直接空冷凝汽器三维流场特性的数值分析

对A字形布置的单排管直接空冷凝汽器单元进行了分析,建立了凝汽器单元内三维流动的物理数学模型,并利用Fluent求解器进行了相应的数值计算.分析了不同运行工况(风机转速、风机叶片安装角)以及环境因素(横向风速度、环境温度)对凝汽器单元流场特性的影响规律,为直接空冷凝汽器设计和优化提供科学依据.     

水平挡板改善直接空冷凝汽器流场特性的数值模拟

以某1000 MW直接空冷机组凝汽器的一组空冷单元为研究对象,建立了物理模型和数学模型,通过计算流体力学模拟分析,研究横向风对空冷机组凝汽器的影响规律和水平挡板改善风机入口侧流场的机理.结果表明：加装水平挡板可以使空冷凝汽器横向风迎风侧第一单元风机入口的负压区前移,有效削弱横向风的不利影响,增加空冷单元进风的质量流量;对于所研究的直接空冷机组凝汽器,水平挡板的最佳长度为15 m.     

直接空冷凝汽器压力特性的耦合计算与分析方法

传统的空冷凝汽器特性计算方法中认为汽轮机低压缸排汽焓保持不变,但实际上空冷凝汽器压力的变化也会反向影响排汽焓,进一步对凝汽器压力产生耦合影响。基于空冷凝汽器背压与排汽焓的耦合分析,提出了一种基于迭代算法的空冷凝汽器模型与分析方法。通过对某600MW机组空冷凝汽器的计算分析,得出其在不同汽轮机负荷、环境温度工况下凝汽器压力的变化特性曲线,定量分析了汽轮机负荷和环境温度变化对凝汽器压力影响的对应关系,对空冷机组的安全经济运行具有一定的参考价值。     

直接空冷凝汽器汽水分布在线计算模型及其应用

直接空冷凝汽器内部流体的流动状况直接影响机组的安全经济运行。而直接空冷凝汽器体积庞大、结构复杂,在运行当中,凝汽器存在换热和汽水分配不均现象。根据流体在空冷岛不同管段内的流动和换热过程,建立了直接空冷凝汽器管内汽水分布在线计算模型。以某300MW直接空冷机组为研究对象,通过在线计算模型软件获得了不同负荷和换热条件下蒸汽和凝结水在凝汽器各单元内的分布情况,实现了内部流场分布特性的在线监测。     

风机出口加装导流板对空冷单元的影响

针对某600 MW直接空冷凝汽器单元的典型结构,建立了在风机出口安装空气导流板的空冷单元物理模型,利用Fluent软件对加装导流板前后空冷单元的内部流场进行了数值模拟,分析了不同导流板数量和形状对内部空气流动和传热特性的影响.结果表明:在空冷单元风机出口加装一定数量和形状的导流板能提高冷却空气流场的均匀性,降低管束表面局部高温区的温度,从而提高空冷凝汽器的换热效果;安装8块导流板时效果最好,且弓形导流板对空冷凝汽器散热效果的改善要比长方形导流板和弯曲面形导流板更为明显.     

电站直接空冷凝汽器变工况计算与特性分析

对电站直接空冷凝汽器变工况计算进行了研究 ,绘制了空冷凝汽器特性曲线 ,分析了迎面风速、环境气温、凝汽器热负荷对空冷凝汽器性能的影响     

环境风对某600MW直接空冷凝汽器影响的数值分析

以某600MW直接空冷机组为例,利用CFD软件对其建立数值模型,采用Fluent软件对流场进行数值模拟.通过数值模拟,分析了环境风对直接空冷凝汽器换热影响.计算结果指出:当风速小于2m/s时环境风对凝汽器换热基本没有影响,当风速大于7m/s时,凝汽器换热恶化严重;在风速由0m/s上升至13m/s时空冷凝汽器的风机流量偏差率增加了41％;当风速由2m/s上升至7m/s时换热效率降低了14.1％;指出了环境风温变化对凝汽器换热的影响.通过分析获得了环境风速、风温变化对直接空冷凝汽器的影响,为空冷凝汽器进一步优化设计提供了理论依据.     

直接空冷凝汽器加装防风网的数值模拟

利用Fluent软件,以国内某600 MW直接空冷机组为例,对迎风侧2个相邻空冷凝汽器进行了数值模拟,得到了不同环境横向风速下空冷凝汽器的传热效率随着风速的增大而降低,而且被环境风冲刷越严重的凝汽器受影响程度越大的结论.针对横向风对空冷凝汽器传热效率的影响,在凝汽器挡风墙下延方向加装了防风网.对加装防风网后的空冷凝汽器进行了数值模拟,分析了防风网的不同结构参数(开孔率、高度)对空冷凝汽器传热效率的影响,结果表明:在加装防风网后凝汽器传热效率显著提高,防风网的结构参数对其防风效果有明显影响,为直接空冷机组的防风网改造提供了理论依据.     

