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Seung Wook Baek - One of the best experts on this subject based on the ideXlab platform.
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Analysis of Radiative Heat Flux for Nozzle Flow
Applied Mechanics and Materials, 2011Co-Authors: Seung Wook BaekAbstract:— A finite volume method with non-Gray Gas model is applied to investigate radiative heat flux on the inside wall of nozzle. The radiative properties of non-Gray Gas are predicted by using weighted sum of Gray Gases model (WSGGM). Again, 4 Gray Gases and narrow band based WSGGM is used to predict total heat flux and spectral intensity on the nozzle wall. Finally, the hybrid use of 4 Gray Gases and narrow band based model is applied to reduce computational time preserving accuracy.
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radiative heat transfer between two concentric spheres separated by a two phase mixture of non Gray Gas and particles using the modified discrete ordinates method
Journal of Quantitative Spectroscopy & Radiative Transfer, 2008Co-Authors: Seung Wook BaekAbstract: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.
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modeling of pulverized coal combustion with non Gray Gas radiation effects
Combustion Science and Technology, 2001Co-Authors: Myoung Jong Yu, Seung Wook Baek, Shin Jae KangAbstract:A numerical study for simulating a swirling pulverized coal combustion in axisymmetric geometry is carried out here by applying the weighted sum of Gray Gases model (WSGGM) approach with the discrete ordinate method (DOM) to model the radiative heat transfer equation. In the radiative transfer equation, the same polynomial equation and coefficients for weighting factors as those for Gas are adopted for the coal/char particles as a function of partial pressure and particle temperature. The Eul-erian balance equations for mass, momentum, energy, and species mass fractions are adopted with the standard k-ϵs turbulence model, whereas the Lagrangian approach is used for the particulate phase. The eddy-dissipation model is employed for the reaction rate for Gaseous mixture, and the single-step first-order reaction model for the devolatili.ation process for coal. By comparing the numerical results with experimental ones, the radiation model used here is confirmed and found to provide sound alternative for simula...
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an extension of the weighted sum of Gray Gases non Gray Gas radiation model to a two phase mixture of non Gray Gas with particles
International Journal of Heat and Mass Transfer, 2000Co-Authors: Myoung Jong Yu, Seung Wook Baek, Jae Hyun ParkAbstract:A great deal of eAorts has been exercised to date to accurately model the non-Gray behavior of the Gases. Among others, the weighted sum of Gray Gases model (WSGGM), which replaces the non-Gray Gas behavior by an equivalent finite number of Gray Gases, is a simplified model yielding reasonable results. However, a discussion on the weighting factors required for an estimation of radiation in a mixture of non-Gray Gas/Gray particulate is not yet established for WSGGM, since they are dependent on the particle number density, particle size distribution, local temperature and partial pressure. Consequently, the relation between the weighting factors used in the WSGGM for a mixture of non-Gray Gas and Gray particles with scattering in the thermal non-equilibrium has been discussed here, which has not been done before to the author’s best knowledge. Weighting factors for the particles, of which temperature is diAerent from that of the Gas, were evaluated analytically for the WSGGM. The results were, then, validated for the problem of isothermal Gas containing soot particulates between two parallel slab walls. For further application, the approach derived here was implemented to examine the non-Gray radiative eAects of the two phase mixture in an axisymmetric cylinder by changing such various parameters as the particle temperature, non-Gray Gas composition and particle concentration. The eAects of thermal non-equilibrium in a mixture of Gas and particles were also discussed in parallel with scattering eAects by particles. Parametric study showed that a variation in the Gas concentration yielded a noticeable change in the radiative heat transfer when the suspended particle temperature was diAerent from the Gas temperature. New contribution of this study consisted in an extension of applicability of the WSGGM non-Gray model to two phase radiation. # 2000 Elsevier Science Ltd. All rights reserved.
