Dépouillements

Heat flux estimation in a nonlinear inverse heat conduction problem with moving boundary / Hosein Molavi in Journal of heat transfer, Vol. 132 N° 8 (Août 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081301-1/10] Titre : Heat flux estimation in a nonlinear inverse heat conduction problem with moving boundary Type de document : texte imprimé Auteurs : Hosein Molavi, Auteur ; Ramin K. Rahmani, Auteur ; Alireza Pourshaghaghy, Auteur Article en page(s) : pp. [081301-1/10] Note générale : Physique Langues : Anglais (eng) Mots-clés : Adjoint  problem  Estimation  of  heat  flux  Gradient-typeods  Inverse  problem  Moving  boundary Index. décimale : 536 Chaleur. Thermodynamique Résumé : The estimation of heat flux in the nonlinear heat conduction problem becomes more challenging when the material at the boundary loses its mass due to phase change, chemical erosion, oxidation, or mechanical removal. In this paper, a new gradient-type method with an adjoint problem is employed to predict the unknown time-varying heat flux at the receding surface in the nonlinear heat conduction problem. Particular features of this novel approach are discussed and examined. Results obtained by the new method for several test cases are benchmarked and analyzed using numerical experiments with simulated exact and noisy measurements. Exceedingly reliable estimation on the heat flux can be obtained from the knowledge of the transient temperature recordings, even in the case with measurement errors. In order to evaluate the performance characteristics of the present inverse scheme, simulations are conducted to analyze the effects of this technique with regard to the conjugate gradient method with an adjoint problem and variable metric method with an adjoint problem. The results obtained show that the present inverse scheme distinguishably accelerates the convergence rate, which approve the well capability of the method for this type of heat conduction problems. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Heat flux estimation in a nonlinear inverse heat conduction problem with moving boundary [texte imprimé] / Hosein Molavi, Auteur ; Ramin K. Rahmani, Auteur ; Alireza Pourshaghaghy, Auteur . - pp. [081301-1/10]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081301-1/10] Mots-clés : Adjoint  problem  Estimation  of  heat  flux  Gradient-typeods  Inverse  problem  Moving  boundary Index. décimale : 536 Chaleur. Thermodynamique Résumé : The estimation of heat flux in the nonlinear heat conduction problem becomes more challenging when the material at the boundary loses its mass due to phase change, chemical erosion, oxidation, or mechanical removal. In this paper, a new gradient-type method with an adjoint problem is employed to predict the unknown time-varying heat flux at the receding surface in the nonlinear heat conduction problem. Particular features of this novel approach are discussed and examined. Results obtained by the new method for several test cases are benchmarked and analyzed using numerical experiments with simulated exact and noisy measurements. Exceedingly reliable estimation on the heat flux can be obtained from the knowledge of the transient temperature recordings, even in the case with measurement errors. In order to evaluate the performance characteristics of the present inverse scheme, simulations are conducted to analyze the effects of this technique with regard to the conjugate gradient method with an adjoint problem and variable metric method with an adjoint problem. The results obtained show that the present inverse scheme distinguishably accelerates the convergence rate, which approve the well capability of the method for this type of heat conduction problems. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Criteria for cross-plane dominated thermal transport in multilayer thin film systems during modulated laser heating / Patrick E. Hopkins in Journal of heat transfer, Vol. 132 N° 8 (Août 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081302-1/10] Titre : Criteria for cross-plane dominated thermal transport in multilayer thin film systems during modulated laser heating Type de document : texte imprimé Auteurs : Patrick E. Hopkins, Auteur ; Justin R. Serrano, Auteur ; Leslie M. Phinney, Auteur Article en page(s) : pp. [081302-1/10] Note générale : Physique Langues : Anglais (eng) Mots-clés : Pump-probe  thermoreflectance  Thin  film  thermal  conductivity  Thermal  boundary  conductance  Radial  heating  Cross-plane  transport Index. décimale : 536 Chaleur. Thermodynamique Résumé : Pump-probe transient thermoreflectance (TTR) techniques are powerful tools for measuring the thermophysical properties of thin films, such as thermal conductivity, Lambda, or thermal boundary conductance, G. This paper examines the assumption of one-dimensional heating on, Lambda and G, determination in nanostructures using a pump-probe transient thermoreflectance technique. The traditionally used one-dimensional and axially symmetric cylindrical conduction models for thermal transport are reviewed. To test the assumptions of the thermal models, experimental data from Al films on bulk substrates (Si and glass) are taken with the TTR technique. This analysis is extended to thin film multilayer structures. The results show that at 11 MHz modulation frequency, thermal transport is indeed one dimensional. Error among the various models arises due to pulse accumulation and not accounting for residual heating. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Criteria for cross-plane dominated thermal transport in multilayer thin film systems during modulated laser heating [texte imprimé] / Patrick E. Hopkins, Auteur ; Justin R. Serrano, Auteur ; Leslie M. Phinney, Auteur . - pp. [081302-1/10]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081302-1/10] Mots-clés : Pump-probe  thermoreflectance  Thin  film  thermal  conductivity  Thermal  boundary  conductance  Radial  heating  Cross-plane  transport Index. décimale : 536 Chaleur. Thermodynamique Résumé : Pump-probe transient thermoreflectance (TTR) techniques are powerful tools for measuring the thermophysical properties of thin films, such as thermal conductivity, Lambda, or thermal boundary conductance, G. This paper examines the assumption of one-dimensional heating on, Lambda and G, determination in nanostructures using a pump-probe transient thermoreflectance technique. The traditionally used one-dimensional and axially symmetric cylindrical conduction models for thermal transport are reviewed. To test the assumptions of the thermal models, experimental data from Al films on bulk substrates (Si and glass) are taken with the TTR technique. This analysis is extended to thin film multilayer structures. The results show that at 11 MHz modulation frequency, thermal transport is indeed one dimensional. Error among the various models arises due to pulse accumulation and not accounting for residual heating. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

