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Heat Transfer: Volume 4 — Combustion and Energy Systems最新文献

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Consideration of the Scattering Effects in the Glass As a Participating Medium Using the Discrete Ordinates Method 用离散坐标法考虑玻璃作为参与介质的散射效应
Pub Date : 2001-11-11 DOI: 10.1115/imece2001/htd-24267
S. C. Rodicio, B. R. Torres
Three-dimensional radiative heat exchange in a commercial type of glass as a participating medium is predicted using the discrete ordinates method. The radiative transfer equation (RTE) is analyzed for an absorbing, re-emitting, and scattering medium enclosed by gray walls. The main objective of this work is to formulate the RTE in a three-dimensional enclosure represented by a rectangular glass furnace where scattering effects are considered in the prediction of the radiant intensity, temperature distribution, incident and emitted energy, and heat flux at the glass surface. A comparative study is performed for glass under scattering and non-scattering conditions. The influence of scattering effects in the radiant intensity will provide further understanding of their impact in the glass thermal behavior. Additionally, the results of a parametric study on the glass for different scattering coefficients, surface heat flux, wall emissivity, and the forward scattering are discussed. The S4 approximation of the discrete ordinates method is employed in this model.
用离散坐标法预测了作为参与介质的商品玻璃的三维辐射热交换。分析了被灰壁包围的吸收、再发射和散射介质的辐射传递方程。本工作的主要目的是在以矩形玻璃炉为代表的三维环境中建立RTE,并考虑散射效应来预测玻璃表面的辐射强度、温度分布、入射和发射能量以及热流密度。对玻璃在散射和非散射条件下进行了比较研究。散射效应对辐射强度的影响将有助于进一步了解它们对玻璃热行为的影响。此外,还讨论了不同散射系数、表面热流密度、壁发射率和前向散射对玻璃的参数化研究结果。该模型采用离散坐标法的S4近似。
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引用次数: 0
Modeling Large-Size Boilers As a Set of Heat Exchangers: Tips and Tricks 大型锅炉作为一组热交换器的建模:技巧和技巧
Pub Date : 2001-11-11 DOI: 10.1115/imece2001/htd-24231
C. Cortés, L. I. Díez, A. Campo
Practical calculation of the heat-recovery sections of large-size boilers is still based on approximate methods. On the one hand, CFD-based models cannot directly handle the geometric intricacy of tube bundles, and thus rely on volume-averaged source terms that demand empirical input. On the other hand, the standard, lumped heat exchanger calculation, which can be a far simpler and more robust alternative, fails in several important aspects, mainly related to the effects of thermal radiation and the coupling between several sections. In this paper, we consider the diverse sections of a coal-fired utility boiler as a case study to show how to deal with these shortcomings. Under the objective of developing a simple monitoring method, we extend the traditional heat exchanger model to take into account most of the peculiarities of boiler superheaters, reheaters and economizers. Techniques range from the re-examination of analytical solutions to the auxiliary use of CFD calculations. The models are assembled to simulate the thermal performance of the boiler as a whole unit. Results are validated against actual measurements taken at a thermoelectric plant.
大型锅炉热回收段的实际计算仍采用近似方法。一方面,基于cfd的模型不能直接处理管束的几何复杂性,因此依赖于需要经验输入的体积平均源项。另一方面,标准的集总换热器计算可能是一个更简单和更可靠的选择,但在几个重要方面失败,主要与热辐射的影响和几个部分之间的耦合有关。在本文中,我们以燃煤公用事业锅炉的不同部分为例来说明如何处理这些缺点。为了开发一种简单的监测方法,我们对传统的换热器模型进行了扩展,以考虑锅炉过热器、再热器和省煤器的大部分特性。技术范围从分析解的重新检验到CFD计算的辅助使用。将这些模型组合起来模拟锅炉作为一个整体的热性能。结果与热电厂的实际测量结果进行了验证。
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引用次数: 2
Heat Flux From Process Burners 过程燃烧器的热流
Pub Date : 2001-11-11 DOI: 10.1115/imece2001/htd-24254
R. Hayes, Prem Singh, C. Baukal, D. Foote
This paper shows the effects of firing rate, excess air, and fuel composition on the heat flux profile from process burners as measured in large pilot-scale test furnaces. Firing rate and excess air had a significant effect on the heat flux profiles while the fuel gas blends studied here had a negligible impact.
