dwlN ch N cell

[0054] The cross-sectional area A of the channels in the direction perpendicular to the air flow direction ch is:

[0055] A ch = dwN ch N cell

[0056] The qualitative temperature ω of the gas in the air-cooled flow channels m is:

[0057]

[0058] The convective heat transfer coefficient h of the inner surface of the air-cooled flow channels f is:

[0059]

[0060] The equivalent diameter d of the air-cooled flow channels e is:

[0061]

[0062] The Nusselt number Nu corresponding to the forced convective heat transfer in the air-cooled flow channels u is:

[0063]

[0064] where k airis the forced convection heat transfer coefficient of air;

[0065] The qualitative temperature is T m If the dimensionless Prandtl number of air under is a constant, the dimensionless Reynolds number Re of the gas flow in the reactor is:

[0066]

[0067] The average flow velocity u in the air-cooled flow channel is:

[0068]

[0069] The air volume flow rate that needs to be provided by the fan is:

[0070]

[0071] The minimum pressure drop ΔP in the flow channel when the heat dissipation requirement is met is:

[0072]

[0073] In step S04, during the thermal simulation of the fuel cell stack, the membrane electrode is used as the heat source, the flow fields of the anode and cathode reaction gases are ignored, and the fan model is used to simulate the temperature field distribution effect inside the fuel cell stack at different duty cycles.

[0074] In step S05, the heat Q generated when the fuel cell stack is operating h is derived as follows:

[0075] Q h = Cω(T out - T in )

[0076] where ω is the inlet mass flow rate of the air-cooled flow channel, C is the specific heat of the gas, T out is the outlet temperature of the fuel cell stack, and T in is the air temperature inhaled by the fuel cell stack under standard conditions;

[0077] The calculation method of the inlet mass flow rate ω of the air-cooled flow channel is:

[0078] ω = A ch u = dwu

[0079] Assuming that the flow state of the air entering the air-cooled flow channel is laminar and the dimensionless Reynolds number Re = 2000, the design reference basis for the heat generation of the fuel cell stack and the cross-sectional size of the air-cooled flow channel can be obtained:

[0080]

[0081] The technical solution of the present invention has the following beneficial effects compared with the prior art:

[0082] Existing air cooling methods are usually applied to low-power fuel cell systems. The ambient air is directly pumped into the cathode flow channel by a fan. The cathode gas supply system and the cooling system are integrated. The air flowing in the cathode flow field provides the required oxygen for the electrochemical reaction and acts as a cooling medium at the same time. There is no intake humidification device, and the structure of the fuel cell system is greatly simplified. However, the high-velocity airflow will carry away a large amount of water in the stack, drying the proton exchange membrane, resulting in a large ohmic loss and reducing the performance of the stack. Therefore, the cathode closed-air-cooled fuel cell stack of the present invention can solve the problems existing in the cathode open-air-cooled fuel cell plate structure, such as the difficulty in balancing oxygen and membrane water content, environmental sensitivity, and unstable performance, improving the stack performance and extending the service life.

[0083] Moreover, the present invention provides a thermal management design method for the air-cooled fuel cell stack. Based on the structure of the above-mentioned cathode closed-air-cooled fuel cell stack, by calculating the heat generation of the stack and matching the specifications of the cooling fan, the opening size of the air-cooled flow channel and the specifications of the matching cooling fan are optimized, so as to realize the thermal management design method of the cathode closed-air-cooled fuel cell stack. Description of the Drawings

[0084] Figure 1 It is a structural diagram of the air-cooled fuel cell stack plate in the embodiment of the present invention;

[0085] Figure 2 It is an assembly schematic diagram of the air-cooled fuel cell stack plate and the membrane electrode in the embodiment of the present invention;

[0086] Figure 3 It is an exploded view of the air-cooled fuel cell stack in the embodiment of the present invention;

[0087] Figure 4 It is a thermal management design technical route diagram of the air-cooled fuel cell stack in the embodiment of the present invention;

[0088] Figure 5 It is a P-Q curve diagram of the system impedance of the air-cooled fuel cell stack and the fan to be selected in the embodiment of the present invention;

[0089] Figure 6 It is a temperature field distribution diagram of the air-cooled fuel cell stack in the embodiment of the present invention; among them, a is the temperature field distribution effect diagram of the stack core when the fan duty ratio is 50%, and b is the temperature field distribution effect diagram of the stack core when the fan duty ratio is 100%.

