锅炉空气预热器螺旋线圈插入物抗积灰机理分析

就锅炉空气预热器螺旋线圈插入物的抗积灰机理，从管内流动特点讨论了造成光管积灰的原因。螺旋线圈插入物抗积灰的流动特点。介绍了电厂空预器应用螺旋线圈的效果。     

Heat transfer behaviors in a tube with combined conical-ring and twisted-tape insert

Heat transfer, friction factor and enhancement efficiency characteristics in a circular tube fitted with conical-ring turbulators and a twisted-tape swirl generator have been investigated experimentally. The heat transfer test section is heated electrically imposing axially and circumferentially constant wall heat flux boundary conditions. In the experiments, two enhancement heat transfer devices are applied. One is the conical-ring used as a turbulator and placed in the tested tube and the other is the twisted-tape swirl generator placed at the core of the conical-ring. Air as the tested fluid is passed both enhancement devices in a Reynolds number range of 6000 to 26,000. Two twisted-tapes of different twist ratios, Y = 3.75, and 7.5, are introduced in each run. The experimental results reveal that the tube fitted with the conical-ring and twisted-tape provides Nusselt number values of around 4 to 10% and enhancement efficiency of 4 to 8% higher than that with the conical-ring alone. A maximum heat transfer rate of 367% and enhancement efficiency of around 1.96 is found for using the conical-ring and the twisted-tape of Y = 3.75. For all the devices used, the enhancement efficiency tends to decrease with the rise of Reynolds number and to be nearly uniform for Reynolds number over 16,000. In addition, correlations for Nusselt number, friction factor and performance evaluation criteria to assess the real benefits in using the turbulator and swirl generator of the enhanced tube are determined.     

紊流器在硫酸余热锅炉上的应用

文章针对大口径管内流动时烟气在管内放热系数低的问题，研制了一种壁、芯结合的烟气紊流器，介绍了该紊流器扰流强化传热原理及其在硫酸余热锅炉改造上的应用，经过一年多的运行实践表明：应用该技术后，该余热锅炉排烟温度比原来降低50℃，不仅锅炉热回收率提高了6．53％，锅炉蒸发量提高27．2％，而且达到了转化炉对硫酸烟气进口温度的工艺要求，硫酸日产量提高4％。年增效益12万元，节能效果明显，经济效益显著。     

Study on nonpremixed methane/air combustion from flame structure and NOX emission aspect for different burner head structures

In the present study, the air turbulator, which is a part of a nonpremixed burner, is investigated numerically in terms of its effects on the diffusion methane flame structure and NO_X emissions. A computational fluid dynamics (CFD) code was used for the numerical analysis. At first, four experiments were conducted using natural gas fuel. In the experimental studies, the excess air ratio was taken constant as 1.2, while the fuel consumption rate was changed between 22 and 51 Nm³/h. After the experimental studies, the CFD studies were carried out. Pure methane was taken as fuel for the simulations. The nonpremixed combustion model with the steady laminar flamelet model (SFM) approach was used in the combustion analyses. Methane‐air extinction mechanism with 17 species and 58 reactions was used for the simulations. The results obtained from the CFD studies were confronted with the measurements of the flue gas emissions in the experimental studies. Then, a modified burner head was analysed numerically for the different air turbulator blade numbers and angles. The CFD results show that increasing the air turbulator blade number and angle causes the thermal NO emissions to be reduced in the flue gas by making the flame in the combustion chamber more uniform than the original case. This new flame structure provides better mixing of the fuel and combustion air. Thus, the diffusion flame structure in the combustion chamber takes the form of the partially premixed flame structure. The maximum reduction in the thermal NO emissions in the flue gas is achieved at 38% according to the original case.     

Fundamentally excited flow past a surface-mounted rib. Part II: Kinetic energy budget details

This paper presents the detailed turbulent kinetic energy budget and higher order statistics of flow behind a surface-mounted rib with and without superimposed acoustic excitation. Pattern recognition technique is used to determine the large-scale structure magnitude. It is observed that most of the turbulence contributions after the reattachment region are from the large-scale structures contrary to the belief that mostly random turbulent structures are present after reattachment. The dissipation is not a small-scale phenomena only. It may result due to the interaction between large-scale structures. From the results of higher order moments, the outer edge of the shear layer is observed to be non-Gaussian in nature with significant deviation from the Gaussian skewness and flatness value. The kinetic energy budget results show positive intermodal production in the outer edge of the shear layer indicating the presence of back scattering. The non-Gaussian velocity distribution, ejection motions and back-scattering present in the outer shear layer may be conjectured to be correlated with each other.     

塔式容器新型扰流减振方法研究

基于塔式容器发生横风向振动的原理,设计了适用于防止塔式容器横风向振动的声波扰流器和喷射扰流器。利用有限元分析软件ANSYS Workbench14.0 建立三维流固耦合数值模型对比分析了两种扰流器在不同扰流速度和扰流频率情况下对塔体周围边界层的干扰效果。结论是速度取一阶临界风速,频率取剪切层不稳定流的脉动频率时,两种扰流器的扰流防振效果最好;同样的扰流参数情况下,喷射扰流器的扰流防振效果比声波扰流器的好。此研究结论为塔器防振措施中扰流器的设计与工程应用提供参考和依据。     

Optimal design of transverse ribs in tubes for thermal performance enhancement

We conducted an optimization using the second-order response surface method to determine the transverse rib geometry required to achieve the highest cooling performance in a circular channel. The best rib geometry was based on three design variables; rib height, rib width, and rib pitch. The turbulent heat transfer coefficients and friction losses were first calculated and then used to determine the thermal performance. We constructed the response surfaces of the three design variables as functions of the average Nusselt number ratio, friction loss, and thermal performance. These functions led to the optimum design point at the highest heat transfer rate in the special case of an actual turbine cooling passage with a constant friction loss.     

扰流子强化换热的数值模拟分析研究

为强化换热,特别是对于热阻大、需强化的气侧换热,需采取一些特别的换热方案才能达到这样的要求。加装扰流子强化换热是一种常用的选择。对不同扰流子方案进行了数值模拟,通过对比分析,找出较理想的强化换热方案。     

Thermohydraulics of Turbulent Flow Through Heat Exchanger Tubes Fitted with Circular-rings and Twisted Tapes

The influences of circular-ring turbulators (CRT) and twisted tape (TT) swirl generators on the heat transfer enhancement, pressure drop and thermal performance factor characteristics in a round tube are reported. The circular-ring turbulators were individually employed and together with the twisted tape swirl generators in the heated section of the tube. Three different pitch ratios (l/D1.0, 1.5, and 2.0) of the CRT and three different twist ratios (y/W 3, 4, and 5) of the TT were introduced. The experiments were conducted using air as the working fluid under a uniform wall heat flux condition, for the Reynolds number between 6000 and 20000. The experimental results reveal that the heat transfer rate, friction factor and thermal performance factor of the combined CRT and TT are considerably higher than those of CRT alone. For the range examined, the increases of mean Nusselt number, friction factor and thermal performance, in the tube equipped with combined devices, respectively, are 25.8%, 82.8% and 6.3% over those in the tube with the CRT alone. The highest thermal performance factor of 1.42 is found for the combined device consisting of the CRT with l/D 1.0 and TT with y/W 3. The correlations of the Nusselt number, friction factor and thermal performance factor of the tubes with combined devices are also developed in terms of Reynolds number, Prandtl number, twist ratio and pitch ratio.