本文展示了在大型中试炉中测量的燃烧速度、多余空气和燃料成分对过程燃烧器热流密度分布的影响。燃烧速率和过量空气对热流分布有显著影响,而本文研究的燃气混合物的影响可以忽略不计。
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引用次数: 0
Thermal and Fluid Dynamic Structures of a Laboratory-Scale Fixed-Frame Fire-Whirl 实验室规模固定框架火涡的热流体动力结构
Pub Date : 2001-11-11 DOI: 10.1115/imece2001/htd-24246
Mohamed I. Hassan, A. Helali, Kozo Saito
Fire whirl is one of the most destructive phenomena in mass fires. To study thermal and fluid dynamic structures of a fire whirl in a laboratory, a fire whirl generator consisting of two vertically oriented split-cylinders were placed in an asymmetric position to form a compartment leaving two open slits in each end. A 5-cm diameter liquid pool fire was placed at the center of the compartment floor, the fire generated buoyancy flow moved upwardly, and fresh air entered to the compartment creating swirl motion. The visible flame height of the generated fire whirl was measured by a video camera, 2-D azimuthal velocity profiles at several different heights by particle image velocimetry (PIV), and the average heat flux input to the fuel surface by a Gardon gauge type heat flux meter.
火旋风是群体性火灾中最具破坏性的现象之一。为了研究实验室火旋风的热流体动力学结构,将两个垂直方向的裂柱组成的火旋风发生器置于非对称位置,形成一个隔室,两端各有两个开缝。在舱室地板中央放置直径为5cm的液体池火,火产生浮力流向上移动,新鲜空气进入舱室产生旋流运动。用摄像机测量了火焰旋涡的可见火焰高度,用粒子图像测速仪(PIV)测量了不同高度下的二维方位速度曲线,用加顿式热流计测量了输入到燃料表面的平均热流密度。
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引用次数: 1
Optimizing the Performance of a Fuel Induced Flue Gas Recirculation (FIR) System for Low Nox Boiler Burner Applications 低氮氧化物锅炉燃烧器燃料诱导烟气再循环(FIR)系统的性能优化
Pub Date : 2001-11-11 DOI: 10.1115/imece2001/htd-24228
Michael A. Lorra, Joseph D. Smith, W. Bussman, T. L. Webster
New burner design technologies are using the momentum of fuel gas injection to entrain flue gas for the purpose of diluting the combustible mixture in order to reduce NOX emissions. Using an eductor, these designs entrain flue gas from above the convection section of a furnace stack and mix with the fuel downstream of the eductor. This diluted fluegas/fuel mixture results in lower local adiabatic flame temperatures providing a reduction in NOX emissions. Test results show that NOX reduction performance is strongly dependent on the mass ratio of flue-gas to fuel. An entrainment mass ratio of flue-gas/fuel typically ranges between 2 to 3 pound flue-gas per pound fuel, leading to a NOX reduction of approximately 50 to 70 % for boiler burner applications. The flue gas entrainment performance is effected by pressure drop through the upstream and downstream FIR piping system. This paper describes optimization of an existing FIR system not meeting initial design performance. To improve the entrainment ratio several tools were used to re-design and optimize the FIR system. These tools included Computational Fluid Dynamics (CFD), semi-empirical modeling and cold flow test results. A detailed description and discussion of the results are presented.