[0090] Figure 7 It is a polarization performance diagram of the air-cooled fuel cell stack in the embodiment of the present invention;

[0091] Figure 8This is the result graph of the average temperature and its temperature difference at the inlet and outlet of the stack corresponding to the polarization performance in the embodiments of the present invention. Detailed implementation manners

[0092] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0093] It should be noted that if there are directional indications (such as up, down, left, right, front, back, top, bottom...) involved in the embodiments of the present invention, the directional indications are only used to explain the relative positional relationship and movement conditions between components in a specific posture (as shown in the drawings). If the specific posture changes, the directional indications will also change accordingly.

[0094] In this application, unless otherwise clearly defined and limited, the terms "installed", "connected", "connected", "fixed", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. It can be the internal communication of two components or the interaction relationship between two components, unless otherwise clearly limited. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific situations.

[0095] It should be noted that when an element is referred to as "fixed to" or "disposed on" another element, it can be directly on the other element or there can also be an intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time.

[0096] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" can explicitly or implicitly include at least one of such features. In addition, the technical solutions between various embodiments can be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present invention.

[0097] At present, existing open-cathode air-cooled fuel cell stacks have problems such as difficulty in balancing oxygen and membrane water content, environmental sensitivity, and unstable performance. To solve the above technical problems, the present invention proposes a core of an air-cooled fuel cell stack, a fuel cell stack, and a thermal management design method thereof. The air-cooled fuel cell stack of the present invention is a closed-cathode air-cooled fuel cell stack. Through the design of the plate structure and the supporting thermal management technology, the problems of existing open-cathode air-cooled fuel cell stacks, such as difficulty in balancing oxygen and membrane water content, environmental sensitivity, and unstable performance, are solved, the performance of the fuel cell stack is improved, and the service life of the fuel cell stack is extended.

[0098] Embodiment

[0099] Combined with Figures 1 to 3 As shown, the embodiment of the present invention provides a core and a fuel cell stack of an air-cooled fuel cell stack.

[0100] As Figure 1 And Figure 2 As shown, a core 10 of an air-cooled fuel cell stack includes a plurality of bipolar plates 11 and a plurality of membrane electrodes 12 stacked in sequence; the bipolar plate 11 is composed of an anode plate 111 and a cathode plate 112, and a hydrogen gas 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-cooled flow channel 115 is provided between the anode plate 111 and the cathode plate 112.

[0101] Preferably, the bipolar plate 11 is provided with a hydrogen gas inlet 116, a hydrogen gas outlet 117, an air inlet 118, and an air outlet 119. Further preferably, the hydrogen gas inlet 116 and the air outlet 119 are provided at one end of the bipolar plate 11, and the air inlet 118 and the hydrogen gas outlet 117 are provided at the other end of the bipolar plate 11.

[0102] Further preferably, the air-cooled flow channel 115 is provided at one end of the anode plate 111 close to the cathode plate 112, and the cathode plate 112 covers the air-cooled flow channel 115 to form a sealed air-cooled flow channel where the air-cooled flow channel 115 does not contact the membrane electrode 12, which is used for heat dissipation of the fuel cell stack.

[0103] Preferably, the opening direction of the air-cooled flow channel 115 is opposite to the air supply direction of the air-cooled fan 20.

[0104] The core 10 of the cathode-closed air-cooled fuel cell stack of the present invention forms closed cavities for the cathode chamber and the anode chamber after the bipolar plate 11 and the membrane electrode 12 are bonded together, ensuring good stability of the electrochemical reaction. The air-cooling channels 115 are located in the middle of the bipolar plate 11, avoiding direct contact with the membrane electrode 12, preventing the membrane drying problem of the cathode-open air-cooled stack, reducing sensitivity to environmental humidity and temperature, and enhancing adaptability.

[0105] As Figure 3 shown, an air-cooled fuel cell stack includes the above-mentioned core 10.

[0106] Preferably, the air-cooled fuel cell stack includes a core 10, a wind guide cover 30, and an air-cooling fan 20. The wind guide cover 30 is arranged outside the core 10, and the air-cooling fan 20 is arranged on the wind guide cover 30. Further preferably, the opening direction of the air-cooling channels 115 on the core 10 is opposite to the air supply direction of the air-cooling fan 20.

[0107] Preferably, the air-cooled fuel cell stack includes a wind guide cover 30, an air-cooling fan 20, and an upper end plate 40, an upper insulating plate 50, an upper current collector plate 60, a core 10, a lower current collector plate 70, a lower insulating plate 80, and a lower end plate 90 arranged and stacked in sequence; the upper end plate 40 and the lower end plate 90 are respectively connected to both end faces of the wind guide cover 30. Further preferably, the connection between the upper end plate 40, the lower end plate 90 and the wind guide cover 30 is fixedly connected by fasteners 31.

