| Proton exchange membrane fuel cell(PEMFC),as an ideal power source,meets the world’s rapidly growing energy demand,and its balance performance largely depends on water management.When the water removal rate of PEMFC is less than the water production rate,the water content will gradually increase and the pores in the gas diffusion layer will be blocked,leading to voltage shock.In contrast,the ionic conductivity of the membrane is strongly dependent on its degree of humidification and is very high when fully hydrated.When the water removal rate exceeds the water production rate,the phenomenon of membrane dehydration and dry cracking will occur,and the internal ohmic loss of PEMFC will increase and the life of PEMFC will be significantly shortened.Therefore,we should pay more attention to the relationship between the change of water content in the fuel cell and the related parameters.In this paper,in order to study the effect of the nonlinear change of water content on the performance of PEMFC,a model of water condensation rate(WCR)was established according to the thermodynamic laws and the conditions of the gas-liquid interface.In this model,the proportional relationship between evaporation rate and condensation rate was determined by switching function,and the two-phase flow change and pressure drop are also considered within the influence range.The influence of such factors as clear the mechanism of the water content changes and to determine the catalyst layer and the gas diffusion layer of water transfer is also considered.Then,an intelligent fuel cell test system was built to conduct cross-test experiments on the PEMFC under given working conditions,and the obtained experimental data were collated and plotted.Since the trajectories of gaseous water and liquid water are calculated independently when Fluent simulates the two-phase flow of fluid,so it is necessary to establish a geometric model and conduct grids division.The checked grid is imported into the UDF model and set as a two-phase flow simulation.The HEXCORE method is used for meshing due to it is adopted to combine the advantages of a cartesian grid and an unstructured grid.Then,the pressure and interface exchange coefficient are coupled to describe the discrete equation in the simulation process.Finally,the contours of H2 O molar concentrations and polarization curves are analyzed and compared.The changes of water content,local pressure,and temperature in PEMFC under different intake pressures were discussed by using the data cloud map obtained,and the influence of the inflection point of the serpentine flow channel on the material transport and the performance of the cell were analyzed.According to the variation of condensation rate under different inlet pressure,the predictive control strategy in the water pipe is developed.The results show that:1)The condensation rate curve moves up as a whole with the increase of air inlet pressure,and the condensation rate of the anode channel is 0.61 – 0.91 times that of the cathode channel during the stable operation of the fuel cell.According to the comparison of the change of water content between the serpentine flow channel and the direct flow channel,it is verified that the flow channel obstacle has a positive effect on the performance improvement of the fuel cell and reduces the energy consumption.2)When the fuel cell inlet relative humidity is 80%,the operating temperature is 75℃,and the inlet pressure is 10 k Pa,20 k Pa,30 k Pa,and 40 k Pa,respectively,the calculation accuracy of the WCR model is increased by 9%,21%,31%,and 20%.When the intake pressure is 30 k Pa,the water content in the PEMFC changes most obviously,the WCR model has the highest accuracy,and the PEMFC performance improves the most. |
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