CN116666696A - Design method of bipolar plate runner of fuel cell, plate runner and cell - Google Patents
Design method of bipolar plate runner of fuel cell, plate runner and cell Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 27
- 239000000446 fuel Substances 0.000 title claims abstract description 24
- 238000013461 design Methods 0.000 title claims abstract description 15
- 238000009792 diffusion process Methods 0.000 claims description 24
- 239000007789 gas Substances 0.000 abstract description 44
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 abstract description 11
- 239000012495 reaction gas Substances 0.000 abstract description 3
- 230000008859 change Effects 0.000 abstract description 2
- 238000011084 recovery Methods 0.000 abstract description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 38
- 239000001301 oxygen Substances 0.000 description 38
- 229910052760 oxygen Inorganic materials 0.000 description 38
- 239000001257 hydrogen Substances 0.000 description 17
- 229910052739 hydrogen Inorganic materials 0.000 description 17
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 16
- 230000000694 effects Effects 0.000 description 12
- 239000003054 catalyst Substances 0.000 description 9
- 239000000376 reactant Substances 0.000 description 9
- 238000006243 chemical reaction Methods 0.000 description 7
- 230000010287 polarization Effects 0.000 description 7
- 238000004088 simulation Methods 0.000 description 7
- 238000003487 electrochemical reaction Methods 0.000 description 6
- 239000012530 fluid Substances 0.000 description 5
- 230000006872 improvement Effects 0.000 description 5
- 230000008569 process Effects 0.000 description 5
- 238000012986 modification Methods 0.000 description 4
- 230000004048 modification Effects 0.000 description 4
- 238000012546 transfer Methods 0.000 description 4
- 230000009471 action Effects 0.000 description 3
- 238000004458 analytical method Methods 0.000 description 3
- 238000004364 calculation method Methods 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000011161 development Methods 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 230000034964 establishment of cell polarity Effects 0.000 description 3
- 239000012528 membrane Substances 0.000 description 3
- 238000012795 verification Methods 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000006727 cell loss Effects 0.000 description 2
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- 238000003912 environmental pollution Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000007800 oxidant agent Substances 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
- H01M8/04298—Processes for controlling fuel cells or fuel cell systems
- H01M8/04305—Modeling, demonstration models of fuel cells, e.g. for training purposes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/02—Details
- H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
- H01M8/0258—Collectors; Separators, e.g. bipolar separators; Interconnectors characterised by the configuration of channels, e.g. by the flow field of the reactant or coolant
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
- H01M8/04291—Arrangements for managing water in solid electrolyte fuel cell systems
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
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Abstract
The application provides a design method of a bipolar plate flow channel of a fuel cell, a plate flow channel and a cell, wherein the cell performance is influenced by analyzing the cathode and anode positions of a pressure-built parallel flow field of a micro-channel, and the pressure-built parallel flow field is arranged on the cathode side of the cell; by analyzing the influence of the size of the micro-channel on the battery performance, arranging the micro-channel between each shunt channel and the inlet main channel to form a channel sequentially comprising the inlet main channel, the micro-channel, the shunt channel and the outlet main channel; according to the application, the resistance of the gas entering the sub-channels is improved through the micro-channels, so that the pressure of the main channel at the inlet is increased, the pressure change of the main channel at the outlet is smaller, and the relative difference of pressure drops among the sub-channels is reduced, so that the gas distribution uniformity is improved, the utilization rate of the reaction gas is further improved, the gas recovery cost is reduced, the water drainage is enhanced, and the battery performance is improved.
Description
Technical Field
The application relates to the technical field of fuel cells, in particular to a design method of a bipolar plate flow channel of a fuel cell, a plate flow channel and a cell.
Background
Based on the current situation that the traditional energy sources are exhausted and the environmental pollution is increasingly serious, the hydrogen energy industry is increasingly becoming an outstanding field under the modern energy crisis. The product of hydrogen combustion is water, which is the cleanest energy source in the world, known as the best seen secondary energy source in the 21 st century. As clean energy with zero emission, the hydrogen energy has the characteristics of wide source, environmental protection, high energy density, wide adaptability and the like. The excellent performance enables the hydrogen energy to have both economic and social benefits. The government in China is very important to the development and utilization of the environmental protection and hydrogen energy industry, so the hydrogen energy industry is in great opportunity in China. However, at present, the manufacturing processes of key materials of a hydrogen fuel cell, such as a catalyst, a proton exchange membrane, a bipolar plate and the like are all in bottleneck period, the production cost of the hydrogen fuel cell is high, and in the hydrogen fuel cell, the bipolar plate is an important component of a galvanic pile, and the cost of the bipolar plate accounts for 20% -40% of the cost of the galvanic pile. The flow channel structure determines the hydrothermal management, mass transport and current density distribution of the PEMFC, and has profound effects on the comprehensive performance of the fuel cell.