新的燃烧器设计技术是利用燃料气体喷射的动量夹带烟气,以稀释可燃混合物,以减少氮氧化物的排放。利用导烟器,这些设计从炉堆的对流部分上方夹带烟气,并与导烟器下游的燃料混合。这种稀释的烟气/燃料混合物导致较低的局部绝热火焰温度,从而减少氮氧化物排放。试验结果表明,烟气与燃料的质量比对NOX减排性能的影响很大。烟气/燃料的夹带质量比通常在每磅燃料2至3磅烟气之间,导致锅炉燃烧器应用的氮氧化物减少约50%至70%。通过上游和下游FIR管道系统的压降影响烟气夹带性能。本文描述了现有FIR系统不满足初始设计性能的优化。为了提高夹带比,采用了多种工具对FIR系统进行了重新设计和优化。这些工具包括计算流体动力学(CFD)、半经验建模和冷流测试结果。对结果进行了详细的描述和讨论。
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引用次数: 1
Numerical Simulation of Methane-Air Nozzle Burners for Aluminum Remelt Furnaces 铝熔炼炉甲烷-空气喷嘴燃烧器的数值模拟
Pub Date : 2001-11-11 DOI: 10.1115/imece2001/htd-24234
A. Mukhopadhyay, I. Puri, Serguei Zelepouga, D. Rue
A turbulent nozzle-mix burner, suitable for industrial use in aluminum remelt furnaces has been numerically simulated using FLUENT software. The burner has been modeled as a vertical axisymmetric arrangement of fuel duct at the center, surrounded by a coaxial annular duct of air. The ducts discharge into a confined environment, formed by a chimney, placed coaxially with the ducts. The effects of fuel velocity and air coflow velocity ratio on the flame height have been investigated. The flame height is found to increase with increase in fuel velocity for a given air-fuel velocity ratio and with decrease in air velocity for a given fuel velocity. The different flame height definitions found in literature give nearly identical flame heights for all the cases studied.
采用FLUENT软件对一种适用于工业铝熔炼炉的湍流喷嘴混合燃烧器进行了数值模拟。燃烧器被模拟成一个垂直轴对称布置的燃料管道在中心,被一个同轴的环形空气管道包围。管道排放到一个封闭的环境中,由烟囱形成,与管道同轴放置。研究了燃料速度和空气共流速度比对火焰高度的影响。对于给定的空气-燃料速度比,火焰高度随着燃料速度的增加而增加,对于给定的燃料速度,火焰高度随着空气速度的减少而增加。在文献中发现的不同火焰高度定义给出了几乎相同的火焰高度的所有研究案例。
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引用次数: 2
The P3 Micro Power Generation System P3微型发电系统
Pub Date : 2001-11-11 DOI: 10.1115/imece2001/htd-24283
C. Richards, D. Bahr, C.-G. Xu, R. Richards
Work toward the development of a new MEMS power generation system, the P3 micro heat engine, is presented. The P3 micro heat engine is an external combustion engine, in which thermal power is converted to mechanical power through the use of a novel thermodynamic cycle that approaches the ideal vapor Carnot cycle. Mechanical power is converted into electrical power through the use of a thin-film piezoelectric membrane generator. A numerical model of the engine, SIMP3, is introduced. The model is used, first to illustrate the micro heat engine’s operation, and then to explore the optimization of the engine. The major parameters controlling the performance of the P3 micro engine are discussed.
介绍了一种新型MEMS发电系统P3微热机的研制工作。P3微型热机是一种外燃机,利用一种接近理想蒸汽卡诺循环的新型热力循环将热能转化为机械能。利用压电薄膜发电机将机械能转化为电能。介绍了发动机的数值模型SIMP3。利用该模型,首先对微热机的运行进行了说明,然后对微热机的优化进行了探讨。讨论了控制P3微型发动机性能的主要参数。
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引用次数: 3
High-Temperature Electron Emission From Diamond Films 金刚石薄膜的高温电子发射
Pub Date : 2001-11-11 DOI: 10.1116/1.1537231
S. Shin, T. Fisher, D. G. Walker, A. Strauss, W. Kang, J. Davidson
This work examines the electron field emission characteristics of polycrystalline diamond films at high temperatures. Diamond is an excellent material as a field emitter because its high mechanical hardness and chemical inertness enable robust reliability. Diamond is also a wide-band gap semiconductor, increasing the probability for selective emission of higher-energy electrons. In recent years, considerable interest has developed in energy conversion applications of polycrystalline diamond films. However, little work has been considered for the field emission characteristics of diamond at elevated temperatures. The motivation behind this study involves direct energy conversion applications in power generation systems, where high temperatures exist. N-doped polycrystalline diamond films were grown by plasma-enhanced chemical-vapor deposition (PECVD). To investigate the effect of increased temperatures on field emission, current-voltage measurements were taken from the same diamond film at varying temperatures. Results from these measurements indicate a decrease in the turn-on voltage with increasing temperature. Further analysis of the temperature dependency of diamond was achieved through the parameter estimation of the effective emitting area, field enhancement factor, and work function. These results suggest that high-energy electrons are responsible for improved emission at high temperature. The resulting possibilities for direct energy conversion via diamond field emission are considered and discussed.