[0108] Preferably, the wind guide cover 30 is of a U-shaped frame structure, and the air-cooling fan 20 is arranged at the bottom of the U-shaped frame structure. After the stack is assembled, the bottom of the U-shaped frame structure with the air-cooling fan 20 is arranged opposite to the opening direction of the air-cooling channels 115 on the core 10.

[0109] Preferably, the air-cooling fan 20 is preferably an axial flow fan.

[0110] As Figure 4 shown, the thermal management design method of the above-mentioned air-cooled fuel cell stack, which conducts the calculation of the heat generation of the stack and the specification matching of the cooling fan, includes the following steps:

[0111] First, according to the input requirements of the fuel cell stack, input the rated operating voltage, rated operating current density, and the number of single cell sheets in the stack.

[0112] S01. Given and evaluate the parameters of the initial air-cooling channels, including the height d, width w, length l of the air-cooling channels, N ch is the number of air-cooling channels, N cell is the number of single cells;

[0113] S02. Calculate the heat generation and heat dissipation of the air-cooled fuel cell stack:

[0114] The heat Q generated during the operation of the stack h is:

[0115]

[0116] P = VI

[0117]

[0118] Q gas = CωΔT

[0119]

[0120] Among them, Q h is the heat generated during the operation of the stack, V is the rated operating voltage of the stack, I is the rated current generated during operation, P is the rated power of the stack during operation, Er is the Nernst reversible electromotive force considering temperature correction, P a is the anode inlet gas pressure, P c is the cathode inlet gas pressure, R is the universal gas constant (8.314 J / (mol·K)), F is the Faraday constant (96485 C / mol); Q gas is the heat carried away by the exhaust gas heat dissipation power; C is the specific heat of the gas, ω is the mass flow rate of the gas, ΔT is the temperature difference between the inlet and outlet; Q rad is the heat carried away by radiation, δ is the emissivity, σ is the Stefan-Boltzmann constant, A stack is the surface area of the stack, T is the battery operating temperature, and T0 is the ambient temperature.

[0121] The rated condition of a single cell in the air-cooled fuel cell stack is 0.76 V@1.3 A / cm 2 , with a total of 10 pieces. The key parameters involved in the theoretical calculation of heat dissipation and heat generation are shown in Table 1.

[0122] Table 1 Key parameters involved in the theoretical calculation of heat dissipation and heat generation

[0123]

[0124] S03. Conduct the fan selection calculation for the air-cooled channel heat dissipation:

[0125] Based on the parameter setting of the initial air-cooled channel in step S01, including the height of the air-cooled channel being d, the width being w, the length being l, N ch is the number of air-cooled channels, and N cell is the number of single cells;

[0126] The total convective heat transfer area A of the internal air-cooled channels of the stackcon is:

[0127] A con = 2dwlN ch N cell ;

[0128] The cross-sectional area A of the channel in the direction perpendicular to the air flow direction ch is:

[0129] A ch = dwN ch N cell ;

[0130] If the convective heat transfer temperature difference is taken as ΔT = 10K, then the characteristic temperature T of the gas in the air-cooled channel m is:

[0131]

[0132] The convective heat transfer coefficient (i.e., the forced convective heat transfer coefficient) h on the inner surface of the air-cooled channel f is:

[0133]

[0134] The equivalent diameter d of the air-cooled channel e is:

[0135]

[0136] The Nusselt number N corresponding to the forced convection heat transfer in the air-cooled channel u is:

[0137]

[0138] Assuming the flow is laminar, the Reynolds number Re of the flow can be derived and determined by the dimensionless Prandtl number Pr (this number is determined by the characteristic temperature T m and is a constant at a certain temperature), and is:

[0139]

[0140] The characteristic temperature T m The density ρ and dynamic viscosity μ of air at this temperature are constants, and can be obtained by obtaining the physical properties of air at the corresponding temperature. Then the average flow velocity (i.e., the flow rate provided by the fan) u in the air-cooled channel is:

[0141]

[0142] The volume flow rate of air that needs to be provided by the fan (i.e., the air volume that satisfies the minimum pressure drop) is:

[0143]

[0144] When the heat dissipation requirement is met, the minimum pressure drop ΔP in the flow channel is as follows:

[0145]

[0146] Select an axial flow fan with a suitable diameter according to the stack size, and calculate the static pressure Ps that the fan needs to provide as follows:

[0147] Table 2 Calculation results of fan selection

[0148]

[0149] As shown in Table 2 are the calculation results of fan selection corresponding to an air-cooled flow channel structure designed in Example 1. As Figure 5 shown, the intersection point of the air-cooled flow field impedance curve and the fan characteristic curve in the figure is the operating point of the fan. When the duty cycle of the fan is 100%, the air flow rate provided by the fan to the stack is 3.1 m 3 / min, which is greater than the required 2.542 m 3 / min of the stack, and the selected fan meets the design requirements.

