2D-simulation of wet steam flow in a steam turbine with spontaneous condensation

Removal of condensates from wet steam flow in the last stages of steam turbines significantly promotes stage efficiency and prevents erosion of rotors. In this paper, homogeneous spontaneous condensation in transonic steam flow in the 2-D rotor-tip section of a stage turbine is investigated. Calculated results agree with experimental data reasonably well. On the basis of the above work, a 2-D numerical simulation of wet steam flow in adjacent root sections of a complex steam turbine stage was carded out. Computational results were analyzed and provide insights into effective removal of humidity.

Prediction of Boiler Drum Pressure and Steam Flow Rate Using Artificial Neural Network

Numerical simulation of complex systems and components by computers is a fundamental phase of any modern engineering activity. The traditional methods of simulation typically entail long, iterative processes which lead to large simulation times, often exceeding transient real time. Artificial neural networks （ANNs） may be advantageous in this context, the main advantage being the speed of computation, the capability of generalizing from the few examples, robustness to noisy and partially incomplete data and the capability of performing empirical input-output mapping without complete knowledge of underlying physics. In this paper, the simulation of steam generator is considered as an example to show the potentialities of this tool. The data required for training and testing the ANN is taken from the steam generator at Abott Power Plant, Champaign （USA）. The total number of samples is 9600 which are taken at a sampling time of three seconds. The performance of boiler （drum pressure, steam flow rate） has been verified and tested using ANN, under the changes in fuel flow rate, air flow rate and load disturbance. Using ANN, input-output mapping is done and it is observed that ANN allows a good reproduction of non-linear behaviors of inputs and outputs.

Catastrophe Model of Steam Flow Excitation Vibration in Steam Turbine Governing Stage

汽流激振是影响大型汽轮机组安全运行的主要故障之一。根据突变理论、非线性振动理论以及流体动力学，从机理分析的角度出发，对汽轮机调节级在部分进汽下导致的汽流激振突变性能进行了定量分析。建立了部分进汽情况下调节级气流激振力模型，以及考虑汽流激振力的调节级非线性动力学模型，通过基于突变理论的推导，得到了调节级汽流激振的尖点突变流形和分岔集，确定了系统汽流激振突变的影响因子，讨论了振幅突变与影响因子的相关性，划分了系统工作的突变区域。最后，利用数值计算方法对汽流激振的幅值响应进行了分析，分析结果验证了基于突变理论的汽流激振突变分析方法的正确性。研究成果为汽轮机汽流激振突变性能的研究提供了一条新的途径。

A COUPLED THERMO-HYDRAULIC MODEL FOR STEAM FLOW IN PIPE NETWORKS

This article aims to establish a coupled thermo-hydraulic mathematical model for steam network by adopting a set of equations, i.e., the continuity equation, motion equation, energy equation, state equation and enthalpy equation and considering the interaction of hydraulic and thermal working conditions. The model is simplified according to steam flow features in pipe networks. The unsteady flow model is simplified to a steady one with considering engineering practice and the solution to the governing equations are obtained by using the standard fourth-order Runge-Kutta method. Many factors of steam flow are generally considered, such as condensability, change of state, friction and heat transfer in the model. It is concluded that coupled iteration can be employed in steam network thermo-hydraulic computation. The numerical results with the model are basically in accordance with practical operation data.

NUMERICAL SIMULATION OF WET STEAM CONDENSING FLOW WITH AN EULERIAN/EULERIAN MODEL

Wet steam condensing flow in low-pressure steam turbine leads to efficiencylosses and blade erosions. In order to investigate this problem by numerical approach, anEulerian/Eulerian model has been developed, in which the wet steam is regarded as mixture comprisingtwo coupled systems: the vapor phase and the liquid phase. These two systems are both described byconservation equations. High resolution TVD scheme is employed to capture condensing phenomena inwet steam flow. This model has been validated by numerical simulations of condensing flows in 1D and2D nozzles. Compared with experimental data, a good agreement is observed. This Eulerian/Eulerianmodel can be extended to 3D calculation of condensing flow.

Correction of Non-Isokinetic Sampling of Wetness Measurement for Wet Steam Flow

A mathematical model for predicting the behavior of wet steam flow in the vicinity of the intake head of the sampling probe is presented. The vapor flow field and droplet trajectory in the calculated region have been obtained. The errors caused by non-isokinetic sampling for different conditions have been analyzed and the analytical results would provide useful data for the design and application of a heating method-based wetness measurement probe in practice.

