同轴旋转分层流燃烧器出口空气动力特性的可视化研究

运用CCD摄像机对一种全新的同轴旋转分层流低NOx燃烧器出口空气动力特性进行了可视化研究 ,并对采集的图像进行了一系列处理。定义了一次风扩展角和一次风转捩长度 ,并对其变化规律进行了研究 ,为同轴旋转分层流燃烧器分层机理的研究打下了基础 ,并为燃烧器运行参数的调节提供了参考依据     

同轴旋转分层流燃烧器一次风扩展角_的实验研究

运用CCD摄像机对同轴旋转分层流低NOx燃烧器出口空气动力特性进行了可视化研究,并对采集的图像和数据进行了一系列处理.对一次风扩展角α进行了定义,分析了一、二次风量比以及一、二次风叶片的位置对一次风扩展角α的影响,并对其变化规律进行了研究,为同轴旋转分层流燃烧器分层机理的研究打下了基础.     

同轴旋转射流燃烧器空气动力场的可视化研究

对同轴旋转射流燃烧器空气动力场进行了可视化实验研究。通过图象处理得到可视区边界，即一、二次风之间的界面。运用分形理论对其分形维数进行了研究，发现在不同的一、二次风旋流强度与不同的一次风率下，分形维数变化呈现一定的分布，据此确定了分层工况。     

煤粉射流火焰的典型形态及其转捩规律

利用Hencken型燃烧器研究了一次风速度、给粉浓度和二次风氧浓度等参数变化对煤粉射流火焰形态的影响规律,得到了煤粉射流火焰形态转捩图谱.实验表明,煤粉射流火焰形态主要分为煤粉群燃火焰(亮黄色,均相燃烧主导)和单颗粒稀释火焰(暗红色,异相稀释的煤颗粒燃烧主导).挥发分含量和煤粉浓度的增大均可促使稀释火焰向群燃火焰的转捩;在二次风氧浓度较高(15.3%,)时,提高一次风速度对火焰形态的影响有限,但同时降低氧浓度到10%,,则可实现群燃火焰向稀释火焰的转捩.     

四角切圆锅炉同轴燃烧系统空气动力特性的研究

对300MW四角切圆煤粉锅炉采用低NOx同轴燃烧系统时炉内流场及燃烧器区域浓度场进行了冷态模化试验研究。分析了当二次风偏置角度、二次风与一次风动压比、燃尽风比率及燃尽风布置方式变化时，对炉内气流相对切圆直径、旋转动量流率矩、湍动度、一二次风混合、燃尽风穿透力等的影响，进而分析了对锅炉工作的影响。图7表4参6     

外直流内旋流同轴射流和二次风平行射流组燃烧器流动特性的研究

某电厂410 t h燃油锅炉改烧水煤浆的改造工程中,采用了外直流内旋流同轴射流和二次风平行射流组的燃烧器结构,针对该结构的单角燃烧器流动特性进行了冷态模化试验与数值模拟研究。研究结果表明:一次风喷口与中心风喷口采用外直流内旋流同轴混合射流的形式,具有很好的调节作用,有利于水煤浆的稳定着火;二次风喷口采用上下平行射流的布置方式,除了可以补充足够的空气保证燃烧外,适当的射流速度可以防止脱火和回火现象的发生,有利于稳定燃烧。图10表1参5     

扩口结构对低NOx旋流燃烧器一、二次风混合特性的影响

针对某电厂燃用烟煤的BWB—2028/17.5-M锅炉,结合炉内整体空气分级技术,对所设计的低NO_x旋流燃烧器按1∶4缩小建立冷态单相模化试验台,采用热质比拟法研究一次风扩口长度/外二次风扩口长度对一次风、二次风混合特性的影响。分析试验数据可知:在燃尽风率为25%条件下,适当增加一次风扩口长度,延迟二次风与一次风/煤粉混合物混合,对抑制氮氧化物是有利的;为了保证燃烧器稳燃性能,一次风扩口长度不宜超过外二次风扩口长度的50%;适当缩短外二次风扩口长度,延迟二次风与一次风/煤粉混合物混合,对抑制氮氧化物是有利的,外二次风扩口长度不宜超过内二次风扩口长度的2倍。     