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Numerical Analysis of a Spray Combustion with NonGray Radiation Using Weighted Sum of Gray Gases Model
Combustion Science and Technology, 1996Co-Authors: Chang Eun Choi, Seung Wook BaekAbstract:Abstract In this study, the effect or radiation has been considered in a liquid spray combustion chamber. The discrete ordinates method (DOM) was employed to solve the radiative transfer equation (RTE) and the weighted sum of Gray Gases model (WSGGM) was applied to model a nonGray radiation effect by C02 and H20 Gases. The absorption coefficients derived from WSGGM were used with DOM by summing solutions of the RTE for each Gray Gas. Eulerian- Lagran-gian scheme was adopted to alalyze the two phase combustion. The interactions between two phases are accounted for by using the particle source in cell(PSIC) model. The results have shown that the Gasfication of the droplets is more quickly completed by radiation, which results in shorter droplet trajectories. The radiation also led to a broader high temperature zone inside the combustor. Therefore, it was found that the performance of the spray combus-tor was enhanced by the radiation effect.
Geraldine Heynderickx - One of the best experts on this subject based on the ideXlab platform.
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impact of radiation models in cfd simulations of steam cracking furnaces
Computers & Chemical Engineering, 2007Co-Authors: Ali Habibi, Bart Merci, Geraldine HeynderickxAbstract:Abstract The endothermic thermal cracking process of hydrocarbons takes place in tubular reactor coils suspended in large Gas-fired pyrolysis furnaces. Heat transfer to the reactor tubes is mostly due to radiation from the furnace refractory walls and the flue Gas. A three-dimensional (3-D) simulation of the flow in an industrial scale steam cracking furnace is performed. The renormalization group (RNG) k − ɛ turbulence model is used. The combustion kinetics is modeled by a three-step reaction mechanism, while turbulence–chemistry interaction is taken into account through the Finite Rate/Eddy-Dissipation model. The Discrete Ordinates model (DOM), the P-1 and the Rosseland Radiation model are used for modeling of the radiative heat transfer. The results of using the different radiation models are compared mutually with adiabatic simulation results. The absorption coefficient of the Gas mixture is calculated by means of a Weighted-Sum-of-Gray-Gas model (WSGGM). The effect is discussed of the use of different radiation models on the predicted wall, tube skin and flue Gas temperature profiles and heat fluxes towards the reactor tubes, as well as on the predicted species concentration profiles and structure of the furnace flames under normal firing conditions.
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Gray nonGray Gas radiation modeling in steam cracker cfd calculations
Aiche Journal, 2007Co-Authors: Georgios Stefanidis, Bart Merci, Geraldine Heynderickx, Guy MarinAbstract:A constant composition Gray Gas and a constant composition nonGray Gas radiation model are developed and applied in computational fluid dynamic simulations of an industrial scale steam cracking furnace. Both models are based on the exponential wide band model. The Gray Gas model simplification, commonly used for simulations of industrial applications, is found to have an effect on predicted variable fields like flue Gas flow, temperature, and heat flux to the reactor tubes. When the nonGray Gas model is used, higher energy absorption by the flue Gas in the furnace and lower energy transfer to the process Gas in the reactor tubes is calculated because of the high absorption coefficients in the strongly absorbing bands of 2.7 and 4.3 mm. Thus, the calculated thermal efficiency increases from 37.5% when using the nonGray Gas model to 42.6% when using the Gray Gas model. A 5% difference in the thermal efficiency is large considering the scale and the importance of the process and should be taken into account by the furnace designer. It is also shown that although both models reproduce the basic characteristics of the flow pattern in the furnace, quantitative differences in the flue Gas speed are predicted in some regions of the furnace domain. 2007 American Institute of Chemical Engineers AIChE J, 53: 1658–1669, 2007
Nenad Crnomarkovic - One of the best experts on this subject based on the ideXlab platform.