Analysis of flow instabilities in forced-convection steam generator

Because of the practical importance of two-phase instabilities, substantial efforts have been made to date to understand the physical phenomena governing such instabilities and to develop computational tools to model the dynamics. The purpose of this study is to present a numerical model for the analysis of flow-induced instabilities in forced-convection steam generator. The model is based on the assumption of homogeneous two-phase flow and ther- modynamic equilibrium of the phases. The thermal capacity of the heater wall has been included in the analysis. The model is used to analyze the flow instabilities in the steam generator and to study the effects of system pressure, mass flux, inlet temperature and inlet/outlet restriction, gap size, the ratio of do / di, and the ratio of qi / qo on the system be- havior.

Optimum Tilt Angle of Flow Guide in Steam Turbine Exhaust Hood Considering the Effect of Last Stage Flow Field

Abstract Heat transfer and vacuum in condenser are influenced by the aerodynamic performance of steam tur- bine exhaust hood. The current research on exhaust hood is mainly focused on analyzing flow loss and optimal design of its structure without consideration of the wet steam condensing flow and the exhaust hood coupled with the front and rear parts. To better understand the aerodynamic performance influenced by the tilt angle of flow guide inside a diffuser, taking a 600 MW steam turbine as an example, a numerical simulator CFX is adopted to solve compressible three-dimensional （3D） Reynolds time-aver- aged N-S equations and standard k-e turbulence model. And the exhaust hood flow field influenced by different tilt angles of flow guide is investigated with consideration of the wet steam condensing flow and the exhaust hood coupled with the last stage blades and the condenser throat. The result shows that the total pressure loss coefficient and the static pressure recovery coefficient of exhaust hood change regularly and monotonously with the gradual increase of tilt angle of flow guide. When the tilt angle of flow guide is within the range of 30~ to 40~, the static pressure recovery coefficient is in the range of 15.27% to 17.03% and the total pressure loss coefficient drops to approximately 51%, the aerodynamic performance of exhaust hood is significantly improved. And the effectiveenthalpy drop in steam turbine increases by 0.228% to 0.274%. It is feasible to obtain a reasonable title angle of flow guide by the method of coupling the last stage and the condenser throat to exhaust hood in combination of the wet steam model, which provides a practical guidance to flow guide transformation and optimal design in exhaust hood.

The Density and Momentum Distributions of 2-Dimensional Transonic Flow in an LP-Steam Turbine

Within turbine blade rows, particularly for cascades of high deflection angle, cross-channel gradients of steam properties may be appreciable. To determine the effects on spontaneous condensation of gradients of supersaturation normal to streamlines, the conservation equations can be incorporated in a two dimensional calculation procedure. With the help of program FORTRAN 90 a developed computational program of calculations is accomplished, whose results are communicated to the pressure and Mach number distribution, direction of flow and streamlines in the field and the drops distribution in the outlet of the stator blade mesh. The procedure contains a program section, which avoids difficulties in the strongly curved profile of the leading and trailing edge by a developed computational mesh construction.

Experimental study on steam-water two-phase flow frictional pressure drops in helical coils

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蒸汽浴-流动分析仪法测定土壤有机碳含量的方法

为了准确高效批量测定土壤有机碳含量,采用比色管代替消煮管,蒸汽加热消煮土壤,利用流动分析仪法测定有机碳。并将此方法与重铬酸钾氧化-外加热法(常规通用)进行了比较,探讨方法的可行性。结果表明,蒸汽浴-流动分析仪法测定土壤有机碳含量重复性试验的相对标准偏差为3.19%~9.41%,回收率为92.21%~97.63%。方法精密度及准确性良好。所测结果与重铬酸钾氧化-外加热法无显著性差异(P>0.05),两种方法拟合的回归方程:y(蒸汽浴-流动分析仪法)=0.947x(重铬酸钾氧化-外加热法)+1.621(r^(2)=0.933),两者呈良好的相关性。用两种方法测定200个土壤有机碳,蒸汽浴-流动分析仪法的检测用时是重铬酸钾氧化-外加热法用时的68%,人工操作用时是重铬酸钾氧化-外加热法用时的44%,蒸汽浴-流动分析仪法无需使用硫酸亚铁,重铬酸钾、硫酸和水用量为重铬酸钾氧化-外加热法的40%。蒸汽浴-流动分析仪法省工省时,人员工作强度低,试剂用量少,环境危害降低,检测准确高效,经济安全,可推荐为大批量土壤有机碳含量测定的方法。

