A device and method for testing the fluid flow rate of a bipolar plate in a fuel cell.

Abstract

This invention provides a device and method for testing the fluid flowability of a bipolar plate in a fuel cell. The testing device includes a transparent, visually accessible gas inlet end plate, a blind end plate, a gas inlet / outlet adapter plate, and a transparent polyester frame. The testing method specifically includes the following steps: Step 1: Cleaning the surface of the bipolar plate to be tested; Step 2: Assembling the bipolar plate fluid flowability testing device; Step 3: Adding liquid droplets; Step 4: Gas purging; By connecting an external gas source through the gas inlet / outlet adapter plate and adjusting the gas pressure and flow rate, the liquid droplets in the flow channel of the bipolar plate to be tested are continuously purged. The purging time is recorded from the start of gas supply until the droplets are completely removed by water; Step 5: Determining the fluid flowability of the bipolar plate. This invention solves the problem in the prior art that the surface characteristic testing of bipolar plate flow channels cannot reflect the dynamic process of droplets under fuel cell operating conditions.

Description

Technical Field

[0001] This invention relates to the field of performance testing technology for bipolar plates in proton exchange membrane fuel cells (PEMFCs), and more particularly to a device and method for testing the fluid flow of a bipolar plate in a fuel cell. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) are characterized by high energy conversion efficiency, rapid low-temperature start-up, and zero pollution, making them ideal as a power source for green new energy vehicles. PEMFCs are also well-suited for stationary power plants, backup power supplies, and combined heat and power (CHP) systems. The bipolar plate is a crucial multifunctional component of PEMFCs. Its primary function is to deliver reactant gases to the membrane electrode assembly through a surface flow field, while simultaneously collecting and conducting current and removing reaction heat and water products. The bipolar plate accounts for approximately 80% of the weight and 30% of the cost of a PEMFC stack. The widespread application of PEMFCs requires bipolar plates to possess high electrical conductivity, high airtightness, good mechanical properties, corrosion resistance, and low cost.

[0003] Qualified bipolar plate products typically undergo a series of characteristic tests, including flatness, corrosion current density, contact resistance, volume resistivity, air permeability, flexural strength, drag drop, area utilization, thickness uniformity, density, and weight. However, testing the hydrophilicity / hydrophobicity or liquid flowability of the bipolar plate's flow channel surface has always been a challenge in the industry. Because both the anode and cathode of the bipolar plate are designed with intricate gas flow channels, it is difficult to find a smooth surface with sufficient area for hydrophilicity / hydrophobicity or surface tension testing, which limits the detection and research of bipolar plate surface characteristics. Fuel cells primarily produce water, especially during high-power operation, generating large amounts of liquid water. If not drained promptly, this can cause "flooding" of the membrane electrode assembly, affecting the fuel cell's performance output and durability. Therefore, changes in the hydrophilicity / hydrophobicity of the bipolar plate surface or the resistance to liquid flow have a significant impact on fuel cell water management. Strengthening the detection and analysis of the dynamic characteristics of liquid water on the surface of bipolar plate flow channels is of great significance for improving the hydrothermal management of fuel cells, especially for improving the low-temperature start-up and shutdown water sweeping strategies of fuel cells.

[0004] Because both the anode and cathode of a bipolar plate are designed with finely detailed flow channels, it is difficult to find a relatively flat or sufficiently large effective area on the surface of the formed bipolar plate for surface characteristic testing, such as electrochemical corrosion testing, surface contact resistance, and hydrophilicity / hydrophobicity testing, all of which involve certain errors. Current technologies for detecting the dynamic characteristics of liquids on the surface of bipolar plate flow channels are usually based on traditional interface contact angle testing, requiring a contact angle meter. Furthermore, the droplets remain static, only detecting a very small area of ​​hydrophilicity / hydrophobicity within the bipolar plate flow channel, and cannot truly reflect the dynamic process of droplet flow and the magnitude of flow resistance throughout the entire gas cavity flow channel. This still falls short of the dynamic process of fuel cell operation. Therefore, developing reasonable methods or devices to simulate and study the dynamic process of droplets on the surface of bipolar plate flow channels is urgently needed. Summary of the Invention

[0005] To address the technical problem that existing technologies for testing the fluid flowability of bipolar plate channels cannot reflect the dynamic process of droplets during fuel cell operation, this paper provides a device and method for testing the fluid flowability of fuel cell bipolar plate channels. Through a visual fixture, the device can detect the fluidity of droplets within a single bipolar plate channel, providing a more intuitive and accurate assessment of the effect and rate of droplet purging on the inner surface of the bipolar plate channel. This more closely reflects the dynamic state of droplets on the bipolar plate surface during actual fuel cell operation. The testing method can be used to study the fluid flowability of bipolar plate channels under different conditions, with different surface treatment technologies and coating types, indirectly reflecting the hydrophilicity / hydrophobicity, surface tension, and fluid flow resistance characteristics of the channel surface.

