Effect Of Locking Bolts On Thermal Deformation Of Bipolar Plates In PEMFC

Proton exchange membrane fuel cell(PEMFC) has an extensive application prospect and huge market potential, because of high power density, low noise, no corrosion, long operating life, high energy conversion efficiency, safety and stability. It can quickly start at room temperature, easy to discharge water and not lose the electrolyte. Therefore, the application of PEMFC has important significance on sustainable economic development, environmental protection and upgrading of industrial structure. PEMFC can be not only apply to the construction of stationary power plants, to act as a removable power source, but also the ideal candidate for electric vehicles and submarine without relying on air driven. PEMFC stack are usually composed of dozens or even hundreds of single cells in the form of superposition of series by screw bolts and nuts with a certain preload. Due to the preload of locking bolts on the end plates and the working temperature, the component will produce uneven distribution of stress and the phenomenon of a certain degree of warping deformation, which will lead to a series of unexpected problems in the fuel cell. Therefore, the assembly technology of PEMFC will directly affect the performance of the fuel cell.First of all, this paper reviews the development history of fuel cell, briefly expounds working principle and the composition of the PEMFC, and analyzes the characteristics of encapsulating and the progress of research on PEMFC. Several empirical models and mechanism model of PEMFC and its associated basic equations are also briefly introduced. Based on the finite element theory, several models of single PEMFC were established to simulate the distribution of deformation before and after working through the methods of combining theoretical analysis and numerical simulation. The main reason of buckling deformation of the components of the PEMFC was analyzed. And it was concluded that the effect of temperature could offset part of deformation generated by the stress.Secondly, the maximum and minimum displacement deformation of the bipolar plates are investigated on stacks composed of 1~4 cells. It is concluded that the performance of PEMFC with an odd number of cells will be better; the maximal displacement of bipolar plates will decrease along with the increasing number of cells and then increase, and the maximum displacement deformation of 2-cell is smallest; the performance of 3-cell is best among 1~4 cells.Thirdly, this article focuses on 3-cell stack and discusses the influence on the deformation of bipolar plates in PEMFC because of the size of locking force and the distribution of bolts and the sequence of locking bolts. We comparative analyze the contours of total deformation and the absolute displacement curves of bipolar plates in the Z direction along three given paths, and also calculate the warping degree along the given path in the bipolar plates. Then, we can obtain an optimum and combined assembly scheme: 3.8 MPa clamping force on the bolt holes of end plates, four-II distribution of locking bolts and longitudinal locking sequence. The scheme can get the best deformation of bipolar plates and improve the performance of PEMFC.Finally, we conducted a visual program design of assembly scheme of 3-cell stack based on C# language. This design included the basic parameters of the main geometry and material properties, selecting the appropriate size of bolts locking force, and appropriate locking sequence. Then, we can obtain the maximum, minimum, and average warping degree and the absolute displacement curves of bipolar plates in the Z direction along the given path, and the corresponding polarization curves. In the end, we can make a comprehensive assessment of the assembly scheme of 3-cell stack through these analysis results.