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Journal of heat transfer: Transactions of the ASME |
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Ajouter le résultat dans votre panierTomography-based analysis of radiative transfer in reacting packed beds undergoing a solid-gas thermochemical transformation / Sophia Haussener in Journal of heat transfer, Vol. 132 N° 6 (Juin 2010)
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061201-1/7]
Titre : Tomography-based analysis of radiative transfer in reacting packed beds undergoing a solid-gas thermochemical transformation Type de document : texte imprimé Auteurs : Sophia Haussener, Auteur ; Wojciech Lipinski, Auteur ; Peter Wyss, Auteur Article en page(s) : pp. [061201-1/7] Note générale : Physique Langues : Anglais (eng) Mots-clés : Packed-bed radiation Solar energy Gasification Chemical reactors Index. décimale : 536 Chaleur. Thermodynamique Résumé : A reacting packed-bed undergoing a high-temperature thermochemical solid-gas transformation is considered. The steam- and dry-gasification of carbonaceous materials to syngas is selected as the model reaction. The exact 3D digital geometrical representation of the packed-bed is obtained by computer tomography and used in direct pore-level simulations to characterize its morphological and radiative transport properties as a function of the reaction extent. Two-point correlation functions and mathematical morphology operations are applied to calculate porosities, specific surfaces, particle-size distributions, and representative elementary volumes. The collision-based Monte Carlo method is applied to determine the probability distribution of attenuation path length and direction of incidence at the solid-fluid boundary, which are linked to the extinction coefficient, scattering phase function, and scattering albedo. These effective properties can be then incorporated in continuum models of the reacting packed-bed.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Tomography-based analysis of radiative transfer in reacting packed beds undergoing a solid-gas thermochemical transformation [texte imprimé] / Sophia Haussener, Auteur ; Wojciech Lipinski, Auteur ; Peter Wyss, Auteur . - pp. [061201-1/7].
Physique
Langues : Anglais (eng)
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061201-1/7]
Mots-clés : Packed-bed radiation Solar energy Gasification Chemical reactors Index. décimale : 536 Chaleur. Thermodynamique Résumé : A reacting packed-bed undergoing a high-temperature thermochemical solid-gas transformation is considered. The steam- and dry-gasification of carbonaceous materials to syngas is selected as the model reaction. The exact 3D digital geometrical representation of the packed-bed is obtained by computer tomography and used in direct pore-level simulations to characterize its morphological and radiative transport properties as a function of the reaction extent. Two-point correlation functions and mathematical morphology operations are applied to calculate porosities, specific surfaces, particle-size distributions, and representative elementary volumes. The collision-based Monte Carlo method is applied to determine the probability distribution of attenuation path length and direction of incidence at the solid-fluid boundary, which are linked to the extinction coefficient, scattering phase function, and scattering albedo. These effective properties can be then incorporated in continuum models of the reacting packed-bed.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061202-1/7]
Titre : Simultaneous measurement of three-dimensional soot temperature and volume fraction fields in axisymmetric or asymmetric small unconfined flames with CCD cameras Type de document : texte imprimé Auteurs : D. Liu, Auteur ; Q. X. Huang, Auteur ; F. Wang, Auteur Article en page(s) : pp. [061202-1/7] Note générale : Physique Langues : Anglais (eng) Mots-clés : Soot temperature Soot volume fraction Axisymmetric flame Asymmetric flame CCD camera Index. décimale : 536 Chaleur. Thermodynamique Résumé : A nonintrusive measurement technique is presented numerically for simultaneous measurement of three-dimensional (3D) soot temperature and volume fraction fields in the axisymmetric or asymmetric flames with charge-coupled device (CCD) cameras. CCD cameras were introduced to capture the flame images for obtaining the line-of-sight radiation intensities. The distributions of local emission source under two wavelengths can be deduced through solving the reconstruction matrix equation by the least-square QR decomposition method from the knowledge of the line-of-sight radiation intensities of the flames. The two-color distributions of the local emission source were used to retrieve the soot temperature and volume fraction distributions. The effects of the discrete ray number of CCD cameras, the number of CCD cameras, and the system signal-to-noise ratio (SNR) on the measurement were investigated. The results show that for accurate measurement of soot volume fraction field, the CCD cameras number should not be less than four and the system SNR can be as low as 54 dB. The proposed technique can be capable for reconstructing the 3D soot temperature and volume fraction fields in both axisymmetric and asymmetric flames well.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Simultaneous measurement of three-dimensional soot temperature and volume fraction fields in axisymmetric or asymmetric small unconfined flames with CCD cameras [texte imprimé] / D. Liu, Auteur ; Q. X. Huang, Auteur ; F. Wang, Auteur . - pp. [061202-1/7].
Physique
Langues : Anglais (eng)
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061202-1/7]
Mots-clés : Soot temperature Soot volume fraction Axisymmetric flame Asymmetric flame CCD camera Index. décimale : 536 Chaleur. Thermodynamique Résumé : A nonintrusive measurement technique is presented numerically for simultaneous measurement of three-dimensional (3D) soot temperature and volume fraction fields in the axisymmetric or asymmetric flames with charge-coupled device (CCD) cameras. CCD cameras were introduced to capture the flame images for obtaining the line-of-sight radiation intensities. The distributions of local emission source under two wavelengths can be deduced through solving the reconstruction matrix equation by the least-square QR decomposition method from the knowledge of the line-of-sight radiation intensities of the flames. The two-color distributions of the local emission source were used to retrieve the soot temperature and volume fraction distributions. The effects of the discrete ray number of CCD cameras, the number of CCD cameras, and the system signal-to-noise ratio (SNR) on the measurement were investigated. The results show that for accurate measurement of soot volume fraction field, the CCD cameras number should not be less than four and the system SNR can be as low as 54 dB. The proposed technique can be capable for reconstructing the 3D soot temperature and volume fraction fields in both axisymmetric and asymmetric flames well.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061301-1/7]
Titre : Theory of fractional order generalized thermoelasticity Type de document : texte imprimé Auteurs : Hamdy M. Youssef, Auteur Article en page(s) : pp. [061301-1/7] Note générale : Physique Langues : Anglais (eng) Mots-clés : Heat conduction Laplace transforms State-space methods Thermoelasticity Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this work, a new model of thermoelasticity theory has been constructed in the context of a new consideration of heat conduction with fractional order, and its uniqueness theorem has been approved also. One-dimensional application for a half-space of elastic material, which is thermally shocked, has been solved by using Laplace transform and state-space techniques. According to the numerical results and its graphs, conclusion about the new theory of thermoelasticity has been constructed.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Theory of fractional order generalized thermoelasticity [texte imprimé] / Hamdy M. Youssef, Auteur . - pp. [061301-1/7].