[0006] The technical means employed in this invention are as follows:

[0007] A fluid flow testing device for a fuel cell bipolar plate includes a transparent and visible gas inlet end plate, a blind end plate, a gas inlet / outlet adapter plate, and a transparent polyester frame. The bipolar plate under test is installed between the transparent and visible gas inlet end plate and the blind end plate, and a transparent polyester frame is provided on each side. The transparent and visible gas inlet end plate is provided with a droplet inlet hole. The gas inlet / outlet adapter plate is installed on the edge of the three-chamber channel hole of the transparent and visible gas inlet end plate, and the gas inlet / outlet adapter plate is used for detachable connection to an external gas source.

[0008] Furthermore, when the bipolar plate under test is installed between the transparent and visible air port end plate and the blind end plate, the droplet inlet hole can correspond to the flow channel groove of the bipolar plate under test.

[0009] Furthermore, it also includes a positioning screw and a fastening screw. The transparent visual air port end plate and the blind end plate are respectively provided with a plurality of positioning holes with corresponding positions at both ends. The positioning screw passes through the positioning holes of the transparent visual air port end plate and the blind end plate in sequence and is fastened by the fastening screw.

[0010] Furthermore, the bipolar plate under test is a graphite bipolar plate, a composite bipolar plate, or a metal bipolar plate.

[0011] Furthermore, the transparent and visible air inlet end plate is made of plexiglass, and the blind end plate 7 is made of stainless steel or aluminum alloy.

[0012] Furthermore, the gas inlet and outlet adapter plate is a stainless steel plate and is equipped with a quick-connect PU tube adapter. The quick-connect PU tube adapter is used to connect the external gas source for purging and the tail exhaust. The front end of the quick-connect PU tube adapter is equipped with a gas flow meter and a pressure controller to monitor the gas flow and pressure.

[0013] This invention also provides a method for testing the fluid flow rate of a bipolar plate in a fuel cell, specifically including the following steps:

[0014] Step 1: Clean the surface of the bipolar plate to be tested.

[0015] Step 2: Assembly of the bipolar plate liquid flowability testing device

[0016] Place the blind end plate 7 at the bottom, and then stack a transparent polyester frame, a bipolar plate to be tested, a transparent polyester frame and a transparent visual gas port end plate 1 in sequence. Insert the positioning screw into the corresponding positioning holes 5 on the transparent visual gas port end plate 1 and the blind end plate 7 in sequence, and tighten it with fastening screws. Then install the gas outlet adapter plate to the gas outlet of the transparent visual gas port end plate 1.

[0017] Step 3: Add liquid dropwise

[0018] A certain volume of liquid is dripped into the flow channel groove of the bipolar plate under test at one time through the droplet inlet hole 4 on the transparent and visible air inlet end plate 1 using a dropper or liquid syringe.

[0019] Step 4: Gas purging

[0020] By connecting an external gas source through the gas inlet and outlet adapter plate, adjusting the gas pressure and flow rate, the droplets in the flow channel groove of the bipolar plate under test are continuously purged. The purging time is recorded from the start of the gas supply until the droplets are completely swept away by water.

[0021] Step 5: Determining the fluidity of the bipolar plate liquid

[0022] (1) Under the same type, flow rate and pressure of purging gas, the longer it takes for the droplets to be completely purged in the same flow channel, the greater the flow resistance and the weaker the liquid flow. Conversely, the shorter the purging time, the smaller the flow resistance and the stronger the liquid flow.

[0023] (2) Under the same type, pressure and time of purging gas, the gas flow rate required to completely purge the droplets in the same position of the flow channel is used to judge. The larger the gas flow rate required for purging, the greater the flow resistance and the weaker the liquid flow. Conversely, the smaller the gas flow rate required for purging, the smaller the flow resistance and the stronger the liquid flow.

[0024] Furthermore, step 2 also includes that after the bipolar plate liquid flowability testing device is assembled, an external gas source is needed to test the airtightness of the bipolar plate liquid flowability testing device. After the airtightness is qualified, step 3 is then performed. The airtightness test adopts the gas pressure holding method or the flow rate method, and the gas used for the airtightness test is nitrogen, air or hydrogen.

[0025] Furthermore, in step 3, the liquid added is deionized water or ethylene glycol; the volume of the liquid added in step 3 is 0.2 μL to 10 μL, and the liquid is added slowly so that the droplets can accurately reach the single flow channel groove of the bipolar plate to be tested.