A meshless finite difference method for conjugate heat conduction problems / Chandrashekhar Varanasi in Journal of heat transfer, Vol. 132 N° 8 (Août 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081303-1/13] Titre : A meshless finite difference method for conjugate heat conduction problems Type de document : texte imprimé Auteurs : Chandrashekhar Varanasi, Auteur ; Jayathi Y. Murthy, Auteur ; Sanjay Mathur, Auteur Article en page(s) : pp. [081303-1/13] Note générale : Physique Langues : Anglais (eng) Mots-clés : Finite  point  method  Weighted  least-squares  Conjugate  heat  conduction Index. décimale : 536 Chaleur. Thermodynamique Résumé : A meshless finite difference method is developed for solving conjugate heat transfer problems. Starting with an arbitrary distribution of mesh points, derivatives are evaluated using a weighted least-squares procedure. The resulting system of algebraic equations is sparse and is solved using an algebraic multigrid method. The implementation of the Neumann, Dirichlet, and mixed boundary conditions within this framework is described. For conjugate heat transfer problems, continuity of the heat flux and temperature are imposed on mesh points at multimaterial interfaces. The method is verified through application to classical heat conduction problems with known analytical solutions. It is then applied to the solution of conjugate heat transfer problems in complex geometries, and the solutions so obtained are compared with more conventional unstructured finite volume methods. The method improves on existing meshless methods for conjugate heat conduction by eliminating spurious oscillations previously observed. Metrics for accuracy are provided and future extensions are discussed. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] A meshless finite difference method for conjugate heat conduction problems [texte imprimé] / Chandrashekhar Varanasi, Auteur ; Jayathi Y. Murthy, Auteur ; Sanjay Mathur, Auteur . - pp. [081303-1/13]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081303-1/13] Mots-clés : Finite  point  method  Weighted  least-squares  Conjugate  heat  conduction Index. décimale : 536 Chaleur. Thermodynamique Résumé : A meshless finite difference method is developed for solving conjugate heat transfer problems. Starting with an arbitrary distribution of mesh points, derivatives are evaluated using a weighted least-squares procedure. The resulting system of algebraic equations is sparse and is solved using an algebraic multigrid method. The implementation of the Neumann, Dirichlet, and mixed boundary conditions within this framework is described. For conjugate heat transfer problems, continuity of the heat flux and temperature are imposed on mesh points at multimaterial interfaces. The method is verified through application to classical heat conduction problems with known analytical solutions. It is then applied to the solution of conjugate heat transfer problems in complex geometries, and the solutions so obtained are compared with more conventional unstructured finite volume methods. The method improves on existing meshless methods for conjugate heat conduction by eliminating spurious oscillations previously observed. Metrics for accuracy are provided and future extensions are discussed. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Numerical simulation of convective heat transfer modes in a rectangular area with a heat source and conducting walls / G. V. Kuznetsov in Journal of heat transfer, Vol. 132 N° 8 (Août 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081401-1/9] Titre : Numerical simulation of convective heat transfer modes in a rectangular area with a heat source and conducting walls Type de document : texte imprimé Auteurs : G. V. Kuznetsov, Auteur ; M. A. Sheremet, Auteur Article en page(s) : pp. [081401-1/9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Convection  modes  Conjugate  heat  transfer  Laminar  flow  Heat  source Index. décimale : 536 Chaleur. Thermodynamique Résumé : Laminar conjugate heat transfer in a rectangular area having finite thickness heat-conducting walls at local heating has been analyzed numerically. The heat source located on the left wall is kept at constant temperature during the whole process. Conjugate heat transfer is complicated by the forced flow. The governing unsteady, two-dimensional flow and energy equations for the gas cavity and unsteady heat conduction equation for solid walls, written in dimensionless form, have been solved using implicit finite-difference method. The solution has been obtained in terms of the stream function and the vorticity vector. The effects of the Grashof number Gr, the Reynolds number Re, and the dimensionless time on the flow structure and heat transfer characteristics have been investigated in detail. Results have been obtained for the following parameters: 103<=Gr<=107, 100<=Re<=1000, and Pr=0.7. Typical distributions of thermohydrodynamic parameters describing features of investigated process have been received. Interference of convective flows (forced, natural, and mixed modes) in the presence of conducting solid walls has been analyzed. The increase in Gr is determined to lead to both the intensification of the convective flow caused by the presence of the heat source and the blocking of the forced flow nearby the upper wall. The nonmonotomic variations in the average Nusselt number with Gr for solid-fluid interfaces have been obtained. The increase in Re is shown to lead to cooling of the gas cavity caused by the forced flow. Evolution of analyzed process at time variation has been displayed. The diagram of the heat convection modes depending on the Grashof and Reynolds numbers has been obtained. The analysis of heat convection modes in a typical subsystem of the electronic equipment is oriented not only toward applied development in microelectronics, but also it can be considered as test database at creation of numerical codes of convective heat transfer simulation in complicated energy systems. Comparison of the obtained results can be made by means of both streamlines and temperature fields at different values of the Grashof number and Reynolds number, and the average Nusselt numbers at solid-fluid interfaces. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Numerical simulation of convective heat transfer modes in a rectangular area with a heat source and conducting walls [texte imprimé] / G. V. Kuznetsov, Auteur ; M. A. Sheremet, Auteur . - pp. [081401-1/9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081401-1/9] Mots-clés : Convection  modes  Conjugate  heat  transfer  Laminar  flow  Heat  source Index. décimale : 536 Chaleur. Thermodynamique Résumé : Laminar conjugate heat transfer in a rectangular area having finite thickness heat-conducting walls at local heating has been analyzed numerically. The heat source located on the left wall is kept at constant temperature during the whole process. Conjugate heat transfer is complicated by the forced flow. The governing unsteady, two-dimensional flow and energy equations for the gas cavity and unsteady heat conduction equation for solid walls, written in dimensionless form, have been solved using implicit finite-difference method. The solution has been obtained in terms of the stream function and the vorticity vector. The effects of the Grashof number Gr, the Reynolds number Re, and the dimensionless time on the flow structure and heat transfer characteristics have been investigated in detail. Results have been obtained for the following parameters: 103<=Gr<=107, 100<=Re<=1000, and Pr=0.7. Typical distributions of thermohydrodynamic parameters describing features of investigated process have been received. Interference of convective flows (forced, natural, and mixed modes) in the presence of conducting solid walls has been analyzed. The increase in Gr is determined to lead to both the intensification of the convective flow caused by the presence of the heat source and the blocking of the forced flow nearby the upper wall. The nonmonotomic variations in the average Nusselt number with Gr for solid-fluid interfaces have been obtained. The increase in Re is shown to lead to cooling of the gas cavity caused by the forced flow. Evolution of analyzed process at time variation has been displayed. The diagram of the heat convection modes depending on the Grashof and Reynolds numbers has been obtained. The analysis of heat convection modes in a typical subsystem of the electronic equipment is oriented not only toward applied development in microelectronics, but also it can be considered as test database at creation of numerical codes of convective heat transfer simulation in complicated energy systems. Comparison of the obtained results can be made by means of both streamlines and temperature fields at different values of the Grashof number and Reynolds number, and the average Nusselt numbers at solid-fluid interfaces. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Experimental investigation of an ultrathin manifold microchannel heat sink for liquid-cooled chips / W. Escher in Journal of heat transfer, Vol. 132 N° 8 (Août 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081402-1/10] Titre : Experimental investigation of an ultrathin manifold microchannel heat sink for liquid-cooled chips Type de document : texte imprimé Auteurs : W. Escher, Auteur ; T. Brunschwiler, Auteur ; B. Michel, Auteur Article en page(s) : pp. [081402-1/10] Note générale : Physique Langues : Anglais (eng) Mots-clés : Manifold  Microchannels  Impinging  jet  Heat  transfer  Electronics  cooling Index. décimale : 536 Chaleur. Thermodynamique Résumé : We report an experimental investigation of a novel, high performance ultrathin manifold microchannel heat sink. The heat sink consists of impinging liquid slot-jets on a structured surface fed with liquid coolant by an overlying two-dimensional manifold. We developed a fabrication and packaging procedure to manufacture prototypes by means of standard microprocessing. A closed fluid loop for precise hydrodynamic and thermal characterization of six different test vehicles was built. We studied the influence of the number of manifold systems, the width of the heat transfer microchannels, the volumetric flow rate, and the pumping power on the hydrodynamic and thermal performance of the heat sink. A design with 12.5 manifold systems and 25 µm wide microchannels as the heat transfer structure provided the optimum choice of design parameters. For a volumetric flow rate of 1.3 l/min we demonstrated a total thermal resistance between the maximum heater temperature and fluid inlet temperature of 0.09 cm2 K/W with a pressure drop of 0.22 bar on a 2×2 cm2 chip. This allows for cooling power densities of more than 700 W/cm2 for a maximum temperature difference between the chip and the fluid inlet of 65 K. The total height of the heat sink did not exceed 2 mm, and includes a 500 µm thick thermal test chip structured by 300 µm deep microchannels for heat transfer. Furthermore, we discuss the influence of elevated fluid inlet temperatures, allowing possible reuse of the thermal energy, and demonstrate an enhancement of the heat sink cooling efficiency of more than 40% for a temperature rise of 50 K. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Experimental investigation of an ultrathin manifold microchannel heat sink for liquid-cooled chips [texte imprimé] / W. Escher, Auteur ; T. Brunschwiler, Auteur ; B. Michel, Auteur . - pp. [081402-1/10]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081402-1/10] Mots-clés : Manifold  Microchannels  Impinging  jet  Heat  transfer  Electronics  cooling Index. décimale : 536 Chaleur. Thermodynamique Résumé : We report an experimental investigation of a novel, high performance ultrathin manifold microchannel heat sink. The heat sink consists of impinging liquid slot-jets on a structured surface fed with liquid coolant by an overlying two-dimensional manifold. We developed a fabrication and packaging procedure to manufacture prototypes by means of standard microprocessing. A closed fluid loop for precise hydrodynamic and thermal characterization of six different test vehicles was built. We studied the influence of the number of manifold systems, the width of the heat transfer microchannels, the volumetric flow rate, and the pumping power on the hydrodynamic and thermal performance of the heat sink. A design with 12.5 manifold systems and 25 µm wide microchannels as the heat transfer structure provided the optimum choice of design parameters. For a volumetric flow rate of 1.3 l/min we demonstrated a total thermal resistance between the maximum heater temperature and fluid inlet temperature of 0.09 cm2 K/W with a pressure drop of 0.22 bar on a 2×2 cm2 chip. This allows for cooling power densities of more than 700 W/cm2 for a maximum temperature difference between the chip and the fluid inlet of 65 K. The total height of the heat sink did not exceed 2 mm, and includes a 500 µm thick thermal test chip structured by 300 µm deep microchannels for heat transfer. Furthermore, we discuss the influence of elevated fluid inlet temperatures, allowing possible reuse of the thermal energy, and demonstrate an enhancement of the heat sink cooling efficiency of more than 40% for a temperature rise of 50 K. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Fluid flow and heat transfer in a horizontal channel with divergent top wall and heated from below / C. S. Yang in Journal of heat transfer, Vol. 132 N° 8 (Août 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081403-1/8] Titre : Fluid flow and heat transfer in a horizontal channel with divergent top wall and heated from below Type de document : texte imprimé Auteurs : C. S. Yang, Auteur ; D. Z. Jeng, Auteur ; C. W. Liu, Auteur Article en page(s) : pp. [081403-1/8] Note générale : Physique Langues : Anglais (eng) Mots-clés : Mixed  convection  in  horizontal  divergent  channel  Divergent  channel  flow  heated  from  below  Secondary  flow  structure  Mixing  convection  heat  transfer Index. décimale : 536 Chaleur. Thermodynamique Résumé : Secondary flow structure and its enhancement on the heat transfer in a horizontal divergent channel have been studied. The bottom wall is horizontal and is heated uniformly while the opposite top wall is insulated and inclined with respect to the horizontal plane so as to create a divergent angle of 3 deg. At the entrance of the channel, the aspect ratios for the width to the height and the channel length to the height are 6.67 and 15, respectively. The Reynolds number ranges from 100 to 2000 and the buoyancy parameter Gr/Re2 from 0 to 405. Both flow visualization and temperature fluctuation measurements at different locations are made to indicate the flow structure and oscillation of the secondary flow. The adverse pressure gradient in the divergent channel causes a thicker heated layer in the bottom and earlier initiation of secondary flow. Interaction between neighboring vortices and plumes becomes more severe and highly unstable. This precludes the formation of steady two-dimensional longitudinal vortex rolls in the downstream and leads to an earlier and larger enhancement of the heat transfer than the case of the parallel-plate channel. The effects of the buoyancy parameter and the divergence of the channel on the secondary flow structure and the Nusselt number are presented and discussed. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Fluid flow and heat transfer in a horizontal channel with divergent top wall and heated from below [texte imprimé] / C. S. Yang, Auteur ; D. Z. Jeng, Auteur ; C. W. Liu, Auteur . - pp. [081403-1/8]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081403-1/8] Mots-clés : Mixed  convection  in  horizontal  divergent  channel  Divergent  channel  flow  heated  from  below  Secondary  flow  structure  Mixing  convection  heat  transfer Index. décimale : 536 Chaleur. Thermodynamique Résumé : Secondary flow structure and its enhancement on the heat transfer in a horizontal divergent channel have been studied. The bottom wall is horizontal and is heated uniformly while the opposite top wall is insulated and inclined with respect to the horizontal plane so as to create a divergent angle of 3 deg. At the entrance of the channel, the aspect ratios for the width to the height and the channel length to the height are 6.67 and 15, respectively. The Reynolds number ranges from 100 to 2000 and the buoyancy parameter Gr/Re2 from 0 to 405. Both flow visualization and temperature fluctuation measurements at different locations are made to indicate the flow structure and oscillation of the secondary flow. The adverse pressure gradient in the divergent channel causes a thicker heated layer in the bottom and earlier initiation of secondary flow. Interaction between neighboring vortices and plumes becomes more severe and highly unstable. This precludes the formation of steady two-dimensional longitudinal vortex rolls in the downstream and leads to an earlier and larger enhancement of the heat transfer than the case of the parallel-plate channel. The effects of the buoyancy parameter and the divergence of the channel on the secondary flow structure and the Nusselt number are presented and discussed. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

