Dépouillements

Modeling and validating the transient behavior of flat miniature heat pipes manufactured in multilayer printed circuit board technology / Wessel W. Wits in Journal of heat transfer, Vol. 133 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081401/1-10] Titre : Modeling and validating the transient behavior of flat miniature heat pipes manufactured in multilayer printed circuit board technology Type de document : texte imprimé Auteurs : Wessel W. Wits, Auteur ; Jim B. W. Kok, Auteur Année de publication : 2011 Article en page(s) : pp. [081401/1-10] Note générale : Physique Langues : Anglais (eng) Mots-clés : Heat  pipe  Electronics  coolings  PCB  cooling  Thermal  management  Control  volume  modeling Index. décimale : 536 Chaleur. Thermodynamique Résumé : A novel, integrated approach in thermal management of electronic products, based on two-phase cooling, is presented. A flat miniature heat pipe, integrated inside the laminated structure of a printed circuit board (PCB), has been developed, based on mainstream PCB multilayer technology. To accurately predict the thermal performance of this two-phase heat transport device and to establish the operational limitations, a numerical model based on control volume elements is discussed. The advantage of this modular approach, compared with, e.g., finite element models, is that the model can be expanded with additional components (e.g., multiple evaporators) very easily. Actual PCBs with several hot spots cooled by flat miniature heat pipes and their parameter effects can be analyzed very quickly, without the necessity of complex and time-consuming finite element analyses. Experimental verification has shown a good comparison with model predictions. Time evolution analyses show that the developed control volume model is well capable of describing the heat pipe transient behavior. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...] [article] Modeling and validating the transient behavior of flat miniature heat pipes manufactured in multilayer printed circuit board technology [texte imprimé] / Wessel W. Wits, Auteur ; Jim B. W. Kok, Auteur . - 2011 . - pp. [081401/1-10]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081401/1-10] Mots-clés : Heat  pipe  Electronics  coolings  PCB  cooling  Thermal  management  Control  volume  modeling Index. décimale : 536 Chaleur. Thermodynamique Résumé : A novel, integrated approach in thermal management of electronic products, based on two-phase cooling, is presented. A flat miniature heat pipe, integrated inside the laminated structure of a printed circuit board (PCB), has been developed, based on mainstream PCB multilayer technology. To accurately predict the thermal performance of this two-phase heat transport device and to establish the operational limitations, a numerical model based on control volume elements is discussed. The advantage of this modular approach, compared with, e.g., finite element models, is that the model can be expanded with additional components (e.g., multiple evaporators) very easily. Actual PCBs with several hot spots cooled by flat miniature heat pipes and their parameter effects can be analyzed very quickly, without the necessity of complex and time-consuming finite element analyses. Experimental verification has shown a good comparison with model predictions. Time evolution analyses show that the developed control volume model is well capable of describing the heat pipe transient behavior. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...]

Flow boiling heat transfer characteristics of a minichannel up to dryout condition / Rashid Ali in Journal of heat transfer, Vol. 133 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081501/1-10] Titre : Flow boiling heat transfer characteristics of a minichannel up to dryout condition Type de document : texte imprimé Auteurs : Rashid Ali, Auteur ; Björn Palm, Auteur ; Mohammad H. Maqbool, Auteur Année de publication : 2011 Article en page(s) : pp. [081501/1-10] Note générale : Physique Langues : Anglais (eng) Mots-clés : Microchannels  Two-phase  Boiling  Heat  transfer  Dryout Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this paper, the experimental flow boiling heat transfer results of a minichannel are presented. A series of experiments was conducted to measure the heat transfer coefficients in a minichannel made of stainless steel (AISI 316) having an internal diameter of 1.70 mm and a uniformly heated length of 220 mm. R134a was used as a working fluid, and experiments were performed at two different system pressures corresponding to saturation temperatures of 27°C and 32°C. Mass flux was varied from 50 kg/m2 s to 600 kg/m2 s, and heat flux ranged from 2 kW/m2 to 156 kW/m2. The test section was heated directly using a dc power supply. The direct heating of the channel ensured uniform heating, which was continued until dryout was reached. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux, while mass flux and vapor quality have no considerable effect. Increasing the system pressure slightly enhances the heat transfer coefficient. The heat transfer coefficient is reduced as dryout is reached. It is observed that the dryout phenomenon is accompanied with fluctuations and a larger standard deviation in outer wall temperatures. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...] [article] Flow boiling heat transfer characteristics of a minichannel up to dryout condition [texte imprimé] / Rashid Ali, Auteur ; Björn Palm, Auteur ; Mohammad H. Maqbool, Auteur . - 2011 . - pp. [081501/1-10]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081501/1-10] Mots-clés : Microchannels  Two-phase  Boiling  Heat  transfer  Dryout Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this paper, the experimental flow boiling heat transfer results of a minichannel are presented. A series of experiments was conducted to measure the heat transfer coefficients in a minichannel made of stainless steel (AISI 316) having an internal diameter of 1.70 mm and a uniformly heated length of 220 mm. R134a was used as a working fluid, and experiments were performed at two different system pressures corresponding to saturation temperatures of 27°C and 32°C. Mass flux was varied from 50 kg/m2 s to 600 kg/m2 s, and heat flux ranged from 2 kW/m2 to 156 kW/m2. The test section was heated directly using a dc power supply. The direct heating of the channel ensured uniform heating, which was continued until dryout was reached. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux, while mass flux and vapor quality have no considerable effect. Increasing the system pressure slightly enhances the heat transfer coefficient. The heat transfer coefficient is reduced as dryout is reached. It is observed that the dryout phenomenon is accompanied with fluctuations and a larger standard deviation in outer wall temperatures. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...]