[0026] Further, in step 4, the gas is nitrogen, helium, air and hydrogen; the gas pressure is 0-20 kPa; the gas flow rate is 200 mL / min-5 L / min; the purging time is the time from the start of gas introduction to the complete purging of the droplets in the bipolar plate channel from the inlet end to the outlet end, and the purging time is 1-20 min.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1. The fuel cell bipolar plate flow channel liquid flow testing device and method provided by this invention can study the liquid flow of the bipolar plate flow channel surface under different types of bipolar plate states, different surface modification technologies, and different coating types from a dynamic perspective. It can reflect the hydrophilicity / hydrophobicity of the coating, the magnitude of liquid flow resistance or surface tension. Through the dynamic process of droplet purging and visualization device, it provides a more intuitive testing method and device that is closer to the online operation state of fuel cells to study the changes in surface characteristics of bipolar plates. The flow state of droplets in the flow channel at different positions of the bipolar plate can be directly observed. It provides important technical support for the research on bipolar plate flow channel structure design, material selection and fuel cell hydrothermal management, especially for the proposal and improvement of fuel cell low temperature start-up and shutdown water purging strategies.

[0029] 2. The fuel cell bipolar plate flow channel liquid flow test device and method provided by the present invention are applicable to any type of bipolar plate with flow channels, filling the gap in the dynamic detection method of surface characteristics of fine bipolar plate flow channels. Moreover, the method is simple, has a wide range of applications, and is more convincing.

[0030] Based on the above reasons, this invention can be widely applied in the field of fuel cell bipolar plate performance testing. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the structure of the fluid flow test device for the bipolar plate flow channel of the fuel cell.

[0033] Figure 2 This is a schematic diagram of the flow channel structure of the bipolar plate under test.

[0034] Figure 3 This is a schematic diagram of the process of droplets entering the flow channel groove of the bipolar plate under test.

[0035] Figure 4 This diagram illustrates the flowability test results of a noble metal coated metal bipolar plate in its initial state and after accelerated durability testing at different times, using the test method described in this invention.

[0036] Figure 5 This diagram illustrates the liquid flow test results of three different types of coatings on metal bipolar plates—B. noble metal coating, C. carbon coating, and D. metal oxide coating—in their initial state using the test method described in this invention.

[0037] Figure 6 The results are based on the test method described in this invention, which measures the liquid flowability of the flow channels at three different locations on the cathode plate of the same precious metal coated metal bipolar plate after a 5000-hour durability test.

[0038] In the diagram: 1. Transparent and visible gas inlet end plate; 2. Three-chamber channel hole; 3. Adhesive line groove; 4. Droplet inlet hole; 5. Positioning hole; 6. Positioning and fastening hole of gas inlet / outlet adapter plate; 7. Blind end plate. Detailed Implementation

[0039] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0042] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0043] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0044] For ease of description, spatial relative terms such as "above," "over," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation besides the orientation of the device as described in the figures. For example, if the device in the figures is inverted, a device described as "above" or "above" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0045] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0046] Example 1

[0047] Detecting the surface characteristics of bipolar plates with fine flow channels has always been a challenge in the industry, especially since some dynamic research methods and detection technologies have been almost non-existent. Studying changes in bipolar plate surface characteristics is of great significance for improving bipolar plate surface modification technology, fuel cell stack hydrothermal management, and fuel cell stack purging strategies. This invention provides a device and method for testing the fluid flowability of fuel cell bipolar plate flow channels, such as... Figure 1 As shown, the testing device includes a transparent and visible gas inlet end plate 1, a blind end plate 7, a gas inlet and outlet adapter plate, and a transparent polyester frame.

[0048] The bipolar plate under test is installed between the transparent and visible air port end plate 1 and the blind end plate 7, and a transparent polyester frame is provided on each side.

[0049] The transparent and visible air inlet end plate 1 is provided with a liquid droplet inlet hole 4;

[0050] The transparent and visible gas port end plate 1 has a gas inlet and outlet adapter plate positioning and fastening hole installed on the edge of the three-chamber channel hole 3. The gas inlet and outlet adapter plate is fixedly installed in the gas inlet and outlet adapter plate positioning and fastening hole. The gas inlet and outlet adapter plate is used for detachable connection to an external gas source.

[0051] Furthermore, when the bipolar plate under test is installed between the transparent and visible air port end plate 1 and the blind end plate 7, the droplet inlet hole 4 can correspond to the flow channel groove of the bipolar plate under test.

[0052] Furthermore, the transparent and visible air vent end plate 1 is provided with three-cavity channel holes 3 on both sides, and the edges of the three-cavity channel holes 3 are provided with adhesive grooves 2 for sealing the adhesive lines, which mainly serve as gas sealing.

[0053] Furthermore, the testing device also includes a positioning screw and a fastening screw. The transparent visual air port end plate 1 and the blind end plate 7 are respectively provided with a plurality of positioning holes 5 corresponding to each other. The positioning screw passes through the positioning holes 5 of the transparent visual air port end plate 1 and the blind end plate 7 in sequence and is fastened by the fastening screw to fix the transparent visual air port end plate 1 and the blind end plate 7.

