侧向布置凝汽器汽相流动与传热特性数值研究及结构优化

联合循环电厂的汽轮机不采用抽汽回热系统，为了减小厂房高度、便于布置，通常将汽轮机设计成侧向排汽或轴向排汽形式，凝汽器也相应布置在与汽轮机高度相同的地面位置上。侧向布置凝汽器中的汽相流动与传热物理模型、传热系数的确定方法以及管束布置要求与常用的下挂式凝汽器有较大差别。国内制造厂家没有开展相关设计制造工作，也无此类凝汽器的设计手段和制造经验。开展侧向布置凝汽器汽相流动与传热特性的研究和产品开发工作，具有一定的学术意义和工程应用价值。 通过对国外A公司侧向布置凝汽器汽相流动与传热特性的数值计算与分析，提出了侧向布置双流程凝汽器汽相流动与传热特性的因素；提出了结构优化方案，并验证了结构优化方案的通用性，对今后开展侧向布置凝汽器的研发具有一定的指导作用。     

电站凝汽器非设计工况汽相流动与换热特性的数值预测

采用数值模拟方法计算与比较了一台300MW汽轮机对分式凝汽器在半负荷工况时冷却水管全部工作和一半冷却水管投入工作两种运行方式下的汽相流动与传热特性。计算结果表明，两种运行方式下的汽相流动与传热特性有明显差别。在一半冷却水管运行方式下，虽然管束传热系数较高，但由于冷却面积减半，而且汽阻显著增大，因而凝汽器总体传热效果较冷却水管全部运行时的差，使得抽气口处未凝结蒸汽量上升，空气泵负荷增大。     

接收侧向排汽凝汽器的设计

凝汽器接收侧向排汽的布置方式,可降低厂房高度,减少工程投资。接收侧向进汽的凝汽器的设计与常规凝汽器有较大的区别,由于进汽流的位置不同,在设计时需要有不同的考虑。该文介绍了接收侧向排汽凝汽器设计过程,重点介绍了设计过程中遇到的一些问题、难点及其解决办法。     

大功率汽轮机凝汽器汽相流动与传热特性的数值分析

介绍凝汽器汽相流场与传热特性的数值计算方法及算例分析。该计算方法采用多孔介质模型，以分布阻力和分布质量汇分别模拟冷却管束区的蒸汽流动阻力和凝结效应，利用控制容积积分法及解压力耦合方程的半隐式方法数值求解控制方程组，得出汽相速度、温度、压力、空气浓度、传热系数及热负荷等重要参数的分布。经试验研究表明，该方法能较好地预测凝汽器的工作特性以及管束布置对汽相流场和传热特性的影响。图９参８。     

N7600凝汽器壳侧汽相流动与传热性能数值计算

采用自行编制的程序对N7600凝汽器壳侧蒸汽的流动与传热特性进行了数值计算,得到了壳侧蒸汽的速度与流线、压力、传热系数以及空气浓度等分布图。结果表明：N7600凝汽车器壳侧整体上呈现“汽流向两侧”的流动特点,与设计的初衰基本相符合,在凝汽器的底部流场中存在小的涡流区．说明管束布置还有不合理的地方;凝汽器汽阻为109．5Pa：平均传热系数为3237,15W／m2·K;随着蒸汽的不断凝结,从冷却管束外围到内部的空气浓度逐渐增大。     

凝汽器内不凝结气体对汽相流动与传热性能影响的数值模拟与分析

采用多孔介质物理概念对1台双流程凝汽器的汽相流动与传热特性进行了数值计算与分析，结果表明：在该冷凝器中存在着严重的不凝结性气体的积聚现象，从而导致了流动与传热特性的恶化。     

侧向进汽凝汽器发展优势和技术问题探讨

本文简要阐述了凝汽器的功能和概况，对侧向进汽式凝汽器与常规顶部进汽式凝汽器的性能特点进行了对比，提出了侧向进汽式凝汽器的发展优势，并对今后侧向进汽式凝汽器的开发设计进行了技术问题探讨。     

凝汽器内不凝结气体对汽相

采用多孔介质物理概念对1台双流程凝汽器的汽相流动与传热进行了数值计算与分析.结果表明:在该冷凝器中存在着严重的不凝结性气体积聚现象,从而导致了流动与传热特性的恶化.对此提出了改进方案,即将抽气口处的挡板开口,从而将积聚的不凝结气体引出,通过数值计算证实该措施有效.     

接收侧向排汽凝汽器的技术特点及研制

介绍了我国首台接收侧向排汽凝汽器的技术特点及研制情况,重点分析了凝汽器在接收侧向排汽时的受力状况及热膨胀变化,并提出了解决问题的方法与途径。利用最新的凝汽器数值模拟软件对该凝汽器的汽相流场进行了分析计算,选取了合理的管束布置型式,从而优化了凝汽器的热力性能。     

准三维数值仿真方法在凝汽器改造中的应用

采用准三维数值仿真方法对Ｎ－１１２２０－１型凝汽器壳侧的流动力 换热性能 计算。根据计算结果分析,提出了改善凝汽器壳侧流动与传热特性的改造方案。     

再析N_11220_1型凝汽器热力特性与改造措施

利用自行开发的最新凝汽器数值模拟软件PPOC3．0对国产的N-11220-1型电站凝汽器设计工况的热力特性重新进行了数值计算和分析。针对该型凝汽器存在汽阻较大这一问题而进行了多次数值模拟,实验表明,造成凝汽器壳侧汽阻较大的主要原因是凝汽器蒸汽通道的布置不合理。然后,通过进一步数值计算和分析,对已投运的该型凝汽器进行了改造,要么加大凝汽器管束周围蒸汽通道的尺寸,要么更换新型更先进的管束才能有效改善其运行性能。     

A New Inundation Correlation for the Prediction of Heat Transfer in Steam Condensers

A new correlation used to account for the inundation effect on the prediction of heat transfer between steam vapor and cooling water in tube-and-shell condensers is proposed in this work. The proposed correlation is validated by comparing the predicted results with the experimental data of a steam surface condenser. A modified k–ε turbulence model for gas–liquid two-phase flows with distributed flow resistance is used in the numerical simulation. The predicted results using the proposed correlation agree better with the experimental data than those obtained using the existing correlations for inundation.     