电站直接空冷凝汽器积灰的计算分析及监测

目前对直接空冷凝汽器积灰现象所做研究不多,且多数忽略了流道截面尺寸及空气流量的变化进行研究,近期发现此结论与凝汽器清洗前后现场监测数据不符.积灰不仅影响换热系数,对管外空气的流量的影响亦不容忽视,在考虑到积灰后流道截面尺寸及管外空气流量变化的条件下,对积灰凝汽器管外空气流动与换热进行了综合计算及分析.结果表明:直接空冷凝汽器积灰后,换热系数有所升高,冷却空气量明显减少,冷却空气流量的减少是导致凝汽器性能降低的根本原因;夏季凝汽器积灰对机组背压影响较大,需严防凝汽器积灰;积灰后出口空气温度升高,实时监测出口空气温度可以作为监测凝汽器局部积灰的一种有效手段.     

环境风对空冷岛换热性能影响的分析及其改善措施

利用CFD软件,采用分步建模的方法对某2×300MW直接空冷凝汽器进行了数值模拟.分析了不同风向和风速对空冷岛外部流场和空冷凝汽器换热效率的影响.找出了环境风影响下热风回流和空冷单元风机出力降低的原因.空冷岛安装防风网,其换热性能会受到防风网的影响.结果表明,低压区的形成是导致热风回流和风机出力降低的主要原因;加装防风网可以有效改善风机入口流场,在风速为9m/s时,可以提高风机容积效率8.5％.     

Operation optimization of cold-end system of direct air-cooled units considering the effect of environmental wind

An air-cooled island can significantly alter the heat transfer performance of an air-cooled condenser due to the reflow of hot air caused by environmental wind. This can result in a considerable deviation between the backpressure calculated by traditional air-cooled condenser models and the actual value. To address the issue, a research study was conducted on a 600-MW direct air-cooled unit. Numerical simulation methods were used to obtain the corresponding air flow rates and fan inlet air temperatures for each air-cooled heat exchanger, which were then combined to establish a backpressure calculation model. From the above model, the backpressure prediction model and unit net output of full conditions were established using a backpropagation neural network. Therefore, taking the net output as the optimization objective, a genetic algorithm was used to compute the optimal backpressure and optimal fan speed in off-design situations. Compared with traditional calculation approaches, the model produces backpressure predictions that were closer to the actual situation under the effect of ambient wind. The results indicate that both the optimal backpressure and fan speed were positively correlated with the exhaust flow and ambient temperature. It has been observed that when a unit was affected by different wind directions, the effect of the forwarding wind on the backpressure was smaller than that of other wind directions, especially under high-load conditions. Moreover, the fan group operates close to full capacity under high-temperature and high-load conditions. Therefore, considering the influence of ambient wind, the obtained optimal backpressure and fan speed under variable working conditions were more realistic.     

空冷汽轮发电机转子风道中气体运动流场分析

针对转子高速转动的特点,分析了转子风道气体运动状态,建立了数值计算模型.分析结果表明,转子风道气体运动是由风扇和转子高速转动共同作用的结果,以吸入式空冷汽轮发电机通风结构为例,转子以3 000 r/min转速绕轴高速转动可以使风道中进风量由0.14 kg/s增加到0.21 kg/s,必须考虑转子转动对风道中气体运动的影响;粘性模型应选择无粘,相同条件下转子风道出口风速模型试验和数值模拟结果对比表明,数值模拟结果符合工程实际.转子风道中气体运动流场合理计算模型应为:以吸入式风扇和转子风道进口为进出口边界条件,流体边界条件考虑转子转动,墙边界条件中反映管壁表面粗糙度的相对粗糙度系数和常量分别取为k~+_s=500～1000和C_(ks)=1.0,粘性模型选择无粘,可用此计算模型对空冷汽轮发电机转子风道中气体运动流场进行分析.     

