Dépouillements

Effect of diamond nanolubricant on R134a pool boiling heat transfer / M.A. Kedzierski in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 08 p. Titre : Effect of diamond nanolubricant on R134a pool boiling heat transfer Type de document : texte imprimé Auteurs : M.A. Kedzierski, Auteur Année de publication : 2012 Article en page(s) : 08 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : additives;  boiling;  diamond;  enhanced  heat  transfer;  nanotechnology;  refrigerant/lubricant  mixtures Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper quantifies the influence of diamond nanoparticles on the pool boiling performance of R134a/polyolester mixtures on a roughened, horizontal, and flat surface. Nanofluids are liquids that contain dispersed nanosize particles. A lubricant based nanofluid (nanolubricant) was made by suspending 10 nm diameter diamond particles in a synthetic ester to roughly a 2.6% volume fraction. For the 0.5% nanolubricant mass fraction, the nanoparticles caused a heat transfer enhancement relative to the heat transfer of pure R134a/polyolester (99.5/0.5) up to 129%. A similar enhancement was observed for the R134a/nanolubricant (99/1) mixture, which had a heat flux that was on average 91% larger than that of the R134a/polyolester (99/1) mixture. Further increase in the nanolubricant mass fraction to 2% resulted in boiling heat transfer degradation of approximately 19% for the best performing tests. It was speculated that the poor quality of the nanolubricant suspension caused the performance of the (99.5/0.5), and the (98/2) nanolubricant mixtures to decay over time to, on average, 36% and 76% of the of pure R134a/polyolester performance, respectively. Thermal conductivity and viscosity measurements and a refrigerant\lubricant mixture pool-boiling model were used to suggest that increases in thermal conductivity and lubricant viscosity are mainly responsible for the heat transfer enhancement due to nanoparticles. Particle size measurements were used to suggest that particle agglomeration induced a lack of performance repeatability for the (99.5/0.5) and the (98/2) mixtures. From the results of the present study, it is speculated that if a good dispersion of nanoparticles in the lubricant is not obtained, then the agglomerated nanoparticles will not provide interaction with bubbles, which is favorable for heat transfer. Further research with nanolubricants and refrigerants are required to establish a fundamental understanding of the mechanisms that control nanofluid heat transfer. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Effect of diamond nanolubricant on R134a pool boiling heat transfer [texte imprimé] / M.A. Kedzierski, Auteur . - 2012 . - 08 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 08 p. Mots-clés : additives;  boiling;  diamond;  enhanced  heat  transfer;  nanotechnology;  refrigerant/lubricant  mixtures Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper quantifies the influence of diamond nanoparticles on the pool boiling performance of R134a/polyolester mixtures on a roughened, horizontal, and flat surface. Nanofluids are liquids that contain dispersed nanosize particles. A lubricant based nanofluid (nanolubricant) was made by suspending 10 nm diameter diamond particles in a synthetic ester to roughly a 2.6% volume fraction. For the 0.5% nanolubricant mass fraction, the nanoparticles caused a heat transfer enhancement relative to the heat transfer of pure R134a/polyolester (99.5/0.5) up to 129%. A similar enhancement was observed for the R134a/nanolubricant (99/1) mixture, which had a heat flux that was on average 91% larger than that of the R134a/polyolester (99/1) mixture. Further increase in the nanolubricant mass fraction to 2% resulted in boiling heat transfer degradation of approximately 19% for the best performing tests. It was speculated that the poor quality of the nanolubricant suspension caused the performance of the (99.5/0.5), and the (98/2) nanolubricant mixtures to decay over time to, on average, 36% and 76% of the of pure R134a/polyolester performance, respectively. Thermal conductivity and viscosity measurements and a refrigerant\lubricant mixture pool-boiling model were used to suggest that increases in thermal conductivity and lubricant viscosity are mainly responsible for the heat transfer enhancement due to nanoparticles. Particle size measurements were used to suggest that particle agglomeration induced a lack of performance repeatability for the (99.5/0.5) and the (98/2) mixtures. From the results of the present study, it is speculated that if a good dispersion of nanoparticles in the lubricant is not obtained, then the agglomerated nanoparticles will not provide interaction with bubbles, which is favorable for heat transfer. Further research with nanolubricants and refrigerants are required to establish a fundamental understanding of the mechanisms that control nanofluid heat transfer. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Thermal nanofluid property model with application to nanofluid flow in a parallel-disk system—part I: a new thermal conductivity model for nanofluid flow / Clement Kleinstreuer in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 11 p. Titre : Thermal nanofluid property model with application to nanofluid flow in a parallel-disk system—part I: a new thermal conductivity model for nanofluid flow Type de document : texte imprimé Auteurs : Clement Kleinstreuer, Auteur ; Yu Feng, Auteur Année de publication : 2012 Article en page(s) : 11 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : nanofluids;  thermal  conductivity  enhancement;  new  theory;  data  comparisons Index. décimale : 536 Chaleur. Thermodynamique Résumé : This is a two-part paper, which proposes a new theory explaining the experimentally observed enhancement of the thermal conductivity, knf, of nanofluids (Part I) and discusses simulation results of nanofluid flow in a radial parallel-plate channel using different knf-models (Part II). Specifically, Part I provides the derivation of the new model as well as comparisons with benchmark experimental data sets and other theories, focusing mainly on aluminum and copper oxide nanoparticles in water. The new thermal conductivity expression consists of a base-fluid static part, kbf, and a new “micromixing” part, kmm, i.e., knf = kbf + kmm. While kbf relies on Maxwell's theory, kmm encapsulates nanoparticle characteristics and liquid properties as well as Brownian-motion induced nanoparticle fluctuations, nanoparticle volume fractions, mixture-temperature changes, particle–particle interactions, and random temperature fluctuations causing liquid-particle interactions. Thus, fundamental physics principles include the Brownian-motion effect, an extended Langevin equation with scaled interaction forces, and a turbulence-inspired heat transfer equation. The new model predicts experimental data for several types of metal-oxide nanoparticles (20 < dp < 50 nm) in water with volume fractions up to 5% and mixture temperatures below 350 K. While the three competitive theories considered match selectively experimental data, their needs for curve-fitted functions and arbitrary parameters make these models not generally applicable. The new theory can be readily extended to accommodate other types of nanoparticle-liquid pairings and to include nonspherical nanomaterial. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Thermal nanofluid property model with application to nanofluid flow in a parallel-disk system—part I: a new thermal conductivity model for nanofluid flow [texte imprimé] / Clement Kleinstreuer, Auteur ; Yu Feng, Auteur . - 2012 . - 11 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 11 p. Mots-clés : nanofluids;  thermal  conductivity  enhancement;  new  theory;  data  comparisons Index. décimale : 536 Chaleur. Thermodynamique Résumé : This is a two-part paper, which proposes a new theory explaining the experimentally observed enhancement of the thermal conductivity, knf, of nanofluids (Part I) and discusses simulation results of nanofluid flow in a radial parallel-plate channel using different knf-models (Part II). Specifically, Part I provides the derivation of the new model as well as comparisons with benchmark experimental data sets and other theories, focusing mainly on aluminum and copper oxide nanoparticles in water. The new thermal conductivity expression consists of a base-fluid static part, kbf, and a new “micromixing” part, kmm, i.e., knf = kbf + kmm. While kbf relies on Maxwell's theory, kmm encapsulates nanoparticle characteristics and liquid properties as well as Brownian-motion induced nanoparticle fluctuations, nanoparticle volume fractions, mixture-temperature changes, particle–particle interactions, and random temperature fluctuations causing liquid-particle interactions. Thus, fundamental physics principles include the Brownian-motion effect, an extended Langevin equation with scaled interaction forces, and a turbulence-inspired heat transfer equation. The new model predicts experimental data for several types of metal-oxide nanoparticles (20 < dp < 50 nm) in water with volume fractions up to 5% and mixture temperatures below 350 K. While the three competitive theories considered match selectively experimental data, their needs for curve-fitted functions and arbitrary parameters make these models not generally applicable. The new theory can be readily extended to accommodate other types of nanoparticle-liquid pairings and to include nonspherical nanomaterial. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Thermal nanofluid property model with application to nanofluid flow in a parallel disk system—part II: nanofluid flow between parallel disks / Yu Feng in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 09 p. Titre : Thermal nanofluid property model with application to nanofluid flow in a parallel disk system—part II: nanofluid flow between parallel disks Type de document : texte imprimé Auteurs : Yu Feng, Auteur ; Clement Kleinstreuer, Auteur Année de publication : 2012 Article en page(s) : 09 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : nanofluid  flow;  augmented  heat  transfer;  parallel  disk  system Index. décimale : 536 Chaleur. Thermodynamique Résumé : This is the second part of a two-part paper which proposes a new theory explaining the experimentally observed enhancement of the thermal conductivity, knf, of nanofluids (Part I) and discusses simulation results of nanofluid flow in an axisymmetric jet-impingement cooling system using different knf-models (Part II). Specifically, Part II provides numerical simulations of convective nanofluid heat transfer in terms of velocity profiles, friction factor, temperature distributions, and Nusselt numbers, employing the new knf-model. Flow structures and the effects of nanoparticle addition on heat transfer and entropy generation are discussed as well. Analytical expressions for velocity profiles and friction factors, assuming quasi-fully-developed flow between parallel disks, have been derived and validated for nanofluids as well. Based on the numerical simulation results for both alumina-water nanofluids and pure water, it can be concluded that nanofluids show better heat transfer performance than convectional coolants with no great penalty in pumping power. Furthermore, the system's entropy generation rate is lower for nanofluids than for pure water. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Thermal nanofluid property model with application to nanofluid flow in a parallel disk system—part II: nanofluid flow between parallel disks [texte imprimé] / Yu Feng, Auteur ; Clement Kleinstreuer, Auteur . - 2012 . - 09 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 09 p. Mots-clés : nanofluid  flow;  augmented  heat  transfer;  parallel  disk  system Index. décimale : 536 Chaleur. Thermodynamique Résumé : This is the second part of a two-part paper which proposes a new theory explaining the experimentally observed enhancement of the thermal conductivity, knf, of nanofluids (Part I) and discusses simulation results of nanofluid flow in an axisymmetric jet-impingement cooling system using different knf-models (Part II). Specifically, Part II provides numerical simulations of convective nanofluid heat transfer in terms of velocity profiles, friction factor, temperature distributions, and Nusselt numbers, employing the new knf-model. Flow structures and the effects of nanoparticle addition on heat transfer and entropy generation are discussed as well. Analytical expressions for velocity profiles and friction factors, assuming quasi-fully-developed flow between parallel disks, have been derived and validated for nanofluids as well. Based on the numerical simulation results for both alumina-water nanofluids and pure water, it can be concluded that nanofluids show better heat transfer performance than convectional coolants with no great penalty in pumping power. Furthermore, the system's entropy generation rate is lower for nanofluids than for pure water. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Non-Fourier heat conduction in carbon nanotubes / Hai-Dong Wang in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 06 p. Titre : Non-Fourier heat conduction in carbon nanotubes Type de document : texte imprimé Auteurs : Hai-Dong Wang, Auteur ; Bing-Yang Cao, Auteur ; Zeng-Yuan Guo, Auteur Année de publication : 2012 Article en page(s) : 06 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : non-Fourier  heat  conduction;  thermomass;  carbon  nanotubes;  thermal  conductivity Index. décimale : 536 Chaleur. Thermodynamique Résumé : Fourier's law is a phenomenological law to describe the heat transfer process. Although it has been widely used in a variety of engineering application areas, it is still questionable to reveal the physical essence of heat transfer. In order to describe the heat transfer phenomena universally, Guo has developed a general heat conduction law based on the concept of thermomass, which is defined as the equivalent mass of phonon gas in dielectrics according to Einstein's mass–energy relation. The general law degenerates into Fourier's law when the thermal inertia is neglected as the heat flux is not very high. The heat flux in carbon nanotubes (CNTs) may be as high as 1012 W/m2. In this case, Fourier's law no longer holds. However, what is estimated through the ratio of the heat flux to the temperature gradient by molecular dynamics (MD) simulations or experiments is only the apparent thermal conductivity (ATC); which is smaller than the intrinsic thermal conductivity (ITC). The existing experimental data of single-walled CNTs under the high-bias current flows are applied to study the non-Fourier heat conduction under the ultrahigh heat flux conditions. The results show that ITC and ATC are almost equal under the low heat flux conditions when the thermal inertia is negligible, while the difference between ITC and ATC becomes more notable as the heat flux increases or the temperature drops. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Non-Fourier heat conduction in carbon nanotubes [texte imprimé] / Hai-Dong Wang, Auteur ; Bing-Yang Cao, Auteur ; Zeng-Yuan Guo, Auteur . - 2012 . - 06 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 06 p. Mots-clés : non-Fourier  heat  conduction;  thermomass;  carbon  nanotubes;  thermal  conductivity Index. décimale : 536 Chaleur. Thermodynamique Résumé : Fourier's law is a phenomenological law to describe the heat transfer process. Although it has been widely used in a variety of engineering application areas, it is still questionable to reveal the physical essence of heat transfer. In order to describe the heat transfer phenomena universally, Guo has developed a general heat conduction law based on the concept of thermomass, which is defined as the equivalent mass of phonon gas in dielectrics according to Einstein's mass–energy relation. The general law degenerates into Fourier's law when the thermal inertia is neglected as the heat flux is not very high. The heat flux in carbon nanotubes (CNTs) may be as high as 1012 W/m2. In this case, Fourier's law no longer holds. However, what is estimated through the ratio of the heat flux to the temperature gradient by molecular dynamics (MD) simulations or experiments is only the apparent thermal conductivity (ATC); which is smaller than the intrinsic thermal conductivity (ITC). The existing experimental data of single-walled CNTs under the high-bias current flows are applied to study the non-Fourier heat conduction under the ultrahigh heat flux conditions. The results show that ITC and ATC are almost equal under the low heat flux conditions when the thermal inertia is negligible, while the difference between ITC and ATC becomes more notable as the heat flux increases or the temperature drops. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

An accurate and stable numerical method for solving a micro heat transfer model in a one-dimensional N-Carrier system in spherical coordinates / Weizhong Dai in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 07 p. Titre : An accurate and stable numerical method for solving a micro heat transfer model in a one-dimensional N-Carrier system in spherical coordinates Type de document : texte imprimé Auteurs : Weizhong Dai, Auteur ; Da Yu Tzou, Auteur Année de publication : 2012 Article en page(s) : 07 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : spherical  coordinates;  micro  heat  transfer  model;  N-carriers  and  Neumann  boundary  condition;  Crank–Nicholson  scheme Index. décimale : 536 Chaleur. Thermodynamique Résumé : We consider the generalized micro heat transfer model in a 1D microsphere with N-carriers and Neumann boundary condition in spherical coordinates, which can be applied to describe nonequilibrium heating in biological cells. An accurate Crank–Nicholson type of scheme is presented for solving the generalized model, where a new second-order accurate numerical scheme for the Neumann boundary condition is developed so that the overall truncation error is second order. The scheme is proved to be unconditionally stable and convergent. The present scheme is then tested by three numerical examples. Results show that the numerical solution is much more accurate than that obtained based on the Crank–Nicholson scheme with the conventional method for the Neumann boundary condition. Furthermore, the convergence rate of the present scheme is about 1.8 with respect to the spatial variable, while the convergence rate of the Crank–Nicholson scheme with the conventional method for the Neumann boundary condition is only 1.0 with respect to the spatial variable. The scheme is ready to apply for thermal analysis in N-carrier systems. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] An accurate and stable numerical method for solving a micro heat transfer model in a one-dimensional N-Carrier system in spherical coordinates [texte imprimé] / Weizhong Dai, Auteur ; Da Yu Tzou, Auteur . - 2012 . - 07 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 07 p. Mots-clés : spherical  coordinates;  micro  heat  transfer  model;  N-carriers  and  Neumann  boundary  condition;  Crank–Nicholson  scheme Index. décimale : 536 Chaleur. Thermodynamique Résumé : We consider the generalized micro heat transfer model in a 1D microsphere with N-carriers and Neumann boundary condition in spherical coordinates, which can be applied to describe nonequilibrium heating in biological cells. An accurate Crank–Nicholson type of scheme is presented for solving the generalized model, where a new second-order accurate numerical scheme for the Neumann boundary condition is developed so that the overall truncation error is second order. The scheme is proved to be unconditionally stable and convergent. The present scheme is then tested by three numerical examples. Results show that the numerical solution is much more accurate than that obtained based on the Crank–Nicholson scheme with the conventional method for the Neumann boundary condition. Furthermore, the convergence rate of the present scheme is about 1.8 with respect to the spatial variable, while the convergence rate of the Crank–Nicholson scheme with the conventional method for the Neumann boundary condition is only 1.0 with respect to the spatial variable. The scheme is ready to apply for thermal analysis in N-carrier systems. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Lagging behavior in biological systems / D. Y. Tzou in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 10 p. Titre : Lagging behavior in biological systems Type de document : texte imprimé Auteurs : D. Y. Tzou, Auteur Année de publication : 2012 Article en page(s) : 10 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : thermal  lagging;  bioheat  transfer;  antitumor  drug  delivery;  blood  mach  number Index. décimale : 536 Chaleur. Thermodynamique Résumé : The lagging behavior is first exemplified by a rapidly stretched spring and a one-dimensional fin to illustrate the phase-lag concept via the thermal and mechanical properties that most engineers are familiar with. The second-order lagging model is then introduced to correlate with drug delivery in tumors and bioheat transfer that involve multiple carriers in heat/mass transport. Analytical expressions for the phase lags are derived, aiming toward revealing different physical origins for delays in different systems. For drug delivery in tumors involving nonequilibrium mass transport, the lagging behavior results from the finite time required for the rupture of liposome in releasing the antitumor drug and the finite time required for tumor cells to absorb drugs. For bioheat transfer involving nonequilibrium heat transport, on the other hand, the lagging behavior results from the finite time required for exchanging heat between tissue and blood. Pharmacodynamical and biological properties affecting the phase lags, as well as the dominating parameters over the lagging response are identified through the nondimensional analysis. Involvement of the thermal Mach number, which measures the speed of blood flow relative to the conventional thermal wave speed, is a new feature in this extension of the lagging model. The second-order effects in lagging are well correlated with the number of carriers involved in nonequilibrium heat and mass transport. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Lagging behavior in biological systems [texte imprimé] / D. Y. Tzou, Auteur . - 2012 . - 10 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 10 p. Mots-clés : thermal  lagging;  bioheat  transfer;  antitumor  drug  delivery;  blood  mach  number Index. décimale : 536 Chaleur. Thermodynamique Résumé : The lagging behavior is first exemplified by a rapidly stretched spring and a one-dimensional fin to illustrate the phase-lag concept via the thermal and mechanical properties that most engineers are familiar with. The second-order lagging model is then introduced to correlate with drug delivery in tumors and bioheat transfer that involve multiple carriers in heat/mass transport. Analytical expressions for the phase lags are derived, aiming toward revealing different physical origins for delays in different systems. For drug delivery in tumors involving nonequilibrium mass transport, the lagging behavior results from the finite time required for the rupture of liposome in releasing the antitumor drug and the finite time required for tumor cells to absorb drugs. For bioheat transfer involving nonequilibrium heat transport, on the other hand, the lagging behavior results from the finite time required for exchanging heat between tissue and blood. Pharmacodynamical and biological properties affecting the phase lags, as well as the dominating parameters over the lagging response are identified through the nondimensional analysis. Involvement of the thermal Mach number, which measures the speed of blood flow relative to the conventional thermal wave speed, is a new feature in this extension of the lagging model. The second-order effects in lagging are well correlated with the number of carriers involved in nonequilibrium heat and mass transport. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Silicon nanowire conductance in the ballistic regime / David Lacroix in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 08 p. Titre : Silicon nanowire conductance in the ballistic regime : models and simulations Type de document : texte imprimé Auteurs : David Lacroix, Auteur ; Karl Joulain, Auteur ; Jerome Muller, Auteur Année de publication : 2012 Article en page(s) : 08 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : nanowire;  silicon;  Landauer  formalism;  confined  phonons Index. décimale : 536 Chaleur. Thermodynamique Résumé : This study deals with phonon heat transport in silicon nanowires. A review of various methods that can be used to assess thermal conductance of such nanodevices is presented. Here, a specific attention is paid to the case of the Landauer Formalism, which can describe extremely thin wires conductance. In order to use this technique, the calculation of propagating modes in a silicon nanowire is necessary. Among the several existing models allowing such calculation, the elastic wave theory has been used to obtain the normal mode number. Besides, in this study, the transmission and reflection of phonon at the interface between two nanostructures are discussed. Using the diffuse mismatch model (DMM), the global transmissivity of the system made of a nanowire suspended between two thermal reservoirs is addressed. Then, the calculations of normal modes' numbers and thermal conductances of several silicon nanowires, with various diameters set between bulk thermal reservoirs, are presented and compared to other models and available experiments. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Silicon nanowire conductance in the ballistic regime : models and simulations [texte imprimé] / David Lacroix, Auteur ; Karl Joulain, Auteur ; Jerome Muller, Auteur . - 2012 . - 08 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 08 p. Mots-clés : nanowire;  silicon;  Landauer  formalism;  confined  phonons Index. décimale : 536 Chaleur. Thermodynamique Résumé : This study deals with phonon heat transport in silicon nanowires. A review of various methods that can be used to assess thermal conductance of such nanodevices is presented. Here, a specific attention is paid to the case of the Landauer Formalism, which can describe extremely thin wires conductance. In order to use this technique, the calculation of propagating modes in a silicon nanowire is necessary. Among the several existing models allowing such calculation, the elastic wave theory has been used to obtain the normal mode number. Besides, in this study, the transmission and reflection of phonon at the interface between two nanostructures are discussed. Using the diffuse mismatch model (DMM), the global transmissivity of the system made of a nanowire suspended between two thermal reservoirs is addressed. Then, the calculations of normal modes' numbers and thermal conductances of several silicon nanowires, with various diameters set between bulk thermal reservoirs, are presented and compared to other models and available experiments. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Precursor film formation process ahead macroscopic contact line of spreading droplet on smooth substrate / Ichiro Ueno in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 04 p. Titre : Precursor film formation process ahead macroscopic contact line of spreading droplet on smooth substrate Type de document : texte imprimé Auteurs : Ichiro Ueno, Auteur ; Kanji Hirose, Auteur ; Yusuke Kizaki, Auteur Année de publication : 2012 Article en page(s) : 04 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : precursor  film;  macroscopic  contact  line;  Brewster-angle  microscopy Index. décimale : 536 Chaleur. Thermodynamique Résumé : The authors pay their special attention to formation process of wafer-thin liquid film, known as “precursor film,” ahead moving macroscopic contact line of a droplet spreading on a solid substrate. The spreading droplet on the solid substrate is accompanied with the movement of a visible boundary line so-called “macroscopic contact line.” Existing studies have indicated there exits a thin liquid film known as precursor film ahead the macroscopic contact line of the droplet. The present author's group has dedicated their special effort to detect the formation process of the precursor film by applying a convectional laser interferometry and a high-speed camera, and to evaluate the spreading rate of the precursor film. In the present study, existing length of the precursor film at a very early stage of the droplet spreading is evaluated by applying a Brewster-angle microscopy as well as the interferometer. The authors extend their attention to the advancing process of the precursor film on inclined substrate. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Precursor film formation process ahead macroscopic contact line of spreading droplet on smooth substrate [texte imprimé] / Ichiro Ueno, Auteur ; Kanji Hirose, Auteur ; Yusuke Kizaki, Auteur . - 2012 . - 04 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 04 p. Mots-clés : precursor  film;  macroscopic  contact  line;  Brewster-angle  microscopy Index. décimale : 536 Chaleur. Thermodynamique Résumé : The authors pay their special attention to formation process of wafer-thin liquid film, known as “precursor film,” ahead moving macroscopic contact line of a droplet spreading on a solid substrate. The spreading droplet on the solid substrate is accompanied with the movement of a visible boundary line so-called “macroscopic contact line.” Existing studies have indicated there exits a thin liquid film known as precursor film ahead the macroscopic contact line of the droplet. The present author's group has dedicated their special effort to detect the formation process of the precursor film by applying a convectional laser interferometry and a high-speed camera, and to evaluate the spreading rate of the precursor film. In the present study, existing length of the precursor film at a very early stage of the droplet spreading is evaluated by applying a Brewster-angle microscopy as well as the interferometer. The authors extend their attention to the advancing process of the precursor film on inclined substrate. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

DSMC scheme for phonon transport in solid thin films / Mitsuhiro Matsumoto in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 07 p. Titre : DSMC scheme for phonon transport in solid thin films Type de document : texte imprimé Auteurs : Mitsuhiro Matsumoto, Auteur ; Masaya Okano, Auteur ; Yusuke Masao, Auteur Année de publication : 2012 Article en page(s) : 07 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : phonon  dynamics;  thermal  analysis;  direct  simulation  Monte  Carlo  (DSMC)  scheme; Index. décimale : 536 Chaleur. Thermodynamique Résumé : Analysis of phonon dynamics based on a linearized Boltzmann transport equation is widely used for thermal analysis of solid thin films, but couplings among various phonon modes appear in some situations. We propose a direct simulation Monte Carlo (DSMC) scheme to simulate the phonon gas starting without the conventional linearization approximation. This requires no relaxation time as an input parameter, and we can investigate the couplings among phonons with different modes. A prototype code based on a simple phonon model was developed, and energy flux was evaluated for thin films of various thickness as a test calculation. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] DSMC scheme for phonon transport in solid thin films [texte imprimé] / Mitsuhiro Matsumoto, Auteur ; Masaya Okano, Auteur ; Yusuke Masao, Auteur . - 2012 . - 07 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 07 p. Mots-clés : phonon  dynamics;  thermal  analysis;  direct  simulation  Monte  Carlo  (DSMC)  scheme; Index. décimale : 536 Chaleur. Thermodynamique Résumé : Analysis of phonon dynamics based on a linearized Boltzmann transport equation is widely used for thermal analysis of solid thin films, but couplings among various phonon modes appear in some situations. We propose a direct simulation Monte Carlo (DSMC) scheme to simulate the phonon gas starting without the conventional linearization approximation. This requires no relaxation time as an input parameter, and we can investigate the couplings among phonons with different modes. A prototype code based on a simple phonon model was developed, and energy flux was evaluated for thin films of various thickness as a test calculation. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

A novel thermal driving force for nanodevices / Zeng-Yuan Guo in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 06 p. Titre : A novel thermal driving force for nanodevices Type de document : texte imprimé Auteurs : Zeng-Yuan Guo, Auteur ; Quan-Wen Hou, Auteur ; Bing-Yang Cao, Auteur Année de publication : 2012 Article en page(s) : 06 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : thermal  driving  force;  thermomass  theory;  carbon  nanotube;  nanodevice Index. décimale : 536 Chaleur. Thermodynamique Résumé : Design and construction of nanomotors are one of the most attractive fields in nanotechnology. Following the introduction of a novel concept of the thermomass, the relative mass of a phonon gas based on the Einstein's energy–mass relation, the continuum and momentum conservation equations for the phonon gas are established to characterize the hydrodynamics of the phonon current in a solid. Like the gas flows in the porous mediums, the phonon current in a dielectric solid imposes a driving force on the solid framework atoms, which can be calculated quantitatively and can be applied to actuate nanomotors. We also predict the dynamic behavior of a nanomotor made up of multiwalled carbon nanotubes in terms of molecular dynamics simulations. A shorter single-walled carbon nanotube with a larger diameter, as a mobile part, surrounds a longer single-walled carbon nanotube with a smaller diameter working as a shaft. When a phonon current passes through the inner shaft, the outer nanotube will translate along and/or rotate around the shaft depending on the chiralities of the carbon nanotubes. The motion traces are found to depend on the chirality pair regularly. This type of nanomotor may be promising, because they are directly driven by thermal energy transport. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] A novel thermal driving force for nanodevices [texte imprimé] / Zeng-Yuan Guo, Auteur ; Quan-Wen Hou, Auteur ; Bing-Yang Cao, Auteur . - 2012 . - 06 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 06 p. Mots-clés : thermal  driving  force;  thermomass  theory;  carbon  nanotube;  nanodevice Index. décimale : 536 Chaleur. Thermodynamique Résumé : Design and construction of nanomotors are one of the most attractive fields in nanotechnology. Following the introduction of a novel concept of the thermomass, the relative mass of a phonon gas based on the Einstein's energy–mass relation, the continuum and momentum conservation equations for the phonon gas are established to characterize the hydrodynamics of the phonon current in a solid. Like the gas flows in the porous mediums, the phonon current in a dielectric solid imposes a driving force on the solid framework atoms, which can be calculated quantitatively and can be applied to actuate nanomotors. We also predict the dynamic behavior of a nanomotor made up of multiwalled carbon nanotubes in terms of molecular dynamics simulations. A shorter single-walled carbon nanotube with a larger diameter, as a mobile part, surrounds a longer single-walled carbon nanotube with a smaller diameter working as a shaft. When a phonon current passes through the inner shaft, the outer nanotube will translate along and/or rotate around the shaft depending on the chiralities of the carbon nanotubes. The motion traces are found to depend on the chirality pair regularly. This type of nanomotor may be promising, because they are directly driven by thermal energy transport. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Characterization of surface roughness effects on laminar flow in microchannels by using fractal cantor structures / Yongping Chen in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 07 p. Titre : Characterization of surface roughness effects on laminar flow in microchannels by using fractal cantor structures Type de document : texte imprimé Auteurs : Yongping Chen, Auteur ; Chengbin Zhang, Auteur ; Panpan Fu, Auteur Année de publication : 2012 Article en page(s) : 07 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : fractal;  surface  roughless;  laminar  flow;  microchannel Index. décimale : 536 Chaleur. Thermodynamique Résumé : The fractal characterization of surface topography by using Cantor set structures is introduced to quantify the microchannel surface. Based on this fractal characterization of surface, a model of laminar flow in rough microchannels is developed and numerically analyzed in this paper. The effects of Reynolds number, relative roughness, and fractal dimension on laminar flow are all discussed. The results indicate that the presence of roughness leads to the form of detachment, and the eddy generation is observed at the shadow of the roughness elements. The pressure drop in the rough microchannels along the flow direction is larger than that in the smooth channel. It is no longer in a linear fashion and the fluctuation in pressure drop along the stream due to the vortex near the wall is found. Differing from the smooth channel, the Poiseuille number for laminar flow in rough microchannels is no longer only dependent on the cross-sectional shape of the channel, but also strongly influenced by the Reynolds number, roughness height, and fractal dimension (spectrum) of the surface. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Characterization of surface roughness effects on laminar flow in microchannels by using fractal cantor structures [texte imprimé] / Yongping Chen, Auteur ; Chengbin Zhang, Auteur ; Panpan Fu, Auteur . - 2012 . - 07 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 07 p. Mots-clés : fractal;  surface  roughless;  laminar  flow;  microchannel Index. décimale : 536 Chaleur. Thermodynamique Résumé : The fractal characterization of surface topography by using Cantor set structures is introduced to quantify the microchannel surface. Based on this fractal characterization of surface, a model of laminar flow in rough microchannels is developed and numerically analyzed in this paper. The effects of Reynolds number, relative roughness, and fractal dimension on laminar flow are all discussed. The results indicate that the presence of roughness leads to the form of detachment, and the eddy generation is observed at the shadow of the roughness elements. The pressure drop in the rough microchannels along the flow direction is larger than that in the smooth channel. It is no longer in a linear fashion and the fluctuation in pressure drop along the stream due to the vortex near the wall is found. Differing from the smooth channel, the Poiseuille number for laminar flow in rough microchannels is no longer only dependent on the cross-sectional shape of the channel, but also strongly influenced by the Reynolds number, roughness height, and fractal dimension (spectrum) of the surface. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Fabrication and experimental characterization of nanochannels / Vinh-Nguyen Phan in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 06 p. Titre : Fabrication and experimental characterization of nanochannels Type de document : texte imprimé Auteurs : Vinh-Nguyen Phan, Auteur ; Nam-Trung Nguyen, Auteur ; Chun Yang, Auteur Année de publication : 2012 Article en page(s) : 06 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : nanofluidics;  nanochannels;  micromachining;  RIE;  DRIE;  capillary  filling Index. décimale : 536 Chaleur. Thermodynamique Résumé : Nanofluidics is the science and technology involving a fluid flowing in or around structures with a least one dimension in the nanoscale, which is defined as the range from 1 nm to 100 nm. In this paper, we present the fabrication and characterization of nanochannels in silicon and glass. Since the lateral dimension of the channels is limited by the wavelength of UV light used in photolithography, the channel width can only be fabricated in the micrometer scale. However, the depth of the channel can be controlled precisely by the etching rate of reactive ion etching (RIE). Microchannels and access holes were etched with deep reactive ion etching (DRIE). Both nanochannels and microchannels were sealed by a Pyrex glass wafer using anodic bonding. The fabricated nanochannels were characterized by capillary filling and evaporation experiments. Due to the small channel height and weak fluorescent signal, fluorescent techniques are not suitable for the characterization of the nanochannels. A long exposure time is needed because of the limited amount of fluorescent molecules inhibit the measurement of transient and dynamic processes. However, as the channel height is shorter than all visible wavelengths, the contrast in refractive indices of air and liquid allows clear visualization of nanochannels filled with liquids. Automatic image processing with matlab allows the evaluation of capillary filling in nanochannels. Interesting phenomena and discrepancies with conventional theories were observed. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Fabrication and experimental characterization of nanochannels [texte imprimé] / Vinh-Nguyen Phan, Auteur ; Nam-Trung Nguyen, Auteur ; Chun Yang, Auteur . - 2012 . - 06 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 06 p. Mots-clés : nanofluidics;  nanochannels;  micromachining;  RIE;  DRIE;  capillary  filling Index. décimale : 536 Chaleur. Thermodynamique Résumé : Nanofluidics is the science and technology involving a fluid flowing in or around structures with a least one dimension in the nanoscale, which is defined as the range from 1 nm to 100 nm. In this paper, we present the fabrication and characterization of nanochannels in silicon and glass. Since the lateral dimension of the channels is limited by the wavelength of UV light used in photolithography, the channel width can only be fabricated in the micrometer scale. However, the depth of the channel can be controlled precisely by the etching rate of reactive ion etching (RIE). Microchannels and access holes were etched with deep reactive ion etching (DRIE). Both nanochannels and microchannels were sealed by a Pyrex glass wafer using anodic bonding. The fabricated nanochannels were characterized by capillary filling and evaporation experiments. Due to the small channel height and weak fluorescent signal, fluorescent techniques are not suitable for the characterization of the nanochannels. A long exposure time is needed because of the limited amount of fluorescent molecules inhibit the measurement of transient and dynamic processes. However, as the channel height is shorter than all visible wavelengths, the contrast in refractive indices of air and liquid allows clear visualization of nanochannels filled with liquids. Automatic image processing with matlab allows the evaluation of capillary filling in nanochannels. Interesting phenomena and discrepancies with conventional theories were observed. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Theoretical two-dimensional modeling of gas conduction between finite parallel plates in high vacuum / Taishan Zhu in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 06 p. Titre : Theoretical two-dimensional modeling of gas conduction between finite parallel plates in high vacuum Type de document : texte imprimé Auteurs : Taishan Zhu, Auteur ; Wenjing Ye, Auteur Année de publication : 2012 Article en page(s) : 06 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : free-molecule  flow;  gaseous  heat  conduction;  theoretical  solution;  DSMC;  Pirani  sensors Index. décimale : 536 Chaleur. Thermodynamique Résumé : A theoretical approach based on gaskinetic theory is described and applied for the modeling of steady-state free-molecule gaseous heat conduction within a diffusive enclosure. With a representative model of microelectromechanical system (MEMS) devices with integrated heaters, the heat transfer between the heated component and its gaseous ambient enclosed in a high vacuum is studied in detail. A molecular simulation based on the direct simulation Monte Carlo (DSMC) method is also employed to validate the theoretical solutions and to study the effects of incomplete thermal accommodation. The impacts of the finite size of the heated beam as well as the gap between the beam and a substrate on the heat transfer are investigated to examine the appropriateness of the common assumptions employed in the modeling of Pirani sensors. Interesting phenomena that are unique in the free-molecule regime are observed and discussed. These studies are valuable to the design of MEMS devices with microheaters. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Theoretical two-dimensional modeling of gas conduction between finite parallel plates in high vacuum [texte imprimé] / Taishan Zhu, Auteur ; Wenjing Ye, Auteur . - 2012 . - 06 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 06 p. Mots-clés : free-molecule  flow;  gaseous  heat  conduction;  theoretical  solution;  DSMC;  Pirani  sensors Index. décimale : 536 Chaleur. Thermodynamique Résumé : A theoretical approach based on gaskinetic theory is described and applied for the modeling of steady-state free-molecule gaseous heat conduction within a diffusive enclosure. With a representative model of microelectromechanical system (MEMS) devices with integrated heaters, the heat transfer between the heated component and its gaseous ambient enclosed in a high vacuum is studied in detail. A molecular simulation based on the direct simulation Monte Carlo (DSMC) method is also employed to validate the theoretical solutions and to study the effects of incomplete thermal accommodation. The impacts of the finite size of the heated beam as well as the gap between the beam and a substrate on the heat transfer are investigated to examine the appropriateness of the common assumptions employed in the modeling of Pirani sensors. Interesting phenomena that are unique in the free-molecule regime are observed and discussed. These studies are valuable to the design of MEMS devices with microheaters. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Microfluidic bubble generation by acoustic field for mixing enhancement / Shasha Wang in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 04 p. Titre : Microfluidic bubble generation by acoustic field for mixing enhancement Type de document : texte imprimé Auteurs : Shasha Wang, Auteur ; Xiaoyang Huang, Auteur ; Chun Yang, Auteur Année de publication : 2012 Article en page(s) : 04 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : acoustic  actuation;  bubble  generation;  mixing;  microchannel;  high  speed  photography Index. décimale : 536 Chaleur. Thermodynamique Résumé : We demonstrate the bubble generation in a microfluidic channel by both experimental observation and numerical simulations. The microfluidic channel contains a nozzle-shaped actuation chamber with an acoustic resonator profile. The actuation is generated by a piezoelectric disk below the chamber. It was observed that for a steady deionized (DI) water flow driven through the channel, bubbles occurred in the channel when the piezoelectric disk was actuated at frequencies between 1 kHz and 5 kHz. Outside this actuation frequency range, no bubble generation was observed in the channel. The experiment showed that the presence of bubbles in this frequency range could significantly enhance the fluid mixing in the microfluidic channel, which otherwise would not happen at all without the bubbles. To further understand the bubble generation, the flow field in the microchannel was numerically simulated by a two-dimensional model. The numerical results show that there is a low pressure region inside the actuation chamber where water pressure is below the corresponding vapor pressure and thus bubbles can be generated. The bubble generation was also experimentally observed in the microchannel by using a high speed camera. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Microfluidic bubble generation by acoustic field for mixing enhancement [texte imprimé] / Shasha Wang, Auteur ; Xiaoyang Huang, Auteur ; Chun Yang, Auteur . - 2012 . - 04 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 04 p. Mots-clés : acoustic  actuation;  bubble  generation;  mixing;  microchannel;  high  speed  photography Index. décimale : 536 Chaleur. Thermodynamique Résumé : We demonstrate the bubble generation in a microfluidic channel by both experimental observation and numerical simulations. The microfluidic channel contains a nozzle-shaped actuation chamber with an acoustic resonator profile. The actuation is generated by a piezoelectric disk below the chamber. It was observed that for a steady deionized (DI) water flow driven through the channel, bubbles occurred in the channel when the piezoelectric disk was actuated at frequencies between 1 kHz and 5 kHz. Outside this actuation frequency range, no bubble generation was observed in the channel. The experiment showed that the presence of bubbles in this frequency range could significantly enhance the fluid mixing in the microfluidic channel, which otherwise would not happen at all without the bubbles. To further understand the bubble generation, the flow field in the microchannel was numerically simulated by a two-dimensional model. The numerical results show that there is a low pressure region inside the actuation chamber where water pressure is below the corresponding vapor pressure and thus bubbles can be generated. The bubble generation was also experimentally observed in the microchannel by using a high speed camera. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Transient Characteristics of Pool Boiling Heat Transfer in Nanofluids / Sang M. Kwark in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 06 p. Titre : Transient Characteristics of Pool Boiling Heat Transfer in Nanofluids Type de document : texte imprimé Auteurs : Sang M. Kwark, Auteur ; Ratan Kumar, Auteur ; Gilberto Moreno, Auteur Année de publication : 2012 Article en page(s) : 06 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : nanofluid;  transient;  critical  heat  flux  (CHF);  nanicoating Index. décimale : 536 Chaleur. Thermodynamique Résumé : This study shows the transient characteristics of the pool boiling curves using nanofluid as the boiling fluid. This time-dependency is in sharp contrast to a unique steady-state pool boiling curve that is typically obtained for a pure fluid. Past nanofluids research has provided interesting information about the thermal characteristics for this potentially promising cooling fluid. Results from these studies have shown some extraordinary critical heat flux (CHF) values and thermal conductivity enhancement that is yet to be explained by existing theories and correlations. The nature of the pool boiling curve for a nanofluid is dependent on the nanoparticle concentration in the base fluid. Higher concentration nanofluids show a perceptible degradation in the boiling heat transfer (BHT) coefficient but have exhibited an enhanced CHF value (up to ~80%) when compared to the CHF value of the base fluid (water). Another key observation has been in the significant deposition of nanoparticles on the heater surface. This fouling of the heater surface by nanoparticles is widely viewed as a main contributor that modifies the pool boiling curve of the base liquid. The deposition of the nanoparticles on the heater surface is dynamic and this in turn makes the nanofluid pool boiling curve exhibit transient characteristics. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Transient Characteristics of Pool Boiling Heat Transfer in Nanofluids [texte imprimé] / Sang M. Kwark, Auteur ; Ratan Kumar, Auteur ; Gilberto Moreno, Auteur . - 2012 . - 06 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 06 p. Mots-clés : nanofluid;  transient;  critical  heat  flux  (CHF);  nanicoating Index. décimale : 536 Chaleur. Thermodynamique Résumé : This study shows the transient characteristics of the pool boiling curves using nanofluid as the boiling fluid. This time-dependency is in sharp contrast to a unique steady-state pool boiling curve that is typically obtained for a pure fluid. Past nanofluids research has provided interesting information about the thermal characteristics for this potentially promising cooling fluid. Results from these studies have shown some extraordinary critical heat flux (CHF) values and thermal conductivity enhancement that is yet to be explained by existing theories and correlations. The nature of the pool boiling curve for a nanofluid is dependent on the nanoparticle concentration in the base fluid. Higher concentration nanofluids show a perceptible degradation in the boiling heat transfer (BHT) coefficient but have exhibited an enhanced CHF value (up to ~80%) when compared to the CHF value of the base fluid (water). Another key observation has been in the significant deposition of nanoparticles on the heater surface. This fouling of the heater surface by nanoparticles is widely viewed as a main contributor that modifies the pool boiling curve of the base liquid. The deposition of the nanoparticles on the heater surface is dynamic and this in turn makes the nanofluid pool boiling curve exhibit transient characteristics. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Performance simulations of a gas turbine disk-blade assembly employing miniature radially rotating heat pipes / Yiding Cao in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 07 p. Titre : Performance simulations of a gas turbine disk-blade assembly employing miniature radially rotating heat pipes Type de document : texte imprimé Auteurs : Yiding Cao, Auteur ; Jian Ling, Auteur Année de publication : 2012 Article en page(s) : 07 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : turbine  disk;  turbine  blade;  gas  turbine  cooling;  rotating  heat  pipe Index. décimale : 536 Chaleur. Thermodynamique Résumé : With a substantially increased gas inlet temperature in modern gas turbines, the cooling of turbine disks is becoming a challenging task. In order to reduce the temperature at the disk rim, a new turbine disk incorporating radially rotating heat pipes has been proposed. The objective of this paper is to conduct a numerical investigation for the cooling effectiveness of the rotating heat pipe. One of the major tasks of this paper is to compare the performance between a proposed disk-blade assembly incorporating radially rotating heat pipes and a conventional disk-blade assembly without the heat pipes under the same heating and cooling conditions. The numerical investigation illustrates that the turbine disk cooling technique incorporating radially rotating heat pipes is feasible. The maximum temperature at the rim of the proposed disk can be reduced by more than 100 °C in comparison with that of a conventional disk without heat pipes. However, the average temperature at the blade airfoil surface can be reduced by only about 10 °C. In addition, both the heat pipe length and diameter have an important effect on the turbine disk cooling. Under the permission of material strength, a longer heat pipe or a larger heat pipe diameter will produce a lower temperature at the disk rim. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Performance simulations of a gas turbine disk-blade assembly employing miniature radially rotating heat pipes [texte imprimé] / Yiding Cao, Auteur ; Jian Ling, Auteur . - 2012 . - 07 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 07 p. Mots-clés : turbine  disk;  turbine  blade;  gas  turbine  cooling;  rotating  heat  pipe Index. décimale : 536 Chaleur. Thermodynamique Résumé : With a substantially increased gas inlet temperature in modern gas turbines, the cooling of turbine disks is becoming a challenging task. In order to reduce the temperature at the disk rim, a new turbine disk incorporating radially rotating heat pipes has been proposed. The objective of this paper is to conduct a numerical investigation for the cooling effectiveness of the rotating heat pipe. One of the major tasks of this paper is to compare the performance between a proposed disk-blade assembly incorporating radially rotating heat pipes and a conventional disk-blade assembly without the heat pipes under the same heating and cooling conditions. The numerical investigation illustrates that the turbine disk cooling technique incorporating radially rotating heat pipes is feasible. The maximum temperature at the rim of the proposed disk can be reduced by more than 100 °C in comparison with that of a conventional disk without heat pipes. However, the average temperature at the blade airfoil surface can be reduced by only about 10 °C. In addition, both the heat pipe length and diameter have an important effect on the turbine disk cooling. Under the permission of material strength, a longer heat pipe or a larger heat pipe diameter will produce a lower temperature at the disk rim. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Thermal management of on-chip hot spot / Avram Bar-Cohen in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 11 p. Titre : Thermal management of on-chip hot spot Type de document : texte imprimé Auteurs : Avram Bar-Cohen, Auteur ; Peng Wang, Auteur Année de publication : 2012 Article en page(s) : 11 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : hot  spot;  electronics  cooling;  thermoelectric  cooler;  two-phase;  micrograp  cooler Index. décimale : 536 Chaleur. Thermodynamique Résumé : The rapid emergence of nanoelectronics, with the consequent rise in transistor density and switching speed, has led to a steep increase in microprocessor chip heat flux and growing concern over the emergence of on-chip hot spots. The application of on-chip high flux cooling techniques is today a primary driver for innovation in the electronics industry. In this paper, the physical phenomena underpinning the most promising on-chip thermal management approaches for hot spot remediation, along with basic modeling equations and typical results are described. Attention is devoted to thermoelectric micro-coolers and two-phase microgap coolers. The advantages and disadvantages of these on-chip cooling solutions for high heat flux hot spots are evaluated and compared. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Thermal management of on-chip hot spot [texte imprimé] / Avram Bar-Cohen, Auteur ; Peng Wang, Auteur . - 2012 . - 11 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 11 p. Mots-clés : hot  spot;  electronics  cooling;  thermoelectric  cooler;  two-phase;  micrograp  cooler Index. décimale : 536 Chaleur. Thermodynamique Résumé : The rapid emergence of nanoelectronics, with the consequent rise in transistor density and switching speed, has led to a steep increase in microprocessor chip heat flux and growing concern over the emergence of on-chip hot spots. The application of on-chip high flux cooling techniques is today a primary driver for innovation in the electronics industry. In this paper, the physical phenomena underpinning the most promising on-chip thermal management approaches for hot spot remediation, along with basic modeling equations and typical results are described. Attention is devoted to thermoelectric micro-coolers and two-phase microgap coolers. The advantages and disadvantages of these on-chip cooling solutions for high heat flux hot spots are evaluated and compared. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Heat conduction of a porous material / Koji Miyazaki in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 07 p. Titre : Heat conduction of a porous material Type de document : texte imprimé Auteurs : Koji Miyazaki, Auteur ; Saburo Tanaka, Auteur ; Daisuke Nagai, Auteur Année de publication : 2012 Article en page(s) : 07 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : heat  conduction;  microscale;  modeling;  nanoporous;  thermoelectrics Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this study, we introduce our numerical and experimental works for the thermal conductivity reduction by using a porous material. Recently thermal conductivity reduction has been one of the key technologies to enhance the figure of merit (ZT) of a thermoelectric material. We carry out numerical calculations of heat conduction in porous materials, such as phonon Boltzmann transport (BTE) and molecular dynamics (MD) simulations, in order to investigate the mechanism of the thermal conductivity reduction of a porous material. In the BTE, we applied the periodic boundary conditions with constant heat flux to calculate the effective thermal conductivity of porous materials.In the MD simulation, we calculated the phonon properties of Si by using the Stillinger–Weber potential at constant temperature with periodic boundary conditions in the x, y, and z directions. Phonon dispersion curves of single crystal of Si calculated from MD results by time-space 2D FFT are agreed well with reference data. Moreover, the effects of nanoporous structures on both the phonon group velocity and the phonon density of states (DOS) are discussed. At last, we made a porous p-type Bi2Te3 by nanoparticles prepared by a beads milling method. The thermal conductivity is one-fifth of that of a bulk material as well as keeping the same Seebeck coefficient as the bulk value. However, electrical conductivity was much reduced, and the ZT was only 0.048. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Heat conduction of a porous material [texte imprimé] / Koji Miyazaki, Auteur ; Saburo Tanaka, Auteur ; Daisuke Nagai, Auteur . - 2012 . - 07 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 07 p. Mots-clés : heat  conduction;  microscale;  modeling;  nanoporous;  thermoelectrics Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this study, we introduce our numerical and experimental works for the thermal conductivity reduction by using a porous material. Recently thermal conductivity reduction has been one of the key technologies to enhance the figure of merit (ZT) of a thermoelectric material. We carry out numerical calculations of heat conduction in porous materials, such as phonon Boltzmann transport (BTE) and molecular dynamics (MD) simulations, in order to investigate the mechanism of the thermal conductivity reduction of a porous material. In the BTE, we applied the periodic boundary conditions with constant heat flux to calculate the effective thermal conductivity of porous materials.In the MD simulation, we calculated the phonon properties of Si by using the Stillinger–Weber potential at constant temperature with periodic boundary conditions in the x, y, and z directions. Phonon dispersion curves of single crystal of Si calculated from MD results by time-space 2D FFT are agreed well with reference data. Moreover, the effects of nanoporous structures on both the phonon group velocity and the phonon density of states (DOS) are discussed. At last, we made a porous p-type Bi2Te3 by nanoparticles prepared by a beads milling method. The thermal conductivity is one-fifth of that of a bulk material as well as keeping the same Seebeck coefficient as the bulk value. However, electrical conductivity was much reduced, and the ZT was only 0.048. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Numerical simulation of laminar liquid film condensation in a horizontal circular minichannel / E. Da Riva in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 08 p. Titre : Numerical simulation of laminar liquid film condensation in a horizontal circular minichannel Type de document : texte imprimé Auteurs : E. Da Riva, Auteur ; D. Del Col, Auteur Année de publication : 2012 Article en page(s) : 08 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : minichannel;  condensation;  VOF;  CFD;  gravity;  surface  tension Index. décimale : 536 Chaleur. Thermodynamique Résumé : A three-dimensional volume of fluid (VOF) simulation of condensation of R134a inside a 1 mm i.d. minichannel is presented. The minichannel is horizontally oriented and the effect of gravity is taken into account. Simulations have been run both with and without taking into account surface tension. A uniform interface temperature and a uniform wall temperature have been fixed as boundary conditions. The mass flux is G = 100 kg m−2 s−1 and it has been assumed that the flow is laminar inside the liquid phase while turbulence inside the vapor phase has been handled by a modified low Reynolds form of the k–omega model. The fluid is condensed till reaching 0.45 vapor quality. The flow is expected to be annular without the presence of waves, therefore the problem was treated as steady state. Computational results displaying the evolution of vapor–liquid interface and heat transfer coefficient are reported and validated against experimental data. The condensation process is found to be gravity dominated, while the global effect of surface tension is found to be negligible. At inlet, the liquid film is thin and evenly distributed all around the tube circumference. Moving downstream the channel, the film thickness remains almost constant in the upper half of the minichannel, while the film at the bottom of the pipe becomes thicker because the liquid condensed at the top is drained by gravity to the bottom. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Numerical simulation of laminar liquid film condensation in a horizontal circular minichannel [texte imprimé] / E. Da Riva, Auteur ; D. Del Col, Auteur . - 2012 . - 08 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 08 p. Mots-clés : minichannel;  condensation;  VOF;  CFD;  gravity;  surface  tension Index. décimale : 536 Chaleur. Thermodynamique Résumé : A three-dimensional volume of fluid (VOF) simulation of condensation of R134a inside a 1 mm i.d. minichannel is presented. The minichannel is horizontally oriented and the effect of gravity is taken into account. Simulations have been run both with and without taking into account surface tension. A uniform interface temperature and a uniform wall temperature have been fixed as boundary conditions. The mass flux is G = 100 kg m−2 s−1 and it has been assumed that the flow is laminar inside the liquid phase while turbulence inside the vapor phase has been handled by a modified low Reynolds form of the k–omega model. The fluid is condensed till reaching 0.45 vapor quality. The flow is expected to be annular without the presence of waves, therefore the problem was treated as steady state. Computational results displaying the evolution of vapor–liquid interface and heat transfer coefficient are reported and validated against experimental data. The condensation process is found to be gravity dominated, while the global effect of surface tension is found to be negligible. At inlet, the liquid film is thin and evenly distributed all around the tube circumference. Moving downstream the channel, the film thickness remains almost constant in the upper half of the minichannel, while the film at the bottom of the pipe becomes thicker because the liquid condensed at the top is drained by gravity to the bottom. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Structure effects on electro-osmosis in microporous media / Moran Wang in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 06 p. Titre : Structure effects on electro-osmosis in microporous media Type de document : texte imprimé Auteurs : Moran Wang, Auteur Année de publication : 2012 Article en page(s) : 06 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : electro-osmosis;  porous  media;  multiphysical  transport;  lattice  Boltzmann;  environment  and  energy Index. décimale : 536 Chaleur. Thermodynamique Résumé : The structure effects on electro-osmosis in microporous media have been studied by modeling the multiphysical transport using our numerical framework. The three-dimensional microstructures of porous media are reproduced by a random generation-growth method, and then the nonlinear governing equations for the electrokinetic transport are solved by a highly efficient lattice Poisson–Boltzmann method. The simulation results indicate that the porous structure type (granular, fibrous, or network) influences the electro-osmotic permeability significantly. At the low porosity regime (<0.4), the network structure exhibits the highest electro-osmotic permeability because of its highest surface–volume ratio among the three types of structure at the same porosity. When the porosity is high (>0.5), the granular structure leads to the highest electro-osmotic permeability due to its lower shape resistance characteristics. The present modeling results improve our understanding of hydrodynamic and electrokinetic transport in geophysical systems, and help guide the design of porous electrodes in micro-energy systems. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Structure effects on electro-osmosis in microporous media [texte imprimé] / Moran Wang, Auteur . - 2012 . - 06 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 06 p. Mots-clés : electro-osmosis;  porous  media;  multiphysical  transport;  lattice  Boltzmann;  environment  and  energy Index. décimale : 536 Chaleur. Thermodynamique Résumé : The structure effects on electro-osmosis in microporous media have been studied by modeling the multiphysical transport using our numerical framework. The three-dimensional microstructures of porous media are reproduced by a random generation-growth method, and then the nonlinear governing equations for the electrokinetic transport are solved by a highly efficient lattice Poisson–Boltzmann method. The simulation results indicate that the porous structure type (granular, fibrous, or network) influences the electro-osmotic permeability significantly. At the low porosity regime (<0.4), the network structure exhibits the highest electro-osmotic permeability because of its highest surface–volume ratio among the three types of structure at the same porosity. When the porosity is high (>0.5), the granular structure leads to the highest electro-osmotic permeability due to its lower shape resistance characteristics. The present modeling results improve our understanding of hydrodynamic and electrokinetic transport in geophysical systems, and help guide the design of porous electrodes in micro-energy systems. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Numerical modeling of the conjugate heat transfer problem for annular laminar film condensation in microchannels / Stefano Nebuloni in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 07 p. Titre : Numerical modeling of the conjugate heat transfer problem for annular laminar film condensation in microchannels Type de document : texte imprimé Auteurs : Stefano Nebuloni, Auteur ; John R. Thome, Auteur Année de publication : 2012 Article en page(s) : 07 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : condensation;  numerical  model;  conjugate  heat  transfer;  annular  flow;  microchannel Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper presents numerical simulations of annular laminar film condensation heat transfer in microchannels of different internal shapes. The model, which is based on a finite volume formulation of the Navier–Stokes and energy equations for the liquid phase only, importantly accounts for the effects of axial and peripheral wall conduction and nonuniform heat flux not included in other models so far in the literature. The contributions of the surface tension, axial shear stresses, and gravitational forces are included. This model has so far been validated versus various benchmark cases and versus experimental data available in literature, predicting microchannel heat transfer data with an average error of 20% or better. It is well known that the thinning of the condensate film induced by surface tension due to gravity forces and shape of the surface, also known as the “Gregorig” effect, has a strong consequence on the local heat transfer coefficient in condensation. Thus, the present model accounts for these effects on the heat transfer and pressure drop for a wide variety of geometrical shapes, sizes, wall materials, and working fluid properties. In this paper, the conjugate heat transfer problem arising from the coupling between the thin film fluid dynamics, the heat transfer in the condensing fluid, and the heat conduction in the channel wall has been studied. In particular, the work has focused on three external channel wall boundary conditions: a uniform wall temperature, a nonuniform wall heat flux, and single-phase convective cooling are presented. As the scale of the problem is reduced, i.e., when moving from mini- to microchannels, the results show that the axial conduction effects can become very important in the prediction of the wall temperature profile and the magnitude of the heat transfer coefficient and its distribution along the channel. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Numerical modeling of the conjugate heat transfer problem for annular laminar film condensation in microchannels [texte imprimé] / Stefano Nebuloni, Auteur ; John R. Thome, Auteur . - 2012 . - 07 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 07 p. Mots-clés : condensation;  numerical  model;  conjugate  heat  transfer;  annular  flow;  microchannel Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper presents numerical simulations of annular laminar film condensation heat transfer in microchannels of different internal shapes. The model, which is based on a finite volume formulation of the Navier–Stokes and energy equations for the liquid phase only, importantly accounts for the effects of axial and peripheral wall conduction and nonuniform heat flux not included in other models so far in the literature. The contributions of the surface tension, axial shear stresses, and gravitational forces are included. This model has so far been validated versus various benchmark cases and versus experimental data available in literature, predicting microchannel heat transfer data with an average error of 20% or better. It is well known that the thinning of the condensate film induced by surface tension due to gravity forces and shape of the surface, also known as the “Gregorig” effect, has a strong consequence on the local heat transfer coefficient in condensation. Thus, the present model accounts for these effects on the heat transfer and pressure drop for a wide variety of geometrical shapes, sizes, wall materials, and working fluid properties. In this paper, the conjugate heat transfer problem arising from the coupling between the thin film fluid dynamics, the heat transfer in the condensing fluid, and the heat conduction in the channel wall has been studied. In particular, the work has focused on three external channel wall boundary conditions: a uniform wall temperature, a nonuniform wall heat flux, and single-phase convective cooling are presented. As the scale of the problem is reduced, i.e., when moving from mini- to microchannels, the results show that the axial conduction effects can become very important in the prediction of the wall temperature profile and the magnitude of the heat transfer coefficient and its distribution along the channel. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Effects of surface topography and colloid particles on the evaporation kinetics of sessile droplets on superhydrophobic surfaces / Wei Xu in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 07 p. Titre : Effects of surface topography and colloid particles on the evaporation kinetics of sessile droplets on superhydrophobic surfaces Type de document : texte imprimé Auteurs : Wei Xu, Auteur ; Chang-Hwan Choi, Auteur Année de publication : 2012 Article en page(s) : 07 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : sessile  droplet;  evaporation  kinetics;  colloids;  superhydrophobic  surface Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this paper, the evaporation kinetics of microliter-sized sessile droplets of gold colloids (~250 nm in particle diameters) was experimentally studied on micropatterned superhydrophobic surfaces, compared with those of pure water on a planar hydrophobic surface. The structural microtopography of superhydrophobic surfaces was designed to have a constant air fraction (~0.8) but varying array patterns including pillars, lines, and wells. During evaporation in a room condition, the superhydrophobic surfaces exhibited a stronger pinning effect than a planar surface, especially in the initial evaporation stage, with significant variations by the surface topographies. Compared to a pure water droplet, colloids exhibited further promoted pinning effects, mainly in the later stage of evaporation. While the well-known evaporative mass transport law of sessile droplets (i.e., linear law of “V2/3[proportional]t”) was generally applicable to the superhydrophobic surfaces, much smaller evaporation rate constants were measured on the patterned superhydrophobic surfaces than on a planar hydrophobic surface. A colloidal droplet further showed lower evaporation rate constants than a pure water droplet as the concentration of particles in the droplets increased over the evaporation. Such transition was more dramatic on a planar surface than on the micropatterned surfaces. Whereas there was no clear correlation between evaporation mode and the evaporation rate observed on the superhydrophobic surfaces, the prominent decrease of the evaporation rate on the planar hydrophobic surface was accompanied with the onset of a second pinning mode. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Effects of surface topography and colloid particles on the evaporation kinetics of sessile droplets on superhydrophobic surfaces [texte imprimé] / Wei Xu, Auteur ; Chang-Hwan Choi, Auteur . - 2012 . - 07 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 07 p. Mots-clés : sessile  droplet;  evaporation  kinetics;  colloids;  superhydrophobic  surface Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this paper, the evaporation kinetics of microliter-sized sessile droplets of gold colloids (~250 nm in particle diameters) was experimentally studied on micropatterned superhydrophobic surfaces, compared with those of pure water on a planar hydrophobic surface. The structural microtopography of superhydrophobic surfaces was designed to have a constant air fraction (~0.8) but varying array patterns including pillars, lines, and wells. During evaporation in a room condition, the superhydrophobic surfaces exhibited a stronger pinning effect than a planar surface, especially in the initial evaporation stage, with significant variations by the surface topographies. Compared to a pure water droplet, colloids exhibited further promoted pinning effects, mainly in the later stage of evaporation. While the well-known evaporative mass transport law of sessile droplets (i.e., linear law of “V2/3[proportional]t”) was generally applicable to the superhydrophobic surfaces, much smaller evaporation rate constants were measured on the patterned superhydrophobic surfaces than on a planar hydrophobic surface. A colloidal droplet further showed lower evaporation rate constants than a pure water droplet as the concentration of particles in the droplets increased over the evaporation. Such transition was more dramatic on a planar surface than on the micropatterned surfaces. Whereas there was no clear correlation between evaporation mode and the evaporation rate observed on the superhydrophobic surfaces, the prominent decrease of the evaporation rate on the planar hydrophobic surface was accompanied with the onset of a second pinning mode. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Feedstock diffusion and decomposition in aligned carbon nanotube arrays / Rong Xiang in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 04 p. Titre : Feedstock diffusion and decomposition in aligned carbon nanotube arrays Type de document : texte imprimé Auteurs : Rong Xiang, Auteur ; Erik Einarsson, Auteur ; Junichiro Shiomi, Auteur Année de publication : 2012 Article en page(s) : 04 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : carbon  nanotube  (CNT);  feedstock  diffusion;  thermal  decomposition;  growth  mechanism Index. décimale : 536 Chaleur. Thermodynamique Résumé : Feedstock diffusion and decomposition in the root growth of aligned carbon nanotube (CNT) arrays is discussed. A nondimensional modulus is proposed to differentiate catalyst poisoning controlled growth deceleration from one which is diffusion controlled. It is found that, at present, aligned multiwalled carbon nanotube (MWNT) arrays are usually free of feedstock diffusion resistance. However, for single-walled carbon nanotube (SWNT) arrays, since the intertube distance is much smaller than the mean free path of carbon source (ethanol here), high diffusion resistance in some currently available samples is significantly limiting the growth rate. The method presented here is also able to predict the critical lengths in different chemical vapor deposition (CVD) processes from which CNT arrays begin to meet this diffusion limit, as well as the possible solutions to this diffusion caused growth deceleration. The diffusion of carbon source inside of an array becomes more important when we found ethanol undergoes severe thermal decomposition at the reaction temperature. This means, in a typical alcohol CVD, hydrocarbons and radicals decomposed from ethanol may collide and react with the outer walls of SWNTs before reaching catalyst particles. When flow rate is low and ethanol is thoroughly decomposed, the produced SWNTs contain more soot structures than the SWNTs obtained at higher ethanol flow rate. Understanding the mass transport and reaction inside a SWNT array is helpful to synthesize longer and cleaner SWNTs. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Feedstock diffusion and decomposition in aligned carbon nanotube arrays [texte imprimé] / Rong Xiang, Auteur ; Erik Einarsson, Auteur ; Junichiro Shiomi, Auteur . - 2012 . - 04 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 04 p. Mots-clés : carbon  nanotube  (CNT);  feedstock  diffusion;  thermal  decomposition;  growth  mechanism Index. décimale : 536 Chaleur. Thermodynamique Résumé : Feedstock diffusion and decomposition in the root growth of aligned carbon nanotube (CNT) arrays is discussed. A nondimensional modulus is proposed to differentiate catalyst poisoning controlled growth deceleration from one which is diffusion controlled. It is found that, at present, aligned multiwalled carbon nanotube (MWNT) arrays are usually free of feedstock diffusion resistance. However, for single-walled carbon nanotube (SWNT) arrays, since the intertube distance is much smaller than the mean free path of carbon source (ethanol here), high diffusion resistance in some currently available samples is significantly limiting the growth rate. The method presented here is also able to predict the critical lengths in different chemical vapor deposition (CVD) processes from which CNT arrays begin to meet this diffusion limit, as well as the possible solutions to this diffusion caused growth deceleration. The diffusion of carbon source inside of an array becomes more important when we found ethanol undergoes severe thermal decomposition at the reaction temperature. This means, in a typical alcohol CVD, hydrocarbons and radicals decomposed from ethanol may collide and react with the outer walls of SWNTs before reaching catalyst particles. When flow rate is low and ethanol is thoroughly decomposed, the produced SWNTs contain more soot structures than the SWNTs obtained at higher ethanol flow rate. Understanding the mass transport and reaction inside a SWNT array is helpful to synthesize longer and cleaner SWNTs. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Chemical vapor deposition growth, optical, and thermal characterization of vertically aligned single-walled carbon nanotubes / Shigeo Maruyama in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 06 p. Titre : Chemical vapor deposition growth, optical, and thermal characterization of vertically aligned single-walled carbon nanotubes Type de document : texte imprimé Auteurs : Shigeo Maruyama, Auteur ; Rong Xiang, Auteur Année de publication : 2012 Article en page(s) : 06 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : single-walled  carbon  nanotube  (SWNT)  Roman  spectroscopy;  growth  mechanism;  patterning;  thermal  property Index. décimale : 536 Chaleur. Thermodynamique Résumé : Vertically aligned single-walled carbon nanotubes (VA-SWNTs) is expected to be an extra-ordinal material for various optical, electrical, energy, and thermal devices. The recent progress in growth control and characterization techniques will be discussed. The chemical vapor deposition (CVD) growth mechanism of VA-SWNTs is studied based on the in situ growth monitoring by laser absorption during CVD. The growth curves are characterized by an exponential decay of the growth rate from the initial rate determined by ethanol pressure. The initial growth rate and decay of it are discussed with carbon over-coat on metal catalysts and gas phase thermal decomposition of precursor ethanol. For the precisely patterned growth of SWNTs, we recently propose a surface-energy-difference driven selective deposition of catalyst for localized growth of SWNTs. For a self-assembled monolayer (SAM) patterned Si surface, catalyst particles deposit and SWNTs grow only on the hydrophilic regions. The proposed all-liquid-based approach possesses significant advantages in scalability and resolution over state-of-the-art techniques, which we believe can greatly advance the fabrication of nanodevices using high-quality as-grown SWNTs. The optical characterization of the VA-SWNT film using polarized absorption, polarized Raman, and photoluminescence spectroscopy will be discussed. Laser-excitation of a vertically aligned film from top means that each nanotube is excited perpendicular to its axis. Because of this predominant perpendicular excitation, interesting cross-polarized absorption and confusing and practically important Raman features are observed. The extremely high and peculiar thermal conductivity of single-walled carbon nanotubes has been explored by nonequilibrium molecular dynamics simulation approaches. The thermal properties of the vertically aligned film and composite materials are studied by several experimental techniques and Monte Carlo simulations based on molecular dynamics inputs of thermal conductivity and thermal boundary resistance. Current understanding of thermal properties of the film is discussed. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Chemical vapor deposition growth, optical, and thermal characterization of vertically aligned single-walled carbon nanotubes [texte imprimé] / Shigeo Maruyama, Auteur ; Rong Xiang, Auteur . - 2012 . - 06 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 06 p. Mots-clés : single-walled  carbon  nanotube  (SWNT)  Roman  spectroscopy;  growth  mechanism;  patterning;  thermal  property Index. décimale : 536 Chaleur. Thermodynamique Résumé : Vertically aligned single-walled carbon nanotubes (VA-SWNTs) is expected to be an extra-ordinal material for various optical, electrical, energy, and thermal devices. The recent progress in growth control and characterization techniques will be discussed. The chemical vapor deposition (CVD) growth mechanism of VA-SWNTs is studied based on the in situ growth monitoring by laser absorption during CVD. The growth curves are characterized by an exponential decay of the growth rate from the initial rate determined by ethanol pressure. The initial growth rate and decay of it are discussed with carbon over-coat on metal catalysts and gas phase thermal decomposition of precursor ethanol. For the precisely patterned growth of SWNTs, we recently propose a surface-energy-difference driven selective deposition of catalyst for localized growth of SWNTs. For a self-assembled monolayer (SAM) patterned Si surface, catalyst particles deposit and SWNTs grow only on the hydrophilic regions. The proposed all-liquid-based approach possesses significant advantages in scalability and resolution over state-of-the-art techniques, which we believe can greatly advance the fabrication of nanodevices using high-quality as-grown SWNTs. The optical characterization of the VA-SWNT film using polarized absorption, polarized Raman, and photoluminescence spectroscopy will be discussed. Laser-excitation of a vertically aligned film from top means that each nanotube is excited perpendicular to its axis. Because of this predominant perpendicular excitation, interesting cross-polarized absorption and confusing and practically important Raman features are observed. The extremely high and peculiar thermal conductivity of single-walled carbon nanotubes has been explored by nonequilibrium molecular dynamics simulation approaches. The thermal properties of the vertically aligned film and composite materials are studied by several experimental techniques and Monte Carlo simulations based on molecular dynamics inputs of thermal conductivity and thermal boundary resistance. Current understanding of thermal properties of the film is discussed. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Particle migration by optical scattering force in microfluidic system with light-absorbing liquid / Masahiro Motosuke in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 06 p. Titre : Particle migration by optical scattering force in microfluidic system with light-absorbing liquid Type de document : texte imprimé Auteurs : Masahiro Motosuke, Auteur ; Jun Shimakawa, Auteur ; Dai Akutsu, Auteur Année de publication : 2012 Article en page(s) : 06 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : microfluidics;  optical  radiation  pressure;  optical  scttering  force;  particle  control;  viscosity;  photothermal  effect Index. décimale : 536 Chaleur. Thermodynamique Résumé : Optical force offers a promise of being applied as a noninvasive manipulation tool for microscopic objects without physical contact. Particle control in a microfluidic system is achieved by optics showing advantages over electric or the other methods. With optics, the fluid need not to be contamination free and there is no need for electrode fabrication. Particles can experience different forces depending on the optical configuration. The scattering force is predominant under parallel or gently focused irradiation, while the gradient force is predominant in tightly focused irradiation. This paper reports the experimental and theoretical investigations of the potential of optical scattering force for particle control technique in a microfluidic system with a light-absorbing liquid. The light-absorption of the incident laser beam in the liquid causes a temperature rise and induces the corresponding property changes of liquid and particles. The experiments were presented for particle migration using the scattering force exerted by a compact diode laser with a wavelength of 635 nm. The absorption of the light in the liquid was controlled by the concentration of dye substance added in a buffer solution. The velocities of polystyrene particles with a diameter of 1.9 µm and the temperature distributions of the liquid under laser irradiation were measured by tracking their movement and by temperature-sensitive fluorophore, respectively. When there is no light absorption in the liquid, the migration velocity of particles under the laser beam is linearly increased with the increase of the laser power, in agreement with the calculations based on ray optics theory. In the case of light-absorbing liquid, the migration speed of particles experiencing the optical force indicates a nonlinear increase as the laser power increases. This enhancement mainly attributes to the temperature-sensitive change of liquid viscosity resulting in a reduction of viscous drag for migrating particles. An appropriate arrangement of light absorption leads to an enhancement in the photophoretic velocity of particles, and eventual performance promotion of particle separation and/or sorting using the optical force. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Particle migration by optical scattering force in microfluidic system with light-absorbing liquid [texte imprimé] / Masahiro Motosuke, Auteur ; Jun Shimakawa, Auteur ; Dai Akutsu, Auteur . - 2012 . - 06 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 06 p. Mots-clés : microfluidics;  optical  radiation  pressure;  optical  scttering  force;  particle  control;  viscosity;  photothermal  effect Index. décimale : 536 Chaleur. Thermodynamique Résumé : Optical force offers a promise of being applied as a noninvasive manipulation tool for microscopic objects without physical contact. Particle control in a microfluidic system is achieved by optics showing advantages over electric or the other methods. With optics, the fluid need not to be contamination free and there is no need for electrode fabrication. Particles can experience different forces depending on the optical configuration. The scattering force is predominant under parallel or gently focused irradiation, while the gradient force is predominant in tightly focused irradiation. This paper reports the experimental and theoretical investigations of the potential of optical scattering force for particle control technique in a microfluidic system with a light-absorbing liquid. The light-absorption of the incident laser beam in the liquid causes a temperature rise and induces the corresponding property changes of liquid and particles. The experiments were presented for particle migration using the scattering force exerted by a compact diode laser with a wavelength of 635 nm. The absorption of the light in the liquid was controlled by the concentration of dye substance added in a buffer solution. The velocities of polystyrene particles with a diameter of 1.9 µm and the temperature distributions of the liquid under laser irradiation were measured by tracking their movement and by temperature-sensitive fluorophore, respectively. When there is no light absorption in the liquid, the migration velocity of particles under the laser beam is linearly increased with the increase of the laser power, in agreement with the calculations based on ray optics theory. In the case of light-absorbing liquid, the migration speed of particles experiencing the optical force indicates a nonlinear increase as the laser power increases. This enhancement mainly attributes to the temperature-sensitive change of liquid viscosity resulting in a reduction of viscous drag for migrating particles. An appropriate arrangement of light absorption leads to an enhancement in the photophoretic velocity of particles, and eventual performance promotion of particle separation and/or sorting using the optical force. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

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