Today, conventional designs are applied to the flow channel portion of the bipolar plate of a hydrogen fuel cell, which have poor gas and water transport properties that affect the performance of the bipolar plate and thus the fuel cell. Water and gas management is an important factor affecting performance, and the limitation of the water and gas management technology is one of the bottlenecks on the development path of fuel cells. In the existing technology for managing the water vapor of the fuel cell flow channels, some conventional flow channel designs have certain drawbacks. For example, in the continuous working process of the battery, the number of the parallel flow channels is large, the flow speed of the air flow is generally low, partial electrode flooding is easy to occur, the unstable performance of the battery is easy to occur, and the supply of the reaction gas is insufficient; the serpentine flow channel can cause excessive reaction air pressure drop due to overlong flow channel, and the reaction air supply at the rear section of the flow channel is insufficient and is easy to be flooded; the spiral flow passage has larger pressure drop, short circuit is easy to occur in the flow, and the processing is more complex.
According to the application, aiming at the defects of parallel flow channels, the micro-channel pressure-build parallel flow field is designed, and micro-channels are arranged at the inlets of all the flow channels, so that the resistance of gas entering the flow channels is improved by the micro-channels, the pressure of the main flow channels at the inlets is increased, the pressure change of the main flow channels at the outlets is smaller, the relative difference of pressure drops among the flow channels is reduced, and the gas distribution uniformity is improved. The utilization rate of the reaction gas is improved, the gas recovery cost is reduced, the drainage capacity is enhanced, and the battery performance is improved. Provides a reference case for the further development of parallel flow channels in the future.
Disclosure of Invention
The application aims to solve the technical problems and provides a design method of a bipolar plate flow channel of a fuel cell, a plate flow channel and a cell, so that gas distribution is more uniform, and cell performance is improved.
Specifically, the application provides a fuel cell bipolar plate flow channel design method, which comprises the following steps:
s1: according to the influence of the cathode and anode positions of the micro-channel pressure-build parallel flow field on the performance of the battery, placing the pressure-build parallel flow field on the cathode side of the battery;
s2: according to the influence of the size of the micro-channel on the battery performance, arranging the micro-channel between each shunt channel and the inlet main channel to form a channel sequentially comprising the inlet main channel, the micro-channel, the shunt channel and the outlet main channel; the cross section of the micro-flow channel along the width direction of the sub-flow channel is square, and the cross section size of the micro-flow channel is smaller than that of the sub-flow channel.
The micro-flow channel is arranged on the surface of the polar plate, and when the battery is assembled, the micro-flow channel is adjacent to the surface of the gas diffusion layer.
The cross-sectional dimension of the micro-channel along the width direction of the sub-channel is preferably set to be 0.2 multiplied by 0.2mm 2 。
Based on the same inventive concept, the application also provides a plate runner, which comprises an inlet main runner and sub runners which are parallel and distributed perpendicular to the inlet main runner; one end of the shunt channel is provided with a micro-channel which is communicated with the inlet main channel; the other end is communicated with the outlet main flow channel; the outlet main runner and the inlet main runner are distributed in parallel.
The cross section of the micro flow channel along the width direction of the sub flow channel is square, and the cross section size of the micro flow channel is smaller than that of the sub flow channel.
The width ratio of the flow dividing channels to the rib plates is 1/2 to 1, and the width of the rib plates is reduced and the width of the flow channels is increased by changing the width ratio of the channels to the rib plates.
The outlet main runner is the same as the inlet main runner in size, and the circulation direction is opposite.
Based on the same inventive concept, the application also provides a battery, wherein a pressure-build parallel flow field is arranged on the cathode side of the battery, and the pressure-build parallel flow field adopts the plate flow channel.