非线性动态特性系数对汽轮机转子-轴承-密封系统运动特性的影响

为准确地反应汽流激振下汽轮机转子-轴承-密封系统的运动特性,推导了包含非线性动态特性(非线性刚度、阻尼)的转子运动微分方程,将数值模拟获得的非线性汽流激振力拟合成方程耦合到运动方程中,采用龙格-库塔法求解对应的运动方程,基于试验对比验证了考察非线性因素的必要性与运动微分方程的准确性。在此基础上,分析汽流激振力作用下不同非线性动态特性系数对转子运动特性与稳定性的影响。结果表明:系统中的非线性动态特性会改变转子不同类型的混沌运动区域与位移,使1/2、1/3、2/3工频的出现范围及幅值改变,密频现象增加;耦合热、动载荷后高负荷区域转子位移减小。对比Lyapunov指数,考虑非线性动态特性后其均值有所上升;合理的非线性刚度能够改善系统的稳定性,高非线性阻尼值能提高系统稳定性;耦合热、动载荷后的系统高负荷运行时更稳定。

窄缝通道内低雷诺数蒸汽流动换热特性数值模拟研究

为探究窄缝通道在大破口失水事故下再淹没过程中低雷诺数(Re_(in)=1 881~10 348)过热蒸汽的流动换热特性,采用计算流体力学(computational fluid dynamics, CFD)方法,基于优选出的湍流模型,探究加热面热流、压力条件和入口速度对低雷诺数过热蒸汽流动换热特性的影响规律。对比了Gnielinski关联式与Dittus-Boelter关联式,并对Dittus-Boelter经验关联式进行修正。计算结果表明:雷诺时均(Reynolds average Navier-Stokes, RANS)湍流模型中SST k-ω的模拟结果与大涡模拟(large eddy simulation, LES)的模拟结果最为接近,且计算量小;过热蒸汽对流换热能力随压力和入口流速的增加而增强,随加热面热流增加而减弱;相对于数值模拟结果,Dittus-Boelter和Gnielinski经验关联式预测的Nu数偏低,修正后的新关联式误差在15%以内,可为再淹没过程低雷诺数过热蒸汽的流动换热分析程序开发提供参考。

进口预旋下三种典型迷宫密封转子动力特性研究

为探讨考虑进口预旋的迷宫密封转子动力特性,基于Murphy小位移涡动理论建立气流激振力与转子涡动位移的控制方程,采用用户自定义函数建立多频椭圆涡动模型,利用FLUENT动网格技术数值求解直通齿式迷宫密封(SLS)、倾斜齿式迷宫密封(ILS)和阶梯式迷宫密封(STLS)在不同预旋比下的激振力,通过快速傅里叶变换得到整机运行时的密封动力特性系数,并对转子稳定性和密封的泄漏量进行分析。结果表明:在40~180 Hz涡动频率范围内3种密封结构的直接刚度系数呈先减小后增大的趋势,表现出很强的频率相关性,而密封结构与进口预旋对阻尼系数的影响可以忽略;阻尼系数随涡动频率增加缓慢减小至负值并趋于平稳,其中STLS的阻尼系数最小,稳定性最差,ILS的稳定性最好;增加进口预旋比会降低有效阻尼系数,并导致泄漏量降低;STLS在不同预旋条件下的密封性能均最佳,相比于SLS与ILS的泄漏量分别减少了15%和7%;在研究的20~200 Hz涡动频率范围内3种类型迷宫密封的交叉刚度由负值增大为正值,而有效阻尼减小为负值,此时迷宫密封转子系统稳定较差,可能会诱发转子失稳。

多相流阻垢热泵蒸发系统特性研究

为验证多相流热泵蒸发系统的在线阻垢及强化换热性能,以蒸氨废液为液相工质、氧化铝及聚甲醛粒子为阻垢颗粒进行实验研究。结果表明,氧化铝颗粒的加入可有效去除蒸发器已有垢层,换热系数由结垢后的392.5 W/(m^(2)·K)提升至1 712.2 W/(m^(2)·K),且连续运行130 h换热系数未降低;蒸发器换热系数受颗粒物性参数影响较大,随着颗粒直径、密度、体积分率增加换热系数逐渐增大,但增加过量时导致流动不畅,换热系数降低;颗粒自身材质导热系数越高强化换热效果越好;循环流量、颗粒分布形式对换热系数也有较大影响,提高循环流量有助于强化换热;不同分布形式在一定程度上均可提高换热系数,双层多孔分布器可实现颗粒逐级输运,增加其进入换热管比例,强化换热效果最佳。

