Closed fuel cell air cooling electric pile

Abstract

The invention provides a closed fuel cell air cooling pile. A first cooling plate and a second cooling plate are respectively connected to a corresponding anode plate and a corresponding cathode plate. Cooling media with the same flowing direction are arranged on the surfaces of the first cooling plate and the second cooling plate, a plurality of cathode flow channels are distributed on the surface of the side, facing the circulating section film electrode, of the cathode plate in the flowing direction of the cooling media, and in the cathode flow channels, the flow direction of the cooling media is larger than that of the cathode flow channels in the flowing direction of the cooling media. And the flow section of the cathode flow channel located at the upstream is larger than that of the cathode flow channel located at the downstream. Under the condition that the upstream and the downstream of a cooling flow field have temperature difference, non-uniformly distributed flow channel flow sections are adopted, so that the flow velocities of reactant media in different flow channels are different, the amount of taken-away moisture is different, the blow-drying speeds of all parts of the membrane electrode are relatively consistent, the humidity of all parts of the membrane electrode is more balanced, and the quality of the membrane electrode is improved. And the reaction efficiency and the cell performance of the fuel cell are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fuel cell stacks, in particular to a closed fuel cell air-cooled stack. BACKGROUND

[0002] A fuel cell is a power generation device that directly converts the chemical energy of fuel and oxidant into electrical energy through an electrochemical reaction. Heat dissipation of the stack is crucial to ensure the normal operation of the fuel cell. The prior art can achieve stack heat dissipation through liquid cooling. For example, the stack structure of a liquid-cooled fuel cell is formed by stacking a membrane electrode and a bipolar plate in sequence, the bipolar plate is formed by stacking and bonding an anode plate and a cathode plate, the front surface of the anode plate is provided with a hydrogen flow field, and the front surface of the cathode plate is provided with an air flow channel. The air flow channel is composed of a plurality of air flow channel grooves, and the back surface of the cathode plate is provided with a cooling liquid flow channel composed of a plurality of cooling liquid flow channel grooves. However, due to the complex, cumbersome and heavy structure of the water cooling system, it is difficult to adapt to various application scenarios. In order to improve this defect, air can be used as a cooling medium instead of water. For example, an air-cooled fuel cell includes a plate body and a cooling flow channel disposed in the plate body and penetrating through the plate body. However, due to the extremely small heat capacity of air, the temperature difference between the inlet and outlet of the cooling flow field is large.

[0003] The relative humidity of the membrane electrode affects the performance of the fuel cell. The calculation formula of the relative humidity of the membrane electrode is:

[0004] Relative humidity = actual water vapor pressure / saturated water vapor pressure.

[0005] Due to the flow of the cooling medium, the temperature of the upstream of the cooling flow field is low, and the temperature of the downstream is high. The saturated water vapor pressure is positively correlated with the temperature, so the saturated water vapor pressure of the cathode flow field area corresponding to the low-temperature region of the upstream of the cooling flow field is low, and the saturated water vapor pressure of the cathode flow field area corresponding to the high-temperature region of the downstream of the cooling flow field is high. According to the calculation formula of the relative humidity, it can be understood that under the condition that the actual water vapor pressure is the same, the smaller saturated water vapor pressure makes the relative humidity of the cathode flow field area corresponding to the low-temperature region of the upstream of the cooling flow field larger, and the larger saturated water vapor pressure makes the relative humidity of the cathode flow field area corresponding to the high-temperature region of the downstream of the cooling flow field smaller. Therefore, the temperature difference between the inlet and outlet of the cooling medium flow field will cause the water content (relative humidity) of the membrane electrode to deviate from the ideal state, thereby affecting the reaction efficiency and performance of the fuel cell.

[0006] Therefore, there is a need for a new technical solution that can make the relative humidity of the membrane electrode in an ideal state under the condition that the temperature difference between the inlet and outlet of the cooling flow field is large, so as to improve the reaction efficiency and performance of the fuel cell. SUMMARY

[0007] The application provides a closed fuel cell air-cooled stack, solves the problem of membrane electrode relative humidity imbalance caused by large temperature difference between the inlet and outlet of the cooling flow field, and can improve the membrane electrode relative humidity balance, keep the membrane electrode relative humidity in an ideal state, and further improve the reaction rate and performance of the fuel cell.

[0008] The application provides a closed fuel cell air-cooled stack, which comprises a plurality of fuel cell single cells arranged in stacks and a plurality of cooling plates.

