Dépouillements

Infrared radiative properties of heavily doped silicon at room temperature / S. Basu in Journal of heat transfer, Vol. 132 N° 2 (n° spécial) (Fevrier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023301-1/8] Titre : Infrared radiative properties of heavily doped silicon at room temperature Type de document : texte imprimé Auteurs : S. Basu, Auteur ; B. J. Lee, Auteur ; Z. M. Zhang, Auteur Article en page(s) : pp. [023301-1/8] Note générale : Physique Langues : Anglais (eng) Mots-clés : Microscale  Doped  silicon  Radiative  properties  Thin  films Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper describes an experimental investigation on the infrared radiative properties of heavily doped Si at room temperature. Lightly doped Si wafers were ion-implanted with either boron or phosphorus atoms, with dosages corresponding to as-implanted peak doping concentrations of 1020 and 1021 cm−3; the peak doping concentrations after annealing are 3.1×1019 and 2.8×1020 cm−3, respectively. Rapid thermal annealing was performed to activate the implanted dopants. A Fourier-transform infrared spectrometer was employed to measure the transmittance and reflectance of the samples in the wavelength range from 2 µm to 20 µm. Accurate carrier mobility and ionization models were identified after carefully reviewing the available literature, and then incorporated into the Drude model to predict the dielectric function of doped Si. The radiative properties of doped Si samples were calculated by treating the doped region as multilayer thin films of different doping concentrations on a thick lightly doped Si substrate. The measured spectral transmittance and reflectance agree well with the model predictions. The knowledge gained from this study will aid future design and fabrication of doped Si microstructures as wavelength selective emitters and absorbers in the midinfrared region. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Infrared radiative properties of heavily doped silicon at room temperature [texte imprimé] / S. Basu, Auteur ; B. J. Lee, Auteur ; Z. M. Zhang, Auteur . - pp. [023301-1/8]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023301-1/8] Mots-clés : Microscale  Doped  silicon  Radiative  properties  Thin  films Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper describes an experimental investigation on the infrared radiative properties of heavily doped Si at room temperature. Lightly doped Si wafers were ion-implanted with either boron or phosphorus atoms, with dosages corresponding to as-implanted peak doping concentrations of 1020 and 1021 cm−3; the peak doping concentrations after annealing are 3.1×1019 and 2.8×1020 cm−3, respectively. Rapid thermal annealing was performed to activate the implanted dopants. A Fourier-transform infrared spectrometer was employed to measure the transmittance and reflectance of the samples in the wavelength range from 2 µm to 20 µm. Accurate carrier mobility and ionization models were identified after carefully reviewing the available literature, and then incorporated into the Drude model to predict the dielectric function of doped Si. The radiative properties of doped Si samples were calculated by treating the doped region as multilayer thin films of different doping concentrations on a thick lightly doped Si substrate. The measured spectral transmittance and reflectance agree well with the model predictions. The knowledge gained from this study will aid future design and fabrication of doped Si microstructures as wavelength selective emitters and absorbers in the midinfrared region. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Near-field radiation calculated with an improved dielectric function model for doped silicon / S. Basu in Journal of heat transfer, Vol. 132 N° 2 (n° spécial) (Fevrier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023302-1/7] Titre : Near-field radiation calculated with an improved dielectric function model for doped silicon Type de document : texte imprimé Auteurs : S. Basu, Auteur ; B. J. Lee, Auteur ; Z. M. Zhang, Auteur Article en page(s) : pp. [023302-1/7] Note générale : Physique Langues : Anglais (eng) Mots-clés : Doped  silicon  Lateral  shift  Near-field  radiation Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper describes a theoretical investigation of near-field radiative heat transfer between doped silicon surfaces separated by a vacuum gap. An improved dielectric function model for heavily doped silicon is employed. The effects of doping level, polarization, and vacuum gap width on the spectral and total radiative transfer are studied based on the fluctuational electrodynamics. It is observed that increasing the doping concentration does not necessarily enhance the energy transfer in the near-field. The energy streamline method is used to model the lateral shift of the energy pathway, which is the trace of the Poynting vectors in the vacuum gap. The local density of states near the emitter is calculated with and without the receiver. The results from this study can help improve the understanding of near-field radiation for applications such as thermophotovoltaic energy conversion, nanoscale thermal imaging, and nanothermal manufacturing. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Near-field radiation calculated with an improved dielectric function model for doped silicon [texte imprimé] / S. Basu, Auteur ; B. J. Lee, Auteur ; Z. M. Zhang, Auteur . - pp. [023302-1/7]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023302-1/7] Mots-clés : Doped  silicon  Lateral  shift  Near-field  radiation Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper describes a theoretical investigation of near-field radiative heat transfer between doped silicon surfaces separated by a vacuum gap. An improved dielectric function model for heavily doped silicon is employed. The effects of doping level, polarization, and vacuum gap width on the spectral and total radiative transfer are studied based on the fluctuational electrodynamics. It is observed that increasing the doping concentration does not necessarily enhance the energy transfer in the near-field. The energy streamline method is used to model the lateral shift of the energy pathway, which is the trace of the Poynting vectors in the vacuum gap. The local density of states near the emitter is calculated with and without the receiver. The results from this study can help improve the understanding of near-field radiation for applications such as thermophotovoltaic energy conversion, nanoscale thermal imaging, and nanothermal manufacturing. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

A quasidependent scattering radiative properties model for high density fiber composites / Siu-Chun Lee in Journal of heat transfer, Vol. 132 N° 2 (n° spécial) (Fevrier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023303-1/8] Titre : A quasidependent scattering radiative properties model for high density fiber composites Type de document : texte imprimé Auteurs : Siu-Chun Lee, Auteur Article en page(s) : pp. [023303-1/8] Note générale : Physique Langues : Anglais (eng) Mots-clés : Dependent  scattering  Fiber  Thermal  insulation  Fiber  composite  Woven  fabric  Heat  shield  Raiative  properties  Infinite  cylinder Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper presents a theoretical model for the radiative properties of fiber composites fabricated of spatially oriented fiber strands that contain closely spaced fibers in the Mie scattering regime. Dependent scattering within the dense fiber strands is accounted for by utilizing the solution of Maxwell's equations that included the near field interaction of cylindrical waves. Scattering between strands is shown to be uncorrelated due to their macroscopic dimensions compared with the wavelength of the incident radiation. The model is called quasidependent scattering approximation (QDA), as the radiative properties are formulated as the uncorrelated sum of the dependent scattering properties of the constituent fiber strands. The extinction coefficient, scattering coefficient, and scattering phase function are derived for fiber composites of arbitrary internal architecture. The application of the QDA model is demonstrated by means of numerical analyses on two types of fiber composites. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] A quasidependent scattering radiative properties model for high density fiber composites [texte imprimé] / Siu-Chun Lee, Auteur . - pp. [023303-1/8]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023303-1/8] Mots-clés : Dependent  scattering  Fiber  Thermal  insulation  Fiber  composite  Woven  fabric  Heat  shield  Raiative  properties  Infinite  cylinder Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper presents a theoretical model for the radiative properties of fiber composites fabricated of spatially oriented fiber strands that contain closely spaced fibers in the Mie scattering regime. Dependent scattering within the dense fiber strands is accounted for by utilizing the solution of Maxwell's equations that included the near field interaction of cylindrical waves. Scattering between strands is shown to be uncorrelated due to their macroscopic dimensions compared with the wavelength of the incident radiation. The model is called quasidependent scattering approximation (QDA), as the radiative properties are formulated as the uncorrelated sum of the dependent scattering properties of the constituent fiber strands. The extinction coefficient, scattering coefficient, and scattering phase function are derived for fiber composites of arbitrary internal architecture. The application of the QDA model is demonstrated by means of numerical analyses on two types of fiber composites. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Experimental and computational characterization of high heat fluxes during transient blackbody calibrations / Amanie N. Abdelmessih in Journal of heat transfer, Vol. 132 N° 2 (n° spécial) (Fevrier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023304-1/13] Titre : Experimental and computational characterization of high heat fluxes during transient blackbody calibrations Type de document : texte imprimé Auteurs : Amanie N. Abdelmessih, Auteur ; Thomas J. Horn, Auteur Article en page(s) : pp. [023304-1/13] Note générale : Physique Langues : Anglais (eng) Mots-clés : Cylindrical  blackbody  calibration  Blackbody  calibration  furnace  Transient  blackbody  calibration  Blackbody  cavity  Heat  flux  calibration  Heat  flux  measurement  Temperature  measurement  Temperature  calibration  Numerical  or  computational  calibration  Experimental  calibration Index. décimale : 536 Chaleur. Thermodynamique Résumé : High heat fluxes are encountered in numerous applications, such as on the surfaces of hypersonic vehicles in flight, in fires, and within engines. The calibration of heat flux gauges may be performed in a dual cavity cylindrical blackbody. Insertion of instruments into the cavity disturbs the thermal equilibrium resulting in a transient calibration environment. To characterize the transient heat fluxes, experiments were performed on a dual cavity cylindrical blackbody at nominal temperatures varying from 800°C to 1900°C in increments of 100°C. The pre-insertion, steady state, axial temperature profile is compared experimentally and numerically. Detailed transient thermal models have been developed to simulate the heat flux calibration process at two extreme fluxes: the high flux is 1 MW/m2 and the relatively low is 70 kW/m2. Based on experiments and numerical analysis, the optimum heat flux sensor insertion location as measured from the center partition was determined. The effect of convection (natural and forced) in the blackbody cavity during the insertion is calculated and found to be less than 2% at high temperatures but reaches much higher values at relatively lower temperatures. The transient models show the effect of inserting a heat flux gauge at room temperature on the thermal equilibrium of the blackbody at 1800°C and 800°C nominal temperatures. Also, heat flux sensor outputs are derived from computed sensor temperature distributions and compared with experimental results. The numerical heat flux agreed with the experimental results to within 5%, which indicates that the numerical models captured the transient thermal physics during the calibration. Based on numerical models and all experimental runs the heat transfer mechanisms are explained. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Experimental and computational characterization of high heat fluxes during transient blackbody calibrations [texte imprimé] / Amanie N. Abdelmessih, Auteur ; Thomas J. Horn, Auteur . - pp. [023304-1/13]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023304-1/13] Mots-clés : Cylindrical  blackbody  calibration  Blackbody  calibration  furnace  Transient  blackbody  calibration  Blackbody  cavity  Heat  flux  calibration  Heat  flux  measurement  Temperature  measurement  Temperature  calibration  Numerical  or  computational  calibration  Experimental  calibration Index. décimale : 536 Chaleur. Thermodynamique Résumé : High heat fluxes are encountered in numerous applications, such as on the surfaces of hypersonic vehicles in flight, in fires, and within engines. The calibration of heat flux gauges may be performed in a dual cavity cylindrical blackbody. Insertion of instruments into the cavity disturbs the thermal equilibrium resulting in a transient calibration environment. To characterize the transient heat fluxes, experiments were performed on a dual cavity cylindrical blackbody at nominal temperatures varying from 800°C to 1900°C in increments of 100°C. The pre-insertion, steady state, axial temperature profile is compared experimentally and numerically. Detailed transient thermal models have been developed to simulate the heat flux calibration process at two extreme fluxes: the high flux is 1 MW/m2 and the relatively low is 70 kW/m2. Based on experiments and numerical analysis, the optimum heat flux sensor insertion location as measured from the center partition was determined. The effect of convection (natural and forced) in the blackbody cavity during the insertion is calculated and found to be less than 2% at high temperatures but reaches much higher values at relatively lower temperatures. The transient models show the effect of inserting a heat flux gauge at room temperature on the thermal equilibrium of the blackbody at 1800°C and 800°C nominal temperatures. Also, heat flux sensor outputs are derived from computed sensor temperature distributions and compared with experimental results. The numerical heat flux agreed with the experimental results to within 5%, which indicates that the numerical models captured the transient thermal physics during the calibration. Based on numerical models and all experimental runs the heat transfer mechanisms are explained. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Tomography-based heat and mass transfer characterization of reticulate porous ceramics for high-temperature processing / Sophia Haussener in Journal of heat transfer, Vol. 132 N° 2 (n° spécial) (Fevrier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023305-1/9] Titre : Tomography-based heat and mass transfer characterization of reticulate porous ceramics for high-temperature processing Type de document : texte imprimé Auteurs : Sophia Haussener, Auteur ; Patrick Coray, Auteur ; Wojciech Lipinski, Auteur Article en page(s) : pp. [023305-1/9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Reticulate  Porous  Ceramic  Computer  tomography  Transport  Radiation  Conduction  Convection  Monte  Carlo  DPLS  Solar  energy  Thermochemical  cycle  Hydrogen Index. décimale : 536 Chaleur. Thermodynamique Résumé : Reticulate porous ceramics employed in high-temperature processes are characterized for heat and mass transfer. The exact 3D digital geometry of their complex porous structure is obtained by computer tomography and used in direct pore-level simulations to numerically calculate their effective transport properties. Two-point correlation functions and mathematical morphology operations are applied for the geometrical characterization that includes the determination of porosity, specific surface area, representative elementary volume edge size, and mean pore size. Finite volume techniques are applied for conductive/convective heat transfer and flow characterization, which includes the determination of the thermal conductivity, interfacial heat transfer coefficient, permeability, Dupuit–Forchheimer coefficient, residence time, tortuosity, and diffusion tensor. Collision-based Monte Carlo method is applied for the radiative heat transfer characterization, which includes the determination of the extinction coefficient and scattering phase function. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Tomography-based heat and mass transfer characterization of reticulate porous ceramics for high-temperature processing [texte imprimé] / Sophia Haussener, Auteur ; Patrick Coray, Auteur ; Wojciech Lipinski, Auteur . - pp. [023305-1/9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023305-1/9] Mots-clés : Reticulate  Porous  Ceramic  Computer  tomography  Transport  Radiation  Conduction  Convection  Monte  Carlo  DPLS  Solar  energy  Thermochemical  cycle  Hydrogen Index. décimale : 536 Chaleur. Thermodynamique Résumé : Reticulate porous ceramics employed in high-temperature processes are characterized for heat and mass transfer. The exact 3D digital geometry of their complex porous structure is obtained by computer tomography and used in direct pore-level simulations to numerically calculate their effective transport properties. Two-point correlation functions and mathematical morphology operations are applied for the geometrical characterization that includes the determination of porosity, specific surface area, representative elementary volume edge size, and mean pore size. Finite volume techniques are applied for conductive/convective heat transfer and flow characterization, which includes the determination of the thermal conductivity, interfacial heat transfer coefficient, permeability, Dupuit–Forchheimer coefficient, residence time, tortuosity, and diffusion tensor. Collision-based Monte Carlo method is applied for the radiative heat transfer characterization, which includes the determination of the extinction coefficient and scattering phase function. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Infrared radiative properties of thin polyethylene coating pigmented with titanium dioxide particles / Mehdi Baneshi in Journal of heat transfer, Vol. 132 N° 2 (n° spécial) (Fevrier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023306-1/12] Titre : Infrared radiative properties of thin polyethylene coating pigmented with titanium dioxide particles Type de document : texte imprimé Auteurs : Mehdi Baneshi, Auteur ; Shigenao Maruyama, Auteur ; Atsuki Komiya, Auteur Article en page(s) : pp. [023306-1/12] Note générale : Physique Langues : Anglais (eng) Mots-clés : Far  field  approximation  Near  field  approximation  Pigmented  coating  Titanium  dioxide Index. décimale : 536 Chaleur. Thermodynamique Résumé : The infrared (IR) radiative properties of TiO2 pigment particles must be known to perform thermal analysis of a TiO2 pigmented coating. Resins generally used in making pigmented coatings are absorbing at IR wavelengths, which means that the conventional Mie solution (MS) may not be adequate in this domain. There are two approaches to evaluating radiative properties in an absorbing medium: far field approximation (FFA) and near field approximation (NFA). In this study, after reviewing these two approaches, we evaluated the radiative properties of TiO2 particles in polyethylene resin as an absorbing matrix in the wavelength range of 1.7–15 µm based on the MS, FFA, and NFA. We then calculated the effective scattering and absorption coefficients for different models. To investigate the effect of the particle size and volume concentration on the transmittance of IR wavelengths, we made a nongray radiative heat transfer in an anisotropic scattering monodisperse pigmented layer, with independent scattering using the radiation element method by the ray emission model. The results showed that all three approaches predicted similar results in the particle size domain and volume fraction range utilized in pigmented coatings. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Infrared radiative properties of thin polyethylene coating pigmented with titanium dioxide particles [texte imprimé] / Mehdi Baneshi, Auteur ; Shigenao Maruyama, Auteur ; Atsuki Komiya, Auteur . - pp. [023306-1/12]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023306-1/12] Mots-clés : Far  field  approximation  Near  field  approximation  Pigmented  coating  Titanium  dioxide Index. décimale : 536 Chaleur. Thermodynamique Résumé : The infrared (IR) radiative properties of TiO2 pigment particles must be known to perform thermal analysis of a TiO2 pigmented coating. Resins generally used in making pigmented coatings are absorbing at IR wavelengths, which means that the conventional Mie solution (MS) may not be adequate in this domain. There are two approaches to evaluating radiative properties in an absorbing medium: far field approximation (FFA) and near field approximation (NFA). In this study, after reviewing these two approaches, we evaluated the radiative properties of TiO2 particles in polyethylene resin as an absorbing matrix in the wavelength range of 1.7–15 µm based on the MS, FFA, and NFA. We then calculated the effective scattering and absorption coefficients for different models. To investigate the effect of the particle size and volume concentration on the transmittance of IR wavelengths, we made a nongray radiative heat transfer in an anisotropic scattering monodisperse pigmented layer, with independent scattering using the radiation element method by the ray emission model. The results showed that all three approaches predicted similar results in the particle size domain and volume fraction range utilized in pigmented coatings. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

A narrow band-based multiscale multigroup full-spectrum k-distribution method for radiative transfer in nonhomogeneous gas-soot mixtures / Gopalendu Pal in Journal of heat transfer, Vol. 132 N° 2 (n° spécial) (Fevrier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023307-1/9] Titre : A narrow band-based multiscale multigroup full-spectrum k-distribution method for radiative transfer in nonhomogeneous gas-soot mixtures Type de document : texte imprimé Auteurs : Gopalendu Pal, Auteur ; Michael F. Modest, Auteur Article en page(s) : pp. [023307-1/9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Absorption  coefficients  Combustion  Flames  Gas  mixtures  Heat  transfer  Radiative  transfer Index. décimale : 536 Chaleur. Thermodynamique Résumé : The full-spectrum k-distribution (FSK) approach has become a promising method for radiative heat transfer calculations in strongly nongray participating media, due to its ability to achieve high accuracy at a tiny fraction of the line-by-line (LBL) computational cost. However, inhomogeneities in temperature, total pressure, and component mole fractions severely challenge the accuracy of the FSK approach. The objective of this paper is to develop a narrow band-based hybrid FSK model that is accurate for radiation calculations in combustion systems containing both molecular gases and nongray particles such as soot with strong temperature and mole fraction inhomogeneities. This method combines the advantages of the multigroup FSK method for temperature inhomogeneities in a single species, and the modified multiscale FSK method for concentration inhomogeneities in gas-soot mixtures. In this new method, each species is considered as one scale; the absorption coefficients within each narrow band of every gas scale are divided into M exclusive spectral groups, depending on their temperature dependence. Accurate and compact narrow band multigroup databases are constructed for combustion gases such as CO2 and H2O. Sample calculations are performed for a 1D medium and also for a 2D axisymmetric combustion flame. The narrow band-based hybrid method is observed to accurately predict heat transfer from extremely inhomogeneous gas-soot mixtures with/without wall emission, yielding close-to-LBL accuracy. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] A narrow band-based multiscale multigroup full-spectrum k-distribution method for radiative transfer in nonhomogeneous gas-soot mixtures [texte imprimé] / Gopalendu Pal, Auteur ; Michael F. Modest, Auteur . - pp. [023307-1/9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023307-1/9] Mots-clés : Absorption  coefficients  Combustion  Flames  Gas  mixtures  Heat  transfer  Radiative  transfer Index. décimale : 536 Chaleur. Thermodynamique Résumé : The full-spectrum k-distribution (FSK) approach has become a promising method for radiative heat transfer calculations in strongly nongray participating media, due to its ability to achieve high accuracy at a tiny fraction of the line-by-line (LBL) computational cost. However, inhomogeneities in temperature, total pressure, and component mole fractions severely challenge the accuracy of the FSK approach. The objective of this paper is to develop a narrow band-based hybrid FSK model that is accurate for radiation calculations in combustion systems containing both molecular gases and nongray particles such as soot with strong temperature and mole fraction inhomogeneities. This method combines the advantages of the multigroup FSK method for temperature inhomogeneities in a single species, and the modified multiscale FSK method for concentration inhomogeneities in gas-soot mixtures. In this new method, each species is considered as one scale; the absorption coefficients within each narrow band of every gas scale are divided into M exclusive spectral groups, depending on their temperature dependence. Accurate and compact narrow band multigroup databases are constructed for combustion gases such as CO2 and H2O. Sample calculations are performed for a 1D medium and also for a 2D axisymmetric combustion flame. The narrow band-based hybrid method is observed to accurately predict heat transfer from extremely inhomogeneous gas-soot mixtures with/without wall emission, yielding close-to-LBL accuracy. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Radiative properties of numerically generated fractal soot aggregates / Fengshan Liu in Journal of heat transfer, Vol. 132 N° 2 (n° spécial) (Fevrier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023308-1/6] Titre : Radiative properties of numerically generated fractal soot aggregates : the importance of configuration averaging Type de document : texte imprimé Auteurs : Fengshan Liu, Auteur ; Gregory J. Smallwood, Auteur Article en page(s) : pp. [023308-1/6] Note générale : Physique Langues : Anglais (eng) Mots-clés : Fractal  aggregates  Soot  Optical  properties  Configuration  averaging Index. décimale : 536 Chaleur. Thermodynamique Résumé : The radiative properties of numerically generated fractal soot aggregates were studied using the numerically accurate generalized multisphere Mie-solution method. The fractal aggregates investigated in this study contain 10–600 primary particles of 30 nm in diameter. These fractal aggregates were numerically generated using a combination of the particle-cluster and cluster-cluster aggregation algorithms with fractal parameters representing flame-generated soot. Ten different realizations were obtained for a given aggregate size measured by the number of primary particles. The wavelength considered is 532 nm, and the corresponding size parameter of primary particle is 0.177. Attention is paid to the effect of different realizations of a fractal aggregate with identical fractal dimension, prefactor, primary particle diameter, and the number of primary particles on its orientation-averaged radiative properties. Most properties of practical interest exhibit relatively small variation with aggregate realization. However, other scattering properties, especially the vertical-horizontal differential scattering cross section, are very sensitive to the variation in geometrical configuration of primary particles. Orientation-averaged radiative properties of a single aggregate realization are not always sufficient to represent the properties of random-oriented ensemble of fractal aggregates. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Radiative properties of numerically generated fractal soot aggregates : the importance of configuration averaging [texte imprimé] / Fengshan Liu, Auteur ; Gregory J. Smallwood, Auteur . - pp. [023308-1/6]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023308-1/6] Mots-clés : Fractal  aggregates  Soot  Optical  properties  Configuration  averaging Index. décimale : 536 Chaleur. Thermodynamique Résumé : The radiative properties of numerically generated fractal soot aggregates were studied using the numerically accurate generalized multisphere Mie-solution method. The fractal aggregates investigated in this study contain 10–600 primary particles of 30 nm in diameter. These fractal aggregates were numerically generated using a combination of the particle-cluster and cluster-cluster aggregation algorithms with fractal parameters representing flame-generated soot. Ten different realizations were obtained for a given aggregate size measured by the number of primary particles. The wavelength considered is 532 nm, and the corresponding size parameter of primary particle is 0.177. Attention is paid to the effect of different realizations of a fractal aggregate with identical fractal dimension, prefactor, primary particle diameter, and the number of primary particles on its orientation-averaged radiative properties. Most properties of practical interest exhibit relatively small variation with aggregate realization. However, other scattering properties, especially the vertical-horizontal differential scattering cross section, are very sensitive to the variation in geometrical configuration of primary particles. Orientation-averaged radiative properties of a single aggregate realization are not always sufficient to represent the properties of random-oriented ensemble of fractal aggregates. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

The simplified-fredholm integral equation solver and its use in thermal radiation / K. G. Terry Hollands in Journal of heat transfer, Vol. 132 N° 2 (n° spécial) (Fevrier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023401-1/6] Titre : The simplified-fredholm integral equation solver and its use in thermal radiation Type de document : texte imprimé Auteurs : K. G. Terry Hollands, Auteur Article en page(s) : pp. [023401-1/6] Note générale : Physique Langues : Anglais (eng) Mots-clés : Thermal  radiation  Integral  equations  Enclosures  Exchange  factors  Cylindrical  cavities  Square  cavities  Kernel  Coupled  enclosures Index. décimale : 536 Chaleur. Thermodynamique Résumé : The application of a new Fredholm integral equation solver to problems in thermal radiation is explored. The new method provides a simplified version of Fredholm's own 1903 solution which, while being highly important from a theoretical point of view, had been considered too complex to provide a practical tool for solving integral equations. The method does not involve solving large arrays of simultaneous equations; rather, the simplified-Fredholm method provides an explicit solution. The solution consists of an infinite series with each term containing multiple integrals. It has been found, however, that the series can be safely truncated after about a dozen terms, and the multiple integrals can be resolved through repeated matrix multiplications, all of this leading to a practical methodology. Implicit in the method and highly useful in radiant analyses is the idea of the resolvent kernel, which permits generalized solutions to be obtained, independent of the forcing function. The method also adapts itself to a simple technique for establishing the possible error in any result. It is illustrated here on some enclosure problems that can be reduced to solving Fredholm's equation in a single variable. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] The simplified-fredholm integral equation solver and its use in thermal radiation [texte imprimé] / K. G. Terry Hollands, Auteur . - pp. [023401-1/6]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023401-1/6] Mots-clés : Thermal  radiation  Integral  equations  Enclosures  Exchange  factors  Cylindrical  cavities  Square  cavities  Kernel  Coupled  enclosures Index. décimale : 536 Chaleur. Thermodynamique Résumé : The application of a new Fredholm integral equation solver to problems in thermal radiation is explored. The new method provides a simplified version of Fredholm's own 1903 solution which, while being highly important from a theoretical point of view, had been considered too complex to provide a practical tool for solving integral equations. The method does not involve solving large arrays of simultaneous equations; rather, the simplified-Fredholm method provides an explicit solution. The solution consists of an infinite series with each term containing multiple integrals. It has been found, however, that the series can be safely truncated after about a dozen terms, and the multiple integrals can be resolved through repeated matrix multiplications, all of this leading to a practical methodology. Implicit in the method and highly useful in radiant analyses is the idea of the resolvent kernel, which permits generalized solutions to be obtained, independent of the forcing function. The method also adapts itself to a simple technique for establishing the possible error in any result. It is illustrated here on some enclosure problems that can be reduced to solving Fredholm's equation in a single variable. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Finite-volume formulation and solution of the P3 equations of radiative transfer on unstructured meshes / Mahesh Ravishankar in Journal of heat transfer, Vol. 132 N° 2 (n° spécial) (Fevrier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023402-1/14] Titre : Finite-volume formulation and solution of the P3 equations of radiative transfer on unstructured meshes Type de document : texte imprimé Auteurs : Mahesh Ravishankar, Auteur ; Sandip Mazumder, Auteur ; Ankan Kumar, Auteur Article en page(s) : pp. [023402-1/14] Note générale : Physique Langues : Anglais (eng) Mots-clés : Radiation  Participating  media  P3  RTE  solver  Finite-volume  Unstructured Index. décimale : 536 Chaleur. Thermodynamique Résumé : The method of spherical harmonics (or PN) is a popular method for approximate solution of the radiative transfer equation (RTE) in participating media. A rigorous conservative finite-volume (FV) procedure is presented for discretization of the P3 equations of radiative transfer in two-dimensional geometry—a set of four coupled, second-order partial differential equations. The FV procedure presented here is applicable to any arbitrary unstructured mesh topology. The resulting coupled set of discrete algebraic equations are solved implicitly using a coupled solver that involves decomposition of the computational domain into groups of geometrically contiguous cells using the binary spatial partitioning algorithm, followed by fully implicit coupled solution within each cell group using a preconditioned generalized minimum residual solver. The RTE solver is first verified by comparing predicted results with published Monte Carlo (MC) results for two benchmark problems. For completeness, results using the P1 approximation are also presented. As expected, results agree well with MC results for large/intermediate optical thicknesses, and the discrepancy between MC and P3 results increase as the optical thickness is decreased. The P3 approximation is found to be more accurate than the P1 approximation for optically thick cases. Finally, the new RTE solver is coupled to a reacting flow code and demonstrated for a laminar flame calculation using an unstructured mesh. It is found that the solution of the four P3 equations requires 14.5% additional CPU time, while the solution of the single P1 equation requires 9.3% additional CPU time over the case without radiation. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Finite-volume formulation and solution of the P3 equations of radiative transfer on unstructured meshes [texte imprimé] / Mahesh Ravishankar, Auteur ; Sandip Mazumder, Auteur ; Ankan Kumar, Auteur . - pp. [023402-1/14]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023402-1/14] Mots-clés : Radiation  Participating  media  P3  RTE  solver  Finite-volume  Unstructured Index. décimale : 536 Chaleur. Thermodynamique Résumé : The method of spherical harmonics (or PN) is a popular method for approximate solution of the radiative transfer equation (RTE) in participating media. A rigorous conservative finite-volume (FV) procedure is presented for discretization of the P3 equations of radiative transfer in two-dimensional geometry—a set of four coupled, second-order partial differential equations. The FV procedure presented here is applicable to any arbitrary unstructured mesh topology. The resulting coupled set of discrete algebraic equations are solved implicitly using a coupled solver that involves decomposition of the computational domain into groups of geometrically contiguous cells using the binary spatial partitioning algorithm, followed by fully implicit coupled solution within each cell group using a preconditioned generalized minimum residual solver. The RTE solver is first verified by comparing predicted results with published Monte Carlo (MC) results for two benchmark problems. For completeness, results using the P1 approximation are also presented. As expected, results agree well with MC results for large/intermediate optical thicknesses, and the discrepancy between MC and P3 results increase as the optical thickness is decreased. The P3 approximation is found to be more accurate than the P1 approximation for optically thick cases. Finally, the new RTE solver is coupled to a reacting flow code and demonstrated for a laminar flame calculation using an unstructured mesh. It is found that the solution of the four P3 equations requires 14.5% additional CPU time, while the solution of the single P1 equation requires 9.3% additional CPU time over the case without radiation. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

