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The development of hydrogen gas turbine is one of the most important ways to achieve energy conversion, but hydrogen fuel affects the combustion temperature and gas composition, which in turn affects the radiative heat transfer of the combustor. In this paper, two global gas models, the weighted sum of grey gas radiation (WSGG) model and the Planck-mean based on the line-by-line (LBL-PM) method, were used to investigate the effect of different gas models on the heat radiation transfer in the combustion chamber of a DLN hydrogen heavy-duty gas turbine. And the Realizable k − ε model, transported probability density function (PDF) combustion model, and Discrete Ordinates (DO) radiation model were used to establish the whole three-dimensional compressible combustion flow radiative heat transfer process. The results show that in the low temperature and low gas concentration region of the combustor, there is a great difference between the radiative heat flux values calculated by the two gas models, while in the latter half of the combustor and near the wall of the combustor where the high temperature and high concentration region, the relative error between the two models remains within 20%. The relative error fluctuation range of radiant heat flux calculated by the two models is related to the fluctuation degree of temperature and gas concentration. The results also showed that the LBL-PM model is more sensitive to changes in temperature and gas composition than the WSGG model. The enhancement of the radiative heat flux by temperature in hydrogen gas turbine is greater than its suppression by the gas absorption coefficient, and the high temperature and high concentration regions, where the large radiative heat flux may be influenced by both the high temperature and the large H 2 O content with weaker absorption properties. • The gas radiation characteristics of hydrogen heavy duty gas turbine was considered. • Differences of WSGG and LBL-PM models are influenced by the degree of temperature and gas concentration fluctuations. • The relative errors of the WSGG and LBL-PM models in high temperature and concentration region are kept within about 20%. • LBL-PM model is more sensitive to changes in temperature and gas concentration compared to WSGG model. [ABSTRACT FROM AUTHOR]

• Gray gas model severely underpredicts (65 %) the maximum soot volume fraction at the centerline of the flame. • Increasing the spectral resolution of the RC-SLW model from 5 to 16 gases reduces the error in the maximum soot volume fraction from 30 % to 1 %. • Including the effects of C2H2 and C2H4 in the RC-SLW model has a minor effect on the maximum soot volume fraction prediction by about 5 %. • With decreasing soot particle diameter that forms agglomerate, maximum soot volume fraction value in the domain increases and maximum difference comes from this behavior is about 6 %. • In addition to the change in maximum soot volume fraction, soot particle sizes affect distribution of the soot volume fraction. The position of maximum soot volume fraction point moves slightly closer to inlet with increasing soot particle size. Effect of radiation transfer is significant part of the overall heat transfer mechanism in sooting flames. The interaction between radiation transfer and soot formation considerably affects the combustion regime and the system efficiency. Spectral radiation models that account for the radiative effects of sooting flames need to be explored in detail to understand this phenomenon. This study numerically investigates the interaction between the radiation and soot formation in a sooting jet diffusion flame. In this regard, a rank correlated spectral line-based weighted sum of gray gases (RC-SLW) global model is implemented in Ansys Fluent and used for the radiation modeling of a jet diffusion flame and results were compared with the domain-based single gray gas weighted sum of gray gases (WSGG) model in Ansys Fluent RC-SLW model, including ethylene and acetylene flame radiation, showing considerable improvement in predicting the soot volume fraction compared to the domain-based single gray gas weighted sum of gray gases (WSGG) model available in Ansys Fluent. Increasing the number of gray gas bins in the RC-SLW model from 5 to 22 reduces the error in the maximum soot volume fraction from 30 % to 1 %. It was found that the effect of ethylene and acetylene radiation in the RC-SLW model has a minor effect on soot formation. Simulations without the effect of ethylene and acetylene radiation in the RC-SLW model underpredict the maximum soot volume fraction by 5 %. In addition, the effect of different possibilities of agglomeration of soot particles on the generated soot volume fraction was also investigated. Results showed that change of absorption coefficient due to change of soot agglomeration size affects maximum soot volume fraction by 6 %. [ABSTRACT FROM AUTHOR]

