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·     

建立工业炉非灰气体辐射虚拟实验室的探讨

简要介绍了非灰气体辐射数学模型,虚拟实验室的基本原理、组成及其在各领域中的应用现状。首次提出建立非灰气体辐射虚拟实验室,阐述了建立非灰气体辐射虚拟实验室的技术思路和方法[1],预测了虚拟实验室在非灰气体辐射中的应用前景。     

高温气体辐射特性计算模型

高温气体辐射特性的准确计算在燃烧、红外探测等工程应用中有重要意义。对国内外气体辐射特性研究现状进行了介绍,分析了3类气体辐射特性计算方法的基本原理和主要特征,着重介绍了新发展起来的全光谱k分布(FSK)模型。列表归纳总结了各辐射特性计算模型的适用条件、计算精度及计算速度。计算了平行平板间水蒸气和二氧化碳混合气体层壁面热流,给出了各模型计算结果与逐线计算间的相对误差比较图。对不同情况下气体辐射特性计算方法的选择提出了建议,针对现有模型的缺陷对今后的研究方向作了展望。     

灰气体加权和模型的发展综述

气体辐射特性的准确计算对辐射换热过程的分析有重要影响。国内外学者对气体辐射特性模型中的灰气体加权和模型(WSGG)和与k分布法相关的模型进行了大量研究,本文对WSGG模型发展现状以及存在的问题进行了总结分析。针对WSGG模型具有效率高、精度低的特点,而k分布法精度高可以弥补其不足,认为可以将k分布法引入WSGG模型,建立一种快速准确且能与任意辐射传递方程求解方法兼容的气体辐射特性计算模型。     

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。     

宽带k分布模型与其他气体辐射特性计算模型精度比较

气体辐射特性计算模型的选择对于辐射热传递的计算至关重要。对采用宽带k分布模型和其它气体辐射特性计算模型计算的于两无限大平板间非等温气体辐射传递的精度进行了比较结果显示:宽带k分布模型与逐线计算结果吻合较好,比总体模型的计算精度高得多。计算结果说明:对于非等温介质,关联k假设在较大的光谱区间内相对有效,且能通过将单一气体的k分布吸收系数相加获得水蒸气和二氧化碳混合气体的k分布吸收系数的,该处理方法简单易行,宽带k分布模型很适合气体辐射换热问题的求解。     

有限体积法在电站锅炉炉膛辐射换热计算中的应用

辐射换热是大型锅炉炉膛内的主要换热形式,准确的计算炉膛内的辐射换热量对大型锅炉设计和优化有重要意义。本文将有限体积法推广用于求解和分析大型电站锅炉炉膛内的辐射换热。给出了有限体积法对辐射传递方程进行离散和求解的基本过程。评估了有限体积法求解大型电站锅炉炉膛辐射换热的可靠性。将有限体积法用于分析某电厂600MW锅炉炉膛内的辐射换热,结果表明有限体积法可以有效的求解大型电站锅炉炉膛内的复杂辐射换热过程。     

反演计算不同炉气温度下非灰气体的当量吸收系数的方法

提出了一种反演计算不同炉气温度下非灰气体的当量吸收系数的方法。此方法以实验数据反演得到的非灰气体的当量吸收系数作为物性参数,由正演算计算不同条件下的炉气温度,并以此为定解条件,反演不同炉气温度下的非灰气体的当量吸收系数,反复迭代,直至收敛。反演计算过程中采用区域法与求目标函数最小值的共轭梯度法相结合的方法。与实验结果比较表明,该方法可以较为准确地反演不同炉气温度下的非灰气体的当量吸收系数。最后,用该方法计算并比较了非灰气体的当量吸收系数随炉气温度的变化。图2表2参9     

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。     

Analysis of Gas Radiative Transfer Using Box Model and Its Comparison with Gray Band Approximation

On the basis of a wide range survey of various models or treatment methods for the calculation of radiative properties of gases, box model, which is similar to the gray band approximation of spectral band model, was applied to evaluate the gas properties in this paper. In order to compare the accuracy of box model with that of gray band approximation of spectral band models, a typical one-dimensional gas radiation problem was analyzed using discrete ordinate method. Comparing with the widely used gray band approximation of narrow band model or exponential wide band model, box model can well evaluate the radiation source term of the radiative problem. It also has the advantages of simplicity and easy to code, so it is practicable and useful for some complex engineering problems.     