Dropwise condensation modeling suitable for superhydrophobic surfaces / Sunwoo Kim in Journal of heat transfer, Vol. 133 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081502/1-8] Titre : Dropwise condensation modeling suitable for superhydrophobic surfaces Type de document : texte imprimé Auteurs : Sunwoo Kim, Auteur ; Kwang J. Kim, Auteur Année de publication : 2011 Article en page(s) : pp. [081502/1-8] Note générale : Physique Langues : Anglais (eng) Mots-clés : Dropwise  condensation  Contact  angle  Hydrophobicity  Surface  wettability  Drop  size  distribution Index. décimale : 536 Chaleur. Thermodynamique Résumé : A mathematical model is developed to represent and predict the dropwise condensation phenomenon on nonwetting surfaces having hydrophobic or superhydrophobic (contact angle greater than 150 deg) features. The model is established by synthesizing the heat transfer through a single droplet with the drop size distribution. The single droplet heat transfer is analyzed as a combination of the vapor-liquid interfacial resistance, the resistance due to the conduction through the drop itself, the resistance from the coating layer, and the resistance due to the curvature of the drop. A population balance model is adapted to develop a drop distribution function for the small drops that grow by direct condensation. Drop size distribution for large drops that grow mainly by coalescence is obtained from a well-known empirical equation. The evidence obtained suggests that both the single droplet heat transfer and drop distribution are significantly affected by the contact angle. More specifically, the model results indicate that a high drop-contact angle leads to enhancing condensation heat transfer. Intense hydrophobicity, which produces high contact angles, causes a reduction in the size of drops on the verge of falling due to gravity, thus allowing space for more small drops. The simulation results are compared with experimental data, which were previously reported. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...] [article] Dropwise condensation modeling suitable for superhydrophobic surfaces [texte imprimé] / Sunwoo Kim, Auteur ; Kwang J. Kim, Auteur . - 2011 . - pp. [081502/1-8]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081502/1-8] Mots-clés : Dropwise  condensation  Contact  angle  Hydrophobicity  Surface  wettability  Drop  size  distribution Index. décimale : 536 Chaleur. Thermodynamique Résumé : A mathematical model is developed to represent and predict the dropwise condensation phenomenon on nonwetting surfaces having hydrophobic or superhydrophobic (contact angle greater than 150 deg) features. The model is established by synthesizing the heat transfer through a single droplet with the drop size distribution. The single droplet heat transfer is analyzed as a combination of the vapor-liquid interfacial resistance, the resistance due to the conduction through the drop itself, the resistance from the coating layer, and the resistance due to the curvature of the drop. A population balance model is adapted to develop a drop distribution function for the small drops that grow by direct condensation. Drop size distribution for large drops that grow mainly by coalescence is obtained from a well-known empirical equation. The evidence obtained suggests that both the single droplet heat transfer and drop distribution are significantly affected by the contact angle. More specifically, the model results indicate that a high drop-contact angle leads to enhancing condensation heat transfer. Intense hydrophobicity, which produces high contact angles, causes a reduction in the size of drops on the verge of falling due to gravity, thus allowing space for more small drops. The simulation results are compared with experimental data, which were previously reported. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...]

Subcooled boiling of PF-5060 dielectric liquid on microporous surfaces / Mohamed S. El-Genk in Journal of heat transfer, Vol. 133 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081503/1-8] Titre : Subcooled boiling of PF-5060 dielectric liquid on microporous surfaces Type de document : texte imprimé Auteurs : Mohamed S. El-Genk, Auteur ; Amir F. Ali, Auteur Année de publication : 2011 Article en page(s) : pp. [081503/1-8] Note générale : Physique Langues : Anglais (eng) Mots-clés : Subcoled  boiling  Microporous  copper  Electrochemical  deposition  Electronic  cooling  Dielectric  liquids Index. décimale : 536 Chaleur. Thermodynamique Résumé : Presented are the results of experiments that investigated nucleate boiling of PF-5060 on microporous Cu surface layers at saturation and 10 K, 20 K, and 30 K subcooling. The three microporous layers, electrochemically deposited on 10×10 mm2 Cu substrates and investigated herein, are ~139 µm, 171 µm, and 220 µm thick. The critical heat flux increases linearly with increased subcooling, Tsub, at an average rate of 4.5%/K. For the 171 µm thick, Cu microporous surface, saturation boiling CHF of 27.8 W/cm2 increases to 63.25 W/cm2 at Tsub=30 K, while the saturation hMNB of 13.5 W/cm2 K decreases slightly to 12.7 W/cm2 K at Tsub=30 K. The values of the surface superheat, Tsat, at hMNB and CHF increase from 2.0 K and 2.16 K at saturation to 4.2 and 6.42 K at 30 K subcooling. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...] [article] Subcooled boiling of PF-5060 dielectric liquid on microporous surfaces [texte imprimé] / Mohamed S. El-Genk, Auteur ; Amir F. Ali, Auteur . - 2011 . - pp. [081503/1-8]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081503/1-8] Mots-clés : Subcoled  boiling  Microporous  copper  Electrochemical  deposition  Electronic  cooling  Dielectric  liquids Index. décimale : 536 Chaleur. Thermodynamique Résumé : Presented are the results of experiments that investigated nucleate boiling of PF-5060 on microporous Cu surface layers at saturation and 10 K, 20 K, and 30 K subcooling. The three microporous layers, electrochemically deposited on 10×10 mm2 Cu substrates and investigated herein, are ~139 µm, 171 µm, and 220 µm thick. The critical heat flux increases linearly with increased subcooling, Tsub, at an average rate of 4.5%/K. For the 171 µm thick, Cu microporous surface, saturation boiling CHF of 27.8 W/cm2 increases to 63.25 W/cm2 at Tsub=30 K, while the saturation hMNB of 13.5 W/cm2 K decreases slightly to 12.7 W/cm2 K at Tsub=30 K. The values of the surface superheat, Tsat, at hMNB and CHF increase from 2.0 K and 2.16 K at saturation to 4.2 and 6.42 K at 30 K subcooling. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...]