An efficient sparse finite element solver for the radiative transfer equatioe / Gisela Widmer in Journal of heat transfer, Vol. 132 N° 2 (n° spécial) (Fevrier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023403-1/7] Titre : An efficient sparse finite element solver for the radiative transfer equatioe Type de document : texte imprimé Auteurs : Gisela Widmer, Auteur Article en page(s) : pp. [023403-1/7] Note générale : Physique Langues : Anglais (eng) Mots-clés : Radiative  transfer  equation  Least-squares  finite  elements  Preconditioning  Sparse  grids Index. décimale : 536 Chaleur. Thermodynamique Résumé : The stationary monochromatic radiative transfer equation is posed in five dimensions, with the intensity depending on both a position in a three-dimensional domain as well as a direction. For nonscattering radiative transfer, sparse finite elements [2007, “Sparse Finite Elements for Non-Scattering Radiative Transfer in Diffuse Regimes,” ICHMT Fifth International Symposium of Radiative Transfer, Bodrum, Turkey; 2008, “Sparse Adaptive Finite Elements for Radiative Transfer,” J. Comput. Phys., 227(12), pp. 6071–6105] have been shown to be an efficient discretization strategy if the intensity function is sufficiently smooth. Compared with the discrete ordinates method, they make it possible to significantly reduce the number of degrees of freedom N in the discretization with almost no loss of accuracy. However, using a direct solver to solve the resulting linear system requires O(N3) operations. In this paper, an efficient solver based on the conjugate gradient method with a subspace correction preconditioner is presented. Numerical experiments show that the linear system can be solved at computational costs that are nearly proportional to the number of degrees of freedom N in the discretization. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] An efficient sparse finite element solver for the radiative transfer equatioe [texte imprimé] / Gisela Widmer, Auteur . - pp. [023403-1/7]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023403-1/7] Mots-clés : Radiative  transfer  equation  Least-squares  finite  elements  Preconditioning  Sparse  grids Index. décimale : 536 Chaleur. Thermodynamique Résumé : The stationary monochromatic radiative transfer equation is posed in five dimensions, with the intensity depending on both a position in a three-dimensional domain as well as a direction. For nonscattering radiative transfer, sparse finite elements [2007, “Sparse Finite Elements for Non-Scattering Radiative Transfer in Diffuse Regimes,” ICHMT Fifth International Symposium of Radiative Transfer, Bodrum, Turkey; 2008, “Sparse Adaptive Finite Elements for Radiative Transfer,” J. Comput. Phys., 227(12), pp. 6071–6105] have been shown to be an efficient discretization strategy if the intensity function is sufficiently smooth. Compared with the discrete ordinates method, they make it possible to significantly reduce the number of degrees of freedom N in the discretization with almost no loss of accuracy. However, using a direct solver to solve the resulting linear system requires O(N3) operations. In this paper, an efficient solver based on the conjugate gradient method with a subspace correction preconditioner is presented. Numerical experiments show that the linear system can be solved at computational costs that are nearly proportional to the number of degrees of freedom N in the discretization. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

A finite element treatment of the angular dependency of the even-parity equation of radiative transfer / R. Becker in Journal of heat transfer, Vol. 132 N° 2 (n° spécial) (Fevrier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023404-1/13] Titre : A finite element treatment of the angular dependency of the even-parity equation of radiative transfer Type de document : texte imprimé Auteurs : R. Becker, Auteur ; R. Koch, Auteur ; H.-J. Bauer, Auteur Article en page(s) : pp. [023404-1/13] Note générale : Physique Langues : Anglais (eng) Mots-clés : Finite  element  analysis  Heat  transfer  Radiative  transfer Index. décimale : 536 Chaleur. Thermodynamique Résumé : The present article introduces a new method to solve the radiative transfer equation (RTE). First, a finite element discretization of the solid angle dependence is derived, wherein the coefficients of the finite element approximation are functions of the spatial coordinates. The angular basis functions are defined according to finite element principles on subdivisions of the octahedron. In a second step, these spatially dependent coefficients are discretized by spatial finite elements. This approach is very attractive, since it provides a concise derivation for approximations of the angular dependence with an arbitrary number of angular nodes. In addition, the usage of high-order angular basis functions is straightforward. In the current paper, the governing equations are first derived independently of the actual angular approximation. Then, the design principles for the angular mesh are discussed and the parameterization of the piecewise angular basis functions is derived. In the following, the method is applied to one-dimensional and two-dimensional test cases, which are commonly used for the validation of approximation methods of the RTE. The results reveal that the proposed method is a promising alternative to the well-established practices like the discrete ordinates method (DOM) and provides highly accurate approximations. A test case, which is known to exhibit the ray effect in the DOM, verifies the ability of the new method to avoid ray effects. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] A finite element treatment of the angular dependency of the even-parity equation of radiative transfer [texte imprimé] / R. Becker, Auteur ; R. Koch, Auteur ; H.-J. Bauer, Auteur . - pp. [023404-1/13]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023404-1/13] Mots-clés : Finite  element  analysis  Heat  transfer  Radiative  transfer Index. décimale : 536 Chaleur. Thermodynamique Résumé : The present article introduces a new method to solve the radiative transfer equation (RTE). First, a finite element discretization of the solid angle dependence is derived, wherein the coefficients of the finite element approximation are functions of the spatial coordinates. The angular basis functions are defined according to finite element principles on subdivisions of the octahedron. In a second step, these spatially dependent coefficients are discretized by spatial finite elements. This approach is very attractive, since it provides a concise derivation for approximations of the angular dependence with an arbitrary number of angular nodes. In addition, the usage of high-order angular basis functions is straightforward. In the current paper, the governing equations are first derived independently of the actual angular approximation. Then, the design principles for the angular mesh are discussed and the parameterization of the piecewise angular basis functions is derived. In the following, the method is applied to one-dimensional and two-dimensional test cases, which are commonly used for the validation of approximation methods of the RTE. The results reveal that the proposed method is a promising alternative to the well-established practices like the discrete ordinates method (DOM) and provides highly accurate approximations. A test case, which is known to exhibit the ray effect in the DOM, verifies the ability of the new method to avoid ray effects. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Radiative transfer in dispersed media / Jaona Randrianalisoa in Journal of heat transfer, Vol. 132 N° 2 (n° spécial) (Fevrier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023405-1/11] Titre : Radiative transfer in dispersed media : comparison between homogeneous phase and multiphase approaches Type de document : texte imprimé Auteurs : Jaona Randrianalisoa, Auteur ; Dominique Baillis, Auteur Article en page(s) : pp. [023405-1/11] Note générale : Physique Langues : Anglais (eng) Mots-clés : Radiative  transfer  Dispersed  media  Opaque  particles  Semitransparent  particles  Ray-tracing  Monte  Carlo  Transmittances  Reflectances Index. décimale : 536 Chaleur. Thermodynamique Résumé : The radiative transfer in dispersed media in the geometric optic regime is investigated through two continuum-based approaches. The first one is the traditional treatment of dispersed media as continuous and homogeneous systems, referred here as the homogeneous phase approach (HPA). The second approach is based on a separate treatment of the radiative transfer in the continuous and dispersed phases, referred here as the multiphase approach (MPA). The effective radiative properties involved in the framework of the HPA are determined using the recent ray-tracing (RT) method, enabled to overcome the modeling difficulties such as the dependent scattering effects and the misunderstanding of the effective absorption coefficient. The two modeling approaches are compared with the direct Monte Carlo simulation. It is shown that (i) the HPA combined with effective radiative properties, such as those from the RT method, is satisfactory in analyzing the radiative transfer in dispersed media constituting of transparent, semitransparent, or opaque particles. Therefore, the use of more complex continuum models such as the dependence included discrete ordinate method (Singh, B. P., and Kaviany, M., 1992, “Modelling Radiative Heat Transfer in Packed Beds,” Int. J. Heat Mass Transfer, 35, pp. 1397–1405) is not imperative anymore. (ii) The MPA, though a possible candidate to handle nonequilibrium problems, is suitable if the particle (geometric) backscattering is weak or absent. It is the case, for example, for dispersed media constituted of opaque particles or air bubbles. However, caution should be taken with the MPA when dealing with the radiative transfer in dispersed media constituted of nonopaque particles having refractive indexes greater than that of the continuous host medium. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Radiative transfer in dispersed media : comparison between homogeneous phase and multiphase approaches [texte imprimé] / Jaona Randrianalisoa, Auteur ; Dominique Baillis, Auteur . - pp. [023405-1/11]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023405-1/11] Mots-clés : Radiative  transfer  Dispersed  media  Opaque  particles  Semitransparent  particles  Ray-tracing  Monte  Carlo  Transmittances  Reflectances Index. décimale : 536 Chaleur. Thermodynamique Résumé : The radiative transfer in dispersed media in the geometric optic regime is investigated through two continuum-based approaches. The first one is the traditional treatment of dispersed media as continuous and homogeneous systems, referred here as the homogeneous phase approach (HPA). The second approach is based on a separate treatment of the radiative transfer in the continuous and dispersed phases, referred here as the multiphase approach (MPA). The effective radiative properties involved in the framework of the HPA are determined using the recent ray-tracing (RT) method, enabled to overcome the modeling difficulties such as the dependent scattering effects and the misunderstanding of the effective absorption coefficient. The two modeling approaches are compared with the direct Monte Carlo simulation. It is shown that (i) the HPA combined with effective radiative properties, such as those from the RT method, is satisfactory in analyzing the radiative transfer in dispersed media constituting of transparent, semitransparent, or opaque particles. Therefore, the use of more complex continuum models such as the dependence included discrete ordinate method (Singh, B. P., and Kaviany, M., 1992, “Modelling Radiative Heat Transfer in Packed Beds,” Int. J. Heat Mass Transfer, 35, pp. 1397–1405) is not imperative anymore. (ii) The MPA, though a possible candidate to handle nonequilibrium problems, is suitable if the particle (geometric) backscattering is weak or absent. It is the case, for example, for dispersed media constituted of opaque particles or air bubbles. However, caution should be taken with the MPA when dealing with the radiative transfer in dispersed media constituted of nonopaque particles having refractive indexes greater than that of the continuous host medium. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Spectral module for photon Monte Carlo calculations in hypersonic nonequilibrium radiation / Takashi Ozawa in Journal of heat transfer, Vol. 132 N° 2 (n° spécial) (Fevrier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023406-1/8] Titre : Spectral module for photon Monte Carlo calculations in hypersonic nonequilibrium radiation Type de document : texte imprimé Auteurs : Takashi Ozawa, Auteur ; Michael F. Modest, Auteur ; Deborah A. Levin, Auteur Article en page(s) : pp. [023406-1/8] Note générale : Physique Langues : Anglais (eng) Mots-clés : Monte  Carlo  methods  Nonequilibrium  Radiation  QSS  Hypersonic  flow  Absorption  coefficients  Flow  simulation  Molecular  electronic  states Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this paper, efficient spectral modules and random number databases are developed for atomic and diatomic species for use in photon Monte Carlo (PMC) modeling of hypersonic nonequilibrium flow radiation. To model nonequilibrium flow conditions, the quasisteady state assumption was used to generate electronic state populations of atomic and diatomic gas species in the databases. For atomic species (N and O), both bound-bound transitions and continuum radiation were included and were separately databased as a function of electron temperature and number density as well as the ratio of atomic ion to neutral number density. For the radiating diatomic species of N2+, N2, O2, and NO databases were generated for each electronic molecular electronic system. In each molecular electronic system, the rovibrational transition lines were separately databased for each electronic upper state population forming the electronic system. The spectral module for the PMC method was optimized toward computational efficiency for emission calculations, wavelength selections of photon bundles and absorption coefficient calculations in the ray tracing scheme. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Spectral module for photon Monte Carlo calculations in hypersonic nonequilibrium radiation [texte imprimé] / Takashi Ozawa, Auteur ; Michael F. Modest, Auteur ; Deborah A. Levin, Auteur . - pp. [023406-1/8]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023406-1/8] Mots-clés : Monte  Carlo  methods  Nonequilibrium  Radiation  QSS  Hypersonic  flow  Absorption  coefficients  Flow  simulation  Molecular  electronic  states Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this paper, efficient spectral modules and random number databases are developed for atomic and diatomic species for use in photon Monte Carlo (PMC) modeling of hypersonic nonequilibrium flow radiation. To model nonequilibrium flow conditions, the quasisteady state assumption was used to generate electronic state populations of atomic and diatomic gas species in the databases. For atomic species (N and O), both bound-bound transitions and continuum radiation were included and were separately databased as a function of electron temperature and number density as well as the ratio of atomic ion to neutral number density. For the radiating diatomic species of N2+, N2, O2, and NO databases were generated for each electronic molecular electronic system. In each molecular electronic system, the rovibrational transition lines were separately databased for each electronic upper state population forming the electronic system. The spectral module for the PMC method was optimized toward computational efficiency for emission calculations, wavelength selections of photon bundles and absorption coefficient calculations in the ray tracing scheme. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