In radiation process, a variety of models can be used to represent the spectral radiative properties of combustion gases. In coal combustion, the high level of soot concentration brings higher complexity to the formulation. Several pieces of research are found, comparing different radiation models usually applied to idealized laboratory situations. Only a few works explore the behavior of such models in real scale applications, such as coal-fired furnaces. Comparisons among different arrangements of the SGG and WSGG models were carried out by means of CFD simulations, applied to a boiler of a real 160 MW coal-fired power plant. Five different cases were simulated. The most simple case was set with a fixed absorption coefficient SGG model, while the most detailed case was achieved by employing a WSGG model with gas and soot absorption coefficients overlay. Temperature fields were well represented by all cases, with maximum deviations of 6%. Predictions on radiative heat flux for the SGG models were significantly lower than the WSGG simulations, with relative deviations up to 16.46%. Even though deviations on radiative heat flux are significant, results suggest the suitability of simple gray gas models in fast assessments of industrial applications such as coal-fired furnaces.

The weighted-sum-of-gray-gas(WSGG)model and Mie theory are applied to study the influents of particle size on the radiative transfer in high temperature homogeneous gas-particle mixtures, such as the flame in aero-engine combustor. The radiative transfer equation is solved by the finite volume method. The particle size is assumed to obey uniform distribution and logarithmic normal(L-N)distribution, respectively. Results reveal that when particle size obeys uniform distribution, increasing particle size with total particle volume fraction fv unchanged will result in the decreasing of the absolute value of radiative heat transfer properties, and the effect of ignoring particle scattering will also be weakened. Opposite conclusions can be obtained when total particle number concentration N0 is unchanged. Moreover, if particle size obeys L-N distribution, increasing the narrowness index σ or decreasing the characteristic diameter D with the total particle volume fraction fv unchanged will increase the absolute value of radiative heat transfer properties. With total particle number concentration N0 unchanged, opposite conclusions for radiative heat source and incident radiation terms can be obtained except for radiative heat flux term. As a whole, the effects of particle size on the radiative heat transfer in the high-temperature homogeneous gas-particle mixtures are complicated, and the particle scattering cannot be ignoring just according to the particle size. [ABSTRACT FROM AUTHOR]

Highlights • An improved WSGG model suitable for the exhaust gases of aero engines is proposed. • The effects of temperature and pressure are included in the improved model. • Comparison between the improved model and existing models is conducted. Abstract Advanced aero engines operate at high temperatures and pressures to improve thermal efficiency and power output, thus thermal radiation becomes a significant mode of heat transfer for exhaust gases. The existing gaseous radiative models for atmosphere are not suitable for the application in aero engines due to the huge pressure variation of exhaust gases. In this work, an improved weighted sum of gray gases (WSGG) model for mixtures of H 2 O and CO 2 within broader ranges of temperature and pressure variations is proposed. The mole ratio of H 2 O and CO 2 is fixed at 1/1, which represents typical products of stoichiometric combustion of kerosene. The weighting factors, which only relate to the temperature in previous WSGG models, are modified by taking into account the effects of both temperatures and pressures. The coefficients of the improved WSGG model are obtained based on the up-to-date HITEMP-2010 database, and they are valid for the temperatures varying from 500 K to 2500 K, pressures ranging from 1 atm to 30 atm, and pressure path-lengths ranging from 0.0001 atm·m to10 atm·m. To access the accuracy of the coefficients, the improved WSGG model and other two traditional WSGG models are applied to the solution of the radiative heat transfer with the discrete ordinate method, and the comparison is conducted with the benchmark line-by-line calculations. The results indicate that the improved WSGG model has much higher accuracy in the simulation of gaseous radiative heat transfer for exhaust gases of aero engines. [ABSTRACT FROM AUTHOR]