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INFLUENCE OF THE Gray GasES NUMBER IN THE WEIGHTED SUM OF Gray GasES MODEL ON THE RADIATIVE HEAT EXCHANGE CALCULATION INSIDE PULVERIZED COAL-FIRED FURNACES
Thermal Science, 2020Co-Authors: Nenad Crnomarkovic, Srđan Belošević, Ivan Tomanovic, Aleksandar MilicevicAbstract:The influence of the number of Gray Gases in the weighted sum in the Gray Gases model on the calculation of the radiative heat transfer is discussed in the paper. A computer code which solved the set of equations of the mathematical model describing the reactive two-phase turbulent flow with radiative heat exchange and with thermal equilibrium between phases inside the pulverized coal-fired furnace was used. Gas-phase radiative properties were determined by the simple Gray Gas model and two combinations of the weighted sum of the Gray Gases models: one Gray Gas plus a clear Gas and two Gray Gases plus a clear Gas. Investigation was carried out for two values of the total extinction coefficient of the dispersed phase, for the clean furnace walls and furnace walls covered by an ash layer deposit, and for three levels of the approximation accuracy of the weighting coefficients. The influence of the number of Gray Gases was analyzed through the relative differences of the wall fluxes, wall temperatures, medium temperatures, and heat transfer rate through all furnace walls. The investigation showed that there were conditions of the numerical investigations for which the relative differences of the variables describing the radiative heat exchange decrease with the increase in the number of Gray Gases. The results of this investigation show that if the weighted sum of the Gray Gases model is used, the complexity of the computer code and calculation time can be reduced by optimizing the number of Gray Gases. [Projekat Ministarstva nauke Republike Srbije, br. TR-33018: Increase in energy and ecology efficiency of processes in pulverized coal-fired furnace and optimization of utility steam boiler air preheater by using in-house developed software tools]
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Weighted sum of Gray Gases model optimization for numerical investigations of processes inside pulverized coal-fired furnaces
Journal of Thermal Science, 2017Co-Authors: Nenad Crnomarkovic, Srdjan Belosevic, Ivan Tomanovic, Aleksandar MilicevicAbstract:The effects of the number of significant figures (NSF) in the interpolation polynomial coefficients (IPCs) of the weighted sum of Gray Gases model (WSGM) on results of numerical investigations and WSGM optimization were investigated. The investigation was conducted using numerical simulations of the processes inside a pulverized coal-fired furnace. The radiative properties of the Gas phase were determined using the simple Gray Gas model (SG), two-term WSGM (W2), and three-term WSGM (W3). Ten sets of the IPCs with the same NSF were formed for every weighting coefficient in both W2 and W3. The average and maximal relative difference values of the flame temperatures, wall temperatures, and wall heat fluxes were determined. The investigation showed that the results of numerical investigations were affected by the NSF unless it exceeded certain value. The increase in the NSF did not necessarily lead to WSGM optimization. The combination of the NSF (CNSF) was the necessary requirement for WSGM optimization.
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numerical investigation of processes in the lignite fired furnace when simple Gray Gas and weighted sum of Gray Gases models are used
International Journal of Heat and Mass Transfer, 2013Co-Authors: Nenad Crnomarkovic, Miroslav Sijercic, Srdjan Belosevic, Dragan Tucakovic, Titoslav ZivanovicAbstract:Abstract Comparison of the numerical investigation results was carried out when the simple Gray Gas (SGG) and weighted sum of Gray Gases (WSGG) models are used to model the radiative properties of the Gas phase inside the lignite fired furnaces. Comprehensive mathematical model of the tangentially fired furnace by pulverized lignite was made. Gas radiative properties were modeled by the SGG and WSGG models. Radiative heat transfer was modeled by the zonal model. Gas-phase variables and absorbed wall fluxes were compared on the basis of the relative differences that were determined for all control volumes and surface zones. Average relative differences of the Gas-phase temperatures were about 1.0%. Average relative differences of the absorbed wall fluxes were from 2.0% to 5.0%. Absorbed wall fluxes determined by the SGG model were bigger than those determined by the WSGG model. Differences of the heat transfer rates of the absorbed radiation through the furnace walls were expressed in percents of heat transfer rates determined by the SGG model and were similar to the average relative differences of absorbed wall fluxes. Results justify application of the SGG model in comprehensive mathematical models of lignite-fired furnaces.
Denis Lemonnier - One of the best experts on this subject based on the ideXlab platform.