A scale analysis based theoretical force balance model for critical heat flux (CHF) during saturated flow boiling in microchannels and minichannels / Satish G. Kandlikar in Journal of heat transfer, Vol. 132 N° 8 (Août 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081501-1/13] Titre : A scale analysis based theoretical force balance model for critical heat flux (CHF) during saturated flow boiling in microchannels and minichannels Type de document : texte imprimé Auteurs : Satish G. Kandlikar, Auteur Article en page(s) : pp. [081501-1/13] Note générale : Physique Langues : Anglais (eng) Mots-clés : Microchannels  Minichannels  CHF  Critical  heat  flux  Flow  boiling  Evaporation  momentum  Boiling Index. décimale : 536 Chaleur. Thermodynamique Résumé : Accurate prediction of critical heat flux (CHF) in microchannels and minichannels is of great interest in estimating the safe operational limits of cooling systems employing flow boiling. Scale analysis is applied to identify the relevant forces leading to the CHF condition. Using these forces, a local parameter model is developed to predict the flow boiling CHF. The theoretical model is an extension of an earlier pool boiling CHF model and incorporates force balance among the evaporation momentum, surface tension, inertia, and viscous forces. Weber number, capillary number, and a new nondimensional group introduced earlier by Kandlikar (2004, “Heat Transfer Mechanisms During Flow Boiling in Microchannels,” ASME J. Heat Transfer, 126, pp. 8–16), K2, representing the ratio of evaporation momentum to surface tension forces, emerged as main groups in quantifying the narrow channel effects on CHF. The constants in the model were calculated from the available experimental data. The mean error with ten data sets is 19.7% with 76% data falling within ±30% error band and 93% within ±50% error band. The length to diameter ratio emerged as a parameter indicating a stepwise regime change. The success of the model indicates that flow boiling CHF can be modeled as a local phenomenon and the scale analysis is able to reveal important information regarding fundamental mechanisms leading to the CHF condition. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] A scale analysis based theoretical force balance model for critical heat flux (CHF) during saturated flow boiling in microchannels and minichannels [texte imprimé] / Satish G. Kandlikar, Auteur . - pp. [081501-1/13]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081501-1/13] Mots-clés : Microchannels  Minichannels  CHF  Critical  heat  flux  Flow  boiling  Evaporation  momentum  Boiling Index. décimale : 536 Chaleur. Thermodynamique Résumé : Accurate prediction of critical heat flux (CHF) in microchannels and minichannels is of great interest in estimating the safe operational limits of cooling systems employing flow boiling. Scale analysis is applied to identify the relevant forces leading to the CHF condition. Using these forces, a local parameter model is developed to predict the flow boiling CHF. The theoretical model is an extension of an earlier pool boiling CHF model and incorporates force balance among the evaporation momentum, surface tension, inertia, and viscous forces. Weber number, capillary number, and a new nondimensional group introduced earlier by Kandlikar (2004, “Heat Transfer Mechanisms During Flow Boiling in Microchannels,” ASME J. Heat Transfer, 126, pp. 8–16), K2, representing the ratio of evaporation momentum to surface tension forces, emerged as main groups in quantifying the narrow channel effects on CHF. The constants in the model were calculated from the available experimental data. The mean error with ten data sets is 19.7% with 76% data falling within ±30% error band and 93% within ±50% error band. The length to diameter ratio emerged as a parameter indicating a stepwise regime change. The success of the model indicates that flow boiling CHF can be modeled as a local phenomenon and the scale analysis is able to reveal important information regarding fundamental mechanisms leading to the CHF condition. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Bubble dynamics for nucleate pool boiling of electrolyte solutions / Seyed Ali Alavi Fazel in Journal of heat transfer, Vol. 132 N° 8 (Août 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081502-1/7] Titre : Bubble dynamics for nucleate pool boiling of electrolyte solutions Type de document : texte imprimé Auteurs : Seyed Ali Alavi Fazel, Auteur ; Seyed Baher Shafaee, Auteur Article en page(s) : pp. [081502-1/7] Note générale : Physique Langues : Anglais (eng) Mots-clés : Pool  boiling  Bubble  diameter  Electrolyte  solutions Index. décimale : 536 Chaleur. Thermodynamique Résumé : Bubble dynamics is the most important subphenomenon, which basically affects the nucleate pool boiling heat transfer coefficient. Previous investigations state that the effect of physical properties of liquid and vapor phases on bubble departure diameter are often conflicting. In this article, extensive new experimental data are presented for the bubble departure diameter for various electrolyte aqueous solutions over a wide range of heat fluxes and concentrations. Experimental results show that the bubble detachment diameter increase with increasing either boiling heat flux or electrolyte concentration. Experimental results also present a close relation between the dimensionless capillary and bond numbers. A new model for the prediction of vapor bubble departure diameter in nucleate boiling for the electrolyte solutions is proposed, which predicts the experimental data with a satisfactory accuracy. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Bubble dynamics for nucleate pool boiling of electrolyte solutions [texte imprimé] / Seyed Ali Alavi Fazel, Auteur ; Seyed Baher Shafaee, Auteur . - pp. [081502-1/7]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081502-1/7] Mots-clés : Pool  boiling  Bubble  diameter  Electrolyte  solutions Index. décimale : 536 Chaleur. Thermodynamique Résumé : Bubble dynamics is the most important subphenomenon, which basically affects the nucleate pool boiling heat transfer coefficient. Previous investigations state that the effect of physical properties of liquid and vapor phases on bubble departure diameter are often conflicting. In this article, extensive new experimental data are presented for the bubble departure diameter for various electrolyte aqueous solutions over a wide range of heat fluxes and concentrations. Experimental results show that the bubble detachment diameter increase with increasing either boiling heat flux or electrolyte concentration. Experimental results also present a close relation between the dimensionless capillary and bond numbers. A new model for the prediction of vapor bubble departure diameter in nucleate boiling for the electrolyte solutions is proposed, which predicts the experimental data with a satisfactory accuracy. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Rendering the transient hot wire experimental method for thermal conductivity estimation to two-phase systems—theoretical leading order results / Peter Vadasz in Journal of heat transfer, Vol. 132 N° 8 (Août 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp.[081601-1/7] Titre : Rendering the transient hot wire experimental method for thermal conductivity estimation to two-phase systems—theoretical leading order results Type de document : texte imprimé Auteurs : Peter Vadasz, Auteur Article en page(s) : pp.[081601-1/7] Note générale : Physique Langues : Anglais (eng) Mots-clés : Transient  hot  wire  Porous  media  Nanofluids  Effective  thermal  conductivity  Two-phase  heat  conduction Index. décimale : 536 Chaleur. Thermodynamique Résumé : The transient hot wire experimental method for estimating the thermal conductivity of fluids and solids is well established as the most accurate, reliable, and robust technique. It essentially relies on a simple analytical formula derived from the solution of the heat conduction from a line heat source embedded in the target medium. This simple and elegant analytical formulation was derived for uniform and homogeneous fluids or solids. Its extension to two-phase or composite systems, while in practical application, does not have any theoretical basis, and it is by no means obvious that the latter may be applied without corrections to such heterogeneous systems. When it is actually applied as for single-phase systems, it is clearly incorrect. This paper presents preliminary results at the leading order (in the sense of an expansion of the solution in powers of time, applicable to short time scales, consistent with the validity of the transient hot wire method), which render the transient hot wire method to two-phase and composite systems. While these leading order approximations extend the applicability of the same analytical formula to two-phase systems, they also produce additional conditions that need to be fulfilled for such an application to provide reliable experimental results. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Rendering the transient hot wire experimental method for thermal conductivity estimation to two-phase systems—theoretical leading order results [texte imprimé] / Peter Vadasz, Auteur . - pp.[081601-1/7]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp.[081601-1/7] Mots-clés : Transient  hot  wire  Porous  media  Nanofluids  Effective  thermal  conductivity  Two-phase  heat  conduction Index. décimale : 536 Chaleur. Thermodynamique Résumé : The transient hot wire experimental method for estimating the thermal conductivity of fluids and solids is well established as the most accurate, reliable, and robust technique. It essentially relies on a simple analytical formula derived from the solution of the heat conduction from a line heat source embedded in the target medium. This simple and elegant analytical formulation was derived for uniform and homogeneous fluids or solids. Its extension to two-phase or composite systems, while in practical application, does not have any theoretical basis, and it is by no means obvious that the latter may be applied without corrections to such heterogeneous systems. When it is actually applied as for single-phase systems, it is clearly incorrect. This paper presents preliminary results at the leading order (in the sense of an expansion of the solution in powers of time, applicable to short time scales, consistent with the validity of the transient hot wire method), which render the transient hot wire method to two-phase and composite systems. While these leading order approximations extend the applicability of the same analytical formula to two-phase systems, they also produce additional conditions that need to be fulfilled for such an application to provide reliable experimental results. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Thermal conductance of a multilayer drift chamber / Manuel Daniel-Leal in Journal of heat transfer, Vol. 132 N° 8 (Août 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081602-1/6] Titre : Thermal conductance of a multilayer drift chamber : an experimental approach Type de document : texte imprimé Auteurs : Manuel Daniel-Leal, Auteur ; Luciano Romero-Barajas, Auteur ; Jose L. Perez-Diaz, Auteur Article en page(s) : pp. [081602-1/6] Note générale : Physique Langues : Anglais (eng) Mots-clés : Thermal  conductance  Thermal  transient  Multilayer  Drift  chamber Index. décimale : 536 Chaleur. Thermodynamique Résumé : Drift chambers in the compact muon solenoid (CMS) detector are piled modular structures joined together by a structural adhesive. This structure is used for the detection and tracking of high energy particles—particularly muons. According to Fourier's law, the conductance of a multilayered drift chamber prototype can be measured using a simple device based on the thermal transience between two heat sinks. The heat gradients in the global CMS detector in operation at the European Council for Nuclear Research are estimated in this way. The resultant values are used to determine whether to include a forced cooling device in the CMS. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Thermal conductance of a multilayer drift chamber : an experimental approach [texte imprimé] / Manuel Daniel-Leal, Auteur ; Luciano Romero-Barajas, Auteur ; Jose L. Perez-Diaz, Auteur . - pp. [081602-1/6]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081602-1/6] Mots-clés : Thermal  conductance  Thermal  transient  Multilayer  Drift  chamber Index. décimale : 536 Chaleur. Thermodynamique Résumé : Drift chambers in the compact muon solenoid (CMS) detector are piled modular structures joined together by a structural adhesive. This structure is used for the detection and tracking of high energy particles—particularly muons. According to Fourier's law, the conductance of a multilayered drift chamber prototype can be measured using a simple device based on the thermal transience between two heat sinks. The heat gradients in the global CMS detector in operation at the European Council for Nuclear Research are estimated in this way. The resultant values are used to determine whether to include a forced cooling device in the CMS. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Thermohydraulics of laminar flow through rectangular and square ducts with axial corrugation roughness and twisted tapes with oblique teeth / Sujoy Kumar Saha in Journal of heat transfer, Vol. 132 N° 8 (Août 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081701-1/12] Titre : Thermohydraulics of laminar flow through rectangular and square ducts with axial corrugation roughness and twisted tapes with oblique teeth Type de document : texte imprimé Auteurs : Sujoy Kumar Saha, Auteur Article en page(s) : pp. [081701-1/12] Note générale : Physique Langues : Anglais (eng) Mots-clés : Augmentation  Enhancement  Forced  convection  Laminar  Axial  corrugation  Twisted-tape  inserts  Oblique  teeth Index. décimale : 536 Chaleur. Thermodynamique Résumé : The heat transfer and the pressure drop characteristics of laminar flow of viscous oil (175 DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Thermohydraulics of laminar flow through rectangular and square ducts with axial corrugation roughness and twisted tapes with oblique teeth [texte imprimé] / Sujoy Kumar Saha, Auteur . - pp. [081701-1/12]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081701-1/12] Mots-clés : Augmentation  Enhancement  Forced  convection  Laminar  Axial  corrugation  Twisted-tape  inserts  Oblique  teeth Index. décimale : 536 Chaleur. Thermodynamique Résumé : The heat transfer and the pressure drop characteristics of laminar