Compared with the prior art, the application has the beneficial effects that:
1. the micro-channel pressure-build parallel flow field provided by the application is a flow field with potential application value, and the method for improving the gas distribution uniformity through pressure build can be further applied to PEMFC stacks, and has an important effect on the improvement of the performance of the stacks. When the micro-channel pressure-build parallel flow field is positioned on the cathode side, concentration polarization phenomenon under high current density can be effectively reduced, and the output performance of the battery is improved; the smaller the size of the micro-flow channel pressure build-up type parallel flow field is, the stronger the build-up capability is, the higher the gas distribution uniformity is, the more obvious the battery performance is improved, and when the size of the micro-flow channel is 0.2mm, the maximum power density of the battery is 22.8% higher than that of the traditional parallel flow field. Therefore, the pressure-build parallel flow field is a flow field with potential application value.
2. According to the application, aiming at the gas distribution effect of the PEMFC flow field, the influence factors of the gas distribution uniformity of the parallel flow field are theoretically calculated, the pressure-build parallel flow field is designed, the internal mass transfer process and the battery performance of the pressure-build parallel flow field are researched, and the gas distribution uniformity of the pressure-build parallel flow field is much higher than that of the traditional parallel flow field. The electrical output performance is obviously improved.
3. The application changes the width ratio of the flow channel and the rib plate at the same time, increases the contact area between the reactant and the GDL by reducing the width of the rib plate and increasing the width of the flow channel, enhances the water removal in the GDL, and effectively improves the flooding phenomenon.
Drawings
Fig. 1 is a flow chart of a flow path design method of a bipolar plate of a material battery according to the application.
Fig. 2 is a schematic diagram of a micro-channel pressure build-up type parallel flow field according to the present application.
FIG. 3 is a schematic diagram of rib/channel distribution in accordance with the present application.
FIG. 4 is a graph of electrical conductivity at various pressures for various rib/channel width ratios in accordance with the present application.
FIG. 5 is a graph showing the comparison of the simulation result with the conventional trend in the present application.
Fig. 6 is a graph of polarization curve and power density of the cell when the micro-channel pressure-build-up parallel flow field is located at different positions of the anode and the cathode in the present application.
FIG. 7 is a graph of gas velocity profile at 0.6V at an interface between a flow field and a gas diffusion layer in accordance with the present application: (a) anode velocity profile of a conventional parallel flow field; (b) Anode speed distribution when the build-up parallel flow field is positioned at the anode; (c) cathode velocity profile of a conventional parallel flow field; (d) And the cathode speed distribution when the build-up parallel flow field is positioned at the cathode.
FIG. 8 is a graph showing the effect of microchannel size on cell polarization curve and power density curve in the present application.
FIG. 9 is a graph showing the relationship between the size of the micro flow channel and the maximum power density of the battery according to the present application.
Fig. 10 shows the pressure drop values of the various sub-channels at 0.6V for the cells of different micro-channel sizes in the present application.
FIG. 11 is a graph of mass flow rate non-uniformity versus the inverse of the average pressure drop for the present application.
Fig. 12 (a) and (b) are graphs showing the relationship between the non-uniformity of the oxygen concentration distribution at the interface of the gas diffusion layer/catalyst layer and the non-uniformity of consumption per unit time of oxygen in each of the flow channels according to the current density at different microchannel sizes.
FIG. 13 is a graph showing the relationship between the non-uniformity of the oxygen concentration distribution at the interface of the gas diffusion layer/catalyst layer and the non-uniformity of the oxygen mass flow rate of each of the partial channels at the output voltage of 0.6V of the cell according to the present application.
FIG. 14 shows the pressure distribution of various flow fields in accordance with the present application (a) conventional parallel flow fields; (b) building up a pressure type parallel flow field.
Wherein 1 is an outlet, 2 is a sub-runner, 3 is an outlet main runner, 4 is an inlet main runner, and 5 is a micro-runner; a 6-bit entry; 7 is the active region.
Detailed Description
The following describes a bipolar plate flow channel design method for a fuel cell, plate flow channels and cells in further detail with reference to specific embodiments and drawings.
The method for designing the bipolar plate flow channel of the fuel cell in the embodiment of the application has the following general ideas, referring to the attached figure 1:
s1: according to the influence of the cathode and anode positions of the micro-channel pressure-build parallel flow field on the performance of the battery, placing the pressure-build parallel flow field on the cathode side of the battery;
s2: according to the influence of the size of the micro-channel on the battery performance, arranging the micro-channel between each shunt channel and the inlet main channel to form a channel sequentially comprising the inlet main channel, the micro-channel, the shunt channel and the outlet main channel; the cross section of the micro-flow channel along the width direction of the sub-flow channel is square, and the cross section size of the micro-flow channel is smaller than that of the sub-flow channel.