Physique
Langues : Anglais (eng)
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061301-1/7]
Mots-clés : Heat conduction Laplace transforms State-space methods Thermoelasticity Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this work, a new model of thermoelasticity theory has been constructed in the context of a new consideration of heat conduction with fractional order, and its uniqueness theorem has been approved also. One-dimensional application for a half-space of elastic material, which is thermally shocked, has been solved by using Laplace transform and state-space techniques. According to the numerical results and its graphs, conclusion about the new theory of thermoelasticity has been constructed.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061302-1/9]
Titre : Determination of time-delay parameters in the dual-phase lagging heat conduction model Type de document : texte imprimé Auteurs : J. Ordonez-Miranda, Auteur ; J. J. Alvarado-Gil, Auteur Article en page(s) : pp. [061302-1/9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Dual-phase lagging model Time delays system Heat conduction Index. décimale : 536 Chaleur. Thermodynamique Résumé : The study of thermal transport based on the dual-phase lagging model involves not only the well known thermal properties but also two additional time parameters. Those parameters permit to take into account the thermal inertia and the microstructural interactions of the media in such a way that they establish the nonsimultaneity between temperature changes and heat flux. In the dual-phase lagging model, heat transport phenomena are extremely sensitive not only to the size of each time parameter but also to the relative size of them. In order to obtain useful and reliable results, it is important to develop methodologies for the determination of those time parameters. Additionally it is necessary to count with tools that allow evaluating easily the sensitivity of the temperature and heat to the changes in those time parameters. In this work, a system formed by a semi-infinite layer in thermal contact with a finite one, which is excited by a modulated heat flux, is studied. When the thermal effusivities of the layers are quite different, it is shown that a frequency range can be found in which the normalized amplitude and phase of the spatial component of the oscillatory surface temperature show strong oscillations. This behavior is used to obtain explicit formulas for determining simultaneously the time parameters as well as additional thermal properties of the finite layer, under the framework of the dual-phase lagging model of heat conduction. The limits of the corresponding equations for single-phase lagging models of heat conduction are also discussed.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Determination of time-delay parameters in the dual-phase lagging heat conduction model [texte imprimé] / J. Ordonez-Miranda, Auteur ; J. J. Alvarado-Gil, Auteur . - pp. [061302-1/9].
Physique
Langues : Anglais (eng)
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061302-1/9]
Mots-clés : Dual-phase lagging model Time delays system Heat conduction Index. décimale : 536 Chaleur. Thermodynamique Résumé : The study of thermal transport based on the dual-phase lagging model involves not only the well known thermal properties but also two additional time parameters. Those parameters permit to take into account the thermal inertia and the microstructural interactions of the media in such a way that they establish the nonsimultaneity between temperature changes and heat flux. In the dual-phase lagging model, heat transport phenomena are extremely sensitive not only to the size of each time parameter but also to the relative size of them. In order to obtain useful and reliable results, it is important to develop methodologies for the determination of those time parameters. Additionally it is necessary to count with tools that allow evaluating easily the sensitivity of the temperature and heat to the changes in those time parameters. In this work, a system formed by a semi-infinite layer in thermal contact with a finite one, which is excited by a modulated heat flux, is studied. When the thermal effusivities of the layers are quite different, it is shown that a frequency range can be found in which the normalized amplitude and phase of the spatial component of the oscillatory surface temperature show strong oscillations. This behavior is used to obtain explicit formulas for determining simultaneously the time parameters as well as additional thermal properties of the finite layer, under the framework of the dual-phase lagging model of heat conduction. The limits of the corresponding equations for single-phase lagging models of heat conduction are also discussed.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061501-1/11]
Titre : On the mechanism of pool boiling critical heat flux enhancement in nanofluids Type de document : texte imprimé Auteurs : Hyungdae Kim, Auteur ; Ho Seon Ahn, Auteur ; Moo Hwan Kim, Auteur Article en page(s) : pp. [061501-1/11] Note générale : Physique Langues : Anglais (eng) Mots-clés : Critical heat flux Evaporating meniscus Nanoparticle deposition Wetting Index. décimale : 536 Chaleur. Thermodynamique Résumé : The pool boiling characteristics of water-based nanofluids with alumina and titania nanoparticles of 0.01 vol % were investigated on a thermally heated disk heater at saturated temperature and atmospheric pressure. The results confirmed the findings of previous studies that nanofluids can significantly enhance the critical heat flux (CHF), resulting in a large increase in the wall superheat. It was found that some nanoparticles deposit on the heater surface during nucleate boiling, and the surface modification due to the deposition results in the same magnitude of CHF enhancement in pure water as for nanofluids. Subsequent to the boiling experiments, the interfacial properties of the heater surfaces were examined using dynamic wetting of an evaporating water droplet. As the surface temperature increased, the evaporating meniscus on the clean surface suddenly receded toward the liquid due to the evaporation recoil force on the liquid-vapor interface, but the nanoparticle-fouled surface exhibited stable wetting of the liquid meniscus even at a remarkably higher wall superheat. The heat flux gain attainable due to the improved wetting of the evaporating meniscus on the fouled surface showed good agreement with the CHF enhancement during nanofluid boiling. It is supposed that the nanoparticle layer increases the stability of the evaporating microlayer underneath a bubble growing on a heated surface and thus the irreversible growth of a hot/dry spot is inhibited even at a high wall superheat, resulting in the CHF enhancement observed when boiling nanofluids.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] On the mechanism of pool boiling critical heat flux enhancement in nanofluids [texte imprimé] / Hyungdae Kim, Auteur ; Ho Seon Ahn, Auteur ; Moo Hwan Kim, Auteur . - pp. [061501-1/11].