Highlights • WSGG coefficients were generated for H 2 O/CO 2 mixtures at pressures from 1 to 40 atm. • Results from WSGG were accurate when compared to the LBL method for all pressures. • Interpolation is shown to be a good alternative to deal with intermediate pressures. • The effect of pressure is significant but diminishes with increasing pressure. • The WSGG model presented better accuracy for non-homogeneous media. Abstract This study presents weighted-sum-of-gray-gases (WSGG) model coefficients for mixtures of H 2 O and CO 2 with fixed mole ratio of 2/1 for high total pressure conditions. The mole ratio represents typical products of stoichiometric combustion of methane in air, which has received significant attention for high pressure applications. The coefficients are based on HITEMP2010 database, and are valid for path-lengths ranging from 0.01 to 30 m, temperatures varying from 400 to 2500 K, and total pressures of 1.0, 2.0, 5.0, 10, 20, and 40 atm. As a first validation of the WSGG model, a comparison with benchmark line-by-line (LBL) total emittance is presented, showing accurate results. Total emittance is shown to have significant pressure dependence, which emphasizes the importance of generating WSGG coefficients fitted to high pressure emittance values. To better assess the model accuracy, calculations for radiative heat flux and volumetric source are performed for two one-dimensional test cases, considering nonisothermal, homogeneous and non-homogeneous conditions. Results show acceptable deviations from the LBL solution for the homogeneous case, with even lower deviations for the non-homogeneous case, as long as the ratio between the species is fixed at 2/1. The effect of pressure is also significant on both radiative heat flux and volumetric source, while its behavior shows that interpolation is a good alternative to obtain WSGG solutions for intermediate pressures. [ABSTRACT FROM AUTHOR]

Oxy-fuel coal combustion is a promising Carbon Capture and Storage technology that allows retro-fitting of existing power plants. Due to high concentrations of CO 2 and H 2 O and the strong and irregular spectral variation of their absorption coefficients, prediction of radiative heat transfer in oxy-fuel combustion systems requires a non-grey gas radiation model. Several models, including narrow-band correlated-k (NBCK), wide-band correlated-k (WBCK), full-spectrum correlated-k (FSCK), and weighted-sum-of-grey-gases (WSGG) models, were used to predict radiative heat transfer by CO 2 and H 2 O in a three-dimensional real-size virtual coal-fired furnace under air- and oxy-fuel (dry and wet flue-gas recycle) conditions. The best agreement with the benchmark solution calculated by the NBCK model with the updated EM2C parameters is achieved by the FSCK model. The WBCK model is less accurate. The WSGG parameter sets of Kangwanpongpan et al. (2012) and Bordbar et al. (2014) are most suited for oxy-fuel combustion among the six sets considered. The FSCK model offers the best performance in terms of both accuracy and computational efficiency among the considered gas radiation models and is recommended for CFD simulations of real-sized oxy-coal systems. [ABSTRACT FROM AUTHOR]

The oxy-fuel combustion is a promising CO 2 capture technology from combustion systems. This process is characterized by much higher CO 2 concentrations in the combustion system compared to that of the conventional air-fuel combustion. To accurately predict the enhanced thermal radiation in oxy-fuel combustion, it is essential to take into account the non-gray nature of gas radiation. In this study, radiation heat transfer in a 3D model gas turbine combustor under two test cases at 20 atm total pressure was calculated by various non-gray gas radiation models, including the statistical narrow-band (SNB) model, the statistical narrow-band correlated-k (SNBCK) model, the wide-band correlated-k (WBCK) model, the full spectrum correlated-k (FSCK) model, and several weighted sum of gray gases (WSGG) models. Calculations of SNB, SNBCK, and FSCK were conducted using the updated EM2C SNB model parameters. Results of the SNB model are considered as the benchmark solution to evaluate the accuracy of the other models considered. Results of SNBCK and FSCK are in good agreement with the benchmark solution. The WBCK model is less accurate than SNBCK or FSCK. Considering the three formulations of the WBCK model, the multiple gases formulation is the best choice regarding the accuracy and computational cost. The WSGG model with the parameters of Bordbar et al. (2014) [20] is the most accurate of the three investigated WSGG models. Use of the gray WSSG formulation leads to significant deviations from the benchmark data and should not be applied to predict radiation heat transfer in oxy-fuel combustion systems. A best practice to incorporate the state-of-the-art gas radiation models for high accuracy of radiation heat transfer calculations at minimal increase in computational cost in CFD simulation of oxy-fuel combustion systems for pressure path lengths up to about 10 bar m is suggested. [ABSTRACT FROM AUTHOR]

