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在O_2/CO_2气氛下,参与性介质的非灰气体辐射特性表现出不同于空气气氛下的特性,因此,非灰气体辐射模型的选择和应用在换热过程中将变得十分重要.基于统计窄谱带模型,本文综合评估近年发展应用较广的灰气体加权和(WSGG)模型.结果表明,几种WSGG模型的预测值总体趋势正确,但仍存在着一定的差别.对于发射率,Dorigon等(2013 Int.J.Heat Mass Transfer 64 863)和Bordbar等(2014 Combust.Flame 161 2435)的WSGG模型与基准模型符合较好,相对误差小于20%.与离散坐标法结合,本文求解了PH_2O/PCO_2=1,2时的一维平行平板间辐射换热问题.结果显示,由Dorigon等和Bordbar等的WSGG模型得到的辐射热源和热流密度分布的相对误差均较小(10%左右).Johansson等(2011 Combust.Flame 158893)和Bordbar等的WSGG模型具有更广的适用范围. 相似文献
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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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在气粒两相流动问题中,颗粒间以及气体与颗粒间的传热问题不可忽略.光滑离散颗粒流体动力学(SDPH)模型作为一种新的求解气粒两相流动问题的方法,已经成功应用于模拟风沙运动等问题.在此基础上,提出了SDPH方法的热传导模型,模拟了气粒两相流动问题中的热传导过程以及颗粒蒸发过程.首先引入各相的能量方程,利用有限差分与光滑粒子流体动力学一阶导数相结合的方法,处理各相内部热传导项中的二阶导数问题,基于气粒两相间温度差及对流换热系数计算颗粒与气体间的热传导量,推导得到了含热传导模型的气粒两相流SDPH计算方程组,模拟计算了圆盘形颗粒团算例及鼓泡流化床内部热传导算例,并与双流体模型计算结果进行对比,结果基本符合;其次利用离散液滴模型中的颗粒蒸发传质传热定律计算颗粒的蒸发过程,数值模拟了颗粒射流蒸发过程,并与离散颗粒模型结果进行对比,两者符合得较好,验证了该方法的准确性及实用性. 相似文献
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具有漫反射边界一维灰性平行平板介质中辐射传递方程的求解 总被引:3,自引:0,他引:3
本文提出一种基于蒙特卡洛法(Monte Carlo Method, MCM)的新方法在具有漫反射边界一维灰性平行平板介质中求解辐射传递方程(Radiative Transfer Equation,RTE)。该方法能以较高的方向分辨率精确地计算任意点的辐射强度而不需要辐射能量平衡。验证结果显示了该方法的有效性和正确性。并且这种方法具有的一些特点,例如不同辐射源对辐射强度分布贡献的可加性和自动满足边界条件等,使得用该方法更容易处理复杂的辐射换热并行计算问题和复杂的边界条件问题。 相似文献
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Much progress has been made in radiative heat transfer modeling with respect to treatment of nongray radiation from both gas-phase species and soot particles, while radiation modeling in turbulent flame simulations is still in its infancy. Aiming at reducing this gap, this paper introduces state-of-the-art models of gas-phase and soot radiation to turbulent flame simulations. The full-spectrum k-distribution method (Modest, M.F., 2003, Journal of Quantitative Spectroscopy & Radiative Transfer, 76, 69–83) is implemented into a three-dimensional unstructured CFD code for nongray radiation modeling. The mixture full-spectrum k-distributions including nongray absorbing soot particles are constructed from a narrow-band k-distribution database created for individual gas-phase species, and an efficient scheme is employed for their construction in CFD simulations. A detailed reaction mechanism including NO x and soot kinetics is used to predict flame structure, and a detailed soot model using a method of moments is employed to determine soot particle size distributions. A spherical-harmonic P1 approximation is invoked to solve the radiative transfer equation. An oxygen-enriched, turbulent, nonpremixed jet flame is simulated, which features large concentrations of gas-phase radiating species and soot particles. Nongray soot modeling is shown to be of greater importance than nongray gas modeling in sooty flame simulations, with gray soot models producing large errors. The nongray treatment of soot strongly influences flame temperatures in the upstream and the flame-tip region and is essential for accurate predictions of NO. The nongray treatment of gases, however, weakly influences upstream flame temperatures and, therefore, has only a small effect on NO predictions. The effect of nongray soot radiation on flame temperature is also substantial in downstream regions where the soot concentration is small. Limitations of the P1 approximation are discussed for the jet flame configuration; the P1 approximation yields large errors in the spatial distribution of the computed radiative heat flux for highly anisotropic radiation fields such as those in flames with localized, near-opaque soot regions. 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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Shigenao Maruyama Atsushi Sakurai 《Journal of Quantitative Spectroscopy & Radiative Transfer》2008,109(1):1-15
Simplifications of the model for nongray radiative heat transfer analysis in participating media comprised of polydisperse water droplets are presented. Databases of the radiative properties for a water droplet over a wide range of wavelengths and diameters are constructed using rigorous Mie theory. The accuracy of the radiative properties obtained from the database interpolation is validated by comparing them with those obtained from the Mie calculations. The radiative properties of polydisperse water droplets are compared with those of monodisperse water droplets with equivalent mean diameters. Nongray radiative heat transfer in the anisotropic scattering fog layer, including direct and diffuse solar irradiations and infrared sky flux, is analyzed using REM2. The radiative heat fluxes within the fog layer containing polydisperse water droplets are compared with those in the layer containing