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非灰气体中辐射全交换面积的计算 总被引:5,自引:1,他引:4
将描术非灰气体辐射特性的指数宽带模型引入均匀离散射线法,推导了非灰气体参与介质条件下,辐射全交换面积的计算式,并计算了二维封闭体系的辐射全交换面积。结果表明,均匀离散射线法可用于模拟非灰气体中的辐射换热问题。 相似文献
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气体夹层作为散热或绝热机构在微传感器、微驱动器等微器件中是经常出现的。通常认为,气体夹层的导热是微结构表面间热量传递的主要方式,而表面间的热辐射可以忽略不计。本文比较了不同尺度和温度下电介质材料表面间导热和辐射换热的相对强弱,发现当辐射表面间距离只有十几个纳米的时候,辐射换热会大大强于导热。根据不同尺度和温度下导热和辐射相对强弱的不同,对微结构中电介质材料表面间热传递的主要方式进行了划分。 相似文献
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CS2在当今化工等领域占据了重要地位,而CS2火灾污染事故危害性极大。通过研究CS2燃烧火焰光谱辐射以探究其火灾污染特性极为必要。搭建了CS2燃烧火焰光谱测试平台,采用黑体辐射源对VSR仪器进行了标定,通过多用途傅里叶变换(VSR)红外光谱辐射仪测试了5,10和20 cm三种燃烧尺度下CS2燃烧的火焰光谱,并通过热电偶测试了整个燃烧时间段内不同燃烧时刻下的火焰温度,以及在火焰上方安装了烟气分析仪对火焰中的燃烧产物浓度进行监测。测量了CS2整个燃烧时间段内火焰温度,以及不同燃烧时间、不同燃烧尺度下的火焰光谱、燃烧产物组分信息。测试结果表明,CS2火焰中主要含有高温SO2,CO2,CO气体和空气中卷入的H2O分子,并获取了特征污染产物SO2的浓度。由于现有光谱仪测量分辨率有限,室内实验测量的火焰尺度有限,为了能实现火灾在线监测需要建立一个火焰光谱辐射模型来反演CS2火灾时的污染物浓度相关信息。基于HITRAN数据库可知在2.7 μm附近为高温水蒸气的发射峰,4.2 μm附近特征峰为高温CO2气体的发射峰,4.7 μm附近有CO微弱的发射峰,在7.4 μm附近特征峰为高温SO2气体的发射峰,并获得了CS2燃烧时产生的SO2,CO2,CO和H2O气体在火焰燃烧相同温度下的吸收系数,通过计算得到了CS2燃烧时产生的SO2,CO2,CO和H2O混合气体的透过率与发射率,并结合气体辐射传输方程、气体吸收系数等方程,创建了CS2燃烧的火焰光谱辐射模型。利用该光谱辐射模型反演了不同燃烧时间下特征污染产物SO2的浓度,并与实验测得的数据进行了对比分析。结果表明,该模型精度高,可用于燃烧产物浓度的定量化反演,SO2分子含量在燃烧时间20,40,60和80 s时的反演精度分别是89.5%,82.5%,85.6%和86.5%。为遥感反演CS2型大尺度火灾中燃烧产物的浓度奠定基础。 相似文献
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本文利用灰气体加权平均模型(Weighted Sum of Gray Gases Model,WSGGM)对对流扩散火焰模型(OPPDIF)中的能量方程进行修正,并对高温扩散均相燃烧结构模型(Hot Diluted Diffusion Ignition,HDDI)在常规空气和富氧环境进行对冲火焰燃烧数值模拟。结果表明,相对于标准模型,采用修正模型所得到的温度分布在常规空气和富氧气氛下均较低且温度分布特性变化较大。本文进一步明确无焰燃烧的临界条件,对高温扩散均相燃烧模型分析表明,在T_f较高且X_f较低时,甲烷燃料的化学热解区域消失,燃料在燃烧周期内只表现出热释放特性。通过建立的燃烧区域和燃烧路径分析得知,无焰富氧燃烧相比于空气无焰燃烧更容易达到但更难维持,而相对于常规有焰燃烧,无论是在常规空气气氛下还是在富氧气氛下,其化学反应速率均下降一个量级。而由于富氧环境下的CO_2富集,抑制了H和OH基团的生成,使得C1反应链更加具有活性。 相似文献
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建立了一种应用于CO_2热泵热水机的内螺旋管式气体冷却器(逆流型)的换热特性稳态仿真模型,且与实验数据吻合较好。在仿真模型基础上,分析气体冷却器内部流体温度沿管长分布情况,研究结构参数和水侧进口温度对气体冷却器换热性能的影响,研究结果表明:由于CO_2侧出口温度不会低于水侧进口温度,因此换热量受水侧进口温度限制,当气体冷却器换热面积增加到一定程度时,换热量增加幅度放缓并逐渐接近其上限值;随着水侧进口温度的增加,水侧与CO_2侧的对数平均温差和换热量降低,水侧出口温度增加幅度越来越小。 相似文献
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Junjun Guo Fan Hu Wei Luo Pengfei Li Zhaohui Liu 《Proceedings of the Combustion Institute》2019,37(3):3081-3089
By using the concept of weighted sum of four gray particles and spectrum k-distribution (WSGP-SK), a non-gray radiative property model for unburnt char particles is developed. Based on the carbon burnout kinetic model for structure during oxidation, and the linear mixed approximation theory for complex index of refraction, spectral radiative properties of unburnt char particles are first calculated as function of the burnout ratio by Mie theory. Referring to the full spectrum k-distribution model, k-distribution is applied to reorder absorption and scattering efficiencies of particles. Then, weighting factors and efficiency factors of the non-gray radiative property model are directly obtained from Gaussian integral points of k-distribution. The model is validated against the benchmark solutions of line-by-line (LBL) model. Maximum relative errors of this model are 3% and 15% for radiative heat fluxes and source terms in non-isothermal inhomogeneous particulate media, respectively. The assumption of linearly varying radiative properties with burnout ratio (Lockwood et al. 1986) will result in a predicted deviation of 53% for radiative source terms. Results also show that this non-gray model is remarkably better than the Planck mean method. Moreover, a satisfactory comparison with LBL solutions is achieved in the gas and particle mixture by combining the non-gray WSGG-SK model (Guo et al. 2015). As a radiation sub-model, this non-gray radiative property model can significantly improve prediction accuracy of radiative heat transfer in oxy-fuel combustion. 相似文献
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R. Porter F. Liu A. Williams 《Journal of Quantitative Spectroscopy & Radiative Transfer》2010,111(14):2084-2094
The exact solution to radiative heat transfer in combusting flows is not possible analytically due to the complex nature of the integro-differential radiative transfer equation (RTE). Many different approximate solution methods for the solution of the RTE in multi-dimensional problems are available. In this paper, two of the principal methods, the spherical harmonics (P1) and the discrete ordinates method (DOM) are used to calculate radiation. The radiative properties of the gases are calculated using a non-gray gas full spectrum k-distribution method and a gray method. Analysis of the effects of numerical quadrature in the DOM and its effect on computation time is performed. Results of different radiative property methods are compared with benchmark statistical narrow band (SNB) data for both cases that simulate air combustion and oxy-fuel combustion. For both cases, results of the non-gray full spectrum k-distribution method are in good agreement with the SNB data. In the case of oxy-fuel simulations with high partial pressures of carbon dioxide, use of gray method for the radiative properties may cause errors and should be avoided. 相似文献
