Dépouillements

Thermal protection of a ground layer with phase change materials / X. Duan in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [011301/9] Titre : Thermal protection of a ground layer with phase change materials Type de document : texte imprimé Auteurs : X. Duan, Auteur ; G. F. Naterer, Auteur Article en page(s) : pp. [011301/9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Phase  change  material  Ground  heat  transfer  Insulation  Foundation  Permafrost Index. décimale : 536 Chaleur. Thermodynamique Résumé : Conventional ground surface insulation can be used to protect power line foundations in permafrost regions from the adverse effects of seasonal freezing and thawing cycles. But previous studies have shown ineffective thermal protection against the receding permafrost with conventional insulation. In this paper, an alternative thermal protection method (phase change materials (PCMs)) is analyzed and studied experimentally. Seasonal ground temperature variations are estimated by an analytical conduction model, with a sinusoidal ground surface temperature variation. A compensation function is introduced to predict temperature variations in the foundation, when the ground surface reaches a certain temperature profile. Measured data are acquired from an experimental test cell to simulate the tower foundation. With thermal energy storage in the PCM layer, the surface temperature of the soil was modified, leading to changes in temperature in the foundation. Measured temperature data show that the PCM thermal barrier effectively reduces the temperature variation amplitude in the foundation, thereby alleviating the seasonal freezing and thawing cycles. Different thermal effects of the PCM thermal barrier were obtained under different air temperature conditions. These are analyzed via melting degree hours and freezing degree hours, compared with a critical number of degree hours. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Thermal protection of a ground layer with phase change materials [texte imprimé] / X. Duan, Auteur ; G. F. Naterer, Auteur . - pp. [011301/9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [011301/9] Mots-clés : Phase  change  material  Ground  heat  transfer  Insulation  Foundation  Permafrost Index. décimale : 536 Chaleur. Thermodynamique Résumé : Conventional ground surface insulation can be used to protect power line foundations in permafrost regions from the adverse effects of seasonal freezing and thawing cycles. But previous studies have shown ineffective thermal protection against the receding permafrost with conventional insulation. In this paper, an alternative thermal protection method (phase change materials (PCMs)) is analyzed and studied experimentally. Seasonal ground temperature variations are estimated by an analytical conduction model, with a sinusoidal ground surface temperature variation. A compensation function is introduced to predict temperature variations in the foundation, when the ground surface reaches a certain temperature profile. Measured data are acquired from an experimental test cell to simulate the tower foundation. With thermal energy storage in the PCM layer, the surface temperature of the soil was modified, leading to changes in temperature in the foundation. Measured temperature data show that the PCM thermal barrier effectively reduces the temperature variation amplitude in the foundation, thereby alleviating the seasonal freezing and thawing cycles. Different thermal effects of the PCM thermal barrier were obtained under different air temperature conditions. These are analyzed via melting degree hours and freezing degree hours, compared with a critical number of degree hours. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Optimal heat distribution among discrete protruding heat sources in a vertical duct / T. V. V. Sudhakar in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [011401-1/10] Titre : Optimal heat distribution among discrete protruding heat sources in a vertical duct : a combined numerical and experimental study Type de document : texte imprimé Auteurs : T. V. V. Sudhakar, Auteur ; Arun Shori, Auteur ; C. Balaji, Auteur Article en page(s) : pp. [011401-1/10] Note générale : Physique Langues : Anglais (eng) Mots-clés : Mixed  convection  Protruding  heat  sources  Three-dimensional  Experimental  Numerical  Optimization  Artifical  networks  Genetic  algorithms Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper reports the results of experimental and numerical investigations of optimal heat distribution among the protruding heat sources under laminar conjugate mixed convection heat transfer in a vertical duct. A printed circuit board with 15 heat sources forms a wall of a duct. Three-dimensional governing equations of flow and heat transfer were solved in the flow domain along with the energy equation in the solid domain using FLUENT 6.3. A database of temperatures of each of the heat sources for different heat distributions is generated numerically. Artificial neural networks (ANNs) were used as a forward model to replace the time consuming complex computational fluid dynamics (CFD) simulations. The functional relationship between heat input distribution and the corresponding temperatures of the heat sources obtained by training the network is used to drive a genetic algorithm based optimization procedure to determine the optimal heat distribution. The optimal distribution here refers to the apportioning of a fixed quantity of heat among 15 heat sources, keeping the maximum of the temperatures of the heat sources to a minimum. Furthermore, the heat distribution corresponding to a set of specified target temperatures of the heat sources is obtained using a network that is trained and tested with a database of temperatures of the heat sources generated using FLUENT 6.3 in the range of total heat dissipation of 5–25 W. Using this network, it was possible to maximize the total heat dissipation from the heat sources for a given target temperature directly. In order to validate the optimization method, a low speed vertical wind tunnel has been used to carry out the mixed convection experiments for different combinations of heat distribution and also for the optimal heat distribution, and the temperatures of the heat sources were measured. The results of the numerical simulations, ANN, and the corresponding experimental results are in good agreement. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Optimal heat distribution among discrete protruding heat sources in a vertical duct : a combined numerical and experimental study [texte imprimé] / T. V. V. Sudhakar, Auteur ; Arun Shori, Auteur ; C. Balaji, Auteur . - pp. [011401-1/10]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [011401-1/10] Mots-clés : Mixed  convection  Protruding  heat  sources  Three-dimensional  Experimental  Numerical  Optimization  Artifical  networks  Genetic  algorithms Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper reports the results of experimental and numerical investigations of optimal heat distribution among the protruding heat sources under laminar conjugate mixed convection heat transfer in a vertical duct. A printed circuit board with 15 heat sources forms a wall of a duct. Three-dimensional governing equations of flow and heat transfer were solved in the flow domain along with the energy equation in the solid domain using FLUENT 6.3. A database of temperatures of each of the heat sources for different heat distributions is generated numerically. Artificial neural networks (ANNs) were used as a forward model to replace the time consuming complex computational fluid dynamics (CFD) simulations. The functional relationship between heat input distribution and the corresponding temperatures of the heat sources obtained by training the network is used to drive a genetic algorithm based optimization procedure to determine the optimal heat distribution. The optimal distribution here refers to the apportioning of a fixed quantity of heat among 15 heat sources, keeping the maximum of the temperatures of the heat sources to a minimum. Furthermore, the heat distribution corresponding to a set of specified target temperatures of the heat sources is obtained using a network that is trained and tested with a database of temperatures of the heat sources generated using FLUENT 6.3 in the range of total heat dissipation of 5–25 W. Using this network, it was possible to maximize the total heat dissipation from the heat sources for a given target temperature directly. In order to validate the optimization method, a low speed vertical wind tunnel has been used to carry out the mixed convection experiments for different combinations of heat distribution and also for the optimal heat distribution, and the temperatures of the heat sources were measured. The results of the numerical simulations, ANN, and the corresponding experimental results are in good agreement. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Subcooled boiling heat transfer for turbulent flow of water in a short vertical tube / Koichi Hata in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [011501-1/11] Titre : Subcooled boiling heat transfer for turbulent flow of water in a short vertical tube Type de document : texte imprimé Auteurs : Koichi Hata, Auteur ; Suguru Masuzaki, Auteur Article en page(s) : pp. [011501-1/11] Note générale : Physique Langues : Anglais (eng) Mots-clés : Subcooled  boiling  heat  transfer  Turbulent  flow  of  water  Short  vertical  tube Index. décimale : 536 Chaleur. Thermodynamique Résumé : The subcooled boiling heat transfer and the critical heat flux (CHF) due to exponentially increasing heat inputs with various periods (Q=Q0 exp(t/tau), tau=22.52 ms–26.31 s) were systematically measured by an experimental water loop flow and observed by an infrared thermal imaging camera. Measurements were made on a 3 mm inner diameter, a 66.5 mm heated length, and a 0.5 mm thickness of platinum test tube, which was divided into three sections (upper, mid, and lower positions). The axial variations of the inner surface temperature, the heat flux, and the heat transfer coefficient from nonboiling to critical heat flux were clarified. The results were compared with other correlations for the subcooled boiling heat transfer and authors' transient CHF correlations. The influence of exponential period (tau) and flow velocity on the subcooled boiling heat transfer and the CHF was investigated and the predictable correlation of the subcooled boiling heat transfer for turbulent flow of water in a short vertical tube was derived based on the experimental data. In this work, the correlation gave 15% difference for subcooled boiling heat transfer coefficients. Most of the CHF data (101 points) were within 15% and −30 to +20% differences of the authors' transient CHF correlations against inlet and outlet subcoolings, respectively DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Subcooled boiling heat transfer for turbulent flow of water in a short vertical tube [texte imprimé] / Koichi Hata, Auteur ; Suguru Masuzaki, Auteur . - pp. [011501-1/11]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [011501-1/11] Mots-clés : Subcooled  boiling  heat  transfer  Turbulent  flow  of  water  Short  vertical  tube Index. décimale : 536 Chaleur. Thermodynamique Résumé : The subcooled boiling heat transfer and the critical heat flux (CHF) due to exponentially increasing heat inputs with various periods (Q=Q0 exp(t/tau), tau=22.52 ms–26.31 s) were systematically measured by an experimental water loop flow and observed by an infrared thermal imaging camera. Measurements were made on a 3 mm inner diameter, a 66.5 mm heated length, and a 0.5 mm thickness of platinum test tube, which was divided into three sections (upper, mid, and lower positions). The axial variations of the inner surface temperature, the heat flux, and the heat transfer coefficient from nonboiling to critical heat flux were clarified. The results were compared with other correlations for the subcooled boiling heat transfer and authors' transient CHF correlations. The influence of exponential period (tau) and flow velocity on the subcooled boiling heat transfer and the CHF was investigated and the predictable correlation of the subcooled boiling heat transfer for turbulent flow of water in a short vertical tube was derived based on the experimental data. In this work, the correlation gave 15% difference for subcooled boiling heat transfer coefficients. Most of the CHF data (101 points) were within 15% and −30 to +20% differences of the authors' transient CHF correlations against inlet and outlet subcoolings, respectively DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Optimal distribution of heat sources in convergent channels cooled by laminar forced convection / E. Jassim in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [011701-1/8] Titre : Optimal distribution of heat sources in convergent channels cooled by laminar forced convection Type de document : texte imprimé Auteurs : E. Jassim, Auteur ; Y. S. Muzychka, Auteur Article en page(s) : pp. [011701-1/8] Note générale : Physique Langues : Anglais (eng) Mots-clés : Discrete  heat  source  Constructal  design  Concective  cooling  Laminar  flow  Electronic  cooling Index. décimale : 536 Chaleur. Thermodynamique Résumé : The constructal theory is applied to the flow in a convergent channel. The primary goals of this work are to analyze the heat source distribution and generalize the formula concerning such configurations, to study the spacing between consecutive elements, and to verify the analysis by comparing the proposed configuration with numerical simulations. The results show that nonuniform distributions enhance the performance of the system by allowing the heat source element to work near its maximum condition. Furthermore, the optimal distribution occurs when the heat sources are placed closer to each other near the leading edge of the channel. While the literature shows that the spacing between any consecutive element increases as the sources move downstream from the leading edge, the present results proved that such conclusions are restricted, depending on the ratio of outlet to inlet freestream velocity. Accordingly, the spacing has a maximum value when the exit freestream velocity is more than twice that of the inlet. For design issues, the study also addresses the minimum heat required to achieve optimal system performance. The results show that the amount of heat needed by the system to work close to its optimal performance varies exponentially with the convergent angle and increases with the increase in the heating element's width. The comparison of the present distribution of the heat source elements with a regular one (fixed spacing) is performed numerically to demonstrate the efficiency of the proposed configuration. The results show that the present model forces the system to work more efficiently than the uniform distribution. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Optimal distribution of heat sources in convergent channels cooled by laminar forced convection [texte imprimé] / E. Jassim, Auteur ; Y. S. Muzychka, Auteur . - pp. [011701-1/8]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [011701-1/8] Mots-clés : Discrete  heat  source  Constructal  design  Concective  cooling  Laminar  flow  Electronic  cooling Index. décimale : 536 Chaleur. Thermodynamique Résumé : The constructal theory is applied to the flow in a convergent channel. The primary goals of this work are to analyze the heat source distribution and generalize the formula concerning such configurations, to study the spacing between consecutive elements, and to verify the analysis by comparing the proposed configuration with numerical simulations. The results show that nonuniform distributions enhance the performance of the system by allowing the heat source element to work near its maximum condition. Furthermore, the optimal distribution occurs when the heat sources are placed closer to each other near the leading edge of the channel. While the literature shows that the spacing between any consecutive element increases as the sources move downstream from the leading edge, the present results proved that such conclusions are restricted, depending on the ratio of outlet to inlet freestream velocity. Accordingly, the spacing has a maximum value when the exit freestream velocity is more than twice that of the inlet. For design issues, the study also addresses the minimum heat required to achieve optimal system performance. The results show that the amount of heat needed by the system to work close to its optimal performance varies exponentially with the convergent angle and increases with the increase in the heating element's width. The comparison of the present distribution of the heat source elements with a regular one (fixed spacing) is performed numerically to demonstrate the efficiency of the proposed configuration. The results show that the present model forces the system to work more efficiently than the uniform distribution. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Three-dimensional magnetic fluid boundary layer flow over a linearly stretching sheet / E. E. Tzirtzilakis in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [011702-1/8] Titre : Three-dimensional magnetic fluid boundary layer flow over a linearly stretching sheet Type de document : texte imprimé Auteurs : E. E. Tzirtzilakis, Auteur ; N. G. Kafoussias, Auteur Article en page(s) : pp. [011702-1/8] Note générale : Physique Langues : Anglais (eng) Mots-clés : FHD  Magnetic  fluid  Three-dimensional  flow  Stretching  sheet  Low  curie  temperature  Moderate  saturation  magnetization Index. décimale : 536 Chaleur. Thermodynamique Résumé : The three-dimensional laminar and steady boundary layer flow of an electrically nonconducting and incompressible magnetic fluid, with low Curie temperature and moderate saturation magnetization, over an elastic stretching sheet, is numerically studied. The fluid is subject to the magnetic field generated by an infinitely long, straight wire, carrying an electric current. The magnetic fluid far from the surface is at rest and at temperature greater of that of the sheet. It is also assumed that the magnetization of the fluid varies with the magnetic field strength H and the temperature T. The numerical solution of the coupled and nonlinear system of ordinary differential equations, resulting after the introduction of appropriate nondimensional variables, with its boundary conditions, describing the problem under consideration, is obtained by an efficient numerical technique based on the common finite difference method. Numerical calculations are carried out for the case of a representative water-based magnetic fluid and for specific values of the dimensionless parameters entering into the problem, and the obtained results are presented graphically for these values of the parameters. The analysis of these results showed that there is an interaction between the motions of the fluid, which are induced by the stretching surface and by the action of the magnetic field, and the flow field is noticeably affected by the variations in the magnetic interaction parameter beta. The important results of the present analysis are summarized in Sec. VI DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Three-dimensional magnetic fluid boundary layer flow over a linearly stretching sheet [texte imprimé] / E. E. Tzirtzilakis, Auteur ; N. G. Kafoussias, Auteur . - pp. [011702-1/8]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [011702-1/8] Mots-clés : FHD  Magnetic  fluid  Three-dimensional  flow  Stretching  sheet  Low  curie  temperature  Moderate  saturation  magnetization Index. décimale : 536 Chaleur. Thermodynamique Résumé : The three-dimensional laminar and steady boundary layer flow of an electrically nonconducting and incompressible magnetic fluid, with low Curie temperature and moderate saturation magnetization, over an elastic stretching sheet, is numerically studied. The fluid is subject to the magnetic field generated by an infinitely long, straight wire, carrying an electric current. The magnetic fluid far from the surface is at rest and at temperature greater of that of the sheet. It is also assumed that the magnetization of the fluid varies with the magnetic field strength H and the temperature T. The numerical solution of the coupled and nonlinear system of ordinary differential equations, resulting after the introduction of appropriate nondimensional variables, with its boundary conditions, describing the problem under consideration, is obtained by an efficient numerical technique based on the common finite difference method. Numerical calculations are carried out for the case of a representative water-based magnetic fluid and for specific values of the dimensionless parameters entering into the problem, and the obtained results are presented graphically for these values of the parameters. The analysis of these results showed that there is an interaction between the motions of the fluid, which are induced by the stretching surface and by the action of the magnetic field, and the flow field is noticeably affected by the variations in the magnetic interaction parameter beta. The important results of the present analysis are summarized in Sec. VI DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Heat transfer and friction factor of coil-springs inserted in the horizontal concentric tubes / Haydar Eren in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [011801-1/11] Titre : Heat transfer and friction factor of coil-springs inserted in the horizontal concentric tubes Type de document : texte imprimé Auteurs : Haydar Eren, Auteur ; Nevin Celik, Auteur ; Seyba Yildiz, Auteur Article en page(s) : pp. [011801-1/11] Note générale : Physique Langues : Anglais (eng) Mots-clés : Heat  exchanger  Coil-spring  Turbulator  Heat  transfer  Pressure  drop Index. décimale : 536 Chaleur. Thermodynamique Résumé : The goal of this investigation is to obtain definitive information about the heat transfer characteristics of circular coil-spring turbulators. This is achieved by measuring the wall temperatures on the inner tube of the exchanger. Also the inlet and outlet temperatures and pressure loss of the fluid are measured. These results are parametrized by Reynolds numbers (2500 DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Heat transfer and friction factor of coil-springs inserted in the horizontal concentric tubes [texte imprimé] / Haydar Eren, Auteur ; Nevin Celik, Auteur ; Seyba Yildiz, Auteur . - pp. [011801-1/11]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [011801-1/11] Mots-clés : Heat  exchanger  Coil-spring  Turbulator  Heat  transfer  Pressure  drop Index. décimale : 536 Chaleur. Thermodynamique Résumé : The goal of this investigation is to obtain definitive information about the heat transfer characteristics of circular coil-spring turbulators. This is achieved by measuring the wall temperatures on the inner tube of the exchanger. Also the inlet and outlet temperatures and pressure loss of the fluid are measured. These results are parametrized by Reynolds numbers (2500 DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Exergy study of fouling factors in heat exchanger networks / Zunlong Jin in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [011802-1/4] Titre : Exergy study of fouling factors in heat exchanger networks Type de document : texte imprimé Auteurs : Zunlong Jin, Auteur ; Qiwu Dong, Auteur ; Minshan Liu, Auteur Article en page(s) : pp. [011802-1/4] Note générale : Physique Langues : Anglais (eng) Mots-clés : Heat  exchanger  networks  Fouling  factors  Exergoeconomic  analysis Index. décimale : 536 Chaleur. Thermodynamique Résumé : Selection of fouling factors is somewhat arbitrary in heat exchanger networks (HENs) synthesis. Fouling factors were reconsidered in this article for heat exchanger networks design. An objective function based on exergoeconomic analysis was introduced to assess optimal less conservative fouling factors. The objective took account of exergy consumption expense and heat exchanger capital cost at the same time. The exergy consumption of heat transfer in HENs was calculated using subsection integral on balanced composite curves. The proposed method was applied to an industrial case. Numerical results indicated that the optimal less conservative fouling factors were 80% of the original values and the heat transfer area of the system saved 350 m2 compared with root design. So it is necessary to reconsider the values of fouling factors for HENs design and that exergoeconomic analysis is useful in determining the optimal less conservative fouling factors. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Exergy study of fouling factors in heat exchanger networks [texte imprimé] / Zunlong Jin, Auteur ; Qiwu Dong, Auteur ; Minshan Liu, Auteur . - pp. [011802-1/4]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [011802-1/4] Mots-clés : Heat  exchanger  networks  Fouling  factors  Exergoeconomic  analysis Index. décimale : 536 Chaleur. Thermodynamique Résumé : Selection of fouling factors is somewhat arbitrary in heat exchanger networks (HENs) synthesis. Fouling factors were reconsidered in this article for heat exchanger networks design. An objective function based on exergoeconomic analysis was introduced to assess optimal less conservative fouling factors. The objective took account of exergy consumption expense and heat exchanger capital cost at the same time. The exergy consumption of heat transfer in HENs was calculated using subsection integral on balanced composite curves. The proposed method was applied to an industrial case. Numerical results indicated that the optimal less conservative fouling factors were 80% of the original values and the heat transfer area of the system saved 350 m2 compared with root design. So it is necessary to reconsider the values of fouling factors for HENs design and that exergoeconomic analysis is useful in determining the optimal less conservative fouling factors. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Heat transfer characteristics of a swirling laminar impinging jet / Koichi Ichimiya in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [012201-1/5] Titre : Heat transfer characteristics of a swirling laminar impinging jet Type de document : texte imprimé Auteurs : Koichi Ichimiya, Auteur ; Koji Tsukamoto, Auteur Article en page(s) : pp. [012201-1/5] Note générale : Physique Langues : Anglais (eng) Mots-clés : Impinging  jet  Swirl  Heat  transfer  enchancement  Swirl  number Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper describes the characteristics of the heat transfer and flow of a swirling laminar impinging jet in a comparatively narrow space with a confined wall. Air is impinged on a flat surface with constant wall temperature. The heat transfer and flow field were analyzed numerically by solving three-dimensional governing equations. Heat transfer experiment and flow visualization were also performed. Numerical heat transfer was compared with experimental results. Temperature distribution and velocity vectors in the space were obtained for various swirl numbers at Reynolds number Re=2000. The numerical and experimental results show that the swirling jet enhances or depresses the local heat transfer, and the average Nusselt number ratio with and without swirl takes a peak at a certain swirl number. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Heat transfer characteristics of a swirling laminar impinging jet [texte imprimé] / Koichi Ichimiya, Auteur ; Koji Tsukamoto, Auteur . - pp. [012201-1/5]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [012201-1/5] Mots-clés : Impinging  jet  Swirl  Heat  transfer  enchancement  Swirl  number Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper describes the characteristics of the heat transfer and flow of a swirling laminar impinging jet in a comparatively narrow space with a confined wall. Air is impinged on a flat surface with constant wall temperature. The heat transfer and flow field were analyzed numerically by solving three-dimensional governing equations. Heat transfer experiment and flow visualization were also performed. Numerical heat transfer was compared with experimental results. Temperature distribution and velocity vectors in the space were obtained for various swirl numbers at Reynolds number Re=2000. The numerical and experimental results show that the swirling jet enhances or depresses the local heat transfer, and the average Nusselt number ratio with and without swirl takes a peak at a certain swirl number. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Thermal properties for bulk silicon based on the determination of relaxation times using molecular dynamics / Javier V. Goicochea in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [012401-1/11] Titre : Thermal properties for bulk silicon based on the determination of relaxation times using molecular dynamics Type de document : texte imprimé Auteurs : Javier V. Goicochea, Auteur ; Marcela Madrid, Auteur ; Cristina Amon, Auteur Article en page(s) : pp. [012401-1/11] Note générale : Physique Langues : Anglais (eng) Mots-clés : Boltzmann  equation  Elemental  semiconductors  Lattice  constants  Molecular  dynamics  method  Phonon  dispersion  relations  Potential  energy  functions  Silicon  Thermal  analysis  Thermal  conductivity  Thermal  expansion  Total  energy Index. décimale : 536 Chaleur. Thermodynamique Résumé : Molecular dynamics simulations are performed to estimate acoustical and optical phonon relaxation times, dispersion relations, group velocities, and specific heat of silicon needed to solve the Boltzmann transport equation (BTE) at 300 K and 1000 K. The relaxation times are calculated from the temporal decay of the autocorrelation function of the fluctuation of total energy of each normal mode in the <100> family of directions, where the total energy of each mode is obtained from the normal mode decomposition of the motion of the silicon atoms over a period of time. Additionally, silicon dispersion relations are directly determined from the equipartition theorem obtained from the normal mode decomposition. The impact of the anharmonic nature of the potential energy function on the thermal expansion of the crystal is determined by computing the lattice parameter at the cited temperatures using a NPT (i.e., constant number of atoms, pressure, and temperature) ensemble, and are compared with experimental values reported in the literature and with those computed analytically using the quasiharmonic approximation. The dependence of the relaxation times with respect to the frequency is identified with two functions that follow the functional form of the relaxation time expressions reported in the literature. From these functions a simplified version of relaxation times for each normal mode is extracted. Properties, such as group and phase velocities, thermal conductivity, and mean free path, needed to further develop a methodology for the thermal analysis of electronic devices (i.e., from nano- to macroscales) are determined once the relaxation times and dispersion relations are obtained. The thermal properties are validated by comparing the BTE-based thermal conductivity against the predictions obtained from the Green–Kubo method. It is found that the relaxation times closely resemble the ones obtained from perturbation theory at high temperatures; the contribution to the thermal conductivity of the transverse acoustic, longitudinal acoustic, and longitudinal optical modes being approximately 30%, 60%, and 10%, respectively, and the contribution of the transverse optical mode negligible. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Thermal properties for bulk silicon based on the determination of relaxation times using molecular dynamics [texte imprimé] / Javier V. Goicochea, Auteur ; Marcela Madrid, Auteur ; Cristina Amon, Auteur . - pp. [012401-1/11]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [012401-1/11] Mots-clés : Boltzmann  equation  Elemental  semiconductors  Lattice  constants  Molecular  dynamics  method  Phonon  dispersion  relations  Potential  energy  functions  Silicon  Thermal  analysis  Thermal  conductivity  Thermal  expansion  Total  energy Index. décimale : 536 Chaleur. Thermodynamique Résumé : Molecular dynamics simulations are performed to estimate acoustical and optical phonon relaxation times, dispersion relations, group velocities, and specific heat of silicon needed to solve the Boltzmann transport equation (BTE) at 300 K and 1000 K. The relaxation times are calculated from the temporal decay of the autocorrelation function of the fluctuation of total energy of each normal mode in the <100> family of directions, where the total energy of each mode is obtained from the normal mode decomposition of the motion of the silicon atoms over a period of time. Additionally, silicon dispersion relations are directly determined from the equipartition theorem obtained from the normal mode decomposition. The impact of the anharmonic nature of the potential energy function on the thermal expansion of the crystal is determined by computing the lattice parameter at the cited temperatures using a NPT (i.e., constant number of atoms, pressure, and temperature) ensemble, and are compared with experimental values reported in the literature and with those computed analytically using the quasiharmonic approximation. The dependence of the relaxation times with respect to the frequency is identified with two functions that follow the functional form of the relaxation time expressions reported in the literature. From these functions a simplified version of relaxation times for each normal mode is extracted. Properties, such as group and phase velocities, thermal conductivity, and mean free path, needed to further develop a methodology for the thermal analysis of electronic devices (i.e., from nano- to macroscales) are determined once the relaxation times and dispersion relations are obtained. The thermal properties are validated by comparing the BTE-based thermal conductivity against the predictions obtained from the Green–Kubo method. It is found that the relaxation times closely resemble the ones obtained from perturbation theory at high temperatures; the contribution to the thermal conductivity of the transverse acoustic, longitudinal acoustic, and longitudinal optical modes being approximately 30%, 60%, and 10%, respectively, and the contribution of the transverse optical mode negligible. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Molecular-scale mechanism of thermal resistance at the solid-liquid interfaces / Daichi Torii in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [012402-1/9] Titre : Molecular-scale mechanism of thermal resistance at the solid-liquid interfaces : influence of interaction parameters between solid and liquid molecules Type de document : texte imprimé Auteurs : Daichi Torii, Auteur ; Taku Ohara, Auteur ; Kenji Ishida, Auteur Article en page(s) : pp. [012402-1/9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Thermal  energy  transfer  Thermal  resistance  Solid-liquid  interface  Crystal  plane  Surface  corrugation Index. décimale : 536 Chaleur. Thermodynamique Résumé : The solid-liquid interfacial thermal resistance is getting more and more important as various solid-liquid systems are utilized in nanoscale, such as micro electro-mechanical systems/nano electro-mechanical systems (MEMS/NEMS) with liquids and nanoparticle suspension in liquids. The present paper deals with the transport of thermal energy through the solid-liquid interfaces, and the goal is to find a molecular-scale mechanism that determines the macroscopic characteristics of the transport phenomena. Nonequilibrium molecular dynamics simulations have been performed for systems of a liquid film confined between atomistic solid walls. The two solid walls have different temperatures to generate a steady thermal energy flux in the system, which is the element of macroscopic heat conduction flux. Three kinds of liquid molecules and three kinds of solid walls are examined, and the thermal energy flux is measured at the control surfaces in the liquid film and at the solid-liquid interfaces. The concept of boundary thermal resistance is extended, and it is defined for each degree of freedom of translational motion of the molecules. It is found that the interaction strength between solid and liquid molecules uniformly affects all boundary thermal resistances defined for each degree of freedom; the weaker interaction increases all the resistances at the same rate and vice versa. The boundary thermal resistances also increase when the solid and liquid molecules are incommensurate, but the incommensurability has a greater influence on the boundary thermal resistances corresponding to the molecular motion parallel to the interface than that for the normal component. From these findings it is confirmed that the thermal resistance for the components parallel to the interface is associated with the molecular-scale corrugation of the surface of the solid wall, and that the thermal resistance for the component normal to the interface is governed by the number density of the solid molecules that are in contact with the liquid. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Molecular-scale mechanism of thermal resistance at the solid-liquid interfaces : influence of interaction parameters between solid and liquid molecules [texte imprimé] / Daichi Torii, Auteur ; Taku Ohara, Auteur ; Kenji Ishida, Auteur . - pp. [012402-1/9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [012402-1/9] Mots-clés : Thermal  energy  transfer  Thermal  resistance  Solid-liquid  interface  Crystal  plane  Surface  corrugation Index. décimale : 536 Chaleur. Thermodynamique Résumé : The solid-liquid interfacial thermal resistance is getting more and more important as various solid-liquid systems are utilized in nanoscale, such as micro electro-mechanical systems/nano electro-mechanical systems (MEMS/NEMS) with liquids and nanoparticle suspension in liquids. The present paper deals with the transport of thermal energy through the solid-liquid interfaces, and the goal is to find a molecular-scale mechanism that determines the macroscopic characteristics of the transport phenomena. Nonequilibrium molecular dynamics simulations have been performed for systems of a liquid film confined between atomistic solid walls. The two solid walls have different temperatures to generate a steady thermal energy flux in the system, which is the element of macroscopic heat conduction flux. Three kinds of liquid molecules and three kinds of solid walls are examined, and the thermal energy flux is measured at the control surfaces in the liquid film and at the solid-liquid interfaces. The concept of boundary thermal resistance is extended, and it is defined for each degree of freedom of translational motion of the molecules. It is found that the interaction strength between solid and liquid molecules uniformly affects all boundary thermal resistances defined for each degree of freedom; the weaker interaction increases all the resistances at the same rate and vice versa. The boundary thermal resistances also increase when the solid and liquid molecules are incommensurate, but the incommensurability has a greater influence on the boundary thermal resistances corresponding to the molecular motion parallel to the interface than that for the normal component. From these findings it is confirmed that the thermal resistance for the components parallel to the interface is associated with the molecular-scale corrugation of the surface of the solid wall, and that the thermal resistance for the component normal to the interface is governed by the number density of the solid molecules that are in contact with the liquid. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Measurement of the heat capacity of copper thin films using a micropulse calorimeter / Yu, Jun in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [012403-1/6] Titre : Measurement of the heat capacity of copper thin films using a micropulse calorimeter Type de document : texte imprimé Auteurs : Yu, Jun, Auteur ; Zhen'an Tang, Auteur ; Fengtian Zhang, Auteur Article en page(s) : pp. [012403-1/6] Note générale : Physique Langues : Anglais (eng) Mots-clés : Micro-/nanoscale  heat  transfer  Thin  film  Heat  capacity  Thermal  characterization Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper presents a micropulse calorimeter for heat capacity measurement of thin films. Optimization of the structure and data processing methods of the microcalorimeter improved the thermal isolation and temperature uniformity and reduced the heat capacity measurement errors. Heat capacities of copper thin films with thicknesses from 20 nm to 340 nm are measured in the temperature range from 300 K to 420 K in vacuum of 1 mPa. The specific heat of the 340 nm Cu film is close to the literature data of bulk Cu. For the thinner films, the data shows that the specific heat increases with the decreasing of film thickness (or the average crystalline size). DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Measurement of the heat capacity of copper thin films using a micropulse calorimeter [texte imprimé] / Yu, Jun, Auteur ; Zhen'an Tang, Auteur ; Fengtian Zhang, Auteur . - pp. [012403-1/6]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [012403-1/6] Mots-clés : Micro-/nanoscale  heat  transfer  Thin  film  Heat  capacity  Thermal  characterization Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper presents a micropulse calorimeter for heat capacity measurement of thin films. Optimization of the structure and data processing methods of the microcalorimeter improved the thermal isolation and temperature uniformity and reduced the heat capacity measurement errors. Heat capacities of copper thin films with thicknesses from 20 nm to 340 nm are measured in the temperature range from 300 K to 420 K in vacuum of 1 mPa. The specific heat of the 340 nm Cu film is close to the literature data of bulk Cu. For the thinner films, the data shows that the specific heat increases with the decreasing of film thickness (or the average crystalline size). DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Boundary conditions and evolution of ballistic heat transport / F. X. Alvarez in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [012404-1/6] Titre : Boundary conditions and evolution of ballistic heat transport Type de document : texte imprimé Auteurs : F. X. Alvarez, Auteur ; D. Jou, Auteur Article en page(s) : pp. [012404-1/6] Note générale : Physique Langues : Anglais (eng) Mots-clés : Heat  transport  Ballistic  regime  Thermal  conductivity  Ballistic  transport Index. décimale : 536 Chaleur. Thermodynamique Résumé : We analyze the effects of boundary conditions on the evolution of ballistic heat transport in four theoretical models and propose that a Fourier equation with an effective size-dependent thermal conductivity is a good candidate for the description of ballistic transport when boundary conditions are suitably imposed. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Boundary conditions and evolution of ballistic heat transport [texte imprimé] / F. X. Alvarez, Auteur ; D. Jou, Auteur . - pp. [012404-1/6]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [012404-1/6] Mots-clés : Heat  transport  Ballistic  regime  Thermal  conductivity  Ballistic  transport Index. décimale : 536 Chaleur. Thermodynamique Résumé : We analyze the effects of boundary conditions on the evolution of ballistic heat transport in four theoretical models and propose that a Fourier equation with an effective size-dependent thermal conductivity is a good candidate for the description of ballistic transport when boundary conditions are suitably imposed. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Sensitivity of the human comfort equation and of free convection in a vertical enclosure as examples of the use of global sensitivity to evaluate parameter interactions / A. F. Emery in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [012501-1/10] Titre : Sensitivity of the human comfort equation and of free convection in a vertical enclosure as examples of the use of global sensitivity to evaluate parameter interactions Type de document : texte imprimé Auteurs : A. F. Emery, Auteur ; M.-H. H. Wu, Auteur ; A. M. Mescher, Auteur Article en page(s) : pp. [012501-1/10] Note générale : Physique Langues : Anglais (eng) Mots-clés : Sensitivity  Global  sensitivity  Interactions  Uncertainty  Free  convection  Human  confort Index. décimale : 536 Chaleur. Thermodynamique Résumé : Many models of engineering and scientific systems involve interactions between and among the parameters, stimuli, and physical properties. The determination of the adequacy of models for predictions and for designing experiments generally involves sensitivity studies. Good designs mandate that the experiments be sensitive to the parameters sought with little interaction between them because such interaction generally confuses the estimation and reduces the precision of the estimates. For design purposes, analysts frequently want to evaluate the sensitivities of the predicted responses to specific variables, but if the variables interact it is often difficult to separate the effects. Global sensitivity is a technique by which one can evaluate the magnitude of the interactions between multiple variables. In this paper, the global sensitivity approach is applied to the human comfort equation and to free convection in a rectangular enclosure. It is found that when occupants are uncomfortable, there is little interaction and that one can predict the effects of changing several environmental conditions at once by adding the separate effects. But when occupants are comfortable, there is a large interaction and the effects cannot be treated separately. Free convective heat transfer in an enclosure is a function of the Rayleigh number Ra and the aspect ratio H/W, and the flow field changes from unicellular to multicellular as Ra increases. There is a strong interaction for H/W<=2 but little for H/W>=2. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Sensitivity of the human comfort equation and of free convection in a vertical enclosure as examples of the use of global sensitivity to evaluate parameter interactions [texte imprimé] / A. F. Emery, Auteur ; M.-H. H. Wu, Auteur ; A. M. Mescher, Auteur . - pp. [012501-1/10]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [012501-1/10] Mots-clés : Sensitivity  Global  sensitivity  Interactions  Uncertainty  Free  convection  Human  confort Index. décimale : 536 Chaleur. Thermodynamique Résumé : Many models of engineering and scientific systems involve interactions between and among the parameters, stimuli, and physical properties. The determination of the adequacy of models for predictions and for designing experiments generally involves sensitivity studies. Good designs mandate that the experiments be sensitive to the parameters sought with little interaction between them because such interaction generally confuses the estimation and reduces the precision of the estimates. For design purposes, analysts frequently want to evaluate the sensitivities of the predicted responses to specific variables, but if the variables interact it is often difficult to separate the effects. Global sensitivity is a technique by which one can evaluate the magnitude of the interactions between multiple variables. In this paper, the global sensitivity approach is applied to the human comfort equation and to free convection in a rectangular enclosure. It is found that when occupants are uncomfortable, there is little interaction and that one can predict the effects of changing several environmental conditions at once by adding the separate effects. But when occupants are comfortable, there is a large interaction and the effects cannot be treated separately. Free convective heat transfer in an enclosure is a function of the Rayleigh number Ra and the aspect ratio H/W, and the flow field changes from unicellular to multicellular as Ra increases. There is a strong interaction for H/W<=2 but little for H/W>=2. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Natural convection inside a bidisperse porous medium enclosure / Arunn Narasimhan in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [012502-1/9] Titre : Natural convection inside a bidisperse porous medium enclosure Type de document : texte imprimé Auteurs : Arunn Narasimhan, Auteur ; B. V. K. Reddy, Auteur Article en page(s) : pp. [012502-1/9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Confined  flow  Finite  volume  methods  Flow  simulation  Flow  through  porous  media  Natural  convection Index. décimale : 536 Chaleur. Thermodynamique Résumé : Bidisperse porous medium (BDPM) consists of a macroporous medium whose solid phase is replaced with a microporous medium. This study investigates using numerical simulations, steady natural convection inside a square BDPM enclosure made from uniformly spaced, disconnected square porous blocks that form the microporous medium. The side walls are subjected to differential heating, while the top and bottom ones are kept adiabatic. The bidispersion effect is generated by varying the number of blocks (N2), macropore volume fraction (phiE), and internal Darcy number (DaI) for several enclosure Rayleigh numbers (Ra). Their effect on the BDPM heat transfer (Nu) is investigated. When Ra is fixed, the Nu increases with an increase in both DaI and DaE. At low Ra values, Nu is strongly affected by both DaI and phiE. When N2 is fixed, at high Ra values, the porous blocks in the core region have negligible effect on the Nu. A correlation is proposed to evaluate the heat transfer from the BDPM enclosure, Nu, as a function of Raphi, DaE, DaI, and N2. It predicts the numerical results of Nu within ±15% and ±9% in two successive ranges of modified Rayleigh number, RaphiDaE. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Natural convection inside a bidisperse porous medium enclosure [texte imprimé] / Arunn Narasimhan, Auteur ; B. V. K. Reddy, Auteur . - pp. [012502-1/9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [012502-1/9] Mots-clés : Confined  flow  Finite  volume  methods  Flow  simulation  Flow  through  porous  media  Natural  convection Index. décimale : 536 Chaleur. Thermodynamique Résumé : Bidisperse porous medium (BDPM) consists of a macroporous medium whose solid phase is replaced with a microporous medium. This study investigates using numerical simulations, steady natural convection inside a square BDPM enclosure made from uniformly spaced, disconnected square porous blocks that form the microporous medium. The side walls are subjected to differential heating, while the top and bottom ones are kept adiabatic. The bidispersion effect is generated by varying the number of blocks (N2), macropore volume fraction (phiE), and internal Darcy number (DaI) for several enclosure Rayleigh numbers (Ra). Their effect on the BDPM heat transfer (Nu) is investigated. When Ra is fixed, the Nu increases with an increase in both DaI and DaE. At low Ra values, Nu is strongly affected by both DaI and phiE. When N2 is fixed, at high Ra values, the porous blocks in the core region have negligible effect on the Nu. A correlation is proposed to evaluate the heat transfer from the BDPM enclosure, Nu, as a function of Raphi, DaE, DaI, and N2. It predicts the numerical results of Nu within ±15% and ±9% in two successive ranges of modified Rayleigh number, RaphiDaE. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Study and optimization of horizontal-base pin-fin heat sinks in natural convection and radiation / D. Sahray in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [012503-1/13] Titre : Study and optimization of horizontal-base pin-fin heat sinks in natural convection and radiation Type de document : texte imprimé Auteurs : D. Sahray, Auteur ; H. Shmueli, Auteur ; G. Ziskind, Auteur Article en page(s) : pp. [012503-1/13] Note générale : Physique Langues : Anglais (eng) Mots-clés : Pin  fin  Natural  convection  Optimum  fin  population  Correlation Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper aims at deeper understanding of heat transfer from horizontal-base pin-fin heat sinks with exposed edges in free convection of air. The effects of fin height and fin population density are studied experimentally and numerically. The sinks are made of aluminum, and there is no contact resistance between the base and the fins. All the sinks studied have the same base dimensions and are heated using foil electrical heaters. The fins have a constant square cross section, whereas the fin height and pitch vary. The heat input is set, and temperatures of the base and fins are measured. In the corresponding numerical study, the sinks and their environment are modeled using the FLUENT 6.3 software. The results show that heat-transfer enhancement due to the fins is not monotonic. The differences between sparsely and densely populated sinks are assessed quantitatively and analyzed for various fin heights. Also analyzed is the heat flux distribution at the edges and center of the sink. A relative contribution of outer and inner fin rows in the sink is assessed, together with the effect of fin location in the array on the heat-transfer rate from an individual fin. By decoupling convection from radiation, a dimensional analysis of the results for natural convection is attempted. A correlation presenting the Nusselt number versus the Rayleigh number is suggested, where the “clear” spacing between fins serves as the characteristic length. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Study and optimization of horizontal-base pin-fin heat sinks in natural convection and radiation [texte imprimé] / D. Sahray, Auteur ; H. Shmueli, Auteur ; G. Ziskind, Auteur . - pp. [012503-1/13]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [012503-1/13] Mots-clés : Pin  fin  Natural  convection  Optimum  fin  population  Correlation Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper aims at deeper understanding of heat transfer from horizontal-base pin-fin heat sinks with exposed edges in free convection of air. The effects of fin height and fin population density are studied experimentally and numerically. The sinks are made of aluminum, and there is no contact resistance between the base and the fins. All the sinks studied have the same base dimensions and are heated using foil electrical heaters. The fins have a constant square cross section, whereas the fin height and pitch vary. The heat input is set, and temperatures of the base and fins are measured. In the corresponding numerical study, the sinks and their environment are modeled using the FLUENT 6.3 software. The results show that heat-transfer enhancement due to the fins is not monotonic. The differences between sparsely and densely populated sinks are assessed quantitatively and analyzed for various fin heights. Also analyzed is the heat flux distribution at the edges and center of the sink. A relative contribution of outer and inner fin rows in the sink is assessed, together with the effect of fin location in the array on the heat-transfer rate from an individual fin. By decoupling convection from radiation, a dimensional analysis of the results for natural convection is attempted. A correlation presenting the Nusselt number versus the Rayleigh number is suggested, where the “clear” spacing between fins serves as the characteristic length. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Experimental and numerical determination of thermal radiative properties of ZnO particulate media / P. Coray in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [012701-1/6] Titre : Experimental and numerical determination of thermal radiative properties of ZnO particulate media Type de document : texte imprimé Auteurs : P. Coray, Auteur ; W. Lipinski, Auteur ; A. Steinfeld, Auteur Article en page(s) : pp. [012701-1/6] Note générale : Physique Langues : Anglais (eng) Mots-clés : Radiation  Radiometry  Radiative  spectroscopy  Monte  Carlo  Zinc  oxide  packed-bed Index. décimale : 536 Chaleur. Thermodynamique Résumé : The radiative characteristics of dependently scattering packed-beds of ZnO particles, applied in the design of high-temperature solar thermochemical reactors, were investigated experimentally. ZnO samples of varying thickness were exposed to a continuous beam of near monochromatic thermal radiation in the 0.5–1 µm wavelength range. The overall transmitted fraction measured as a function of sample thickness s obeys an exponential trend exp(−As), with the fit parameter A ranging from 4000±100 m−1 at 555 nm to 2100±100 m−1 at 1 µm. In the forward directions, the measured intensity distribution is approximately isotropic, whereas in the backward directions it is well approximated by a Henyey–Greenstein equation with asymmetry factors g[approximate]−0.4 at 555 nm and g[approximate]−0.1 at 1 µm. A Monte Carlo ray-tracing model of the experimental setup is employed to extract the extinction coefficient and the scattering albedo for the case of a nongray absorbing-scattering medium. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Experimental and numerical determination of thermal radiative properties of ZnO particulate media [texte imprimé] / P. Coray, Auteur ; W. Lipinski, Auteur ; A. Steinfeld, Auteur . - pp. [012701-1/6]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [012701-1/6] Mots-clés : Radiation  Radiometry  Radiative  spectroscopy  Monte  Carlo  Zinc  oxide  packed-bed Index. décimale : 536 Chaleur. Thermodynamique Résumé : The radiative characteristics of dependently scattering packed-beds of ZnO particles, applied in the design of high-temperature solar thermochemical reactors, were investigated experimentally. ZnO samples of varying thickness were exposed to a continuous beam of near monochromatic thermal radiation in the 0.5–1 µm wavelength range. The overall transmitted fraction measured as a function of sample thickness s obeys an exponential trend exp(−As), with the fit parameter A ranging from 4000±100 m−1 at 555 nm to 2100±100 m−1 at 1 µm. In the forward directions, the measured intensity distribution is approximately isotropic, whereas in the backward directions it is well approximated by a Henyey–Greenstein equation with asymmetry factors g[approximate]−0.4 at 555 nm and g[approximate]−0.1 at 1 µm. A Monte Carlo ray-tracing model of the experimental setup is employed to extract the extinction coefficient and the scattering albedo for the case of a nongray absorbing-scattering medium. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Non-darcy mixed convection with thermal dispersion in a saturated porous medium / V. V. Sobha in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [014501-1/4] Titre : Non-darcy mixed convection with thermal dispersion in a saturated porous medium Type de document : texte imprimé Auteurs : V. V. Sobha, Auteur ; R. Y. Vasudeva, Auteur Article en page(s) : pp. [014501-1/4] Note générale : Physique Langues : Anglais (eng) Mots-clés : Porous  medium  Melting  Thermal  dispersion  Mixed  convection Index. décimale : 536 Chaleur. Thermodynamique Résumé : Thermal dispersion due to local flows is significant in heat transfer with forced convection in porous media. The effects of parametrized melting (M), thermal dispersion (D), inertia (F), and mixed convection (Ra/Pe) on the velocity distribution, temperature, and Nusselt number on non-Darcy, mixed convective heat transfer from an infinite vertical plate embedded in a saturated porous medium are examined. It is observed that the Nusselt number decreases with increase in melting parameter and increases with increase in thermal dispersion. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Non-darcy mixed convection with thermal dispersion in a saturated porous medium [texte imprimé] / V. V. Sobha, Auteur ; R. Y. Vasudeva, Auteur . - pp. [014501-1/4]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [014501-1/4] Mots-clés : Porous  medium  Melting  Thermal  dispersion  Mixed  convection Index. décimale : 536 Chaleur. Thermodynamique Résumé : Thermal dispersion due to local flows is significant in heat transfer with forced convection in porous media. The effects of parametrized melting (M), thermal dispersion (D), inertia (F), and mixed convection (Ra/Pe) on the velocity distribution, temperature, and Nusselt number on non-Darcy, mixed convective heat transfer from an infinite vertical plate embedded in a saturated porous medium are examined. It is observed that the Nusselt number decreases with increase in melting parameter and increases with increase in thermal dispersion. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Initial buoyancy reduction in exhausting smoke with solar chimney design / C. L. Chow in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [014502-1/3] Titre : Initial buoyancy reduction in exhausting smoke with solar chimney design Type de document : texte imprimé Auteurs : C. L. Chow, Auteur ; W. K. Chow, Auteur Article en page(s) : pp. [014502-1/3] Note générale : Physique Langues : Anglais (eng) Mots-clés : Full-scale  burning  test  Glass  solar  chimney  Buoyancy  Smoke  exhaust Index. décimale : 536 Chaleur. Thermodynamique Résumé : A possible problem in using solar chimney as a natural smoke exhaust system will be identified in this paper. Smoke generated in a fire might not be removed effectively if the glazing walls are heated up due to exposure to solar radiation. It is because the buoyancy of the smoke is reduced initially in the solar chimney. This phenomenon of reducing buoyancy will be discussed. A simple equation of motion on smoke movement was set up. Some of the results of full-scale burning experiments carried out earlier for assessing the fire response of a glass façade system were applied to support the argument. Experiments indicated that smoke would take a longer time to move up when the glazing wall temperature is higher. A better smoke exhaust design accounting the reduction in buoyancy at this early stage of a fire should be worked out. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Initial buoyancy reduction in exhausting smoke with solar chimney design [texte imprimé] / C. L. Chow, Auteur ; W. K. Chow, Auteur . - pp. [014502-1/3]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [014502-1/3] Mots-clés : Full-scale  burning  test  Glass  solar  chimney  Buoyancy  Smoke  exhaust Index. décimale : 536 Chaleur. Thermodynamique Résumé : A possible problem in using solar chimney as a natural smoke exhaust system will be identified in this paper. Smoke generated in a fire might not be removed effectively if the glazing walls are heated up due to exposure to solar radiation. It is because the buoyancy of the smoke is reduced initially in the solar chimney. This phenomenon of reducing buoyancy will be discussed. A simple equation of motion on smoke movement was set up. Some of the results of full-scale burning experiments carried out earlier for assessing the fire response of a glass façade system were applied to support the argument. Experiments indicated that smoke would take a longer time to move up when the glazing wall temperature is higher. A better smoke exhaust design accounting the reduction in buoyancy at this early stage of a fire should be worked out. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Buoyant convection in superposed metal foam and water layers / V. Kathare in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [014503-1/4] Titre : Buoyant convection in superposed metal foam and water layers Type de document : texte imprimé Auteurs : V. Kathare, Auteur ; F. A. Kulacki, Auteur ; Jane H. Davidson, Auteur Article en page(s) : pp. [014503-1/4] Note générale : Physique Langues : Anglais (eng) Mots-clés : Natural  convection  Metal  foam  Heat  transfer  enhancement Index. décimale : 536 Chaleur. Thermodynamique Résumé : Heat transfer measurements for natural convection in superposed metal foam and water layers are reported. Two systems heated at the lower boundary are considered: a water-filled cavity with a foam layer on the heated surface and a water-filled cavity with foam layers on the upper and lower surfaces. The present experiments use open cell copper foams with a nominal porosity of 92%, and the relative thicknesses of the water and foam layers are varied. Steady state Nusselt numbers show that the presence of foam on the boundaries enhances overall heat transfer coefficients over that for the water-only layer. Enhancement of overall Nusselt numbers varies from 12% to 60% depending on Rayleigh number. Sublayer configurations with foam on both heat transfer surfaces are more effective for enhancement than a configuration with foam only on the heated surface. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Buoyant convection in superposed metal foam and water layers [texte imprimé] / V. Kathare, Auteur ; F. A. Kulacki, Auteur ; Jane H. Davidson, Auteur . - pp. [014503-1/4]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [014503-1/4] Mots-clés : Natural  convection  Metal  foam  Heat  transfer  enhancement Index. décimale : 536 Chaleur. Thermodynamique Résumé : Heat transfer measurements for natural convection in superposed metal foam and water layers are reported. Two systems heated at the lower boundary are considered: a water-filled cavity with a foam layer on the heated surface and a water-filled cavity with foam layers on the upper and lower surfaces. The present experiments use open cell copper foams with a nominal porosity of 92%, and the relative thicknesses of the water and foam layers are varied. Steady state Nusselt numbers show that the presence of foam on the boundaries enhances overall heat transfer coefficients over that for the water-only layer. Enhancement of overall Nusselt numbers varies from 12% to 60% depending on Rayleigh number. Sublayer configurations with foam on both heat transfer surfaces are more effective for enhancement than a configuration with foam only on the heated surface. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Contributions of inter- and intraband excitations to electron heat capacity and electron-phonon coupling in noble metals / Patrick E. Hopkins in Journal of heat transfer, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [014504-1/4] Titre : Contributions of inter- and intraband excitations to electron heat capacity and electron-phonon coupling in noble metals Type de document : texte imprimé Auteurs : Patrick E. Hopkins, Auteur Article en page(s) : pp. [014504-1/4] Note générale : Physique Langues : Anglais (eng) Mots-clés : Intraband  transition  Interband  transition  Electronphonon  coupling  factor  Short  pulsed  laser  heating  Electronic  band  structure Index. décimale : 536 Chaleur. Thermodynamique Résumé : This work examines the effects of photonically induced interband excitations from the d-band to states at the Fermi energy on thermophysical properties in noble metals. The change in the electron population in the d-band and the conduction band causes a change in electron heat capacity and electron-phonon coupling factor, which in turn impacts the evolution of the temperature after pulse absorption and electron thermalization. Expressions for heat capacity and electron-phonon coupling factor are derived for electrons undergoing both inter- and intraband transitions. In noble metals, due to the large d-band to Fermi energy separation, the contributions to electron heat capacity and electron-phonon coupling factor of intra- and interband transitions can be separated. At high absorbed laser fluences and pulse energies greater than the interband transition threshold, the interband and intraband contributions to thermophysical properties differ. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Contributions of inter- and intraband excitations to electron heat capacity and electron-phonon coupling in noble metals [texte imprimé] / Patrick E. Hopkins, Auteur . - pp. [014504-1/4]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 1 (Janvier 2010) . - pp. [014504-1/4] Mots-clés : Intraband  transition  Interband  transition  Electronphonon  coupling  factor  Short  pulsed  laser  heating  Electronic  band  structure Index. décimale : 536 Chaleur. Thermodynamique Résumé : This work examines the effects of photonically induced interband excitations from the d-band to states at the Fermi energy on thermophysical properties in noble metals. The change in the electron population in the d-band and the conduction band causes a change in electron heat capacity and electron-phonon coupling factor, which in turn impacts the evolution of the temperature after pulse absorption and electron thermalization. Expressions for heat capacity and electron-phonon coupling factor are derived for electrons undergoing both inter- and intraband transitions. In noble metals, due to the large d-band to Fermi energy separation, the contributions to electron heat capacity and electron-phonon coupling factor of intra- and interband transitions can be separated. At high absorbed laser fluences and pulse energies greater than the interband transition threshold, the interband and intraband contributions to thermophysical properties differ. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

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