【作者】 李宴君；

【导师】 唐大伟；

【作者基本信息】 中国科学院研究生院（工程热物理研究所） ， 工程热物理， 2014， 博士

【摘要】 直接空冷系统具有节约冷却水、系统结构简单等优点,可以有效带动富煤缺水地区的电力发展,因此近些年来,直接空冷系统在我国北方得到了大范围的应用。但由于直接空冷系统采用阵列式风机平台和A型框架结构单元以及以环境空气为冷却介质的特点,使得机组在运行中会出现诸如风机集群运行效率不高、气流分配不均以及易受环境气象影响等问题,这一系列问题会直接影响到空冷凝汽器的换热性能。因此,如何揭示、掌握直接空冷系统空气侧气流的流动特性及其对空冷凝汽器换热性能的影响机理成为目前直接空冷系统设计、研发过程中比较棘手的问题。本文对直接空冷系统中空气侧气流流动特性及表征方法的研究,以空冷机组受环境气象条件影响大、风机集群运行效率不高等问题为起因,通过采集空冷风机及单元周遭气流的脉动时序信号开展实验研究,研究环境自然风与风机机械风的区别,揭示风机入口干涉效应和风机群抽机理,探究空冷单元流场的分布特性,最后将研究拓展到基于空冷电厂环境气象时序数据,将多元环境引入到空冷系统设计的典型年优化上。本文结合空冷系统本身受环境自然风和风机机械风共同影响的特点,将功率谱分析方法应用于空冷风机周遭气流动态特性研究,确定了采用热线风速仪获取气流湍流脉动时序信号的实验方案,用表征气流动态特性的代表性参数(功率谱指数、能量累积因子)对环境自然风和风机机械风的频域动态特性进行了定量区分。将功率谱分析方法可区分自然风和机械风的结论应用于风机入口气流流动特性的实验研究中,定量分析了风机入口气流速度、湍流强度、功率谱指数及能量在频域的分配状况,得到了风机入口机械风的定量影响范围。逐步增加被测风机周遭风机的台数,对风机的集群运行特性进行研究,主要内容包括：1)被测风机的流量并不随周遭风机台数的增加而单调减小；2)风机入口的对称性是影响风机流量的主要因素之一；3)在风机集群运行时,被测风机主流区的流量和速度较单台风机运行时降低,而被测风机近壁区的流量和速度较单台风机运行时增大；4)风机入口气流的湍流强度会随着风机台数的增多而增加。针对空冷A型框架单元开展流场实验研究,探究单元内部A型框架倾斜面出口气流的速度分布特性,揭示了空冷单元气流分配不均的原因,实验结果表明：在远离风机中心截面的区域存在流场分布的不对称性,空冷单元底角处存在流动死区,中心区域存在低速区,A型框架倾斜面出口速度和湍流强度在风机中心截面两侧表现出明显的不对称性。依托电厂当地气象环境历史时序数据,提出了一种基于多元环境因子的FS统计气象典型年的表征方法。该方法可以兼顾到所有对系统有影响的气象参数(环境温度、环境风速、太阳辐射等),并且能够反映直接空冷系统最为敏感的冬夏季节的气候长期规律,可为空冷系统的设计、研发提供更为合理的指导。更多还原

【Abstract】 The primary advantages for direct air cooling system are water-saving and simple structure, which can promote the electric power development of the areas in shortage of water but rich in coal. Because of this, in the recent years direct air cooling system is used extensively in the northern of china. However, due to the array-fans platform and A-type frame are adopt in direct air cooling system and the ambient air is used as cooling medium, some problems such as low operating efficiency of fan cluster, uneven distribution of airflow and being vulnerable to environmental impact will be occurred during the fans operation in cluster. These problems will directly affect the heat exchange performance of air condenser. Therefore, how to reveal and grasp the flowing property of air-side flow in direct air cooling system and its effect mechanism on heat transfer performance of air condensers have became the troublesome problems in the design and development stage of direct air cooling system.The studies about the flowing property and characterization method of air-side flow in direct air cooling system presented in the paper are originates from the problems of environment-sensitive of air cooling unit and low operating efficiency of fan cluster. The experimental study is carried out by collecting the pulsation timing signals of air cooling fan and its around air flows. In this study, the difference between environmental wind and mechanical wind are investigated, the interference effects of fan inlet and the mechanism of fan cluster pumping are revealed, the distribution property of flow field in air cooling unit is explored, and then the study is extended to the optimization of typical year in air cooling system design on the basis of meteorological timing series data of air cooling plant.Firstly, on the basis of the combined effects of environmental wind and mechanical wind on air cooling system, the method of power spectral analysis is used in the study of dynamic property of airflows around air cooling fans. The experiment plan is determined by collecting the pulsation timing signals of turbulent flows using hot-wire anemometer. The representative parameters (such as power spectral index and energy accumulation factor) which characterize the dynamic property of air flows are used to distinguish the dynamic property in frequency domain of environmental wind and mechanical wind.Secondly, the paper applies the conclusion which is the ability of power spectral analysis method to distinguish the environmental wind and mechanical wind to the flowing performance experiment of fan inlet so as to analyze the air velocity, turbulence intensity, power spectral index and the energy distribution in frequency domain quantitatively, and then obtain the quantitative effective range of mechanical wind in fan inlet.Thirdly, increasing the number of fans around the measured fan slowly, the cluster operating performances of fans are studied, the major conclusions are obtained as follows:1) the flow rate of measured fan is not decreased monotonously as the increase of the number of ambient fans;2) whether the fan inlet is symmetry is one of the major factors affecting the flow rate of fan;3) when the fan is running in cluster, the air flow rate and velocity of the mainstream region of measured fan is lower than that in single fan, the air flow rate and velocity of the wall-closed region of measured fan is larger than that in single fan;4) the turbulence intensity in fan inlet is increased as increasing the fans number.Fourthly, the experimental study about the flow field of A-type frame in air cooling unit is conducted so as to investigate the feature of velocity distribution in the interior of unit and the outlet of A-type frame, and reveal the reason why the distribution of flow rate of air cooling unit is not uniform. The experiment results show that the flow field far from the center cross section of fan is not symmetry, the bottom-corner of air cooling unit exists flowing dead-zone, the center region of air cooling unit exists low-velocity zone, the velocity distribution and turbulence intensity of A-type frame outlet are not take center cross plane as symmetry plane.Fifthly, according to the meteorology timing data of local power plants, a characterization method about FS statistics meteorology typical year with multiple environmental factors introduced is proposed. This method can take into account all meteorological parameters (such as environment temperature, wind velocity, solar radiation, etc.) affecting the air cooling system, and reflect the long-term meteorological law of winter and summer to which the air cooling system is most sensitive, which provide a more reasonable guidance for air-cooling system design and improvement.更多还原