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.

Exhaust hood performance and its improvement technologies in industrial buildings:A literatu rereview

The pollutant control performance of exhaust hoods plays a crucial role in the indoor air quality and energy consumption of ventilation systems in industrial buildings.To better understand the impact of local ventilation on the industrial indoor environment,this paper presents a literature review of exhaust hood performance and its improvement technologies.To create an index for evaluating the performance of exhaust hoods,the capture velocity,capture efficiency,flow ratio of pollutant emissions and exhaust airflow and energy consumption are first introduced.A number of factors affecting exhaust hood performance are assessed such as hood type,hood opening size,exhaust rate,installation distance,pollution source emission and environmental disturbance.Compared to structural improvement methods,the use of active airflow is a more effective way to improve the exhaust hood performance.The most commonly used methods for determining the exhaust rate are the controlled speed method and the flow ratio method.The use of an exhaust hood with an appropriate exhaust rate and jet parameters(for an active air-assisted hood)can effectively improve the pollutant control performance and reduce the energy consumption that would be wasted on the redundant exhaust rate.With more information focused on exhaust hood performance,this work suggests more effective strategies for improving indoor air quality and reducing energy consumption in industrial buildings.

Multiple indicators and analytic hierarchy process(AHP)for comprehensive performance evaluation of exhaust hood

Indicators are the basis for judging the working performance of exhaust hood and capture performance are usually used as the only indicator.An evaluation index system including three factors of cooking oil fumes(COF)instantaneous capture,health risk impact and thermal comfort was proposed to assess the comprehensive performance of exhaust hood in the present study.The primary capture efficiency(PCE)of formaldehyde,the PCE of particulate matter with the diameter less than or equal to 2.5μm(PM_(2.5)),the incremental lifetime cancer risk(ILCR)of formaldehyde,the ILCR of PM_(2.5)and the predicted mean vote(PMV),which can all be quantified with the aid of computational fluid dynamics(CFD),were selected as the indicators.And the analytic hierarchy process(AHP)method was introduced to perform the comprehensive performance evaluation of exhaust hood.The performance of two exhaust hood structures(grille and orifice type)with three exhaust rates(3000,4000,and 5000 m^(3)/h)in two cooking zones of a university canteen kitchen were evaluated.The result showed that the reduction of ILCR of COF exposure is the most important to the performance of exhaust hood.The comprehensive performance of orifice exhaust hood with exhaust rate of 4000 and 5000 m^(3)/h are optimal;the orifice exhaust hood with exhaust of 3000 m^(3)/h and grille exhaust hood with exhaust rate of 5000 m^(3)/h are moderate;the grille exhaust hood with exhaust rate of 3000 and 4000 m^(3)/h are low.Decision-making priorities based on comprehensive and individual performance are not exactly the same in the two cooking zones.It is necessary to use the index system to evaluate the comprehensive performance of exhaust hood that considers the impact on human health and thermal comfort.

Influences of Inflow Condition on Non-Axisymmetric Flows in Turbine Exhaust Hoods

在一台蒸气汽轮机的复杂 3D 流动与不同入口用尽兜帽模型打漩并且入口总数压力光线的分布被采用 CFX-5 模仿了并且在这分析了纸。它发现了在中心的正切的流动角度有的入口 exhaust 兜帽表演上的否定效果，当时光线的分发有的入口总数压力的一个否定坡度兜帽表演上的积极影响。它数字地也证实了在兜帽入口罐头的全部的压力的合适的分布成功地消除由不恰当的入口引起的否定效果打漩分发并且改进兜帽空气动力学的性能。

Investigations on the Improving Aerodynamic Performances of Last Stage Steam Turbine and Exhaust Hood under Design and Off Design Conditions

The purpose of this paper is to improve the aerodynamic performances of the last stage turbine and the exhaust hood of a 600 MW steam turbine under design and off design conditions. During operation, strong flow interactions between the turbine and the exhaust hood impose influences on the flow behavior in the hood and lead to the unsatisfactory aerodynamic performance of the turbine and exhaust hood. So the exhaust hood has the potential to be improved in terms of aerodynamic efficiency. Considering the flow interactions between the turbine and the exhaust hood, the profiles of the diffuser end-wall were optimized. The coupled model turbine and model exhaust hood calculations and experiments were carried out to validate the effects of the optimization. Model experiments show that the design modifications resulted in a substantial increase in the overall pressure recovery coefficient. The flow and aerodynamic performances of the full-scale last stage turbine and full-scale exhaust hood were simulated to explore the flow physics alterations to the modification of diffuser geometry. The wet steam was selected as the flow medium. The actual flow fields under different operation conditions were analyzed.

