蒙特卡洛法求二维矩形散射性介质内的辐射传递

引入辐射传递因子RDij的概念，由于该因子与温度的关系较小，因此可以将蒙特卡洛法模拟与温度场的迭代求解分开来进行。建立任意几何形状条件下蒙特卡洛法求解辐射传递因子的计算模型，并对二维矩形黑体及灰体壁面条件下的纯散射灰介质内辐射传递问题进行了模拟计算。其中，黑体壁面计算结果与文献[5,6]的结果吻合较好。另外，计算了二维矩形灰体壁面、灰体吸收散射性介质内的温度场及壁面热流分布，其结果可以供比较参考。     

聚合物火焰辐射的通风影响

根据通风条件不同，受限燃烧可分为燃料控制和通风控制两种燃烧状况。通风对于受限燃烧的火焰辐射有重要影响，尤其在通风控制燃烧时。本文以火焰中热量和炭颗粒的生成规律为基础，提出了描述通风影响的聚合物燃烧火焰辐射近似模型。针对几种典型聚合物计算了其火焰辐射放热分数和火焰平均辐射温度，并讨论了通风条件、燃烧构成和燃烧尺度的影响、以及火焰辐射放热分数与燃料烟点之间的关系。进而，在改进的基础上，以ｄｅ Ｒｉｓ和     

非轴对称层流自由火焰温度场的辐射反演

将CT技术中的ART(代数重建)算法应用于火焰的反演，提出了一种基于发射-透射辐射测量的反演非对称层流自由火焰温度场的新方法。模拟算例表明：即使存在辐射量的测量误差，用ART算法反演非轴对称火焰的温度场亦可得到较为精确的结果。     

柴油机缸内火焰辐射传热新模型

柴油机缸机的火焰辐射受诸多因素的影响,用理论分析法来确定它是相当困难的,由于柴油机缸内火焰辐射特性依赖于缸内的燃烧过程,而燃烧过程中的实际热力状态又可用示功图来分析,因此借助于火焰辐射与缸内热力参数之间的这种间接关系,建立了一种计算柴油机缸内火焰辐射传热的新模型,利用该模型对一台直喷柴油机缸内火焰辐射热流量随曲轴转角的变化情况进行了计算,将计算结果与实测结果进行了比较,表明该模型能较好预测缸内火焰     

碳氢火焰辐射特性快速判定方法研究

针对比色法计算碳氢火焰温度时要判定其是否为灰体，提出了一种基于图像处理的辐射特性判定方法。该方法用黑体炉标定CCD相机，拟合得到三基色值与单色辐射强度的函数关系，再根据普朗克定律和比色法测温原理计算蜡烛火焰的温度以及三基色值下的辐射率，计算三个辐射率的均方差并进行辐射特性判定。实验结果表明，三个快门速度下，计算温度的相对误差均小于0.500%，计算辐射率的相对误差均小于5.000%，说明标定实验的有效性；以蜡烛火焰为研究对象，其辐射率的均方差均大于0.024，可判定蜡烛火焰为非灰体。     

基于火焰辐射图像的温度分布与浓度分布联合重建

讨论了基于火焰辐射图像的截面温度分布和碳粒浓度分布的重建测试方法。分析并建立了测试系统理模型和优化模型，设计了相应的求解算法，针对电站锅炉燃煤火焰进行了实际测试。计算结果与实际测试结果进行比较和分析，温度分布和浓度分布与模型重建结果比较接近，表明重建结果合理、可信。     

辐射离散传播法在三维圆柱腔体辐射传热计算中的应用

运用空间解析几何理论与数值计算相结合的方法,实现了辐射离散传播法（OTM）在三维圆柱腔体内辐射传热计算的应用。采用坐标转换建立了辐射射线方程,通过直接求解所有发射点上各立体角内的辐射射线与各辐射单元体的交点,确定射线经过的路径及各交点与发射点的距离,然后按距离远近对交点进行排序,得到适合DTM法求解辐射能量传递方程的交点顺序。运用该方法对圆柱腔体内辐射换热进行三维计算,得到与精确解基本相符的结果;将DTM法运用于煤粉燃烧火焰辐射换热的计算,得到的温度场与实验结果基本一致,表面辐射热流密度分布合理,由此表明本文设计的方法是可行的。     