monodisperse water droplets. Through numerical simulation of the radiative heat transfer, polydisperse water droplets can be approximated by using the Sauter diameter, a technique that can be useful in several research fields, such as engineering and atmospheric science. Although this approximation is valid in the case of pure radiative transfer problems, the Sauter diameter is reconfirmed to be the appropriate diameter for approximating problems in radiative heat transfer, although volume-length mean diameter shows better accordance in some cases. The CPU time for nongray radiative heat transfer analysis with a fog model is evaluated. It is proved that the CPU time is decreased by using the databases and the approximation method for polydisperse particulate media. 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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Michael F. Modest Robert J. Riazzi 《Journal of Quantitative Spectroscopy & Radiative Transfer》2005,90(2):169-189
Full-spectrum k-distributions provide great accuracy combined with outstanding numerical efficiency for the evaluation of radiative transfer in absorbing-emitting molecular gases, but they do have several shortcomings: (1) It is difficult to assemble k-distributions for gas mixtures from precalculated full-spectrum k-distributions of individual gas species (i.e., without calculating the mixture k-distribution directly from the HITRAN/HITEMP database), (2) it is impossible to assemble k-distributions for a gas mixed with nongray absorbing particles (such as soot) from gas-only full-spectrum k-distributions, and (3) like all global models, full-spectrum k-distributions cannot accommodate nongray scattering behavior and/or nongray wall reflectances. In the present paper we show how these restrictions can be relaxed by (1) assembling full-spectrum k-distributions for a gas mixture from a narrow-band k-distribution database created for individual gas species, (2) by assembling gas and nongray absorbing particle mixture full-spectrum k-distributions from the same narrow-band database, and finally (3) by showing how a group of part-spectrum k-distributions can be generated from the same database to accommodate nongray scattering and nongray walls. 相似文献
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Arthur T. Mattick 《Journal of Quantitative Spectroscopy & Radiative Transfer》1980,24(4):323-334
Coupled radiative and convective heat transfer is investigated for an absorbing gas flowing in a finite length channel and heated by blackbody radiation directed along the flow axis. The problem is formulated in one dimension and numerical solutions are obtained for the temperature profile of the gas and for the radiation escaping the channel entrance, assuming both gray and nongray absorption spectra. Due to radiation trapping, the flowing gas is found to have substantially smaller radiation losses for a given peak gas temperature than a solid surface that is radiatively heated to this temperature. A greenhouse effect is also evident whereby radiation losses are minimized for a gas having stronger absorption at long wavelengths. 相似文献
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A.L. Crosbie H.K. Khalil 《Journal of Quantitative Spectroscopy & Radiative Transfer》1973,13(4):359-367
The problem of radiative transfer in a nongray, absorbing-emitting spherical layer is investigated. The absorption coefficient is assumed to be only a function of frequency, i.e. kv = α(v)k, and the function α(v) is allowed only two values, zero or unity (simplified rectangular model). The nongray radiative transfer problem is reduced to a gray solution without the use of any approximation (such asthe Plank or Rosseland means) for an isothermal layer and for radiative equilibr 相似文献
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Hong-Liang Yi Hao-Chun Zhang He-Ping Tan 《Journal of Quantitative Spectroscopy & Radiative Transfer》2009,110(18):1978-1992
A hybrid ray-tracing method is developed for the solution to the radiative transfer in a plane-parallel participating medium having one specular surface and another diffuse surface. By this method, radiative transfer coefficients (RTCs) for specular–diffuse (S–D) surfaces are deduced. The medium surfaces are considered to be semitransparent. The effects of convection–radiation parameter, conduction–radiation parameter and refractive index on transient coupled heat transfer are investigated. Results show that the temperature curves of the medium having S–D surfaces is higher than those of the medium having S–S surfaces (two specular surfaces); the total heat flux at steady state for the S–D surfaces is lower than that for the S–S surfaces. 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