| Proton exchange membrane fuel cell?PEMFC?has been considered as a promising clean and efficient energy device due to the advantages such as high power density,pollution-free characteristic,and quickly start-up at room temperature.However,the high cost of PEM fuel cell is hindering its commercial development.Bipolar plate is the key component of PEM fuel cell,it costs 30-45 percentage of the total cost of PEM fuel cell,metal bipolar plate has become the research hotspot of PEM fuel cell because of its excellent properties of machinability,electrical conductivity,mechanical shock resistance as well as low cost.It has an important influence on the formability of metal bipolar plate and output performance of the fuel cell that the selection of bipolar plate materials,flow field type and flow field parameters,particularly micro-scale of the bipolar plate flow channel,which leads to the formability of metal bipolar plate and fluid flow in the channel different from the macro-scale materials.This study investigates the formability of austenitic 304 stainless steel and novel Fe-Ni-Cr alloy during stamping forming process through both numerical simulation and experimental method,it analyzes the effect of forming process and flow field parameter on plastic deformation;in addition,the measurement and analysis of water flow in bipolar plate micro-channel is executed by visualization of micro-fluid velocity measurement technology,and the Fluent software numerical simulation method is revised by the velocity measurement results to improve the reliability of numerical simulation on fuel cell performance.This research work and results are as follows:?1?304 stainless steel bipolar plate tensile tests are conducted,studying the influence of strain rate on the plastic deformation of tensile samples,for phase analysis and microstructure test,the results show that the 304 austenitic stainless steel generates strain induced martensite phase transformation during the plastic deformation,the martensite phase transformation could improve the plastic deformation ability of material.The constitutive relation curve is built through the Jaynes-Cummings model,which is fitting well with the experimental results;?2?The 3D model is established by using the finite element software Dynaform,simulating stamping process of the 304 stainless steel and alloy bipolar plate,the wrinkling and cracking defects are forecasted and eliminated based on the forming limit diagram?FLD?and blank thinning situation during forming,thereby obtaining the best forming process and the safe size range of flow field,verification for the numerical simulation by experimental results indicates that the experimental results and numerical simulation ones match very well.The research shows that the formability of alloy is similar to that of 304 stainless steel bipolar plate,which indicates that the alloy is a very promising bipolar plate materials;?3?Fuel cell module in CFD software Fluent is used to establish three-dimensional mathematical model of the fuel cell,and to investigate the influence factors of fuel cell power output,mainly considering the bipolar plate material,flow channel dimensions and flow field type,the numerical simulation results show that voltage decreases gradually with the increase of current density,and the power density increases with the increase of current density at first,and then decreases after arriving the peak.At low current density,the bipolar plate material,channel width and channel depth have little influence on the performance of fuel cell,while the above factors have a greater influence on the output performance with the increase of current density.Carve graphite and 304 stainless steel coated with oxide film bipolar plate with a serpentine flow field,then assemble them into a single cell for performance test,when the current density loads to 3.6 A·cm-2,the power density of graphite bipolar plate single cell is about 1.4 W·cm-2,when the current density loads to 0.9 A·cm-2,the power density of 304 stainless steel coated with oxide film bipolar plate reaches to the maximum value of 0.38 W·cm-2,and then decreases when current density continues to increase.The numerical result of output performance of 304 stainless steel coated with oxide film bipolar plate single cell is less than the experimental result,because of that the numerical model ignores the effect of micro-flow channel wall properties,and could not reflect the fuel cell performance truly;?4?Microfluidics visualization research is carried out on the water flow in bipolar plate micro-channel through microfluidics technology,it mainly analyzes the influence of bipolar plate material,the surface properties and surface modification technology on water flow rate,and the Micro-PIV velocity measuring results show that it is laminar flow both in the graphite and 304 stainless steel bipolar plate micro-channel.The maximum velocity is related to the surface conditions,while the numerical simulation is unrelated to the surface conditions,and the experimental results are relatively different from the simulation results.It improves the reliability of numerical simulation when revised it by the velocity measurement results,the single cell output performance obtained by revised numerical simulation method is close to the experimental one,and thereby it is an effective method to utilize the microfluidics technology for fuel cell performance research.The research in this paper analyzes the plastic forming regularity of metal bipolar plate through stamping process numerical simulation and experimental study,which providing guidance for forming technology and flow field dimension optimization of metal bipolar plate;fluid flow visualization research on the flow regularity in bipolar plate micro-channel reveals the influence of wall properties on water flow in micro-channel,which provides theoretical basis for improving the fuel cell performance by surface modification treatment. |
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