A numerical study of a laminar methane partial oxidation flame (POX-flame) is presented to investigate different radiation modeling approaches. A laminar reference flame for large-scale gasification, which was previously investigated both experimentally and numerically by Stelzner et al. [1], is particularly suitable for such a study because of the distinct temperatures and radiating species concentrations. A second study of a well-known methane–air flame [2] is also included. The fully resolved and coupled solution of the reactive flows was achieved with an OpenFOAM ® based solver using detailed approaches for diffusion and chemistry. Different combinations for solving the radiative transfer equation (RTE) and the evaluation of the radiative properties were implemented and investigated. The discrete ordinate method (DOM), the modified differential approximation (MDA), the P1 model and the optically thin model (OTM) were used for the solution of the RTE, whereas the spectral line-based weighted sum of gray gases model (SLW), the weighted sum of gray gases model (WSGG) and gray absorption (RADCAL) was used for the evaluation of the radiative properties. In both flame setups gaseous radiation was found to be important and needs to be considered. In the POX-flame radiative absorption has a significant impact on the radiative source terms and significant non-gray gas effects were found. Simple radiation modeling approaches, typical for combustion regimes, namely the OTM with RADCAL, were not able to capture these effects. More sophisticated radiation models were required. The MDA with both the SLW and the WSGG provided reasonable results at still acceptable computational costs. In contrast, in the methane–air flame, the simple radiation models achieved a reasonable agreement with the temperature measurements. Finally, particular combinations of RTE solution methods and property models are recommended for the different flame setups based on the differences in the temperature and the radiating species concentrations in the different flame regions. [ABSTRACT FROM AUTHOR]

SUMMARY A new weighted-sum-of-gray gases (WSGG) model that is based on the statistical narrow band model (SNB) RADCAL is proposed for use in computational fluid dynamic (CFD) simulations of air and oxy-combustion. When employed in conjunction with the discrete ordinates (DO) method, the model predictions compare well against line-by-line benchmark data that have been made available recently that are based on the latest spectroscopic databases. Furthermore, the model compares well against the EM2C SNB model calculations that have served as benchmark data in three-dimensional geometries. Radiative transfer calculations in these prototypical problems therefore confirm recent experimental observations that SNB RADCAL and EM2C SNB serve as good model databases to develop approximate radiative property models. To achieve an optimum balance of speed and accuracy in computationally intensive CFD simulations, non-gray formulations of the WSGG model are also employed with the P1 model and solutions are compared against those generated by the DO model. While the P1 model gave favorable comparisons when cold, black walls were present, the errors in the surface incident radiative flux predictions increased in the presence of hot, reflecting walls. Finally, in fully coupled simulations of natural gas combustion under air-firing and oxy-firing modes, the predicted incident radiative flux profiles were distinctly different between the gray and non-gray calculations at regions of high temperature gradients, while the centerline temperature predictions were comparatively unaffected. The effects of turbulence radiation interactions were also accounted for through the temperature self-correlation term. However, the magnitudes of the temperature fluctuations were small and localized within this furnace and did not significantly alter our predictions. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: In this study, new coefficients for the weighted-sum-of-gray-gas (WSGG) model are proposed based on the up-to-date HITEMP2010 database. The coefficients are determined for gas mixtures of water vapor and carbon dioxide with partial pressure (or molar concentration) ratios equal to 1.0 and 2.0, representing typical products of the combustion of fuel oil and methane. The correlations are valid for pressure path-lengths ranging from 0.001atmm to 10atmm, and for temperatures varying between 400K and 2500K. The WSGG model with the new coefficients are applied to the solution of the radiation heat transfer in non-isothermal, non-homogeneous gas mixtures, which are then compared with benchmark line-by-line solutions to access the accuracy of the model for a few illustrative test cases. Results show that, in spite of its simplicity in comparison to modern gas models, the WSGG model is still a competitive alternative to provide fast but reliable solutions of radiation heat transfer in non-uniform media. [Copyright &y& Elsevier]

Abstract: Presumed shape multi-environment Eulerian PDF Transport method (MEPDF), which involves representing the joint composition PDF shape as a collection of finite number of Delta functions, has been used to model the turbulence-chemistry interactions. The governing transport equations are solved for the probability and the probability weighted mass fraction of species and enthalpy in an Eulerian frame. The radiation heat transfer is included using the non-gray modeling of the radiative properties of the medium by weighted sum of gray gases (WSGG) considering four fictitious gray gases. The absorption coefficients as well as the weight functions of the gray gases are calculated from published literature as a function of the species mass fraction and temperature. The effect of turbulence radiation interaction (TRI) is included using an empirical relations for emission enhancement. The combined tool is then used to model two pilot stabilized hydrocarbon flames (Sandia Flame D and Delft Flame III) with realistic finite rate chemistry. A parametric study of the micro-mixing constant is performed to understand its impact in flame stabilization. In case of Delft Flame III, two different pilot treatments are considered and also the impact of pilot flame power is studied with the MEPDF model. The current model results have been compared with the experimental data and also with the Lagrangian solution of the joint composition PDF transport equation. The discrepancies of the current predictions with the experimental data and other published results have been quantified and discussed. [Copyright &y& Elsevier]