[0054] Furthermore, the bipolar plate to be tested is a bipolar plate of different materials, processes or structures, such as graphite bipolar plate, composite bipolar plate or metal bipolar plate, and the bipolar plate is composed of two single plates, a cathode and an anode, and a sealing adhesive line.

[0055] Furthermore, the transparent and visible air inlet end plate 1 is made of plexiglass, or other materials with certain strength, good air barrier properties, transparency, and good resistance to high and low temperatures.

[0056] Furthermore, the diameter of the positioning hole 5 is 5-10 mm;

[0057] Furthermore, the shape and size of the three-cavity channel hole 3 are consistent with the three-cavity opening of the bipolar plate under test.

[0058] Furthermore, the blind end plate 7 is made of stainless steel or aluminum alloy, which have certain strength, good gas barrier properties, and good resistance to high and low temperatures.

[0059] Furthermore, the external dimensions of the blind end plate 7 are the same as those of the transparent visual air vent end plate 1.

[0060] Furthermore, the gas inlet and outlet adapter plate is a stainless steel plate and is equipped with a quick-connect PU tube adapter. The quick-connect PU tube adapter is used to connect the external gas source for purging and the tail exhaust. The front end of the quick-connect PU tube adapter is equipped with a gas flow meter and a pressure controller to monitor the gas flow and pressure.

[0061] Furthermore, the positioning screw is a solid stainless steel rod with threads, and its diameter is 1mm smaller than the inner diameter of the positioning hole 5.

[0062] Furthermore, the transparent polyester frame serves as a transition layer between the transparent visual air port end plate 1 and the blind end plate 7 and the bipolar plate under test, thereby improving the sealing performance and stress uniformity of the device. Its external dimensions are consistent with those of the transparent visual air port end plate 1, and its edges are provided with frame positioning holes corresponding to the positioning holes 5. The three-cavity channel holes on the transparent polyester frame are also consistent with those of the transparent visual air port end plate 1. The thickness of the transparent polyester frame is 200μm to 1mm.

[0063] Furthermore, the droplet inlet hole 4 is located on the gas inlet side of the three-chamber channel hole 3 on the transparent and visible gas port end plate 1, corresponding to the transition area from the flow channel distribution area to the active area of ​​the bipolar plate under test. This ensures that each droplet inlet hole 4 corresponds as closely as possible to the position of a single flow channel groove in the bipolar plate under test, allowing the droplet to accurately enter the single flow channel under test. This is more conducive to studying the flowability of droplets in different single flow channels. The opening diameter of the droplet inlet hole 4... satisfy like Figure 2 As shown, L1 represents the minimum platform width of the flow channel groove bottom of the bipolar plate under test, and L2 represents the maximum width of the flow channel groove opening of the bipolar plate under test. Preferably, It meets the requirements of 0.2mm to 2mm.

[0064] When using the testing device described in this invention, the surface of the bipolar plate to be tested is first cleaned. Then, the bipolar plate to be tested is installed between the transparent and visual gas inlet end plate 1 and the blind end plate 7. A certain volume of droplets is dripped into the droplet inlet hole 4 on the transparent and visual gas inlet end plate 1 so that the droplets accurately reach the flow channel groove of the bipolar plate to be tested. The droplet inlet hole 4 is connected to a gas cylinder to purge it with gas at a certain flow rate and pressure. The flow state of the droplets in the flow channel of the bipolar plate to be tested can be observed in real time through the transparent and visual gas inlet end plate 1. The liquid flow resistance on the surface of the flow channel of the bipolar plate to be tested is determined by calculating the time it takes for the droplets to be completely purged in the flow channel groove of the bipolar plate to be tested. This allows for the study of the changes in the hydrophilicity and hydrophobicity, surface tension, and other properties of the bipolar plate flow channel surface. This is of great significance for improving the hydrothermal management of fuel cells, especially for improving the low-temperature start-up and shutdown water purging strategies of fuel cells.

[0065] This invention also provides a method for testing the fluid flow rate of a bipolar plate in a fuel cell, specifically including the following steps:

[0066] Step 1: Clean the surface of the bipolar plate to be tested. Use an alcohol swab soaked in alcohol-based cleaning agents such as ethanol or acetone to repeatedly wipe and clean the surface of the bipolar plate flow channel, and then let it air dry or bake it for later use.

[0067] Step 2: Assembly of the bipolar plate liquid flowability testing device

[0068] Place the blind end plate 7 at the bottom, and then stack a transparent polyester frame, a bipolar plate to be tested, a transparent polyester frame and a transparent visual gas port end plate 1 in sequence. Insert the positioning screw into the corresponding positioning holes 5 on the transparent visual gas port end plate 1 and the blind end plate 7 in sequence, and tighten it with fastening screws. Then install the gas outlet adapter plate to the gas outlet of the transparent visual gas port end plate 1.