Effects of Inlet Swirl on the Flow in a Steam Turbine Exhaust Hood

The flow in the exhaust hood of a condensing steam turbine depends to a considerable extent on the inlet swirl of the flow which changes in tandem with the volumetric flow of steam through the last stage. This study gives a description of experiments which were carried out on the exhaust hood of a 500 MW steam turbine under various conditions, e.g. when there is rated power, when there is an idle run, or when there are various pressures in the condenser. The flow in a model exhaust hood was investigated by means of CFD methods. Computations were performed with the help of the FLUENT 5 code which is based on solving the Navier-Stokes equations while taking the RSM and LES models of turbulence into consideration. The results of the computations are in full conformity with the experiments.

Three-Dimensional Simulation of Nonstationary Flow Phenomena in "Last Stage-Exhaust Hood"Compartment

Three-dimensional nonstationary model of aerodynamical interaction of turbine stage and exhaust hood is realized, based on nonstationary 3D codes for calculation of inviscid transonic flow through stage[3] and exhaust hood[4] which consist of diffuser and space under casing. The codes are built with the use of the explicit Godunov’s 2nd order difference scheme. Some results of flow simulation through the compartments "stage-exhaust hood," "stage-exhaust axial-radial diffuser" for wide range of volumetric flow rates are represented.

3D Flow in the Axial-Radial Exhaust Hood of a Steam Turbine

The computation model of the 3D viscous flow is used for the analysis of the flow conditions in the model of steam turbine exhaust hood, that was in previous time investigated experimentally. The computation method and the obtained results are described. The calculation is concentrated on the finding of the influence of inlet velocity field and on the influence of compressibility of the flow medium.Especially it followed the fluid motion in the outlet vortex and the occurrence of the areas with flow separation.

铝熔炼炉排烟罩捕集性能分析及优化数值模拟

铝加工厂房熔炼工艺中高温烟尘散发强度大、浓度高,对建筑室内外环境和人员健康危害大。为提高铝熔炼炉局部排烟罩捕集效率,本文研究了排烟罩捕集效率与量纲一排风量(排烟罩排风量/烟尘散发量)的关系;基于消涡原理及气流卷吸特性,提出了排烟罩捕集性能优化方法。研究表明,当量纲一排风量小于3.2时,增大排风量会显著提升排烟罩的捕集效率,为风量经济区。排烟罩几何特征优化后,在风量经济区内烟尘逃逸率降低了20%左右,系统排风量降低了6.1%~44.1%。

用于铝压延厂房油雾控制的环吸式排风罩设计方法

环吸式排风罩是针对铝压延加工工艺油雾散发特征而提出的一种高效捕集设备,可以大幅降低系统风量,从而减少能耗和降低碳排放量,但目前仍缺乏此类排风罩的通用设计方法。本文选取10个铝压延车间铝冷轧机及排风罩为研究对象,探究了不同轧机尺寸组合下排风罩罩口处污染物扩散断面尺寸和排风罩捕集性能,通过回归分析得到了排风罩罩口设计尺寸和设计风量的计算方法,可供工程设计人员参考。

切削机床油雾颗粒局部排风的优化研究

切削加工过程中产生的油雾颗粒会给从业人员带来严重的健康危害,局部排风罩可减少油雾颗粒散逸。本文采用CFD方法,研究了排风量和排风罩高度对不同粒径颗粒捕集效率的影响,提出了特征拖曳比参数,通过回归得到特征拖曳比与捕集效率的关系式;采用增加柔性围挡的方式对局部排风罩进行了优化,上吸罩增加围挡后的捕集效率与将排风罩高度降低60 cm的捕集效率相近。

G510MW重型燃机排气缸制造工艺研究

就如何保证引进型G510MW重型燃机排气缸制造质量和生产效率等问题,对缸的工作状态、结构、加工要求、加工难点、制造工艺性等方面进行了分析。结合现有加工设备和目前生产条件,拟定并实施了切合实际的制造工艺方案和保证加工精度的各种工艺措施,很好保证了缸的尺寸精度、形位公差、表面粗糙度和密封效果,实现了技术先进、经济效益显著的目标,结果好于预期。

带内部支撑结构的低压排汽缸气动性能分析

The static pressure recovery of low-pressure exhaust hood is important for the overall effectiveness of steam turbines.The tubular and plate stiffeners inside the exhaust contribute to the structural safety of exhaust,which affect the aerodynamic performance.Given the complicated exhaust model coupled with the last stage of turbine,this paper intends to investigate the aerodynamic performance of exhaust hood with individual stiffeners using highfidelity numerical simulations in order to figure out the corresponding effects.The results show that(1)the types of stiffeners have different effects on the aerodynamic performance;and(2)different installation positions and types of plate stiffeners have different effects on aerodynamic performance.The above investigations highlight the future demand regarding reasonable layout and quantity of stiffeners to improve the aerodynamic performance of exhaust as well as maintaining the structural safety.