Physique
Langues : Anglais (eng)
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061501-1/11]
Mots-clés : Critical heat flux Evaporating meniscus Nanoparticle deposition Wetting Index. décimale : 536 Chaleur. Thermodynamique Résumé : The pool boiling characteristics of water-based nanofluids with alumina and titania nanoparticles of 0.01 vol % were investigated on a thermally heated disk heater at saturated temperature and atmospheric pressure. The results confirmed the findings of previous studies that nanofluids can significantly enhance the critical heat flux (CHF), resulting in a large increase in the wall superheat. It was found that some nanoparticles deposit on the heater surface during nucleate boiling, and the surface modification due to the deposition results in the same magnitude of CHF enhancement in pure water as for nanofluids. Subsequent to the boiling experiments, the interfacial properties of the heater surfaces were examined using dynamic wetting of an evaporating water droplet. As the surface temperature increased, the evaporating meniscus on the clean surface suddenly receded toward the liquid due to the evaporation recoil force on the liquid-vapor interface, but the nanoparticle-fouled surface exhibited stable wetting of the liquid meniscus even at a remarkably higher wall superheat. The heat flux gain attainable due to the improved wetting of the evaporating meniscus on the fouled surface showed good agreement with the CHF enhancement during nanofluid boiling. It is supposed that the nanoparticle layer increases the stability of the evaporating microlayer underneath a bubble growing on a heated surface and thus the irreversible growth of a hot/dry spot is inhibited even at a high wall superheat, resulting in the CHF enhancement observed when boiling nanofluids.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061502-1/7]
Titre : Heat transport capability and fluid flow neutron radiography of three-dimensional oscillating heat pipes Type de document : texte imprimé Auteurs : B. Borgmeyer, Auteur ; C. Wilson, Auteur ; R. A. Winholtz, Auteur Article en page(s) : pp. [061502-1/7] Note générale : Physique Langues : Anglais (eng) Mots-clés : Oscillating heat pipe Heat transfer Fluid flow Neutron radiography Index. décimale : 536 Chaleur. Thermodynamique Résumé : An experimental investigation into the parameters affecting heat transport in two three-dimensional oscillating heat pipes (OHPs) was implemented. A three-dimensional OHP is one in which the center axis of the circular channels containing the internal working fluid do not lie in the same plane. This novel design allows for more turns in a more compact size. The OHPs in the current investigation is made of copper tubings (3.175 mm outside diameter, 1.65 mm inside diameter) wrapped in a three-dimensional fashion around two copper spreaders that act as the evaporator and condenser. The two OHPs have 10 and 20 turns in both the evaporator and condenser. The 20-turn OHP was filled to 50% of the total volume with a high performance liquid chromatography grade water. Transient and steady state temperature data were recorded at different locations for various parameters. Parameters such as heat input, operating temperature, and filling ratio were varied to determine its effect on the overall heat transport. Neutron radiography was simultaneously implemented to create images of the internal working fluid flow at a rate of 30 frames per second. Results show the average temperature drop from the evaporator to condenser decreases at higher heat inputs due to an increase in temperature throughout the condenser region due to greater oscillations. These large oscillations were visually observed using neutron radiography. As the operating temperature is increased, the thermal resistance is reduced. A decrease in filling ratio tends to create more steady fluid motion; however, the heat transfer performance is reduced.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Heat transport capability and fluid flow neutron radiography of three-dimensional oscillating heat pipes [texte imprimé] / B. Borgmeyer, Auteur ; C. Wilson, Auteur ; R. A. Winholtz, Auteur . - pp. [061502-1/7].
Physique
Langues : Anglais (eng)
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061502-1/7]
Mots-clés : Oscillating heat pipe Heat transfer Fluid flow Neutron radiography Index. décimale : 536 Chaleur. Thermodynamique Résumé : An experimental investigation into the parameters affecting heat transport in two three-dimensional oscillating heat pipes (OHPs) was implemented. A three-dimensional OHP is one in which the center axis of the circular channels containing the internal working fluid do not lie in the same plane. This novel design allows for more turns in a more compact size. The OHPs in the current investigation is made of copper tubings (3.175 mm outside diameter, 1.65 mm inside diameter) wrapped in a three-dimensional fashion around two copper spreaders that act as the evaporator and condenser. The two OHPs have 10 and 20 turns in both the evaporator and condenser. The 20-turn OHP was filled to 50% of the total volume with a high performance liquid chromatography grade water. Transient and steady state temperature data were recorded at different locations for various parameters. Parameters such as heat input, operating temperature, and filling ratio were varied to determine its effect on the overall heat transport. Neutron radiography was simultaneously implemented to create images of the internal working fluid flow at a rate of 30 frames per second. Results show the average temperature drop from the evaporator to condenser decreases at higher heat inputs due to an increase in temperature throughout the condenser region due to greater oscillations. These large oscillations were visually observed using neutron radiography. As the operating temperature is increased, the thermal resistance is reduced. A decrease in filling ratio tends to create more steady fluid motion; however, the heat transfer performance is reduced.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061701-1/12]
Titre : Effect of return bend and entrance on heat transfer in thermally developing laminar flow in round pipes of some heat transfer fluids with high prandtl numbers Type de document : texte imprimé Auteurs : Predrag S. Hrnjak, Auteur ; S. H. Hong, Auteur Article en page(s) : pp. [061701-1/12] Note générale : Physique Langues : Anglais (eng) Mots-clés : Laminar flow Effect of U-bend High Pr number Secondary coolant Index. décimale : 536 Chaleur. Thermodynamique Résumé : The paper presents experimental results and analysis of heat transfer in a thermally developing region of round pipes for three fluids typically used as low temperature coolants, in the range of 0–−40°C. The experiments were performed at low Re (200–1000) and high Pr (80–140) numbers that are typically found in secondary refrigeration loop conditions. The effect of horizontal U-bend is also presented. It is shown that the positive effect of thermal development (high Nu number) lasts long because of the technically significant length of the thermally developing region. Secondary flows developed in and after the U-bend are so significant that they have almost an identical effect as the thermal development at the pipe entrance. That is a reason for the extremely good performance of the heat exchangers with secondary refrigerants in laminar flow regimes. Experimental data are presented with developed empirical correlations, which show good relationships to several existing correlations.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Effect of return bend and entrance on heat transfer in thermally developing laminar flow in round pipes of some heat transfer fluids with high prandtl numbers [texte imprimé] / Predrag S. Hrnjak, Auteur ; S. H. Hong, Auteur . - pp. [061701-1/12].
Physique
Langues : Anglais (eng)
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061701-1/12]
Mots-clés : Laminar flow Effect of U-bend High Pr number Secondary coolant Index. décimale : 536 Chaleur. Thermodynamique Résumé : The paper presents experimental results and analysis of heat transfer in a thermally developing region of round pipes for three fluids typically used as low temperature coolants, in the range of 0–−40°C. The experiments were performed at low Re (200–1000) and high Pr (80–140) numbers that are typically found in secondary refrigeration loop conditions. The effect of horizontal U-bend is also presented. It is shown that the positive effect of thermal development (high Nu number) lasts long because of the technically significant length of the thermally developing region. Secondary flows developed in and after the U-bend are so significant that they have almost an identical effect as the thermal development at the pipe entrance. That is a reason for the extremely good performance of the heat exchangers with secondary refrigerants in laminar flow regimes. Experimental data are presented with developed empirical correlations, which show good relationships to several existing correlations.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061702-1/8]
Titre : Effect of pin density on heat-mass transfer and fluid flow at low reynolds numbers in minichannels Type de document : texte imprimé Auteurs : N. K. C. Selvarasu, Auteur ; Danesh K. Tafti, Auteur ; Neal E. Blackwell, Auteur Article en page(s) : pp. [061702-1/8] Note générale : Physique Langues : Anglais (eng) Mots-clés : Heat transfer Pin fins Low Reynolds number Thermal performance Entropy generation minimization (EGM) Minichannels Index. décimale : 536 Chaleur. Thermodynamique Résumé : Previous investigations on the performance of straight pins, pins with tip clearance, and profiled fins showed that closely packed cylindrical pin fins are very competitive with the modified pins. Therefore, the objective of this paper is to investigate the effect of pin density on performance. Steady/time-dependent calculations are performed to investigate the effect of pin density on friction and heat transfer. Pins packed at distances of SD=1.1, 1.2, 1.3, 1.4, 1.5, 2.0, 2.5, and 3 pin diameters (D) are investigated for 10<=ReD<=600. Two performance measures are used to compare the different pin fin densities. The first measure is to maximize heat transfer capacity for a given pumping power compared with a plane channel. The second measure used is based on entropy generation minimization (EGM), where the objective is to reduce the total irreversibility of the pin fin array to obtain an optimal spacing. Based on the performance measure of maximizing heat capacity, it is shown that for plain channels operating in the laminar range using denser pin packing has distinct advantages with SD=1.1 providing the best augmentation. However, the augmentation in heat capacity becomes relatively independent of the pin density for a channel operating in the turbulent regime. Based on the EGM method, at ReD>200, SD=1.3, 1.4, and 1.5 are the most suitable, with the least entropy generation observed at SD=1.4. At ReD<200, SD=1.1, 1.2, and 1.3 are also suitable for keeping entropy generation low.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Effect of pin density on heat-mass transfer and fluid flow at low reynolds numbers in minichannels [texte imprimé] / N. K. C. Selvarasu, Auteur ; Danesh K. Tafti, Auteur ; Neal E. Blackwell, Auteur . - pp. [061702-1/8].
