Dépouillements

Entropy generation in thin films evaluated from phonon radiative transport / T. J. Bright in Journal of heat transfer, Vol. 132 N° 10 (Octobre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [101301-1/9] Titre : Entropy generation in thin films evaluated from phonon radiative transport Type de document : texte imprimé Auteurs : T. J. Bright, Auteur ; Z. M. Zhang, Auteur Année de publication : 2010 Article en page(s) : pp. [101301-1/9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Conduction  Entropy  Phonon  radiative  transfer  Thermodynamics  Thin  film Index. décimale : 536 Chaleur. Thermodynamique Résumé : One of the approaches for micro/nanoscale heat transfer in semiconductors and dielectric materials is to use the Boltzmann transport equation, which reduces to the equation of phonon radiative transfer under the relaxation time approximation. Transfer and generation of entropy are processes inherently associated with thermal energy transport, yet little has been done to analyze entropy generation in solids at length scales comparable with or smaller than the mean free path of heat carriers. This work extends the concept of radiation entropy in a participating medium to phonon radiation, thus, providing a method to evaluate entropy generation at both large and small length scales. The conventional formula for entropy generation in heat diffusion can be derived under the local equilibrium assumption. Furthermore, the phonon brightness temperature is introduced to describe the nature of nonequilibrium heat conduction. A diamond film is used as a numerical example to illustrate the distribution of entropy generation at the walls and inside the film at low temperatures. A fundamental knowledge of the entropy generation processes provides a thermodynamic understanding of heat transport in solid microstructures; this is particularly important for the performance evaluation of thermal systems and microdevices. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Entropy generation in thin films evaluated from phonon radiative transport [texte imprimé] / T. J. Bright, Auteur ; Z. M. Zhang, Auteur . - 2010 . - pp. [101301-1/9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [101301-1/9] Mots-clés : Conduction  Entropy  Phonon  radiative  transfer  Thermodynamics  Thin  film Index. décimale : 536 Chaleur. Thermodynamique Résumé : One of the approaches for micro/nanoscale heat transfer in semiconductors and dielectric materials is to use the Boltzmann transport equation, which reduces to the equation of phonon radiative transfer under the relaxation time approximation. Transfer and generation of entropy are processes inherently associated with thermal energy transport, yet little has been done to analyze entropy generation in solids at length scales comparable with or smaller than the mean free path of heat carriers. This work extends the concept of radiation entropy in a participating medium to phonon radiation, thus, providing a method to evaluate entropy generation at both large and small length scales. The conventional formula for entropy generation in heat diffusion can be derived under the local equilibrium assumption. Furthermore, the phonon brightness temperature is introduced to describe the nature of nonequilibrium heat conduction. A diamond film is used as a numerical example to illustrate the distribution of entropy generation at the walls and inside the film at low temperatures. A fundamental knowledge of the entropy generation processes provides a thermodynamic understanding of heat transport in solid microstructures; this is particularly important for the performance evaluation of thermal systems and microdevices. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Optimal thin-film topology design for specified temperature profiles in resistive heaters / François Mathieu-Potvin in Journal of heat transfer, Vol. 132 N° 10 (Octobre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [101302-1/9] Titre : Optimal thin-film topology design for specified temperature profiles in resistive heaters Type de document : texte imprimé Auteurs : François Mathieu-Potvin, Auteur ; Louis Gosselin, Auteur Année de publication : 2010 Article en page(s) : pp. [101302-1/9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Inverse  condition  Thin-film  Topology  optimization  Uniform  temperature  resistive  heater  Conjugate  gradient  Genetic  algorithm Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this paper, we optimized the topology of a thin-film resistive heater as well as the electrical potential of the electrodes on the boundaries. The objective was to minimize the difference between the actual and prescribed temperature profiles. The thin-film thickness was represented by 100 design variables, and the electrical potential at each electrode were also design variables. The topology optimization problem (inverse problem) has been solved with two methods, i.e., with a genetic algorithm (GA) and with a conjugate gradient method using adjoint and sensitivity problems (CGA). The genetic algorithm used here was modified in order to prevent nonconvergence due to the nonuniqueness of topology representation. The conjugate gradient method used in inverse conduction was extended to cope with our electrothermal problem. The GA and CGA methods started with random topologies and random electrical potential values at electrodes. Both the CGA and GA succeeded in finding optimal thin-film thickness distributions and electrode potential values, even with 100 topology design variables. For most cases, the maximum discrepancy between the optimized and prescribed temperature profiles was under 0.5°C, relative to temperature profiles of the order of 70°C. The CGA method was faster to converge, but was more complex to implement and sometimes led to local minima. The GA was easier to implement and was more unlikely to lead to a local minimum, but was much slower to converge. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Optimal thin-film topology design for specified temperature profiles in resistive heaters [texte imprimé] / François Mathieu-Potvin, Auteur ; Louis Gosselin, Auteur . - 2010 . - pp. [101302-1/9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [101302-1/9] Mots-clés : Inverse  condition  Thin-film  Topology  optimization  Uniform  temperature  resistive  heater  Conjugate  gradient  Genetic  algorithm Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this paper, we optimized the topology of a thin-film resistive heater as well as the electrical potential of the electrodes on the boundaries. The objective was to minimize the difference between the actual and prescribed temperature profiles. The thin-film thickness was represented by 100 design variables, and the electrical potential at each electrode were also design variables. The topology optimization problem (inverse problem) has been solved with two methods, i.e., with a genetic algorithm (GA) and with a conjugate gradient method using adjoint and sensitivity problems (CGA). The genetic algorithm used here was modified in order to prevent nonconvergence due to the nonuniqueness of topology representation. The conjugate gradient method used in inverse conduction was extended to cope with our electrothermal problem. The GA and CGA methods started with random topologies and random electrical potential values at electrodes. Both the CGA and GA succeeded in finding optimal thin-film thickness distributions and electrode potential values, even with 100 topology design variables. For most cases, the maximum discrepancy between the optimized and prescribed temperature profiles was under 0.5°C, relative to temperature profiles of the order of 70°C. The CGA method was faster to converge, but was more complex to implement and sometimes led to local minima. The GA was easier to implement and was more unlikely to lead to a local minimum, but was much slower to converge. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Revisit of laminar film condensation boundary layer theory for solution of mixed convection condensation with or without noncondensables / Y. Liao in Journal of heat transfer, Vol. 132 N° 10 (Octobre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [101501-1/6] Titre : Revisit of laminar film condensation boundary layer theory for solution of mixed convection condensation with or without noncondensables Type de document : texte imprimé Auteurs : Y. Liao, Auteur Année de publication : 2010 Article en page(s) : pp. [101501-1/6] Note générale : Physique Langues : Anglais (eng) Mots-clés : Mixed  convection  Film  condensation  Noncondensables Index. décimale : 536 Chaleur. Thermodynamique Résumé : This work presents a unique and unified formulation to solve the laminar film condensation two-phase boundary layer equations for the free, mixed, and forced convection regimes in the absence or presence of noncondensables. This solution explores the vast space of mixed convection across the four cornerstones of laminar film condensation boundary layer theory, two established by Koh for pure vapor condensation in the free or forced convection regimes and the other two established by Sparrow corresponding to condensation with noncondensables. This formulation solves the space of mixed convection completely with Koh and Sparrow's solutions shown to be merely four specific cases of the current solution. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Revisit of laminar film condensation boundary layer theory for solution of mixed convection condensation with or without noncondensables [texte imprimé] / Y. Liao, Auteur . - 2010 . - pp. [101501-1/6]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [101501-1/6] Mots-clés : Mixed  convection  Film  condensation  Noncondensables Index. décimale : 536 Chaleur. Thermodynamique Résumé : This work presents a unique and unified formulation to solve the laminar film condensation two-phase boundary layer equations for the free, mixed, and forced convection regimes in the absence or presence of noncondensables. This solution explores the vast space of mixed convection across the four cornerstones of laminar film condensation boundary layer theory, two established by Koh for pure vapor condensation in the free or forced convection regimes and the other two established by Sparrow corresponding to condensation with noncondensables. This formulation solves the space of mixed convection completely with Koh and Sparrow's solutions shown to be merely four specific cases of the current solution. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Forced flow of vapor condensing over a horizontal plate (Problem of Cess and Koh): steady and unsteady solutions of the full 2D problem / S. Kulkarni in Journal of heat transfer, Vol. 132 N° 10 (Octobre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - 101502-1/18] Titre : Forced flow of vapor condensing over a horizontal plate (Problem of Cess and Koh): steady and unsteady solutions of the full 2D problem Type de document : texte imprimé Auteurs : S. Kulkarni, Auteur ; A. Narain, Auteur ; Mitra, S., Auteur Année de publication : 2010 Article en page(s) : 101502-1/18] Note générale : Physique Langues : Anglais (eng) Mots-clés : Film  condensation  Phase-change  heat  transfer  Two-phase  flows  Stability  Instability  Interfacial  waves Index. décimale : 536 Chaleur. Thermodynamique Résumé : Accurate steady and unsteady numerical solutions of the full 2D governing equations—which model the forced film condensation flow of saturated vapor over a semi-infinite horizontal plate (the problem of Cess and Koh)—are obtained over a range of flow parameters. The results presented here are used to better understand the limitations of the well-known similarity solutions given by Koh. It is found that steady/quasisteady filmwise solution exists only if the inlet speed is above a certain threshold value. Above this threshold speed, steady/quasisteady film condensation solutions exist and their film thickness variations are approximately the same as the similarity solution given by Koh. However, these steady solutions differ from the Koh solution regarding pressure variations and associated effects in the leading part of the plate. Besides results based on the solutions of the full steady governing equations, this paper also presents unsteady solutions that characterize the steady solutions' attainability, stability (response to initial disturbances), and their response to ever-present minuscule noise on the condensing-surface. For this shear-driven flow, the paper finds that if the uniform vapor speed is above a threshold value, an unsteady solution that begins with any reasonable initial-guess is attracted in time to a steady solution. This long time limiting solution is the same—within computational errors—as the solution of the steady problem. The reported unsteady solutions that yield the steady solution in the long time limit also yield “attraction rates” for nonlinear stability analysis of the steady solutions. The attraction rates are found to diminish gradually with increasing distance from the leading edge and with decreasing inlet vapor speed. These steady solutions are generally found to be stable to initial disturbances on the interface as well as in any flow variable in the interior of the flow domain. The results for low vapor speeds below the threshold value indicate that the unsteady solutions exhibit nonexistence of any steady limit of filmwise flow in the aft portion of the solution. Even when a steady solution exists, the flow attainability is also shown to be difficult (because of waviness and other sensitivities) at large downstream distances. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Forced flow of vapor condensing over a horizontal plate (Problem of Cess and Koh): steady and unsteady solutions of the full 2D problem [texte imprimé] / S. Kulkarni, Auteur ; A. Narain, Auteur ; Mitra, S., Auteur . - 2010 . - 101502-1/18]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - 101502-1/18] Mots-clés : Film  condensation  Phase-change  heat  transfer  Two-phase  flows  Stability  Instability  Interfacial  waves Index. décimale : 536 Chaleur. Thermodynamique Résumé : Accurate steady and unsteady numerical solutions of the full 2D governing equations—which model the forced film condensation flow of saturated vapor over a semi-infinite horizontal plate (the problem of Cess and Koh)—are obtained over a range of flow parameters. The results presented here are used to better understand the limitations of the well-known similarity solutions given by Koh. It is found that steady/quasisteady filmwise solution exists only if the inlet speed is above a certain threshold value. Above this threshold speed, steady/quasisteady film condensation solutions exist and their film thickness variations are approximately the same as the similarity solution given by Koh. However, these steady solutions differ from the Koh solution regarding pressure variations and associated effects in the leading part of the plate. Besides results based on the solutions of the full steady governing equations, this paper also presents unsteady solutions that characterize the steady solutions' attainability, stability (response to initial disturbances), and their response to ever-present minuscule noise on the condensing-surface. For this shear-driven flow, the paper finds that if the uniform vapor speed is above a threshold value, an unsteady solution that begins with any reasonable initial-guess is attracted in time to a steady solution. This long time limiting solution is the same—within computational errors—as the solution of the steady problem. The reported unsteady solutions that yield the steady solution in the long time limit also yield “attraction rates” for nonlinear stability analysis of the steady solutions. The attraction rates are found to diminish gradually with increasing distance from the leading edge and with decreasing inlet vapor speed. These steady solutions are generally found to be stable to initial disturbances on the interface as well as in any flow variable in the interior of the flow domain. The results for low vapor speeds below the threshold value indicate that the unsteady solutions exhibit nonexistence of any steady limit of filmwise flow in the aft portion of the solution. Even when a steady solution exists, the flow attainability is also shown to be difficult (because of waviness and other sensitivities) at large downstream distances. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Effect of upstream shear on flow and heat (Mass) transfer over a flat plate. Part I, Velocity measurements / K. Ghosh in Journal of heat transfer, Vol. 132 N° 10 (Octobre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [101701-1/7] Titre : Effect of upstream shear on flow and heat (Mass) transfer over a flat plate. Part I, Velocity measurements Type de document : texte imprimé Auteurs : K. Ghosh, Auteur ; R. J. Goldstein, Auteur Année de publication : 2010 Article en page(s) : pp. [101701-1/7] Note générale : Physique Langues : Anglais (eng) Mots-clés : Turbulent  flow  Wall  shear  Clauser  technique  Boundary  layer  Scaling  laws Index. décimale : 536 Chaleur. Thermodynamique Résumé : A parametric study investigates the effects of wall shear on a two-dimensional turbulent boundary layer. A belt translating along the direction of the flow imparts the shear. Velocity measurements are performed at 12 streamwise locations with four surface-to-freestream velocity ratios (0, 0.38, 0.52, and 0.65) and a momentum-based Reynolds number between 770 and 1776. The velocity data indicate that the location of the “virtual origin” of the turbulent boundary layer “moves” downstream toward the trailing edge of the belt with increasing surface velocity. The highest belt velocity ratio (0.65) results in the removal of the “inner” region of the boundary layer. Measurements of the streamwise turbulent kinetic energy show an inner scaling at locations upstream and downstream of the belt, and the formation of a new self-similar structure on the moving surface itself. Good agreement is observed for the variation in the shape factor (H) and the skin friction coefficient (cf) with the previous studies. The distribution of the energy spectrum downstream of the belt indicates peak values concentrated around 1 kHz for the stationary belt case in the near wall region (30 DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Effect of upstream shear on flow and heat (Mass) transfer over a flat plate. Part I, Velocity measurements [texte imprimé] / K. Ghosh, Auteur ; R. J. Goldstein, Auteur . - 2010 . - pp. [101701-1/7]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [101701-1/7] Mots-clés : Turbulent  flow  Wall  shear  Clauser  technique  Boundary  layer  Scaling  laws Index. décimale : 536 Chaleur. Thermodynamique Résumé : A parametric study investigates the effects of wall shear on a two-dimensional turbulent boundary layer. A belt translating along the direction of the flow imparts the shear. Velocity measurements are performed at 12 streamwise locations with four surface-to-freestream velocity ratios (0, 0.38, 0.52, and 0.65) and a momentum-based Reynolds number between 770 and 1776. The velocity data indicate that the location of the “virtual origin” of the turbulent boundary layer “moves” downstream toward the trailing edge of the belt with increasing surface velocity. The highest belt velocity ratio (0.65) results in the removal of the “inner” region of the boundary layer. Measurements of the streamwise turbulent kinetic energy show an inner scaling at locations upstream and downstream of the belt, and the formation of a new self-similar structure on the moving surface itself. Good agreement is observed for the variation in the shape factor (H) and the skin friction coefficient (cf) with the previous studies. The distribution of the energy spectrum downstream of the belt indicates peak values concentrated around 1 kHz for the stationary belt case in the near wall region (30 DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Effect of upstream shear on flow and heat (Mass) transfer over a flat plate. Part II, Mass transfer measurements / K. Ghosh in Journal of heat transfer, Vol. 132 N° 10 (Octobre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [101702-1/6] Titre : Effect of upstream shear on flow and heat (Mass) transfer over a flat plate. Part II, Mass transfer measurements Type de document : texte imprimé Auteurs : K. Ghosh, Auteur ; R. J. Goldstein, Auteur Année de publication : 2010 Article en page(s) : pp. [101702-1/6] Note générale : Physique Langues : Anglais (eng) Mots-clés : Heat/mass  transfer  analogy  Naphthalene  sublimation  Turbulent  flow  Wall  motion  Boundary  layer  Constant  temperature  Constant  concentration Index. décimale : 536 Chaleur. Thermodynamique Résumé : Mass transfer measurements on a flat plate downstream of a belt moving in the same direction of the freestream study the effect of the upstream shear on the heat (mass) transfer for four belt-freestream velocity ratios. With an increase in this ratio, the “virtual origin” of the turbulent boundary layer “moves” downstream toward the trailing edge of the belt. This is verified from the variation of the Stanton number versus the Reynolds number plots. As the “inner” region of the boundary layer is removed for a belt speed of uw=10 m/s (freestream velocity uin[approximate]15.4 m/s), a corresponding local minimum in the variation of the Stanton number is observed. Downstream of this minimum, the characteristics of the turbulent boundary layer are restored and the data fall back on the empirical variation of Stanton with Reynolds number. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Effect of upstream shear on flow and heat (Mass) transfer over a flat plate. Part II, Mass transfer measurements [texte imprimé] / K. Ghosh, Auteur ; R. J. Goldstein, Auteur . - 2010 . - pp. [101702-1/6]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [101702-1/6] Mots-clés : Heat/mass  transfer  analogy  Naphthalene  sublimation  Turbulent  flow  Wall  motion  Boundary  layer  Constant  temperature  Constant  concentration Index. décimale : 536 Chaleur. Thermodynamique Résumé : Mass transfer measurements on a flat plate downstream of a belt moving in the same direction of the freestream study the effect of the upstream shear on the heat (mass) transfer for four belt-freestream velocity ratios. With an increase in this ratio, the “virtual origin” of the turbulent boundary layer “moves” downstream toward the trailing edge of the belt. This is verified from the variation of the Stanton number versus the Reynolds number plots. As the “inner” region of the boundary layer is removed for a belt speed of uw=10 m/s (freestream velocity uin[approximate]15.4 m/s), a corresponding local minimum in the variation of the Stanton number is observed. Downstream of this minimum, the characteristics of the turbulent boundary layer are restored and the data fall back on the empirical variation of Stanton with Reynolds number. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Second-law thermodynamic comparison and maximal velocity ratio design of shell-and-tube heat exchangers with continuous helical baffles / Qiu-Wang Wang in Journal of heat transfer, Vol. 132 N° 10 (Octobre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [101801-1/9] Titre : Second-law thermodynamic comparison and maximal velocity ratio design of shell-and-tube heat exchangers with continuous helical baffles Type de document : texte imprimé Auteurs : Qiu-Wang Wang, Auteur ; Gui-Dong Chen, Auteur ; Jing Xu, Auteur Année de publication : 2010 Article en page(s) : pp. [101801-1/9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Continuous  helical  baffles  Segmental  baffles  Entropy  generation  number  Ex-ergy  losses  Second-law  thermodynamic  analysis  Shell-and-tube  heat  exchangers Index. décimale : 536 Chaleur. Thermodynamique Résumé : Shell-and-tube heat exchangers (STHXs) have been widely used in many industrial processes. In the present paper, flow and heat transfer characteristics of the shell-and-tube heat exchanger with continuous helical baffles (CH-STHX) and segmental baffles (SG-STHX) were experimentally studied. In the experiments, these STHXs shared the same tube bundle, shell geometrical structures, different baffle arrangement, and number of heat exchange tubes. Experimental results suggested that the CH-STHX can increase the heat transfer rate by 7–12% than the SG-STHX for the same mass flow rate although its effective heat transfer area had 4% decrease. The heat transfer coefficient and pressure drop of the CH-STHX also had 43–53% and 64–72% increase than those of the SG-STHX, respectively. Based on second-law thermodynamic comparisons in which the quality of energy are evaluated by the entropy generation number and exergy losses, the CH-STHX decreased the entropy generation number and exergy losses by 30% and 68% on average than the SG-STHX for the same Reynolds number. The analysis from nondimensional correlations for Nusselt number and friction factor also revealed that if the maximal velocity ratio R>2.4, the heat transfer coefficient of CH-STHX was higher than that of SG-STHX, and the corresponding friction factor ratio kept at constant fo,CH/fo,SG=0.28. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Second-law thermodynamic comparison and maximal velocity ratio design of shell-and-tube heat exchangers with continuous helical baffles [texte imprimé] / Qiu-Wang Wang, Auteur ; Gui-Dong Chen, Auteur ; Jing Xu, Auteur . - 2010 . - pp. [101801-1/9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [101801-1/9] Mots-clés : Continuous  helical  baffles  Segmental  baffles  Entropy  generation  number  Ex-ergy  losses  Second-law  thermodynamic  analysis  Shell-and-tube  heat  exchangers Index. décimale : 536 Chaleur. Thermodynamique Résumé : Shell-and-tube heat exchangers (STHXs) have been widely used in many industrial processes. In the present paper, flow and heat transfer characteristics of the shell-and-tube heat exchanger with continuous helical baffles (CH-STHX) and segmental baffles (SG-STHX) were experimentally studied. In the experiments, these STHXs shared the same tube bundle, shell geometrical structures, different baffle arrangement, and number of heat exchange tubes. Experimental results suggested that the CH-STHX can increase the heat transfer rate by 7–12% than the SG-STHX for the same mass flow rate although its effective heat transfer area had 4% decrease. The heat transfer coefficient and pressure drop of the CH-STHX also had 43–53% and 64–72% increase than those of the SG-STHX, respectively. Based on second-law thermodynamic comparisons in which the quality of energy are evaluated by the entropy generation number and exergy losses, the CH-STHX decreased the entropy generation number and exergy losses by 30% and 68% on average than the SG-STHX for the same Reynolds number. The analysis from nondimensional correlations for Nusselt number and friction factor also revealed that if the maximal velocity ratio R>2.4, the heat transfer coefficient of CH-STHX was higher than that of SG-STHX, and the corresponding friction factor ratio kept at constant fo,CH/fo,SG=0.28. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Exergy analysis of coil-spring turbulators inserted in the horizontal concentric tubes / Haydar Eren in Journal of heat transfer, Vol. 132 N° 10 (Octobre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [101802-1/10] Titre : Exergy analysis of coil-spring turbulators inserted in the horizontal concentric tubes Type de document : texte imprimé Auteurs : Haydar Eren, Auteur ; Nevin Celik, Auteur ; Irfan Kurbas, Auteur Année de publication : 2010 Article en page(s) : pp. [101802-1/10] Note générale : Physique Langues : Anglais (eng) Mots-clés : Heat  transfer  enhancement  Heat  exchangers  Spring  turbulator  Exergy  transfer Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this study, to obtain definitive information about the effects of spring-type turbulators located in the inner pipe of a concentric heat exchanger, the rates of exergy transfer Nusselt number (Nue) and exergy loss (E*) were obtained. The results were parametrized by the Reynolds number (2500 DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Exergy analysis of coil-spring turbulators inserted in the horizontal concentric tubes [texte imprimé] / Haydar Eren, Auteur ; Nevin Celik, Auteur ; Irfan Kurbas, Auteur . - 2010 . - pp. [101802-1/10]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [101802-1/10] Mots-clés : Heat  transfer  enhancement  Heat  exchangers  Spring  turbulator  Exergy  transfer Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this study, to obtain definitive information about the effects of spring-type turbulators located in the inner pipe of a concentric heat exchanger, the rates of exergy transfer Nusselt number (Nue) and exergy loss (E*) were obtained. The results were parametrized by the Reynolds number (2500 DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Front tracking based macroscopic calculations of columnar and equiaxed solidification of a binary alloy / M. Seredynski in Journal of heat transfer, Vol. 132 N° 10 (Octobre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [102301/1-10] Titre : Front tracking based macroscopic calculations of columnar and equiaxed solidification