[0150] S04. Thermal simulation verification of the cathode closed air-cooled fuel cell stack:

[0151] After giving the structural parameters of the initial air-cooled channel and performing theoretical calculations of heat generation and heat dissipation, a suitable heat dissipation air-cooled fan is matched. Then, through numerical simulation technology, it is confirmed whether the fan to be selected can meet the heat dissipation target of the stack; during the thermal simulation of the stack, the membrane electrode is used as the heat source, the flow fields of the anode and cathode reaction gases are ignored, and the fan model is used to simulate the temperature field distribution effect inside the stack at different duty cycles.

[0152] Table 3 Obtaining the battery heat source after simulation post-processing

[0153]

[0154] As shown in Table 3 are the heat sources inside each component of the single cell obtained after simulation post-processing, which are used as the heat sources given when using the fan model in thermal simulation. During thermal simulation, the temperature field distribution of the stack core is compared when the duty cycles of the selected fan are 50% and 100% respectively. As Figure 6 (a) shows the temperature field distribution effect of the stack core when the duty cycle of the fan is 50%, Figure 6 (b) is the temperature field distribution effect of the stack core when the duty cycle of the fan is 100%.

[0155] When the fan duty cycle is 50%, the average core temperature is 69.7°C, the maximum temperature is 94.9°C, the average static pressure at the outlet is 393 Pa, the average extraction wind speed is 16.32 m / s, and the heat dissipation of the fan is 351 W;

[0156] When the fan duty cycle is 100%, the average core temperature is 47.6°C, the maximum temperature is 61.7°C, the average static pressure at the outlet is 433 Pa, the average extraction wind speed is 17.69 m / s, and the heat dissipation of the fan is 570 W.

[0157] Through the simulation results, it is verified that the temperature field distribution effect of the core of the cathode closed air-cooled battery stack is reasonable and the overall heat dissipation performance meets the standard when the fan duty cycle is 50% and 100%, and the involved scheme can be output.

[0158] Measured performance of the closed air-cooled stack prototype

[0159] As Figure 7 and Figure 8 show the polarization performance and temperature performance of the closed air-cooled stack prototype under actual measurement. Among them, polarization 1 was carried out at a reaction gas inlet temperature of 70°C, an anode relative humidity (RH) of 40%, a cathode relative humidity of 60%, an anode inlet pressure of 140 KPa, a cathode inlet pressure of 130 KPa, a cathode stoichiometric ratio of 1.6, an anode stoichiometric ratio of 3.7, and a room temperature of 25°C; the corresponding conditions for polarization 2 are 65°C, 40 / 60 RH, 140 / 130 KPa, 1.6 / 2.2; the corresponding conditions for polarization 3 are 65°C, 40 / 60 RH, 95 / 75 KPa, 1.6 / 2.2. Judging from the performance, the performance of the stack is close under the three polarization test conditions, and the output voltage at a current density of 1.2 is about 0.7 V. The whole stack contains 10 membrane electrodes with an active area of 300 cm 2 , the stack output power is 2.52 kW. Considering Figure 8 the obtained temperature performance, the inlet and outlet temperatures are greatly affected by the test conditions. The highest outlet temperature is about 81°C under the polarization 1 condition, and the temperature difference between the inlet and outlet is about 13°C at this time. The performance and temperature performance meet the structural and thermal management design methods of this closed air-cooled stack.

[0160] The existing air cooling method is usually applied to low-power fuel cell systems. The ambient air is directly pumped into the cathode flow channel by a fan. The cathode air supply system and the cooling system are integrated. The air flowing in the cathode flow field provides the required oxygen for the electrochemical reaction and acts as a cooling medium at the same time. There is no intake humidification device, and the structure of the fuel cell system is greatly simplified. However, the high-velocity air flow will carry away a large amount of water in the stack, drying the proton exchange membrane, resulting in a large ohmic loss and reducing the performance of the stack. Therefore, the cathode closed-air-cooled fuel cell stack of the present invention can solve the problems existing in the cathode open-air-cooled fuel cell plate structure, such as the difficulty in balancing the oxygen and membrane water content, environmental sensitivity, and unstable performance, improving the stack performance and extending the service life.