Physique
Langues : Anglais (eng)
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061702-1/8]
Mots-clés : Heat transfer Pin fins Low Reynolds number Thermal performance Entropy generation minimization (EGM) Minichannels Index. décimale : 536 Chaleur. Thermodynamique Résumé : Previous investigations on the performance of straight pins, pins with tip clearance, and profiled fins showed that closely packed cylindrical pin fins are very competitive with the modified pins. Therefore, the objective of this paper is to investigate the effect of pin density on performance. Steady/time-dependent calculations are performed to investigate the effect of pin density on friction and heat transfer. Pins packed at distances of SD=1.1, 1.2, 1.3, 1.4, 1.5, 2.0, 2.5, and 3 pin diameters (D) are investigated for 10<=ReD<=600. Two performance measures are used to compare the different pin fin densities. The first measure is to maximize heat transfer capacity for a given pumping power compared with a plane channel. The second measure used is based on entropy generation minimization (EGM), where the objective is to reduce the total irreversibility of the pin fin array to obtain an optimal spacing. Based on the performance measure of maximizing heat capacity, it is shown that for plain channels operating in the laminar range using denser pin packing has distinct advantages with SD=1.1 providing the best augmentation. However, the augmentation in heat capacity becomes relatively independent of the pin density for a channel operating in the turbulent regime. Based on the EGM method, at ReD>200, SD=1.3, 1.4, and 1.5 are the most suitable, with the least entropy generation observed at SD=1.4. At ReD<200, SD=1.1, 1.2, and 1.3 are also suitable for keeping entropy generation low.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061703-1/6]
Titre : Heat and mass transfer on the unsteady magnetohydrodynamic flow due to a porous rotating disk subject to a uniform outer radial flow Type de document : texte imprimé Auteurs : Mustafa Turkyilmazoglu, Auteur Article en page(s) : pp. [061703-1/6] Note générale : Physique Langues : Anglais (eng) Mots-clés : Radial flow Unsteady MHD flow Porous rotating disk Heat transfer Index. décimale : 536 Chaleur. Thermodynamique Résumé : An unsteady flow and heat transfer of an incompressible electrically conducting fluid over a porous rotating infinite disk impulsively set into motion are studied in the present paper. The disk finds itself subjected to a uniform normal magnetic field. The particular interest lies in searching for the effects of an imposed uniform outer radial flow far above the disk on the behavior of the physical flow. The governing Navier–Stokes and Maxwell equations of the hydromagnetic fluid, together with the energy equation, are converted into self-similar forms using suitable similarity transformations. A compact, unconditionally stable, and highly accurate implicit spectral numerical integration algorithm is then employed in order to resolve the transient behavior of the velocity and temperature fields. The time evolution and steady state case of some parameters of fundamental physical significance such as the surface shear stresses in the radial and tangential directions and the heat transfer rate are also fully examined for the entire family of magnetic interaction, radial flow, and suction/blowing parameters.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Heat and mass transfer on the unsteady magnetohydrodynamic flow due to a porous rotating disk subject to a uniform outer radial flow [texte imprimé] / Mustafa Turkyilmazoglu, Auteur . - pp. [061703-1/6].
Physique
Langues : Anglais (eng)
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061703-1/6]
Mots-clés : Radial flow Unsteady MHD flow Porous rotating disk Heat transfer Index. décimale : 536 Chaleur. Thermodynamique Résumé : An unsteady flow and heat transfer of an incompressible electrically conducting fluid over a porous rotating infinite disk impulsively set into motion are studied in the present paper. The disk finds itself subjected to a uniform normal magnetic field. The particular interest lies in searching for the effects of an imposed uniform outer radial flow far above the disk on the behavior of the physical flow. The governing Navier–Stokes and Maxwell equations of the hydromagnetic fluid, together with the energy equation, are converted into self-similar forms using suitable similarity transformations. A compact, unconditionally stable, and highly accurate implicit spectral numerical integration algorithm is then employed in order to resolve the transient behavior of the velocity and temperature fields. The time evolution and steady state case of some parameters of fundamental physical significance such as the surface shear stresses in the radial and tangential directions and the heat transfer rate are also fully examined for the entire family of magnetic interaction, radial flow, and suction/blowing parameters.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061801-1/8]
Titre : Thermal hydraulic study of a single row heat exchanger with helically finned tubes Type de document : texte imprimé Auteurs : H. Huisseune, Auteur ; C. T'Joen, Auteur ; P. Brodeoux, Auteur Article en page(s) : pp. [061801-1/8] Note générale : Physique Langues : Anglais (eng) Mots-clés : Helical fin Single row Heat exchanger Heat transfer Friction Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this study, the heat transfer and friction correlation of a single row heat exchanger with helically finned tubes are experimentally determined. The transversal tube pitch was parametrically varied. A detailed description of the test rig and the data reduction procedure is given. A thorough uncertainty analysis was performed to validate the results. The proposed heat transfer correlation can describe 95% of the data within ±11% and shows a 4.49% mean deviation. The friction correlation predicts 95% of the data within ±19% with a mean deviation of 6.84%. The new correlations show the same trend as most correlations from open literature, but none of the literature correlations are able to accurately predict the results of this study.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Thermal hydraulic study of a single row heat exchanger with helically finned tubes [texte imprimé] / H. Huisseune, Auteur ; C. T'Joen, Auteur ; P. Brodeoux, Auteur . - pp. [061801-1/8].