of a binary alloy Type de document : texte imprimé Auteurs : M. Seredynski, Auteur ; J. Banaszek, Auteur Année de publication : 2010 Article en page(s) : pp. [102301/1-10] Note générale : Physique Langues : Anglais (eng) Mots-clés : Solidification  Front  tracking  Binary  alloy Index. décimale : 536 Chaleur. Thermodynamique Résumé : The paper explores the potential of a recently developed special front tracking method in the identification of the interface between columnar and equiaxed structures formed during a binary alloy solidification, driven by thermosolutal convection. The method, based on theoretical and experimental dendrite tip kinetics, is capable of directly distinguishing between the columnar mush and the undercooled liquid/equiaxed region developing ahead of the dendrite tip curve. A new numerical model and its computational algorithm are proposed, where the classical Eulerian volume averaged description of the transport processes is coupled with the Lagrangian front tracking method on a fixed control-volume grid. Having thus distinguished zones of different dendrite structures, distinct simulation models are used within each of the zones, e.g., the Darcy's porous medium model in the stationary dendrite region, and a model of slurry with floating dendrites in the equiaxed part of the mush. The calculated temperature and solute concentration fields are compared with the relevant results of the classical enthalpy-porosity model, for an example problem of Pb-48 wt % Sn alloy solidification driven by diffusion and thermosolutal convection. And a good match with both solutions is exhibited. A preliminary validation study is also presented by comparing the available experimental data with the model predictions. Possible reasons for some observed discrepancies between the calculations and the experimental findings are discussed. Finally, the proposed front tracking approach is used to address the question of the impact of dendrites floating in the liquid on the flow pattern and macrosegregation in the solidifying alloy. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Front tracking based macroscopic calculations of columnar and equiaxed solidification of a binary alloy [texte imprimé] / M. Seredynski, Auteur ; J. Banaszek, Auteur . - 2010 . - pp. [102301/1-10]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [102301/1-10] Mots-clés : Solidification  Front  tracking  Binary  alloy Index. décimale : 536 Chaleur. Thermodynamique Résumé : The paper explores the potential of a recently developed special front tracking method in the identification of the interface between columnar and equiaxed structures formed during a binary alloy solidification, driven by thermosolutal convection. The method, based on theoretical and experimental dendrite tip kinetics, is capable of directly distinguishing between the columnar mush and the undercooled liquid/equiaxed region developing ahead of the dendrite tip curve. A new numerical model and its computational algorithm are proposed, where the classical Eulerian volume averaged description of the transport processes is coupled with the Lagrangian front tracking method on a fixed control-volume grid. Having thus distinguished zones of different dendrite structures, distinct simulation models are used within each of the zones, e.g., the Darcy's porous medium model in the stationary dendrite region, and a model of slurry with floating dendrites in the equiaxed part of the mush. The calculated temperature and solute concentration fields are compared with the relevant results of the classical enthalpy-porosity model, for an example problem of Pb-48 wt % Sn alloy solidification driven by diffusion and thermosolutal convection. And a good match with both solutions is exhibited. A preliminary validation study is also presented by comparing the available experimental data with the model predictions. Possible reasons for some observed discrepancies between the calculations and the experimental findings are discussed. Finally, the proposed front tracking approach is used to address the question of the impact of dendrites floating in the liquid on the flow pattern and macrosegregation in the solidifying alloy. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Hierarchical modeling of heat transfer in silicon-based electronic devices / Javier V. Goicochea in Journal of heat transfer, Vol. 132 N° 10 (Octobre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [102401/1-11] Titre : Hierarchical modeling of heat transfer in silicon-based electronic devices Type de document : texte imprimé Auteurs : Javier V. Goicochea, Auteur ; Marcela Madrid, Auteur ; Cristina Amon, Auteur Année de publication : 2010 Article en page(s) : pp. [102401/1-11] Note générale : Physique Langues : Anglais (eng) Mots-clés : Boltzmann  equation  Heat  transfer  Microfluidics  Molecular  dynamics  method  Phonons  Silicon  Thermal  conductivity Index. décimale : 536 Chaleur. Thermodynamique Résumé : A hierarchical model of heat transfer for the thermal analysis of electronic devices is presented. The integration of participating scales (from nanoscale to macroscales) is achieved by (i) estimating the input parameters and thermal properties to solve the Boltzmann transport equation (BTE) for phonons using molecular dynamics (MD), including phonon relaxation times, dispersion relations, group velocities, and specific heat, (ii) applying quantum corrections to the MD results to make them suitable for the solution of BTE, and (iii) numerically solving the BTE in space and time subject to different boundary and initial conditions. We apply our hierarchical model to estimate the silicon out-of-plane thermal conductivity and the thermal response of an silicon on insulator (SOI) device subject to Joule heating. We have found that relative phonon contribution to the overall conductivity changes as the dimension of the domain is reduced as a result of phonon confinement. The observed reduction in the thermal conductivity is produced by the progressive transition of modes in the diffusive regime (as in the bulk) to transitional and ballistic regimes as the film thickness is decreased. In addition, we have found that relaxation time expressions for optical phonons are important to describe the transient response of SOI devices and that the characteristic transport regimes, determined with Holland and Klemens phonon models, differ significantly. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Hierarchical modeling of heat transfer in silicon-based electronic devices [texte imprimé] / Javier V. Goicochea, Auteur ; Marcela Madrid, Auteur ; Cristina Amon, Auteur . - 2010 . - pp. [102401/1-11]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [102401/1-11] Mots-clés : Boltzmann  equation  Heat  transfer  Microfluidics  Molecular  dynamics  method  Phonons  Silicon  Thermal  conductivity Index. décimale : 536 Chaleur. Thermodynamique Résumé : A hierarchical model of heat transfer for the thermal analysis of electronic devices is presented. The integration of participating scales (from nanoscale to macroscales) is achieved by (i) estimating the input parameters and thermal properties to solve the Boltzmann transport equation (BTE) for phonons using molecular dynamics (MD), including phonon relaxation times, dispersion relations, group velocities, and specific heat, (ii) applying quantum corrections to the MD results to make them suitable for the solution of BTE, and (iii) numerically solving the BTE in space and time subject to different boundary and initial conditions. We apply our hierarchical model to estimate the silicon out-of-plane thermal conductivity and the thermal response of an silicon on insulator (SOI) device subject to Joule heating. We have found that relative phonon contribution to the overall conductivity changes as the dimension of the domain is reduced as a result of phonon confinement. The observed reduction in the thermal conductivity is produced by the progressive transition of modes in the diffusive regime (as in the bulk) to transitional and ballistic regimes as the film thickness is decreased. In addition, we have found that relaxation time expressions for optical phonons are important to describe the transient response of SOI devices and that the characteristic transport regimes, determined with Holland and Klemens phonon models, differ significantly. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