Specifically, the micro-flow channel is arranged on the surface of the polar plate, and when the battery is assembled, the micro-flow channel is adjacent to the surface of the gas diffusion layer.
According to the application, the mass transfer mechanism, the gas distribution theory and the application effect of the pressure-build parallel flow field are analyzed by the CFD simulation method, so that the pressure-build parallel flow field can obviously improve the uniformity of the gas flow rate distribution among the sub-channels, the concentration polarization phenomenon is reduced under high current density, and the output efficiency of the battery is improved.
The uniformity of the gas distribution on the cathode side is improved by the pressure-build parallel flow field, so that the service performance of the battery is obviously improved. And the anode side has low loss, the hydrogen diffusion is fast, and the gas distribution uniformity of the flow field is improved to have weak influence on the cell performance. Compared with the traditional parallel flow field, the micro-channel pressure-build parallel flow field overcomes the defects of the traditional parallel flow field, so that the conversion of hydrogen and oxygen is smoother, and the redox conversion efficiency is improved.
Preferably, the flow channel design of the present application begins primarily with a reduction in the size of the micro-channel. The diffusion rate of oxygen from the flow field to the gas diffusion layer becomes critical to the cell performance, while the microchannels can increase the diffusion rate of oxygen. The maximum power density occurs at about 0.6V for different microchannel sizes, where the optimum operating state of the cell. Therefore, a cell state of 0.6V is preferable to investigate the influence of the micro flow channel size on the uniformity of oxygen distribution. As the microchannel size is reduced, the maximum power density of the cell increases non-linearly. When the size of the micro-flow channel is 0.2mm, the battery can provide about 0.7Wcm < -2 > of output power density which is about 23% higher than that of the traditional parallel flow field, so that the cross section size of the micro-flow channel along the width direction of the sub-flow channel is set to be 0.2 multiplied by 0.2mm 2 。
Furthermore, the application starts from the width ratio of the flow channel to the rib plate, and preferably, the width ratio of the flow channel to the rib plate is between 1/2 and 1, so that the performance of the battery is improved.
Good reactant transport and water removal are ensured by the wider flow channels, while the wide ribs ensure good electrical and thermal conductivity and mechanical stability. The total flow channel area ratio (total flow channel area/cell active area) and the total flow channel width ratio (total flow channel width/total cell width) can also show the influence of different flow channel and rib plate width ratios on the performance of the PEMFC to a certain extent. The ratio of flow channel to rib width was also used to study the effect of flow channel area ratio and cathode flow rate on cell performance and local transport characteristics. As the total flow area ratio increases, fuel is transported into the diffusion layer and reaches the catalyst layer primarily by diffusion. A larger flow area ratio increases the contact area between the fuel and the diffusion layer, which allows more fuel to diffuse directly into the porous layer to participate in the electrochemical reaction, thereby increasing the reaction rate. In addition to the effects on mass transfer, the width ratio of the runners to the ribs directly affects voltage loss and mechanical stability. Since the voltage loss decreases with decreasing rib/channel width ratio over a range. The corresponding relation is that the contact area between the reactant and the GDL is increased by reducing the width of the rib plate and increasing the width of the flow channel, the water removal in the GDL is enhanced, and the flooding phenomenon is effectively improved. But on the other hand it will reduce the transfer of current and heat. And as the channel width increases, or the rib width decreases, the maximum deflection of the MEA into the channel increases due to the reduced mechanical support for the MEA.
Based on the same inventive concept, the application also provides a plate runner, which is shown in fig. 2: the plate runner comprises an inlet main runner and sub-runners which are parallel and distributed perpendicular to the inlet main runner; one end of the shunt channel is provided with a micro-channel which is communicated with the inlet main channel; the other end is communicated with the outlet main flow channel; the outlet main runner and the inlet main runner are distributed in parallel.
The cross section of the micro flow channel along the width direction of the sub flow channel is square, and the cross section size of the micro flow channel is smaller than that of the sub flow channel.
Preferably, the ratio of widths of the runners and ribs is between 1/2 and 1 as shown in FIG. 3. As shown in fig. 4, which shows the ratio of the widths of the different rib/flow channels, the experimental data demonstrate that the voltage loss is reduced with the reduction of the ratio of the widths of the rib/flow channels within a certain range.