Modelling flow in an experimental marine condenser

A Computational Fluid Dynamics (CFD) model is described for simulating flow and heat transfer in a condenser. A single-phase approach is used which predicts the flow of a steam-air mixture within the condenser shell, and the heat and mass transfer processes are modelled using empirical correlations. The model is used to calculate the overall performance of an experimental marine condenser with a superheated steam supply.     

Evaluations of Closure Correlations for the Simulation of Two-Phase Flows in Condensers

The effects of different closure correlations on numerical simulations of vapor-liquid two-phase flow and heat transfer in steam surface condensers are critically assessed in this study. A modified k-? turbulence model for two-phase flows is used in the simulation. The closure correlations are those for condensation vapor shear, interphase drag forces, non-condensable air, tube-side fluid flow, inundation, and hydraulic resistance due to the tube bundle. Numerical simulations of a steam surface condenser are carried out using different closure correlations, and the numerical results are compared with the experimental data. Recommendations are given for different closure correlations.     

Complete condensation in a vertical tube passive condenser

An experimental study is performed for the steam condensation in a vertical tube where steam is completely condensed. A condenser tube is submerged in a water pool where the heat from the condenser tube is removed through boiling heat transfer. The experiment data showed that the operating pressure is uniquely determined by inlet steam flow rate for the complete condensation. The condensation heat transfer rate increases and the condensation heat transfer coefficient decreases with the system pressure. For the condenser submerged in a saturated water pool, strong primary pressure dependency was observed on the condensation heat transfer.     

Effect of an interfacial shear stress on steam condensation in the presence of a noncondensable gas in a vertical tube

Experimental and analytical studies were performed to examine local condensation heat transfer coefficients in the presence of a noncondensable gas inside a vertical tube. The experimental data for pure steam and steam/nitrogen mixture bypass modes were compared to study the effects of noncondensable nitrogen gas on annular film condensation phenomena. The condenser tube had a relatively small inner diameter of 13 mm. The experimental results demonstrated that the local heat transfer coefficients increased as the inlet steam flow rate increased and the inlet nitrogen mass fraction decreased. The results obtained using steam/nitrogen mixtures with a low inlet nitrogen mass fraction were similar to those obtained using pure steam. Therefore, the effects of noncondensable gas on steam condensation were weak in the small-diameter condenser tube because of interfacial shear stress. A new correlation based on dimensionless shear stress and noncondensable gas mass fraction variables was developed to evaluate the condensation heat transfer coefficient inside a vertical tube with noncondensable gas, irrespective of the condenser tube diameter. A theoretical model using a heat and mass transfer analogy and simple models using four empirical correlations were developed and compared with the experimental data obtained under various experimental conditions. The predictions of the theoretical model and the simple model based on a new correlation were in good agreement with the experimental results.     

凝汽器喉部蒸汽流动的三维数值模拟

应用具有超粒子模型的直接模拟蒙特卡罗方法,对汽轮机凝汽器喉部进行区域分解和数学建模,及对具有典型结构的凝汽器喉部蒸汽流动进行了三维数值模拟,重点分析了凝汽器喉部流场的流动分布情况,揭示了喉部流场不均匀性流动特点及其产生原因。     

Condensation in a vertical tube bundle passive condenser – Part 1: Through flow condensation

An experimental study and a boundary layer analysis were performed for the steam condensation in a vertical tube bundle passive condenser operating in a through flow mode. Four condenser tubes were submerged in a water pool and the heat from the condenser tube was removed through boiling. Experimental data were obtained for various system pressures (100–170 kPa), inlet steam flow rates (15–47 g/s) and non-condensable gas concentration (0–15%). The experimental results showed substantial deterioration in condensation when non-condensable gas was present. With increase in steam flow rate and system pressure the condensate rate increased. The boundary layer thickness and non-condensable gas concentration increased along the condenser tube length.     

凝汽器冷却管的腐蚀及预防措施

介绍了凝汽器冷却管在汽、水侧的腐蚀原因和机理,汽侧腐蚀与低压缸的高速排汽流、凝汽器的负荷、附加流体的排入等有关,水侧的腐蚀与冷却水质、水速、冷却管材质等诸因素有关,还与附加保护、管侧清洗方式等有关。如何预防汽、水侧的腐蚀,直接影响到凝汽器的运行和使用寿命,同时还对汽轮机组的安全性、经济性有重大影响,从设计、选材观点出发介绍不同水质的选材要领及相关数据。     

A modified k–ε turbulence model for the simulation of two-phase flow and heat transfer in condensers

A modified k–ε turbulence model is developed in this study to simulate the gas–liquid two-phase flow and heat transfer in steam surface condensers. A quasi-three-dimensional algorithm is used to simulate the fluid flow and heat transfer in steam surface condensers. The numerical method is based on the conservation equations of mass and momentum for both gas-phase and liquid-phase, and mass fraction conservation equation for non-condensable gases. The numerical simulation of an experimental steam surface condenser has been conducted using the proposed modified k–ε turbulence model. The results obtained from the proposed model agree well with the experimental results and the results also show an obvious improvement in the prediction accuracy comparing with previous results where a constant value for the turbulent viscosity was used.