Physique
Langues : Anglais (eng)
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061801-1/8]
Mots-clés : Helical fin Single row Heat exchanger Heat transfer Friction Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this study, the heat transfer and friction correlation of a single row heat exchanger with helically finned tubes are experimentally determined. The transversal tube pitch was parametrically varied. A detailed description of the test rig and the data reduction procedure is given. A thorough uncertainty analysis was performed to validate the results. The proposed heat transfer correlation can describe 95% of the data within ±11% and shows a 4.49% mean deviation. The friction correlation predicts 95% of the data within ±19% with a mean deviation of 6.84%. The new correlations show the same trend as most correlations from open literature, but none of the literature correlations are able to accurately predict the results of this study.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [062301-1/11]
Titre : Melting of phase change materials with volume change in metal foams Type de document : texte imprimé Auteurs : Zhen Yang, Auteur ; Suresh V. Garimella, Auteur Article en page(s) : pp. [062301-1/11] Note générale : Physique Langues : Anglais (eng) Mots-clés : Convection Enthalpy Finite volume methods Flow simulation Flow through porous media Melting Metal foams Phase change materials Thermal diffusivity Index. décimale : 536 Chaleur. Thermodynamique Résumé : Melting of phase change materials (PCMs) embedded in metal foams is investigated. The two-temperature model developed accounts for volume change in the PCM upon melting. Volume-averaged mass and momentum equations are solved, with the Brinkman–Forchheimer extension to Darcy's law employed to model the porous-medium resistance. Local thermal equilibrium does not hold due to the large difference in thermal diffusivity between the metal foam and the PCM. Therefore, a two-temperature approach is adopted, with the heat transfer between the metal foam and the PCM being coupled by means of an interstitial Nusselt number. The enthalpy method is applied to account for phase change. The governing equations are solved using a finite-volume approach. Effects of volume shrinkage/expansion are considered for different interstitial heat transfer rates between the foam and PCM. The detailed behavior of the melting region as a function of buoyancy-driven convection and interstitial Nusselt number is analyzed. For strong interstitial heat transfer, the melting region is significantly reduced in extent and the melting process is greatly enhanced as is heat transfer from the wall; the converse applies for weak interstitial heat transfer. The melting process at a low interstitial Nusselt number is significantly influenced by melt convection, while the behavior is dominated by conduction at high interstitial Nusselt numbers. Volume shrinkage/expansion due to phase change induces an added flow, which affects the PCM melting rate.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Melting of phase change materials with volume change in metal foams [texte imprimé] / Zhen Yang, Auteur ; Suresh V. Garimella, Auteur . - pp. [062301-1/11].
Physique
Langues : Anglais (eng)
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [062301-1/11]
Mots-clés : Convection Enthalpy Finite volume methods Flow simulation Flow through porous media Melting Metal foams Phase change materials Thermal diffusivity Index. décimale : 536 Chaleur. Thermodynamique Résumé : Melting of phase change materials (PCMs) embedded in metal foams is investigated. The two-temperature model developed accounts for volume change in the PCM upon melting. Volume-averaged mass and momentum equations are solved, with the Brinkman–Forchheimer extension to Darcy's law employed to model the porous-medium resistance. Local thermal equilibrium does not hold due to the large difference in thermal diffusivity between the metal foam and the PCM. Therefore, a two-temperature approach is adopted, with the heat transfer between the metal foam and the PCM being coupled by means of an interstitial Nusselt number. The enthalpy method is applied to account for phase change. The governing equations are solved using a finite-volume approach. Effects of volume shrinkage/expansion are considered for different interstitial heat transfer rates between the foam and PCM. The detailed behavior of the melting region as a function of buoyancy-driven convection and interstitial Nusselt number is analyzed. For strong interstitial heat transfer, the melting region is significantly reduced in extent and the melting process is greatly enhanced as is heat transfer from the wall; the converse applies for weak interstitial heat transfer. The melting process at a low interstitial Nusselt number is significantly influenced by melt convection, while the behavior is dominated by conduction at high interstitial Nusselt numbers. Volume shrinkage/expansion due to phase change induces an added flow, which affects the PCM melting rate.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [062401-1/9]
Titre : Effect of particle migration on flow and convective heat transfer of nanofluids flowing through a circular pipe Type de document : texte imprimé Auteurs : M. M. Heyhat, Auteur ; F. Kowsary, Auteur Article en page(s) : pp. [062401-1/9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Nonofluids Heat transfer Thermophoresis Brownian motion Nonuniform particle distribution Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper aims to study the effect of particle migration on flow and heat transfer of nanofluids flowing through a circular pipe. To do this, a two-component model proposed by Buongiorno (2006, “Convective Transport in Nanofluids,” ASME J. Heat Transfer, 128, pp. 240–250) was used and a numerical study on laminar flow of alumina-water nanofluid through a constant wall temperature tube was performed. The effects of nonuniform distribution of particles on heat-transfer coefficient and wall shear stress are shown. Obtained results illustrate that by considering the particle migration, the heat-transfer coefficient increases while the wall shear stress decreases, compared with uniform volume fraction. Thus, it can be concluded that the enhancement of the convective heat transfer could not be solely attributed to the enhancement of the effective thermal conductivity, and beside other reasons, which may be listed as this higher enhancement, particle migration is proposed to be an important reason.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Effect of particle migration on flow and convective heat transfer of nanofluids flowing through a circular pipe [texte imprimé] / M. M. Heyhat, Auteur ; F. Kowsary, Auteur . - pp. [062401-1/9].
Physique
Langues : Anglais (eng)
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [062401-1/9]
Mots-clés : Nonofluids Heat transfer Thermophoresis Brownian motion Nonuniform particle distribution Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper aims to study the effect of particle migration on flow and heat transfer of nanofluids flowing through a circular pipe. To do this, a two-component model proposed by Buongiorno (2006, “Convective Transport in Nanofluids,” ASME J. Heat Transfer, 128, pp. 240–250) was used and a numerical study on laminar flow of alumina-water nanofluid through a constant wall temperature tube was performed. The effects of nonuniform distribution of particles on heat-transfer coefficient and wall shear stress are shown. Obtained results illustrate that by considering the particle migration, the heat-transfer coefficient increases while the wall shear stress decreases, compared with uniform volume fraction. Thus, it can be concluded that the enhancement of the convective heat transfer could not be solely attributed to the enhancement of the effective thermal conductivity, and beside other reasons, which may be listed as this higher enhancement, particle migration is proposed to be an important reason.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [062402-1/9]
Titre : Heat transfer augmentation of parallel flows by means of electric conduction phenomenon in macro- and microscales Type de document : texte imprimé Auteurs : Miad Yazdani, Auteur ; Jamal Seyed-Yagoobi, Auteur Article en page(s) : pp. [062402-1/9] Note générale : Physique Langues : Anglais (eng) Mots-clés : EHD conduction Parallet flow Heat transfer enhancement Index. décimale : 536 Chaleur. Thermodynamique Résumé : Electrohydrodynamic conduction phenomenon takes advantage of the electrical Coulomb force exerted on a dielectric liquid generated by externally applied electric field and dissociated charges from electrolytes. The electric conduction phenomenon can be applied to enhance or control mass transport and heat transfer in both terrestrial and microgravity environments with advantages of simplicity and no degradation of fluid properties for isothermal as well as nonisothermal liquids. This paper numerically studies the heat transfer augmentation of externally driven macro- and microscale parallel flows by means of electric conduction phenomenon. The electric conduction is generated via electrode pairs embedded against the channel wall to mainly enhance the heat transfer and not necessarily to pump the liquid. Two cases of Poiseuille and Couette parallel flows are considered where for the former, a constant external pressure gradient is applied along the channel and for the latter, the channel wall moves with a constant velocity. The electric field and electric body force distributions along with the resultant velocity fields are presented. The heat transfer enhancements are illustrated under various operating conditions for both macro- and microscales.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Heat transfer augmentation of parallel flows by means of electric conduction phenomenon in macro- and microscales [texte imprimé] / Miad Yazdani, Auteur ; Jamal Seyed-Yagoobi, Auteur . - pp. [062402-1/9].
