Dépouillements

Limiting length, steady spread, and nongrowing flames in concurrent flow over solids / Ya-Ting Tseng in Journal of heat transfer, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091201-1/9] Titre : Limiting length, steady spread, and nongrowing flames in concurrent flow over solids Type de document : texte imprimé Auteurs : Ya-Ting Tseng, Auteur ; James S. T'ien, Auteur Article en page(s) : pp. [091201-1/9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Solid  flame  spread  Fire  growth  Limiting  flame  length  Microgravity Index. décimale : 536 Chaleur. Thermodynamique Résumé : A detailed two-dimensional transient model has been formulated and numerically solved for concurrent flames over thick and thin solids in low-speed forced flows. The processes of flame growth leading to steady states are numerically simulated. For a thick solid, the steady state is a nongrowing stationary flame with a limiting length. For a thin solid, the steady state is a spreading flame with a constant spread rate and a constant flame length. The reason for a nongrowing limiting flame for the thick solid is the balance between the flame heat feedback and the surface radiative heat loss at the pyrolysis front, as first suggested by Honda and Ronney. The reason for achieving a steady spread for thin solids is the balance between the solid burnout rate and the flame tip advancing rate. Detailed transient flame and thermal profiles are presented to illustrate the different flame growth features between the thick- and thin-solid fuel samples. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Limiting length, steady spread, and nongrowing flames in concurrent flow over solids [texte imprimé] / Ya-Ting Tseng, Auteur ; James S. T'ien, Auteur . - pp. [091201-1/9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091201-1/9] Mots-clés : Solid  flame  spread  Fire  growth  Limiting  flame  length  Microgravity Index. décimale : 536 Chaleur. Thermodynamique Résumé : A detailed two-dimensional transient model has been formulated and numerically solved for concurrent flames over thick and thin solids in low-speed forced flows. The processes of flame growth leading to steady states are numerically simulated. For a thick solid, the steady state is a nongrowing stationary flame with a limiting length. For a thin solid, the steady state is a spreading flame with a constant spread rate and a constant flame length. The reason for a nongrowing limiting flame for the thick solid is the balance between the flame heat feedback and the surface radiative heat loss at the pyrolysis front, as first suggested by Honda and Ronney. The reason for achieving a steady spread for thin solids is the balance between the solid burnout rate and the flame tip advancing rate. Detailed transient flame and thermal profiles are presented to illustrate the different flame growth features between the thick- and thin-solid fuel samples. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Effect of selective accommodation on soot aggregate shielding in time-resolved laser-induced incandescence experiments / K. J. Daun in Journal of heat transfer, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091202-1/8] Titre : Effect of selective accommodation on soot aggregate shielding in time-resolved laser-induced incandescence experiments Type de document : texte imprimé Auteurs : K. J. Daun, Auteur Article en page(s) : pp. [091202-1/8] Note générale : Physique Langues : Anglais (eng) Mots-clés : Combustion  Laser-induced  incandescence  Soot  Free-molecular  conduction  Gas-surface  scattering Index. décimale : 536 Chaleur. Thermodynamique Résumé : Time-resolved laser-induced incandescence is an emerging diagnostic for characterizing primary particle size distributions within soot-laden aerosols. This measurement requires an accurate model of heat conduction between the laser-energized soot and the surrounding gas, which is complicated by the fractal-like structure of soot aggregates since primary particles on the aggregate exterior shield the interior from approaching gas molecules. Previous efforts to characterize aggregate shielding through direct simulation Monte Carlo analysis assume a Maxwell scattering kernel, which poorly represents actual gas/surface interactions. This paper shows how selective thermal accommodation into the translational and rotational modes of the gas molecule influences the aggregate shielding effect using the Cercignani–Lampis–Lord kernel and thermal accommodation coefficients derived from molecular dynamics simulations. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Effect of selective accommodation on soot aggregate shielding in time-resolved laser-induced incandescence experiments [texte imprimé] / K. J. Daun, Auteur . - pp. [091202-1/8]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091202-1/8] Mots-clés : Combustion  Laser-induced  incandescence  Soot  Free-molecular  conduction  Gas-surface  scattering Index. décimale : 536 Chaleur. Thermodynamique Résumé : Time-resolved laser-induced incandescence is an emerging diagnostic for characterizing primary particle size distributions within soot-laden aerosols. This measurement requires an accurate model of heat conduction between the laser-energized soot and the surrounding gas, which is complicated by the fractal-like structure of soot aggregates since primary particles on the aggregate exterior shield the interior from approaching gas molecules. Previous efforts to characterize aggregate shielding through direct simulation Monte Carlo analysis assume a Maxwell scattering kernel, which poorly represents actual gas/surface interactions. This paper shows how selective thermal accommodation into the translational and rotational modes of the gas molecule influences the aggregate shielding effect using the Cercignani–Lampis–Lord kernel and thermal accommodation coefficients derived from molecular dynamics simulations. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Reacting turbulent flow and thermal field in a channel with inclined bluff body flame holders / Cheng-Xian Lin in Journal of heat transfer, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091203-1/11] Titre : Reacting turbulent flow and thermal field in a channel with inclined bluff body flame holders Type de document : texte imprimé Auteurs : Cheng-Xian Lin, Auteur ; Richard Jack Holder, Auteur Article en page(s) : pp. [091203-1/11] Note générale : Physique Langues : Anglais (eng) Mots-clés : Chimically  reacting  flow  Combustion  Turbulent  heat  transfer  Flame  holder  Channel  flow Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this paper, a numerical study has been carried out to investigate the effects of inlet turbulent intensity and angle of attack on the chemically reacting turbulent flow and thermal fields in a channel with an inclined bluff body V-gutter flame holder. With a basic geometry used in a previous experimental study, the inlet turbulent intensity was varied from 2% to 100%, while the angle of attack of the V-gutter was varied from 0 deg to 30 deg. The turbulent flow was modeled with a realizable k-epsilon two-equation turbulence model. The chemical reaction was premixed propane-air combustion with an equivalence ratio of 0.6. The chemistry-turbulence interaction was simulated with an eddy-dissipation model. Numerical results indicated that increasing the inlet turbulent intensity and V-gutter angle of attack resulted in an increase not only in the size, but also in the magnitude of the downstream high turbulence areas with shedding vortexes. The recirculation flow behind the flame holder tended to maintain the rear wall at constant temperature, except at the edges of the wall. The friction factor of the flow channel was more sensitive to the change in inlet turbulence intensity at smaller angle of attack of the V-gutter. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Reacting turbulent flow and thermal field in a channel with inclined bluff body flame holders [texte imprimé] / Cheng-Xian Lin, Auteur ; Richard Jack Holder, Auteur . - pp. [091203-1/11]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091203-1/11] Mots-clés : Chimically  reacting  flow  Combustion  Turbulent  heat  transfer  Flame  holder  Channel  flow Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this paper, a numerical study has been carried out to investigate the effects of inlet turbulent intensity and angle of attack on the chemically reacting turbulent flow and thermal fields in a channel with an inclined bluff body V-gutter flame holder. With a basic geometry used in a previous experimental study, the inlet turbulent intensity was varied from 2% to 100%, while the angle of attack of the V-gutter was varied from 0 deg to 30 deg. The turbulent flow was modeled with a realizable k-epsilon two-equation turbulence model. The chemical reaction was premixed propane-air combustion with an equivalence ratio of 0.6. The chemistry-turbulence interaction was simulated with an eddy-dissipation model. Numerical results indicated that increasing the inlet turbulent intensity and V-gutter angle of attack resulted in an increase not only in the size, but also in the magnitude of the downstream high turbulence areas with shedding vortexes. The recirculation flow behind the flame holder tended to maintain the rear wall at constant temperature, except at the edges of the wall. The friction factor of the flow channel was more sensitive to the change in inlet turbulence intensity at smaller angle of attack of the V-gutter. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Theoretical study on transient hot-strip method by numerical analysis / Gaosheng Wei in Journal of heat transfer, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091301-1/7] Titre : Theoretical study on transient hot-strip method by numerical analysis Type de document : texte imprimé Auteurs : Gaosheng Wei, Auteur ; Xiaoze Du, Auteur ; Xinxin Zhang, Auteur Article en page(s) : pp. [091301-1/7] Note générale : Physique Langues : Anglais (eng) Mots-clés : Numerical  simulation  Thermal  conductivity  Thermophysical  properties  Transient  hot-strip  method Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper presented the effects of finite dimensions of the sample and nonzero heat capacity of the strip on thermal conductivity determination with the transient hot-strip method. Through the numerical analysis of the temperature field within the system composed of the samples and the strip, the temperature transients at the strip surface were obtained to calculate the thermal conductivities of materials, which were compared with the exact values. The effect of heat losses out of the external surfaces of the sample and the heat capacity of the strip on thermal conductivity determination were then analyzed comprehensively. It is shown that the sample finite dimensions have a great effect on thermal conductivity determination, especially on the materials with relatively higher thermal diffusivities, and the measured thermal conductivity is always lower than the exact value due to the lower convective heat transfer coefficient out of the external surfaces of the sample. The measurement error is estimated to be less than 2.1% for the material with thermal diffusivity less than 4.0×10−6 m2/s with the sample dimensions of 120×60 mm2 (width×thickness) and the fitting time interval of 20–300 s. The nonzero heat capacity of the strip has a great effect on thermal conductivity determinations of the materials with relatively lower thermal diffusivities. The measurement error is estimated to be less than 5% for the material with thermal diffusivity larger than 0.8×10−7 m2/s with Cr20Ni80 alloy as the strip. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Theoretical study on transient hot-strip method by numerical analysis [texte imprimé] / Gaosheng Wei, Auteur ; Xiaoze Du, Auteur ; Xinxin Zhang, Auteur . - pp. [091301-1/7]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091301-1/7] Mots-clés : Numerical  simulation  Thermal  conductivity  Thermophysical  properties  Transient  hot-strip  method Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper presented the effects of finite dimensions of the sample and nonzero heat capacity of the strip on thermal conductivity determination with the transient hot-strip method. Through the numerical analysis of the temperature field within the system composed of the samples and the strip, the temperature transients at the strip surface were obtained to calculate the thermal conductivities of materials, which were compared with the exact values. The effect of heat losses out of the external surfaces of the sample and the heat capacity of the strip on thermal conductivity determination were then analyzed comprehensively. It is shown that the sample finite dimensions have a great effect on thermal conductivity determination, especially on the materials with relatively higher thermal diffusivities, and the measured thermal conductivity is always lower than the exact value due to the lower convective heat transfer coefficient out of the external surfaces of the sample. The measurement error is estimated to be less than 2.1% for the material with thermal diffusivity less than 4.0×10−6 m2/s with the sample dimensions of 120×60 mm2 (width×thickness) and the fitting time interval of 20–300 s. The nonzero heat capacity of the strip has a great effect on thermal conductivity determinations of the materials with relatively lower thermal diffusivities. The measurement error is estimated to be less than 5% for the material with thermal diffusivity larger than 0.8×10−7 m2/s with Cr20Ni80 alloy as the strip. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Analytical solutions for anisotropic heat conduction problems in a trimaterial with heat sources / Ming-Ho Shen in Journal of heat transfer, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091302-1/8] Titre : Analytical solutions for anisotropic heat conduction problems in a trimaterial with heat sources Type de document : texte imprimé Auteurs : Ming-Ho Shen, Auteur ; Fu-Mo Chen, Auteur ; Shih-Yu Hung, Auteur Article en page(s) : pp. [091302-1/8] Note générale : Physique Langues : Anglais (eng) Mots-clés : Heat  conduction  Anisotropic  trimaterial  Analytical  continuation Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this work, the analytical solution of a fundamental problem of heat conduction in anisotropic medium is derived. The steady-state temperature field in an anisotropic trimaterial subject to an arbitrary heat source is analyzed. “Trimaterial” denotes an infinite body composed of three dissimilar materials bonded along two parallel interfaces. The method of analytical continuation is applied across the two parallel interfaces in order to derive the trimaterial solution in a series form from the corresponding homogeneous solution. A variety of problems, e.g., bimaterial, a finite thin film on a semi-infinite substrate, and a finite strip, can be analyzed as special cases of the present study. The numerical results of the temperature distributions for some practical examples are provided in graphic form and discussed in details. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Analytical solutions for anisotropic heat conduction problems in a trimaterial with heat sources [texte imprimé] / Ming-Ho Shen, Auteur ; Fu-Mo Chen, Auteur ; Shih-Yu Hung, Auteur . - pp. [091302-1/8]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091302-1/8] Mots-clés : Heat  conduction  Anisotropic  trimaterial  Analytical  continuation Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this work, the analytical solution of a fundamental problem of heat conduction in anisotropic medium is derived. The steady-state temperature field in an anisotropic trimaterial subject to an arbitrary heat source is analyzed. “Trimaterial” denotes an infinite body composed of three dissimilar materials bonded along two parallel interfaces. The method of analytical continuation is applied across the two parallel interfaces in order to derive the trimaterial solution in a series form from the corresponding homogeneous solution. A variety of problems, e.g., bimaterial, a finite thin film on a semi-infinite substrate, and a finite strip, can be analyzed as special cases of the present study. The numerical results of the temperature distributions for some practical examples are provided in graphic form and discussed in details. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Thermal modeling of a multilayer insulation system / D. K. Kim in Journal of heat transfer, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091303-1/9] Titre : Thermal modeling of a multilayer insulation system Type de document : texte imprimé Auteurs : D. K. Kim, Auteur ; E. E. Marotta, Auteur ; L. S. Fletcher, Auteur Article en page(s) : pp. [091303-1/9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Shims  Thermal  insulation  Thermal  resistance  Wires Index. décimale : 536 Chaleur. Thermodynamique Résumé : An analytical investigation of a novel multilayer insulation concept was conducted using an extended analytical model. This model was developed to accommodate a multilayer screen wire insulation system with interstitial shim layers. The goal of this study was to provide a simplified model for evaluating this insulation system, which included either a single or multilayer composite structure in order to predict optimal performance. With the present model, the feasibility and performance characteristics of the insulation concept were predicted. The thermal predictions have demonstrated a very good comparison with previously published experimental data. By adding a radiative resistance to the model, improved performance predictions of overall thermal resistance/conductance were possible, leading to the extension of single layer analytical model to multiple-layered cases. From the parametric study, the key thermophysical property of the screen wire was found to be the wire's thermal conductivity. The present model provided excellent performance prediction capability for other screen wire materials, and these results were also validated with a comparison to previously published experimental results. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Thermal modeling of a multilayer insulation system [texte imprimé] / D. K. Kim, Auteur ; E. E. Marotta, Auteur ; L. S. Fletcher, Auteur . - pp. [091303-1/9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091303-1/9] Mots-clés : Shims  Thermal  insulation  Thermal  resistance  Wires Index. décimale : 536 Chaleur. Thermodynamique Résumé : An analytical investigation of a novel multilayer insulation concept was conducted using an extended analytical model. This model was developed to accommodate a multilayer screen wire insulation system with interstitial shim layers. The goal of this study was to provide a simplified model for evaluating this insulation system, which included either a single or multilayer composite structure in order to predict optimal performance. With the present model, the feasibility and performance characteristics of the insulation concept were predicted. The thermal predictions have demonstrated a very good comparison with previously published experimental data. By adding a radiative resistance to the model, improved performance predictions of overall thermal resistance/conductance were possible, leading to the extension of single layer analytical model to multiple-layered cases. From the parametric study, the key thermophysical property of the screen wire was found to be the wire's thermal conductivity. The present model provided excellent performance prediction capability for other screen wire materials, and these results were also validated with a comparison to previously published experimental results. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

A novel approach to low profile heat sink design / Jason Stafford in Journal of heat transfer, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091401-1/8] Titre : A novel approach to low profile heat sink design Type de document : texte imprimé Auteurs : Jason Stafford, Auteur ; Ed Walsh, Auteur ; Vanessa Egan, Auteur Article en page(s) : pp. [091401-1/8] Note générale : Physique Langues : Anglais (eng) Mots-clés : Electronic  cooling  Heat  exchangers  Forced  convection Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper discusses the importance of developing cooling solutions for low profile devices. This is addressed with an experimental and theoretical study on forced convection cooling solution designs that could be implemented into such devices. Conventional finned and corresponding finless designs of equal exterior dimensions are considered for three different heat sink profiles ranging from 1 mm to 4 mm in combination with a commercially available radial blower. The results show that forced convection heat transfer rates can be enhanced by up to 55% using finless designs at low profiles with relatively small footprint areas. Overall, this paper provides optimization and geometry selection criteria, which are relevant to designers of low profile cooling solutions. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] A novel approach to low profile heat sink design [texte imprimé] / Jason Stafford, Auteur ; Ed Walsh, Auteur ; Vanessa Egan, Auteur . - pp. [091401-1/8]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091401-1/8] Mots-clés : Electronic  cooling  Heat  exchangers  Forced  convection Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper discusses the importance of developing cooling solutions for low profile devices. This is addressed with an experimental and theoretical study on forced convection cooling solution designs that could be implemented into such devices. Conventional finned and corresponding finless designs of equal exterior dimensions are considered for three different heat sink profiles ranging from 1 mm to 4 mm in combination with a commercially available radial blower. The results show that forced convection heat transfer rates can be enhanced by up to 55% using finless designs at low profiles with relatively small footprint areas. Overall, this paper provides optimization and geometry selection criteria, which are relevant to designers of low profile cooling solutions. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Momentum conservation and condensing vapor bubbles / I. Eames in Journal of heat transfer, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp.[091501-1/9] Titre : Momentum conservation and condensing vapor bubbles Type de document : texte imprimé Auteurs : I. Eames, Auteur Article en page(s) : pp.[091501-1/9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Boiling  Heatexchanger  Momentum  Vapor  bubbles Index. décimale : 536 Chaleur. Thermodynamique Résumé : Boiling is a common feature of many daily processes, such as making tea, cooking, and heating. The growth, rise, collapse, and final disappearance of vapor bubbles are ubiquitous features of nucleate boiling. New experimental observations show that a vortex is generated as a consequence of the bubble disappearing. We categorize the possible mechanisms that lead to the generation of a vortex by bubbles. When the bubble collapses but does not change topology, the vortex is created by viscous effects, where the attached wake behind the vapor bubble persists after the bubble has disappeared. But when the bubbles collapse so rapidly that they change topology, the vortex is created by an inviscid mechanism. The total momentum communicated to the flow by the collapse processes is calculated and compared with the measurements of the vortex impulse. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Momentum conservation and condensing vapor bubbles [texte imprimé] / I. Eames, Auteur . - pp.[091501-1/9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp.[091501-1/9] Mots-clés : Boiling  Heatexchanger  Momentum  Vapor  bubbles Index. décimale : 536 Chaleur. Thermodynamique Résumé : Boiling is a common feature of many daily processes, such as making tea, cooking, and heating. The growth, rise, collapse, and final disappearance of vapor bubbles are ubiquitous features of nucleate boiling. New experimental observations show that a vortex is generated as a consequence of the bubble disappearing. We categorize the possible mechanisms that lead to the generation of a vortex by bubbles. When the bubble collapses but does not change topology, the vortex is created by viscous effects, where the attached wake behind the vapor bubble persists after the bubble has disappeared. But when the bubbles collapse so rapidly that they change topology, the vortex is created by an inviscid mechanism. The total momentum communicated to the flow by the collapse processes is calculated and compared with the measurements of the vortex impulse. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Gravity scaling parameter for pool boiling heat transfer / Rishi Raj in Journal of heat transfer, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091502-1/9] Titre : Gravity scaling parameter for pool boiling heat transfer Type de document : texte imprimé Auteurs : Rishi Raj, Auteur ; Jungho Kim, Auteur ; John McQuillen, Auteur Article en page(s) : pp. [091502-1/9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Scaling  parameter  Variable  gravity  Pool  boiling  Microgravity Index. décimale : 536 Chaleur. Thermodynamique Résumé : Although the effects of microgravity, earth gravity, and hypergravity (>1.5 g) on pool boiling heat flux have been studied previously, pool boiling heat flux data over a continuous range of gravity levels (0–1.7 g) was unavailable until recently. The current work uses the results of a variable gravity, subcooled pool boiling experiment to develop a gravity scaling parameter for n-perfluorohexane/FC-72 in the buoyancy-dominated boiling regime (Lh/Lc>2.1). The heat flux prediction was then validated using heat flux data at different subcoolings and dissolved gas concentrations. The scaling parameter can be used as a tool to predict boiling heat flux at any gravity level in the buoyancy dominated regime if the data under similar experimental conditions are available at any other gravity level. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Gravity scaling parameter for pool boiling heat transfer [texte imprimé] / Rishi Raj, Auteur ; Jungho Kim, Auteur ; John McQuillen, Auteur . - pp. [091502-1/9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091502-1/9] Mots-clés : Scaling  parameter  Variable  gravity  Pool  boiling  Microgravity Index. décimale : 536 Chaleur. Thermodynamique Résumé : Although the effects of microgravity, earth gravity, and hypergravity (>1.5 g) on pool boiling heat flux have been studied previously, pool boiling heat flux data over a continuous range of gravity levels (0–1.7 g) was unavailable until recently. The current work uses the results of a variable gravity, subcooled pool boiling experiment to develop a gravity scaling parameter for n-perfluorohexane/FC-72 in the buoyancy-dominated boiling regime (Lh/Lc>2.1). The heat flux prediction was then validated using heat flux data at different subcoolings and dissolved gas concentrations. The scaling parameter can be used as a tool to predict boiling heat flux at any gravity level in the buoyancy dominated regime if the data under similar experimental conditions are available at any other gravity level. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Heater size and gravity based pool boiling regime map / Rishi Raj in Journal of heat transfer, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091503-1/10] Titre : Heater size and gravity based pool boiling regime map : transition criteria between buoyancy and surface tension dominated boiling Type de document : texte imprimé Auteurs : Rishi Raj, Auteur ; Jungho Kim, Auteur Article en page(s) : pp. [091503-1/10] Note générale : Physique Langues : Anglais (eng) Mots-clés : Pool  boiling  Capillary  length  Heater  size  Gravity  Surface  tension  Buoyancy  Regime  map Index. décimale : 536 Chaleur. Thermodynamique Résumé : A pool boiling regime map demarcating the boundary between the surface tension and buoyancy dominated boiling regimes is developed based on heater size and gravity. For large heaters and/or high gravity conditions, boiling is dominated by buoyancy, and the ebullition cycle dominates the contribution to heat transfer. As the gravity level and/or heater size is decreased, surface tension forces become increasingly dominant, and a decrease in heat transfer is observed. The ratio of the heater size Lh (length of a side for a square heater) to the capillary length Lc is found to be a suitable parameter to define the transition criterion between these regimes. Based on the data obtained using FC-72 and pentane, the threshold value of Lh/Lc above which pool boiling is buoyancy dominated was found to be about 2.1. This transition criterion was found to be the same for gravity levels between ~0g–1.7g and liquid subcoolings between 6.6°C and 26.6°C. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Heater size and gravity based pool boiling regime map : transition criteria between buoyancy and surface tension dominated boiling [texte imprimé] / Rishi Raj, Auteur ; Jungho Kim, Auteur . - pp. [091503-1/10]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091503-1/10] Mots-clés : Pool  boiling  Capillary  length  Heater  size  Gravity  Surface  tension  Buoyancy  Regime  map Index. décimale : 536 Chaleur. Thermodynamique Résumé : A pool boiling regime map demarcating the boundary between the surface tension and buoyancy dominated boiling regimes is developed based on heater size and gravity. For large heaters and/or high gravity conditions, boiling is dominated by buoyancy, and the ebullition cycle dominates the contribution to heat transfer. As the gravity level and/or heater size is decreased, surface tension forces become increasingly dominant, and a decrease in heat transfer is observed. The ratio of the heater size Lh (length of a side for a square heater) to the capillary length Lc is found to be a suitable parameter to define the transition criterion between these regimes. Based on the data obtained using FC-72 and pentane, the threshold value of Lh/Lc above which pool boiling is buoyancy dominated was found to be about 2.1. This transition criterion was found to be the same for gravity levels between ~0g–1.7g and liquid subcoolings between 6.6°C and 26.6°C. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Numerical investigation of local entropy generation for laminar flow in rotating-disk systems / Mohammad Shanbghazani in Journal of heat transfer, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091701-1/7] Titre : Numerical investigation of local entropy generation for laminar flow in rotating-disk systems Type de document : texte imprimé Auteurs : Mohammad Shanbghazani, Auteur ; Vahid Heidarpoor, Auteur ; Marc A. Rosen, Auteur Article en page(s) : pp. [091701-1/7] Note générale : Physique Langues : Anglais (eng) Mots-clés : Numerical  study  Rotating  disk  Entropy  generation  Irreversibility  Bejan  number  Rotational  Reynolds  number Index. décimale : 536 Chaleur. Thermodynamique Résumé : The entropy generation is investigated numerically in axisymmetric, steady-state, and incompressible laminar flow in a rotating single free disk. The finite-volume method is used for solving the momentum and energy equations needed for the determination of the entropy generation due to heat transfer and fluid friction. The numerical model is validated by comparing it to previously reported analytical and experimental data for momentum and energy. Results are presented in terms of velocity distribution, temperature, local entropy generation rate, Bejan number, and irreversibility ratio distribution for various rotational Reynolds number and physical cases, using dimensionless parameters. It is demonstrated that increasing rotational Reynolds number increases the local entropy generation rate and irreversibility rate, and that the irreversibility is mainly due to heat transfer while the irreversibility associated with fluid friction is minor. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Numerical investigation of local entropy generation for laminar flow in rotating-disk systems [texte imprimé] / Mohammad Shanbghazani, Auteur ; Vahid Heidarpoor, Auteur ; Marc A. Rosen, Auteur . - pp. [091701-1/7]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091701-1/7] Mots-clés : Numerical  study  Rotating  disk  Entropy  generation  Irreversibility  Bejan  number  Rotational  Reynolds  number Index. décimale : 536 Chaleur. Thermodynamique Résumé : The entropy generation is investigated numerically in axisymmetric, steady-state, and incompressible laminar flow in a rotating single free disk. The finite-volume method is used for solving the momentum and energy equations needed for the determination of the entropy generation due to heat transfer and fluid friction. The numerical model is validated by comparing it to previously reported analytical and experimental data for momentum and energy. Results are presented in terms of velocity distribution, temperature, local entropy generation rate, Bejan number, and irreversibility ratio distribution for various rotational Reynolds number and physical cases, using dimensionless parameters. It is demonstrated that increasing rotational Reynolds number increases the local entropy generation rate and irreversibility rate, and that the irreversibility is mainly due to heat transfer while the irreversibility associated with fluid friction is minor. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Transient behavior of crossflow heat exchangers due to sinusoidal excitation / Manish Mishra in Journal of heat transfer, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091801-1/9] Titre : Transient behavior of crossflow heat exchangers due to sinusoidal excitation Type de document : texte imprimé Auteurs : Manish Mishra, Auteur ; P. K. Das, Auteur ; Sunil Sarangi, Auteur Article en page(s) : pp. [091801-1/9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Axial  dispersion  Crossflow  Heat  exchanger  Longitudinal  conduction  Sinusoidal  Transient Index. décimale : 536 Chaleur. Thermodynamique Résumé : Transient temperature response of crossflow heat exchangers with both fluids unmixed and finite wall capacitance is investigated numerically for sinusoidal excitation provided in hot fluid inlet temperature. The effect of two-dimensional longitudinal conduction in separating sheet and the axial dispersion in fluids has also been considered on the thermal performance of the heat exchanger. The present method has good accuracy and simplicity. An attempt has also been made to study the performance of the sinusoidal excitation in the graphical form. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Transient behavior of crossflow heat exchangers due to sinusoidal excitation [texte imprimé] / Manish Mishra, Auteur ; P. K. Das, Auteur ; Sunil Sarangi, Auteur . - pp. [091801-1/9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091801-1/9] Mots-clés : Axial  dispersion  Crossflow  Heat  exchanger  Longitudinal  conduction  Sinusoidal  Transient Index. décimale : 536 Chaleur. Thermodynamique Résumé : Transient temperature response of crossflow heat exchangers with both fluids unmixed and finite wall capacitance is investigated numerically for sinusoidal excitation provided in hot fluid inlet temperature. The effect of two-dimensional longitudinal conduction in separating sheet and the axial dispersion in fluids has also been considered on the thermal performance of the heat exchanger. The present method has good accuracy and simplicity. An attempt has also been made to study the performance of the sinusoidal excitation in the graphical form. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Transient thermal analyses of midwall cooling and external cooling methods for a gun barrel / Avanish Mishra in Journal of heat transfer, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091901-1/8] Titre : Transient thermal analyses of midwall cooling and external cooling methods for a gun barrel Type de document : texte imprimé Auteurs : Avanish Mishra, Auteur ; Amer Hameed, Auteur ; Bryan Lawton, Auteur Article en page(s) : pp. [091901-1/8] Note générale : Physique Langues : Anglais (eng) Mots-clés : Cook-off  External  cooling  Gun  barrel  Howitzer  Midwall  cooling  Temperature  history Index. décimale : 536 Chaleur. Thermodynamique Résumé : Liquid cooling methods are often used for thermal management of a large caliber gun barrel. In this work, transient thermal analyses of midwall-cooled and externally cooled gun barrels were performed. At first, a novel simulation scheme was developed for the computation of the gun barrel temperature history (temperature variation over time), and its experimental validation was performed. In the computational scheme an internal ballistics code, GUNTEMP8.EXE, was developed to simulate the total heat transfer per cycle for the given ammunition parameters. Subsequently, a finite element (FE) model of the barrel was developed in ANSYS 11.0. Heat transfer to the barrel was approximated by an exponentially decaying heat flux. The FE model was solved to compute for barrel temperature history. Simulations were performed for a burst of 9 cycles, and the results were found to agree with the experimental measurements. Subsequently, the simulation scheme was extended to analyze a burst of 40 cycles at 10 shots per minute (spm). Three cases were investigated as follows: (1) a naturally cooled gun barrel, (2) a gun barrel with midwall cooling channels, and (3) an externally cooled gun barrel. Natural cooling was found insufficient to prevent cook-off, whereas midwall and external cooling methods were found to eliminate any possibility of it. In the context of a self-propelled howitzer, a midwall-cooled gun barrel connected to an engine cooling system was also analyzed. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Transient thermal analyses of midwall cooling and external cooling methods for a gun barrel [texte imprimé] / Avanish Mishra, Auteur ; Amer Hameed, Auteur ; Bryan Lawton, Auteur . - pp. [091901-1/8]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091901-1/8] Mots-clés : Cook-off  External  cooling  Gun  barrel  Howitzer  Midwall  cooling  Temperature  history Index. décimale : 536 Chaleur. Thermodynamique Résumé : Liquid cooling methods are often used for thermal management of a large caliber gun barrel. In this work, transient thermal analyses of midwall-cooled and externally cooled gun barrels were performed. At first, a novel simulation scheme was developed for the computation of the gun barrel temperature history (temperature variation over time), and its experimental validation was performed. In the computational scheme an internal ballistics code, GUNTEMP8.EXE, was developed to simulate the total heat transfer per cycle for the given ammunition parameters. Subsequently, a finite element (FE) model of the barrel was developed in ANSYS 11.0. Heat transfer to the barrel was approximated by an exponentially decaying heat flux. The FE model was solved to compute for barrel temperature history. Simulations were performed for a burst of 9 cycles, and the results were found to agree with the experimental measurements. Subsequently, the simulation scheme was extended to analyze a burst of 40 cycles at 10 shots per minute (spm). Three cases were investigated as follows: (1) a naturally cooled gun barrel, (2) a gun barrel with midwall cooling channels, and (3) an externally cooled gun barrel. Natural cooling was found insufficient to prevent cook-off, whereas midwall and external cooling methods were found to eliminate any possibility of it. In the context of a self-propelled howitzer, a midwall-cooled gun barrel connected to an engine cooling system was also analyzed. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Experimental study on heat transfer and pressure drop of recuperative heat exchangers using carbon foam / Y. R. Lin in Journal of heat transfer, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091902-1/10] Titre : Experimental study on heat transfer and pressure drop of recuperative heat exchangers using carbon foam Type de document : texte imprimé Auteurs : Y. R. Lin, Auteur ; J. H. Du, Auteur ; W. Wu, Auteur Article en page(s) : pp. [091902-1/10] Note générale : Physique Langues : Anglais (eng) Mots-clés : Heat  transfer  Recuperators  Cryogenics Index. décimale : 536 Chaleur. Thermodynamique Résumé : This work focuses on the development of high-effectiveness recuperative heat exchangers using solid and corrugated carbon foam blocks. Characterization tests were conducted on heat transfer and pressure drop for a single carbon foam block with different sizes. Results show that carbon foam can be an effective medium for heat transfer enhancement, and a short length in the flow direction yields a high heat transfer coefficient. The corrugation can enhance heat transfer and reduce pressure drop at the same time. A recuperative heat exchanger with carbon foam, which consists of separate blocks of carbon foams packed between thin sheets of stainless steel, was designed. The hot and cold flow paths were arranged in counterflow in the recuperator. The heat exchanger was designed in a modular manner so that it can be scaled up for a larger heat transfer requirement or a higher overall effectiveness. The anisotropic property of carbon foam was exploited to achieve higher effectiveness for one pair of foam blocks. Experiments with four pairs of carbon foams were conducted to evaluate the performance of carbon foam used in the recuperative heat exchanger. Measurements were made for both solid and corrugated foams for comparison. With four pairs of carbon foam blocks, an overall effectiveness epsilontotal greater than 80% was achieved. This paper demonstrates an approach to reach an effectiveness epsilontotal of 98% by placing many pairs of carbon foams in series. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Experimental study on heat transfer and pressure drop of recuperative heat exchangers using carbon foam [texte imprimé] / Y. R. Lin, Auteur ; J. H. Du, Auteur ; W. Wu, Auteur . - pp. [091902-1/10]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [091902-1/10] Mots-clés : Heat  transfer  Recuperators  Cryogenics Index. décimale : 536 Chaleur. Thermodynamique Résumé : This work focuses on the development of high-effectiveness recuperative heat exchangers using solid and corrugated carbon foam blocks. Characterization tests were conducted on heat transfer and pressure drop for a single carbon foam block with different sizes. Results show that carbon foam can be an effective medium for heat transfer enhancement, and a short length in the flow direction yields a high heat transfer coefficient. The corrugation can enhance heat transfer and reduce pressure drop at the same time. A recuperative heat exchanger with carbon foam, which consists of separate blocks of carbon foams packed between thin sheets of stainless steel, was designed. The hot and cold flow paths were arranged in counterflow in the recuperator. The heat exchanger was designed in a modular manner so that it can be scaled up for a larger heat transfer requirement or a higher overall effectiveness. The anisotropic property of carbon foam was exploited to achieve higher effectiveness for one pair of foam blocks. Experiments with four pairs of carbon foams were conducted to evaluate the performance of carbon foam used in the recuperative heat exchanger. Measurements were made for both solid and corrugated foams for comparison. With four pairs of carbon foam blocks, an overall effectiveness epsilontotal greater than 80% was achieved. This paper demonstrates an approach to reach an effectiveness epsilontotal of 98% by placing many pairs of carbon foams in series. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Experimental and numerical investigation of heat transfer characteristics of inline and staggered arrays of impinging jets / Yunfei Xing in Journal of heat transfer, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [092201-1/11] Titre : Experimental and numerical investigation of heat transfer characteristics of inline and staggered arrays of impinging jets Type de document : texte imprimé Auteurs : Yunfei Xing, Auteur ; Sebastian Spring, Auteur ; Bernhard Weigand, Auteur Article en page(s) : pp. [092201-1/11] Note générale : Physique Langues : Anglais (eng) Mots-clés : Impingement  cooling  Heat  transfer  Inline  Staggered  CFD Index. décimale : 536 Chaleur. Thermodynamique Résumé : A combined experimental and numerical investigation of the heat transfer characteristics within an array of impinging jets has been conducted. The experiments were carried out in a perspex model using a transient liquid crystal method. Local jet temperatures were measured at several positions on the impingement plate to account for an exact evaluation of the heat transfer coefficient. The effects of the variation in different impingement patterns, jet-to-plate spacing, crossflow schemes, and jet Reynolds number on the distribution of the local Nusselt number and the related pressure loss were investigated experimentally. In addition to the measurements, a numerical investigation was conducted. The motivation was to evaluate whether computational fluid dynamics (CFD) can be used as an engineering design tool in the optimization of multijet impingement configurations. This required, as a first step, a validation of the numerical results. For the present configuration, this was achieved assessing the degree of accuracy to which the measured heat transfer rates could be computed. The overall agreement was very good and even local heat transfer coefficients were predicted at high accuracy. The numerical investigation showed that state-of-the-art CFD codes can be used as suitable means in the thermal design process of such configurations. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Experimental and numerical investigation of heat transfer characteristics of inline and staggered arrays of impinging jets [texte imprimé] / Yunfei Xing, Auteur ; Sebastian Spring, Auteur ; Bernhard Weigand, Auteur . - pp. [092201-1/11]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [092201-1/11] Mots-clés : Impingement  cooling  Heat  transfer  Inline  Staggered  CFD Index. décimale : 536 Chaleur. Thermodynamique Résumé : A combined experimental and numerical investigation of the heat transfer characteristics within an array of impinging jets has been conducted. The experiments were carried out in a perspex model using a transient liquid crystal method. Local jet temperatures were measured at several positions on the impingement plate to account for an exact evaluation of the heat transfer coefficient. The effects of the variation in different impingement patterns, jet-to-plate spacing, crossflow schemes, and jet Reynolds number on the distribution of the local Nusselt number and the related pressure loss were investigated experimentally. In addition to the measurements, a numerical investigation was conducted. The motivation was to evaluate whether computational fluid dynamics (CFD) can be used as an engineering design tool in the optimization of multijet impingement configurations. This required, as a first step, a validation of the numerical results. For the present configuration, this was achieved assessing the degree of accuracy to which the measured heat transfer rates could be computed. The overall agreement was very good and even local heat transfer coefficients were predicted at high accuracy. The numerical investigation showed that state-of-the-art CFD codes can be used as suitable means in the thermal design process of such configurations. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Nanofluid convection in microtubes / Joohyun Lee in Journal of heat transfer, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [092401-1/5] Titre : Nanofluid convection in microtubes Type de document : texte imprimé Auteurs : Joohyun Lee, Auteur ; Patricia E. Gharagozloo, Auteur ; Babajide Kolade, Auteur Article en page(s) : pp. [092401-1/5] Note générale : Physique Langues : Anglais (eng) Mots-clés : Nanofluid  Convection  Heat  transfer  Carbon  nanotubes  Heat  exchanger Index. décimale : 536 Chaleur. Thermodynamique Résumé : While there has been much previous research on the thermal conductivity and convection performance of nanofluids, these data are rarely reported together with effective viscosity data that govern the relevance for heat exchanger applications. We report here the effective convection coefficient and viscosity in microtubes (D=0.5 mm) along with stationary thermal conductivity measurements for nanofluids based on spherical particles (Al2O3, ZnO, and CuO) and carbon nanotubes. Sample data include an effective convection coefficient increase of 5% for 3 vol % Al2O3/DI water nanofluid, 13.3% for 4 vol % CuO/DI water nanofluid, and 11.6% for 0.2 vol % Carbon nanotube(CNT)/DI water nanofluid. When considered together with our viscosity measurement on the same fluids, we find that the only the CNT-based nanofluids are promising for microfluidic heat exchangers. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Nanofluid convection in microtubes [texte imprimé] / Joohyun Lee, Auteur ; Patricia E. Gharagozloo, Auteur ; Babajide Kolade, Auteur . - pp. [092401-1/5]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [092401-1/5] Mots-clés : Nanofluid  Convection  Heat  transfer  Carbon  nanotubes  Heat  exchanger Index. décimale : 536 Chaleur. Thermodynamique Résumé : While there has been much previous research on the thermal conductivity and convection performance of nanofluids, these data are rarely reported together with effective viscosity data that govern the relevance for heat exchanger applications. We report here the effective convection coefficient and viscosity in microtubes (D=0.5 mm) along with stationary thermal conductivity measurements for nanofluids based on spherical particles (Al2O3, ZnO, and CuO) and carbon nanotubes. Sample data include an effective convection coefficient increase of 5% for 3 vol % Al2O3/DI water nanofluid, 13.3% for 4 vol % CuO/DI water nanofluid, and 11.6% for 0.2 vol % Carbon nanotube(CNT)/DI water nanofluid. When considered together with our viscosity measurement on the same fluids, we find that the only the CNT-based nanofluids are promising for microfluidic heat exchangers. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Harvesting nanoscale thermal radiation using pyroelectric materials / Jin Fang in Journal of heat transfer, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp.[092701-1/10] Titre : Harvesting nanoscale thermal radiation using pyroelectric materials Type de document : texte imprimé Auteurs : Jin Fang, Auteur ; Hugo Frederich, Auteur ; Laurent Pilon, Auteur Article en page(s) : pp.[092701-1/10] Note générale : Physique Langues : Anglais (eng) Mots-clés : Pyroelectric  effet  Ferroelectric  Direct  energy  conversion  Nanoscale  thermal  radiation  Waste  heat  harvesting Index. décimale : 536 Chaleur. Thermodynamique Résumé : Pyroelectric energy conversion offers a way to convert waste heat directly into electricity. It makes use of the pyroelectric effect to create a flow of charge to or from the surface of a material as a result of heating or cooling. However, an existing pyroelectric energy converter can only operate at low frequencies due to a relatively small convective heat transfer rate between the pyroelectric materials and the working fluid. On the other hand, energy transfer by thermal radiation between two semi-infinite solids is nearly instantaneous and can be enhanced by several orders of magnitude from the conventional Stefan–Boltzmann law as the gap separating them becomes smaller than Wien's displacement wavelength. This paper explores a novel way to harvest waste heat by combining pyroelectric energy conversion and nanoscale thermal radiation. A new device was investigated numerically by accurately modeling nanoscale radiative heat transfer between a pyroelectric element and hot and cold plates. Silica absorbing layers on top of every surface were used to further increase the net radiative heat fluxes. Temperature oscillations with time and performances of the pyroelectric converter were predicted at various frequencies. The device using 60/40 porous poly(vinylidene fluoride–trifluoroethylene) achieved a 0.2% efficiency and a 0.84 mW/cm2 electrical power output for the cold and hot sources at 273 K and 388 K, respectively. Better performances could be achieved with 0.9Pb(Mg1/3Nb2/3)–0.1PbTiO3 (0.9PMN-PT), namely, an efficiency of 1.3% and a power output of 6.5 mW/cm2 between the cold and hot sources at 283 K and 383 K, respectively. These results are compared with alternative technologies, and suggestions are made to further improve the device. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Harvesting nanoscale thermal radiation using pyroelectric materials [texte imprimé] / Jin Fang, Auteur ; Hugo Frederich, Auteur ; Laurent Pilon, Auteur . - pp.[092701-1/10]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp.[092701-1/10] Mots-clés : Pyroelectric  effet  Ferroelectric  Direct  energy  conversion  Nanoscale  thermal  radiation  Waste  heat  harvesting Index. décimale : 536 Chaleur. Thermodynamique Résumé : Pyroelectric energy conversion offers a way to convert waste heat directly into electricity. It makes use of the pyroelectric effect to create a flow of charge to or from the surface of a material as a result of heating or cooling. However, an existing pyroelectric energy converter can only operate at low frequencies due to a relatively small convective heat transfer rate between the pyroelectric materials and the working fluid. On the other hand, energy transfer by thermal radiation between two semi-infinite solids is nearly instantaneous and can be enhanced by several orders of magnitude from the conventional Stefan–Boltzmann law as the gap separating them becomes smaller than Wien's displacement wavelength. This paper explores a novel way to harvest waste heat by combining pyroelectric energy conversion and nanoscale thermal radiation. A new device was investigated numerically by accurately modeling nanoscale radiative heat transfer between a pyroelectric element and hot and cold plates. Silica absorbing layers on top of every surface were used to further increase the net radiative heat fluxes. Temperature oscillations with time and performances of the pyroelectric converter were predicted at various frequencies. The device using 60/40 porous poly(vinylidene fluoride–trifluoroethylene) achieved a 0.2% efficiency and a 0.84 mW/cm2 electrical power output for the cold and hot sources at 273 K and 388 K, respectively. Better performances could be achieved with 0.9Pb(Mg1/3Nb2/3)–0.1PbTiO3 (0.9PMN-PT), namely, an efficiency of 1.3% and a power output of 6.5 mW/cm2 between the cold and hot sources at 283 K and 383 K, respectively. These results are compared with alternative technologies, and suggestions are made to further improve the device. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