[0069] Step 3: Add liquid dropwise

[0070] A certain volume of liquid is dripped into the flow channel groove of the bipolar plate under test at one time through the droplet inlet hole 4 on the transparent and visible air inlet end plate 1 using a dropper or liquid syringe.

[0071] Figure 3 A schematic diagram of the process of droplets falling into the flow channel groove of the bipolar plate under test is shown. In the figure, (1) is the droplet inlet hole 4 on the transparent and visible air port end plate 1, (2) represents the droplet's falling path, (3) is the flow channel groove of the bipolar plate under test, and (4) represents the droplet that is dropped into a certain flow channel groove of the bipolar plate under test.

[0072] Step 4: Gas purging

[0073] By connecting an external gas source through the gas inlet and outlet adapter plate, adjusting the gas pressure and flow rate, the droplets in the flow channel groove of the bipolar plate under test are continuously purged. The purging time is recorded from the start of the gas supply until the droplets are completely swept away by water.

[0074] Step 5: Determining the fluidity of the bipolar plate liquid

[0075] (1) Under the same type, flow rate and pressure of purging gas, the longer it takes for the droplets to be completely purged in the same flow channel, the greater the flow resistance and the weaker the liquid flow. Conversely, the shorter the purging time, the smaller the flow resistance and the stronger the liquid flow.

[0076] The fluidity of the bipolar plate under different types or conditions is mainly determined by the flow resistance of the droplet flowing through the gas cavity channel. The magnitude of the flow resistance of the droplet is determined by the time it takes for the droplet to be completely purged in the same channel under the same type, flow rate and pressure of purging gas. The longer the purging time, the greater the flow resistance and the weaker the fluidity of the liquid. Conversely, the shorter the purging time, the smaller the flow resistance and the stronger the fluidity of the liquid.

[0077] (2) Under the same type, pressure and time of purging gas, the gas flow rate required to completely purge the droplets in the same position of the flow channel is used to judge. The larger the gas flow rate required for purging, the greater the flow resistance and the weaker the liquid flow. Conversely, the smaller the gas flow rate required for purging, the smaller the flow resistance and the stronger the liquid flow.

[0078] Based on the above judgment results, we can further analyze the changes in hydrophilicity or surface tension of the bipolar plate channel surface and study the impact of changes in the surface characteristics of the bipolar plate channel on the droplet purging efficiency.

[0079] Furthermore, the cleaning time for the surface of the bipolar plate flow channel to be tested in step 1 is 3 to 5 minutes.

[0080] Furthermore, step 2 also includes that after the bipolar plate liquid flow test device is assembled, an external air source is needed to test the airtightness of the bipolar plate liquid flow test device. Only after the airtightness is qualified can the process proceed to step 3.

[0081] Furthermore, the airtightness test adopts the gas pressure holding method or the flow rate method. The airtightness test gas is an inert gas such as nitrogen or air. The gas used for airtightness test is consistent with the type of purging gas used when testing the liquid flowability of the bipolar plate under test. When the bipolar plates under test are stacked, the test surface (cathode plate or anode plate) should face upwards to correspond to the transparent and visible gas port end plate 1.

[0082] Furthermore, in step 3, the liquid added is deionized water or ethylene glycol or other liquids that are to be studied; the volume of the liquid added in step 3 is 0.2 μL to 10 μL, and the liquid is added slowly so that the droplets can accurately reach the single flow channel groove of the bipolar plate to be tested.

[0083] Furthermore, in step 4, the gas is an inert gas such as nitrogen or helium, or air and hydrogen. If hydrogen is used for purging, hydrogen safety testing and exhaust treatment must be strengthened. Nitrogen and air are preferred. The gas pressure is 0-20 kPa, i.e., low-pressure conditions. The gas flow rate is 200 mL / min-5 L / min, which can be adjusted appropriately according to the size of the active area of ​​the bipolar plate. The purging time is the time from the start of gas introduction to the complete purging of the droplets in the flow channel of the bipolar plate under test from the inlet end to the outlet end. The purging time is generally 1-20 min.

[0084] The method for testing the fluid flow of bipolar plate flow channels in proton exchange membrane fuel cells provided by this invention can be used to study the fluid flow of bipolar plate flow channels under different conditions (such as the initial state, the state after durability testing, or the state after environmental testing), different surface treatment technologies, and different coating types. It reflects the hydrophilicity / hydrophobicity, surface tension, and fluid flow resistance of the flow channel surface. Through the dynamic purging process of the liquid and the visualization device, the flow state of droplets in different flow channels of the bipolar plate can be directly observed, and the magnitude of the fluid flow resistance can be calculated. This provides important technical support for the structural design of bipolar plate flow channels, material selection, improvement of fuel cell hydrothermal management, and especially for the proposal and improvement of low-temperature start-up and shutdown water purging strategies for fuel cells.