直流二次风率对径向浓淡旋流煤粉燃烧器空气动力特性的影响

本文阐述了径向浓淡旋流煤粉燃烧器的基本原理，通过在一台４１０ｔ／ｈ的锅炉上的冷态，热态实验，研究了直流二次风率对燃烧器空气动力特性的影响，得到了直流二次风率与射流的扩展角，中心回流区直径及长度，一，二次风混合的关系，以及对燃烧器高效，稳燃，低污染，防结渣及防高温腐蚀性能的影响。     

侧边射流横向混合扩散特性研究

本文利用气体示踪法研究燃烧器一、二次风混合扩散特性，对弱旋流（一次风）燃烧器和直流（侧边二次风）燃烧器组成的燃烧器组各股风混合情况进行了详细研究，得出各截面混合物浓度分布规律及混合强度分布规律，分析对燃烧着火的影响，对燃烧器设计参数的选择有指导意义。     

一种用于携带流反应器试验台的煤粉燃烧器的优化设计

为了优化一种用于携带流反应器系统的煤粉燃烧器结构参数,降低氮氧化物排放,本文利用计算流体动力学软件FLUENT对该煤粉燃烧器结构参数的优化过程进行了数值模拟研究,并与试验结果进行了对比验证。结果表明,燃烧器一次风喷口采用扩口结构以及对冲二次风的引入均能有效的促进二次风与一次风煤粉的混合,增强煤粉着火及燃烧的稳定性。适当增加二次风喷口与一次风喷口的间距可以加速煤粉的燃尽。采用优化后的结构参数可以获得更低的氮氧化物排放,为基于携带流反应器系统的燃煤污染物减排研究提供了坚实的基础。     

Experimental studies on heat transfer and thermal performance characteristics of thermosyphon solar water heating system with helical and Left–Right twisted tapes

Experimental investigation of heat transfer, friction factor and thermal performance of thermosyphon solar water heater system fitted with helical and Left–Right twist of twist ratio 3 has been performed and presented. The helical twisted tape induces swirl flow inside the riser tubes unidirectional over the length. But, in Left–Right system the swirl flow is bidirectional which increases the heat transfer and pressure drop when compared to the helical system. The experimental heat transfer and friction factors characteristics are validated with theoretical equations and the deviation falls with in the acceptable limits. The results show that heat transfer enhancement in twisted tape collector is higher than the plain tube collector. Compared to helical and Left–Right twisted tape system of same twist ratio 3, maximum thermal performance is obtained for Left–Right twisted tape collector with increase in solar intensity.     

Numerical Study of the Swirl Effect on a Coaxial Jet Combustor Flame Including Radiative Heat Transfer

A numerical study of the swirl effect on a coaxial jet combustor flame including radiative heat transfer is presented. In this work, the standard k-ε model is applied to investigate the turbulence effect, and the eddy dissipation model (EDM) is used to model combustion. The radiative heat transfer and the properties of gases and soot are considered using a coupled of the finite-volume method (FVM), and the narrow-band based weighted-sum-of-gray gases (WSGG-SNB) model. The results of this work are validated by experiment data. The results clearly show that radiation must be taken into account to obtain good accuracy for turbulent diffusion flame in combustor chamber. Flame is very influenced by the radiation of gases, soot, and combustor wall. However, swirl is an important controlling variable on the combustion characteristics and pollutant formation.     

中心射流对旋流燃烧器热声振动的影响

在CH4与空气的化学当量比为0.7、空气量为25 m/s时进行了旋流燃烧器热声振动试验.分析了不同中心风量下旋流燃烧的热声不稳定特性.结果表明:在中心风量为10%时,旋流核心区明显受到中心射流的影响,热声振动振幅明显下降,最大峰值脉动压力下降216 Pa;中心射流对热声振动的影响存在一个阈值,提高射流速度可使中心射流作用于旋流核心区,从而影响燃烧与声波的耦合,以实现对热声振动的被动控制.     