[0009] Each fuel cell single cell comprises an anode plate, a cathode plate and a membrane electrode between the anode plate and the cathode plate; the anode plate of at least part of the fuel cell single cells is provided with a first cooling plate away from the corresponding membrane electrode, and the cathode plate of at least part of the fuel cell single cells is provided with a second cooling plate away from the corresponding membrane electrode; the first cooling plate and the second cooling plate are respectively connected to the corresponding anode plate and cathode plate. The surfaces of the first cooling plate and the second cooling plate are provided with cooling medium with the same flow direction, the surface of the cathode plate on the side facing the membrane electrode is distributed with a plurality of cathode flow channels along the cooling medium flow direction, and among the plurality of cathode flow channels, the flow cross section of the cathode flow channel located upstream is greater than the flow cross section of the cathode flow channel located downstream along the cooling medium flow direction.

[0010] The application can separate the cooling medium (for example, air) from the oxidant (for example, air) by arranging the first cooling plate on the side of the cathode plate away from the membrane electrode, and because the temperature of the cooling medium gradually increases along the flow direction of the cooling medium, there is a temperature distribution unevenness, the application arranges the flow passage section of the cathode flow channel to be: along the flow direction of the cooling medium, the flow passage section of the upstream cathode flow channel is greater than the flow passage section of the downstream cathode flow channel, or it can be understood that the flow passage section of the cathode flow channel close to the upstream of the cooling flow field is greater than the flow passage section of the cathode flow channel close to the downstream of the cooling flow field, the size of the flow passage section affects the flow rate of the reactant medium, that is, the average flow rate, that is, the greater the flow passage section, the faster the flow rate, the smaller the flow passage section, the slower the flow rate, and then the relative humidity adjustment capability of the membrane electrode is affected, the relative humidity is small at the downstream of the cooling medium with high temperature, the flow rate is slow with small flow passage section, and the humidity carried is small; the relative humidity is large at the upstream of the cooling medium with low temperature, the flow rate is fast with large flow passage section, and the humidity carried is large, in the case that there is a temperature difference between the upstream and downstream of the cooling flow field, the non-uniformly distributed flow passage section of the flow channel is adopted to make the average flow rate of the reactant medium in different flow channels different, and then the amount of humidity carried is different, so that the drying speed of the membrane electrode is more uniform, thereby the water content adjustment capability gradient compensation of the membrane electrode under a large temperature difference is realized, the humidity of the membrane electrode is more balanced, the relative humidity of the membrane electrode is in an ideal state, and then the reaction efficiency of the fuel cell and the cell performance are improved. Although the fast flow rate of the upstream cathode flow channel and the slow flow rate of the downstream cathode flow channel can further cause the temperature difference to expand a little, that is, the temperature difference is reversely compensated, but the influence on the humidity balance is not large.

[0011] Optionally, along the flow direction of the cooling medium, the flow passage sections of the plurality of cathode flow channels are gradually decreased.

[0012] Optionally, among the plurality of cathode flow channels, the plurality of cathode flow channels include a first flow channel group and a second flow channel group, the first flow channel group is located upstream in the flow direction of the cooling medium, and the second flow channel group is located downstream in the flow direction of the cooling medium.

[0013] The flow passage section of each cathode flow channel of the first flow channel group is greater than the flow passage section of each cathode flow channel of the second flow channel group.

[0014] Optionally, the flow passage sections of each cathode flow channel in the first flow channel group are the same, and the flow passage sections of each cathode flow channel in the second flow channel group are the same.

[0015] Optionally, in each fuel cell single cell, the anode flow field is between the anode plate and the membrane electrode, and the cathode flow field is between the cathode plate and the membrane electrode.

[0016] The flow direction of the fluid in the anode flow field is opposite to the flow direction of the fluid in the cathode flow field.

[0017] The application can balance the humidity of the cathode flow field and the anode flow field by the opposite flow of the cathode flow field and the anode flow field, so that the membrane electrode has better humidity balance, which is beneficial to the working performance of the battery.

[0018] Optionally, the first end of the anode plate is provided with an anode fluid inlet, and the second end of the anode plate is provided with an anode fluid outlet.

[0019] The first end of the cathode plate is provided with a cathode fluid outlet, and the second end of the cathode plate is provided with a cathode fluid inlet.

[0020] Optionally, the first cooling plate and the second cooling plate are wave-shaped plates.

[0021] Optionally, the application further comprises an upper pressing plate, a lower pressing plate and a fastener.

[0022] The upper pressing plate is arranged on the upper side of the fuel cell single cells and the cooling plates in the stacking direction, the lower pressing plate is arranged on the lower side of the fuel cell single cells and the cooling plates in the stacking direction, and the fastener is fixed to the edges of the upper pressing plate and the lower pressing plate to press and fix the fuel cell single cells.

[0023] Optionally, the fluid between the anode plate and the membrane electrode is hydrogen, and the fluid between the cathode plate and the membrane electrode is air.

