【作者】 刘璿；

【导师】 马重芳；

【作者基本信息】 北京工业大学 ， 热能工程， 2008， 博士

【摘要】 1965年,质子交换膜燃料电池作为空间项目主电源首次应用于美国国家航空航天局的双子星载人飞船并登入太空。上世纪90年代起,质子交换膜燃料电池由于取得了技术上的突破,逐渐取代了碱性燃料电池在空间领域的应用。质子交换膜燃料电池由于其具有较高的能量转化效率高,零排放,运行温度低和燃料可再生等优点,有希望成为新一代的空间任务主电源。质子交换膜燃料电池技术在工程应用上的一个关键问题是液态水管理。目前,所有关于质子交换膜燃料电池内部液态水动态特性及其对电池性能影响的研究都是在地面常重力环境下进行。关于质子交换膜燃料电池在微重力环境中的运行特性未见公开发表物报道。微重力环境下气/液两相流呈现出与地面常重力环境迥然不同的特性,受气/液两相流动态特性的影响,微重力环境中的氢质子交换膜燃料电池的运行特性将与地面常重力环境不同。因此,研究氢质子交换膜燃料电池在微重力环境下的运行特性及其内部的流体管理则显得尤为重要。首先,本文建立了氢质子交换膜燃料电池流场内液态水传递的基本理论体系,采用理论分析和实验研究方法研究了氢质子交换膜燃料电池内液态水传递及两相流动的动态特性。其次,本文设计了新型紧凑式透明氢质子交换膜燃料电池,采用透明电池直接可视化方法,研究了具有单蛇形通道流场方位的氢质子交换膜燃料电池在短时微重力环境中的运行特性。全部微重力实验在中国科学院力学研究所国家微重力实验室完成,该实验室的落塔微重力实验设施为本文实验提供了3.6秒的短时微重力实验环境。最后,本文建立了燃料电池流道内气/液两相区环形膜状凝结数学模型,选用MATLAB软件编程进行数值求解,得到了描述氢质子交换膜燃料电池流道内凝结段两相流体动力学特性参量的数值结果。本文主要工作和取得的主要成果包括:1.对常重力环境下采用直接可视化方法研究氢质子交换膜燃料电池内两相流体动力学特性的公开发表物进行了全面回顾。2.理论分析与实验研究氢质子交换膜燃料电池阴极侧液态水流体动力学特性。建立氢质子交换膜燃料电池流场内液态水传递的基本理论体系,计算并预测液态水开始凝结的临界曲线,得到了由运行参数划分的单相区与两相区。实验研究氧气流量,运行温度,电池角度对氢质子交换膜燃料电池流场内两相流特性和电池性能的影响。3.设计并建立用于落塔短时微重力氢质子交换膜燃料电池实验系统,并实现实验系统中的电气与控制系统与落舱电气与控制系统对接。实验系统包括:物料供应,物料排放与回收系统,电池温度测控系统,数据采集系统,可视化拍摄系统。设计制作了发光二极管直流驱动电路照明系统。设计建立了实验系统设备的主,控电路系统。4.改进设计并加工了紧凑式轻型透明氢质子交换膜燃料电池。高性能稳定运行的透明燃料电池能够真实反应氢质子交换膜燃料电池的实际运行特性。校核计算了螺栓,螺纹强度以及螺杆在冲击载荷下抗剪切能力。5.研究了竖直角度放置的流道方位内,重力因素变化对不同运行工况下流场内两相流体动力学特性以及电池的伏安输出特性的影响。结果表明,电池外电路电阻为0.01?时,电池产水量较多。进入微重力环境后强化竖直流道上升段排水,消除流道淹没,电池性能得到提升。电池外电路电阻为0.03?时,电池产水量较少。进入微重力环境后,重力消失促进了液态水在竖直流道上升段的移动。但重力因素对液态水的动态特性及电池性能变化影响不一致。实验结果同时表明,重力因素变化越大,电池内的流动特性和电池输出特性变化越明显。6.研究了竖直角度放置的流道方位内,重力因素变化对不同运行工况下流场内两相流体动力学特性以及电池的伏安输出特性的影响。结果表明,水平角度放置的流道内液态水量较少,液态水主要以液滴形式存在。微重力环境下,液滴脱落直径将增大。在水平方位的流道内,短时微重力持续时间内产生的液态水滞留在流道空间内,降低电池性能。落舱入网瞬间形成15g左右的冲击加速度造成的超重作用,改变了氢质子的迁移方向,使电池电势暂时升高,电流降低。7.建立了燃料电池流道内气/液两相流动区环形膜状凝结数学模型,选用MATLAB软件编程进行数值求解,得到描述氢质子交换膜燃料电池流道内凝结段两相流体动力学特性参量的数值结果。结果表明,两相区长度受表面张力,气相主流速度和流道当量尺寸影响。流道当量尺寸减小,两相区长度减小;增大气相主流速度,两相区长度增加;表面张力增大,两相区长度增加。凝结过程受电池温度和环境温度影响。电池温度升高,凝结加速,凝结放热量增加;环境温度升高,凝结速度减慢,凝结放热量减小。更多还原