The outlet main runner is the same as the inlet main runner in size, and the circulation direction is opposite.
According to the design, a corresponding 3DPEMFC model is constructed, and the model is compared with a traditional parallel flow field and a structural diagram of a traditional serpentine flow field as an experiment. Wherein the effective area is 5.1X15.1 cm 2 . The thicknesses of the gas diffusion layer, the catalyst layer and the proton exchange membrane are respectively 0.2mm, 0.01mm and 0.05mm, and the width and depth of the flow channel and the width of the ridge are all 1.0mm. For the micro flow channel pressure build-up type parallel flow field, it is considered that if water droplets occur in the inlet main flow channel, the water droplets may hardly pass through the micro flow channel, and thus the active region of the cell is disposed after the micro flow channel. Wherein the active region represents an effective region in which electrochemical reactions can occur.
All operating conditions for each model were the same, the battery operating temperature was set to 333K, and the fluid output was the limit for the pressure output. The pressure value was 1.01X105 Pa. Hydrogen and air are used as fuel and oxidant, respectively. The flow direction of hydrogen in the anode flow field is opposite to the flow direction of air in the cathode flow field. The anode and cathode gas flows were 6.4X107 kgs-1 and 2.2X10-5 kgs-1, respectively, and the relative humidity of the hydrogen and air inlets was 30% and 60%, respectively, and the other electrochemical parameters are shown in the following table:
model verification:
and the simulation control equation and the PEMFC module of the related parameters in Fluent are calculated, and the calculation method is a control volume method. In each control volume, the relative residual of the iterative convergence is set to 1 x 10-5. All grids in the model are hexahedral N grids, four groups of grids with different numbers are divided into traditional parallel flow fields for determining proper grid size, and the grid numbers are respectively 54 multiplied by 306 multiplied by 33 (representing X multiplied by Y multiplied by Z coordinates)) 62×408×41, 70×510×52, and 78×612×63, the x direction is parallel to the split flow path, the Y direction is parallel to the main flow path, and Z represents a direction perpendicular to the active region. The current density of the PEMFC at 0.6V under different grid numbers is calculated by simulation, and the calculation results are 0.9908A respectivelycm-2，0.9541A/>cm-2,0.9604A/>cm-2 and 0.9622A->cm-2, the difference in current density of all four groups is less than 5%. Meanwhile, the two factors of calculation precision and time consumption are considered, and finally, 70 multiplied by 510 multiplied by 52 grids are selected, wherein the total number of grids of the current collecting plate, the flow field, the gas diffusion layer, the catalyst M and the proton exchange membrane in thickness is 10, 4 and 4.
Verifying the reliability of the model: the numerical simulation results in a polarization curve of a conventional parallel flow field, and the result is shown in fig. 5. From the figure, it can be seen that the simulation results of the present application are consistent with the conventional trend. It is shown that the analysis of the effect of the constructed model according to the application on the cell performance is reliable.
Based on the analysis of the influence of the cathode and anode positions of the micro-channel pressure-build parallel flow field on the battery performance, the micro-channel pressure-build parallel flow field is arranged at two different positions of the cathode and the anode, and the influence of the flow field on the battery performance at different electrode sides is analyzed. The section size of the micro-flow channel pressure build-up type parallel flow field is 0.20 multiplied by 0.2mm 2 。
Fig. 6 shows the cell polarization curve and power density curve of a conventional parallel flow field with the voltage build-up parallel flow field on the anode side, cathode side, and both sides. It can be seen that the cell polarization curves in the three cases substantially coincide at low current densities. Because the electrochemical reaction is slower at lower current densities. The consumption speed of the reactant is low, the requirement on the concentration of the reactant is low, and the normal running of the electrochemical reaction can be satisfied under the gas distribution condition of the traditional parallel flow field. The electrochemical reaction rate increases with increasing current density. The rate of reactant consumption increases, especially after a current density of greater than 0.9 Am-2. At this time, for the traditional parallel flow field, due to the uneven distribution of the reactant gas, the reactant concentration of part of the active region is insufficient to support the consumption of the electrochemical reaction, a larger concentration polarization phenomenon occurs, and the voltage loss is larger.
For the case of the build-up parallel flow field on the cathode side, when the current density is higher than 0.7Acm -2 And then, under the same current density, the voltage value is obviously higher than that of the traditional parallel flow field, which indicates that the voltage loss is small, the concentration polarization phenomenon is weak, namely, the concentration of oxygen is still at a higher level in the whole active area range, and the distribution uniformity is higher than that of the traditional flow field.