Space characteristics of the thermal performance for air-cooled condensers at ambient winds

Ambient winds may lead to poor fan performance, exhaust air recirculation and mal-distribution of the air across the tube bundles of the air-cooled condensers in a power plant. Investigations of the impacts of the ambient winds on the air-cooled condensers are key area of focus. Based on a representative 2 × 600 MW direct dry cooling power plant, the physical and mathematical models of the air-side fluid and heat flow in the air-cooled condensers at various ambient wind speeds and directions are set up by introducing the radiator model to the fin-tube bundles. The volumetric flow rate, inlet air temperature and heat rejection for different air-cooled condensers as a whole, condenser cells and fin-tube bundles are obtained by using CFD simulation. The results show that the thermo-flow performances for the air-cooled condenser as a whole, condenser cells and heat exchanger bundles vary widely in space. The thermal performances of the air-cooled condensers, condenser cells and fin-tube bundles at the downstream are generally superior to those at the upwind. It is of use for the upwind fan regulations and the A-frame condenser cell geometric optimization to investigate the space characteristics of the thermal performance for the air-cooled condensers in a power plant.     

防风网在直接空冷系统中防风效应的分析

讨论了自然风对空冷风机入口的影响情况,阐述了防风网的防风机理,并分析了防风网在空冷系统中的防风效果,其可以有效降低风机入口横向风速,增加空冷凝汽器换热效率进而提高机组的经济性和安全性。     

Performance prediction of an improved air-cooled steam condenser with deflector under strong wind

For an air-cooled steam condenser (ACSC), environmental wind can cause a large flow rate reduction in the axial fans mainly near the windward side of the air-cooled platform due to cross-flow effects, resulting in a heat transfer reduction. This leads to an increase of turbine back pressure, and occasional turbine trips occur under extremely gusty conditions. A new method is proposed in this paper to remove the strong wind effect by adding deflecting plates under the air-cooled platform, which contributes to forming a uniform air mass flow rate in the axial fans by leading enough cooling air to the fans in the upwind region. Numerical simulation is made of the thermal-flow characteristics and heat transfer performance of the improved ACSC with deflectors. A heat exchanger model is used for simulating the flow and heat transfer in the ACSC, in which the heat exchanger is simplified to a porous medium and all flow losses are taken into account by a viscous and an inertial loss coefficient. A fan model is used for reaching the flow condition at the heat exchanger inlet with the actual performance curves of the fan. It is found that the improved ACSC with deflector shows a significant enhancement in both the cooling air mass flow rate and the heat rejection rate compared with the conventional ACSC. The higher the wind speed is, the larger the heat transfer enhancement of the improved ACSC is. The effect of the plate inclination is also investigated, and the inclination angle of 45° is found to be the optimum value for the arrangement of the deflector.     

某型气冷涡轮级的三维优化设计

1引言随着叶轮机械设计技术的不断进步,对叶片造型理论和设计方法提出了更高要求,叶片设计往往决定着效率、压比、重量等诸多性能参数,涉及到来源于不同准则的许多目标和约束。与叶轮机械设计相关联的优化问题通常涉及到许多约束和大量参数,一般导致目标函数有许多极值点。目前     

风冷发动机冷却风扇试验和数据处理的探讨

论述了风冷发动机冷却风扇的试验法和用无因次特性系数法制取风扇特性曲线的方法,阐述了无因次特性系数法是制取风扇特性曲线行之有效的方法。     

边界元法在气冷涡轮叶栅气热耦合计算中的应用

将边界元计算方法应用到三维N-S方程求解程序中,流体部分采用有限差分法求解N-S方程,边界元法求解固体区域热传导方程。开发气热耦合计算程序对NASA-MarkII高压气冷涡轮叶栅热环境进行气热耦合分析。利用边界元法特有的优势(降维、解析与离散相结合的特点),避免了固体区域的网格生成和内部节点求解工作,提高了计算精度。结果表明,耦合计算程序能够高效、准确求解多场的气热耦合问题,计算结果与实验结果吻合的较好,二者平均误差为3%。     

环境因素对直接空冷机组的影响

直接空冷机组的运行状况受周围环境的影响很大,不同的风速、风向不仅会影响到机组运行的经济性,甚至还会造成掉闸停机事故。本文在总结火力发电厂空冷系统特点的基础上,对现场环境及所采集数据进行了系统分析,重点研究了环境作用对直接空冷机组空冷风机吸入风量和入口温度以及空冷机组背压影响,同时分析了环境温度的变化对空冷机组供电煤耗的影响。     

空冷凝汽器椭圆翅片椭圆管束外空气的流动与传热特性

研究空冷凝汽器椭圆翅片椭圆管管束外空气的流动与传热特性,对火电站空冷岛的设计与运行具有重要意义.通过CFD模拟,获得了椭圆翅片椭圆管管束外冷却空气的流场和温度场,计算得到了空冷凝汽器冷却空气对流换热平均Nu和摩擦系数f随Re的变化规律,并采用最小二乘法拟合得到了相应的关联式.结果表明:随冷却空气流动Re的增大,Nu增大,f减小.