Physique
Langues : Anglais (eng)
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [062402-1/9]
Mots-clés : EHD conduction Parallet flow Heat transfer enhancement Index. décimale : 536 Chaleur. Thermodynamique Résumé : Electrohydrodynamic conduction phenomenon takes advantage of the electrical Coulomb force exerted on a dielectric liquid generated by externally applied electric field and dissociated charges from electrolytes. The electric conduction phenomenon can be applied to enhance or control mass transport and heat transfer in both terrestrial and microgravity environments with advantages of simplicity and no degradation of fluid properties for isothermal as well as nonisothermal liquids. This paper numerically studies the heat transfer augmentation of externally driven macro- and microscale parallel flows by means of electric conduction phenomenon. The electric conduction is generated via electrode pairs embedded against the channel wall to mainly enhance the heat transfer and not necessarily to pump the liquid. Two cases of Poiseuille and Couette parallel flows are considered where for the former, a constant external pressure gradient is applied along the channel and for the latter, the channel wall moves with a constant velocity. The electric field and electric body force distributions along with the resultant velocity fields are presented. The heat transfer enhancements are illustrated under various operating conditions for both macro- and microscales.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [062501-1/12]
Titre : Buoyancy driven heat transfer of nanofluids in a tilted enclosure Type de document : texte imprimé Auteurs : Kamil Kahveci, Auteur Article en page(s) : pp. [062501-1/12] Note générale : Physique Langues : Anglais (eng) Mots-clés : Naturel convection Nanofluid Enclosure PDQ Vorticity Stream function Index. décimale : 536 Chaleur. Thermodynamique Résumé : Buoyancy driven heat transfer of water-based nanofluids in a differentially heated, tilted enclosure is investigated in this study. The governing equations (obtained with the Boussinesq approximation) are solved using the polynomial differential quadrature method for an inclination angle ranging from 0 deg to 90 deg, two different ratios of the nanolayer thickness to the original particle radius (0.02 and 0.1), a solid volume fraction ranging from 0% to 20%, and a Rayleigh number varying from 104 to 106. Five types of nanoparticles, Cu, Ag, CuO, Al2O3, and TiO2 are taken into consideration. The results show that the average heat transfer rate from highest to lowest is for Ag, Cu, CuO, Al2O3, and TiO2. The results also show that for the particle radius generally used in practice (beta=0.1 or beta=0.02), the average heat transfer rate increases to 44% for Ra=104, to 53% for Ra=105, and to 54% for Ra=106 if the special case of theta=90 deg, which also produces the minimum heat transfer rates, is not taken into consideration. As for theta=90 deg, the heat transfer enhancement reaches 21% for Ra=104, 44% for Ra=105, and 138% for Ra=106. The average heat transfer rate shows an increasing trend with an increasing inclination angle, and a peak value is detected. Beyond the peak point, the foregoing trend reverses and the average heat transfer rate decreases with a further increase in the inclination angle. Maximum heat transfer takes place at theta=45 deg for Ra=104 and at theta=30 deg for Ra=105 and 106.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Buoyancy driven heat transfer of nanofluids in a tilted enclosure [texte imprimé] / Kamil Kahveci, Auteur . - pp. [062501-1/12].
Physique
Langues : Anglais (eng)
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [062501-1/12]
Mots-clés : Naturel convection Nanofluid Enclosure PDQ Vorticity Stream function Index. décimale : 536 Chaleur. Thermodynamique Résumé : Buoyancy driven heat transfer of water-based nanofluids in a differentially heated, tilted enclosure is investigated in this study. The governing equations (obtained with the Boussinesq approximation) are solved using the polynomial differential quadrature method for an inclination angle ranging from 0 deg to 90 deg, two different ratios of the nanolayer thickness to the original particle radius (0.02 and 0.1), a solid volume fraction ranging from 0% to 20%, and a Rayleigh number varying from 104 to 106. Five types of nanoparticles, Cu, Ag, CuO, Al2O3, and TiO2 are taken into consideration. The results show that the average heat transfer rate from highest to lowest is for Ag, Cu, CuO, Al2O3, and TiO2. The results also show that for the particle radius generally used in practice (beta=0.1 or beta=0.02), the average heat transfer rate increases to 44% for Ra=104, to 53% for Ra=105, and to 54% for Ra=106 if the special case of theta=90 deg, which also produces the minimum heat transfer rates, is not taken into consideration. As for theta=90 deg, the heat transfer enhancement reaches 21% for Ra=104, 44% for Ra=105, and 138% for Ra=106. The average heat transfer rate shows an increasing trend with an increasing inclination angle, and a peak value is detected. Beyond the peak point, the foregoing trend reverses and the average heat transfer rate decreases with a further increase in the inclination angle. Maximum heat transfer takes place at theta=45 deg for Ra=104 and at theta=30 deg for Ra=105 and 106.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [062502-1/10]
Titre : Effects of insulated and isothermal baffles on pseudosteady-state natural convection inside spherical containers Type de document : texte imprimé Auteurs : Yuping Duan, Auteur ; S. F. Hosseinizadeh, Auteur ; J. M. Khodadadi, Auteur Article en page(s) : pp. [062502-1/10] Note générale : Physique Langues : Anglais (eng) Mots-clés : Boundary layer turbulence Finite volume methods Flow simulation Fluid oscillations Iterative methods Natural convection Stratified flow Vortices Index. décimale : 536 Chaleur. Thermodynamique Résumé : The effects of insulated and isothermal thin baffles on pseudosteady-state natural convection within spherical containers were studied computationally. The computations are based on an iterative, finite-volume numerical procedure using primitive dependent variables. Natural convection effect is modeled via the Boussinesq approximation. Parametric studies were performed for a Prandtl number of 0.7. For Rayleigh numbers of 104, 105, 106, and 107, baffles with three lengths positioned at five different locations were investigated (120 cases). The fluid that is heated adjacent to the sphere rises replacing the colder fluid, which sinks downward through the stratified stable thermal layer. For high Ra number cases, the hot fluid at the bottom of the sphere is also observed to rise along the symmetry axis and encounter the sinking colder fluid, thus causing oscillations in the temperature and flow fields. Due to flow obstruction (blockage or confinement) effect of baffles and also because of the extra heating afforded by the isothermal baffle, multi-cell recirculating vortices are observed. This additional heat is directly linked to creation of another recirculating vortex next to the baffle. In effect, hot fluid is directed into the center of the sphere disrupting thermal stratified layers. For the majority of the baffles investigated, the Nusselt numbers were generally lower than the reference cases with no baffle. The extent of heat transfer modification depends on Ra, length, and location of the extended surface. With an insulated baffle, the lowest amount of absorbed heat corresponds to a baffle positioned horizontally. Placing a baffle near the top of the sphere for high Ra number cases can lead to heat transfer enhancement that is linked to disturbance of the thermal boundary layer. With isothermal baffles, heat transfer enhancement is achieved for a baffle placed near the bottom of the sphere due to interaction of the counterclockwise rotating vortex and the stratified layer. For some high Ra cases, strong fluctuations of the flow and thermal fields indicating departure from the pseudosteady-state were observed.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Effects of insulated and isothermal baffles on pseudosteady-state natural convection inside spherical containers [texte imprimé] / Yuping Duan, Auteur ; S. F. Hosseinizadeh, Auteur ; J. M. Khodadadi, Auteur . - pp. [062502-1/10].