A numerical simulation of combined radiation and natural convection in a differential heated cubic cavity / P. Kumar in Journal of heat transfer, Vol. 132 N° 2 (n° spécial) (Fevrier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023501-1/13] Titre : A numerical simulation of combined radiation and natural convection in a differential heated cubic cavity Type de document : texte imprimé Auteurs : P. Kumar, Auteur ; V. Eswaran, Auteur Article en page(s) : pp. [023501-1/13] Note générale : Physique Langues : Anglais (eng) Mots-clés : Multimode  heat  transfer  Rdiative  heat  transfer  Transparent  and  participating  medium  Three-dimensional  natural  convection  Variable  density  formulation Index. décimale : 536 Chaleur. Thermodynamique Résumé : This article presents a numerical simulation of combined radiation and natural convection in a three-dimensional differentially heated rectangular cavity with two opposite side walls kept at a temperature ratio Th/Tc=2.0 and Tc=500 K, with others walls insulated. A non-Boussinesq variable density approach is used to incorporate density changes due to temperature variation. The Navier–Stokes (NSE), temperature, as well as the radiative transfer (RTE) equations are solved numerically by a finite volume method, with constant thermophysical fluid properties (except density) for Rayleigh number Ra=105 and Prandtl number Pr=0.71. The convective, radiative, and total heat transfer on the isothermal and adiabatic walls is studied along with the flow phenomena. The results reveal an extraordinarily complex flow field, wherein, along with the main flow, many secondary flow regions and singular points exist at the different planes and are affected by the optical properties of the fluid. The heat transfer decreases with increase in optical thickness and the pure convection Nusselt number is approached as the optical thickness tau>100, but with substantially different velocity field. The wall emissivity has a strong influence on the heat transfer but the scattering albedo does not. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] A numerical simulation of combined radiation and natural convection in a differential heated cubic cavity [texte imprimé] / P. Kumar, Auteur ; V. Eswaran, Auteur . - pp. [023501-1/13]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023501-1/13] Mots-clés : Multimode  heat  transfer  Rdiative  heat  transfer  Transparent  and  participating  medium  Three-dimensional  natural  convection  Variable  density  formulation Index. décimale : 536 Chaleur. Thermodynamique Résumé : This article presents a numerical simulation of combined radiation and natural convection in a three-dimensional differentially heated rectangular cavity with two opposite side walls kept at a temperature ratio Th/Tc=2.0 and Tc=500 K, with others walls insulated. A non-Boussinesq variable density approach is used to incorporate density changes due to temperature variation. The Navier–Stokes (NSE), temperature, as well as the radiative transfer (RTE) equations are solved numerically by a finite volume method, with constant thermophysical fluid properties (except density) for Rayleigh number Ra=105 and Prandtl number Pr=0.71. The convective, radiative, and total heat transfer on the isothermal and adiabatic walls is studied along with the flow phenomena. The results reveal an extraordinarily complex flow field, wherein, along with the main flow, many secondary flow regions and singular points exist at the different planes and are affected by the optical properties of the fluid. The heat transfer decreases with increase in optical thickness and the pure convection Nusselt number is approached as the optical thickness tau>100, but with substantially different velocity field. The wall emissivity has a strong influence on the heat transfer but the scattering albedo does not. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

An extension of the large-cell radiation model for the case of semitransparent nonisothermal particles / Leonid A. Dombrovsky in Journal of heat transfer, Vol. 132 N° 2 (n° spécial) (Fevrier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023502-1/8] Titre : An extension of the large-cell radiation model for the case of semitransparent nonisothermal particles Type de document : texte imprimé Auteurs : Leonid A. Dombrovsky, Auteur Article en page(s) : pp. [023502-1/8] Note générale : Physique Langues : Anglais (eng) Mots-clés : Thermal  radiation  Multiphase  flow  Melt-coolant  interaction  Combined  heat  transfer  Semitransparent  particle  Solidification Index. décimale : 536 Chaleur. Thermodynamique Résumé : The recently developed model for thermal radiation in multiphase flows typical of melt-coolant interactions is generalized to account for transient temperature profile in large semitransparent particles of solidifying melt. A modification of the large-cell radiation model (LCRM) is based on the approximate solution for coupled radiation and conduction in optically thick spherical particles of a refractive material. The simplicity of the suggested approximation enables one to implement the modified model in a multiphase computational fluid dynamics code. The LCRM extension makes possible the use of this approach not only for the core melt in nuclear fuel-coolant interactions but also for other melt substances, which are widely used in the laboratory experiments. The numerical data demonstrate an effect of absorption coefficient of the particle substance on the rate of particle cooling and solidification. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] An extension of the large-cell radiation model for the case of semitransparent nonisothermal particles [texte imprimé] / Leonid A. Dombrovsky, Auteur . - pp. [023502-1/8]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023502-1/8] Mots-clés : Thermal  radiation  Multiphase  flow  Melt-coolant  interaction  Combined  heat  transfer  Semitransparent  particle  Solidification Index. décimale : 536 Chaleur. Thermodynamique Résumé : The recently developed model for thermal radiation in multiphase flows typical of melt-coolant interactions is generalized to account for transient temperature profile in large semitransparent particles of solidifying melt. A modification of the large-cell radiation model (LCRM) is based on the approximate solution for coupled radiation and conduction in optically thick spherical particles of a refractive material. The simplicity of the suggested approximation enables one to implement the modified model in a multiphase computational fluid dynamics code. The LCRM extension makes possible the use of this approach not only for the core melt in nuclear fuel-coolant interactions but also for other melt substances, which are widely used in the laboratory experiments. The numerical data demonstrate an effect of absorption coefficient of the particle substance on the rate of particle cooling and solidification. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Effect on radiant heat transfer at the surface of a pool fire interacting with a water mist / J. P. Garo in Journal of heat transfer, Vol. 132 N° 2 (n° spécial) (Fevrier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023503-1/9] Titre : Effect on radiant heat transfer at the surface of a pool fire interacting with a water mist Type de document : texte imprimé Auteurs : J. P. Garo, Auteur ; J. P. Vantelon, Auteur ; D. Lemonnier, Auteur Article en page(s) : pp. [023503-1/9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Pool  fire  Fire  suppression  Water  mist  Radiation Index. décimale : 536 Chaleur. Thermodynamique Résumé : It is well established that the use of water mist can be an attractive alternative to gaseous suppression agents to extinguish fires for specific scenarios. Among the main mechanisms, which act together to extinguish fires when using a water mist: heat extraction, oxygen displacement, and radiant heat attenuation, the last one has received the less attention, especially regarding the energy balance at the fuel surface and, therefore, the rate of generation of flammable vapors. The objective of this work is to analyze, on the one hand, the perturbing influence of a mist addition as an opposed flow to a small-scale liquid (heptane) pool fire structure, especially at its base, the more interesting zone regarding the mechanisms of flame stabilization and extinction and, on the other hand, the effect on the surface radiant heat feedback. Experiments conducted give an order of magnitude estimate in essential agreement with a radiation computation, based on the mappings, previously obtained, of the two major parameters: temperature and extinction coefficient, that determine the thermal radiation of the flame. The important information is the confirmation that radiation attenuation cannot be identified as a predominant mechanism of extinguishment. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Effect on radiant heat transfer at the surface of a pool fire interacting with a water mist [texte imprimé] / J. P. Garo, Auteur ; J. P. Vantelon, Auteur ; D. Lemonnier, Auteur . - pp. [023503-1/9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023503-1/9] Mots-clés : Pool  fire  Fire  suppression  Water  mist  Radiation Index. décimale : 536 Chaleur. Thermodynamique Résumé : It is well established that the use of water mist can be an attractive alternative to gaseous suppression agents to extinguish fires for specific scenarios. Among the main mechanisms, which act together to extinguish fires when using a water mist: heat extraction, oxygen displacement, and radiant heat attenuation, the last one has received the less attention, especially regarding the energy balance at the fuel surface and, therefore, the rate of generation of flammable vapors. The objective of this work is to analyze, on the one hand, the perturbing influence of a mist addition as an opposed flow to a small-scale liquid (heptane) pool fire structure, especially at its base, the more interesting zone regarding the mechanisms of flame stabilization and extinction and, on the other hand, the effect on the surface radiant heat feedback. Experiments conducted give an order of magnitude estimate in essential agreement with a radiation computation, based on the mappings, previously obtained, of the two major parameters: temperature and extinction coefficient, that determine the thermal radiation of the flame. The important information is the confirmation that radiation attenuation cannot be identified as a predominant mechanism of extinguishment. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Fixed grid simulation of radiation-conduction dominated solidification process / Piotr Lapka in Journal of heat transfer, Vol. 132 N° 2 (n° spécial) (Fevrier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023504 -1/10] Titre : Fixed grid simulation of radiation-conduction dominated solidification process Type de document : texte imprimé Auteurs : Piotr Lapka, Auteur ; Piotr Furmanski, Auteur Article en page(s) : pp. [023504 -1/10] Note générale : Physique Langues : Anglais (eng) Mots-clés : Semitransparent  material  Solidification  Thermal  radiation  Conduction-radiation  heat  transfer Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this paper conduction-radiation controlled solidification process of semitransparent materials was numerically analyzed. New approach in this kind of simulations, which is based on the fixed grid front tracking method combined with the immersed boundary technique, was adopted and examined. The presented method enables accurate dealing with solidification processes of semitransparent materials which have different optical and thermophysical properties of solid and liquid phases as well as with absorption, emission, and reflection of the thermal radiation at the solid-liquid interface without applying moving mesh methods. The proposed numerical approach was examined by solving several simplified thermal radiation problems with complex fixed and moving boundaries both in two-dimensional and axisymmetric spaces. For some of them the accuracy of obtained results was proved by comparing with reference works, other showed capabilities of the proposed method. For simplified solidification processes of semitransparent materials three configurations of optical properties, i.e., semitransparent solid phase and opaque liquid phase, opaque solid phase and semitransparent liquid phase, and semitransparent both phases were considered. The interface between solid and liquid phases was treated to be opaque, absorbing, emitting, and reflecting diffusely the thermal radiation. Results of the numerical simulations show that the presented numerical approach works well in this kind of problems and is promising for simulation of real solidification processes of semitransparent materials. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Fixed grid simulation of radiation-conduction dominated solidification process [texte imprimé] / Piotr Lapka, Auteur ; Piotr Furmanski, Auteur . - pp. [023504 -1/10]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023504 -1/10] Mots-clés : Semitransparent  material  Solidification  Thermal  radiation  Conduction-radiation  heat  transfer Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this paper conduction-radiation controlled solidification process of semitransparent materials was numerically analyzed. New approach in this kind of simulations, which is based on the fixed grid front tracking method combined with the immersed boundary technique, was adopted and examined. The presented method enables accurate dealing with solidification processes of semitransparent materials which have different optical and thermophysical properties of solid and liquid phases as well as with absorption, emission, and reflection of the thermal radiation at the solid-liquid interface without applying moving mesh methods. The proposed numerical approach was examined by solving several simplified thermal radiation problems with complex fixed and moving boundaries both in two-dimensional and axisymmetric spaces. For some of them the accuracy of obtained results was proved by comparing with reference works, other showed capabilities of the proposed method. For simplified solidification processes of semitransparent materials three configurations of optical properties, i.e., semitransparent solid phase and opaque liquid phase, opaque solid phase and semitransparent liquid phase, and semitransparent both phases were considered. The interface between solid and liquid phases was treated to be opaque, absorbing, emitting, and reflecting diffusely the thermal radiation. Results of the numerical simulations show that the presented numerical approach works well in this kind of problems and is promising for simulation of real solidification processes of semitransparent materials. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Heat transfer augmentation / Andreas Hantsch in Journal of heat transfer, Vol. 132 N° 2 (n° spécial) (Fevrier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023505-1/6] Titre : Heat transfer augmentation : radiative-convective heat transfer in a tube with fiber array inserts Type de document : texte imprimé Auteurs : Andreas Hantsch, Auteur ; Ulrich Gross, Auteur ; Andrew R. Martin, Auteur Article en page(s) : pp. [023505-1/6] Note générale : Physique Langues : Anglais (eng) Mots-clés : Convection  Porosity  Silicon  compounds  Stainless  steel  Turbulence Index. décimale : 536 Chaleur. Thermodynamique Résumé : Gas-phase heat transfer plays a critical role in many high temperature applications, such as preheaters, combustors, and other thermal equipment. In such cases common heat transfer augmentation methods rely on the convective component alone to achieve improved internal performance. Radiatively assisted heat transfer augmentation has been suggested as a way to overcome limitations in convective-only enhancement. One example of such a technique is the fiber array insert; thermal radiation emitted by tube walls is captured by a large number of slender fibers, which in turn convect heat to the flowing fluid. Previous numerical studies have indicated that this technique represents a promising enhancement method warranting further investigation. This paper presents results from an experimentally based feasibility study of fiber array inserts for heat transfer augmentation in an externally heated duct. Fibers composed of 140 µm silicon carbide and 150 µm stainless steel were assembled in arrays with porosities around 0.98, and were tested for empty-tube Reynolds numbers ranging from 17,500 to 112,500 and wall temperatures from ambient up to 750°C. The arrays cause a significant pressure drop—roughly two orders of magnitude higher than the empty-tube case—but tube-side heat transfer coefficients were improved by up to 100% over the convective-only case in the low flow rate regime. The stainless steel fiber array exhibited similar heat transfer performance as the silicon carbide case, although pressure drop characteristics differed owing to variations in fluid-structure flow phenomena. Pressure drop data were roughly within the range of d'Arcy law predictions for both arrays, and deviations could be explained by inhomogeneities in fiber-to-fiber spacing. Heat transfer was found to depend nonlinearly on wall temperature and flow rate, in contrast to previously reported numerical data. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Heat transfer augmentation : radiative-convective heat transfer in a tube with fiber array inserts [texte imprimé] / Andreas Hantsch, Auteur ; Ulrich Gross, Auteur ; Andrew R. Martin, Auteur . - pp. [023505-1/6]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 2 (n° spécial) (Fevrier 2010) . - pp. [023505-1/6] Mots-clés : Convection  Porosity  Silicon  compounds  Stainless  steel  Turbulence Index. décimale : 536 Chaleur. Thermodynamique Résumé : Gas-phase heat transfer plays a critical role in many high temperature applications, such as preheaters, combustors, and other thermal equipment. In such cases common heat transfer augmentation methods rely on the convective component alone to achieve improved internal performance. Radiatively assisted heat transfer augmentation has been suggested as a way to overcome limitations in convective-only enhancement. One example of such a technique is the fiber array insert; thermal radiation emitted by tube walls is captured by a large number of slender fibers, which in turn convect heat to the flowing fluid. Previous numerical studies have indicated that this technique represents a promising enhancement method warranting further investigation. This paper presents results from an experimentally based feasibility study of fiber array inserts for heat transfer augmentation in an externally heated duct. Fibers composed of 140 µm silicon carbide and 150 µm stainless steel were assembled in arrays with porosities around 0.98, and were tested for empty-tube Reynolds numbers ranging from 17,500 to 112,500 and wall temperatures from ambient up to 750°C. The arrays cause a significant pressure drop—roughly two orders of magnitude higher than the empty-tube case—but tube-side heat transfer coefficients were improved by up to 100% over the convective-only case in the low flow rate regime. The stainless steel fiber array exhibited similar heat transfer performance as the silicon carbide case, although pressure drop characteristics differed owing to variations in fluid-structure flow phenomena. Pressure drop data were roughly within the range of d'Arcy law predictions for both arrays, and deviations could be explained by inhomogeneities in fiber-to-fiber spacing. Heat transfer was found to depend nonlinearly on wall temperature and flow rate, in contrast to previously reported numerical data. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

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