气体介质的非灰辐射计算研究

为得到更加精确的碳氢燃烧火焰的辐射计算结果,采用将基于HITEMP光谱数据库而建立的光谱模型——FSK模型与可准确计算高方向分辨率辐射强度的DRESOR法相耦合的方式,对一维平板系统内的CO2和H2O的混合气体介质的辐射情况在不同工况下展开计算,得到辐射强度及辐射热流分布,并与其他方法进行分析比较,从而检验该方法的精确性及适用性。     

炉内辐射换热过程的有限体积法

简要分析了含吸收散射性介质的三维空腔内辐射传递方程的有限体积法求解过程,应用该方法对四角切圆炉膛内的辐射换热过程进行模拟计算,得出了炉膛内温度分布,并将计算结果与实测值进行了比较。通过数值计算表明：有限体积法计算速度快,对不规则边界适应性强,具有很高的工程可用性。     

各向异性散射介质的辐射传热分析

利用Ｍｏｎｔｅ－ＣａｒｌｏＺｏｎｅ相结合的数值计算方法（简称ＭＣＺ方法）分析各向同性和各向异性散射介质的辐射换热。为了便于对照,本文选取了一维平板系统,利用编程序对各向同性散射吸收介质和线性相函数各向异性纯散射介质的半球透射率和半球反射率以及线性相函数各向异性散射吸收介质的平板中辐射传热分别进行了计算,获得了较好的结论。     

粒子辐射换热计算中散射相函数处理方法的探讨

对粒子散射相函数的各种处理方法进行了总结归纳,并以黑体平行大平壁均匀粒子介质层的辐射换热问题为研究对象,在辐射平衡条件下,对比研究了采用Mie散射理论和线性散射相函数近似处理粒子散射相函数时介质内的辐射热流及温度分布情况。辐射传递方程采用离散坐标法求解,并在求解过程中对散射相函数进行了重新归一化处理。研究表明,Mie散射相函数计算过程复杂费时,均匀粒子的Mie散射相函数随散射角强烈波动,这使辐射传递方程的求解更加困难;线性散射相函数近似简单易行,当所选线性系数基本符合Mie散射相函数前向或后向散射特征时,采用线性相函数近似可以大大简化计算,并可正确估算粒子介质内的辐射热流与温度分布情况,是一种较好的处理散射相函数的方法。     

降维后的离散传递法及其在煤粉火焰传热中的应用

针对具有二维特征的辐射传热问题，介绍了一种降维方法。用经过降维处理的离散传递法（DTM）对含有吸收、发射性介质的圆管形腔体和煤粉火焰的辐射传热进行数值计算，并与按三维辐射计算的结果和试验数据进行比较，结合符合很好。这表明：用降维后的离散传递法描述煤粉火焰的辐射传热过程是可行和精确的。     

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。     

大容量超临界和超超临界压力锅炉炉膛传热公式

分析了以两个平行平面辐射换热公式作为蒸汽锅炉炉内火焰对四周水冷壁进行辐射传热计算方法仍是基本公式,推导出一维(横截面的径向)的辐射能在从炉膛中心向四周壁面传递时因火焰介质的吸收、自身辐射和散射作用造成的辐射强度的减弱,并在此基础上得出考虑了辐射能沿截面方向从炉膛中心向四周壁面减弱后的炉内辐射传热公式.以该公式和现有某些计算方法,对超临界和超超临界的大型煤粉电站锅炉在燃用含灰量不同的3种典型烟煤时分别进行了炉膛出口烟温的计算,和有关方法进行了比较,分析了这些方法存在的不足.     

用改进的离散坐标法计算炉内三维辐射传热

采用离散坐标法进行炉内三维辐射传热的计算,首先在正方体炉膛内验证了该法的精确性,计算结果与区域法进行比较,表明离散坐标法算法可靠,计算工作量小,适合于炉内辐射传热的计算。然后针对长方体炉膛计算了吸收－发射－散射介质的传热问题,表明传统的离散坐标法不适合计算具有复杂相函数曲线的辐射传热问题,因此采用改进的离散坐标法,并得到了合理的结果。最后,对于煤粉燃烧炉膛将辐射传热问题和炉内流动、燃烧过程耦合起来进行计算,表明离散坐标法是一种很有工程应用价值的炉内辐射传热计算方法。     