[0024] Optionally, the flow direction of the cathode flow channel is perpendicular to the flow direction of the cooling medium; the temperature in each cathode flow channel is uniform, the flow cross section from the inlet to the outlet in each cathode flow channel is the same, a plurality of cathode flow channels are arranged in parallel and share the inlet and outlet of the cathode flow field to keep the pressure difference of the inlet and outlet of the plurality of cathode flow channels consistent; the influencing factors of the size of the flow cross section of the cathode flow channel include the distance from the flow channel wall to the center of the flow channel, so that the size of the flow cross section in different cathode flow channels is positively correlated with the flow velocity, so as to keep the relative humidity of the membrane electrode balanced.

[0025] The flow direction of the cathode flow channel of the application is perpendicular to the cooling medium flow direction, the temperature in each cathode flow channel is uniform, and the flow cross section from the inlet to the outlet in each cathode flow channel is the same, the inlet and outlet of the plurality of parallel cathode flow channels are shared, the pressure difference of the inlet and outlet of the plurality of cathode flow channels is kept consistent, the size of the flow cross section of the cathode flow channel can be adjusted by changing the distance from the flow channel wall to the center of the flow channel, the corresponding flow rate of the cathode flow channel is changed, in the case that there is a temperature difference between the upstream and downstream of the cooling flow field, the cathode flow channel with a large flow cross section in the upstream of the cooling flow field has a fast flow rate and carries more moisture, the cathode flow channel with a small flow cross section in the downstream of the cooling flow field has a slow flow rate and carries less moisture, the drying speed of the membrane electrode is kept consistent, the relative humidity of the membrane electrode is balanced, the relative humidity of the membrane electrode is in an ideal state, and the fuel cell reaction efficiency and the battery performance are improved. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a partial structure schematic diagram of the closed fuel cell air-cooled stack of the embodiment of the application.

[0027] Figure 2 It is a structure schematic diagram of the closed fuel cell air-cooled stack of the embodiment of the application.

[0028] Figure 3 It is a schematic diagram of the arrangement of the plurality of cathode flow channels of the embodiment of the application.

[0029] Figure 4 It is a schematic diagram of the principle of fluid mechanics of the embodiment of the application.

[0030] Figure 5 It is a schematic diagram of the change of the depth of the cathode flow channel of the embodiment of the application.

[0031] BRIEF DESCRIPTION OF DRAWINGS:

[0032] 11: fuel cell single cell; 111: anode plate; 112: cathode plate; 113: membrane electrode; 114: cathode flow channel; 115A: first flow channel group; 115B: second flow channel group; 116: anode flow channel;

[0033] 121: first cooling plate; 122: second cooling plate;

[0034] 131: anode flow field; 132: cathode flow field; 133: anode fluid inlet; 134: anode fluid outlet; 135: cathode fluid inlet; 136: cathode fluid outlet;

[0035] L: cooling medium flow direction. DETAILED DESCRIPTION

[0036] The application will be described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments are implemented on the premise of the technical solutions of the application, and detailed implementation modes and specific operation processes are given, but the protection scope of the application is not limited to the following embodiments.

[0037] It should be noted that in the present specification, similar reference numbers and letters represent similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0038] In the description of the embodiments, it should be noted that the terms "upper", "lower", "inner", "bottom", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the application is usually placed, which is only for the convenience of describing the application and simplifying the description, and does not indicate or imply that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the application.

[0039] The terms "first", "second", etc. are only used for differentiation in description, and cannot be understood as indicating or implying relative importance.

[0040] In the description of the embodiments, it should also be noted that, unless otherwise explicitly specified and limited, the terms "provided", "connected", "connected" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be connected inside two elements. For those skilled in the art, the specific meaning of the above terms in the embodiments can be understood according to the specific circumstances.

[0041] In order to make the purpose, technical solutions and advantages of the application more clear, the embodiments of the application will be further described in detail below in conjunction with the drawings.

[0042] The application provides a closed fuel cell air-cooled stack, as shown in Figure 1 The closed fuel cell air-cooled stack includes a plurality of fuel cell single cells 11 arranged in stacks and a plurality of cooling plates (for example, first cooling plates 121 and second cooling plates 122). Each fuel cell single cell 11 includes an anode plate 111, a cathode plate 112 and a membrane electrode 113 between the anode plate 111 and the cathode plate 112. The anode plate 111 of at least part of the fuel cell single cells is provided with a first cooling plate 121 away from the corresponding cathode plate 112, and the cathode plate 112 of at least part of the fuel cell single cells is provided with a second cooling plate 122 away from the corresponding anode plate 111. The first cooling plate 121 and the second cooling plate 122 are respectively connected to the corresponding anode plate 111 and cathode plate 112.

[0043] In one embodiment, the outer side of the anode plate and the outer side of the cathode plate of each fuel cell single cell are provided with cooling plates. In one embodiment, the outermost fuel cell single cell in the entire air-cooled fuel cell stack is not provided with the first cooling plate and / or the second cooling plate.