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Non-Gray Gas radiation effect on mixed convection in lid driven square cavity
2016Co-Authors: Mohammed Cherifi, Abderrahmane Benbrik, Siham Laouar-meftah, Denis LemonnierAbstract:A numerical study is performed to investigate the effect of non-Gray radiation on mixed convection in a vertical two sided lid driven square cavity filled with air-H2O-CO2 Gas mixture. The vertical moving walls of the enclosure are maintained at two different but uniform temperatures. The horizontal walls are thermally insulated and considered as adiabatic walls. The governing differential equations are solved by a finite-volume method and the SIMPLE algorithm was adopted to solve the pressure–velocity coupling. The radiative transfer equation (RTE) is solved by the discrete ordinates method (DOM). The spectral line weighted sum of Gray Gases model (SLW) is used to account for non-Gray radiation properties. Simulations are performed in configurations where thermal and shear forces induce cooperating buoyancy forces. Streamlines, isotherms, and Nusselt number are analyzed for three different values of Richardson’s number (from 0.1 to 10) and by considering three different medium (transparent medium, Gray m...
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interaction of radiation with double diffusive natural convection in a three dimensional cubic cavity filled with a non Gray Gas mixture in cooperating cases
Numerical Heat Transfer Part A-applications, 2016Co-Authors: Mohamed Cherifi, Siham Laouarmeftah, Abderrahmane Benbrik, Denis Lemonnier, Didier SauryAbstract:ABSTRACTA three-dimensional (3D) numerical study has been performed to investigate the effects of non-Gray Gas radiation on double-diffusive natural convection in a cubic enclosure filled with either air–H2O or air–CO2 mixtures in cooperating situations. Gas radiation was taken into account by the discrete ordinates method (DOM) associated with the spectral line weighted-sum-of-Gray-Gases (SLW) spectral model. Results obtained for two average concentrations of H2O and CO2 (10% and 20%) show that radiation modifies the temperature and concentration structures by creating oblique stratifications. The heat transfer rate is decreased, whereas mass transfer is not much modified. In addition, a comparison between 2D and 3D results is presented.
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Effect of horizontal walls emissivity on coupled double diffusive convection and non Gray-Gas radiation of air-H2O mixture in a cooperating case
2015 International Conference on Industrial Engineering and Operations Management (IEOM), 2015Co-Authors: Mohamed Cherifi, Abderrahmane Benbrik, Siham Laouar-meftah, Denis LemonnierAbstract:A numerical study is performed to investigate the effect of the adiabatic walls emissivity on coupled double diffusive natural convection and Gas radiation in a differentially heated square enclosure filled with non-Gray air-H2O mixtures in a cooperating case. The vertical walls of the enclosure are maintained at two different but uniform temperatures. The remaining boundaries are thermally insulated and considered as adiabatic walls. These walls are assumed to be opaque, diffuse and Gray. Their emissivity is variable (ε=0, 0.1, 0.5 and 1). The governing differential equations are solved by a finite-volume method and the SIMPLE algorithm was adopted to solve the pressure-velocity coupling. The discrete ordinates method (DOM) associated with the spectral line weighted-sum-of-Gray-Gases (SLW) is used to solve the radiative transfer equation. Simulations are performed in configurations where thermal and concentration gradient induces cooperating buoyancy forces. Results obtained for three average molar fractions of H2O (5%, 10% and 20%). The effects of walls emissivity on the flow and temperature fields and heat transfer rates are analyzed.
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effect of horizontal walls emissivity on coupled double diffusive convection and non Gray Gas radiation of air h 2 o mixture in a cooperating case
International Conference on Industrial Engineering and Operations Management, 2015Co-Authors: Mohamed Cherifi, Siham Laouarmeftah, Abderrahmane Benbrik, Denis LemonnierAbstract:A numerical study is performed to investigate the effect of the adiabatic walls emissivity on coupled double diffusive natural convection and Gas radiation in a differentially heated square enclosure filled with non-Gray air-H 2 O mixtures in a cooperating case. The vertical walls of the enclosure are maintained at two different but uniform temperatures. The remaining boundaries are thermally insulated and considered as adiabatic walls. These walls are assumed to be opaque, diffuse and Gray. Their emissivity is variable (e=0, 0.1, 0.5 and 1). The governing differential equations are solved by a finite-volume method and the SIMPLE algorithm was adopted to solve the pressure-velocity coupling. The discrete ordinates method (DOM) associated with the spectral line weighted-sum-of-Gray-Gases (SLW) is used to solve the radiative transfer equation. Simulations are performed in configurations where thermal and concentration gradient induces cooperating buoyancy forces. Results obtained for three average molar fractions of H 2 O (5%, 10% and 20%). The effects of walls emissivity on the flow and temperature fields and heat transfer rates are analyzed.