A dynamic film model of the pulsating heat pipe / Vadim S. Nikolayev in Journal of heat transfer, Vol. 133 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081504/1-9] Titre : A dynamic film model of the pulsating heat pipe Type de document : texte imprimé Auteurs : Vadim S. Nikolayev, Auteur Année de publication : 2011 Article en page(s) : pp. [081504/1-9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Oscillating  Pulsating  Heat  pipe  Simulation Index. décimale : 536 Chaleur. Thermodynamique Résumé : This article deals with the numerical modeling of the pulsating heat pipe (PHP) and is based on the film evaporation/condensation model recently applied to the single-bubble PHP (Das et al., 2010, “Thermally Induced Two-Phase Oscillating Flow Inside a Capillary Tube,” Int. J. Heat Mass Transfer, 53(19–20), pp. 3905–3913). The described numerical code can treat the PHP of an arbitrary number of bubbles and branches. Several phenomena that occur inside the PHP are taken into account: coalescence of liquid plugs, film junction or rupture, etc. The model reproduces some of the experimentally observed regimes of functioning of the PHP such as chaotic or intermittent oscillations of large amplitudes. Some results on the PHP heat transfer are discussed. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...] [article] A dynamic film model of the pulsating heat pipe [texte imprimé] / Vadim S. Nikolayev, Auteur . - 2011 . - pp. [081504/1-9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081504/1-9] Mots-clés : Oscillating  Pulsating  Heat  pipe  Simulation Index. décimale : 536 Chaleur. Thermodynamique Résumé : This article deals with the numerical modeling of the pulsating heat pipe (PHP) and is based on the film evaporation/condensation model recently applied to the single-bubble PHP (Das et al., 2010, “Thermally Induced Two-Phase Oscillating Flow Inside a Capillary Tube,” Int. J. Heat Mass Transfer, 53(19–20), pp. 3905–3913). The described numerical code can treat the PHP of an arbitrary number of bubbles and branches. Several phenomena that occur inside the PHP are taken into account: coalescence of liquid plugs, film junction or rupture, etc. The model reproduces some of the experimentally observed regimes of functioning of the PHP such as chaotic or intermittent oscillations of large amplitudes. Some results on the PHP heat transfer are discussed. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...]

Optical measurement of thermal conductivity using fiber aligned frequency domain thermoreflectance / Jonathan A. Malen in Journal of heat transfer, Vol. 133 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081601/1-7] Titre : Optical measurement of thermal conductivity using fiber aligned frequency domain thermoreflectance Type de document : texte imprimé Auteurs : Jonathan A. Malen, Auteur ; Kanhayalal Baheti, Auteur ; Tao Tong, Auteur Année de publication : 2011 Article en page(s) : pp. [081601/1-7] Note générale : Physique Langues : Anglais (eng) Mots-clés : Thermal  conductivity  Thermal  diffusivity  Thermometry  Photothermal  Thermoreflectance  Frequency  Domaines Index. décimale : 536 Chaleur. Thermodynamique Résumé : Fiber aligned frequency domain thermoreflectance (FAFDTR) is a simple noncontact optical technique for accurately measuring the thermal conductivity of thin films and bulk samples for a wide range of materials, including electrically conducting samples. FAFDTR is a single-sided measurement that requires minimal sample preparation and no microfabrication. Like existing thermoreflectance techniques, a modulated pump laser heats the sample surface, and a probe laser monitors the resultant thermal wave via the temperature dependent reflectance of the surface. Via the use of inexpensive fiber coupled diode lasers and common mode rejection, FAFDTR addresses three challenges of existing optical methods: complexity in setup, uncertainty in pump-probe alignment, and noise in the probe laser. FAFDTR was validated for thermal conductivities spanning three orders of magnitude (0.1–100 W/m K), and thin film thermal conductances greater than 10 W/m2 K. Uncertainties of 10–15% were typical, and were dominated by uncertainties in the laser spot size. A parametric study of sensitivity for thin film samples shows that high thermal conductivity contrast between film and substrate is essential for making accurate measurements. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...] [article] Optical measurement of thermal conductivity using fiber aligned frequency domain thermoreflectance [texte imprimé] / Jonathan A. Malen, Auteur ; Kanhayalal Baheti, Auteur ; Tao Tong, Auteur . - 2011 . - pp. [081601/1-7]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081601/1-7] Mots-clés : Thermal  conductivity  Thermal  diffusivity  Thermometry  Photothermal  Thermoreflectance  Frequency  Domaines Index. décimale : 536 Chaleur. Thermodynamique Résumé : Fiber aligned frequency domain thermoreflectance (FAFDTR) is a simple noncontact optical technique for accurately measuring the thermal conductivity of thin films and bulk samples for a wide range of materials, including electrically conducting samples. FAFDTR is a single-sided measurement that requires minimal sample preparation and no microfabrication. Like existing thermoreflectance techniques, a modulated pump laser heats the sample surface, and a probe laser monitors the resultant thermal wave via the temperature dependent reflectance of the surface. Via the use of inexpensive fiber coupled diode lasers and common mode rejection, FAFDTR addresses three challenges of existing optical methods: complexity in setup, uncertainty in pump-probe alignment, and noise in the probe laser. FAFDTR was validated for thermal conductivities spanning three orders of magnitude (0.1–100 W/m K), and thin film thermal conductances greater than 10 W/m2 K. Uncertainties of 10–15% were typical, and were dominated by uncertainties in the laser spot size. A parametric study of sensitivity for thin film samples shows that high thermal conductivity contrast between film and substrate is essential for making accurate measurements. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...]

Inverse estimation for heat flux distribution at the metal-mold interface using fuzzy inference / Lina Zhu in Journal of heat transfer, Vol. 133 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081602/1-6] Titre : Inverse estimation for heat flux distribution at the metal-mold interface using fuzzy inference Type de document : texte imprimé Auteurs : Lina Zhu, Auteur ; Guangjun Wang, Auteur ; Chen, Hong, Auteur Année de publication : 2011 Article en page(s) : pp. [081602/1-6] Note générale : Physique Langues : Anglais (eng) Mots-clés : Inverse  approach  Fuzzy  inference  Heat  flux  distribution  Continuous  casting Index. décimale : 536 Chaleur. Thermodynamique Résumé : This study provides a new inverse approach based on fuzzy inference for solving the problem of estimating heat flux distribution at the metal-mold interface in the continuous casting process. Measured temperatures acquired with the thermocouples buried in the mold are used to obtain corresponding inference results with the fuzzy inference. Then according to the importance of measured information for estimating the heat flux distribution, inference results are weighted to realize estimation of heat flux distribution at the metal-mold interface. Some numerical tests are presented to discuss the validity of the present approach by using different initial guesses of heat flux distribution, the number of measuring points, and measurement errors. In comparison with the conjugate gradient method, it is concluded that the method based on fuzzy inference is of a good anti-ill-posed characteristic. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...] [article] Inverse estimation for heat flux distribution at the metal-mold interface using fuzzy inference [texte imprimé] / Lina Zhu, Auteur ; Guangjun Wang, Auteur ; Chen, Hong, Auteur . - 2011 . - pp. [081602/1-6]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081602/1-6] Mots-clés : Inverse  approach  Fuzzy  inference  Heat  flux  distribution  Continuous  casting Index. décimale : 536 Chaleur. Thermodynamique Résumé : This study provides a new inverse approach based on fuzzy inference for solving the problem of estimating heat flux distribution at the metal-mold interface in the continuous casting process. Measured temperatures acquired with the thermocouples buried in the mold are used to obtain corresponding inference results with the fuzzy inference. Then according to the importance of measured information for estimating the heat flux distribution, inference results are weighted to realize estimation of heat flux distribution at the metal-mold interface. Some numerical tests are presented to discuss the validity of the present approach by using different initial guesses of heat flux distribution, the number of measuring points, and measurement errors. In comparison with the conjugate gradient method, it is concluded that the method based on fuzzy inference is of a good anti-ill-posed characteristic. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...]