[0044] In one embodiment, the fluid between the anode plate 111 and the membrane electrode 113 is hydrogen, and the fluid between the cathode plate 112 and the membrane electrode 113 is air.

[0045] The form and material of the first cooling plate 121 and the second cooling plate 122 are not limited, and in one embodiment, the first cooling plate 121 and the second cooling plate 122 are both corrugated plates (or can be understood as fin plates). In one embodiment, the first cooling plate 121 includes a partition plate and fins provided on the partition plate. The fins are welded to the partition plate, and the actual contact area can be increased by adding resistance welding points, or the actual heat dissipation capacity of the cathode plate and the anode plate can be improved by special cooling flow field plate feature design. Compared with the brazing form of the traditional fin heat exchanger, the contact and heat conduction capacity between the fins and the partition plate can be improved. In a further embodiment, the fins are perpendicular or close to perpendicular to the surface of the anode plate 111 or the cathode plate 112 to achieve wind cutting effect on the surface.

[0046] Specifically, in one embodiment, the first cooling plate 121 and the second cooling plate 122 are respectively connected to the corresponding anode plate 111 and cathode plate 112, which can be understood as follows: the edge of the first cooling plate 121 is connected to the edge of the anode plate 111 to form a cavity between them for cooling medium to flow through, and the edge of the second cooling plate 122 is connected to the edge of the cathode plate 112 to form a cavity between them for cooling medium to flow through. In other embodiments, the surface of the first cooling plate 121 facing the anode plate 111 is tightly attached to the surface of the anode plate 111, and the corrugated grooves on the first cooling plate 121 are for cooling medium to flow through. The surface of the second cooling plate 122 facing the cathode plate 112 is tightly attached to the surface of the cathode plate 112, and the corrugated grooves on the second cooling plate 122 are for cooling medium to flow through.

[0047] In one embodiment, as shown in FIG. 1, the first cooling plate 121 and the second cooling plate 122 are respectively connected to the corresponding anode plate 111 and cathode plate 112. Figure 1 and Figure 2As shown, the two opposite surfaces of the first cooling plate 121 and the second cooling plate 122 are provided with cooling medium with same flow direction. Or it can be understood that the cathode plate 112 separates the cathode flow field and the cooling flow field on both sides to avoid mixing of the fluids, and the anode plate 111 separates the anode flow field and the cooling flow field on both sides to avoid mixing of the fluids. The cathode plate 112 is provided with a plurality of cathode flow channels 114 on the side surface facing the membrane electrode 113. Among the plurality of cathode flow channels 114, the flow passage cross section of the cathode flow channel 114 located upstream is larger than the flow passage cross section of the cathode flow channel 114 located downstream along the cooling medium flow direction L. In one embodiment, the flow passage cross section of the cathode flow channel 114 located upstream is larger than the flow passage cross section of the cathode flow channel 114 located downstream along the cooling medium flow direction L. Figure 1 As can be seen, the flow direction L of the cooling medium is perpendicular to the extension direction of the flow channel. The flow passage cross section of the cathode flow channel 114 along the cooling medium flow direction L is equivalent to the cathode gas flow rate that can pass through the flow channel per unit time. The gaps between the flow channels are equal.

[0048] Specifically, the flow passage cross section of the cathode flow channel 114 located upstream is larger than the flow passage cross section of the cathode flow channel 114 located downstream, which can be specifically understood as follows: among the plurality of cathode flow channels 114 located upstream of the cooling flow field, the flow passage cross section of a single cathode flow channel 114 is larger than that of a single cathode flow channel 114 located downstream, and further more preferably, the flow passage cross section of all cathode flow channels 114 located upstream of the cooling flow field is larger than that of all cathode flow channels 114 located downstream of the cooling flow field.

[0049] As can be understood by those skilled in the art, the temperature of the cooling medium gradually increases along the cooling medium flow direction. In the conventional technology, the oxidant air and the cooling medium air are mixed in the same space, i.e., the air in the same space is used as both the oxidant and the cooling medium. At this time, if a large amount of air is used as both the oxidant and the cooling medium, the large flow rate of the cooling medium will take away the moisture of the membrane electrode, affecting the working performance of the membrane electrode. If the amount of air is reduced, the cooling effect is difficult to guarantee, and the problem of poor cooling effect is easy to occur. It can be seen that the prior art cannot simultaneously consider the working humidity requirement and the cooling requirement of the membrane electrode.

