质子交换膜燃料电池流道内两相流动的数值模拟研究

发布时间：2018-08-28 12:46

【摘要】：质子交换膜燃料电池（PEMFC）是一种清洁高效的能源转换装置。PEMFC的水管理是影响其工作性能、稳定性和可靠性的一个关键技术。液态水在PEMFC流道内的高效传输和去除是PEMFC水管理的一个重要方面。研究和分析PEMFC阴极流道内的气液两相流动问题，特别是液态水在流道内的传输和去除过程，一方面有助于深入认识液态水在微观流道内的传输特点和去除机理，另一方面可以指导PEMFC流道的设计，进而改善PEMFC的水管理和提高PEMFC的工作性能。本文以PEMFC流道内的两相流动问题为研究对象，在一个现有静态润湿模型（只包含一个静态接触角（Static Contact Angle）的作用）的基础上，建立了PEMFC流道内空气-水两相流动的动态润湿模型（包含滑动角（Sliding Angle）和动态接触角（Dynamic Contact Angle）的作用），并在此模型基础上，开展了一系列的研究工作。本文的主要研究工作包括： 1. PEMFC流道内两相流的动态润湿模型的建立和模拟。首先，采用椭圆形液固接触面形状和线性动态接触角分布，推导出了滑动角和动态接触角这两个表征固体表面动态润湿性的参数之间的理论关系式，明确了两者之间的相互作用关系。其次，采用合适的数值方法，将由此关系式确定的滑动角和动态接触角的作用应用到一个数值模型中，建立了PEMFC流道内两相流动的动态润湿模型。采用此动态润湿模型，研究了动态润湿性对水滴在PEMFC流道中传输过程的影响。研究表明，在相同静态接触角下，滑动角越小，动态接触角的变化范围或接触角差异（Contact Angle Hysteresis）越小，水滴的高度越大，水滴在气体扩散层（GDL）表面的运动速度越大。因而，小的GDL表面滑动角有利于水滴在PEMFC流道中的传输和去除。 2.水滴在GDL表面的渗透位置对其传输过程的影响。详细研究了水滴在GDL表面沿流道宽度方向不同位置处的传输过程。研究发现了水滴在流道宽度方向做周期性摆动的现象，并且，随着水滴偏离GDL表面中心的距离变大，其摆动的幅度会变大。当水滴的渗透位置偏离GDL表面中心一定距离后，水滴会接触到流道表面。此时，当流道表面接触角较小时，水滴会由于流道表面毛细力的作用脱离GDL表面，最终运动到由流道侧面和流道底面形成的流道角落处。这表明流道表面接触角对液态水从GDL表面的去除有重要作用。 3.设计了两种加快GDL表面除水的新型流道，分别为带有亲水针的流道和带有亲水薄板的流道。研究了水滴在这两种新型流道中的传输过程，特别是从GDL表面的去除过程。研究发现在GDL表面上传输的水滴与亲水针或亲水薄板接触后，会在亲水针或亲水薄板表面毛细力作用下从GDL表面去除。研究表明，采用在流道中安装亲水针或亲水薄板的方法，可以在流道压降增加较小的情况下，有效地起到GDL表面除水的作用，特别适合于在平行直流道中的应用。研究同时还表明，与带有亲水针的流道相比，带有亲水薄板的流道的GDL表面除水效果更好，，流道的压降也更低。
[Abstract]:Proton exchange membrane fuel cell (PEMFC) is a clean and efficient energy conversion device. The water management of PEMFC is a key technology affecting the performance, stability and reliability of PEMFC. The problem of phase flow, especially the transfer and removal of liquid water in the channel, is helpful to understand the transport characteristics and removal mechanism of liquid water in the microchannel. On the other hand, it can guide the design of PEMFC channel, improve the water management of PEMFC and improve the performance of PEMFC.
In this paper, a dynamic wetting model (including Sliding Angle and Dynamic Contac Angle) for air-water two-phase flow in PEMFC runner is established based on a static wetting model (including only one static Contact Angle). On the basis of this model, a series of research work has been carried out.
1. Establishment and Simulation of dynamic wettability model of two-phase flow in PEMFC runner. Firstly, by using elliptical liquid-solid contact surface shape and linear dynamic contact angle distribution, the theoretical relationship between sliding angle and dynamic contact angle, which characterize the dynamic wettability of solid surface, is deduced, and the interaction between them is clarified. Secondly, a dynamic wettability model of two-phase flow in a PEMFC channel is established by applying the sliding angle and dynamic contact angle determined by the equation to a numerical model. The influence of dynamic wettability on the droplet transport in the PEMFC channel is studied by using the dynamic wettability model. Under the same static contact angle, the smaller the sliding angle, the smaller the range of dynamic contact angle or the difference of contact angle (Contact Angle Hysteresis), and the larger the height of water droplets, the greater the velocity of water droplets moving on the surface of gas diffusion layer (GDL).
2. The influence of the penetration position of water droplets on the GDL surface on its transport process is studied in detail. The transmission process of water droplets on the GDL surface is studied in different positions along the channel width direction. When the penetration position of the droplets deviates from the center of the GDL surface, the droplets will contact the runner surface. At this time, when the contact angle of the runner surface is small, the droplets will be separated from the GDL surface due to the capillary force of the runner surface, and eventually move to the corner of the runner formed by the runner side and the bottom of the runner. It plays an important role in the removal of liquid water from the surface of GDL.
3. Two kinds of new runners are designed to accelerate the surface dewatering of GDL, one with hydrophilic needle and the other with hydrophilic sheet. Hydrophilic needle or hydrophilic sheet can be removed from the surface of GDL by capillary force. The results show that the method of installing hydrophilic needle or hydrophilic sheet in the runner can effectively remove water from the surface of GDL when the pressure drop in the runner increases slightly. It is especially suitable for the application in parallel direct current channels. Compared with the runner with hydrophilic needle, the runner with hydrophilic thin plate has better surface dewatering effect and lower pressure drop.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM911.4

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