[0161] Moreover, the present invention provides a thermal management design method for the air-cooled fuel cell stack. Based on the structure of the above-mentioned cathode closed-air-cooled fuel cell stack, by calculating the heat generation of the stack and matching the specifications of the cooling fan, the opening size of the air-cooled flow channel and the matching specifications of the cooling fan are optimized, so as to realize the thermal management design method of the cathode closed-air-cooled fuel cell stack.

[0162] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

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

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

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

6. An air-cooled fuel cell stack, characterized in that: A core comprising the core described in any one of claims 1 to 5.

7. The air-cooled fuel cell stack according to claim 6, characterized in that: It includes a core, an air guide cover and an air-cooling fan. The air guide cover is arranged on the outside of the core, and the air-cooling fan is arranged on the air guide cover; the opening direction of the air-cooling flow channel on the core is opposite to the air supply direction of the air-cooling fan.

8. The air-cooled fuel cell stack according to claim 6, characterized in that: The air-cooled fuel cell stack comprises an air duct, an air-cooling fan, and an upper end plate, an upper insulating plate, an upper current collecting plate, a core, a lower current collecting plate, a lower insulating plate, and a lower end plate which are stacked in sequence; the upper end plate and the lower end plate are respectively connected to the two end surfaces of the air duct. Further preferably, the upper end plate, the lower end plate and the air duct are fixedly connected by fasteners.

9. A thermal management design method for an air-cooled fuel cell stack, characterized in that: The specific steps include: S01. The parameters of the initial air-cooling channel are given, including the height of the air-cooling channel as d, the width as w, the length as l, and N ch is the number of air cooling channels, N cell is the number of single batteries; S02. Calculate the heat generation and heat dissipation of the air-cooled fuel cell stack: The heat generated when the battery stack is working is Q h for: P=VI Among them, Q h is the heat generated when the battery stack is working, V is the rated voltage of the battery stack, I is the rated current generated when working, P is the rated power of the battery stack when working, Er is the Nernst reversible electromotive force considering temperature correction, P a is the anode inlet gas pressure, P c is the cathode inlet gas pressure, R is the universal gas constant, and F is the Faraday constant; S03. Calculate the fan selection required for air-cooling channel heat dissipation: Select an axial fan with a suitable diameter according to the size of the battery stack. The technical specifications of the fan are as follows: air inlet area A fan , so that the fan needs to provide a static pressure P S The air inlet area of ​​the fan is A fan The following relationship exists between them: Among them, Ps is the static pressure that the fan needs to provide, A fan The air inlet area of ​​the fan, ρ is the density of the incoming air, u is the average flow velocity in the air cooling channel, A ch is the cross-sectional area of ​​the channel in the direction perpendicular to the air flow, and ΔP is the minimum pressure drop in the flow channel when the heat dissipation requirement is met; Then, the intersection of the air-cooling flow field impedance curve and the fan characteristic curve is determined as the fan operating point, and whether the design requirements are met is determined based on the flow rate provided by the fan at the operating point; S04. Thermal simulation verification of cathode sealed air-cooled fuel cell stack: The structural parameters of the initial air-cooling channel are given and the heat generation and heat dissipation are calculated theoretically to match the appropriate heat dissipation air-cooling fan. Then, numerical simulation technology is used to confirm whether the fan to be selected can meet the heat dissipation target of the fuel cell stack. S05. Calculation of air cooling channel cross-section size: According to the heat parameter Q generated when the battery stack is working h and the inlet and outlet temperature difference (T out -T in ) is used to optimize the actual design size of the air cooling channel. After determining the size of the air cooling channel, the fan is matched and selected again in combination with the fan PQ curve to complete the thermal management design of the cathode closed 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 actual design size of the air cooling channel is optimized, and the specific steps are as follows: based on the cross-sectional size of the air cooling channel to obtain the best heat dissipation effect of the battery stack, the reference design size of the air cooling channel is optimized in combination with the heat generation theory calculation, fan selection calculation and battery stack thermal simulation verification process; the inlet cross-sectional area of ​​the air cooling channel is determined by the height d and width w of the channel. After satisfying the plate support strength and easy processing factors, the specific calculation method is as follows: Among them, Q h The heat generated when the battery stack is working, T out is the stack outlet temperature, T in is the air temperature of the stack under standard conditions, d is the height of the air-cooling channel, w is the width of the air-cooling 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-cooling channel.

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