生物质气双旋流燃烧器燃烧特性的研究

针对生物质气的特性,设计了一台双旋流燃烧器,采用数值模拟与实验的方法研究了不同配风比、不同过量空气系数及燃气组成对燃烧器燃烧特性的影响.燃烧室存在中心回流区,有利于卷吸更多高温烟气,形成稳定高温区,提高燃烧效率;内环空气量占总风量的70％时,中心回流区回流效果最佳,射流刚性最好;增加燃气中氢气的含量和过量空气系数,有利于燃烧反应的提前,但氢气燃烧速度和温度峰值将下降.     

锅炉二次风系统数值模拟计算研究

为了研究锅炉二次风系统内部流场的分布特性,采用ANSYA CFX数值模拟计算软件对平顶山平东热电厂某机组四角切圆燃烧锅炉的二次风系统进行计算分析,对二次风系统建立模型,进行网格划分,并在给定边界条件下进行不同工况下的数值模拟,同时提出结构优化的方法,合理分配二次风道内的风量,以提高锅炉的燃烧效率。结果表明:将总风管过渡到二次风箱的90°角换成45°角后,二次风道内的流量分配出现了沿程增大的现象,合理地分配了二次风道内的风量。     

平流式沉淀池内水流运动的数值模拟

给出了描述沉淀池内水流运动的控制方程,采用基于有限体积法求解原理的商用软件Fluent6.1求解了k-epsilon双方程模型,速度与压强解耦采用了SIMPLE算法,计算结果与已验证的其它模拟资料吻合良好。基于Fluent平台可以进行二次程序开发,如进一步加入沉降模型,而水动力学计算是进行后序工作的基础,本文指出了基于Fluent进行平流式沉淀池流速场模拟的准确可靠性。计算结果表明池内存在两处死水区:在挡板后存在一个较大的回流区,该处的旋涡逆时针旋转;另一个回流区在出水堰底板附近,该处的旋涡顺时针旋转。     

长隧道火灾烟气运动三维数值模拟

对某长隧道在50 MW释热率、不同风速条件下的火灾过程进行模拟,采用扩散燃烧模型对燃烧过程加以描述,分别利用k-ε模型和P-1模型计算湍流流动和辐射作用。计算结果表明,纵向风速较小时会形成烟气回流,对50 MW的隧道火灾,2 m/s的纵向通风能有效抑制烟气回流;纵向通风隧道内,烟气运动表现为径向扩散与纵向蔓延的结合;隧道通风风速越大,火源下游烟气起伏运动越剧烈。隧道发生火灾时,纵向风速应以刚好抑制烟气出现回流为宜。     

典型风向下平屋盖低矮结构的流场研究

文章针对干扰效应下的屋面风压系数和屋面荷载,分别进行了3风向下孤立平屋盖低矮结构的风洞试验和CFD模拟。风洞试验在北京交通大学回流式风洞完成,CFD模拟基于软件Fluent17.0,使用大涡模拟(Large Eddy Simulation,LES)的Smagorinsky压格子切应力模型。对比两种方法得出的速度剖面、屋面各分区压力系数、各中线压力值、升力系数、阻力系数以及各向力矩系数,验证了CFD模拟的可靠性,对3风向下孤立平屋盖低矮结构的绕流模式进行解释。     

上进风燃气灶烟气分析

选取两台单眼上进风嵌入式燃气灶为试验样机,分别测试燃烧15 min、20 min、25min、30 min和35 min时的烟气数据。结果表明,上进风燃气灶烟气排放性能与燃烧器结构有密切关系。为了使上进风燃气灶燃烧充分,降低干烟气中一氧化碳和氮氧化物的体积分数,可以改变燃烧器结构来增加一次空气量,适当提高锅支架高度或改变燃烧方式来增加二次空气量。     

夹层结构：万和燃气灶N—B06X

为保证在半封闭燃烧室内有足够的氧气,这款燃气灶采用完全上进风夹层结构设计。这种上进风夹层结构不仅有利于在燃烧时形成涡流式负压,令新鲜空气在负压力作用下补充充足,保证燃烧充分,还可预热燃烧所需的二次空气,最大限度地回收散失的热量,减少再次加热消耗的热量。     