The classical nature of thermal conduction in nanofluids / Jacob Eapen in Journal of heat transfer, Vol. 132 N° 10 (Octobre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [102402/1-14] Titre : The classical nature of thermal conduction in nanofluids Type de document : texte imprimé Auteurs : Jacob Eapen, Auteur ; Roberto Rusconi, Auteur ; Roberto Piazza, Auteur Année de publication : 2010 Article en page(s) : pp. [102402/1-14] Note générale : Physique Langues : Anglais (eng) Mots-clés : Aggregation  Colloids  Fractals  Heat  conduction  Nanoparticles  Percolation  Thermal  conductivity Index. décimale : 536 Chaleur. Thermodynamique Résumé : We show that a large set of nanofluid thermal conductivity data falls within the upper and lower Maxwell bounds for homogeneous systems. This indicates that the thermal conductivity of nanofluids is largely dependent on whether the nanoparticles stay dispersed in the base fluid, form large aggregates, or assume a percolating fractal configuration. The experimental data, which are strikingly analogous to those in most solid composites and liquid mixtures, provide strong evidence for the classical nature of thermal conduction in nanofluids. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] The classical nature of thermal conduction in nanofluids [texte imprimé] / Jacob Eapen, Auteur ; Roberto Rusconi, Auteur ; Roberto Piazza, Auteur . - 2010 . - pp. [102402/1-14]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [102402/1-14] Mots-clés : Aggregation  Colloids  Fractals  Heat  conduction  Nanoparticles  Percolation  Thermal  conductivity Index. décimale : 536 Chaleur. Thermodynamique Résumé : We show that a large set of nanofluid thermal conductivity data falls within the upper and lower Maxwell bounds for homogeneous systems. This indicates that the thermal conductivity of nanofluids is largely dependent on whether the nanoparticles stay dispersed in the base fluid, form large aggregates, or assume a percolating fractal configuration. The experimental data, which are strikingly analogous to those in most solid composites and liquid mixtures, provide strong evidence for the classical nature of thermal conduction in nanofluids. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Molecular dynamics simulation of phonon scattering at silicon/germanium interfaces / Lin Sun in Journal of heat transfer, Vol. 132 N° 10 (Octobre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [102403/1-9] Titre : Molecular dynamics simulation of phonon scattering at silicon/germanium interfaces Type de document : texte imprimé Auteurs : Lin Sun, Auteur ; Jayathi Y. Murthy, Auteur Année de publication : 2010 Article en page(s) : pp. [102403/1-9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Molecular  dynamics  Phonon  transport  Interface  Wave  packet Index. décimale : 536 Chaleur. Thermodynamique Résumé : Detailed phonon transport at Si/Ge interfaces is studied using the molecular dynamics wave-packet method. Three types of interfaces are investigated: A smooth interface, an interface with random roughness, and an interface with a regularly patterned roughness. The phonon transmissivity for each case is calculated as a function of phonon frequency, roughness characteristic length, and atomic structure. For a smooth interface, the transmissivities predicted by the MD simulations agree well with the acoustic mismatch model based on the continuum assumption. The rough interface simulation results indicate that random roughness is the source of incoherent phonon scattering and decreases the phonon transmission. Periodic structures such as the regularly patterned roughness employed in this paper cause strong phonon wave interference and may restore phonon transmission as the layer thickness increases. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Molecular dynamics simulation of phonon scattering at silicon/germanium interfaces [texte imprimé] / Lin Sun, Auteur ; Jayathi Y. Murthy, Auteur . - 2010 . - pp. [102403/1-9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [102403/1-9] Mots-clés : Molecular  dynamics  Phonon  transport  Interface  Wave  packet Index. décimale : 536 Chaleur. Thermodynamique Résumé : Detailed phonon transport at Si/Ge interfaces is studied using the molecular dynamics wave-packet method. Three types of interfaces are investigated: A smooth interface, an interface with random roughness, and an interface with a regularly patterned roughness. The phonon transmissivity for each case is calculated as a function of phonon frequency, roughness characteristic length, and atomic structure. For a smooth interface, the transmissivities predicted by the MD simulations agree well with the acoustic mismatch model based on the continuum assumption. The rough interface simulation results indicate that random roughness is the source of incoherent phonon scattering and decreases the phonon transmission. Periodic structures such as the regularly patterned roughness employed in this paper cause strong phonon wave interference and may restore phonon transmission as the layer thickness increases. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Critical heat flux (CHF) of subcooled flow boiling of alumina nanofluids in a horizontal microchannel / Saeid Vafaei in Journal of heat transfer, Vol. 132 N° 10 (Octobre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [102404/1-7] Titre : Critical heat flux (CHF) of subcooled flow boiling of alumina nanofluids in a horizontal microchannel Type de document : texte imprimé Auteurs : Saeid Vafaei, Auteur ; Dongsheng Wen, Auteur Année de publication : 2010 Article en page(s) : pp. [102404/1-7] Note générale : Physique Langues : Anglais (eng) Mots-clés : Flow  boiling  Microchannel  Nanofluids  Critical  heat  flux  Burnout Index. décimale : 536 Chaleur. Thermodynamique Résumé : This work investigates subcooled flow boiling of aqueous based alumina nanofluids in 510 µm single microchannels with a focus on the effect of nanoparticles on the critical heat flux. The surface temperature distribution along the pipe, the inlet and outlet pressures and temperatures are measured simultaneously for different concentrations of alumina nanofluids and de-ionized water. To minimize the effect of nanoparticle depositions, all nanofluid experiments are performed on fresh microchannels. The experiment shows an increase of ~51% in the critical heat flux under very low nanoparticle concentrations (0.1 vol %). Different burnout characteristics are observed between water and nanofluids, as well as different pressure and temperature fluctuations and flow pattern development during the stable boiling period. Detailed observations of the boiling surface show that nanoparticle deposition and a subsequent modification of the boiling surface are common features associated with nanofluids, which should be responsible for the different boiling behaviors of nanofluids. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Critical heat flux (CHF) of subcooled flow boiling of alumina nanofluids in a horizontal microchannel [texte imprimé] / Saeid Vafaei, Auteur ; Dongsheng Wen, Auteur . - 2010 . - pp. [102404/1-7]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [102404/1-7] Mots-clés : Flow  boiling  Microchannel  Nanofluids  Critical  heat  flux  Burnout Index. décimale : 536 Chaleur. Thermodynamique Résumé : This work investigates subcooled flow boiling of aqueous based alumina nanofluids in 510 µm single microchannels with a focus on the effect of nanoparticles on the critical heat flux. The surface temperature distribution along the pipe, the inlet and outlet pressures and temperatures are measured simultaneously for different concentrations of alumina nanofluids and de-ionized water. To minimize the effect of nanoparticle depositions, all nanofluid experiments are performed on fresh microchannels. The experiment shows an increase of ~51% in the critical heat flux under very low nanoparticle concentrations (0.1 vol %). Different burnout characteristics are observed between water and nanofluids, as well as different pressure and temperature fluctuations and flow pattern development during the stable boiling period. Detailed observations of the boiling surface show that nanoparticle deposition and a subsequent modification of the boiling surface are common features associated with nanofluids, which should be responsible for the different boiling behaviors of nanofluids. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Natural convection in a partially heat generating rod bundle inside an enclosure / D. Jaya Krishna in Journal of heat transfer, Vol. 132 N° 10 (Octobre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp.[102501/1-11] Titre : Natural convection in a partially heat generating rod bundle inside an enclosure Type de document : texte imprimé Auteurs : D. Jaya Krishna, Auteur ; M. R. Thansekhar, Auteur ; S. P. Venkateshan, Auteur Année de publication : 2010 Article en page(s) : pp.[102501/1-11] Note générale : Physique Langues : Anglais (eng) Mots-clés : Natural  convection  Non-darcy  porous  medium  Heat  generating  rod  bundle  Partially  heat  generating  enclosure Index. décimale : 536 Chaleur. Thermodynamique Résumé : Buoyancy induced flows in a partially heat generating rod bundle enclosed inside a tall cavity are investigated. First, a detailed experimental study is carried out, and the thermal hydraulics is analyzed at different power inputs and boundary cooling rates of the enclosure. Later, a generalized non-Darcy simulation is developed using a heat generating orthotropic porous media approach and is compared with the experimental results. The results of a numerical simulation for natural convection in enclosed partially heat generating rod bundles satisfactorily predict the temperature distribution within the rod bundle. Finally, a parametric study is carried out by varying the porosity (pitch to diameter ratio of the rod bundle) of the considered enclosure for the understanding of flow physics and heat transfer in such applications. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Natural convection in a partially heat generating rod bundle inside an enclosure [texte imprimé] / D. Jaya Krishna, Auteur ; M. R. Thansekhar, Auteur ; S. P. Venkateshan, Auteur . - 2010 . - pp.[102501/1-11]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp.[102501/1-11] Mots-clés : Natural  convection  Non-darcy  porous  medium  Heat  generating  rod  bundle  Partially  heat  generating  enclosure Index. décimale : 536 Chaleur. Thermodynamique Résumé : Buoyancy induced flows in a partially heat generating rod bundle enclosed inside a tall cavity are investigated. First, a detailed experimental study is carried out, and the thermal hydraulics is analyzed at different power inputs and boundary cooling rates of the enclosure. Later, a generalized non-Darcy simulation is developed using a heat generating orthotropic porous media approach and is compared with the experimental results. The results of a numerical simulation for natural convection in enclosed partially heat generating rod bundles satisfactorily predict the temperature distribution within the rod bundle. Finally, a parametric study is carried out by varying the porosity (pitch to diameter ratio of the rod bundle) of the considered enclosure for the understanding of flow physics and heat transfer in such applications. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Influence of intense symmetric heating and variable physical properties on the thermo-buoyant airflow inside vertical parallel-plate channels / Biagio Morrone in Journal of heat transfer, Vol. 132 N° 10 (Octobre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp.[104501/1-5] Titre : Influence of intense symmetric heating and variable physical properties on the thermo-buoyant airflow inside vertical parallel-plate channels Type de document : texte imprimé Auteurs : Biagio Morrone, Auteur ; Antonio Campo, Auteur Année de publication : 2010 Article en page(s) : pp.[104501/1-5] Note générale : Physique Langues : Anglais (eng) Mots-clés : Natural  convection  Vertical  parallel-plate  channel  Variable  physical  properties  Elliptic  conservation  equations  Enlarged  computational  domain Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper deals with the steady, laminar, and two-dimensional natural convection inside vertical parallel-plate channels with isoflux heating. The main objective of this paper is to assess the joint influence of intense heating and variable physical properties on the flow and heat transfer characteristics of the upward air. To capture the physics of the problem, the discretized conservation equations are solved by the finite-volume technique in an aggrandized computational domain that is much larger than the physical domain. Representative numerical results based on the FLUENT computer program are presented in terms of local quantities such as air velocity and temperature profiles, as well as global quantities such as the average heat transfer coefficients and mass flow rates, all in response to the controlling geometrical and thermal parameters. A detailed comparison of these results is made against those produced by the simple model limited to constant physical properties. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Influence of intense symmetric heating and variable physical properties on the thermo-buoyant airflow inside vertical parallel-plate channels [texte imprimé] / Biagio Morrone, Auteur ; Antonio Campo, Auteur . - 2010 . - pp.[104501/1-5]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp.[104501/1-5] Mots-clés : Natural  convection  Vertical  parallel-plate  channel  Variable  physical  properties  Elliptic  conservation  equations  Enlarged  computational  domain Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper deals with the steady, laminar, and two-dimensional natural convection inside vertical parallel-plate channels with isoflux heating. The main objective of this paper is to assess the joint influence of intense heating and variable physical properties on the flow and heat transfer characteristics of the upward air. To capture the physics of the problem, the discretized conservation equations are solved by the finite-volume technique in an aggrandized computational domain that is much larger than the physical domain. Representative numerical results based on the FLUENT computer program are presented in terms of local quantities such as air velocity and temperature profiles, as well as global quantities such as the average heat transfer coefficients and mass flow rates, all in response to the controlling geometrical and thermal parameters. A detailed comparison of these results is made against those produced by the simple model limited to constant physical properties. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Performance of a convectively heated rectangular fin with a step change in cross-sectional area and losing heat by simultaneous convection and radiation (Step fins under radiation environment) / B. Kundu in Journal of heat transfer, Vol. 132 N° 10 (Octobre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [104502/1-6] Titre : Performance of a convectively heated rectangular fin with a step change in cross-sectional area and losing heat by simultaneous convection and radiation (Step fins under radiation environment) Type de document : texte imprimé Auteurs : B. Kundu, Auteur ; A. Aziz, Auteur Année de publication : 2010 Article en page(s) : pp. [104502/1-6] Note générale : Physique Langues : Anglais (eng) Mots-clés : Base  convection  Convection-radiation  Step  rectangular  fin  Temperature  dependent  thermal  conductivity Index. décimale : 536 Chaleur. Thermodynamique Résumé : A numerical procedure has been used to study the thermal performance of a step convective-radiative fin with temperature dependent thermal conductivity and convective base heating. An analytical solution has been developed for a pure convective fin with constant thermal conductivity, with its base exposed to a hot fluid. The effects of geometrical and thermophysical parameters on the temperature profiles in the fin, the fin efficiency, and the fin effectiveness are illustrated. The step fin is found to deliver a superior thermal performance compared with the uniformly thick fin. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Performance of a convectively heated rectangular fin with a step change in cross-sectional area and losing heat by simultaneous convection and radiation (Step fins under radiation environment) [texte imprimé] / B. Kundu, Auteur ; A. Aziz, Auteur . - 2010 . - pp. [104502/1-6]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [104502/1-6] Mots-clés : Base  convection  Convection-radiation  Step  rectangular  fin  Temperature  dependent  thermal  conductivity Index. décimale : 536 Chaleur. Thermodynamique Résumé : A numerical procedure has been used to study the thermal performance of a step convective-radiative fin with temperature dependent thermal conductivity and convective base heating. An analytical solution has been developed for a pure convective fin with constant thermal conductivity, with its base exposed to a hot fluid. The effects of geometrical and thermophysical parameters on the temperature profiles in the fin, the fin efficiency, and the fin effectiveness are illustrated. The step fin is found to deliver a superior thermal performance compared with the uniformly thick fin. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Thermal characterizations of fin-thin film systems / A.-R. A. Khaled in Journal of heat transfer, Vol. 132 N° 10 (Octobre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [104503/1-6] Titre : Thermal characterizations of fin-thin film systems Type de document : texte imprimé Auteurs : A.-R. A. Khaled, Auteur Année de publication : 2010 Article en page(s) : pp. [104503/1-6] Note générale : Physique Langues : Anglais (eng) Mots-clés : Conduction  Convection  Fins  Enhancements  Thin  films Index. décimale : 536 Chaleur. Thermodynamique Résumé : This work considers heat transfer in fin-thin film systems. Two types of these systems are analyzed: (A) a thin film sandwiched between two identical fin halves, and (B) a fin sandwiched between two identical thin films. The corresponding coupled energy equations are solved numerically by an implicit, iterative, finite-difference scheme. Comparisons with derived approximate closed-form solutions are performed and good agreement is obtained. A parametric study of all involved parameters is conducted and presented graphically. Useful correlations containing the various physical parameters for both types are reported. It is found that thermal efficiencies of fins can be increased significantly by introducing an internal flow inside the fin material. Moreover, factors producing more internal convections are found to increase the fin-thin film thermal efficiency. In addition, thermal efficiencies of type A systems are found to be higher than those of type B systems. Moreover, the resulting system thermal efficiency is found to have at most one local maximum and one local minimum over the whole relative heights ratio spectrum. Finally, this work paves a way for an effective combined passive and active method for enhancing heat transfer. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Thermal characterizations of fin-thin film systems [texte imprimé] / A.-R. A. Khaled, Auteur . - 2010 . - pp. [104503/1-6]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 10 (Octobre 2010) . - pp. [104503/1-6] Mots-clés : Conduction  Convection  Fins  Enhancements  Thin  films Index. décimale : 536 Chaleur. Thermodynamique Résumé : This work considers heat transfer in fin-thin film systems. Two types of these systems are analyzed: (A) a thin film sandwiched between two identical fin halves, and (B) a fin sandwiched between two identical thin films. The corresponding coupled energy equations are solved numerically by an implicit, iterative, finite-difference scheme. Comparisons with derived approximate closed-form solutions are performed and good agreement is obtained. A parametric study of all involved parameters is conducted and presented graphically. Useful correlations containing the various physical parameters for both types are reported. It is found that thermal efficiencies of fins can be increased significantly by introducing an internal flow inside the fin material. Moreover, factors producing more internal convections are found to increase the fin-thin film thermal efficiency. In addition, thermal efficiencies of type A systems are found to be higher than those of type B systems. Moreover, the resulting system thermal efficiency is found to have at most one local maximum and one local minimum over the whole relative heights ratio spectrum. Finally, this work paves a way for an effective combined passive and active method for enhancing heat transfer. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

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