基于主动学习方法的汽轮机排缸参数分析

It is well known that the efficiency of a steam turbine is affected by the pressure recovery performance of its low-pressure exhaust hood,and therefore,parametric analysis of the exhaust hood is of great importance in the steam turbine design process.In recent years,computationally inexpensive metamodels have been widely used in the parametric analysis of exhaust hood.However,the prediction accuracy of metamodels is highly dependent on the number and distribution of sample points in the design space.The purpose of active learning is selecting informative samples sequentially to obtain an accurate metamodel within a reasonable computational budget.However,the impact of active learning on the accuracy of metamodels such as exhaust hood parameter analysis has not been fully explored.Therefore,this paper investigates and compares four representative active learning methods on the parametric modeling of turbine exhaust hoods,and the comparison results highlight the advantages of active learning and the analysis of the exhaust hood based on the metamodel with the highest accuracy.

大型半封闭矿热炉用静压过渡集排烟罩

介绍了大型工业硅半封闭矿热炉用的静压过渡集排烟罩的设计,通过对工业硅炉口反应产物的稳定燃烧进行火源模拟,结合燃烧产生的火烟羽流生成机理、流动机理、防排烟系统设计原理对烟罩进行优化,强化烟罩均压、导向缓、冲、储烟等排烟作用,并分析了烟罩对实际生产过程中容易出现的炉门漏烟、吸穿带料、塌料冒烟等问题的抑制作用.为静压过渡集排烟罩的成功应用提供理论基础,助力烟罩的推广应用.

浅谈实验室通风设施存在问题及改善方法

目的了解目前实验室通风设施运行现状,降低危害因素对分析化验人员的健康影响。方法针对多个职业病危害现状实验室展开通风设施现场调查,并对某石化企业检验计量中心实验室中的排风设施进行控制风速检测。结果目前实验室排风系统存在设计类型不合理、设计风量不足、气流组织错误以及维修、使用不到位等诸多问题。结论对于存在问题的实验室应尽快进行隐患整改,同时加强实验室通风设施的使用维护管理,保证通风设施高效运行,降低有毒有害物质对实验室分析化验人员的危害。

大型客船厨房集气罩排风控制系统节能优化设计

大型客船通常配置多种厨房以保障不同乘客的需求,每个厨房都需配置1台或多台排风机,因此厨房需求的排风量非常大,对应的排风风机能耗也较高。厨房集气罩用于收集厨房里各类设备工作时产生的水蒸气和油烟,是厨房排风系统的重要组成部分,目前的大型客船厨房排风一般都采取集气罩进行集中局部排风。文中对大型客船厨房传统集气罩排风系统控制技术进行分析,针对其排风量大、能耗高的缺点,基于风机变频及变风量控制技术,提出了1种新型厨房集气罩节能排风控制系统的设计方法。通过在某客滚船上进行试验验证,对比分析传统排风系统与节能排风系统中厨房排风机的风量数据,验证了该新型厨房集气罩排风系统具有显著的节能效果,可在其他船型进行推广应用。

汽轮机低压排汽缸与末两级耦合流动的三维数值模拟

数值模拟一直是研究大功率汽轮机低压排汽缸内流场的主要方法之一。但是,国内外的研究大多只构造单个排汽缸模型进行分析,并未考虑到末级动叶排出汽流的不均匀性等因素的影响。为了更加透彻地认识排汽缸内三维流动的细节,文中通过求解由RNGk-ε双方程湍流模型封闭的三维时均N-S方程对汽轮机低压排汽缸和末两级耦合流动进行了数值分析,并采用"混合平面"方法处理末两级叶栅及其与排汽缸之间动静面的参数传递和相互干扰的问题,获得了排汽缸内部的压力和速度分布。与单独排汽缸数值分析相比,该方法能够获得更为接近实际的数值结果,并为汽轮机通流部分及排汽缸的设计研究提供了新思路,所得到的结果可为排汽缸的优化设计提供参考。

烹饪油烟污染与处理技术探讨

为了降低油烟对环境的污染,分析了油烟中的主要污染物成分及油烟对人体健康的几种危害。讨论了五种油烟净化技术:惯性分离法、过滤分离法、液体洗涤法、静电沉积法、复合技术。分析了液体洗涤油烟净化技术的原理、水循环利用时对洗涤废液进行的油水分离,提出了采用流场分析喷淋,以了解其流场的特性。结果表明,采用液体洗涤法去除油烟效率高,安全可靠。

某600MW汽轮机低压末级排汽通道耦合流动三维数值模拟及其结构优化

利用计算流体软件基于Spalart-Allmaras单方程模型分别对600MW机组的排汽缸、凝汽器喉部和两者耦合的排汽通道进行三维数值模拟,以便更加清晰地了解排汽通道的整体流场,并对排汽通道进行合理优化改造。计算结果表明,单独结构模拟结果与排汽通道耦合模拟的结果存在很大差异,主要体现在流场和压力损失上。在有进口漩流的模型中,蒸汽流场分布不对称,因此,不能为简化而采用1/2模型进行研究。针对排汽通道内流场分布,在排汽缸拱顶处加装导流挡板和在扩压管处加装分流板,能有效改善通道内的流场。