三种运行参数对PEMFC动态响应的数值分析

Numerical Analysis of Three Operating Parameters on Dynamic Cell Performance of Proton Exchange Membrane Fuel Cell

摘要:

为了探究在电流阶跃变化中工作温度、相对湿度和背压等运行参数对质子交换膜燃料电池（PEMFC）性能的影响，运用相对湿度和工作温度之间的耦合变化推导出了动态计算（DT）模型。该模型通过工作温度和相对湿度来阐述膜电极参数和PEMFC性能之间的特性关系，并分析在电流阶跃变化中这两种运行参数对质子交换膜（PEM）内水传递特性、输出电压和功率密度随时间变化的瞬态响应的差异。采用理论计算结合试验的方式，首先通过自定义函数（UDF）将DT模型导入到Fluent软件中进行计算并应用有限体积法进行求解；其次开展PEMFC动态负载性能测试，测量工作温度为50℃、60℃、70℃，背压为0、10 kPa，相对湿度为50%、75%、100%，同时改变电流负载（阶跃幅度为5 A）来实现PEMFC对电流阶跃动态响应的测试；最后通过极化曲线和I-P曲线对DT模型和试验数据进行比较分析。结果表明：实验数据与DT模型的仿真结果之间有很好的相关性；不对称加湿是影响功率密度的一个主导参数；阳极相对湿度决定了功率密度在发生阶跃电流后稳定运行的能力；PEM水含量与功率密度下冲幅度和响应时间有关。因此，工作温度为60℃、背压为10 kPa、阳极相对湿度为75%、阴极相对湿度为100%时，PEMFC的动态性能最佳。

Abstract:

In order to characterize the effects of operating temperature， relative humidity， and back pressure on the proton exchange membrane fuel cell （PEMFC） performance at the applied step current， a dynamic transfer （DT） model that accounts for the coupled variation between relative humidity and operating temperature is established， which illustrates the characteristic relationship between membrane electrode parameters and PEMFC performance parameters in terms of operating temperature and relative humidity， and analyses the differences between two operating parameters on the transient response of water transport inside PEM， output voltage， and power density distribution with time at the applied step current. A combination of theoretical calculations and experiments is proposed. First， the DT model including geometry and meshes is embedded into Fluent and the data in the solver of Fluent is called to simulate the electrochemical reactions. Secondly， experiments are conducted regarding the effect of temperature（50 ℃， 60 ℃ and 70 ℃）， back pressure（0 and 10 kPa）， and relative humidity（50%， 75% and 100%） on the transient response like voltage and power density. Finally， the transient response for voltage output， water transport inside the PEM， and power density distribution with time via polarization curves， contours， and I-P curves with time are compared and analyzed. The results indicate that the DT model is in good agreement with the experimental data observed， which elucidates that the anode relative humidity determines the capability of power density to operate steadily after the applied step current and the power density response time and the amplitude of undershoot are related to membrane. When the back pressure is 10 kPa，the anode relative humidity is 75%， and the cathode relative humidity is 100% at an operating temperature of 60 °C， PEMFC has the best dynamic performance.