[0085] Example 1

[0086] This embodiment uses the bipolar plate flow channel liquid flowability testing device and method proposed in this invention to test the liquid flowability of a noble metal coated metal bipolar plate in its initial state and after accelerated durability testing at different times. The specific steps are as follows:

[0087] Step 1: Clean the surface of the flow channel of the A precious metal coating metal bipolar plate in its initial state. Use an alcohol swab to repeatedly wipe and clean the surface of the bipolar plate cathode plate flow channel by soaking it in ethanol for 3 minutes, and then let it air dry for later use.

[0088] Step 2: Assembly of the bipolar plate liquid flowability testing device

[0089] Place the blind end plate 7 at the bottom, and then stack a transparent polyester frame, a bipolar plate to be tested, another transparent polyester frame, and a transparent visual air port end plate 1 in sequence. Insert the positioning screw into the corresponding positioning holes 5 on the transparent visual air port end plate 1 and the blind end plate 7 in sequence, and tighten them with fastening screws. Then install the gas outlet adapter plate to the gas outlet of the transparent visual air port end plate 1. After the bipolar plate liquid flowability test device is assembled, an external air source is required to test the air tightness of the bipolar plate liquid flowability test device. After the air tightness is qualified, proceed to step 3.

[0090] In the testing apparatus used in this embodiment, the transparent visual air inlet end plate 1 is made of plexiglass with a thickness of 50mm; the diameter of the positioning hole 5 is 6mm; the diameter of the positioning screw is 5mm; the thickness of the transparent polyester frame is 500μm; and the opening diameter of the droplet inlet hole 4 is... It is 0.5mm;

[0091] Step 3: Add liquid dropwise

[0092] Using a dropper or liquid syringe, slowly drip 2 μL of deionized water into the flow channel groove of the bipolar plate under test through the droplet inlet hole 4 on the transparent and visible air inlet end plate 1.

[0093] Step 4: Gas purging

[0094] Nitrogen gas was used for purging. An external gas source was connected through the gas inlet and outlet adapter plate. The pressure of nitrogen gas was adjusted to 5 kPa and the flow rate was 500 mL / min. The droplets in the flow channel groove of the bipolar plate under test were continuously purged. The purging time was recorded from the start of the gas supply until the droplets were completely removed by water.

[0095] Step 5: Determining the fluidity of the bipolar plate liquid

[0096] In this embodiment, the fluid flow of the A precious metal coated metal bipolar plate after different durability test times was tested. The fluid flow was mainly determined by the magnitude of the flow resistance of deionized water droplets flowing through the cathode gas cavity. The flow resistance of the droplets was determined by different purging times under the same purging gas type, gas flow rate and pressure. The longer the purging time, the greater the flow resistance and the weaker the fluid flow. Conversely, the shorter the purging time, the smaller the flow resistance and the stronger the fluid flow.

[0097] Statistical results of droplet purging time of bipolar cathode plate after durability tests at different times are as follows: Figure 4 As shown, after 1000 hours of accelerated durability testing, the purging time of the bipolar plate increased by 2.6 times compared to the initial state. After 2000 hours and 3000 hours, the purging time of the bipolar plate continued to increase, but the rate of increase decreased. After 4000 hours and 5000 hours, the purging time gradually stabilized at around 5 minutes. With the increase of durability time, the purging time showed a trend of first increasing and then gradually stabilizing. This indicates that in the early stage of the accelerated durability testing of the fuel cell stack, the coating surface of the bipolar plate will undergo significant changes, especially changes in hydrophilicity and hydrophobicity. The coating surface of the bipolar plate is prone to oxidation, corrosion, coating peeling or agglomeration under the frequent high and low temperature changes, high and low voltage changes, dry and wet cycles and weak acid environment of the fuel cell, which will cause changes in the hydrophilicity and hydrophobicity of the coating surface and changes in surface roughness. It often becomes more hydrophilic. Increased roughness will lead to increased flow resistance of water droplets on the surface of the flow channel, thus increasing the purging time of the droplets. However, as the fuel cell stack's accelerated durability operation time increases, the state and microstructure of the bipolar plate coating will gradually stabilize, and its physicochemical properties will also stabilize, so the droplet purging time will gradually stabilize.

[0098] Based on the experimental results of this embodiment, the purging strategy during the fuel cell stack durability operation process can be further optimized. For example, the purging time or gas volume can be appropriately increased at a certain time during the fuel cell stack durability test to improve the purging efficiency of liquid water in the bipolar plate.

[0099] Example 2

[0100] The difference between Example 2 and Example 1 is that the research object is changed to three different types of metal bipolar plates with coatings: B is a noble metal coating, C is a carbon coating, and D is a metal oxide coating. The rest, such as the substrate, forming and welding process, plate flow channel structure, and size, are the same. Only the coating materials are different. The liquid flowability of the metal plate in its initial state is tested.