大功率家用燃气灶的数值模拟

采用数值模拟的方法,对燃气灶不同功率、不同一次空气系数的燃烧状况进行了模拟研究。揭示了大功率、高一次空气系数在现有燃气灶火孔形式下的燃烧情况。模拟结果表明,相同一次空气系数下,燃烧功率增大会增大锅架处的烟气流速波动范围和烟气高温区域范围;而相同功率下,不同一次空气系数对燃烧火焰形态影响较大,进而影响同一高度处的温度分布。为大功率高一次空气系数的家用燃气灶的设计及优化提供了参考依据。     

数值模拟在高耸结构设计分析中的应用

以沿海地区某输电塔结构为原型,采用数值模拟的方法对结构在风荷载作用下的极限承载力进行了分析,结果表明:台风多发地区的输电塔设计必须考虑台风高湍流引起的动力风荷载增大效应,并指出数值模拟是高耸结构设计分析中经济有效的方法。     

冷却塔回流影响数值分析及优化研究

从建筑外观、空间限制、运行噪音等角度考虑,冷却塔一般被布置在隐蔽的区域。冷却塔的布置决定了热湿空气回流的情况,并直接影响冷却塔的运行性能。横流冷却塔侧面进风,逆流是塔身下部四周进风。冷却塔回流导致进风温湿度增高,同时,恶化周边微环境。采用数值模拟方法研究逆流与横流冷却塔布置方式的回流及影响。通过对比2种塔进风口空气的温升,来判断两种塔的回流量情况,并提出可行的措施来减少回流量。模拟表明逆流的进风温升和回流率都低于横流的,是因为逆流布置使进风气流更均匀,且排风风速大。模拟了横流冷却塔出风圆管口加15°向上百叶、加2.2 m进风百叶的优化措施,该措施可有效减少回流量。研究结果可为工程设计提供参考,以降低由于冷却塔设计不当引起不利的回流影响。     

Air flow behavior and gas dispersion in the recirculation ventilation system of a twin-tunnel construction

Forced ventilation and recirculation systems are usually used in the construction of long twin tunnels as they offer large amounts of fresh air economically. However, because of the confluence near the cross-aisle, the fluid behavior and gas concentration are very different than in traditional forced ventilation for a single tunnel. A three-dimensional numerical model was built to study the air flow behavior and hazardous gas dispersion near the cross-aisle of a twin-tunnel construction. Field measurements were also carried out to validate the numerical model. The results show that there is a “dead zone” ahead of the cross-aisle which has a much lower air velocity than in other parts of the twin tunnels and where hazardous gases are more concentrated and uniformly distributed. In the cross-aisle and confluence zone of the air flow-out tunnel, methane tends to gather at the top and hydrogen sulfide tends to gather at the bottom. Increasing the recirculation velocity does not eliminate the “dead zone” near the cross-aisle although it consumes a huge amount of energy. Increasing the air velocity of the duct is an effective method to improve the air quality, but it is also expensive, especially when the air duct is long. When a jet fan was placed ahead of the cross-aisle in this study, the “dead zone” was eliminated completely. With respect to the recirculation ventilation system of twin tunnels, local jet fans offer an effective and economical way to eliminate the “dead zone”.     

