Documents disponibles écrits par cet auteur

A level set method coupled with a volume of fluid method for modeling of gas-liquid interface in bubbly flow / Bogdan A. Nichita in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 8 (Août 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 8 (Août 2010) . - 15 p. Titre : A level set method coupled with a volume of fluid method for modeling of gas-liquid interface in bubbly flow Type de document : texte imprimé Auteurs : Bogdan A. Nichita, Auteur ; Iztok Zun, Auteur ; John R. Thome, Auteur Année de publication : 2010 Article en page(s) : 15 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : surface  tension;  fluids;  bubbles;  engineering  simulation;  equations Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : This paper describes the implementation of a 3D parallel and Cartesian level set (LS) method coupled with a volume of fluid (VOF) method into the commercial CFD code FLUENT for modeling the gas-liquid interface in bubbly flow. Both level set and volume of fluid methods belong to the so called “one” fluid methods, where a single set of conservation equations is solved and the interface is captured via a scalar function. Since both LS and VOF have advantages and disadvantages, our aim is to couple these two methods to obtain a method, which is superior to both standalone LS and VOF and verify it versus a selection of test cases. VOF is already available in FLUENT , so we implemented an LS method into FLUENT via user defined functions. The level set function is used to compute the surface tension contribution to the momentum equations, via curvature and its normal to the interface, using the Brackbill method while the volume of fluid function is used to capture the interface itself. A re-initialization equation is implemented and solved at every time step using a fifth-order weighted essentially nonoscillatory scheme for the spatial derivative, and a first-order Euler method for time integration. The coupling effect is introduced by solving at the end of each time step an equation, which connects the volume fractions with the level set function. The verification of parasitic currents and interfacial deformation due to numerical error is assessed in comparison to original VOF scheme. Validation is presented for free rising bubbles of different diameters for Morton numbers ranging from 102 to 10−11. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] A level set method coupled with a volume of fluid method for modeling of gas-liquid interface in bubbly flow [texte imprimé] / Bogdan A. Nichita, Auteur ; Iztok Zun, Auteur ; John R. Thome, Auteur . - 2010 . - 15 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 8 (Août 2010) . - 15 p. Mots-clés : surface  tension;  fluids;  bubbles;  engineering  simulation;  equations Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : This paper describes the implementation of a 3D parallel and Cartesian level set (LS) method coupled with a volume of fluid (VOF) method into the commercial CFD code FLUENT for modeling the gas-liquid interface in bubbly flow. Both level set and volume of fluid methods belong to the so called “one” fluid methods, where a single set of conservation equations is solved and the interface is captured via a scalar function. Since both LS and VOF have advantages and disadvantages, our aim is to couple these two methods to obtain a method, which is superior to both standalone LS and VOF and verify it versus a selection of test cases. VOF is already available in FLUENT , so we implemented an LS method into FLUENT via user defined functions. The level set function is used to compute the surface tension contribution to the momentum equations, via curvature and its normal to the interface, using the Brackbill method while the volume of fluid function is used to capture the interface itself. A re-initialization equation is implemented and solved at every time step using a fifth-order weighted essentially nonoscillatory scheme for the spatial derivative, and a first-order Euler method for time integration. The coupling effect is introduced by solving at the end of each time step an equation, which connects the volume fractions with the level set function. The verification of parasitic currents and interfacial deformation due to numerical error is assessed in comparison to original VOF scheme. Validation is presented for free rising bubbles of different diameters for Morton numbers ranging from 102 to 10−11. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Numerical modeling of the conjugate heat transfer problem for annular laminar film condensation in microchannels / Stefano Nebuloni in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 07 p. Titre : Numerical modeling of the conjugate heat transfer problem for annular laminar film condensation in microchannels Type de document : texte imprimé Auteurs : Stefano Nebuloni, Auteur ; John R. Thome, Auteur Année de publication : 2012 Article en page(s) : 07 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : condensation;  numerical  model;  conjugate  heat  transfer;  annular  flow;  microchannel Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper presents numerical simulations of annular laminar film condensation heat transfer in microchannels of different internal shapes. The model, which is based on a finite volume formulation of the Navier–Stokes and energy equations for the liquid phase only, importantly accounts for the effects of axial and peripheral wall conduction and nonuniform heat flux not included in other models so far in the literature. The contributions of the surface tension, axial shear stresses, and gravitational forces are included. This model has so far been validated versus various benchmark cases and versus experimental data available in literature, predicting microchannel heat transfer data with an average error of 20% or better. It is well known that the thinning of the condensate film induced by surface tension due to gravity forces and shape of the surface, also known as the “Gregorig” effect, has a strong consequence on the local heat transfer coefficient in condensation. Thus, the present model accounts for these effects on the heat transfer and pressure drop for a wide variety of geometrical shapes, sizes, wall materials, and working fluid properties. In this paper, the conjugate heat transfer problem arising from the coupling between the thin film fluid dynamics, the heat transfer in the condensing fluid, and the heat conduction in the channel wall has been studied. In particular, the work has focused on three external channel wall boundary conditions: a uniform wall temperature, a nonuniform wall heat flux, and single-phase convective cooling are presented. As the scale of the problem is reduced, i.e., when moving from mini- to microchannels, the results show that the axial conduction effects can become very important in the prediction of the wall temperature profile and the magnitude of the heat transfer coefficient and its distribution along the channel. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Numerical modeling of the conjugate heat transfer problem for annular laminar film condensation in microchannels [texte imprimé] / Stefano Nebuloni, Auteur ; John R. Thome, Auteur . - 2012 . - 07 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 07 p. Mots-clés : condensation;  numerical  model;  conjugate  heat  transfer;  annular  flow;  microchannel Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper presents numerical simulations of annular laminar film condensation heat transfer in microchannels of different internal shapes. The model, which is based on a finite volume formulation of the Navier–Stokes and energy equations for the liquid phase only, importantly accounts for the effects of axial and peripheral wall conduction and nonuniform heat flux not included in other models so far in the literature. The contributions of the surface tension, axial shear stresses, and gravitational forces are included. This model has so far been validated versus various benchmark cases and versus experimental data available in literature, predicting microchannel heat transfer data with an average error of 20% or better. It is well known that the thinning of the condensate film induced by surface tension due to gravity forces and shape of the surface, also known as the “Gregorig” effect, has a strong consequence on the local heat transfer coefficient in condensation. Thus, the present model accounts for these effects on the heat transfer and pressure drop for a wide variety of geometrical shapes, sizes, wall materials, and working fluid properties. In this paper, the conjugate heat transfer problem arising from the coupling between the thin film fluid dynamics, the heat transfer in the condensing fluid, and the heat conduction in the channel wall has been studied. In particular, the work has focused on three external channel wall boundary conditions: a uniform wall temperature, a nonuniform wall heat flux, and single-phase convective cooling are presented. As the scale of the problem is reduced, i.e., when moving from mini- to microchannels, the results show that the axial conduction effects can become very important in the prediction of the wall temperature profile and the magnitude of the heat transfer coefficient and its distribution along the channel. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Two-phase flow pressure drops in U-tubes / Ricardo J. da Silva Lima in International journal of refrigeration, Vol. 36 N° 2 (N° spécial) (Mars 2013) 

Public ISBD [article]  in International journal of refrigeration > Vol. 36 N° 2 (N° spécial) (Mars 2013) . - pp. 492–503 Titre : Two-phase flow pressure drops in U-tubes : Towards more accurate measurement methods and prediction models Titre original : Chutes de pression diphasiques à l'intérieur des tubes en U: développement de méthodes de mesure et de modèles prévisionnels plus précis Type de document : texte imprimé Auteurs : Ricardo J. da Silva Lima, Auteur ; John R. Thome, Auteur Année de publication : 2013 Article en page(s) : pp. 492–503 Note générale : Refrigeration Langues : Anglais (eng) Mots-clés : U-bend;  U-tube;  Experimental;  Flow  pattern;  Visualization;  Two-phase;  Frictional  pressure  drop Résumé : In this study, flow pattern observations and pressure drop measurements in a U-bend and contiguous straight tubes are presented. The flow pattern observations were made with R134a at an inlet saturation temperature of 5 °C flowing at a mass flux of 300 kg s−1 m−2 inside a horizontal test section with an internal and bend diameters of 13 and 66 mm, respectively. The experimental data were obtained for the same experimental conditions, but with two test sections with one internal diameter of 11.7 mm and two bend diameters (31.7 and 54.8 mm) for different U-bend orientations. The experimental data was compared to the predictions of a new multi-orientation flow pattern based frictional pressure drop method for U-bends of Silva Lima and Thome (2012c) showing that the model predicts 97% of the database within an error window of ±30%. An extensive discussion was made on the benefits of using a data reduction method that allows obtaining the pressure drops effectively occurring in the U-bend and reducing the errors associated with that measure. En ligne : http://www.sciencedirect.com/science/article/pii/S0140700712003489 [article] Two-phase flow pressure drops in U-tubes = Chutes de pression diphasiques à l'intérieur des tubes en U: développement de méthodes de mesure et de modèles prévisionnels plus précis : Towards more accurate measurement methods and prediction models [texte imprimé] / Ricardo J. da Silva Lima, Auteur ; John R. Thome, Auteur . - 2013 . - pp. 492–503. Refrigeration Langues : Anglais (eng) in International journal of refrigeration > Vol. 36 N° 2 (N° spécial) (Mars 2013) . - pp. 492–503 Mots-clés : U-bend;  U-tube;  Experimental;  Flow  pattern;  Visualization;  Two-phase;  Frictional  pressure  drop Résumé : In this study, flow pattern observations and pressure drop measurements in a U-bend and contiguous straight tubes are presented. The flow pattern observations were made with R134a at an inlet saturation temperature of 5 °C flowing at a mass flux of 300 kg s−1 m−2 inside a horizontal test section with an internal and bend diameters of 13 and 66 mm, respectively. The experimental data were obtained for the same experimental conditions, but with two test sections with one internal diameter of 11.7 mm and two bend diameters (31.7 and 54.8 mm) for different U-bend orientations. The experimental data was compared to the predictions of a new multi-orientation flow pattern based frictional pressure drop method for U-bends of Silva Lima and Thome (2012c) showing that the model predicts 97% of the database within an error window of ±30%. An extensive discussion was made on the benefits of using a data reduction method that allows obtaining the pressure drops effectively occurring in the U-bend and reducing the errors associated with that measure. En ligne : http://www.sciencedirect.com/science/article/pii/S0140700712003489