【作者】 涂海涛；

【导师】 孙文策；

【作者基本信息】 大连理工大学 ， 工程热物理， 2007， 博士

【摘要】 本文首先针对质子交换膜燃料电池（PEMFC）提出一种单相数学模型,在详细考虑电池内的组分传递、传热、电化学反应以及由电渗、浓差扩散和压力渗透引起的质子膜内水传递的基础上,对PEMFC内的二维和三维稳态传递特性进行了模拟分析,研究了不同流道结构和物性参数对电池性能的影响,分析了PEMFC内的瞬态传递响应特性,然后在单相模型的基础上考虑了多孔介质内的相变和液态水的毛细流动,提出一种混合的两相模型,并利用此模型对电池内的传递特性进行了模拟和参数化的研究。主要工作及结论包括:1.二维和三维的稳态模拟。利用单相模型对PEMFC进行了二维等温和三维非等温的基本参数数值模拟,研究了电池内的二维和三维传递特性以及质子膜内水传递对膜电导率和组分传递的影响,对各特性参数的分布规律进行了分析和对比。结果表明,三维传递特性跟二维的情况有很大差别;由于忽略了集流板的影响,二维模型低估了PEMFC的活化极化和欧姆损失;2.单相模型参数化分析。利用单相模型对不同流道结构和几何参数、物性参数以及操作参数等对电池性能的影响进行了模拟和分析。结果表明,质子膜厚度的减小优化了质子膜内的水传递过程,特别是在大电流密度下,大大提高了电池性能;交指型流道的设计强化了多孔介质内的对流作用,提高了高电流密度下的电池性能。而在较低的操作压力和进气当量系数时交指型流道相对直流道的优势更加明显;在阴、阳极无操作压力差的情况下,质子膜平均电导率随输出电流密度的变化比较平缓,但此时膜阳极侧更容易失水;3.PEMFC内传递过程的三维瞬态分析。分别在忽略膜内水积累和考虑膜内水积累过程的情况下对PEMFC的变工况响应过程进行模拟,分析了电池内的组分传递特性以及膜内水积累过程对电池响应特性的影响。结果表明,交指型流道的组分传递响应特性要明显好于直流道的情况,更适合于车用PEMFC系统;不考虑膜内水积累过程时在所模拟的条件下所有直流道PEMFC的变工况响应时间基本在0.5～0.6s左右;而考虑膜内水传递过程时,电池输出电压和氧气组分传递的响应分别比不考虑膜内水积累的情况延长了超过1s和0.5s的时间;膜内温度分布的响应时间最长,但其对电池总体响应的影响很小;4.三维两相模拟。以前面单相模型为基础提出一种混合的两相模型,模型考虑了多孔介质内的相变过程和液态水的毛细流动,对电池内的传递特性进行了模拟分析,并研究了不同多孔介质物性参数及结构对传递过程和电池性能的影响。结果表明,单相模型高估了电池的活化极化损失而低估了质子膜的欧姆损失;由于汽化潜热的影响,两相模拟的膜温度高于单相模拟的结果;在大部分范围内,增加多孔介质的碳纤维直径、憎水性和孔隙率都有利于组分传递的优化和电池性能的提高;对于双层扩散层,在第一层厚度L_dl较小时第一层碳纤维直径d_fl的减小有利于电池性能的提高;随着L_dl的增大,L_dl和d_fl的变化对电池性能的影响相互制约,这两个参数需得到优化。更多还原

【Abstract】 In this paper, a single-phase mathematical model is firstly developed for proton exchange membrane fuel cell （PEMFC） and the steady two- and three-dimensional transport properties of PEMFC are simulated considering heat and mass transfer, electrochemical reactions and water transport in membrane driven by electro-osmotic drag, concentration difference diffusion and pressure permeation. The effects of flow channel configuration and different physical parameters on cell performance and the transient response property of transport processes in PEMFC are analyzed and discussed. And then, a hybrid two-phase mathematical model is developed based on the forenamed single-phase model considering water phase change and capillary flow of liquid water in porous media. The simulation of two-phase effects and the parametric study of porous media are also carried out using this model. The main work and conclusions are listed as follows.1. Two- and three-dimensional steady simulation. The two-dimensional isothermal and the three-dimensional non-isothermal simulations of PEMFC for base parameters are carried out using the single-phase model. The multi-dimensional transport properties and the effects of water transport in membrane on species transport and ionic conductivity of membrane are analyzed. And the distributions of characteristic parameters are discussed and compared. The results indicate that there is a large difference between the two-dimensional and three-dimensional transport properties. The two-dimensional results underestimate the activation and ohmic losses for ignoring the effects of the shoulder of current collector.2. Parametric analysis using single-phase model. The effects of different configurations of flow channel, geometric and physical parameters and operation conditions on cell performance are simulated and analyzed using the single-phase model. It can be concluded that the decrease of the thickness of membrane optimizes the water transport in membrane and improves the output performance of PEMFC, especially for large current densities. The interdigitated design of flow channel enhances the convection flow in porous media and improves the cell performance, which is especially obvious for low operation pressures and stoichiometric ratios. The change of averaged ionic conductivity of membrane vs. output current density is not sharp at the condition of zero operation pressure difference between anode and cathode. However, the anode side of membrane is easier to be dehydrated in that case. 3. Three-dimensional transient analysis of transport processes in PEMFC. The simulations of the transient responses under varying conditions are carried out for ignoring and considering the water accumulation process in membrane. The transient characteristics of species transport and the effect of water accumulation in membrane on cell’s response are analyzed and discussed. The results indicate that the response characteristics of species transport for interdigitated design of flow channel are obviously better than that for straight channel, which shows the advantage of PEMFC system with interdigitated flow fields for vehicle usage. The response times of PEMFC with straight channels under varying conditions are all about 0.5～0.65 for ignoring water accumulation in membrane. And the response times of output cell voltage and O₂ species transport are prolonged for about 1s and 0.5s respectively considering water accumulation in membrane. The temperature distribution of membrane has the longest response time, but it has little effect on cell response.4. Three-dimensional and two-phase simulation. Based on the single-phase model, a hybrid two-phase model is developed considering the phase change and capillary flow of liquid water in porous media, while ignoring the two-phase effect in flow channels. The transport processes under the effects of liquid water are simulated, and the effects of porous media’s structure and physical parameters on transport characteristics and cell performance are analyzed and discussed in detail. The results indicate that the single-phase model overestimates the activation loss and underestimates the ohmic loss of membrane. The simulated temperatures of two-phase model are higher than those of single-phase model for the effect of the heat of vaporization. The increases of the diameter of carbon fiber, hydrophobility and porosity of porous media will benefit the species transport and cell performance in most cases. For two-layer diffusion layer, the decrease of carbon fiber’s diameter of the first layer dfl improves the cell performance when the thickness of the first layer L_dl is small. With the increase of L_dl, the effects of L_dl and d_fl on cell performance contradict each other and the two parameters need to be optimized.更多还原