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首页> 外文会议>International Conference on Fuel Cell Science, Engineering and Technology; 20040614-20040616; Rochester,NY; US >A TWO-PHASE FLOW MATHEMATICAL MODEL FOR PROTON EXCHANGE MEMBRANE FUEL CELLS WITH ENHANCED GEOMETRY
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A TWO-PHASE FLOW MATHEMATICAL MODEL FOR PROTON EXCHANGE MEMBRANE FUEL CELLS WITH ENHANCED GEOMETRY

机译：几何形状增强的质子交换膜燃料电池的两相流数学模型

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摘要

The produced water vapor in the vicinity of the membrane, of a proton exchange membrane fuel cell (PEMFC), may condense into liquid water, if the water mass fraction is higher than the saturation value corresponding to the local temperature. In this case the flowing fluid inside the layers of the PEMFC is a 2-phase flow. The present mathematical model is based on the locally homogeneous flow model (LHFM) where the slip velocity between the two phases is assumed negligibly small. Therefore, the governing gas-phase and liquid-phase, for each dependent variable, can be economically added together. The resulting equations contain a 'mixture density', which is a function of the void fraction, species mass fractions, pressure and temperature. The resulting governing equations for u, v, T and species mass fractions together with the electric potential and mass continuity equations are solved iteratively using the SIMPLE algorithm. One solution domain is superimposed over all the layers of the PEMFC with appropriate boundary conditions applied at inlet, exit and sidewalls of the fuel cell. Special care is devoted to the electric potential, 'Poisson-type', equation boundary condition to prevent any escape of protons through the two diffuser layers and simultaneously insuring a non-singular matrix of finite-difference coefficients. This is because Poisson equation is notoriously known for having problems with zero gradient boundary condition. Numerical computations are carried out for a typical proton exchange membrane fuel cell that has experimental data. In order to obtain complete performance results, the computations are repeated for increasing fuel cell electric current densities until the voltage vanishes. The obtained 2-phase and 1-phase simulations are compared with the corresponding experimental and numerical data available in the literature. Systematically, the 1-phase current density is under predicted especially for values of the cell potential less than 0.8 V. On the other hand, the two-phase simulation current density, of the parallel geometry FC, is in very good agreement with the corresponding experimental data. The 2-phase flow simulations show that most of the liquid phase is concentrated in the cathode, reaching maximum value near the cathode catalyst layer- membrane interface. A new design of the serpentine PEMFC is suggested and is tested numerically. The new design involves blocking the outlet sections, either partially or fully, of the anode and/or the cathode gas channels to force the flowing fluids to diffuse into the catalyst layers at rates higher than a typical parallel geometry PEMFC. The new serpentine PEMFC design is expected to increase the concentrations of the hydrogen fuel and the oxidant in the catalyst layers and hence increase the transfer current densities. In order to obtain full simulation of the enhanced geometry of the fuel cell, the end boundary condition of the gas channels is adjusted using zero porosity to prevent any flow through the blocked area which automatically reduces the local velocity to zero value. The two-phase flow numerical results, for the modified serpentine PEMFC, indicate that the performance of the fuel cell could be enhanced appreciably.
机译：如果水质量分数高于对应于局部温度的饱和度值，则质子交换膜燃料电池（PEMFC）的膜附近产生的水蒸气可能凝结成液态水。在这种情况下，PEMFC层内部的流动流体为两相流。本数学模型基于局部均质流模型（LHFM），其中假设两相之间的滑移速度可忽略不计。因此，对于每个因变量，可将控制的气相和液相经济地加在一起。所得方程式包含“混合物密度”，它是空隙率，物质质量分数，压力和温度的函数。使用SIMPLE算法迭代求解得到的u，v，T和物质质量分数的控制方程以及电势和质量连续性方程。一个解决方案域叠加在PEMFC的所有层上，并在燃料电池的入口，出口和侧壁施加适当的边界条件。特别注意电位“泊松型”方程边界条件，以防止质子通过两个扩散层逸出并同时确保有限差分系数的非奇异矩阵。这是因为众所周知，泊松方程具有零梯度边界条件的问题。对于具有实验数据的典型质子交换膜燃料电池进行了数值计算。为了获得完整的性能结果，重复进行计算以增加燃料电池的电流密度，直到电压消失。将获得的2相和1相仿真与文献中可用的相应实验和数值数据进行比较。系统地，尤其是对于电池电势小于0.8 V的情况，预测的是一相电流密度。另一方面，并​​联几何FC的两相仿真电流密度与相应的实验数据。两相流动模拟表明，大多数液相都集中在阴极中，在阴极催化剂层-膜界面附近达到最大值。提出了蛇形PEMFC的新设计并进行了数值测试。新设计涉及部分或全部阻塞阳极和/或阴极气体通道的出口部分，以迫使流动的流体以比典型的平行几何PEMFC更高的速率扩散到催化剂层中。新的蛇形PEMFC设计有望提高催化剂层中氢燃料和氧化剂的浓度，从而提高转移电流密度。为了获得增强的燃料电池几何形状的完整模拟，使用零孔隙率调整气体通道的端边界条件，以防止任何流经阻塞区域的流量自动将局部速度降低为零。改进的蛇形PEMFC的两相流数值结果表明，燃料电池的性能可以得到显着提高。

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