燃料电池流道内的两相分布特性对于提升燃料电池水管理能力至关重要,探究多液滴在流道表面流动行为利于优化结构及运行条件.使用流体体积(Volume of Fluid)法对液态水从气体扩散层(Gas diffusion layer)涌出到流道内的动态过程进行模拟,研究流道内气体流速、GDL表面接触角和水孔间距对水涌出过程和流动行为影响.结果表明,液滴在GDL表面经历了生长、分离、传输和碰撞凝并等过程.气体流速明显影响压降和液滴分离周期,随着气体流速增加,压降增加,液滴分离周期从14.7 ms降至4.7 ms,水去除能力显著增强,高气体流速造成液滴形态和流动情况不稳定.GDL表面润湿性改变了表面张力,影响液滴形态和流动,显著影响水覆盖率,随着接触角增大,GDL表面平均水覆盖率从20.03%降至9.01%;水孔间距对液滴碰撞周期影响大,小水孔间距时液滴在生长中发生凝并,大液滴飞溅造成流道内气流速度下降,压降和GDL表面水覆盖率产生大波动;大水孔间距时,流道内速度场受影响明显,前一液滴获得大速度后发生碰撞更易造成液滴飞溅,导致最大水孔间距时水覆盖率下降,从16.84%(D=0.8 cm)骤降至14.69(D=1.2 cm).研究结果为流道表面接触角,GDL孔隙分布、进气条件等参数优化提供理论指导和技术借鉴,改善质子交换膜燃料电池水传输能力提高工作效率.
Liquid phase emission behavior of gas diffusion layer surface in fuel cells
The two-phase distribution characteristics within the fuel cell flow channel are crucial for enhancing the fuel cell water manage-ment capability,and investigating the flow behavior of multiple liquid droplets on the surface of the flow channel can help to optimize the structure and operating conditions.The dynamic process of liquid water emergence from the gas diffusion layer(GDL)into the flow chan-nel was simulated using the volume of fluid(VOF)method,and the effects of the gas flow rate inside the flow channel,the contact angle on the surface of the GDL,and the pore spacing on the water emergence process and flow behavior were investigated.The results show that the droplets undergo the processes of growth,separation,transport and collisional condensation within the GDL surface.The gas flow rate significantly affects the pressure drop and droplet separation period,with the increase of gas flow rate,the pressure drop increases,the droplet separation period decreases from 14.7 to 4.7 ms,and the water removal ability is significantly enhanced,and the high gas flow rate causes the unstable droplet morphology and flow condition.The wettability of the GDL surface modifies the surface tension,which in turn affects the droplet morphology and flow,and significantly influences the water coverage,and the average water coverage of the GDL surface is significantly affected by the increasing contact angle.The average water coverage on the GDL surface decreases from 20.03%to 9.01%;the water orifice spacing has a greater impact on the droplet collision cycle,small water orifice spacing when the droplets are growing in the process of condensation and large droplet splashing caused by a decrease in airflow velocity in the flow channel,the pressure drop and the water coverage on the GDL surface generates large fluctuations;large water orifice spacing,the velocity field in the flow channel is significantly affected by the previous droplet to obtain a larger velocity after collision is more likely to cause droplet splas-hing.At large water orifice spacing,the velocity field in the flow channel is significantly affected,and the previous droplet obtains a larger velocity,which is more likely to cause droplet splashing due to collision,resulting in a decrease in water coverage at the maximum water orifice spacing,from 16.84%(D=0.8 cm)to 14.69%(D=1.2 cm).The results provide theoretical guidance and technical reference for the optimization of flow channel surface contact angle,GDL pore distribution,air inlet conditions,etc.,which can improve the water transport capacity and efficiency of PEMFC.
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