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Extension of the exact SLW model to non-isothermal Gaseous media
Journal of Quantitative Spectroscopy & Radiative Transfer, 2014Co-Authors: Vladimir P. Solovjov, Denis Lemonnier, Brent W. WebbAbstract:Absract The exact limit of the spectral line weighted-sum-of-Gray-Gases (SLW) model in isothermal media is extended to the case of non-isothermal media following the reference approach. The problem is thus expressed in terms of a continuously varying absorption cross-section in the limit as the number of Gray Gases tends to infinity. The limiting case of the SLW reference approach is developed for spectral integration of the RTE in non-isothermal environments. Analytical solutions of the Exact SLW model are obtained for a multilayer system of isothermal layers, and the analytical solutions for a non-isothermal medium are obtained in the limit when the number of sublayers approaches infinity. The Exact SLW model is applied also for construction of the optimized efficient SLW-1 model consisting of a single Gray Gas and a single clear Gas. The Exact SLW model is a theoretical approach which is useful for better understanding of the possibilities and limitations of the SLW method, but it also has implications for practical applications.
Bart Merci - One of the best experts on this subject based on the ideXlab platform.
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impact of radiation models in cfd simulations of steam cracking furnaces
Computers & Chemical Engineering, 2007Co-Authors: Ali Habibi, Bart Merci, Geraldine HeynderickxAbstract:Abstract The endothermic thermal cracking process of hydrocarbons takes place in tubular reactor coils suspended in large Gas-fired pyrolysis furnaces. Heat transfer to the reactor tubes is mostly due to radiation from the furnace refractory walls and the flue Gas. A three-dimensional (3-D) simulation of the flow in an industrial scale steam cracking furnace is performed. The renormalization group (RNG) k − ɛ turbulence model is used. The combustion kinetics is modeled by a three-step reaction mechanism, while turbulence–chemistry interaction is taken into account through the Finite Rate/Eddy-Dissipation model. The Discrete Ordinates model (DOM), the P-1 and the Rosseland Radiation model are used for modeling of the radiative heat transfer. The results of using the different radiation models are compared mutually with adiabatic simulation results. The absorption coefficient of the Gas mixture is calculated by means of a Weighted-Sum-of-Gray-Gas model (WSGGM). The effect is discussed of the use of different radiation models on the predicted wall, tube skin and flue Gas temperature profiles and heat fluxes towards the reactor tubes, as well as on the predicted species concentration profiles and structure of the furnace flames under normal firing conditions.
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Gray nonGray Gas radiation modeling in steam cracker cfd calculations
Aiche Journal, 2007Co-Authors: Georgios Stefanidis, Bart Merci, Geraldine Heynderickx, Guy MarinAbstract:A constant composition Gray Gas and a constant composition nonGray Gas radiation model are developed and applied in computational fluid dynamic simulations of an industrial scale steam cracking furnace. Both models are based on the exponential wide band model. The Gray Gas model simplification, commonly used for simulations of industrial applications, is found to have an effect on predicted variable fields like flue Gas flow, temperature, and heat flux to the reactor tubes. When the nonGray Gas model is used, higher energy absorption by the flue Gas in the furnace and lower energy transfer to the process Gas in the reactor tubes is calculated because of the high absorption coefficients in the strongly absorbing bands of 2.7 and 4.3 mm. Thus, the calculated thermal efficiency increases from 37.5% when using the nonGray Gas model to 42.6% when using the Gray Gas model. A 5% difference in the thermal efficiency is large considering the scale and the importance of the process and should be taken into account by the furnace designer. It is also shown that although both models reproduce the basic characteristics of the flow pattern in the furnace, quantitative differences in the flue Gas speed are predicted in some regions of the furnace domain. 2007 American Institute of Chemical Engineers AIChE J, 53: 1658–1669, 2007
