基于红外热图的空气预热器热点检测系统

提出了一种基于空气预热器转子红外热图分析的空气预热器热点检测方法．通过对采集到的图像数据进行坐标转换并采用三次样条法进行像素的插值,获取空气预热器转子的红外热图,然后采用小波变换的软阈值去噪法对其进行滤波,在此基础上提取能量特征,并采用能量特征对空气预热器的不同工作状态(正常、异常)进行识别．实验结果表明,该方法可以有效识别空气预热器的异常工作状态．     

锅炉排烟温度偏差分析及空气预热器检修评估

通过对某330 MW锅炉排烟温度DCS值偏差大、排烟温度偏高原因进行分析,并对空气预热器检修效果进行了评估。对于排烟温度偏差问题,主要从温度标定、燃烧偏差及空气预热器换热效果等方面进行分析。结果表明:DCS排烟温度平均数据能较好反映空气预热器出口截面温度数据,炉右侧排烟温度DCS值偏差大的原因为炉右侧烟道靠右DCS值与实测值存在较大负偏差;330 MW负荷下空气预热器检修后与检修前相比,空气预热器烟气侧换热效率降低约0.5%,排除空气预热器漏风率变化对排烟温度的影响,检修后比检修前空气预热器出口烟气平均温度(修正后)升高约3.0℃。建议从空气预热器更换的换热元件材质、间隙或安装工艺等方面查找原因,以解决空气预热器检修无效的问题。     

全焊接型大风量板式空气预热器的传热特性研究

对全焊接型大风量板式空气预热器的换热和流动特性进行数值模拟,并搭建实验台验证了模拟所用物理模型和数学模型的正确性,采用努塞尔数Nu和Fanning摩擦因子f分别对空气预热器的换热和流动性能进行评估,分析了板间距B、烟气每层椭圆通道数n和烟气条形通道高度H对空气预热器性能的影响,通过最小二乘法拟合得到全焊接型大风量板式空气预热器的传热关系准则式。结果表明:当B变大或H增加时,换热性能提高;当B减小,n减小或H减小时,流动性能变好;且H的最佳取值为7 mm。     

一种新型空气预热器及其性能分析

提出了一种新型空气预热器,该预热器依靠8个阀门的不同开闭来控制空气与烟气交替流过2个蓄热体,从而实现烟气对空气的加热.分析表明,新型空气预热器与回转式空气预热器相比,漏风率大大降低,不到3%.     

燃煤锅炉空气预热器跳闸原因分析及对策

空气预热器是利用锅炉等装置的排烟热量来预热的换热器。运行中引起空气预热器跳闸的连锁条件有空气预热器变频器停止、转子停转信号触发,空气预热器跳闸后会连锁运行中的同侧引风机、送风机、一次风机跳闸,从而造成机组RB动作,因此保证空气预热器安全运行至关重要,文中从几个实际案例分析出发,分析了不同原因造成空气预热器跳闸的因素,对确保空气预热器跳闸保护机组的安全起到一定的指导意义。     

1000MW超超临界机组锅炉运行测试

针对某火力发电厂2号机组的锅炉热效率、NOx排放及空气预热器漏风率进行了测试,检验锅炉能否达到供货商对其提供产品所作的性能保证值。结果显示其锅炉效率和NOx排放量达到性能保证值,但空气预热器的漏风率略高于其保证值。     

三维内肋管管式空气预热器的设计与可行性研究

采用强化传热性能优良的新型三维内肋管与传统热能力强、漏风系数小的热管双级布置的方案对300MW电站锅炉机组空气预热器进行了优化设计和可行性研究。空气预热器总的漏风系数设计值为5％,加热一、二次风的上级三维内肋管卧式空气预热器的布置空间分别为螺纹管空气预热器的64．46％和47．87％,相应的受热面积为42．61％和37．32％,这有效地解决了回转式空气预热器漏系大,以及一航管式空气预热器体积庞大、难以布置的问题。     

600MW超临界锅炉燃用劣质高硫煤空气预热器堵塞的原因及改造措施

针对福泉电厂600 MW超临界锅炉调试运行时空气预热器出现严重的堵灰问题进行了原因分析,认为堵灰主要是由于煤质硫、灰含量高及空气预热器设计选型不合理造成的。通过实施空气预热器改造,更换空气预热器中温段换热元件以扩大通流面积及采取一系列合理的运行调控措施使得空气预热器阻力达到设计值,保证了机组的安全、经济运行,对高灰分、高硫分劣质燃煤锅炉中出现的类似问题有一定的借鉴和指导作用。     