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Mohamed Naceur Borjini Kamel Guedri 《Journal of Quantitative Spectroscopy & Radiative Transfer》2007,105(2):167-179
The radiative heat transfer problem is solved for 3D complex industrial boiler with five baffles containing a mixture of carbon dioxide and water vapor for non-uniform temperature fields. A numerical formulation using the FTn finite volume method coupled with the bounded high-order resolution CLAM scheme, the blocked-off-region procedure and the narrow-band based weighted-sum-of-gray-gases (WSGG) [Kim OJ, Song T-H. Data base of WSGGM-based spectral model for radiation properties of combustion products, JQSRT 2000; 64: 379-94] model is adapted. The effect of soot volumetric fraction, particle temperature and uniform particle concentration on the radiative heat flux and radiative heat source is investigated and discussed. Also the advantages, in non-gray media, of the FTnFVM compared to the classical FVM are highlighted. 相似文献
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P.J. Coelho 《Journal of Quantitative Spectroscopy & Radiative Transfer》2002,74(3):307-328
The discrete ordinates and the discrete transfer methods are applied to the numerical simulation of radiative heat transfer from non-gray gases in three-dimensional enclosures. Several gas radiative property models are used, namely the correlated k-distribution (CK), the spectral line-based weighted-sum-of-gray-gases (SLW) and the weighted-sum-of-gray-gases (WSGG) methods. The results are compared with recently published accurate calculations based on the statistical narrow band model. The WSGG model is computationally efficient, but often yields relatively large errors. It should be used only if moderate accuracy is sufficient. The SLW model is the best alternative regarding the compromise between accuracy and numerical efficiency. However, an optimization of the coefficients of the model is essential to reduce the computational requirements, especially in the case of gas mixtures. The CK model is the most accurate of the methods evaluated here, but too time consuming for engineering applications, although recent developments may partly overcome this shortcoming. 相似文献
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A. Maurente 《Journal of Quantitative Spectroscopy & Radiative Transfer》2008,109(10):1758-1770
This paper presents the computation of radiation heat transfer in a cylindrical enclosure in which the dimensions, the chemical species concentrations and the temperature fields make a realistic representation of an actual combustion chamber. Two gas models are applied and compared: the absorption-line blackbody distribution function (ALBDF), and the standard weighted-sum-of-gray-gases (WSGG) based on coefficients and correlations that are widely used in engineering. While the standard WSGG is restricted to the assumption of homogeneous gas mixture, the ALBDF can be applied to both homogeneous and non-homogeneous media. For the two gas models, the radiative exchanges are computed with the aid of the Monte Carlo method. The results show considerable discrepancies between the WSGG and the ALBDF models for the homogeneous medium. In addition, the importance of considering the non-homogeneity of the medium for an accurate computation of the radiative heat transfer is shown. 相似文献
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Kihwan Kim 《Journal of Quantitative Spectroscopy & Radiative Transfer》2008,109(15):2579-2589
The discrete ordinates interpolation method (DOIM) is applied to three groups of problems of radiative heat transfer in three-dimensional rectangular enclosures containing non-gray or scattering medium. The original DOIM is first extended to a gray gas model using a new geometric interpolation scheme. It is applied to participating media for different scattering phase functions and optical thicknesses. For the non-gray gas model, the DOIM coupled with the narrow band-based weighted-sum-of-gray-gases (WSGG) model is developed. A few test problems with real gases such as pure H2O and a mixture of CO2, H2O and N2 are taken. The wall heat flux is calculated and compared with the exact solutions or reference values. All results of test problems are found to be reliable in this study. The DOIM closely reproduces the Monte Carlo reference solutions for different scattering phase functions and optical thicknesses. The non-gray gas results are compared with reference calculations based on the statistical narrow band model and they also show good agreements. The DOIM shows a remarkable merit in the computation time and the grid compatibility, to prove its usefulness for engineering applications. 相似文献