[0050] In order to solve the above problems, the present application provides a membrane electrode assembly and a fuel cell stack. Figure 1The embodiment shown is an example, the right side of the cathode plate 112 (upstream of the cooling medium) is a low temperature zone, the left side of the cathode plate 112 (downstream of the cooling medium) is a high temperature zone, the high temperature zone is easy to dry, the humidity is low, the low temperature zone is not easy to dry, the humidity is higher, the application can separate the cooling medium (such as air) and the oxidant (such as air) by arranging the first cooling plate 121 away from the membrane electrode 113 on one side of the cathode plate 112, and because the temperature of the cooling medium gradually increases along the flow direction of the cooling medium, there is a temperature distribution, the application sets the flow cross section between the cathode flow channels 114 to be: along the flow direction of the cooling medium, the flow cross section of the upstream cathode flow channel 114 is greater than the flow cross section of the downstream cathode flow channel 114, or it can be understood that the flow cross section of the cathode flow channel close to the upstream of the cooling flow field is greater than the flow cross section of the cathode flow channel close to the downstream of the cooling flow field, the non-uniform distribution of the flow channel flow cross section offsets the non-uniform distribution of the temperature, and the influence of the flow rate difference of the oxidant on the water content adjustment capability of the membrane electrode is utilized to compensate for the uneven water content of the membrane electrode caused by the temperature difference of the cooling medium, so that the drying speed of the membrane electrode is more uniform, thereby realizing gradient compensation of the heat dissipation capacity, making the temperature and humidity of the membrane electrode more balanced, and further improving the reaction efficiency of the fuel cell and the performance of the fuel cell.

[0051] Or it can be understood that, by different cathode flow channel duty ratios, the application utilizes the non-uniformity of the cathode reaction flow field flow rate and the metering ratio to offset the cooling medium (such as air) temperature gradient change with the heat dissipation capacity gradient change, and compensate for the influence of temperature difference on saturated vapor pressure and relative humidity, thereby reducing the relative humidity difference between the reaction areas of the cooling air upstream and downstream.

[0052] In an example embodiment, along the cooling medium flow direction L, the flow cross-sectional areas of the plurality of cathode flow channels 114 are sequentially decreased, preferably in a linear manner.

[0053] In another example embodiment, as shown in the figure, Figure 2 Among the plurality of cathode flow channels, the plurality of cathode flow channels 114 include a first flow channel group 115A and a second flow channel group 115B, the first flow channel group 115A is located upstream of the cooling medium flow direction L, and the second flow channel group 115B is located downstream of the cooling medium flow direction L. The flow cross section of each cathode flow channel of the first flow channel group 115A is greater than the flow cross section of each cathode flow channel of the second flow channel group 115B. Among them, the flow cross sections of the cathode flow channels in the first flow channel group 115A can be the same or different, and the flow cross sections of the cathode flow channels in the second flow channel group 115B can be the same or different. In an embodiment, as shown in the figure, Figure 2 The flow cross sections of each cathode flow channel in the first flow channel group 115A are the same, and the flow cross sections of each cathode flow channel in the second flow channel group 115B are the same.

[0054] Those skilled in the art can understand that the anode plate 111 can be provided with a plurality of anode flow channels, and the flow cross sections (or can be understood as the widths) of the plurality of anode flow channels can be the same as the layout of the cathode flow channels.

[0055] In one embodiment, as shown in FIG. 1, in each fuel cell single cell 11, the anode plate 111 and the membrane electrode 113 form an anode flow field 131, and the cathode plate 112 and the membrane electrode 113 form a cathode flow field 132. Figure 1

[0056] The flow direction of the fluid in the anode flow field 131 is opposite to that of the fluid in the cathode flow field 132.

[0057] Since the moisture generated upstream of the cathode flow field 132 will be carried downstream, the reverse arrangement of the anode flow field 131 and the cathode flow field 132 can bring the moisture downstream of the cathode back to the upstream of the cathode through the upstream of the anode to the downstream of the anode, thereby achieving uniform distribution of relative humidity.

[0058] As can be seen, through the opposite flow of the cathode flow field 132 and the anode flow field 131, the humidity difference of the cathode flow field 132 and the anode flow field 131 can be offset and complemented, thereby balancing the humidity of the cathode flow field 132 and the anode flow field 131, so that the membrane electrode 113 has better humidity balance, which is beneficial to the working performance of the battery. Or can be understood as, the embodiment of the present application can realize the optimization of temperature and humidity in the reaction area through the gradient compensation of heat dissipation capacity, the compensation of cathode flow field metering ratio, the compensation of anode flow field drainage capacity, the compensation of cooling flow field, etc., to realize better overall performance.

[0059] In a specific embodiment, as shown in FIG. 1, the first end of the anode plate 111 is provided with an anode fluid inlet 133, and the second end of the anode plate 111 is provided with an anode fluid outlet 134. Figure 1

[0060] The first end of the cathode plate 112 is provided with a cathode fluid outlet 136, and the second end of the cathode plate 112 is provided with a cathode fluid inlet 135; the anode fluid inlet 133 and the cathode fluid outlet 136 are located on the same side, and the anode fluid outlet 134 and the cathode fluid inlet 135 are located on the same side.