As shown in fig. 7 (c) and (d), when the cathode side is a conventional parallel flow field and the anode side is a pressure-build parallel flow field, and the anode side is a conventional parallel flow field, the speed distribution at the interface between the cathode flow field and the gas diffusion layer can be seen that in the conventional parallel flow field, the speeds of several sub-channels far from the inlet are far higher than those of other sub-channels, the oxygen concentration at the far from the inlet is high, and the oxygen concentration at other positions is low; in the build-up pressure type parallel flow field, the speed distribution of all the sub-channels is basically consistent, the distribution of oxygen in each sub-channel is very uniform, and the oxygen is timely supplied in the whole active area, so that the concentration polarization is smaller.
Fig. 7 (a) and (b) show the velocity distribution at the interface between the anode flow field and the gas diffusion layer when the anode side is a conventional parallel flow field and the cathode side is a conventional parallel flow field, respectively. It can be seen that the build-up parallel flow field on the anode side can also improve the flow distribution uniformity significantly, but the cell performance is hardly enhanced (see fig. 6), mainly because the cell loss on the anode side of the PEMFC is typically lower than the cell loss on the cathode side. In addition, hydrogen has a much higher diffusion coefficient than oxygen, so hydrogen as an anode side reactant can diffuse more rapidly to provide for consumption of the chemical reaction. Thus, the improved design of the cathode flow field is more important than the anode side, and the improved build-up parallel flow field should be placed on the cathode side of the cell. In the subsequent simulation analysis, the build-up parallel flow fields were all placed on the cathode side.
In a preferred embodiment, the plate channel of the present application is improved in terms of microchannel size. The method comprises the following steps:
fig. 8 is a graph showing the effect of micro flow channel size on cell output performance. When the size of the micro flow channel is reduced, the battery performance is improved, and in the high current density range, the improvement of the micro flow channel to the battery performance is more obvious than in the low current density range. This is due to the increased current density. The diffusion rate of oxygen from the flow field to the gas diffusion layer becomes critical to the cell performance, while the microchannels can increase the diffusion rate of oxygen. The maximum power density occurs at about 0.6V for different microchannel sizes, where the optimum operating state of the cell. Therefore, a cell state of 0.6V was selected to investigate the influence of the micro flow channel size on the uniformity of oxygen distribution. Fig. 9 shows the relationship between the size of the micro flow channel and the maximum output power density of the battery. The graph shows that as the microchannel size is reduced, the maximum power density of the cell increases non-linearly. When the microchannel size is 0.2mm, the cell can provide an output power density of about 0.7Wcm-2, which is about 23% higher than that of a conventional parallel flow field.
FIG. 10 shows the distribution of the manifold pressure drop at 0.6V for different manifold sizes. In the figure, the coordinates represent the distance from the center of each split channel inlet to the total flow field inlet along the main flow channel direction. It can be seen that the direction of flow of the gas in the main flow channel. The pressure drop of the flow dividing channels is reduced and then gradually increased, and the difference of the pressure drop among the flow dividing channels is a main reason for uneven gas flow distribution of the flow dividing channels of the parallel flow field. Since the size of the micro-channel is reduced from 1mm to 0.2mm. The average value of the manifold pressure drop increases from 20Pa to 305Pa, and the maximum difference in pressure drop between the manifolds increases from 104Pa to 124Pa, indicating that the microchannel size greatly affects the average value of the pressure drop in the manifolds and has little effect on the pressure drop difference between the manifolds. Therefore, when the size of the micro-channel is reduced, the difference of the pressure drop of each split channel is greatly reduced. Since the gas flow rate in the flow divider is proportional to the pressure drop, for a given total flow rate, a decrease in the microchannel size will reduce the flow rate difference between the flow dividers and improve the uniformity of flow distribution between the flow dividers.
The effect of microchannel size on cell output performance is primarily due to its changing distribution of oxygen mass flow rate. Reducing the size of the micro-channels can improve the uniformity of the mass flow rate of oxygen in each sub-channel, thereby improving the uniformity of the oxygen concentration at the interface of the gas diffusion layer/the catalyst layer. And the improvement of the uniformity of the interface oxygen concentration can obviously improve the output performance of the battery. In addition, the improvement of the uniformity of the mass flow rate of oxygen in each sub-runner is also beneficial to improving the drainage performance and preventing flooding.