Optimisation of structured grid spacing parameters for separated flow simulation using mathematical optimisation

This paper describes the use of computational fluid dynamics (CFD) and mathematical optimisation techniques to minimise the error in predicting the recirculation zone for a separated flow topology. Grid spacing parameters are varied in the optimisation process. The accuracy of separated flow solutions is known to be dependent on the grid resolution and clustering. Although general guidelines have been developed for grid generation of separated flow topologies, the flow solutions using the resulting grids often under-predict features like recirculation zones. This study addresses this aspect by providing an automatic tool for optimising the grid for solution accuracy. This approach has until recently been too expensive, but is becoming more viable with ever-increasing computer power. A two-dimensional sinusoidal hill is used as an example of a separated flow topology. The CFD simulation employs the commercial CFD solver STAR-CD to solve the Reynolds-Averaged Navier–Stokes equations with the RNG k– turbulence model. CFD solution time is drastically reduced by making use of initial field restarts. The optimisation is carried out by means of Snyman's DYNAMIC-Q method, which is specifically designed to handle constrained problems where the objective or constraint functions are expensive to evaluate. Six design variables (grid spacing parameters) are considered in this study. The results indicate that the re-attachment point of the recirculation zone is predicted to within 1% of the specified experimental value in four optimisation iterations and therefore represents a cost-effective way to determine grids based on solution accuracy.     

秸秆燃气增氧燃烧特性的数值模拟

采用ANSYS Fluent软件对秸秆燃气增氧燃烧特性进行二维数值模拟,对燃烧室进行模型设计以及模型假设,运用网格生成软件ANSYS ICEM对燃烧室进行网格划分,结合实际工况以及理论计算值,设置较合理的边界条件,利用Fluent软件对燃烧模型进行仿真求解。针对4种不同入口氧气体积分数(21%,24%,27%,30%)工况下秸秆燃气燃烧室内的温度分布、速度分布及各烟气组分体积分数和污染物NOx生成情况,得出以下结论。增氧燃烧通过提高入口氧气体积分数,减少了加热助燃空气中氮气所需的热量,提升燃烧温度,促进燃烧完全。此燃烧室最适合入口氧气体积分数等于30%的秸秆燃气增氧燃烧。增氧燃烧中,随着入口氧气体积分数的提高,燃烧室最高当地速度和出口平均速度均增加。增氧燃烧中,随着入口氧气体积分数的增加,生成的烟气中H2O、CO2的体积分数均提高,N2的体积分数降低,在入口氧气体积分数为30%时,H2O和CO2这两种辐射能力较强的气体体积分数达到23.7%,增强了燃烧过程的辐射换热。增氧燃烧中,温度对于污染物NOx的影响较大。在燃烧室的局部高温区,NOx质量分数较高,说明热力型NOx占据污染物NOx的大部分,温度的上升导致NOx生成量明显增大。入口体积分数大于等于27%时,NOx排放体积分数明显高于相关标准限定值,所以在追求增氧高温燃烧的同时,要注意烟气的降硝处理,从而满足氮氧化物低排放标准的要求。     

机械化装出轮窑

本文论述了机械化装出轮窑在焙烧过程中预热带、焙烧带、冷却带的变化情况以及焙烧方法和码窑形式.机械化装出轮窑是在一般轮窑基础上发展起来的一种新型轮窑,它能够实现装出窑的机械化操作,改善工人的劳动环境,减轻工人的劳动强度,减少人为因素对烧成过程的影响,使轮窑的许多优良性能得到充分发挥.     

石灰窑结构及性能的优化设计措施

以亿利2×520TPD环形套筒窑工程为例,简要介绍了现代化新技术石灰窑发展历程及该工程概况;叙述了新型石灰窑的主体结构及其煅烧原理、原料筛分运输体系、上料体系、该窑的煅烧体系、出灰体系、空气、废气及燃气体系等重点体系中的技术运用和石灰窑出灰系统问题及改进;总结了该石灰窑的一些工艺特点及仍然存在的一些现有技术不能解决的问题,以期为工程的顺利运行提供帮助,为我国石灰生产业的发展贡献一点微薄的力量。     

Large eddy simulation of thermal stratification effect on convective and turbulent diffusion fluxes concerning gaseous pollutant dispersion around a high-rise model building

In this paper, the large eddy simulation (LES) approach is employed to investigate the role of different thermal stratification conditions (stable, neutral and unstable) in the air flow and gaseous pollutant dispersion processes around a high-rise non-isolated model building with 1:1:2 shape placed within a non-isothermal boundary layer. The simulation results are initially validated with available experimental measurements and then applied to study the characteristics of pollutant dispersion. Predictions show a low-velocity zone behind the model building. The major effect of a stable stratification on flow field is the formation of a weak recirculation flow in the wake region. Results represent an intense temperature gradient close to the sides of the model building for both stable and unstable conditions. Moreover, the convective and turbulent diffusion fluxes are compared under different thermal stratification conditions, and it is shown that the LES approach is capable of predicting the counter-gradient mechanism.     