Effect of gas radiation on radiative heat transfer in urban street canyon model

In this paper, we describe the results of numerical simulation of radiative heat transfer between the human body and an urban street canyon (building walls, pavement, and the sky) in the presence of participating non‐gray gas mixtures consisting of H₂O and CO₂. The ambient temperature in typical summer conditions and the concentration of gas mixtures during summer in Tokyo were assumed. Further, the parallel infinite plane model and simple urban street canyon model were used. The results show that the participating gas significantly affects the infrared radiation field in an urban street canyon. The radiation flux emitted by the participating gas is approximately 35% of the total radiation flux incident on the human body surface. This causes a homogenization of the infrared radiation field surrounding the human body. Gas radiation plays an important role in the heat transfer between the human body and the environment under hot and humid summer conditions. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20258     

On the discrete ordinates method for radiative heat transfer in anisotropically scattering media

In the discrete ordinates method (DOM), the normalized condition for the numerical quadrature of some complex scattering phase functions may not be satisfied. In this paper, a revised discrete ordinates method (RDOM) is developed to overcome this problem, in which a renormalizing factor is added into the numerical quadrature of in-scattering term. The RDOM is used to solve the radiative transfer problem in one-dimensional anisotropically scattering media with complex phase function. The radiative heat fluxes obtained by the RDOM are compared with those obtained by the conventional discrete ordinates method (CDOM) and Monte Carlo method. The results show the RDOM can overcome the false scattering resulted from the numerical quadrature of in-scattering term and improve largely the accuracy of solution of the radiative transfer equation by comparison with the CDOM.     

Numerical study of radiative heat transfer effects on a complex configuration of rack storage fire

This work describes the application and the performance of a new radiation model in CFD calculations for the simulation of thermal radiation transfer effects on a fire scenario. A 3D Cartesian coordinates radiative heat transfer procedure based on coupling of the FTn finite volume method (FTnFVM) with the bounded high-order resolution CLAM scheme is developed. The narrow-band based weighted-sum-of-gray-gases (NB-WSGG) model is applied to take account of nongray effects by CO₂, H₂O and soot. To treat irregular boundaries, the present model used the blocked-off-region procedure. This radiation code is implemented in the Fire Dynamics Simulator (FDS), a Computational-Fluid-Dynamics-based fire model, where a the combustion is represented by means of the mixture fraction with a single step chemical reaction model and the Large Eddy Simulation (LES) is used to model the dissipative processes. Computational results with and without radiation effects are compared against available experimental data and quasi-steady state law correlations of in-rack storage fire, which consists a complex configuration of double tri-wall corrugated paper cartons placed onto a wood pallet. Sensibility analyses of spatial and angular grids demonstrate the improvements due to the FTnFVM and to the CLAM scheme in the configuration studied. Results show that the simulations of the flame height, the gas temperature and the gas velocity are strongly influenced by thermal radiation. Overall, simulations predicted closer profiles to the experimental results only when the nongray-sooting radiation model was incorporated and an over-prediction of the gas temperature and the flame height is found when radiation is neglected. A sensibility analysis has shown that the flame characteristics are strongly affected by the soot yield.     

Numerical simulation of coupled radiation‐convection heat transfer of high‐temperature developing flow in tube

By combining the discrete ordinate method with the control volume method, the coupled radiation‐convection heat transfer of high‐temperature developing laminar flow in a tube is investigated numerically. The radiative transfer is solved by the discrete ordinate method and its contribution to thermal balance is dealt with as a source term in the energy equation, which is solved, as well as the momentum equation, by the control volume method. The effects of medium optical thickness and tube wall temperature on the temperature distribution in medium as well as the heat flux and local Nusselt number on wall are analyzed. The results show that the radiation heat transfer of high‐temperature medium influences the temperature distribution and convection heat transfer greatly, and plays an important role in the heat transfer of developing laminar flow in a tube. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(1): 53–63, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10135     