本文研究了多晶金刚石薄膜在高温下的电子场发射特性。金刚石具有较高的机械硬度和化学惰性,是一种优良的磁场发射材料。金刚石也是一种宽带隙半导体,增加了选择性发射高能电子的可能性。近年来,人们对多晶金刚石薄膜的能量转换应用产生了极大的兴趣。然而,对金刚石在高温下的场发射特性的研究却很少。这项研究背后的动机涉及在高温存在的发电系统中的直接能量转换应用。采用等离子体增强化学气相沉积(PECVD)法制备了n掺杂多晶金刚石薄膜。为了研究温度升高对场发射的影响,在不同温度下对同一金刚石薄膜进行了电流-电压测量。这些测量结果表明,导通电压随着温度的升高而降低。通过对有效发射面积、场增强因子和功函数的参数估计,进一步分析了金刚石的温度依赖性。这些结果表明,高能电子是提高高温辐射的原因。考虑并讨论了通过金刚石场发射直接转换能量的可能性。
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引用次数: 21
Effects of Initial Diameter on Burning of Nonane Droplets in a Non-Buoyant and Buoyant Ambience: Burning Rate, Soot Formation and Flame Structure 初始直径对非浮力和浮力环境下壬烷液滴燃烧的影响:燃烧速率、烟灰形成和火焰结构
Pub Date : 2001-11-11 DOI: 10.1115/imece2001/htd-24237
J. Bae, C. Avedisian
The results from nonane droplet combustion experiments conducted at 1g and μg are analyzed and compared in the following aspects: the burning rate, soot formation, flame structure. By varying the initial droplet diameter, we observe and discuss the effect of Do on droplet burning. The μg experiments were performed in a drop tower and a drag shield was used to create a low buoyant environment All experiments were fiber-supported and used the same experimental instruments. The droplet size between 0.40 to 0.95mm was examined in the experiments. Results showed that droplet burning is nonlinear in both a buoyant and a non-buoyant environment for the initial droplet diameters examined. Soot formation, which is influenced by Do may strongly affect the droplet burning process in both environments. The large droplet produces more soot and bums slowly whereas the small droplet bums fast because there is less soot.
对壬烷液滴在1g和μg下的燃烧实验结果进行了分析和比较:燃烧速度、烟尘形成、火焰结构。通过改变液滴初始直径,观察并讨论了Do对液滴燃烧的影响。所有实验均采用纤维支撑,并使用相同的实验仪器。实验考察了0.40 ~ 0.95mm之间的液滴尺寸。结果表明,无论在浮力环境下还是在非浮力环境下,液滴燃烧都是非线性的。在这两种环境下,受Do影响的烟尘形成可能强烈影响液滴燃烧过程。大液滴产生更多的烟灰,燃烧得慢,而小液滴燃烧得快,因为烟灰少。
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引用次数: 0
A Review of Micro Heat Exchanger Flow Physics, Fabrication Methods and Applications 微热交换器流动物理、制造方法及应用综述
Pub Date : 2001-11-11 DOI: 10.1115/imece2001/htd-24280
W. Bowman, D. Maynes
A review of the literature in the area of micro heat exchangers is presented to provide a concise overview of the recent advances in this field of study. The review is divided into six sections. The first section reviews research focused on understanding friction and heat transfer in microchannels. The second section deals with heat exchanger design, optimization and comparison studies. The third section deals with fabrication methods used for constructing micro heat exchangers. The fourth section reviews applications of micro heat exchangers. The last two sections of the paper deal with miscellaneous topics and other reviews on the subject. The total review focuses on advances made after the early 1990’s.
对微热交换器领域的文献进行了综述,简要介绍了这一研究领域的最新进展。这篇综述分为六个部分。第一部分回顾了对微通道中摩擦和热传递的研究。第二部分是换热器的设计、优化和比较研究。第三部分讨论了用于构造微型热交换器的制造方法。第四部分综述了微型换热器的应用。论文的最后两部分涉及杂项主题和对该主题的其他评论。总审查的重点是1990年代初以后取得的进展。
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引用次数: 16
期刊
Heat Transfer: Volume 4 — Combustion and Energy Systems
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