Casing convective heat transfer coefficient and reference freestream temperature determination near an axial flow turbine rotor / C. Camci in Journal of heat transfer, Vol. 133 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081603/1-9] Titre : Casing convective heat transfer coefficient and reference freestream temperature determination near an axial flow turbine rotor Type de document : texte imprimé Auteurs : C. Camci, Auteur ; B. Gumusel, Auteur Année de publication : 2011 Article en page(s) : pp. [081603/1-9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Convection  Rotational  flow  Rotors  Turbines Index. décimale : 536 Chaleur. Thermodynamique Résumé : The present study explains a steady-state method of measuring convective heat transfer coefficient on the casing of an axial flow turbine. The goal is to develop an accurate steady-state heat transfer method for the comparison of various casing surface and tip designs used for turbine performance improvements. The freestream reference temperature, especially in the tip gap region of the casing, varies monotonically from the rotor inlet to rotor exit due to work extraction in the stage. In a heat transfer problem of this nature, the definition of the freestream temperature is not as straightforward as constant freestream temperature type problems. The accurate determination of the convective heat transfer coefficient depends on the magnitude of the local freestream reference temperature varying in axial direction, from the rotor inlet to exit. The current study explains a strategy for the simultaneous determination of the steady-state heat transfer coefficient and freestream reference temperature on the smooth casing of a single stage rotating turbine facility. The heat transfer approach is also applicable to casing surfaces that have surface treatments for tip leakage control. The overall uncertainty of the method developed is between 5% and 8% of the convective heat transfer coefficient. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...] [article] Casing convective heat transfer coefficient and reference freestream temperature determination near an axial flow turbine rotor [texte imprimé] / C. Camci, Auteur ; B. Gumusel, Auteur . - 2011 . - pp. [081603/1-9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081603/1-9] Mots-clés : Convection  Rotational  flow  Rotors  Turbines Index. décimale : 536 Chaleur. Thermodynamique Résumé : The present study explains a steady-state method of measuring convective heat transfer coefficient on the casing of an axial flow turbine. The goal is to develop an accurate steady-state heat transfer method for the comparison of various casing surface and tip designs used for turbine performance improvements. The freestream reference temperature, especially in the tip gap region of the casing, varies monotonically from the rotor inlet to rotor exit due to work extraction in the stage. In a heat transfer problem of this nature, the definition of the freestream temperature is not as straightforward as constant freestream temperature type problems. The accurate determination of the convective heat transfer coefficient depends on the magnitude of the local freestream reference temperature varying in axial direction, from the rotor inlet to exit. The current study explains a strategy for the simultaneous determination of the steady-state heat transfer coefficient and freestream reference temperature on the smooth casing of a single stage rotating turbine facility. The heat transfer approach is also applicable to casing surfaces that have surface treatments for tip leakage control. The overall uncertainty of the method developed is between 5% and 8% of the convective heat transfer coefficient. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...]

Transient thermal response of turbulent compressible boundary layers / Hongwei Li in Journal of heat transfer, Vol. 133 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081701/1-8] Titre : Transient thermal response of turbulent compressible boundary layers Type de document : texte imprimé Auteurs : Hongwei Li, Auteur ; M. Razi Nalim, Auteur ; Charles L. Merkle, Auteur Année de publication : 2011 Article en page(s) : pp. [081701/1-8] Note générale : Physique Langues : Anglais (eng) Mots-clés : Boundary  layer  Turbulent  Wave  rotor  Transient Index. décimale : 536 Chaleur. Thermodynamique Résumé : A numerical method is developed with the capability to predict transient thermal boundary layer response under various flow and thermal conditions. The transient thermal boundary layer variation due to a moving compressible turbulent fluid of varying temperature was numerically studied on a two-dimensional semi-infinite flat plate. The compressible Reynolds-averaged boundary layer equations are transformed into incompressible form through the Dorodnitsyn–Howarth transformation and then solved with similarity transformations. Turbulence is modeled using a two-layer eddy viscosity model developed by Cebeci and Smith, and the turbulent Prandtl number formulation originally developed by Kays and Crawford. The governing differential equations are discretized with the Keller-box method. The numerical accuracy is validated through grid-independence studies and comparison with the steady state solution. In turbulent flow as in laminar, the transient heat transfer rates are very different from that obtained from quasi-steady analysis. It is found that the time scale for response of the turbulent boundary layer to far-field temperature changes is 40% less than for laminar flow, and the turbulent local Nusselt number is approximately 4 times that of laminar flow at the final steady state. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...] [article] Transient thermal response of turbulent compressible boundary layers [texte imprimé] / Hongwei Li, Auteur ; M. Razi Nalim, Auteur ; Charles L. Merkle, Auteur . - 2011 . - pp. [081701/1-8]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081701/1-8] Mots-clés : Boundary  layer  Turbulent  Wave  rotor  Transient Index. décimale : 536 Chaleur. Thermodynamique Résumé : A numerical method is developed with the capability to predict transient thermal boundary layer response under various flow and thermal conditions. The transient thermal boundary layer variation due to a moving compressible turbulent fluid of varying temperature was numerically studied on a two-dimensional semi-infinite flat plate. The compressible Reynolds-averaged boundary layer equations are transformed into incompressible form through the Dorodnitsyn–Howarth transformation and then solved with similarity transformations. Turbulence is modeled using a two-layer eddy viscosity model developed by Cebeci and Smith, and the turbulent Prandtl number formulation originally developed by Kays and Crawford. The governing differential equations are discretized with the Keller-box method. The numerical accuracy is validated through grid-independence studies and comparison with the steady state solution. In turbulent flow as in laminar, the transient heat transfer rates are very different from that obtained from quasi-steady analysis. It is found that the time scale for response of the turbulent boundary layer to far-field temperature changes is 40% less than for laminar flow, and the turbulent local Nusselt number is approximately 4 times that of laminar flow at the final steady state. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...]