三分仓回转式空气预热器积灰分段监测模型研究

针对三分仓回转式空气预热器热段和冷段积灰分段监测的需求,基于空气预热器的传热模型,定义空气预热器利用系数作为清洁因子并建立积灰分段监测模型.通过分析空气预热器实时运行参数,根据热平衡原理确定了清洁因子计算步骤.以某1 000MW超超临界直流锅炉的三分仓回转式空气预热器为例,研究了热段、冷段清洁因子在空气预热器积灰和吹灰时的变化趋势.结果表明:根据所建模型计算出的分段清洁因子变化趋势在稳定负荷下能够反映此空气预热器的分段积灰情况,而在变负荷情况下虽有一定偏离,但由于电厂变负荷工况下很少吹灰故影响较小;该积灰监测模型可作为三分仓回转式空气预热器热冷分段积灰监测的有效手段.     

转速对三分仓回转式空气预热器热力性能的影响

基于有限差分法,将三分仓回转式空气预热器沿旋转方向周向展开,在蓄热元件单元和流体之间划分网格,通过建立每一有限单元内流体和蓄热单元间热平衡方程,利用改良的高斯塞德尔迭代方法计算得到蓄热元件的流体温度场分布。以某600 MW机组三分仓回转式空气预热器为例,详细分析了转速变化时,流体和金属温度场分布、ABS(硫酸氢铵)沉积区域等的变化趋势和规律。研究结果显示:(1)蓄热元件温度随转动角度分布的非线性特征,随转速降低而增加,可以用非稳定换热影响因子Π表征,各个分仓的Π值不同;(2)不同转速下,蓄热元件温度分布曲线,在加热和冷却周期内,各存在一个相对稳定的平衡位置;(3)三分仓空气预热器出口一次风、二次风平均温度随转速的变化趋势,与转子旋向和各空气分仓角度有关。     

Second law analysis of a disturbed flow in a thin slit with wall suction or injection

Fully-developed laminar flow in a horizontal thin slit having plates at different temperature is considered for the case of lower plate movement and/or the pressure gradient-and-upper plate movement. The flow under these conditions is analyzed in terms of entropy generations as function of the Prandtl number, the Eckert number, cross-flow Reynolds number and dimensionless temperature difference. In this context, the governing equations for distributions of temperature, the dimensionless entropy generation number and Bejan number are analytically derived with the aid of expressions for velocity distributions. The effect of each parameter on the temperature and the entropy generation are investigated by varying one of the parameters and keeping the rest of them constant for each flow case. The effects of viscous dissipation, rates of mass suction/injection and dimensionless temperature differences on the fluid temperature and entropy generation are examined. The magnitudes of mass suction and/or injection have a large influence on the temperature profile of the fluid. It is observed that the Prandtl number and the Eckert number affect fluid temperature in similar way. It is found that an increase in values of the cross-flow Reynolds number (mass suction/injection) enhances the entropy generation in boundary layer. The velocity profiles are found to be in agreement with the distributions of the dimensionless entropy generation number (N_S) for two flow cases.     

基于小波熵和BP神经网络的孤岛检测与扰动辨识

提出基于小波熵和BP神经网络的孤岛检测技术,将小波变换的多分辨率分析与信息熵技术结合,能够有效地区分电网扰动与孤岛现象的内在不同。仿真实验表明该方法具有较高的准确性。     

Effect of aspect ratio on entropy generation in a rectangular cavity with differentially heated vertical walls

In the present study, entropy generation in rectangular cavities with the same area but different aspect ratios is numerically investigated. The vertical walls of the cavities are at different constant temperatures while the horizontal walls are adiabatic. Heat transfer between vertical walls occurs by laminar natural convection. Based on the obtained dimensionless velocity and temperature values, the distributions of local entropy generation due to heat transfer and fluid friction, the local Bejan number and local entropy generation number are determined and related maps are plotted. The variation of the total entropy generation and average Bejan number for the whole cavity volume at different aspect ratios for different values of the Rayleigh number and irreversibility distribution ratio are also evaluated. It is found that for a cavity with high value of Rayleigh number (i.e., Ra = 10⁵), the total entropy generation due to fluid friction and total entropy generation number increase with increasing aspect ratio, attain a maximum and then decrease. The present results are compared with reported solutions and excellent agreement is observed. The study is performed for 10² < Ra < 10⁵, 10^− 4 < ? < 10^− 2, and Pr = 0.7.     

Entropy production analysis for mechanism reduction

A systematic approach based on the relative contribution of each elementary reaction to the total entropy production is developed for eliminating species from detailed reaction mechanisms in order to generate skeletal schemes. The approach is applied to a database of solutions for homogeneous constant pressure auto-ignition of n-heptane to construct two skeletal schemes for different threshold values defining the important reactions contributing to the total entropy production. The accuracy of the skeletal mechanisms is evaluated in spatially homogeneous systems for ignition delay time, a single-zone engine model, and a perfectly stirred reactor in a wide range of thermodynamic conditions. High accuracy is also demonstrated for the speed and structure of spatially-varying premixed laminar flames.     