含吸收散射粒子半透明介质层的容积吸收特性分析

将Ｍｉｅ散射理论与蒙特卡罗法相结合分析了含吸收散射粒子半透明介质层的容积吸收特性。考虑了半透明入射表面的折射与反射,不透明壁面的漫反射,半透明介质的吸收以及粒子系的吸收和独立多次非规则各向异性散射。直接由粒子复折射率,粒径及入射辐射波长等基本参数,根据Ｍｉｅ散射理论确定粒子系的吸收,散射因子以及非规则的各向异性散射分布。计算分析了介质层光学厚度、粒子复折射率、尺度参数、粒子系特征参数以及锥形入射时     

燃烧产物辐射特性的误差对炉内辐射传热计算精度的影响

本文用离散坐标法对含吸收散射性介质矩形空腔内的３维辐射传递过程进行了模拟，并编写了相应的数值计算程序。利用该程序分析了介质的吸收系数、散射系数、相函数、光谱特性及壁面灰渣沉积层黑度的不确定性对矩形燃烧室内烟气温度及热流计算精度的影响。结果表明计算精度很大程度上取决于燃烧产物辐射特性的取值精度，特别是壁面灰渣沉积层黑度的取值精度。在煤粉燃烧室中，介质的散射不宜忽略。     

Solution of radiative transfer in a one‐dimensional anisotropic scattering media with different boundary conditions using the DRESOR method

The DRESOR method was applied to analyze the radiative transfer process in anisotropic scattering media with different boundary conditions in this paper. The method was validated by the integral formulation of the radiative transfer equation at first. Some variation regulations about the emissivity were obtained by extensive numerical simulations. When the optical thickness of the media became very large, the emissivity converged to a constant value. The converged emissivity in the forward scattering medium was the largest and that for the backward scattering medium was the smallest. Also the converged emissivity was associated with the scattering albedo of the media. The greater the scattering albedo was, the smaller the converged emissivity was. When the scattering albedo decreased to zero the converged emissivity reached the blackbody emissivity at the same temperature. Furthermore, different boundary conditions were considered. The results showed that if the temperature of the medium and the boundary was equal, the intensity at boundary was the same as that for the blackbody emission at the same temperature, whether the boundary reflectivity was 1.0 or not. When the temperature of the boundary was lower than that of the medium, the boundary emissivity can reach 1.0 only if ρ=1.0. Finally, the radiation flux was studied with different phase functions and different boundary conditions. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(3): 138–152, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20198     

The Combined Radiative Integral Equations and Finite-Element Method for Radiation in Anisotropic Scattering Media

A combined procedure of the radiative integral equation and finite-element method (IEFEM) is proposed for handling radiative heat transfer in linearly anisotropic scattering media. The IEFEM can eliminate the angular discretization and easily handle irregular geometries. The present work provides a solution of radiative transfer in rectangular and irregular quadrilateral enclosures containing participating media. The influences of emissivities, albedos, and anisotropy on the boundary fluxes or incident intensity have been analyzed. Compared with the results in published references, the present IEFEM has no limitation to geometry and can predict the radiative heat transfer in linearly anisotropic scattering media accurately.     

The effect of a nonlinear scattering gray medium on the radiative intensity by integral moment method

The integral moment method is proposed to solve radiative intensity in nonlinear scattering gray medium. In this paper, this proposed method was to deal with the anisotropic scattering, emitting and absorbing media with different optical depths, orders and boundary conditions. This method was validated by the data from literature. The radiative intensities with high directional resolution at any point can be given by the present method. It is found that the scattering phase function has little effect on the radiative intensity for thin optical thickness, for example, 0.1. It is also found that there is a largest radiative intensity for the nonlinear scattering gray medium with the largest forward scattering capability, and the smallest one with the largest backward scattering capability at the top and bottom boundary.     

Second-order-accurate discrete ordinates solutions of transient radiative transfer in a scattering slab with variable refractive index

The discrete ordinates method (DOM) with a second-order upwind interpolation scheme is applied to solve transient radiative transfer in a graded index slab suddenly exposed to a diffuse strong irradiation at one of its boundaries. The planar medium is absorbing and anisotropically scattering. From the comparison of the results obtained by the first-order DOM, the second-order DOM, the modified DOM and the Monte Carlo method, it can be seen that the numerical diffusion in the transient solutions obtained by the second-order DOM is less than that in the solutions obtained by the first-order DOM, but the numerical diffusion is still noticeable, especially for optically thin and moderate cases. By contrast, for optically thick cases the numerical diffusion due to the finite difference of the advection term of the transient radiative transfer equation is minor. In general, it is still necessary to adopt a DOM with a higher order scheme to capture the wave front of transient radiative transfer accurately. Besides, the influence of numerical diffusion is a little less noticeable for the case with a larger gradient of refractive index, and the distribution of direction-integrated intensity around the irradiation boundary decreases and that around the other boundary increases with the increase of the anisotropically scattering coefficient.     