Thermal and hydraulic performance of counterflow microchannel heat exchangers with and without nanofluids / Hamid Reza Seyf in Journal of heat transfer, Vol. 133 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081801/1-9] Titre : Thermal and hydraulic performance of counterflow microchannel heat exchangers with and without nanofluids Type de document : texte imprimé Auteurs : Hamid Reza Seyf, Auteur ; Shahabeddin Keshavarz Mohammadian, Auteur Année de publication : 2011 Article en page(s) : pp. [081801/1-9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Numerical  simulation  Nanofluid  Brownian  motion  Effectiveness  Thermal  performance Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper analyzes the thermal and hydraulic performance of a counterflow microchannel heat exchanger (CFMCHE) with and without nanofluid as working fluid. A 3D conjugate heat transfer simulation is carried out using a finite volume approach to evaluate the effects of inlet Reynolds number, Brownian motion, and volume fraction of nanoparticles on the pumping power, effectiveness, and performance index of CFMCHE. The accuracy of the code has been verified by comparing the results with those available in the literature. A single phase approach is used for the nanofluid modeling. The base fluid used in the analyses as a basis for comparison was pure water. Two types of nanofluids, namely, water-Al2O3 with a mean diameter of 47 nm and water-CuO with a mean diameter of 29 nm, each one with three different volume fractions, are utilized. In addition, two temperature dependent models for the thermal conductivity and viscosity of nanofluids that account for the fundamental role of Brownian motion are used. Calculated results demonstrate that the effectiveness and performance index of CFMCHE decrease with increasing Reynolds number. Moreover, it is observed that the relative enhancements in the pumping power become more prominent for higher values of Reynolds numbers. It was also found that the performance index and pumping power are not sensitive to volume fraction at higher and lower Reynolds numbers, respectively. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...] [article] Thermal and hydraulic performance of counterflow microchannel heat exchangers with and without nanofluids [texte imprimé] / Hamid Reza Seyf, Auteur ; Shahabeddin Keshavarz Mohammadian, Auteur . - 2011 . - pp. [081801/1-9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081801/1-9] Mots-clés : Numerical  simulation  Nanofluid  Brownian  motion  Effectiveness  Thermal  performance Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper analyzes the thermal and hydraulic performance of a counterflow microchannel heat exchanger (CFMCHE) with and without nanofluid as working fluid. A 3D conjugate heat transfer simulation is carried out using a finite volume approach to evaluate the effects of inlet Reynolds number, Brownian motion, and volume fraction of nanoparticles on the pumping power, effectiveness, and performance index of CFMCHE. The accuracy of the code has been verified by comparing the results with those available in the literature. A single phase approach is used for the nanofluid modeling. The base fluid used in the analyses as a basis for comparison was pure water. Two types of nanofluids, namely, water-Al2O3 with a mean diameter of 47 nm and water-CuO with a mean diameter of 29 nm, each one with three different volume fractions, are utilized. In addition, two temperature dependent models for the thermal conductivity and viscosity of nanofluids that account for the fundamental role of Brownian motion are used. Calculated results demonstrate that the effectiveness and performance index of CFMCHE decrease with increasing Reynolds number. Moreover, it is observed that the relative enhancements in the pumping power become more prominent for higher values of Reynolds numbers. It was also found that the performance index and pumping power are not sensitive to volume fraction at higher and lower Reynolds numbers, respectively. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...]

The effect of the corrugation rib angle of attack on the fluid flow and heat transfer characteristics inside corrugated ribbed passage / A. M. I. Mohamed in Journal of heat transfer, Vol. 133 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081901/1-10] Titre : The effect of the corrugation rib angle of attack on the fluid flow and heat transfer characteristics inside corrugated ribbed passage Type de document : texte imprimé Auteurs : A. M. I. Mohamed, Auteur ; R. Hoettiba, Auteur ; A. M. Saif, Auteur Année de publication : 2011 Article en page(s) : pp. [081901/1-10] Note générale : Physique Langues : Anglais (eng) Mots-clés : Heat  exchanger  Fluid  flow  Heat  transfer  enhancement  Heat  transfer  coefficient  Corrugated  ribbed  passage  CFD Index. décimale : 536 Chaleur. Thermodynamique Résumé : Heat transfer enhancement using corrugated ribbed passages is one of the common enhancement techniques inside heat exchangers. The present study investigated numerically the effect of the corrugation rib angle of attack on the fluid flow and heat transfer characteristics inside the corrugated ribbed passage. The commercial computational fluid dynamics code PHOENICS 2006 was used to perform the numerical analysis by solving the Navier–Stokes and energy equations. The experimental part of this study was used only to validate the numerical model, and a good agreement between the experimental results and the model was obtained. The flow field characteristics and heat transfer enhancement were numerically investigated for different corrugated rib angles of attack as follows: 90 deg, 105 deg, 120 deg, 135 deg, and 150 deg. The corrugation rib angle of attack has a great effect on the reversed flow zone, the flow reattachments, and the enhancement of the heat transfer coefficient through the duct. The recommended rib angle of attack, which gives the optimum thermohydraulic performance, is found to be between 135 deg and 150 deg. The value of the maximum thermohydraulic performance is about 3.6 for the 150 deg rib angle of attack at a Reynolds number equal to 10,000. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...] [article] The effect of the corrugation rib angle of attack on the fluid flow and heat transfer characteristics inside corrugated ribbed passage [texte imprimé] / A. M. I. Mohamed, Auteur ; R. Hoettiba, Auteur ; A. M. Saif, Auteur . - 2011 . - pp. [081901/1-10]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081901/1-10] Mots-clés : Heat  exchanger  Fluid  flow  Heat  transfer  enhancement  Heat  transfer  coefficient  Corrugated  ribbed  passage  CFD Index. décimale : 536 Chaleur. Thermodynamique Résumé : Heat transfer enhancement using corrugated ribbed passages is one of the common enhancement techniques inside heat exchangers. The present study investigated numerically the effect of the corrugation rib angle of attack on the fluid flow and heat transfer characteristics inside the corrugated ribbed passage. The commercial computational fluid dynamics code PHOENICS 2006 was used to perform the numerical analysis by solving the Navier–Stokes and energy equations. The experimental part of this study was used only to validate the numerical model, and a good agreement between the experimental results and the model was obtained. The flow field characteristics and heat transfer enhancement were numerically investigated for different corrugated rib angles of attack as follows: 90 deg, 105 deg, 120 deg, 135 deg, and 150 deg. The corrugation rib angle of attack has a great effect on the reversed flow zone, the flow reattachments, and the enhancement of the heat transfer coefficient through the duct. The recommended rib angle of attack, which gives the optimum thermohydraulic performance, is found to be between 135 deg and 150 deg. The value of the maximum thermohydraulic performance is about 3.6 for the 150 deg rib angle of attack at a Reynolds number equal to 10,000. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...]