[0101] Example 2 maintains the same testing methods, detection devices, and detection parameters as Example 1. The liquid flowability test results are also determined by the duration of the purging process under the same purging gas type, flow rate, and pressure. The results are as follows: Figure 5 As shown, the liquid flow detection results of the three different types of coatings are not significantly different, with similar purging times. However, relatively speaking, the purging time of droplets on the flow channel surface of the C carbon coated metal bipolar plate is greater than that of the D metal oxide coated metal bipolar plate, which is greater than that of the B noble metal coated metal bipolar plate. This indicates that, relatively speaking, the liquid flow resistance on the flow channel surface of the deionized C carbon coated metal bipolar plate is smaller, which also reflects that the C carbon coating surface may have higher hydrophobicity, making it more conducive to the discharge of liquid water.

[0102] This embodiment demonstrates that the bipolar plate liquid flowability detection device and method proposed in this invention are applicable to bipolar plates with any type of coating. Through parallel testing and comparison, the hydrophilic and hydrophobic properties or surface tension of coating surfaces of different types or preparation processes can be reflected indirectly. Most importantly, the droplet flow state and flow resistance of liquid on the flow channel surface of bipolar plates with different coatings can be directly observed, providing important technical support for the improvement of coating processes and materials and the proposal of purging strategies for different coated bipolar plates.

[0103] Example 3

[0104] The difference between Example 3 and Example 1 lies in changing the research object to different flow channels of the same bipolar plate, especially for bipolar plates after different environmental tests or durability tests. In this example, an old metal bipolar plate that has undergone accelerated durability testing was selected to study the differences in liquid flowability on the surface of the flow channels at three different locations on its cathode plate, such as... Figure 5 As shown.

[0105] Example 3 uses the same test method, detection device, and detection parameters as Example 1. The liquid flowability test results are also determined by the duration of the purging time under the same purging gas type, flow rate, and pressure. The results are as follows: Figure 6As shown, the surface liquid flowability of different channels on the old metal bipolar plate after accelerated durability testing varies significantly. Channel 1 has a significantly longer purging time than channels 2 and 3, indicating that this channel has the greatest flow resistance, reflecting a more hydrophilic surface or the lowest surface tension, which is unfavorable for timely purging and removal of liquid water. This further illustrates that the surface state changes at different locations on the same bipolar plate are inconsistent after accelerated durability testing. Due to factors such as liquid water condensation, gas distribution, or uneven current and voltage distribution during online operation of the fuel cell stack, different chemical reactions occur in different areas of the bipolar plate, leading to different structural changes or corrosion levels in the bipolar plate coating, thus resulting in different surface liquid flowability between different channels.

[0106] This embodiment demonstrates that the bipolar plate liquid flowability testing device and method proposed in this invention are applicable to the state analysis of the flow channel surface at different positions of the same bipolar plate under different conditions. By conducting parallel tests and observations of liquid flowability, the magnitude of droplet flow resistance or surface tension at different positions of the flow channel can be compared, thereby determining the degree of damage or corrosion of the coating structure at different positions. This facilitates a more in-depth and specific failure analysis of the bipolar plate and provides important technical support for the proposal and modification of coating structure modification and durability testing strategies.

[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A fuel cell bipolar plate flow channel liquid flowability testing apparatus characterized by comprising: The application relates to a transparent visual gas port end plate, a blind end end plate, a gas inlet and outlet adapter plate and a transparent polyester frame; a to-be-tested bipolar plate is arranged between the transparent visual gas port end plate and the blind end end plate, and one transparent polyester frame is arranged on each side of the bipolar plate; the transparent visual gas port end plate is provided with liquid drop dropping holes; the gas inlet and outlet adapter plate is arranged at the edge of a three-cavity channel hole of the transparent visual gas port end plate, and the gas inlet and outlet adapter plate is used for detachably connecting an external gas source. When the to-be-tested bipolar plate is arranged between the transparent visual gas port end plate and the blind end end plate, the liquid drop dropping holes can correspond to flow channel grooves of the to-be-tested bipolar plate. Liquid drops are dropped into the liquid drop dropping holes on the transparent visual gas port end plate, so that the liquid drops can accurately enter the flow channel grooves of the to-be-tested bipolar plate; the liquid drop dropping holes are connected with gas cylinders, and the liquid drop dropping holes are purged by gas; the flowing state of the liquid drops in the flow channel grooves of the to-be-tested bipolar plate can be observed in real time through the transparent visual gas port end plate; and the liquid flow resistance of the flow channel groove surface of the to-be-tested bipolar plate can be judged by calculating the time length during which the liquid drops in the flow channel groove of the to-be-tested bipolar plate are completely purged; the liquid drop dropping holes are located on the gas inlet side of the three-cavity channel hole of the transparent visual gas port end plate, correspond to the transition region from the flow distribution region to the active region of the flow channel groove of the to-be-tested bipolar plate, and make each liquid drop dropping hole correspond to a single flow channel groove position of the to-be-tested bipolar plate, so that the liquid drops can be accurately dropped into the single flow channel of the to-be-tested bipolar plate.