Scaling anisotropic scattering in radiative transfer in three-dimensional nonhomogeneous media

Radiative heat transfer in three-dimensional nonhomogeneous participating medium was investigated by using REM² method. The anisotropic scattering phase function was dealt with the scaling technique based on delta function approximation. The three-dimensional scaled isotropic results were compared with the published anisotropic scattering computations. A good agreement between the scaled isotropic approaches and the anisotropic solutions was found. The effects of scattering albedo, forward fraction of phase function, and wall emissivity were discussed. It was found that, with the increase of the scattering albedo, the radiative heat flux increases for forward scattering media, but decreases for backward scattering media. The radiative heat flux is increased with the increases of forward fraction of phase function and wall emissivity. The emissive power at the center of a cubical nonhomogeneous medium in radiative equilibrium with gray diffuse walls equals to the averaged blackbody emissive power of the six walls.     

Conduction and radiation in a rectangular isotropic scattering medium with black surfaces by the RTNAM

The ray tracing-node analyzing method (RTNAM) has been successfully developed to solve 1-D coupled heat transfer in isotropic and anisotropic scattering media in the past, and in this paper it is further extended to solving the 2-D coupled heat transfer in a rectangular isotropic scattering medium. Using the control-volume method, the partial transient energy equation is discretized in implicit scheme. The effect of radiation on heat transfer is considered as a radiative source term (RST) in the discretized energy equation, and in combination with spectral band model, the RST is calculated using the radiative transfer coefficients (RTCs), which are deduced by the ray tracing method. The Patankar’s linearization method is used to linearize the RST and the opaque boundary condition, and the linearized equations are solved by the ADI method. Before solving the RTCs for isotropic scattering media, the RTCs without considering scattering must be solved at first. And then, the RTCs without considering scattering are normalized according to their integrality relationships. In addition, the correctness of the results obtained by the RTNAM is validated, and effects of scattering albedo and refractive index on transient temperature distribution are investigated.     

SLA (Second-law analysis) of transient radiative transfer processes

This paper concerns a SLA (second-law analysis) of transient radiative heat transfer in an absorbing, emitting and scattering medium. Based on Planck’s definition of radiative entropy, transient radiative entropy transfer equation and local radiative entropy generation in semitransparent media with uniform refractive index are derived. Transient radiative exergy transfer equation and local radiative exergy destruction are also derived based on Candau’s definition of radiative exergy. The analytical results are consistent with the Gouy–Stodola theorem of classical thermodynamics. As an application concerning transient radiative transfer, exergy destruction of diffuse pulse radiation in a semitransparent slab is studied. The transient radiative transfer equation is solved using the discontinuous finite element based discrete ordinates equation. Transient radiative exergy destruction is calculated by a post-processing procedure.     

Inverse Radiation Problem of Boundary Incident Radiation Heat Flux in Semitransparent Planar Slab with Semitransparent Boundaries

INTRODUCTI0NInverseradiati0nproblemshavedefinedasubjectofinterestf0rthepast3Oyears0nsoandthereex-istsac0nsiderablebody0fknowledgesurroundingthesubjectthathasbeenextensivelyreviewedinaseries0fpapersbyM.C.rmick[1-4].Theyarecon-cernedwiththedeterminati0noftheradiativepr0p-ertiesandthetemperaturedistributionsofmediaus-ingvari0ustypesofradiationmeasurements.Despitetherelativelylargeinterestexpressedininverseradia-tionproblems,mostoftheworkfocusedontheinverseestimati0noftemperaturedistributions…     

Chebyshev collocation spectral method for one-dimensional radiative heat transfer in graded index media

Chebyshev spectral collocation method based on discrete ordinates equation is developed to solve radiative transfer problems in a one-dimensional absorbing, emitting and scattering semitransparent slab with spatially variable refractive index. For radiative transfer equation, the angular domain is discretized by discrete ordinates method, and the spatial domain is discretized by Chebyshev collocation spectral method. Due to the exponential convergence of spectral methods, a very high accuracy can be obtained even using few nodes for present problems. Numerical results by the Chebyshev collocation spectral-discrete ordinates method (SP-DOM) are compared with those available data in references. Effects of refractive index gradient on radiative intensity are studied for space dependent scattering media. The results show that SP-DOM has a good accuracy and efficiency for solving radiative heat transfer problems in even spatially varying absorbing, emitting, scattering, and graded index media.