基于遗传算法的核电站汽轮机抽汽流量优化计算

为提高核电站汽轮机系统的效率和运行性能,确保经济、稳定和可靠的电力供应,开展基于遗传算法的核电站汽轮机抽汽流量优化计算研究。利用神经网络预测核电站汽轮机抽汽流量,以核电站汽轮机抽汽流量为优化目标,各抽汽口抽汽流量和一、二级再热蒸汽流量为优化变量,采用遗传算法进行核电站汽轮机抽汽流量优化计算目标函数求解,所得最优解即为抽汽流量优化计算结果。实验结果表明,该方法的核电站汽轮机抽汽流量优化计算结果与实际值更接近,说明该方法的计算精准度高,应用效果好。

Oxy-Steam燃烧方式下的NO生成特性

以甲烷掺混氨气为燃料对oxy-steam气氛下NO生成特性进行实验和模拟研究.在常压柱塞流反应器中开展了一系列O_2/N_2和O_2/H_2O气氛的对比实验,当量比从富燃至贫燃(1.6、1.0、0.2),温度范围为973~1,773,K.实验结果表明,O2/H_2O气氛下高浓度的水蒸气在当量和贫燃工况下抑制NO的生成,而在富燃工况下促进NO生成.更新并构建的详细化学机理能够很好地重现并解释实验中NO的生成特性.当量和贫燃工况下,极少的O基团抑制了反应NH_2+O H+HNO从而抑制了NH_2→HNO→NO反应路径,最终降低了NO的生成.富燃工况下,充足的OH基团显著促进了反应NH_2+OH=NH+H_2O从而促进了NH_2→NH→HNO→NO反应路径,最终增加了NO的生成.

某小功率汽轮机三维通流计算及分析优化

文章主要采用CFD手段,对某小功率汽轮机进行了三维通流计算。根据计算结果,对机组质量流量、焓降分配、反动度、汽封漏汽进行了分析,并根据分析结果对机组进行了优化设计。

基于凝汽器蒸汽流场的管束汽流激振评估研究

凝汽器管束在高速蒸汽冲刷作用下可能会产生汽流激振现象,全面评估管束的汽流激振对保障机组安全运行具有重要的安全意义。采用数值模拟方法,在某核电机组凝汽器若干工况下,对其喉部和壳侧进行蒸汽流场的数值模拟,然后基于凝汽器蒸汽流场分布,分别以最大许用跨距和临界横流速度为评估准则对管束进行汽流激振评估。研究结果表明:对于所研究的核电机组凝汽器,在管束轴向方向上,靠近壳体壁面侧的管束的中段位置为发生汽流激振的危险区;在管束横截面方向上,靠近壳体壁面侧的管束模块上方“树枝”通道外层的冷却管发生汽流激振的可能性很大,且高加疏水工况会加大靠近有闪蒸器这一侧壳体壁面的管束模块在该处汽流激振的可能性;半侧隔离工况下,各管束模块两侧中间位置“树枝”通道外层冷却管有发生汽流激振的可能性。

蒸汽爆破对木质纤维素高值化利用的研究进展

木质纤维素生物质是一种量大面广且廉价易得的可再生资源,已逐步实现由生物质向生物燃料、饲料原料和其他附加值产品的开发及应用,这样的高值转化与综合利用成为“走绿色发展道路、构建绿色生产体系”的重要部分。然而,木质纤维素的天然抗降解屏障及其独特的理化性质,纤维素-半纤维素-木质素三大组分的刚性网络一直是高效转化的瓶颈所在,合理有效的预处理技术则是资源化进程的关键步骤。本文落脚于木质纤维素生物质的基本组成和结构特性分析,在总结物理法、化学法、生物法等传统预处理方法优劣势的基础上,着重阐述了蒸汽爆破的发展历程、加工类型、适用范围、工作原理、反应阶段、技术特点、影响因素、主要参数和可能的副产物效应等,以及在生物质的纤维改性、结构变化、溶解特性、低聚糖制备、活性成分提取与反刍饲料化利用层面的研究进展。此外,还指出蒸汽爆破辅以真菌、细菌为主的微生物发酵,以及糖酶外源添加的后处理流程的发展趋势。最后,归纳了蒸汽爆破在未来商业化、工业化和规模化生产推广中可能面临的困难和挑战,分析提出相应的突破点和解决策略。并就蒸汽爆破技术对常见副产物类型饲料原料的降解效果,及其在单胃动物日粮中的合理应用进行展望,以期为该技术对生物质资源的开发、增值、饲料化应用的诸多潜能提供新思路和技术指导。