Parameterization of aerosols from burning biomass in the Brazil-SR radiative transfer model

A new aerosol parameterization was developed and implemented for operational use with the BRASIL-SR model. The goal is to improve the assessment of solar energy resources in Brazil. Optical properties of the aerosols from burning biomass were obtained using software package OPAC and are in good agreement with previous field measurements made in Brazil. Three different mixture ratios of black carbon were used to cover the full range of typical measured values. The atmospheric transport model SMOKE provided the aerosol profile. An evaluating period of 11 days in August/1995 and ground measurements from six sites situated in Amazon region was used to validate the results. The global solar irradiation estimates obtained with new aerosol parameterization, presented smaller mean bias error in all ground sites. The correlation among estimates and measured values for surface global solar irradiation improved about 2.5 times by adopting an aerosol composition with 5% of black carbon.     

Analysis of Conduction and Radiation Heat Transfer in a Differentially Heated 2‐D Square Enclosure

Radiative heat transfer with and without conduction in a differentially heated 2‐D square enclosure is analyzed. The enclosure with diffuse gray boundaries contains radiating and/or conducting gray homogeneous medium. Radiatively, the medium is absorbing, emitting and scattering. On the south boundary, four types of discrete heated regions, viz., the full boundary, the left one‐third, left two third and middle one third, are considered. In the absence of conduction, distributions of heat flux along the south boundary are studied for the effect of extinction coefficient. In the presence of conduction, distributions of radiation, conduction and total heat fluxes along the south boundary are analyzed for the effects of extinction coefficient, scattering albedo, conduction–radiation parameter, and south boundary emissivity. Effects of these parameters on centerline temperature distribution are also studied. To assess the performance of three commonly used radiative transfer methods, in all cases, the radiative transfer equation is solved using the discrete ordinate method (DOM), the conventional discrete ordinate method (CDOM) and the finite volume method (FVM). In the combined mode problem, with volumetric radiative information known from one of the three methods, viz., DOM, CDOM, and FVM, the energy equation is solved using the finite difference method (FDM). In all cases, the results from FDM‐DOM, FDM‐CDOM, and FDM‐FVM are in good agreement. Computationally, all three sets of methods are equally efficient.     

Characteristics of combined heat transfer of superheated steam drying: Numerical study on coupled convection and gas radiation heat transfer

A numerical study on a combined radiation and forced convection heat transfer of superheated steam, which is a radiation participating real gas, in thermally developing laminar flow through a parallel‐plate channel has been conducted to investigate characteristics of superheated steam drying. The integrodifferential energy equation was solved using an implicit finite‐difference technique with a marching solution procedure and an exponential wide‐band model for the treatment of the radiative transfer part. Comparison of results with and without gas radiation in various conditions shows that fluid radiation decreases the temperature of the main stream, but increases the total heat flux at a heat transfer surface. Furthermore, the results show that the fluid radiation decreases the inversion point temperature approximately to 150 to 240 °C with the increase of optical thickness. This numerical result agrees in an order of magnitude with the previous experimental studies, but is about 100 K lower than that of former theoretical predictions without considering fluid radiation. © 2000 Scripta Technica, Heat Trans Asian Res, 29(5): 385–399, 2000     

Radiation Characteristic Study of Flue Gas from Oxygen-enriched Combustion Using WBCK Model and Discrete Ordinate Method

针对富氧燃烧方式下由高体积分数水蒸气和CO2混合构成的烟气辐射传热难题,推导出描述非灰气体辐射特性的宽带关联k分布模型与离散坐标法相结合的计算公式.以文献中O2/CO2燃烧方式下炉内水蒸气和CO2的生成为例,采用宽带关联k分布模型计算了不同算例下混合气体的辐射强度和壁面热流量,并与统计窄谱带模型、全光谱关联k分布模型以及灰体加权和模型的计算结果进行了比较.结果表明：宽带关联k分布模型与统计窄带模型的计算结果吻合较好;与文献中的两个模型进行了对比,其计算精度有所提高,并且对混合气体的处理更加简便灵活,适用于O2/CO2燃烧方式下烟气辐射特性的计算.