[0061] In a further embodiment, since the temperature of the cathode air or anode hydrogen inlet is low, a fan and a wind box inner wall structure can be arranged near the re-flow channel to adjust the air to compensate for the temperature difference between the middle region and the inlet and outlet regions.

[0062] In one embodiment, the closed fuel cell air-cooled stack further comprises an upper pressing plate, a lower pressing plate and a fastener (not shown in the figure).

[0063] ​​The upper pressing plate is arranged on the upper side of the plurality of fuel cell units and the plurality of cooling plates in the stacking direction, the lower pressing plate is arranged on the lower side of the plurality of fuel cell units and the plurality of cooling plates in the stacking direction, and the fastener is fixed to the edges of the upper pressing plate and the lower pressing plate to press and fix the plurality of fuel cell units.

[0064] Those skilled in the art can understand that the sealing condition of the cathode flow field is not strict, and a certain degree of leakage is allowed.

[0065] In one embodiment, the flow direction of the cathode flow channel 114 is perpendicular to the cooling medium flow direction L; the temperature in each cathode flow channel 114 is uniform, and the flow cross section from the inlet to the outlet in each cathode flow channel 114 is the same; a plurality of cathode flow channels 114 are arranged in parallel, and the inlets and outlets of the plurality of cathode flow channels 114 share the inlet and outlet of the cathode flow field 132, so as to keep the pressure difference of the inlets and outlets of the plurality of cathode flow channels 114 consistent; the influencing factors of the size of the flow cross section of the cathode flow channel 114 include the distance from the flow channel wall to the flow channel center of the cathode flow channel 114, so that the size of the flow cross section in different cathode flow channels 114 is positively correlated with the flow rate; the cathode flow channel 114 carries away moisture through the flowing reactant medium, so as to keep the relative humidity of the membrane electrode 113 balanced in the case that there is a temperature difference between the upstream and downstream of the cooling flow field.

[0066] The flow cross section of a single cathode flow channel 114 remains unchanged, that is, the flow cross section of a single cathode flow channel 114 is consistent from the inlet to the outlet, and the size and shape remain unchanged; the temperature in each cathode flow channel 114 is uniform, so that the moisture carried away in each cathode flow channel 114 is stable and uniform, and the moisture carried away by the membrane electrode 113 as a whole is stable. The influencing factors of the size of the flow cross section include the distance from the flow channel wall to the flow channel center of the cathode flow channel 114, and the flow channel wall of the cathode flow channel 114 can be the flow channel wall at the same position in the same direction. The flow cross section of the cathode flow channel 114 can also be rectangular, circular, triangular, etc., and the flow channel center can be the intersection point of the four vertices of a rectangular, the center of a circle, or the center of a triangle. The distance from the flow channel wall to the flow channel center of the cathode flow channel 114 can be adjusted by changing the depth and width of the flow channel, that is, the size of the flow cross section can be adjusted by adjusting the depth and / or width. As shown in the figure, each cathode flow channel 114 is a pipe structure with uniform width, and the upper and lower widths are equal. There are two medium flow directions in the fuel cell unit, one is the cooling medium flow direction, and the other is the reactant medium flow direction, and the two directions are nearly perpendicular. The plurality of cathode flow channels 114 arranged along the cooling medium flow direction are distributed from large to small in size of the flow cross section, for example, in the case that the depth of the flow channel remains unchanged, the width of the flow channel is adjusted. Figure 3 As shown in the figure, each cathode flow channel 114 is a pipe structure with uniform width, and the upper and lower widths are equal. There are two medium flow directions in the fuel cell unit, one is the cooling medium flow direction, and the other is the reactant medium flow direction, and the two directions are nearly perpendicular. The plurality of cathode flow channels 114 arranged along the cooling medium flow direction are distributed from large to small in size of the flow cross section, for example, in the case that the depth of the flow channel remains unchanged, the width of the flow channel is adjusted.Figure 5 As shown, the depth of the flow channel is adjusted without changing the width of the flow channel.