In this work, radiative heat transfer in axisymmetric Controlled Profile Reactor, fired with a pulverized coal combustion jet is studied. Radiation is investigated numerically by the Finite Volume Method (FVM). The developed numerical code is validated by comparing its predictions of the radiative heat flux with published experimental measurements. The non gray feature of the medium is analyzed using the Weighted Sum of Gray Gases Model (WSGG). Then the effects of the gas and particles distribution on the radiative heat flux and on the radiative source term are presented. Finally, the influence of the gas and particle distributions and of the temperature fluctuations on the radiative transfer is investigated. [ABSTRACT FROM AUTHOR]

Using the high-resolution experimental spectral absorption coefficients of six fuel gases and the line by line absorption spectra of CO and CH 4 based on HITRAN and HITEMP spectral databases, in this paper, novel coefficients for weighted-sum-of-gray-gases (WSGG) model are presented for Heptane, Methane, Methanol, MMA, Propane, Propylene, Toluene, and CO. Moreover, for soot, the spectral absorption coefficients were calculated assuming Rayleigh regime implementing the complex index of refraction obtained from the correlations of Chang and Charalampopoulos. The presented WSGG models were coupled with those of literature for CO 2 and H 2 O by means of the superposition method. The models were first validated in several one-dimensional benchmarks representing various levels of inhomogeneous conditions in temperature, gas concentration and soot loading. Then, the WSGG models were employed in solving a three-dimensional case representing a Heptane pool fire. Using the time averaged 3-D CFD profiles, the WSGG models solved the spectral radiative heat transfer exhibiting excellent agreement with the results of line by line calculations in terms of radiative heat flux and radiative heat source. Moreover, the emissivity charts were provided comparing the emissivity calculated by LBL calculations with those of the new WSGG models. [ABSTRACT FROM AUTHOR]

• WSGSA can study heat transfer in the medium of soot aggregates. • WSGSA coupled with WSGG can study heat transfer in gas and soot aggregates mixture. • Effect of soot radiation cannot be ignored even with small volume faction. Soot, a product of insufficient combustion, is usually in the form of aggregate. The multi-scattering of soot fractal aggregates has been proved to play an important role in studying the soot radiative properties, which is rarely considered in predicting the radiative heat transfer in combustion flame. In the present study, based on the Rayleigh-Debey-Gans-Fractal-Aggregate (RDG-FA) theory, a model, named Weighted Sum of Gray Soot fractal Aggregates (WSGSA), used to calculate the radiative properties of nongray soot fractal aggregates in gas-soot mixture is developed by combining the features of full-spectrum k-distribution (FSK) model and Weighted-Sum-of-Gray-Gases (WSGG) model. Four gray soot fractal aggregates obtained from reordering in the form of the k-distribution at Gauss-Legendre integral points are selected to represent the nongray soot fractal aggregate, while corresponding weighting factors are obtained by fitting the radiation data obtained by the line-by-line (LBL) model with soot radiation data. Then, the WSGSA model is systematically validated by studying the radiative heat transfer properties in a one-dimensional plane-parallel slab system only with soot aggregates. The maximum relative discrepancies of emittance under different temperatures and different path lengths are less than 12%, while the maximum relative discrepancies of radiative heat source term and radiative heat flux are both less than 11% with path length less than 3 m. Moreover, combined with the WSGG model, the performance of the WSGSA model is further validated by predicting the radiative heat transfer properties in the mixture consisted of gases and soot aggregates, and acceptable results are also obtained. All the results reveal that the developed model can be applied to predict the radiative heat transfer in the mixture containing gases and soot aggregates, even in the case of significant changes in temperature and species concentration. [ABSTRACT FROM AUTHOR]