水蒸汽非灰辐射光谱吸收系数

辐射显著影响燃烧的化学动力学和火焰结构.火焰燃烧辐射传输问题的计算,需要考虑气体辐射的非灰特性.辐射传输方程微分方法的近似解通常以吸收系数为基本参数.基于此,研究了总压0.1MPa,分压0.0～0.1MPa,压力行程0.01～1.0MPa·     

对称与非对称碳氢火焰温度场重建实验研究

为了测量碳氢火焰的截面温度场分布,根据火焰烟黑辐射传递特性,提出了基于火焰发射辐射能图像的温度场重建模型,使用最小二乘QR矩阵分解法（LSQR法）求解该模型。数值模拟重建了轴对称和非对称分布的两类温度场,重建结果精度较高。进而对实验室的甲烷扩散火焰截面二维温度场进行了重建,结果与已有文献相比符合较好,特别是对非对称火焰,能准确还原其温度场分布特征,实验得到了较好的结果。     

采用优化算法分析燃烧火焰辐射光谱求取火焰温度

通过对优化算法的尝试利用从气体燃烧火焰发出的辐射光谱拟合分析出火焰燃烧温度的方法,简化了传统测温用双色法所要求的火焰绝对辐射强度的标定,同时有助于了解火焰辐射黑度随波长的变化规律。通过和热电偶测量值的比较,证明经该方法得到的计算结果具有一定的精度,使燃烧火焰温度的在线监测成为可能。     

Radiative heat transfer during turbulent combustion process

We investigate the radiative heat transfer in a co-flowing turbulent nonpremixed propane-air flame inside a three-dimensional cylindrical combustion chamber. The radiation from the luminous flame, which is due to the appearance of soot particles in the flame, is studied here, through the balance equation of radiative transfer which is solved by the Discrete Ordinates Method (DOM) coupling with a Large Eddy Simulation (LES) of the flow, temperature, combustion species and soot formation. The effect of scattering is ignored as it is found that the absorption dominates the radiating medium. Assessments of the various orders of DOM are also made and we find that the results of the incident radiation predicted by the higher order approximations of the DOM are in good agreement.     

Coupled large eddy simulations of turbulent combustion and radiative heat transfer

Radiative heat transfer is known to play an important role in combustion processes but is often neglected in simulations because of its complexity and the related numerical costs. An original approach is proposed here to perform large eddy simulations of turbulent combustion including radiation: unsteady combustion and radiative heat transfer are computed by two independent codes that exchange data when needed through a specialized language, CORBA, working on an internal computer network or over the Internet. The radiation code gets temperature and mass-fraction fields from the combustion code and returns radiative energy source terms. This coupling technique is easy to implement, portable, flexible, and versatile. Each code keeps its own structure and may be developed and optimized independently, especially when running on massively parallel machines. Preliminary results show that taking radiative heat transfer into account strongly modifies the flame dynamics, probably because the burnt gas temperature decreases, making the flame stabilization weaker and increasing the flame sensitivity to turbulent motions. Comparisons with experimental data are very encouraging.     

Radiative extinction of gaseous spherical diffusion flames in microgravity

Radiative extinction of spherical diffusion flames was investigated experimentally and numerically. The experiments involved microgravity spherical diffusion flames burning ethylene and propane at 0.98 bar. Both normal (fuel flowing into oxidizer) and inverse (oxidizer flowing into fuel) flames were studied, with nitrogen supplied to either the fuel or the oxygen. Flame conditions were chosen to ensure that the flames extinguished within the 2.2 s of available test time; thus extinction occurred during unsteady flame conditions. Diagnostics included color video and thin-filament pyrometry. The computations, which simulated flow from a porous sphere into a quiescent environment, included detailed chemistry, transport, and radiation and yielded transient results. Radiative extinction was observed experimentally and simulated numerically. Extinction time, peak temperature, and radiative loss fraction were found to be independent of flow rate except at very low flow rates. Radiative heat loss was dominated by the combustion products downstream of the flame and was found to scale with flame surface area, not volume. For large transient flames the heat release rate also scaled with surface area and thus the radiative loss fraction was largely independent of flow rate. Peak temperatures at extinction onset were about 1100 K, which is significantly lower than for kinetic extinction. An important observation of this work is that while radiative heat losses can drive transient extinction, this is not only because radiative losses are increasing with time but also because the heat release rate is falling off as the flame expands away from the burner and the reactant supply to the flame decreases.     