考虑CEEMDAN样本熵和SVR的短期风速预测

为降低由于风速信号的非线性和非平稳性带来的风速预测难度,提高短期风速预测的准确性,提出一种考虑样本熵的组合分解模式和支持向量回归（SVR）相结合的预测模型。首先采用自适应噪声的完全集合经验模态分解（CEEMDAN）方法分解风速历史数据,并计算各模态分量的样本熵;然后采用变分模态分解（VMD）方法对样本熵最大的模态分量进行二次分解,充分削弱风速分量的非平稳性;接着对分解得到所有模态分量分别建立SVR预测模型;最后将各分量的预测值求和完成最终风速预测。实例分析表明,所提模型对比其他模型的预测误差最小,预测精度最高,可有效预测短期风速。     

A Computational Study of Swirl Number Effects on Entropy Generation in Gas Turbine Combustors

In this paper, local and global entropy generation features are studied numerically in two research flames and a real combustor problem. The research flames are the well-known Burner Engineering Research Laboratory and Sandia flame D experimental flame databases and the real combustor is a gas-turbine can-type combustor. The main focus is on investigating the effect of the swirl number, in the range 0.0–2.4, on entropy generation characteristics due to different phenomena, including viscous, mass transfer, heat transfer, heat-mass coupling, reaction, and specifically radiation. For this purpose, the surface and volumetric local entropy generation rates are formulated based on the first-order spherical harmonics model known as “P1,” a frequently used model in combustion applications. It is observed that heat transfer and reactions are dominant causes of entropy generation with the leading contribution of reaction at lower swirl numbers and heat transfer at higher swirl values. The radiation entropy generation is slightly affected by the swirl number and is of prime importance only in near stoichiometric conditions. Moreover, it is indicated how this local entropy generation analysis can be used to discover the weaknesses in the design of a real combustor.     

Entropy generation in natural convection in a symmetrically and uniformly heated vertical channel

In this study numerical predictions of local and global entropy generation rates in natural convection in air in a vertical channel symmetrically heated at uniform heat flux are reported. Results of entropy generation analysis are obtained by solving the entropy generation equation based on the velocity and temperature data. The analyzed regime is two-dimensional, laminar and steady state. The numerical procedure expands an existing computer code on natural convection in vertical channels. Results in terms of fields and profiles of local entropy generation, for various Rayleigh number, Ra, and aspect ratio values, L/b, are given. The distributions of local values show different behaviours for the different Ra values. A correlation between global entropy generation rates, Rayleigh number and aspect ratio is proposed in the ranges 10³ ⩽ Ra ⩽ 10⁶ and 5 ⩽ L/b ⩽ 20.     

Entropy generation between two vertical cylinders in the presence of MHD flow subjected to constant wall temperature

An analytical solution is presented on the entropy generation due to mixed convection between two isothermal cylinders where a transverse magnetic field is applied to the system. The governing equations in cylindrical coordinates are simplified and solved to obtain the distribution of entropy generation and the effects of MHD flow on it. The results for the entropy generation number (N_S), the Bejan number (Be) and average entropy generation number (N_S,ave) are presented for different values of the Hartmann numbers, radius ratios and a flow parameter, Gr/Re. The results show that the entropy generation decreases with increases in the magnetic field. In addition, it is found that with decreases in the radius ratio, the effects of MHD flow on the entropy generation are reduced.     

Numerical investigation of unsteady natural convection heat transfer and entropy generation from a pair of cylinders in a porous enclosure

Abstract

The present study analyses numerically the unsteady heat transfer and entropy generation characteristics in a two-dimensional porous enclosure embedded with two heated circular cylinders at different positions at the vertical mid-plane. The heat transfer is primarily due to conduction for lower values of Darcy number (10^?4), while heat transfer by convection becomes significant for higher values of Darcy number (10^?3, 10^?2). Contrasting features are observed in the variation of time-average Nusselt number with interspacing distance. The major contributor of irreversibility is the entropy generation due to heat transfer for lower values of Darcy number, while for larger values of Darcy number, it varies with Rayleigh number.     

Entropy parameters for heat exchanger design

A general expression for entropy generation in counter-current heat exchangers is developed. It is applicable to incompressible liquids and perfect gases. Two new entropy generation numbers are defined, N_M and N_Q. The analysis is applied to an air-air counter-current heat exchanger. The three entropy generation numbers, N_S, N_M and N_Q, have a different variation with NTU at the various values of the capacity flow rate ratio employed in the calculations.