2. The fuel cell bipolar plate flow channel liquid flowability test apparatus according to claim 1, characterized by, The transparent visual gas port end plate and the blind end end plate are respectively provided with a plurality of position corresponding positioning holes at two ends, a positioning screw rod is sequentially inserted into the positioning holes of the transparent visual gas port end plate and the blind end end plate, and the positioning screw rod is fastened through a fastening screw.

3. The fuel cell bipolar plate flow channel liquid flowability test apparatus according to claim 1, characterized by, The to-be-tested bipolar plate is a graphite bipolar plate, a composite bipolar plate or a metal bipolar plate.

4. The fuel cell bipolar plate flow channel liquid flowability test apparatus according to claim 1, characterized by The transparent visual gas port end plate is made of organic glass, and the blind end end plate is made of stainless steel or aluminum alloy.

5. The fuel cell bipolar plate flow channel liquid flowability test apparatus according to claim 1, characterized by, The gas inlet and outlet adapter plate is a stainless steel flat plate, and is provided with a quick plug PU pipe adapter, which is used for connecting an external gas source for purging and tail gas exhaust; the front end of the quick plug PU pipe adapter is provided with a gas flow meter and a pressure controller, which are used for monitoring the flow and pressure of the gas.

6. A method for testing the liquid flowability of a fuel cell bipolar plate flow field using the fuel cell bipolar plate flow field liquid flowability testing device according to claim 1, characterized by, The application further comprises the following steps: Step 1: cleaning the surface of the to-be-tested bipolar plate; Step 2: assembling the bipolar plate liquid flow test device The blind end end plate (7) is placed at the bottom, a piece of transparent polyester frame, a piece of to-be-tested bipolar plate, a piece of transparent polyester frame and a transparent visual gas port end plate (1) are sequentially stacked, the positioning screw rod is sequentially inserted into the corresponding positioning holes (5) of the transparent visual gas port end plate (1) and the blind end end plate (7), the fastening screw is used for fastening, and the gas outlet adapter plate is arranged at the gas outlet of the transparent visual gas port end plate (1); Step 3: adding liquid A certain volume of liquid is added into the flow channel groove of the to-be-tested bipolar plate through the liquid drop dropping hole (4) of the transparent visual gas port end plate (1) by using a dropper or a liquid injector. Step 4: gas blowing Through the gas inlet and outlet adapter plate connected to the gas source, adjust the pressure and flow of the gas, and continuously blow the liquid droplets in the flow channel of the bipolar plate. From the start of the gas blowing, until the liquid droplets are completely blown away, record the blowing time. Step 5: determination of bipolar plate liquid flowability (1) Under the same blowing gas type, gas flow and pressure, the longer the time for liquid droplets to be completely blown away in the same flow channel, the greater the flow resistance and the weaker the liquid flowability. Conversely, the shorter the blowing time, the smaller the flow resistance and the stronger the liquid flowability. (2) Under the same blowing gas type, pressure and blowing time, determine the gas flow required to completely blow away the liquid droplets in the same position flow channel. The greater the gas flow required, the greater the flow resistance and the weaker the liquid flowability. Conversely, the smaller the gas flow required, the smaller the flow resistance and the stronger the liquid flowability.

7. The method for testing the fluid flowability of the bipolar plate flow channel in a fuel cell according to claim 6, characterized in that, Step 2 also includes, after the bipolar plate liquid flowability testing device is assembled, it needs to be connected to a gas source for air tightness detection. After the air tightness is qualified, it can enter step 3. The air tightness detection uses gas pressure retention method or flow method, and the air tightness detection gas uses nitrogen, air or hydrogen.

8. The method of claim 6, wherein the liquid flowability of the fuel cell bipolar plate flow field is determined by the following equation: ###0001### wherein, A is the area of the flow field, L is the length of the flow field, and H is the height of the flow field. In step 3, the liquid added is deionized water or ethylene glycol; the volume of the liquid added in step 3 is 0.2 μL~10 μL, and the liquid is slowly added so that the liquid droplets can accurately reach the single flow channel of the bipolar plate to be tested.

9. The method of claim 6, wherein the liquid flowability of the fuel cell bipolar plate flow field is determined by the following equation: ###0001### wherein, A is the area of the flow field, L is the length of the flow field, and H is the height of the flow field. In step 4, the gas is nitrogen, helium, air and hydrogen; the pressure of the gas is 0~20 kPa; the flow of the gas is 200 mL / min~5 L / min; the blowing time is from the start of the gas blowing to the time when the liquid droplets in the flow channel of the bipolar plate to be tested are completely blown away from the inlet end to the outlet end, and the blowing time is 1~20 min.

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