基于实时辐射能信号的锅炉燃烧优化

基于热辐射图像处理的可视化监测技术,实时采集炉内燃烧火焰图像信息,以此计算炉膛辐射能信号。该方法获取的辐射能信号与机组发电功率具有相同的量程,其值直接反映出当前炉内能量所具备的发电能力。在此基础上分析了辐射能信号参与入炉煤量优化调整的控制策略,并在一台300 MW锅炉上进行了优化系统投运实验。结果表明,引入辐射能信号到锅炉燃烧控制回路是可行的,改善了机组协调控制的品质。     

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.     

Analysis of Radiative Transport in a 2-D Cylindrical Participating Medium Subjected to Collimated Radiation

This article deals with the numerical analysis of radiative transport in a 2-D axisymmetric cylindrical enclosure containing absorbing, emitting, and scattering medium. The participating medium receives collimated radiation from the top boundary of the enclosure. Attenuation of the collimated radiation in the medium gives rise to the diffuse radiation. Thus, the governing radiative transfer equation accounts for both collimated and diffuse radiation. The radiative transfer equation is solved using the modified discrete ordinate method. Effects of extinction coefficient, scattering albedo, and aspect ratio on radial and axial distributions of heat flux and incident radiation are studied. In all cases, results are validated against those available in the literature. Modified discrete ordinate method has been found to provide accurate results.     

Investigation of heat transfer characteristics of hydrogen combustion process in cylindrical combustors from microscale to mesoscale

In the field of micro and mesoscale combustion, the feature of flame-wall thermal coupling is of great significance because of its small scale nature. Thus, this work provides a comprehensive heat transfer analysis in cylindrical combustors from the perspective of numerical simulation. The combustor has a fixed length-to-diameter aspect ratio of 10, and the channel diameter is scaling up from 1 mm to 11 mm to explore the influence of chamber dimension on heat transfer and flame structure. The distribution of convective and radiative heat flux on inner surface, contribution of thermal radiation are given. Moreover, the role of radiation in flame structure is analyzed, and the convective and radiative heat losses are quantitatively analyzed. We find that radiative heat flux is smaller compared to convective heat flux, and the proportion of radiative heat flux becomes larger with an increasing diameter. Thermal radiation does not change the flame structure when the diameter is less than 3 mm. When the diameter is greater than 5 mm, thermal radiation changes the location of flame front. The heat loss becomes larger at a smaller diameter, and heat loss ratio can reach approximately 73.6% in the combustor with diameter of 1 mm.     

Three-Dimensional Radiative Exchange Factors for Nongray,Nondiffuse Surfaces

Abstract

A computer program using a variation of the Monte Carlo method was developed to predict radiative exchange factors in three-dimensional configurations with curved surfaces. The model allows for arbitrary emission, absorption, and reflection characteristics and for radiation exchange between surfaces as well as external irradiation through openings. It was shown that exchange factors can be determined efficiently by using the normal Monte Carlo method for closed configurations and/or high surface emissivities, while energy partitioning is vastly superior in the case of open configurations and/or low surface emissivities. Comparison with some experiments performed on the Space Shuttle heat rejection system demonstrates the model's accuracy as well as its superiority over a simplified diffuse-surface analysis, which requires similar amounts of computer time.     

Radiative heat transfer in preforms for microstructured optical fibres

Air inclusions in any preform for microstructured optical fibres can greatly reduce conductive heat transfer. Modelling the heat transfer therefore requires that radiation be properly included. In this paper we use the Rosseland approximation to consider radiative heat transfer within the matrix material and present a method of including radiative heat transfer across the air inclusions for the first time. We apply the thermal model to the transient heating process of a silica preform with a hole structure that restricts conduction. The resultant heat transfer model yields realistic heating times.     

使用放热率计算总体辐射热流量的研究

本文发展了一个预测直喷式柴油机缸内总体辐射热流量的模型。该模型利用单区放热率所得资料，配合适当的碳粒形成和氧化的子模型，以计算辐射温度，燃烧区温度，碳粒浓度，碳粒发射率和总体辐射热流量等，计算结果与已发表的实验数据吻合。