In a preferred embodiment, the plate flow channel of the present application is improved in the ratio of the widths of the flow dividing channels to the ribs, reducing the rib width and increasing the channel width. In summary, the channel width should be kept below 1.5mm to maintain mechanical stability, while the rib/channel width value should be kept as low as possible to minimize voltage losses.
The micro-channel designed by the application is further verified to obtain: the pressure drop non-uniformity between the various flow channels is constant, independent of the microchannel size and the average pressure drop across the flow channels. The specific verification is that the distribution of the gas in the split runner is calculated, and the specific verification is as follows:
for steady-state flow in parallel flow field runners, there is a pressure differential between the runner inlet and outlet due to the presence of wall shear forces: (P) f -P e )A ch ＝τ w P ch L ch ；
Wherein P is f For split-flow inlet pressure, P e For the pressure of the outlet of the shunt channel, A ch To the sectional area of the shunt, P ch Is the circumference of the flow channel, L ch Is the length of the flow channel.
Wall shear stress τ w Is calculated according to the formula:
where f is a dimensionless coefficient of friction, ρ is the fluid density, and u is the fluid average velocity. The product of the friction coefficient f and the reynolds number Re is a constant, ref=constant.
For a circular flow channel, ref=constant, and the reynolds number Re is calculated as:
wherein μ is the fluid viscosity, D ch Is the hydraulic diameter. For rectangular runner Ref and runner aspect ratioAnd (5) correlation.
For square cross-section channels, ref≡14 and for high aspect ratio channels, ref≡24.
For a determined Ref value, the relationship between the mass flow rate in the flow channel and the inlet-outlet pressure difference can be determined:
defining a constant Kc for representing the relationship between two flow rates and the inlet-outlet pressure difference of the flow channel:
definition pressure drop ΔP represents the pressure difference between the inlet and the outlet of the subchannel
Δp=pf-PC;
it can be seen that for a flow field with a fixed flow channel size and fluid type, the mass flow rate of each sub-channel depends on the pressure distribution of the main flow channel, and the larger the pressure difference between the sub-channels is, the more uneven the mass flow rate distribution is. For a certain cell, there is a relationship:
wherein D is m And D P The standard deviation of the mass flow rate and the pressure drop of each shunt channel is respectively obtained finally:
for a given inlet gas flow rate, the non-uniformity of the gas flow distribution is inversely proportional to the average pressure drop across each of the sub-channels, and directly proportional to the pressure drop non-uniformity. To verify this equation, the non-uniformity (Dm) of the mass flow rate and the inverse of the average pressure drop for each of the channels at different microchannel sizes were calculated. As a result, as shown in fig. 11, it can be seen that the data fitting exhibits a linear relationship, and the coefficient of determination of the data linear fitting is as high as 0.997, and the non-uniformity of the pressure drop between the individual flow paths is constant regardless of the micro-channel size and the average pressure drop size of the flow paths. Thus, for the present work study, the non-uniformity of flow distribution in parallel flow fields depends only on the average pressure drop across the flow channels, and this non-uniformity of flow distribution can be reduced by increasing the average pressure drop. Good regression of the data in the figures also shows that the equation does describe the flow distribution behavior within the fluidic channel.
Fig. 12 (a) shows the variation of the oxygen concentration in the gas diffusion layer/catalyst layer interface with the output current density. The graph shows that the non-uniformity of oxygen concentration is close to zero when no current is output. However, as the current density increases, the non-uniform oxygen concentration increases rapidly. Fig. 12 (b) shows the variation of the consumption amount of oxygen per unit time of each shunt with the current density. The graph shows that the dependence of the oxygen conversion unevenness of each shunt channel on the current density is similar to that of the oxygen concentration unevenness in the oxygen concentration unit time. This means that the non-uniformity of the oxygen concentration is caused by the output current, and the problem of the non-uniformity of the oxygen concentration is more serious when the output current is increased. In addition, the non-uniformity of the oxygen concentration distribution is also related to the oxygen flow rate distribution of each of the flow field sub-channels.
Fig. 13 shows the relationship between the non-uniformity of oxygen concentration in the gas diffusion layer/catalyst layer interface and the non-uniformity of the mass flow rate of oxygen in each of the partial channels at a cell output voltage of 0.6 v. The graph shows that the non-uniformity of the oxygen concentration distribution is closely related to the non-uniformity of the split-channel oxygen flow rate and increases almost linearly in the range where the oxygen mass flow rate non-uniformity is high.