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Jiawei Wan Junjun Guo Pengfei Li Zhaohui Liu 《Proceedings of the Combustion Institute》2021,38(3):4281-4290
Particle radiation has a spectral dependence and is closely related to the chemical composition of the material. Iron oxide, one of the main components of fly ash, observably affects the complex index of refraction of the particles. In this study, following the theory of the spectrum k-distribution based weighted sum of gray particles model (Guo et al. [4,13]), a non-gray fly ash radiative property model involving the chemical composition was developed. First, four typical fly ash particles with different iron oxide contents were selected, and the corresponding particle radiative parameters were obtained using the Mie theory. Then, the absorption efficiency and weighting factors of the non-gray model were directly obtained from the Gaussian integral points of the k-distribution. The scattering efficiency of the particles was obtained from the Planck mean. The accuracy of the newly developed model was evaluated in a one-dimensional plane-parallel slab system through comparison with the line-by-line (LBL) model and two commonly used gray radiative property models. The results show that the new non-gray model agrees well with the LBL solution and becomes more accurate as the iron oxide content increases. When the iron oxide content of the fly ash increased from 5.47% to 30.50%, the maximum relative error of the radiative heat flux and the radiative source term decreased from 12.50% to 5.68% and from 20.97% to 12.62%, respectively. The new model can improve the prediction accuracy of radiative heat transfer in pulverized coal-fired furnaces. 相似文献
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Man Young Kim Ju Hyeong Cho 《Journal of Quantitative Spectroscopy & Radiative Transfer》2008,109(9):1607-1621
The radiative heat transfer between two concentric spheres separated by a two-phase mixture of non-gray gas and a cloud of particles is investigated by using the combined finite-volume and discrete-ordinates method, named modified discrete-ordinates method (MDOM), which integrates the radiative transfer equation (RTE) over a control volume and a control angle simultaneously like in the finite-volume method (FVM) and treats the angular derivative terms due to spherical geometry as the conventional discrete-ordinates method (DOM). The radiative properties involving non-gray gas and particle behavior are modeled by using the extended weighted sum of gray gases model (WSGGM) with particles. Mathematical formulation and final discretization equations for the RTE are introduced by considering the behavior of a two-phase mixture of non-gray gas and particles in a spherically symmetric concentric enclosure. The present approach is validated by comparing with the results of previous works including gray and non-gray radiative heat transfer. Finally, a detailed investigation of the radiative heat transfer with non-gray gases and/or a two-phase mixture is conducted to examine the dependence of the radiative heat transfer upon temperature ratio between inner and outer spherical enclosure, particle concentration, and particle temperature. 相似文献
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Yue Zhou Ran Duan Xijuan Zhu Jie Wu Jing Ma Xia Li 《Combustion Theory and Modelling》2020,24(5):829-851
Radiative heat transfer plays an important role in the chemical reactions in the combustor. The widely used WSGG model proposed by Smith is established for normal pressure, which shows inevitable computational errors when dealing with radiative heat transfer problems at reduced or elevated pressures. In this paper, an improved global model is established to calculate the radiant energy exchanges between combustion gases and combustor chamber walls. Compared with the Smith model, the new model shows better performance in a wide range of pressure regions. The model accuracy is examined by computing the emissivity, radiative heat flux as well as the radiative source of H2O–CO2 gas mixtures at different pressure values. Finally, the radiative heat transfer inside a 3D TBCC(turbine-based combined cycle) engine exhaust system where strong gradients of pressure and temperature exist, is also addressed. The computational results show that the developed model provides approximate results at much less computational costs than the high-precision MSMGFSK-c8 model, which makes it competitive in complicated combustion systems. 相似文献