Physique
Langues : Anglais (eng)
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [062502-1/10]
Mots-clés : Boundary layer turbulence Finite volume methods Flow simulation Fluid oscillations Iterative methods Natural convection Stratified flow Vortices Index. décimale : 536 Chaleur. Thermodynamique Résumé : The effects of insulated and isothermal thin baffles on pseudosteady-state natural convection within spherical containers were studied computationally. The computations are based on an iterative, finite-volume numerical procedure using primitive dependent variables. Natural convection effect is modeled via the Boussinesq approximation. Parametric studies were performed for a Prandtl number of 0.7. For Rayleigh numbers of 104, 105, 106, and 107, baffles with three lengths positioned at five different locations were investigated (120 cases). The fluid that is heated adjacent to the sphere rises replacing the colder fluid, which sinks downward through the stratified stable thermal layer. For high Ra number cases, the hot fluid at the bottom of the sphere is also observed to rise along the symmetry axis and encounter the sinking colder fluid, thus causing oscillations in the temperature and flow fields. Due to flow obstruction (blockage or confinement) effect of baffles and also because of the extra heating afforded by the isothermal baffle, multi-cell recirculating vortices are observed. This additional heat is directly linked to creation of another recirculating vortex next to the baffle. In effect, hot fluid is directed into the center of the sphere disrupting thermal stratified layers. For the majority of the baffles investigated, the Nusselt numbers were generally lower than the reference cases with no baffle. The extent of heat transfer modification depends on Ra, length, and location of the extended surface. With an insulated baffle, the lowest amount of absorbed heat corresponds to a baffle positioned horizontally. Placing a baffle near the top of the sphere for high Ra number cases can lead to heat transfer enhancement that is linked to disturbance of the thermal boundary layer. With isothermal baffles, heat transfer enhancement is achieved for a baffle placed near the bottom of the sphere due to interaction of the counterclockwise rotating vortex and the stratified layer. For some high Ra cases, strong fluctuations of the flow and thermal fields indicating departure from the pseudosteady-state were observed.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [062801-1/15]
Titre : CFD-Based design of microtubular solid oxide fuel cells Type de document : texte imprimé Auteurs : Stefano Cordiner, Auteur ; Alessandro Mariani, Auteur ; Vincenzo Mulone, Auteur Article en page(s) : pp. [062801-1/15] Note générale : Physique Langues : Anglais (eng) Mots-clés : Heat transfer in fuel cells Solid oxide fuel cells Computational fluid-dynamics Hydrogen Index. décimale : 536 Chaleur. Thermodynamique Résumé : Microtubular solid oxide fuel cells (MT-SOFCs) are interesting for portable and auxiliary power units energy production systems, due to their extremely fast startup time. However, a single cell provides power in the range of 1 W, thus the number of microtubes to reach a kW scale is relevant and packaging design issues arise also. In this paper a specifically developed design procedure is presented to face with system issues and bringing into account fluid-dynamic and thermal influence on system performance. The procedure also simplifies the stack manifold design by means of a modular scale-up procedure starting from a basic optimized configuration. To this aim, a computational fluid dynamics (CFD) model has been integrated with specific models for fuel cell simulation and then validated with tailored experimental data by varying operating conditions in terms of fuel utilization and electric load. A comprehensive three–dimensional (3D) thermal-fluid-dynamic model has then been applied to the analysis of both micro-assembly (i.e., 15 tube assembly) and midi-assembly (up to 45 tubes), showing an important role of local phenomena as current homogeneity and reactant local concentration that have a strong influence on power density and temperature distribution. Microreactor power density in the range of 0.3 kW/l have been demonstrated and a specific manifold design has been realized paving the way toward a modular realization of a 1 kW MT-SOFC.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] CFD-Based design of microtubular solid oxide fuel cells [texte imprimé] / Stefano Cordiner, Auteur ; Alessandro Mariani, Auteur ; Vincenzo Mulone, Auteur . - pp. [062801-1/15].