Constructal design of complex assembly of fins / Giulio Lorenzini in Journal of heat transfer, Vol. 133 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081902/1-7] Titre : Constructal design of complex assembly of fins Type de document : texte imprimé Auteurs : Giulio Lorenzini, Auteur ; Roberta Lima Correa, Auteur ; Luiz Alberto Oliveira Rocha, Auteur Année de publication : 2011 Article en page(s) : pp. [081902/1-7] Note générale : Physique Langues : Anglais (eng) Mots-clés : Constructal  design  Enhanced  heat  transfer  Fins  Optimization Index. décimale : 536 Chaleur. Thermodynamique Résumé : Constructal design is a method that conducts the designer toward flow (e.g., heat flux) architectures that have greater global performance. This numerical work uses this method to seek for the best geometry of a complex assembly of fins, i.e., an assembly where there is a cavity between the two branches of the T-Y-assembly of fins and two additional extended surfaces. The global thermal resistance of the assembly is minimized four times by geometric optimization subject to the following constraints: the total volume, the volume of fin material, the volume of the cavity, and the volume of the two additional extended surfaces. Larger amount of fin material improves the performance of the assembly of fins. The three times optimized global thermal resistance of the complex assembly of fins performs 32% better than the best T-Y-configuration under the same thermal and geometric conditions. The three times minimized global thermal resistance of the complex assembly of fins was correlated by power laws as a function of its corresponding optimal configurations. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...] [article] Constructal design of complex assembly of fins [texte imprimé] / Giulio Lorenzini, Auteur ; Roberta Lima Correa, Auteur ; Luiz Alberto Oliveira Rocha, Auteur . - 2011 . - pp. [081902/1-7]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [081902/1-7] Mots-clés : Constructal  design  Enhanced  heat  transfer  Fins  Optimization Index. décimale : 536 Chaleur. Thermodynamique Résumé : Constructal design is a method that conducts the designer toward flow (e.g., heat flux) architectures that have greater global performance. This numerical work uses this method to seek for the best geometry of a complex assembly of fins, i.e., an assembly where there is a cavity between the two branches of the T-Y-assembly of fins and two additional extended surfaces. The global thermal resistance of the assembly is minimized four times by geometric optimization subject to the following constraints: the total volume, the volume of fin material, the volume of the cavity, and the volume of the two additional extended surfaces. Larger amount of fin material improves the performance of the assembly of fins. The three times optimized global thermal resistance of the complex assembly of fins performs 32% better than the best T-Y-configuration under the same thermal and geometric conditions. The three times minimized global thermal resistance of the complex assembly of fins was correlated by power laws as a function of its corresponding optimal configurations. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...]

Surface functionalization mechanisms of enhancing heat transfer at solid-liquid interfaces / Javier V. Goicochea in Journal of heat transfer, Vol. 133 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [082401/1-6] Titre : Surface functionalization mechanisms of enhancing heat transfer at solid-liquid interfaces Type de document : texte imprimé Auteurs : Javier V. Goicochea, Auteur ; Ming Hu, Auteur Année de publication : 2011 Article en page(s) : pp. [082401/1-6] Note générale : Physique Langues : Anglais (eng) Mots-clés : Surface  functionalization  Vivrational  matching  Interface  resistance  Conductance  Heat  transfer  Molecular  dynamics  Solid-liquid Index. décimale : 536 Chaleur. Thermodynamique Résumé : Two mechanisms that enhance heat dissipation at solid-liquid interfaces are investigated from the atomistic point of view using nonequilibrium molecular dynamics simulation. The mechanisms include surface functionalization, where –OH terminated headgroups and self-assembled monolayers (SAMs) with different chain lengths are used to recondition and modify the hydrophilicity of silica surface, and vibrational matching between crystalline silica and liquid water, where three-dimensional nanopillars are grown at the interface in the direction of the heat flux with different lengths to rectify the vibrational frequencies of surface atoms. The heat dissipation is measured in terms of the thermal conductance of the solid-liquid interface and is obtained by imposing a one-dimensional heat flux along the simulation domain. A comparison with reported numerical and experimental thermal conductance measurements for similar interfaces indicates that the thermal conductance is enhanced by 1.8–3.2 times when the silica surface is reconditioned with hydrophilic groups. The enhancement is further promoted by SAMs, which results in a 20% higher thermal conductance compared with that of the fully hydroxylated silica surface. Likewise, the presence of nanopillars enhances the interface thermal conductance by 2.6 times compared with a bare surface (without nanopillars). Moreover, for different nanopillar densities, the conductance increases linearly with the length of the pillar and saturates at around 4.26 nm. Changes in the vibrational spectrum of surface atoms and water confinement effects are found to be responsible for the increase in conductance. The modification of surface vibrational states provides a tunable path to enhance heat dissipation, which can also be easily applied to other fluids and interfaces. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...] [article] Surface functionalization mechanisms of enhancing heat transfer at solid-liquid interfaces [texte imprimé] / Javier V. Goicochea, Auteur ; Ming Hu, Auteur . - 2011 . - pp. [082401/1-6]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [082401/1-6] Mots-clés : Surface  functionalization  Vivrational  matching  Interface  resistance  Conductance  Heat  transfer  Molecular  dynamics  Solid-liquid Index. décimale : 536 Chaleur. Thermodynamique Résumé : Two mechanisms that enhance heat dissipation at solid-liquid interfaces are investigated from the atomistic point of view using nonequilibrium molecular dynamics simulation. The mechanisms include surface functionalization, where –OH terminated headgroups and self-assembled monolayers (SAMs) with different chain lengths are used to recondition and modify the hydrophilicity of silica surface, and vibrational matching between crystalline silica and liquid water, where three-dimensional nanopillars are grown at the interface in the direction of the heat flux with different lengths to rectify the vibrational frequencies of surface atoms. The heat dissipation is measured in terms of the thermal conductance of the solid-liquid interface and is obtained by imposing a one-dimensional heat flux along the simulation domain. A comparison with reported numerical and experimental thermal conductance measurements for similar interfaces indicates that the thermal conductance is enhanced by 1.8–3.2 times when the silica surface is reconditioned with hydrophilic groups. The enhancement is further promoted by SAMs, which results in a 20% higher thermal conductance compared with that of the fully hydroxylated silica surface. Likewise, the presence of nanopillars enhances the interface thermal conductance by 2.6 times compared with a bare surface (without nanopillars). Moreover, for different nanopillar densities, the conductance increases linearly with the length of the pillar and saturates at around 4.26 nm. Changes in the vibrational spectrum of surface atoms and water confinement effects are found to be responsible for the increase in conductance. The modification of surface vibrational states provides a tunable path to enhance heat dissipation, which can also be easily applied to other fluids and interfaces. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...]