燃烧区负压对大气式燃烧器调节特性的影响

对大气式燃烧器,当燃烧器头部燃烧区产生负压时,其自动调节特性会受到影响。分析了燃烧器引射能力与燃烧区负压的关系,结合典型案例,量化分析了燃烧区负压对燃烧器一次空气系数的影响。大气式燃烧器引射的一次空气量对燃烧区负压非常敏感,负压会增大一次空气系数。     

可燃液体自由表面燃烧特性的数值模拟

依据小尺度汽油燃烧实验模拟法确定边界条件,采用数值模拟方法进行汽油池火燃烧模拟。数值模拟结果和实验结果具有一致性:用非稳态数值模拟的火焰热辐射随燃烧的进行逐步增加;热辐射分布以火焰的高温区分布较强;火焰中各组分如氧气消耗量、C(s)等质量浓度与燃烧时间的无量纲关系曲线与燃烧过程的温度分布一致,且遵循双曲线变化规律。采用稳态模拟方法得到不同风速条件下火焰倾角与风速之间的变化曲线,有风时火焰温度较无风时增加,且随着风速的增加而增加(实际上存在某个临界风速);有风时火焰热辐射分布随火焰的倾斜而改变,下风向热辐射明显,上风向则较低,且热辐射波及范围较无风时增大。     

Numerical study on effects of air leakages from abandoned galleries on hill-side coal fires

In this paper, our main aims are to present a numerical model for hill-side coal fires and to analyze influences of air leakages from abandoned galleries on hill-side coal fires. A two-dimensional unsteady-state model for hill-side coal fires is developed. The coupling between chemical reactions in the coal seam and oxygen transport through adjacent rocks is involved. Heterogeneous permeability of different porous zones induced by rock mechanical failure is considered. Based on the single-particle reaction–diffusion model, a novel approach is proposed to estimate oxygen consumption rate controlled by oxygen transport at high temperature.Simulation results show that hill-side coal fires are remarkably intensified and accelerated by air leakage from the abandoned gallery: (1) the hottest spot is approximately 500 K higher than that for the case of no air leakage from the abandoned gallery; (2) temperature rise is much speedier than that in the case of no air leakage; (3) coal in the combustion zone starts to spontaneously combust approximately 50 days earlier compared to the sealed abandoned gallery; (4) high temperature zones including drying zone, baked zone and melting zone are larger than those in the condition of no air leakage from the abandoned gallery.     

CFD and experimental studies of room fire growth on wall lining materials

CFD simulation and experimental tests have been carried out to study the room corner fire growth on combustible wall-lining materials. In the CFD simulation, the turbulent mass and heat transfer, and combustion were considered. The discrete transfer (DT) method was employed to calculate the radiation with an absorptivity and emissivity model employed to predict the radiation property of combustion products including soot, CO₂ and H₂O, which are usually the primary radiating species in the combustion of hydrocarbon fuels. The temperature of the solid boundary was determined by numerical solution of the heat conduction equation. A simple and practical pyrolysis model was developed to describe the response of the solid fuel. This pyrolysis model was first tested against the Cone Calorimeter data for both charring and non-charring materials under different irradiance levels and then coupled to CFD calculations. Both full and one-third scale room corner fire growths on particle board were modelled with CFD. The calculation was tested with various numbers of rays and grid sizes, showing that the present choice gives practically grid- and ray number-independent predictions. The heat release rate, wall surface temperature, char depth, gas temperature and radiation flux are compared with experimental measurements. The results are reasonable and the comparison between prediction and experiment is fairly good and promising.