入流条件对同轴射流旋流燃烧室内湍流流动模拟的影响

应用一种新的代数Reynolds应力模型对同轴射流旋流燃烧室内两股射流为同向旋转和反向旋转条件下的湍流旋流流动进行了数值模拟。为得到合理的流场分布结果，研究了入流条件对同轴射流旋流燃烧室内湍流流动模拟结果的影响。计算中对旋流燃烧室进口处两股旋转射流的轴向与切向速度采用了均匀分布和实验测量分布两种方式来给定。将两种进口速度分布条件下得到的燃烧室内气体轴向与切向速度分布计算结果与实验数据进行了比较。     

燃气轮机燃烧室内NOx生成影响因素的数值研究

低NOx燃气轮机燃烧室的燃烧特性受到旋流的强烈影响，旋流特性的分析对燃烧室的设计和优化具有非常重要的作用。本文对燃气轮机燃烧室的旋流燃烧流动，应用商用程序FLUENT进行了数值模拟，并分析了旋流数、压强、湍流度对燃烧室内燃烧特性和NOx生成特性的影响。模拟结果表明，随着压强的增加，NOx排放逐渐增加，随着燃料入口湍流度的增加，NOx排放将减少，而随着旋流数的增加，NOx排放先是增加而后减小，同时，NOx随压强变化呈指数规律变化，但不同的燃烧组织形式对指数值有较大的影响。     

斯特林发动机天然气扩散燃烧的数值分析和试验

应用数值模拟,对斯特林发动机中天然气的燃烧进行了全尺寸三维模拟。分析和优化对斯特林发动机燃烧室速度场、温度场分布以及排放有着重要影响的参数,如空气预热温度、旋流数和过量空气系数等。预测了优化后燃烧室的速度场、温度场分布,以及NO_x和CO的浓度场分布,得到了吸热部件周围的流动形式。模拟结果为抑制NOx和CO的排放和提高换热效率以及发动机的效率提供了指导,设计结果得到了试验验证。     

Combustion in swirling flows: A review

Swirling flows have been commonly used for a number of years for the stabilization of high-intensity combustion processes. In general these swirling flows are poorly understood because of their compelexity. This paper describes the recent progress in understanding and using these swirling flows. The main effects of swirl are to improve flame stability as a result of the formation of toroidal recirculation zones and to reduce combustion lengths by producing high rates of entrainment of the ambient fluid and fast mixing, particularly near to the boundaries of recirculation zones. Two main types of swirl combustor can be identified as follows:The Swirl Burner. Here swirling flow exhausts into a furnace or cavity combustion occurs in and just outside the burner exit.The Cyclone Combustion Chamber. Here air is injected tangentially into a large, usually, cylindrical chamber and exhausts through a centrally located exit hole in one end. Combustion mostly occurs inside the cyclone chamber.Initially the isothermal performance of swirl combustors is considered, and it is demonstrated that, contrary to many previous assumptions, the flow is often not axisymmetric but three-dimensional time-dependent. Under most normal nonpremixed combustion conditions, the swirling flow returns to axisymmetry, although there is still a residual presence of the three-dimensionality, particularly on the boundary of the reverse flow zone. Swirl increases considerably the stability limits of most flames; in fact with certain swirl burners, the blow-off limits are virtually infinite. Cyclone combustion chambers have large internal reverse flow zones which provide very long residence times for the fuel/air mixture. They are typically used for the combustion of difficult materials such as poor quality coal or vegetable refuse. In contrast to the swirl burner which usually has one central toroidal, recirculation zone, the cyclone combustor often has up to three concentric toroidal recirculation zones. Sufficient information is also available to indicate that stratified or staged fuel or air entry may be used to minimize noise, hydrocarbon, and NO_x emissions from swirl combustors.     

Investigation on heat transfer and pressure drop during swirl flow boiling of R-134a in a horizontal tube

An experimental investigation has been carried out to study the effect of twisted tape inserts on heat transfer enhancement and pressure drop in a horizontal tube during swirl flow boiling of R-134a. The test-evaporator was an electrically heated horizontal copper tube and twisted tapes with different twist ratios of 6, 9, 12 and 15 were inserted one by one. The data were acquired at the refrigerant mass velocities of 54, 86, 114 and 136 kg/s m². The twisted tape inserts increases the boiling heat transfer coefficients and the pressure drop across the test-evaporator. An empirical correlation has also been developed to predict the swirl flow pressure drop in the test-evaporator.     

某型燃气轮机燃烧室燃烧流场数值研究

燃气轮机燃烧室的燃烧特性受到旋流强度、雾化特性等因素的强烈影响,旋流强度和雾化特性分析对燃烧室的设计和优化具有非常重要的作用。对燃气轮机燃烧室的燃烧流场,应用商用程序FLUENT进行了数值模拟,并分析了空气过量系数α和燃油雾化粒径对燃烧室内燃烧特性的影响。模拟结果表明,控制空气过量系数和燃油雾化粒径对提高燃烧室工作性能和降低污染物排放具有重要意义。