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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= [...]

Scale effects in generalized Newtonian elastohydrodynamic films / Ilya I. Kudish in Transactions of the ASME . Journal of tribology, Vol. 130 N° 4 (Octobre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 N° 4 (Octobre 2008) . - 8 p. Titre : Scale effects in generalized Newtonian elastohydrodynamic films Type de document : texte imprimé Auteurs : Ilya I. Kudish, Auteur ; P. Kumar, Auteur ; M. M. Khonsari, Auteur Article en page(s) : 8 p. Note générale : Tribologgy Langues : Anglais (eng) Mots-clés : Pressure  Viscosity  Lubricants  Shear  (Mechanics)  Film  thickness  Rheology  Fluids Résumé : The estimation or prediction of elastohydrodynamic lubrication (EHL) film thickness requires knowledge of the lubricant properties. Today, in many instances, the lubricant properties have been obtained from a measurement of the central film thickness and the assumption of a classical Newtonian film-thickness formula. This technique has the practical advantage of using an effective pressure-viscosity coefficient, which compensates for shear-thinning. We have shown by a perturbation analysis of limiting cases for fluid with Carreau rheology (represented by Newtonian and power fluid) and by a full EHL numerical solution for Carreau fluid that the practice of extrapolating from a laboratory scale measurement of film thickness to the film thickness of an operating contact may substantially overestimate the film thickness in the real machine if the machine scale is smaller and the lubricant is shear-thinning within the inlet zone. The intention here is to show that errors result from extrapolation of Newtonian formulas to different scale and not to provide advice regarding quantitative engineering calculations. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468110 [article] Scale effects in generalized Newtonian elastohydrodynamic films [texte imprimé] / Ilya I. Kudish, Auteur ; P. Kumar, Auteur ; M. M. Khonsari, Auteur . - 8 p. Tribologgy Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 N° 4 (Octobre 2008) . - 8 p. Mots-clés : Pressure  Viscosity  Lubricants  Shear  (Mechanics)  Film  thickness  Rheology  Fluids Résumé : The estimation or prediction of elastohydrodynamic lubrication (EHL) film thickness requires knowledge of the lubricant properties. Today, in many instances, the lubricant properties have been obtained from a measurement of the central film thickness and the assumption of a classical Newtonian film-thickness formula. This technique has the practical advantage of using an effective pressure-viscosity coefficient, which compensates for shear-thinning. We have shown by a perturbation analysis of limiting cases for fluid with Carreau rheology (represented by Newtonian and power fluid) and by a full EHL numerical solution for Carreau fluid that the practice of extrapolating from a laboratory scale measurement of film thickness to the film thickness of an operating contact may substantially overestimate the film thickness in the real machine if the machine scale is smaller and the lubricant is shear-thinning within the inlet zone. The intention here is to show that errors result from extrapolation of Newtonian formulas to different scale and not to provide advice regarding quantitative engineering calculations. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468110