Design Features Of Fuel Cell Bipolar Plate
Design Features Of Fuel Cell Bipolar Plate – Ultrasonic Spray – Cheersonic
Bipolar plate is the main structural support of fuel cell stack, and its structural design forms the flow channel of hydrogen, air and water in the stack. As the main structure of the stack, the thickness of bipolar plate directly affects the power density of the stack. At present, due to the relatively high threshold of membrane electrode technology in the industry, the breakthrough progress is slow, and the starting point of improving the performance of stack products is mainly on bipolar plate.
The bipolar plate of fuel cell must meet the following performance requirements:
In order to play a series role in single cell, the bipolar plate must have high conductivity; to isolate the reaction gas and heat dissipation water in each cavity, the gas permeability of bipolar plate should meet the requirements;
The heat of the reaction area is transferred to the coolant quickly, and the bipolar plate should have high thermal conductivity; considering the structure strength, vibration, power density and low temperature start-up, the strength, density and heat capacity of the bipolar plate material should also meet the product performance requirements.
Metal materials have high conductivity and conductivity, high gas resistance and high strength, which are suitable for thinner plates, but they are easy to corrode and need special coating process. The graphite plate is relatively thick, but the material is relatively stable and has certain advantages in durability.
1 meet the requirements of active area
2 consider all aspects of tolerance
The design of bipolar plate should first consider meeting the requirements of active area of stack power, as shown in the red box power generation area on the left side of the figure below. The selection of active area area is closely related to the location of uniform gas distribution area and uniform temperature distribution area of stack, otherwise it will affect the durability of stack. At present, with the increasing power demand of fuel cell, the active area of membrane electrode is required to be larger and larger. While increasing the area, it is necessary to consider whether the molding and stamping processes can meet the processing requirements of large area electrode plate.
3 material characteristics and forming process
In addition, the dimensional tolerance, form and position tolerance of bipolar plate, membrane electrode and sealing line as well as the fit tolerance in the assembly process should be fully considered in the design of electrode plate. Reasonable tolerance design can ensure the reliability, consistency and durability of products. The matching section of bipolar plate, sealing line and membrane electrode is shown in the figure below. The reasonable design of the matching area has an important influence on the assembly performance, dry and wet durability and the proportion of active area.
The design process of bipolar plate should fully consider the material characteristics and forming process. The strength of graphite plate is lower than that of metal plate, and the gas permeability is higher. Therefore, there should be a safety margin in the plate thickness. At present, the thinnest part of carved graphite plate should be at least 0.3mm thick, and the material thickness of die plate will be thinner. As shown in the figure below, there is a thick material separation distance between the bottom of the left graphite plate channel, while when the right metal plate is formed, the other side of the hydrogen and air cavity is combined to form a water channel, and the plate is only 0.1 mm thick, which is thinner than the graphite bipolar plate single cell.
4 air distribution port and structural strength design
There are two ways to design at the inlet of the plate
One is that there is a gas distribution partition between the cathode and anode plate, and the structure is relatively complex. There is a partition structure used to isolate gas inside the hot pressed rubber of Toyota metal plate; the other is the Z-shaped gas distribution structure, which will increase the width of the sealing area, but the overall structure is simple.
The graphite bipolar plate uses the perforation way, uses the anode plate and the cathode plate to form the gas distribution port, the structure is relatively simple
The maximum power of the stack needs to be matched with the design of gas distribution port and structural strength. The area of gas distribution port will affect the upper limit of the number of batteries assembled. The structural design of the electrode plate will affect the strength of the stack in all directions after assembly. In addition, the gas flow direction, stack placement direction, process hole location, power collection by patrol inspection, power collection by power collection board and other factors should be considered in the design stage. Different manufacturers of metal bipolar plate, there are three ways of medium import and export on the same side of the design, there are also different designs for other needs.
5. Uniform distribution of media in flow field
In the aspect of flow field design, the design of air, hydrogen and water should ensure the uniform distribution of medium, the reasonable pressure drop design should ensure the uniform distribution of different single tanks, especially in the hydrogen and air side, the influence of liquid water should be reduced, and the matching engine system and corresponding working conditions should be considered in the design of flow channel, which is different from the design of various manufacturers Same as. Toyota innovatively uses 3D flow field to strengthen water management and air diffusion plate design, as shown in the figure below:
Honda improves the heat dissipation capacity and method of the plate, changing the original single cell heat dissipation into two single cells, using the same heat dissipation flow field, ensuring the heat dissipation capacity and improving the power density of the whole stack.
Honda added a numerical structure between the plates to promote the uniform distribution of reaction medium, and improve the assembly performance of parts and the mechanical properties between plates.
It is believed that in the future, with the continuous progress of fuel cell technology, more innovative designs will emerge.
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