Fig. 14 shows pressure distribution of different flow fields, where the inlet pressure of the conventional parallel flow field is about 230Pa, and the pressure-build parallel flow field is due to the existence of the micro flow channels. The inlet pressure was increased to about 800Pa, 570Pa higher than in conventional parallel flow fields. The result shows that the output performance of the pressure build-up type parallel flow field is far higher than that of the traditional parallel flow field. The method for improving the gas distribution uniformity through pressure build-up can be further applied to the PEMFC stack, and has an important effect on the improvement of the performance of the stack.
Based on the same inventive concept, the application also provides a battery, wherein a pressure-build parallel flow field is arranged on the cathode side of the battery, and the pressure-build parallel flow field adopts the plate flow channel.
Although the illustrative embodiments have been described herein with reference to the accompanying drawings, it is to be understood that the above illustrative embodiments are merely illustrative and are not intended to limit the scope of the present application thereto. Various changes and modifications may be made therein by one of ordinary skill in the art without departing from the scope and spirit of the application. All such changes and modifications are intended to be included within the scope of the present application as set forth in the appended claims.
In the several embodiments provided by the present application, it should be understood that the disclosed apparatus and method may be implemented in other ways. For example, the above-described device embodiments are merely illustrative, e.g., the division of the elements is merely a logical functional division, and there may be additional divisions when actually implemented, e.g., multiple elements or components may be combined or integrated into another device, or some features may be omitted or not performed.
It is noted that relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
While the application has been described in conjunction with the specific embodiments above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, all such alternatives, modifications, and variations are included within the spirit and scope of the following claims.
Claims (8)
1. A fuel cell bipolar plate flow channel design method, comprising the steps of:
s1: according to the influence of the cathode and anode positions of the micro-channel pressure-build parallel flow field on the performance of the battery, placing the pressure-build parallel flow field on the cathode side of the battery;
s2: according to the influence of the size of the micro-channel on the battery performance, arranging the micro-channel between each shunt channel and the inlet main channel to form a channel sequentially comprising the inlet main channel, the micro-channel, the shunt channel and the outlet main channel; the cross section of the micro-flow channel along the width direction of the sub-flow channel is square, and the cross section size of the micro-flow channel is smaller than that of the sub-flow channel.
2. The method of claim 1, wherein the micro-channels are disposed on the surface of the plate adjacent to the surface of the gas diffusion layer when assembled into a cell.
3. The method for designing a bipolar plate channel for a fuel cell according to claim 2, wherein the cross-sectional dimension of said micro-channels in the width direction of the sub-channels is set to 0.2 x 0.2mm 2 。
4. A plate flow channel for a fuel cell bipolar plate flow channel design method according to any one of claims 1-3, wherein said plate flow channel comprises an inlet main flow channel and sub-flow channels arranged in parallel perpendicular to said inlet main flow channel; one end of the shunt channel is provided with a micro-channel which is communicated with the inlet main channel; the other end is communicated with the outlet main flow channel; the outlet main runner and the inlet main runner are distributed in parallel.
5. The plate channel according to claim 4, wherein the micro flow channel has a square cross section in the width direction of the sub flow channel and a cross section smaller than the cross section of the sub flow channel.
6. The plate flow channel of claim 5 wherein the ratio of widths of the flow channels and ribs is between 1/2 and 1.
7. The plate flow channel of claim 6 wherein said outlet primary flow channel is the same size as said inlet primary flow channel and the flow direction is opposite.
8. A cell characterized in that a pressure build-up parallel flow field is placed on the cathode side of the cell, said pressure build-up parallel flow field employing the plate flow channels of claim 4.
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| CN117709287A (en) * | 2024-02-06 | 2024-03-15 | 中国石油大学(华东) | Dimension optimization design method for flexible bipolar plate of high-efficiency solid oxide fuel cell |
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| CN117709287A (en) * | 2024-02-06 | 2024-03-15 | 中国石油大学(华东) | Dimension optimization design method for flexible bipolar plate of high-efficiency solid oxide fuel cell |
| CN117709287B (en) * | 2024-02-06 | 2024-05-07 | 中国石油大学(华东) | Dimension optimization design method for flexible bipolar plate of high-efficiency solid oxide fuel cell |
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