Flow structure and heat transfer in a stagnation flow CVD reactor / Nasir Memon in Journal of heat transfer, Vol. 133 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [082501/1-6] Titre : Flow structure and heat transfer in a stagnation flow CVD reactor Type de document : texte imprimé Auteurs : Nasir Memon, Auteur ; Yogesh, Jaluria, Auteur Année de publication : 2011 Article en page(s) : pp. [082501/1-6] Note générale : Physique Langues : Anglais (eng) Mots-clés : CVD  Stagnation  flow  Chemical  vapor  deposition  Buoyancy  effects Index. décimale : 536 Chaleur. Thermodynamique Résumé : An experimental study is undertaken to investigate the flow structure and heat transfer in a stagnation flow chemical vapor deposition (CVD) reactor at atmospheric pressure. It is critical to develop models that predict flow patterns in such a reactor to achieve uniform deposition across the substrate. Free convection can negatively affect the gas flow as cold inlet gas impinges on the heated substrate, leading to vortices and disturbances in the normal flow path. This experimental research will be used to understand the buoyancy-induced and momentum driven flow structure encountered in an impinging jet CVD reactor. Investigations are conducted for various operating and design parameters. A modified stagnation flow reactor is built where the height between the inlet and substrate is reduced when compared with a prototypical stagnation flow reactor. By operating such a reactor at certain Reynolds and Grashof numbers, it is feasible to sustain smooth and vortex free flow at atmospheric pressure. The modified stagnation flow reactor is compared with other stagnation flow geometries with either a varied inlet length or varied heights between the inlet and substrate. Comparisons are made to understand the impact of such geometric changes on the flow structure and the thermal boundary layer. In addition, heat transfer correlations are obtained for the substrate temperature. Overall, the results obtained provide guidelines for curbing the effects of buoyancy and for improving the flow field to obtain greater film uniformity when operating a stagnation flow CVD reactor at atmospheric pressure. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...] [article] Flow structure and heat transfer in a stagnation flow CVD reactor [texte imprimé] / Nasir Memon, Auteur ; Yogesh, Jaluria, Auteur . - 2011 . - pp. [082501/1-6]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [082501/1-6] Mots-clés : CVD  Stagnation  flow  Chemical  vapor  deposition  Buoyancy  effects Index. décimale : 536 Chaleur. Thermodynamique Résumé : An experimental study is undertaken to investigate the flow structure and heat transfer in a stagnation flow chemical vapor deposition (CVD) reactor at atmospheric pressure. It is critical to develop models that predict flow patterns in such a reactor to achieve uniform deposition across the substrate. Free convection can negatively affect the gas flow as cold inlet gas impinges on the heated substrate, leading to vortices and disturbances in the normal flow path. This experimental research will be used to understand the buoyancy-induced and momentum driven flow structure encountered in an impinging jet CVD reactor. Investigations are conducted for various operating and design parameters. A modified stagnation flow reactor is built where the height between the inlet and substrate is reduced when compared with a prototypical stagnation flow reactor. By operating such a reactor at certain Reynolds and Grashof numbers, it is feasible to sustain smooth and vortex free flow at atmospheric pressure. The modified stagnation flow reactor is compared with other stagnation flow geometries with either a varied inlet length or varied heights between the inlet and substrate. Comparisons are made to understand the impact of such geometric changes on the flow structure and the thermal boundary layer. In addition, heat transfer correlations are obtained for the substrate temperature. Overall, the results obtained provide guidelines for curbing the effects of buoyancy and for improving the flow field to obtain greater film uniformity when operating a stagnation flow CVD reactor at atmospheric pressure. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...]

Underhood buoyancy driven flow / Parviz Merati in Journal of heat transfer, Vol. 133 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [082502/1-9] Titre : Underhood buoyancy driven flow : an experimental study Type de document : texte imprimé Auteurs : Parviz Merati, Auteur ; Charles Davis, Auteur ; K. H. Chen, Auteur Année de publication : 2011 Article en page(s) : pp. [082502/1-9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Underhood  buoyancy  PIV  Thermal  measurements  Thermal  soak Index. décimale : 536 Chaleur. Thermodynamique Résumé : Particle image velocimetry and thermal measurements using thermocouples are used to measure the buoyant flow of a simplified full-scale model of an engine compartment. The engine block surface temperature and exhaust heaters are kept at about 100 and 600°C, respectively. Thermal measurements include enclosure surface temperature, temperature difference on the enclosure wall at midplane, engine block temperatures, and air temperatures under the hood. The highest surface temperatures were concentrated near the top of the enclosure around the exhaust heaters. This effect was due primarily to radiation from the exhaust heaters. Highest measured air temperature was about 300°C immediately above the right exhaust heater. The measured dominant flow structures are two larger counter rotating vortices over the top right side of the engine block and two counter rotating vortices over the top left side. These flow structures weaken considerably during the first 35 min of the transient cool down of the engine block and the exhaust heaters. Colder ambient air is sucked into the engine compartment at the vents near the bottom of the compartment with some exiting as hot air through the top slots. The time scale of the fluid exchange at the vents is in the order of seconds, indicating that this process is occurring very slowly. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...] [article] Underhood buoyancy driven flow : an experimental study [texte imprimé] / Parviz Merati, Auteur ; Charles Davis, Auteur ; K. H. Chen, Auteur . - 2011 . - pp. [082502/1-9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [082502/1-9] Mots-clés : Underhood  buoyancy  PIV  Thermal  measurements  Thermal  soak Index. décimale : 536 Chaleur. Thermodynamique Résumé : Particle image velocimetry and thermal measurements using thermocouples are used to measure the buoyant flow of a simplified full-scale model of an engine compartment. The engine block surface temperature and exhaust heaters are kept at about 100 and 600°C, respectively. Thermal measurements include enclosure surface temperature, temperature difference on the enclosure wall at midplane, engine block temperatures, and air temperatures under the hood. The highest surface temperatures were concentrated near the top of the enclosure around the exhaust heaters. This effect was due primarily to radiation from the exhaust heaters. Highest measured air temperature was about 300°C immediately above the right exhaust heater. The measured dominant flow structures are two larger counter rotating vortices over the top right side of the engine block and two counter rotating vortices over the top left side. These flow structures weaken considerably during the first 35 min of the transient cool down of the engine block and the exhaust heaters. Colder ambient air is sucked into the engine compartment at the vents near the bottom of the compartment with some exiting as hot air through the top slots. The time scale of the fluid exchange at the vents is in the order of seconds, indicating that this process is occurring very slowly. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...]

