具有一侧渗液侧面的微小矩形流道内气液两相流动研究

发布时间：2018-03-27 16:12

本文选题：液滴　切入点：可视化　出处：《天津大学》2014年博士论文

【摘要】：质子交换膜燃料电池(PEMFC)运行过程中,在其流道内部往往形成气液两相流,弄清该类气液两相流的特点,对提高燃料电池水管理水平,具有重要的科学意义和应用价值。在有关PEMFC的研究中,如何在不发生水淹的同时保证电解质膜的质子传导性的水管理问题是一个十分重要的课题。虽然近年来有关燃料电池水管理方面的研究报告很多,但尚有很多深层次的机理问题并未弄清。这也严重的制约了相关研究的深入开展。基于此,本文以燃料电池阴极流道气液两相流动为研究基础,从对单一液滴的研究入手,进而对流道内的气液两相流动进行研究。液滴在微小流道内的运动现象有很多应用背景,包括化学工程、航空动力工程等领域,而燃料电池也是其中的一个应用背景。对于PEMFC,在运行过程中,随化学反应的进行,气体扩散层表面将逐渐产生小液滴,而且小液滴会逐渐长大,并在来流作用下发生形变。本文将此现象提取出来,研究单一液滴在不锈钢金属底板上在来流作用下其出现、生长、脱离乃至贴附、破碎的整个过程。为便于对单一液滴进行研究,本文设计了可视化流道,研究液滴在流道内在来流作用下且自身不断长大的过程中的变形情况以及脱离或者贴附行为。采用高速摄像系统获取液滴变形这一瞬态过程中的动态信息,而后对所获取信息进行处理,并变换参数的不同组合,做组合实验,研究液滴的前进接触角、后退接触角以及前后接触角之差等液滴物性参数与液滴高度、来流雷诺数、液滴浸润直径等之间的关系,并对现象产生的原因进行具体分析,进而总结出各物理参数之间的影响规律。对不锈钢表面进行疏水性处理,通过对比研究不同表面特性对液滴存在状态的影响。为便于研究微小流道内的气液两相流动,本文设计了微小流道气液两相流动可视化实验系统,对一个侧面由透气性多孔材料构成的毫米尺寸的方形流道内,沿着流道内气体流动方向液体水不断地通过渗液侧面渗入到气体流道内而形成的气液两相流动现象进行了实验研究。实验过程中,流道尺寸选择了三种规格,气液参数各选择多组,并进行组合,作为渗液侧面的透气性多孔材料共选择两种,一种是普通碳纸,另一种为经PTFE浸润的碳纸。基于可视化观察的结果,对这种特殊的两相流动的流型进行了分类,并分析了气体流量和渗液速度对流型的影响。同时,发现由于液体的渗入流道两端压差表现出明显的脉动性,这种压差脉动的频率不仅依赖于渗液量还依赖于气体流量,但脉动的振幅几乎不受渗液量的影响。碳纸的PTFE浸润处理,主要作用不在于改变流道内流型,而在于改变特定流型在流道中出现的位置。另外,两种渗液侧面特性下,压降大小及其脉动特性也存在很大的差异,反映了两者排液机理的差异。
[Abstract]:In the process of PEMFC (Proton Exchange membrane fuel Cell) running, gas-liquid two-phase flow is often formed in the flow channel of PEMFC. The characteristics of this kind of gas-liquid two-phase flow are clarified, and the water management level of the fuel cell is improved. It has important scientific significance and application value. In the research of PEMFC, How to ensure the proton conductivity of electrolyte membrane without flooding is a very important issue, although there have been many researches on water management of fuel cell in recent years. However, there are still many deep-seated mechanism problems that have not been clarified. This also seriously restricts the further development of related research. Based on this, this paper takes the gas-liquid two-phase flow in the cathode channel of fuel cell as the research foundation, starting with the study of single droplet. Then the gas-liquid two-phase flow in the channel is studied. The motion of droplets in micro-channels has many application backgrounds, including chemical engineering, aerodynamics engineering and so on. The fuel cell is also one of the applications. For PEMFC, as the chemical reaction goes on, the surface of the gas diffusion layer will gradually produce small droplets, and small droplets will gradually grow up. This phenomenon is extracted from this phenomenon to study the appearance, growth, detachment and even attachment of a single droplet on the stainless steel metal substrate under the action of the incoming flow. The whole process of fragmentation. In order to facilitate the study of a single droplet, a visual flow channel is designed in this paper. This paper studies the deformation of droplets in the process of internal flow in the channel and their growing up. The dynamic information of the transient process of droplet deformation is obtained by using a high-speed camera system, which is used to obtain the dynamic information during the transient process of droplet deformation. Then the obtained information is processed, the different combinations of parameters are transformed, and combined experiments are done to study the drop physical parameters and drop height, such as the forward contact angle, the backward contact angle and the difference between the front and back contact angles, and the flow Reynolds number. The relationship between droplet wetting diameter and so on, and the causes of the phenomenon are analyzed in detail, and the influence laws among various physical parameters are summarized. The surface of stainless steel is treated with hydrophobicity. In order to study the gas-liquid two-phase flow in micro-channel, a visualized experimental system for gas-liquid two-phase flow in micro-channel is designed. In the case of a square passage of millimeter size on the side of a porous material, The gas-liquid two-phase flow phenomenon formed by the continuous infiltration of liquid water into the gas channel through the seepage side along the gas flow direction in the channel has been studied experimentally. In the course of the experiment, three specifications have been selected for the flow channel size. Each of the gas-liquid parameters is composed of two kinds of porous materials, one is ordinary carbon paper, the other is carbon paper infiltrated by PTFE, which is based on the results of visual observation. The flow patterns of this special two-phase flow are classified, and the effects of gas flow rate and seepage velocity on the convection pattern are analyzed. It is also found that the pressure difference between the two ends of the liquid permeating channel shows obvious pulsation. The frequency of the differential pressure pulsation depends not only on the amount of seepage but also on the flow rate of gas, but the amplitude of the pulsation is almost independent of the amount of percolation. The main function of the PTFE soakage treatment of carbon paper is not to change the flow pattern of the flow channel. In addition, the pressure drop and its pulsation characteristics are also very different under the side characteristics of the two kinds of seepage, which reflects the difference of the drainage mechanism between them.
【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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