[0067] The purpose of the present application is to control the water content of the membrane electrode 113, that is, to keep the relative humidity of the membrane electrode 113 stable. In theory, if the temperature of the stack is uniform, the cross section of a single cathode flow channel 114 is the same, and the flow rate is uniform, the relative humidity is also uniform. However, in practice, due to the flow of the cooling medium, the temperature of the upstream of the cooling flow field is low, and the temperature of the downstream of the cooling flow field is high. The saturation water vapor pressure is positively correlated with the temperature, so the saturation water vapor pressure of the cathode flow field 132 region corresponding to the low-temperature area of the upstream of the cooling flow field is lower, and the saturation water vapor pressure of the cathode flow field 132 region corresponding to the high-temperature area of the downstream of the cooling flow field is higher. According to the calculation formula of the relative humidity, under the same actual water vapor generated by the reaction of the membrane electrode 113 and the same water vapor carrying speed of the cathode medium, that is, under the same actual water vapor pressure, the smaller saturation water vapor pressure makes the relative humidity of the cathode flow field 132 region corresponding to the low-temperature area of the upstream of the cooling flow field larger, and the larger saturation water vapor pressure makes the relative humidity of the cathode flow field 132 region corresponding to the high-temperature area of the downstream of the cooling flow field smaller. Therefore, the temperature difference between the inlet and outlet of the cooling medium flow field will cause the water content (relative humidity) of the membrane electrode 113 to deviate from the appropriate state. Under the premise that the flow rate of the medium in each cathode flow channel 114 is uniform, the temperature distribution imbalance will lead to the deviation of the relative humidity. In the case of the same flow cross section of the cathode flow channel 114 in the existing conventional technology, if the flow rate of the cathode flow channel 114 is uniform, the relative humidity will deviate in the case of temperature imbalance.

[0068] To solve this problem, the technical idea of the present application is to directly change the actual water vapor pressure of the cathode flow field 132 region corresponding to the upstream and downstream of the cooling flow field. The technical means of the present application is to change the flow rate of the reaction medium in the cathode flow channel 114 by setting different flow cross sections of the cathode flow channel 114 distributed along the direction of the cooling medium flow, Figure 3 The flow cross section of the cathode flow channel 114 on the upstream of the right cooling flow field is larger, and the flow rate of the reaction medium is larger, so as to carry away more water vapor, that is, to make the actual water vapor pressure smaller, and to make the relative humidity originally increased due to low temperature smaller to the target value. The flow cross section of the cathode flow channel 114 on the downstream of the left cooling flow field is smaller, and the flow rate of the reaction medium is smaller, so as to carry away less water vapor, that is, to make the actual water vapor pressure larger, and to make the relative humidity originally decreased due to high temperature larger to the target value, thereby realizing the balance of the relative humidity along the direction of the cooling medium.

[0069] The pressure difference between the inlet and outlet of the multiple parallel cathode flow channels 114 in the present application is the same, according to Figure 4The principle of fluid mechanics: the horizontal coordinate represents the position in the cross section of the flow channel, the vertical coordinate represents the linear velocity of the fluid at the position, the left side represents the flow channel with smaller cross-sectional area, and the right side represents the flow channel with larger cross-sectional area. The two vertical lines represent the side of the flow channel, that is, the flow channel wall. The average linear velocity of the fluid in the flow channel is represented by the transverse dashed line. The fluid is attached to the flow channel wall, and then the shear force between adjacent fluids due to the velocity difference is generated, thereby generating the attachment resistance of the flow channel to the fluid. Therefore, in the flow channel, the closer to the wall, the lower the linear velocity of the fluid, until it is attached to the wall and stationary, the farther away from the wall, in the center of the flow channel, the higher the speed, and the linear velocity distribution of the entire cross section is like an upper convex type. Therefore, under the condition that the pressure difference of the inlet and outlet is the same, the linear velocity of the flow channel with large flow cross section is faster, and more actual water vapor can be carried away, which matches the saturation water vapor pressure reduced due to low temperature, and maintains moderate relative humidity; and vice versa, the linear velocity of the flow channel with small flow cross section is slower, and less actual water vapor can be carried away, which increases the actual water vapor pressure, matches the saturation water vapor pressure increased due to high temperature, and maintains moderate relative humidity.

[0070] The flow direction of the cathode flow channel 114 of the application is perpendicular to the flow direction of the cooling medium, and a plurality of parallel cathode flow channels 114 share an inlet and outlet to keep the pressure difference of the inlet and outlet of the plurality of cathode flow channels 114 consistent. The size of the flow cross section of the cathode flow channel 114 can be adjusted by changing the distance from the flow channel wall to the center of the cathode flow channel 114, for example, by changing the width and / or depth of the flow channel, to change the corresponding flow rate of the cathode flow channel 114. In the case of temperature difference between the upstream and downstream of the cooling flow field, the cathode flow channel 114 with large flow cross section upstream of the cooling flow field has fast flow rate and actively carries more moisture, and the cathode flow channel 114 with small flow cross section downstream of the cooling flow field has slow flow rate and actively carries less moisture, keeping the drying speed of the membrane electrode 113 consistent everywhere, balancing the relative humidity of the membrane electrode 113 everywhere, keeping the relative humidity of the membrane electrode 113 in an ideal state, and improving the fuel cell reaction efficiency and battery performance.