【Abstract】 In the field of space engineering, PEMFC (Proton exchange membrane fuel cell) with the membrane of polystyrene was firstly applied to GEMINI space missions of NASA (National Aeronautics and Space Administration). Since 1990s, the AFC was replaced by PEMFC gradually in the space mission application due to both the breakthrough of PEMFC in technologies and the disadvantage of AFC. PEMFC is the prospective candidates as power sources for space application with short-term missions due to the characteristics including: high energy conversion efficiency, zero emission, low temperature, regenerative operation etc.A significant technical challenge in PEMFC applied operation is the liquid management. All the studies of the two-phase flow dynamic inside PEMFC and it’s effect on cell performance mentioned above were performed in the earth environment (normal gravity), however, it seems that no publication reports the liquid water transport and dynamic characteristics inside PEMFC in micro-gravity environment until now. In microgravity condition, the liquid/gas fluid flow is great different from that in normal gravity condition due to the absence of the gravity. Therefore, PEMFCs will show distinct behaviors in the reduced gravity environment because both the two phase flow dynamic inside PEMFC and cell performance are different. The study of fluid flow dynamic inside PEMFC and cell performance under the micro gravity condition will supply the approach for the reference of PEMFC operating characteristics and the liquid management in reduced gravity environment, for example in the space.First of all, in this study, the basic mathematic model for liquid water mass transport inside the PEMFC was built. The liquid water transport and two phase flow dynamic characteristic was studied both theritically and experimentally.Secondly, in this study, a noval, compact transparent PEMFC was designed, and the PEMFC operating characteristics with a single serpentine channel in a short-term micro gravity environment based on the 3.6s drop tower in the National Microgravity Laboratory, Institute of Mechanics, Chinese Academy Sciences, were performed.At last, in this study, a mathematical model of annular film condensation in the flow channel of PEMFC was developed, and the mathematical model was resolved numerically by MATLAB. The results of two phase flow characteristic parameter to predict the shape of the gas-liquid interface were obtained.The main work and results of this study are presented as the following:1. An extensive review on the direct visual study of two phase flow dynamic inside PEMFC by the aid of transparent PEMFC in normal gravity condition was summarized.2. The dynamic characteristic of liquid water in the flow channel of PEMFC was studied theritically and experimentally. The basic mathematic model for liquid water mass transport inside the PEMFC was built, and the critical curve to separate the single phase zone and the two phase flow zone depending on the liquid water condensation were obtained. The effects of oxygen flow rate, operating temperature, and cell orientation on the cell performance were studied experimentally.3. A PEMFC test system was designed for the study of two phase flow dynamic inside PEMFC under short-term micro gravity condition. The power system and driver circuit of the test system were successfully connected to the control system of drop capsule. The test system includes: reactants supply system, excess reactant gas release system, liquid recovery system, cell temperature controller unit, data acquisition and control system, and high-speed video recording system. A group of LEDs (light-emitting diode) was employed to meet the lighting requirement for captureing images. The power circuit and driver circuit of test system were designed.4. A noval, compact transparent PEMFC was designed in this study. A good design transparent fuel cell can reflect the real transport process inside practical operating PEMFCs. Verification of the screw and rod of bolts was performed to confirm the strength of bolts.5. The study on the effect of gravity level on the two phase flow dynamic inside PEMFC and cell performance of PEMFC with the vertical orientation configuration was performed. The results showed that when the load with resistant of 0.01? was connected to the fuel cell, the water production was high. The accumulated liquid water in the vertical parts of flow channel was removed easily by the reactant gas in the micro gravity environment. The cell performance was enhanced dramatically in the micro gravity condition because the flooded area in the flow channel was exposed to the reactant gas again. While, when the load with resistant of 0.03? was conneted to the fuel cell, the water production was low. In the micro gravity condition, the liquid water was removed upward by the gas phase due to the absence of gravity. But the effect on the liquid water dynamic and cell performance was not coincident. The results also showed that the more the gravity level changed, the more the cell performance was influenced.6. The study on the effect of gravity level on the two phase flow dynamic inside PEMFC and cell performance of PEMFC with the horizontal orientation configuration was performed. The results showed that little liquid water was found in the horizontal orientation configuration flow channel, and the water columns to pinch off the flow channel were difficult to be formed. In micro gravity condition, the water droplets departure diameter increased. The liquid water formed during the micro gravity condition duration was prone to stay in the flow channel, therefore, the cell performance was deteriorated due to the liquid water flooding in the flow channel in the micro gravity condition. A hyper gravity condition with the gravity of about 15g was induced when the drop capsule fell into the recovery string bag. The results also showed that the hyper gravity effect change the proton transport direction lead to a dynamic of current decreasing and voltage increasing.7. A mathematical model of annular film condensation in the flow channel of PEMFC was developed in this study, and the mathematical model was resolved numerically by MATLAB. The results of two phase flow characteristic parameter to predict the shape of the gas-liquid interface were obtained. The results showed that the length of two phase flow regime was influenced by the surface tension, the gas flow rate and equivalent diameter of flow channel. The length of two phase flow regime decreased with the decreasing of equivalent diameter; the length of two phase flow regime increased with the increasing of gas flow rate; and the length of two phase flow regime increased with the increasing of surface tension. The results also showed that the condensation was influenced by the cell temperature and environmental temperature. Increasing the cell temperature accelerated the condensation and enhanced the heat transport; increasing the environmental temperature reduced the condensation and reduced the heat transport.更多还原