An experimental study to show the effect of thermal stress on thermal contact conductance at sub-megapascal contact pressures / Prashant Misra in Journal of heat transfer, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [094501-1/4] Titre : An experimental study to show the effect of thermal stress on thermal contact conductance at sub-megapascal contact pressures Type de document : texte imprimé Auteurs : Prashant Misra, Auteur ; J. Nagaraju, Auteur Article en page(s) : pp. [094501-1/4] Note générale : Physique Langues : Anglais (eng) Mots-clés : OFHC  Cu  Thermal  contact  conductance  Thermal  stress  Load  correction  factor Index. décimale : 536 Chaleur. Thermodynamique Résumé : Experimental studies are presented to show the effect of thermal stresses on thermal contact conductance (TCC) at low contact pressures. It is observed that in a closed contact assembly, contact pressure acting on the interface changes with the changing temperature of contact members. This change in contact pressure consequently causes variations in the TCC of the junction. A relationship between temperature change and the corresponding magnitude of developed thermal stress in a contact assembly is determined experimentally. Inclusion of a term called temperature dependent load correction factor is suggested in the theoretical model for TCC to make it capable of predicting TCC values more accurately in contact assemblies that experience large temperature fluctuations. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] An experimental study to show the effect of thermal stress on thermal contact conductance at sub-megapascal contact pressures [texte imprimé] / Prashant Misra, Auteur ; J. Nagaraju, Auteur . - pp. [094501-1/4]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [094501-1/4] Mots-clés : OFHC  Cu  Thermal  contact  conductance  Thermal  stress  Load  correction  factor Index. décimale : 536 Chaleur. Thermodynamique Résumé : Experimental studies are presented to show the effect of thermal stresses on thermal contact conductance (TCC) at low contact pressures. It is observed that in a closed contact assembly, contact pressure acting on the interface changes with the changing temperature of contact members. This change in contact pressure consequently causes variations in the TCC of the junction. A relationship between temperature change and the corresponding magnitude of developed thermal stress in a contact assembly is determined experimentally. Inclusion of a term called temperature dependent load correction factor is suggested in the theoretical model for TCC to make it capable of predicting TCC values more accurately in contact assemblies that experience large temperature fluctuations. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

Heat flux and temperature field estimation using differential interferometer / S. Prasanna in Journal of heat transfer, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [094502-1/4] Titre : Heat flux and temperature field estimation using differential interferometer Type de document : texte imprimé Auteurs : S. Prasanna, Auteur ; S. P. Venkateshan, Auteur Article en page(s) : pp. [094502-1/4] Note générale : Physique Langues : Anglais (eng) Mots-clés : Differential  interferometer  Digital  analysis  Thermal  visualization Index. décimale : 536 Chaleur. Thermodynamique Résumé : A new methodology based on least-squares approach has been developed to estimate the temperature field from an interferogram recorded using a Differential interferometer (DI). The interferograms are digitally evaluated using two dimensional Fourier transforms to retrieve the temperature gradient field. Temperature field is constructed by fitting a cubic spline to the first derivatives data. The methodology has been applied to both experimental and synthetic interferograms. Both convective heat flux and temperature field were predicted accurately. The role of image noise and errors in the temperature measurements on the temperature field estimation have been studied with the aid of synthetic interferograms. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Heat flux and temperature field estimation using differential interferometer [texte imprimé] / S. Prasanna, Auteur ; S. P. Venkateshan, Auteur . - pp. [094502-1/4]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [094502-1/4] Mots-clés : Differential  interferometer  Digital  analysis  Thermal  visualization Index. décimale : 536 Chaleur. Thermodynamique Résumé : A new methodology based on least-squares approach has been developed to estimate the temperature field from an interferogram recorded using a Differential interferometer (DI). The interferograms are digitally evaluated using two dimensional Fourier transforms to retrieve the temperature gradient field. Temperature field is constructed by fitting a cubic spline to the first derivatives data. The methodology has been applied to both experimental and synthetic interferograms. Both convective heat flux and temperature field were predicted accurately. The role of image noise and errors in the temperature measurements on the temperature field estimation have been studied with the aid of synthetic interferograms. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

On the mechanism of dropwise condensation of steam on ion implanted metallic surfaces / Michael H. Rausch in Journal of heat transfer, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [094503-1/3] Titre : On the mechanism of dropwise condensation of steam on ion implanted metallic surfaces Type de document : texte imprimé Auteurs : Michael H. Rausch, Auteur ; Alfred Leipertz, Auteur ; Andreas P. Froba, Auteur Article en page(s) : pp. [094503-1/3] Note générale : Physique Langues : Anglais (eng) Mots-clés : Dropwise  condensation  Nucleation  Microscopic  mechanism  Wetting  Ion  implantation Index. décimale : 536 Chaleur. Thermodynamique Résumé : Our recent experimental studies indicate that nanostructured, chemically inhomogeneous surfaces are the origin of dropwise condensation of steam on ion implanted metals. Yet, the underlying microscopic mechanism governing this special condensation form is still not clear. We suggest a condensation model based on droplet nucleation and growth on elevated precipitates, resulting in short-term steam entrapment after droplet coalescence. According to the wetting theory, this transition state yields increased macroscopic contact angles. Condensation phenomena such as enlarging dropwise condensation areas in spite of increasing condensation rate become comprehensible by our model. Furthermore, it points out that for this special surface type, contact angles and surface free energies measured under ambient air conditions are not usable for predicting the condensation form of steam. Although the suggested microscopic model cannot be directly proved by experiment, its validity is supported by its capability of explaining experimental observations colliding with previous theoretical approaches. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] On the mechanism of dropwise condensation of steam on ion implanted metallic surfaces [texte imprimé] / Michael H. Rausch, Auteur ; Alfred Leipertz, Auteur ; Andreas P. Froba, Auteur . - pp. [094503-1/3]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 9 (Septembre 2010) . - pp. [094503-1/3] Mots-clés : Dropwise  condensation  Nucleation  Microscopic  mechanism  Wetting  Ion  implantation Index. décimale : 536 Chaleur. Thermodynamique Résumé : Our recent experimental studies indicate that nanostructured, chemically inhomogeneous surfaces are the origin of dropwise condensation of steam on ion implanted metals. Yet, the underlying microscopic mechanism governing this special condensation form is still not clear. We suggest a condensation model based on droplet nucleation and growth on elevated precipitates, resulting in short-term steam entrapment after droplet coalescence. According to the wetting theory, this transition state yields increased macroscopic contact angles. Condensation phenomena such as enlarging dropwise condensation areas in spite of increasing condensation rate become comprehensible by our model. Furthermore, it points out that for this special surface type, contact angles and surface free energies measured under ambient air conditions are not usable for predicting the condensation form of steam. Although the suggested microscopic model cannot be directly proved by experiment, its validity is supported by its capability of explaining experimental observations colliding with previous theoretical approaches. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

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