flow of viscous oil (175 DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Multi-objective optimization of heat exchanger design by entropy generation minimization / Jiangfeng Guo in Journal of heat transfer, Vol. 132 N° 8 (Août 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081801-1/8] Titre : Multi-objective optimization of heat exchanger design by entropy generation minimization Type de document : texte imprimé Auteurs : Jiangfeng Guo, Auteur ; Lin Cheng, Auteur ; Mingtian Xu, Auteur Article en page(s) : pp. [081801-1/8] Note générale : Physique Langues : Anglais (eng) Mots-clés : Heat  exchanger  Heat  and  mass  transfer  Heat  conduction  Genetic  algorithm  Pareto  optimisation Index. décimale : 536 Chaleur. Thermodynamique Résumé : In the present work, a multi-objective optimization of heat exchanger thermal design in the framework of the entropy generation minimization is presented. The objectives are to minimize the dimensionless entropy generation rates related to the heat conduction under finite temperature difference and fluid friction under finite pressure drop. Constraints are specified by the admissible pressure drop and design standards. The genetic algorithm is employed to search the Pareto optimal set of the multi-objective optimization problem. It is found that the solutions in the Pareto optimal set are trade-off between the pumping power and heat exchanger effectiveness. In some sense, the optimal solution in the Pareto optimal set achieves the largest exchanger effectiveness by consuming the least pumping power under the design requirements and standards. In comparison with the single-objective optimization design, the multi-objective optimization design leads to the significant decrease in the pumping power for achieving the same heat exchanger effectiveness and presents more flexibility in the design process. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Multi-objective optimization of heat exchanger design by entropy generation minimization [texte imprimé] / Jiangfeng Guo, Auteur ; Lin Cheng, Auteur ; Mingtian Xu, Auteur . - pp. [081801-1/8]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [081801-1/8] Mots-clés : Heat  exchanger  Heat  and  mass  transfer  Heat  conduction  Genetic  algorithm  Pareto  optimisation Index. décimale : 536 Chaleur. Thermodynamique Résumé : In the present work, a multi-objective optimization of heat exchanger thermal design in the framework of the entropy generation minimization is presented. The objectives are to minimize the dimensionless entropy generation rates related to the heat conduction under finite temperature difference and fluid friction under finite pressure drop. Constraints are specified by the admissible pressure drop and design standards. The genetic algorithm is employed to search the Pareto optimal set of the multi-objective optimization problem. It is found that the solutions in the Pareto optimal set are trade-off between the pumping power and heat exchanger effectiveness. In some sense, the optimal solution in the Pareto optimal set achieves the largest exchanger effectiveness by consuming the least pumping power under the design requirements and standards. In comparison with the single-objective optimization design, the multi-objective optimization design leads to the significant decrease in the pumping power for achieving the same heat exchanger effectiveness and presents more flexibility in the design process. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Modeling carrier-phonon nonequilibrium due to pulsed laser interaction with nanoscale silicon films / Arvind Pattamatta in Journal of heat transfer, Vol. 132 N° 8 (Août 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [082401-1/5] Titre : Modeling carrier-phonon nonequilibrium due to pulsed laser interaction with nanoscale silicon films Type de document : texte imprimé Auteurs : Arvind Pattamatta, Auteur ; Cyrus K. Madnia, Auteur Article en page(s) : pp. [082401-1/5] Note générale : Physique Langues : Anglais (eng) Mots-clés : Si  Boltzmann  transport  model  Carrier-phonon  nonequilibrium  Nanoscale  energy  transport  Ultrashort-pulsed  laser  RKDG Index. décimale : 536 Chaleur. Thermodynamique Résumé : Ultrashort-pulsed laser irradiation on semiconductors creates a thermal nonequilibrium between carriers and phonons. Previous computational studies used the “two-temperature” model and its variants to model this nonequilibrium. However, when the laser pulse duration is smaller than the relaxation time of the carriers or phonons or when the carriers' or phonons' mean free path is larger than the material dimension, these macroscopic models fail to capture the physics accurately. In this article, the nonequilibrium between carriers and phonons in silicon films is modeled via numerical solution of the Boltzmann transport model (BTM), which is applicable over a wide range of length and time scales. The BTM is solved using the discontinuous Galerkin finite element method for spatial discretization and the three-stage Runge–Kutta temporal discretization. The BTM results are compared with previous computational studies on laser heating of macroscale silicon films. The model is then used to study laser heating of nanometer size silicon films, by varying parameters such as the laser fluence and pulse duration. From the laser pulse duration study, it is observed that the peak carrier number density, and maximum carrier and phonon temperatures are the highest for the shortest pulse duration of 0.05 ps and decreases with increasing pulse duration. From the laser fluence study, it is observed that for fluences equal to or higher than 1000 J/m2, due to the Auger recombination, a second peak in carrier temperature is observed. The use of carrier-acoustic phonon coupling leads to equilibrium phonon temperatures, which are approximately 400 K higher than that of carrier-optical phonon-acoustic phonon coupling. Both the laser pulse duration and fluence are found to strongly affect the equilibrium time and temperature in Si films. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Modeling carrier-phonon nonequilibrium due to pulsed laser interaction with nanoscale silicon films [texte imprimé] / Arvind Pattamatta, Auteur ; Cyrus K. Madnia, Auteur . - pp. [082401-1/5]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [082401-1/5] Mots-clés : Si  Boltzmann  transport  model  Carrier-phonon  nonequilibrium  Nanoscale  energy  transport  Ultrashort-pulsed  laser  RKDG Index. décimale : 536 Chaleur. Thermodynamique Résumé : Ultrashort-pulsed laser irradiation on semiconductors creates a thermal nonequilibrium between carriers and phonons. Previous computational studies used the “two-temperature” model and its variants to model this nonequilibrium. However, when the laser pulse duration is smaller than the relaxation time of the carriers or phonons or when the carriers' or phonons' mean free path is larger than the material dimension, these macroscopic models fail to capture the physics accurately. In this article, the nonequilibrium between carriers and phonons in silicon films is modeled via numerical solution of the Boltzmann transport model (BTM), which is applicable over a wide range of length and time scales. The BTM is solved using the discontinuous Galerkin finite element method for spatial discretization and the three-stage Runge–Kutta temporal discretization. The BTM results are compared with previous computational studies on laser heating of macroscale silicon films. The model is then used to study laser heating of nanometer size silicon films, by varying parameters such as the laser fluence and pulse duration. From the laser pulse duration study, it is observed that the peak carrier number density, and maximum carrier and phonon temperatures are the highest for the shortest pulse duration of 0.05 ps and decreases with increasing pulse duration. From the laser fluence study, it is observed that for fluences equal to or higher than 1000 J/m2, due to the Auger recombination, a second peak in carrier temperature is observed. The use of carrier-acoustic phonon coupling leads to equilibrium phonon temperatures, which are approximately 400 K higher than that of carrier-optical phonon-acoustic phonon coupling. Both the laser pulse duration and fluence are found to strongly affect the equilibrium time and temperature in Si films. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Particle aspect-ratio and agglomeration-state effects on the effective thermal conductivity of aqueous suspensions of multiwalled carbon nanotubes / Anna S. Cherkasova in Journal of heat transfer, Vol. 132 N° 8 (Août 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [082402-1/11] Titre : Particle aspect-ratio and agglomeration-state effects on the effective thermal conductivity of aqueous suspensions of multiwalled carbon nanotubes Type de document : texte imprimé Auteurs : Anna S. Cherkasova, Auteur ; Jerry W. Shan, Auteur Article en page(s) : pp. [082402-1/11] Note générale : Physique Langues : Anglais (eng) Mots-clés : Nanofluid  Multiwalled  nonotubes  Thermal  conductivity  Aspect  ratio  Agglomeration  Interfacial  resistance  Effective  medium  theory Index. décimale : 536 Chaleur. Thermodynamique Résumé : The effective thermal conductivities of aqueous nanofluids containing surfactant-stabilized multiwalled carbon nanotubes were measured and compared with the predictions of effective medium theory (Nan, C.-W., et al., 1997, “Effective Thermal Conductivity of Particulate Composites With Interfacial Thermal Resistance,” J. Appl. Phys., 81(10), pp. 6692–6699). Detailed characterization of nanotube morphology was carried out through electron microscopy, while the nanotube agglomeration state was monitored through optical microscopy and absorption measurements. An optimum surfactant-to-nanotube mass ratio was found for the particular surfactant, sodium dodecylbenzene sulfonate, which resulted in the greatest increase in thermal conductivity. Taking into consideration the volume-weighted aspect ratio of the nanotubes, the measured thermal conductivities of the suspensions were shown to be in good agreement with calculations for a reasonable choice of interfacial resistance on the particle/liquid interface. The effect of particle aspect ratio on the suspension's thermal conductivity was further demonstrated and compared with theory by reducing the nanotube length through intense ultrasonication. The effect of particle aggregation on the thermal conductivity was also investigated by destabilizing previously stable suspensions with ethanol addition, which causes surfactant desorption and bundling of nanotubes. The measured thermal conductivities were correlated with absorption measurements and microscopic visualizations to show that particle aggregation decreases the thermal conductivity of the nanofluid by reducing the effective particle aspect ratio. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Particle aspect-ratio and agglomeration-state effects on the effective thermal conductivity of aqueous suspensions of multiwalled carbon nanotubes [texte imprimé] / Anna S. Cherkasova, Auteur ; Jerry W. Shan, Auteur . - pp. [082402-1/11]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [082402-1/11] Mots-clés : Nanofluid  Multiwalled  nonotubes  Thermal  conductivity  Aspect  ratio  Agglomeration  Interfacial  resistance  Effective  medium  theory Index. décimale : 536 Chaleur. Thermodynamique Résumé : The effective thermal conductivities of aqueous nanofluids containing surfactant-stabilized multiwalled carbon nanotubes were measured and compared with the predictions of effective medium theory (Nan, C.-W., et al., 1997, “Effective Thermal Conductivity of Particulate Composites With Interfacial Thermal Resistance,” J. Appl. Phys., 81(10), pp. 6692–6699). Detailed characterization of nanotube morphology was carried out through electron microscopy, while the nanotube agglomeration state was monitored through optical microscopy and absorption measurements. An optimum surfactant-to-nanotube mass ratio was found for the particular surfactant, sodium dodecylbenzene sulfonate, which resulted in the greatest increase in thermal conductivity. Taking into consideration the volume-weighted aspect ratio of the nanotubes, the measured thermal conductivities of the suspensions were shown to be in good agreement with calculations for a reasonable choice of interfacial resistance on the particle/liquid interface. The effect of particle aspect ratio on the suspension's thermal conductivity was further demonstrated and compared with theory by reducing the nanotube length through intense ultrasonication. The effect of particle aggregation on the thermal conductivity was also investigated by destabilizing previously stable suspensions with ethanol addition, which causes surfactant desorption and bundling of nanotubes. The measured thermal conductivities were correlated with absorption measurements and microscopic visualizations to show that particle aggregation decreases the thermal conductivity of the nanofluid by reducing the effective particle aspect ratio. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Impact of thermodiffusion on carbon nanotube growth by chemical vapor deposition / Andrew C. Lysaght in Journal of heat transfer, Vol. 132 N° 8 (Août 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [084501-1/4] Titre : Impact of thermodiffusion on carbon nanotube growth by chemical vapor deposition Type de document : texte imprimé Auteurs : Andrew C. Lysaght, Auteur ; Wilson K. S. Chiu, Auteur Article en page(s) : pp. [084501-1/4] Note générale : Physique Langues : Anglais (eng) Mots-clés : Carbon  nanotube  Chemical  vapor  deposition  Thermodiffusion Index. décimale : 536 Chaleur. Thermodynamique Résumé : Thermal diffusion, the process by which a multicomponent mixture develops a concentration gradient when exposed to a temperature gradient, has been studied in order to understand if its inclusion is warranted in the modeling of single-wall carbon nanotubes (SWNTs) synthesis by thermal chemical vapor deposition (CVD). A fully coupled reactor-scale model employing conservation of mass, momentum, species, and energy equations with detailed gas phase and surface reaction mechanisms has been utilized to describe the evolution of hydrogen and hydrocarbon feed streams as they undergo transport, as well as homogeneous and heterogeneous chemical reaction within a CVD reactor. Steady state velocity, temperature, and concentration fields within the reactor volume are determined, as well as concentrations of adsorbed species and SWNT growth rates. The effect of thermodiffusion in differing reactor conditions has been investigated to understand the impact on SWNT growth. Thermal diffusion can have a significant impact on SWNT growth, and the first approximation of the thermal diffusion factor, based on the Chapman–Enskog molecular theory, is sufficient for modeling thermophoretic behavior within a CVD reactor. This effect can be facilitatory or inhibitory, based on the thermal and mass flux conditions. The results of this investigation are useful in order to optimize model and reactor designs to promote optimal SWNT deposition rates. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Impact of thermodiffusion on carbon nanotube growth by chemical vapor deposition [texte imprimé] / Andrew C. Lysaght, Auteur ; Wilson K. S. Chiu, Auteur . - pp. [084501-1/4]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [084501-1/4] Mots-clés : Carbon  nanotube  Chemical  vapor  deposition  Thermodiffusion Index. décimale : 536 Chaleur. Thermodynamique Résumé : Thermal diffusion, the process by which a multicomponent mixture develops a concentration gradient when exposed to a temperature gradient, has been studied in order to understand if its inclusion is warranted in the modeling of single-wall carbon nanotubes (SWNTs) synthesis by thermal chemical vapor deposition (CVD). A fully coupled reactor-scale model employing conservation of mass, momentum, species, and energy equations with detailed gas phase and surface reaction mechanisms has been utilized to describe the evolution of hydrogen and hydrocarbon feed streams as they undergo transport, as well as homogeneous and heterogeneous chemical reaction within a CVD reactor. Steady state velocity, temperature, and concentration fields within the reactor volume are determined, as well as concentrations of adsorbed species and SWNT growth rates. The effect of thermodiffusion in differing reactor conditions has been investigated to understand the impact on SWNT growth. Thermal diffusion can have a significant impact on SWNT growth, and the first approximation of the thermal diffusion factor, based on the Chapman–Enskog molecular theory, is sufficient for modeling thermophoretic behavior within a CVD reactor. This effect can be facilitatory or inhibitory, based on the thermal and mass flux conditions. The results of this investigation are useful in order to optimize model and reactor designs to promote optimal SWNT deposition rates. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Analytical solution for forced convection in a sector duct filled with a porous medium / Wang, C. Y. in Journal of heat transfer, Vol. 132 N° 8 (Août 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [084502-1/4] Titre : Analytical solution for forced convection in a sector duct filled with a porous medium Type de document : texte imprimé Auteurs : Wang, C. Y., Auteur Article en page(s) : pp. [084502-1/4] Note générale : Physique Langues : Anglais (eng) Mots-clés : Darcy-Brinkman  Porous  Sector  duct  Fully  developed  flow  Heat  transfer Index. décimale : 536 Chaleur. Thermodynamique Résumé : The fully developed viscous flow through a sector duct filled with a porous medium is studied. The Darcy–Brinkman and energy equations are solved analytically by series expansions in Bessel functions of the first kind. The problem is governed by a porous medium parameter s, which is proportional to the inverse square root of the permeability. For large s there exists a boundary layer on the walls, and the resistance increases greatly. The Nusselt number for the H1 heat transfer problem also increases. If the apex angle is acute, the local velocity and heat transfer are very low. If the apex angle is obtuse, the local shear and heat transfer are large. Tables for the friction factor-Reynolds number products and Nusselt numbers are determined for various s and apex angles. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Analytical solution for forced convection in a sector duct filled with a porous medium [texte imprimé] / Wang, C. Y., Auteur . - pp. [084502-1/4]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [084502-1/4] Mots-clés : Darcy-Brinkman  Porous  Sector  duct  Fully  developed  flow  Heat  transfer Index. décimale : 536 Chaleur. Thermodynamique Résumé : The fully developed viscous flow through a sector duct filled with a porous medium is studied. The Darcy–Brinkman and energy equations are solved analytically by series expansions in Bessel functions of the first kind. The problem is governed by a porous medium parameter s, which is proportional to the inverse square root of the permeability. For large s there exists a boundary layer on the walls, and the resistance increases greatly. The Nusselt number for the H1 heat transfer problem also increases. If the apex angle is acute, the local velocity and heat transfer are very low. If the apex angle is obtuse, the local shear and heat transfer are large. Tables for the friction factor-Reynolds number products and Nusselt numbers are determined for various s and apex angles. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Transient temperature data analysis for a supersonic flight test / Niranjan Sahoo in Journal of heat transfer, Vol. 132 N° 8 (Août 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [084503-1/5] Titre : Transient temperature data analysis for a supersonic flight test Type de document : texte imprimé Auteurs : Niranjan Sahoo, Auteur ; Ravi Kumar Peetala, Auteur Article en page(s) : pp. [084503-1/5] Note générale : Physique Langues : Anglais (eng) Mots-clés : Surface  heat  flux  Semi-infinite  analysis  Thin  film  approximation  Inverse  analysis Index. décimale : 536 Chaleur. Thermodynamique Résumé : Determination of transient surface heat flux from the temperature data is one of the traditional techniques applied in many engineering applications. With respect to high speed flight experiments, the time scale of measured temperature data is usually very small (~ms). So, one-dimensional heat conduction analysis is expensively used to infer surface heating rates on the body. For an analytical modeling, it is necessary to obtain a closed form solution from experimentally measured temperature data. In this paper, a temperature data obtained from a nickel film sensor during a supersonic flight test is considered for analysis. Three different curve fitting techniques are used to recover the temperature history of real time flight, namely, piecewise linear fit, polynomial fitting, and cubic-spline method. A one-dimensional transient heat transfer modeling is used to infer surface heating rates from the closed form temperature solutions. Results obtained from these analysis are compared and it is seen that peak surface heat flux values match very closely for polynomial and cubic-spline fitting of temperature data. But, the piecewise linear fit of temperature data underpredicts the peak surface heat flux value by four times from its counterparts. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Transient temperature data analysis for a supersonic flight test [texte imprimé] / Niranjan Sahoo, Auteur ; Ravi Kumar Peetala, Auteur . - pp. [084503-1/5]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 8 (Août 2010) . - pp. [084503-1/5] Mots-clés : Surface  heat  flux  Semi-infinite  analysis  Thin  film  approximation  Inverse  analysis Index. décimale : 536 Chaleur. Thermodynamique Résumé : Determination of transient surface heat flux from the temperature data is one of the traditional techniques applied in many engineering applications. With respect to high speed flight experiments, the time scale of measured temperature data is usually very small (~ms). So, one-dimensional heat conduction analysis is expensively used to infer surface heating rates on the body. For an analytical modeling, it is necessary to obtain a closed form solution from experimentally measured temperature data. In this paper, a temperature data obtained from a nickel film sensor during a supersonic flight test is considered for analysis. Three different curve fitting techniques are used to recover the temperature history of real time flight, namely, piecewise linear fit, polynomial fitting, and cubic-spline method. A one-dimensional transient heat transfer modeling is used to infer surface heating rates from the closed form temperature solutions. Results obtained from these analysis are compared and it is seen that peak surface heat flux values match very closely for polynomial and cubic-spline fitting of temperature data. But, the piecewise linear fit of temperature data underpredicts the peak surface heat flux value by four times from its counterparts. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

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