Differential approximations to the radiation transfer equation by Chapman–Enskog expansion / A. V. Gusarov in Journal of heat transfer, Vol. 133 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [082701/1-7] Titre : Differential approximations to the radiation transfer equation by Chapman–Enskog expansion Type de document : texte imprimé Auteurs : A. V. Gusarov, Auteur Année de publication : 2011 Article en page(s) : pp. [082701/1-7] Note générale : Physique Langues : Anglais (eng) Mots-clés : Absorbing-emitting-scattering  medium  Eigenfunction  Eigenvalue  Heat  flow  Scattering  integral Index. décimale : 536 Chaleur. Thermodynamique Résumé : Direct numerical solution of the radiation transfer equation is often easier than implementation of its differential approximations with their cumbersome boundary conditions. Nevertheless, these approximations are still used, for example, in theoretical analysis. The existing approach to obtain a differential approximation based on expansion in series of the spherical harmonics is revised and expansion in series of the eigenfunctions of the scattering integral is proposed. A system of eigenfunctions is obtained for an arbitrary phase function, and explicit differential approximations are built up to the third Chapman–Enskog order. The results are tested by its application to the problem of a layer. The third-order Chapman–Enskog approximation is found to match the boundary conditions better than the first-order one and gives considerably more accurate value for the heat flow. The accuracy of the both first- and third-order heat flows generally increases with the optical thickness. In addition, the third-order heat flow tends to the rigorous limit value when the optical thickness tends to zero. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...] [article] Differential approximations to the radiation transfer equation by Chapman–Enskog expansion [texte imprimé] / A. V. Gusarov, Auteur . - 2011 . - pp. [082701/1-7]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [082701/1-7] Mots-clés : Absorbing-emitting-scattering  medium  Eigenfunction  Eigenvalue  Heat  flow  Scattering  integral Index. décimale : 536 Chaleur. Thermodynamique Résumé : Direct numerical solution of the radiation transfer equation is often easier than implementation of its differential approximations with their cumbersome boundary conditions. Nevertheless, these approximations are still used, for example, in theoretical analysis. The existing approach to obtain a differential approximation based on expansion in series of the spherical harmonics is revised and expansion in series of the eigenfunctions of the scattering integral is proposed. A system of eigenfunctions is obtained for an arbitrary phase function, and explicit differential approximations are built up to the third Chapman–Enskog order. The results are tested by its application to the problem of a layer. The third-order Chapman–Enskog approximation is found to match the boundary conditions better than the first-order one and gives considerably more accurate value for the heat flow. The accuracy of the both first- and third-order heat flows generally increases with the optical thickness. In addition, the third-order heat flow tends to the rigorous limit value when the optical thickness tends to zero. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...]

Heat transfer in double U-tube boreholes with two independent circuits / Parham Eslami-nejad in Journal of heat transfer, Vol. 133 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [082801/1-12] Titre : Heat transfer in double U-tube boreholes with two independent circuits Type de document : texte imprimé Auteurs : Parham Eslami-nejad, Auteur ; Michel Bernier, Auteur Année de publication : 2011 Article en page(s) : pp. [082801/1-12] Note générale : Physique Langues : Anglais (eng) Mots-clés : Ground  source  heat  pump  Geothermal  boreholes  U-tubes  Laplace  transforms Index. décimale : 536 Chaleur. Thermodynamique Résumé : This study presents the development of an analytical model to predict steady-state heat transfer in double U-tube geothermal boreholes equipped with two independent circuits. Such boreholes can be used for heat extraction in one circuit, combined with a heat pump, for example, and simultaneous thermal recharging in the other circuit. The model accounts for a thermal interaction among pipes, and it predicts the fluid temperature profiles in both circuits along the borehole depth, including the exit fluid temperature. Different circuit configurations are assessed under typical borehole operating conditions. For a typical borehole geometry, results show that double U-tube boreholes with two independent circuits connected to a relatively low temperature heat source are superior to single U-tube and regular (one circuit) double U-tube boreholes. The axial variation in fluid temperature and the heat exchange among pipes show that most of the heat transfer occurs in the downward legs. Furthermore, in some cases, the fluid in the heat extraction leg gets cooled as it flows upward, which is contrary to the desired effect. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...] [article] Heat transfer in double U-tube boreholes with two independent circuits [texte imprimé] / Parham Eslami-nejad, Auteur ; Michel Bernier, Auteur . - 2011 . - pp. [082801/1-12]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 133 N° 8 (Août 2011) . - pp. [082801/1-12] Mots-clés : Ground  source  heat  pump  Geothermal  boreholes  U-tubes  Laplace  transforms Index. décimale : 536 Chaleur. Thermodynamique Résumé : This study presents the development of an analytical model to predict steady-state heat transfer in double U-tube geothermal boreholes equipped with two independent circuits. Such boreholes can be used for heat extraction in one circuit, combined with a heat pump, for example, and simultaneous thermal recharging in the other circuit. The model accounts for a thermal interaction among pipes, and it predicts the fluid temperature profiles in both circuits along the borehole depth, including the exit fluid temperature. Different circuit configurations are assessed under typical borehole operating conditions. For a typical borehole geometry, results show that double U-tube boreholes with two independent circuits connected to a relatively low temperature heat source are superior to single U-tube and regular (one circuit) double U-tube boreholes. The axial variation in fluid temperature and the heat exchange among pipes show that most of the heat transfer occurs in the downward legs. Furthermore, in some cases, the fluid in the heat extraction leg gets cooled as it flows upward, which is contrary to the desired effect. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO00013300 [...]

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