[0071] The application adopts the unique design of cathode flow channel 114 to change the water vapor carrying effect by arranging different flow cross section cathode channels along the flow direction of the cooling medium, and the core of water vapor regulation is to change the flow rate by changing the flow cross section, to carry more water vapor by the medium, to realize non-uniform water vapor partial pressure under non-uniform temperature field, to realize humidity balance under temperature imbalance, to keep the water content and relative humidity of the membrane electrode 113 in an ideal state under the condition of temperature imbalance of the stack, and to ensure the operation efficiency of the membrane electrode 113.

[0072] The preferred embodiments of the present application have been described above in detail. It should be understood that modifications and variations to the preferred embodiments could be made by those skilled in the art in light of the teachings above. It is therefore contemplated that the application can encompass other variations and modifications that fall within the scope of the claims.

Claims

1. A closed-loop air-cooled fuel cell stack, characterized in that, Includes multiple stacked fuel cell cells and multiple cooling plates; Each fuel cell includes an anode plate, a cathode plate, and a membrane electrode assembly located between the anode plate and the cathode plate; at least some of the fuel cell anode plates have a first cooling plate on the side away from the corresponding membrane electrode, and at least some of the fuel cell anode plates have a second cooling plate on the side away from the corresponding membrane electrode; the first cooling plate and the second cooling plate are respectively connected to the corresponding anode plate and cathode plate; The surfaces of the first cooling plate and the second cooling plate are provided with cooling media with the same flow direction. The side of the cathode plate facing the membrane electrode has multiple cathode channels distributed along the flow direction of the cooling media. Among the multiple cathode channels, the flow cross-section of the upstream cathode channel is larger than that of the downstream cathode channel along the flow direction of the cooling media.

2. The closed-loop air-cooled fuel cell stack according to claim 1, characterized in that, Along the flow direction of the cooling medium, the cross-sectional area of ​​the multiple cathode channels decreases sequentially.

3. The closed-loop air-cooled fuel cell stack according to claim 1, characterized in that, Among the plurality of cathode channels, the plurality of cathode channels include a first channel group and a second channel group, wherein the first channel group is located upstream of the cooling medium flow direction and the second channel group is located downstream of the cooling medium flow direction; The flow cross-section of each cathode flow channel in the first flow channel group is larger than that of each cathode flow channel in the second flow channel group.

4. The closed-loop air-cooled fuel cell stack according to claim 3, characterized in that, The flow cross-section of each cathode channel in the first flow channel group is the same, and the flow cross-section of each cathode channel in the second flow channel group is the same.

5. The closed-loop air-cooled fuel cell stack according to claim 1, characterized in that, In each fuel cell, the flow field between the anode plate and the membrane electrode is the anode flow field, and the flow field between the cathode plate and the membrane electrode is the cathode flow field. The flow direction of the fluid in the anode flow field is opposite to that of the fluid in the cathode flow field.

6. The closed-loop air-cooled fuel cell stack according to claim 5, characterized in that, The anode plate has an anode fluid inlet at its first end and an anode fluid outlet at its second end. The cathode plate has a cathode fluid outlet at its first end and a cathode fluid inlet at its second end; the anode fluid inlet and the cathode fluid outlet are located on the same side.

7. The closed-loop air-cooled fuel cell stack according to claim 1, characterized in that, Both the first cooling plate and the second cooling plate are corrugated plates.

8. The closed-loop air-cooled fuel cell stack according to claim 1, characterized in that, It also includes an upper pressure plate, a lower pressure plate, and fasteners; The upper pressure plate is disposed on the upper side of the plurality of stacked fuel cell cells and the plurality of cooling plates along the stacking direction, and the lower pressure plate is disposed on the lower side of the plurality of stacked fuel cell cells and the plurality of cooling plates along the stacking direction. The fasteners are fixed to the edges of the upper pressure plate and the lower pressure plate to press and fix the plurality of stacked fuel cell cells.

9. The closed-loop air-cooled fuel cell stack according to any one of claims 1 to 8, characterized in that, The fluid between the anode plate and the membrane electrode is hydrogen, and the fluid between the cathode plate and the membrane electrode is air.

10. The enclosed air-cooled fuel cell stack according to any one of claims 1 to 8, characterized in that, The flow direction of the cathode channel is perpendicular to the flow direction of the cooling medium; the temperature is uniform in each cathode channel, and the flow cross-section from the inlet to the outlet is the same in each cathode channel. Multiple cathode channels are connected in parallel and share the inlet and outlet of the cathode flow field to maintain a consistent inlet and outlet pressure difference among multiple cathode channels. The influencing factors of the flow cross-section size of the cathode channel include the distance from the channel wall to the center of the channel, so that the flow cross-section size in different cathode channels is positively correlated with the flow velocity to maintain a balanced relative humidity of the membrane electrode.

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