Physique
Langues : Anglais (eng)
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [062801-1/15]
Mots-clés : Heat transfer in fuel cells Solid oxide fuel cells Computational fluid-dynamics Hydrogen Index. décimale : 536 Chaleur. Thermodynamique Résumé : Microtubular solid oxide fuel cells (MT-SOFCs) are interesting for portable and auxiliary power units energy production systems, due to their extremely fast startup time. However, a single cell provides power in the range of 1 W, thus the number of microtubes to reach a kW scale is relevant and packaging design issues arise also. In this paper a specifically developed design procedure is presented to face with system issues and bringing into account fluid-dynamic and thermal influence on system performance. The procedure also simplifies the stack manifold design by means of a modular scale-up procedure starting from a basic optimized configuration. To this aim, a computational fluid dynamics (CFD) model has been integrated with specific models for fuel cell simulation and then validated with tailored experimental data by varying operating conditions in terms of fuel utilization and electric load. A comprehensive three–dimensional (3D) thermal-fluid-dynamic model has then been applied to the analysis of both micro-assembly (i.e., 15 tube assembly) and midi-assembly (up to 45 tubes), showing an important role of local phenomena as current homogeneity and reactant local concentration that have a strong influence on power density and temperature distribution. Microreactor power density in the range of 0.3 kW/l have been demonstrated and a specific manifold design has been realized paving the way toward a modular realization of a 1 kW MT-SOFC.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [064501-1/4]
Titre : Semi-analytical solution for heat transfer in a water film flowing over a heated plane Type de document : texte imprimé Auteurs : Adrien Aubert, Auteur ; Fabien Candelier, Auteur ; Camille Solliec, Auteur Article en page(s) : pp. [064501-1/4] Note générale : Physique Langues : Anglais (eng) Mots-clés : Water film Thermal boundary layer Semi-analytical solution Whittaker's functions Index. décimale : 536 Chaleur. Thermodynamique Résumé : Film flow coupled with heat and mass transfer is a widely open domain due to the range of its applications. However, the coupling between the different phenomena makes the analytical resolution difficult, and thus, coerces most authors into performing numerical studies. Although efficient, the numerical approach does not reveal the real link between the different parameters when studying heat transfer. This lack of meaningful formulation motivates the present paper, which proposes a semi-analytical solution for the establishment of the thermal boundary layer of a film flowing down an inclinated heated plane. The formula is obtained by a truncated sum of Whittaker's functions, and is validated by comparison with a full numerical solution of the problem (assuming the same hypotheses). The semi-analytical nature of the equation provides better understanding of the physical phenomena and could help in reducing numerical computational time.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Semi-analytical solution for heat transfer in a water film flowing over a heated plane [texte imprimé] / Adrien Aubert, Auteur ; Fabien Candelier, Auteur ; Camille Solliec, Auteur . - pp. [064501-1/4].
Physique
Langues : Anglais (eng)
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [064501-1/4]
Mots-clés : Water film Thermal boundary layer Semi-analytical solution Whittaker's functions Index. décimale : 536 Chaleur. Thermodynamique Résumé : Film flow coupled with heat and mass transfer is a widely open domain due to the range of its applications. However, the coupling between the different phenomena makes the analytical resolution difficult, and thus, coerces most authors into performing numerical studies. Although efficient, the numerical approach does not reveal the real link between the different parameters when studying heat transfer. This lack of meaningful formulation motivates the present paper, which proposes a semi-analytical solution for the establishment of the thermal boundary layer of a film flowing down an inclinated heated plane. The formula is obtained by a truncated sum of Whittaker's functions, and is validated by comparison with a full numerical solution of the problem (assuming the same hypotheses). The semi-analytical nature of the equation provides better understanding of the physical phenomena and could help in reducing numerical computational time.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [064502-1/4]
Titre : Boundary-condition-independent reduced-order modeling of heat transfer in complex objects by POD-Galerkin methodology : 1D case study Type de document : texte imprimé Auteurs : Arun P. Raghupathy, Auteur ; Urmila Ghia, Auteur ; Karman Ghia, Auteur Article en page(s) : pp. [064502-1/4] Note générale : Physique Langues : Anglais (eng) Mots-clés : Computational fluid dynamics Finite volume methods Galerkin method Heat transfer Matrix decomposition Thermal management (packaging) Index. décimale : 536 Chaleur. Thermodynamique Résumé : This technical note presents an introduction to boundary-condition-independent reduced-order modeling of complex electronic components using the proper orthogonal decomposition (POD)-Galerkin approach. The current work focuses on how the POD methodology can be used along with the finite volume method to generate reduced-order models that are independent of their boundary conditions. The proposed methodology is demonstrated for the transient 1D heat equation, and preliminary results are presented.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Boundary-condition-independent reduced-order modeling of heat transfer in complex objects by POD-Galerkin methodology : 1D case study [texte imprimé] / Arun P. Raghupathy, Auteur ; Urmila Ghia, Auteur ; Karman Ghia, Auteur . - pp. [064502-1/4].
Physique
Langues : Anglais (eng)
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [064502-1/4]
Mots-clés : Computational fluid dynamics Finite volume methods Galerkin method Heat transfer Matrix decomposition Thermal management (packaging) Index. décimale : 536 Chaleur. Thermodynamique Résumé : This technical note presents an introduction to boundary-condition-independent reduced-order modeling of complex electronic components using the proper orthogonal decomposition (POD)-Galerkin approach. The current work focuses on how the POD methodology can be used along with the finite volume method to generate reduced-order models that are independent of their boundary conditions. The proposed methodology is demonstrated for the transient 1D heat equation, and preliminary results are presented.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [064503-1/5]
Titre : Combined effects of joule heating and viscous dissipation on magnetohydrodynamic flow past a permeable, stretching surface with free convection and radiative heat transfer Type de document : texte imprimé Auteurs : Chien-Hsin Chen, Auteur Article en page(s) : pp. [064503-1/5] Note générale : Physique Langues : Anglais (eng) Mots-clés : MHD flow Joule and viscous heating Stretching surface Free convection Thermal radiation Suction/blowing Index. décimale : 536 Chaleur. Thermodynamique Résumé : The combined effects of Joule heating and viscous dissipation on the momentum and thermal transport are studied for the Magnetohydrodynamic (MHD) flow over a stretching sheet. Effects of free convection, thermal radiation, and surface suction/blowing on the flow and heat transfer characteristics are also examined. Results demonstrate that the reduction in heat transfer due to Joule and viscous heating is more pronounced at a higher Prandtl number. The Eckert number changes appreciably the velocity profile as the buoyancy effect becomes significant, while the Eckert number has an unimpressive effect on the velocity when the free convection is week. Increasing the radiation parameter will increase the temperature profile noticeably, and thus reduce the heat transfer rate accordingly. The heat transfer is enhanced markedly by imposing surface fluid suction, while the opposite trend is observed for blowing.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Combined effects of joule heating and viscous dissipation on magnetohydrodynamic flow past a permeable, stretching surface with free convection and radiative heat transfer [texte imprimé] / Chien-Hsin Chen, Auteur . - pp. [064503-1/5].
Physique
Langues : Anglais (eng)
in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [064503-1/5]
Mots-clés : MHD flow Joule and viscous heating Stretching surface Free convection Thermal radiation Suction/blowing Index. décimale : 536 Chaleur. Thermodynamique Résumé : The combined effects of Joule heating and viscous dissipation on the momentum and thermal transport are studied for the Magnetohydrodynamic (MHD) flow over a stretching sheet. Effects of free convection, thermal radiation, and surface suction/blowing on the flow and heat transfer characteristics are also examined. Results demonstrate that the reduction in heat transfer due to Joule and viscous heating is more pronounced at a higher Prandtl number. The Eckert number changes appreciably the velocity profile as the buoyancy effect becomes significant, while the Eckert number has an unimpressive effect on the velocity when the free convection is week. Increasing the radiation parameter will increase the temperature profile noticeably, and thus reduce the heat transfer rate accordingly. The heat transfer is enhanced markedly by imposing surface fluid suction, while the opposite trend is observed for blowing.
DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]
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