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Critical heat flux in submerged jet impingement boiling of water under subatmospheric conditions / Ruander Cardenas in Journal of heat transfer, Vol. 134 N° 8 (special issue) (Août 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 8 (special issue) (Août 2012) . - 10 p. Titre : Critical heat flux in submerged jet impingement boiling of water under subatmospheric conditions Type de document : texte imprimé Auteurs : Ruander Cardenas, Auteur ; Vinod Narayanan, Auteur Année de publication : 2012 Article en page(s) : 10 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : jet  impingement;  critical  heat  flux;  submerged;  subatmospheric;  electronics;  cooling Index. décimale : 536 Chaleur. Thermodynamique Résumé : Critical heat flux (CHF) characteristics in submerged jet impingement boiling of water on a heated copper surface are investigated at subatmospheric conditions. Data are reported at a fixed surface-to-nozzle diameter ratio of 23.8 and a fixed surface-to-nozzle height of 6 nozzle diameters. Three subatmospheric pressures of 0.176 bars, 0.276 bars, and 0.477 bars are considered, corresponding to fluid saturation temperatures of 57.3 °C, 67.2 °C, and 80.2 °C and liquid-to-vapor density ratios of 8502, 5544, and 3295, respectively. At each pressure, CHF for varying jet Reynolds numbers (Re) in the range 0–14,000 are compared for two different surface finishes of roughness average values of 123 nm and 33 nm. The CHF enhancement observed with increasing Re is depicted in a nondimensional CHF map. Existing correlations available in the literature, which are out of range of the current experimental conditions, are found to poorly predict the obtained CHF data. A CHF correlation that captures the entire experimental data set within an average error of ±3% and a maximum error of ±13% is developed. The effect of fluid subcooling on submerged jet CHF is studied at the lowest pressure of 0.176 bars. Subcooled jet CHF is found to be well predicted from saturated jet CHF by using a typical subcooled pool boiling CHF correction factor. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000008 [...] [article] Critical heat flux in submerged jet impingement boiling of water under subatmospheric conditions [texte imprimé] / Ruander Cardenas, Auteur ; Vinod Narayanan, Auteur . - 2012 . - 10 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 8 (special issue) (Août 2012) . - 10 p. Mots-clés : jet  impingement;  critical  heat  flux;  submerged;  subatmospheric;  electronics;  cooling Index. décimale : 536 Chaleur. Thermodynamique Résumé : Critical heat flux (CHF) characteristics in submerged jet impingement boiling of water on a heated copper surface are investigated at subatmospheric conditions. Data are reported at a fixed surface-to-nozzle diameter ratio of 23.8 and a fixed surface-to-nozzle height of 6 nozzle diameters. Three subatmospheric pressures of 0.176 bars, 0.276 bars, and 0.477 bars are considered, corresponding to fluid saturation temperatures of 57.3 °C, 67.2 °C, and 80.2 °C and liquid-to-vapor density ratios of 8502, 5544, and 3295, respectively. At each pressure, CHF for varying jet Reynolds numbers (Re) in the range 0–14,000 are compared for two different surface finishes of roughness average values of 123 nm and 33 nm. The CHF enhancement observed with increasing Re is depicted in a nondimensional CHF map. Existing correlations available in the literature, which are out of range of the current experimental conditions, are found to poorly predict the obtained CHF data. A CHF correlation that captures the entire experimental data set within an average error of ±3% and a maximum error of ±13% is developed. The effect of fluid subcooling on submerged jet CHF is studied at the lowest pressure of 0.176 bars. Subcooled jet CHF is found to be well predicted from saturated jet CHF by using a typical subcooled pool boiling CHF correction factor. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000008 [...]

Heat and mass transfer characteristics of a constrained thin-film ammonia–water bubble absorber / Ruander Cardenas in International journal of refrigeration, Vol. 34 N° 1 (Janvier 2011) 

Public ISBD [article]  in International journal of refrigeration > Vol. 34 N° 1 (Janvier 2011) . - pp. 113-128 Titre : Heat and mass transfer characteristics of a constrained thin-film ammonia–water bubble absorber Titre original : Absorbeur à bulles à ammoniac-eau aux pellicules minces limitées: caractéristiques du transfert de chaleur et de masse Type de document : texte imprimé Auteurs : Ruander Cardenas, Auteur ; Vinod Narayanan, Auteur Année de publication : 2011 Article en page(s) : pp. 113-128 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Absorber  Microchannel  Bubble  Ammonia–water Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : A study of absorption of ammonia vapour bubbles into a constrained thin-film of ammonia–water solution is presented. A large-aspect-ratio microchannel constrains the thickness of the weak solution film and ammonia vapour bubbles are injected from a porous wall. A counter flowing coolant in a minichannel removes the generated heat of absorption. Experiments and a simple one-dimensional numerical model are used to characterize the absorber performance at a nominal system pressure of 6.2 bar absolute. Effect of varying the mass flow rate of the weak solution, vapour flow rate, solution inlet temperature, and coolant inlet temperature on absorption heat and mass transfer rates and exit subcooling are discussed. Two absorber channel geometries, each of 600 μm nominal depth, are considered: 1) a smooth-wall channel, and 2) a stepped-wall channel that has 2-mm deep trenches across the width of a channel wall. Results indicate that the reduction in coolant inlet temperature significantly enhances the mass transfer rates in both absorber geometries. While the stepped-wall geometry exhibits higher mass transfer rates at lower coolant inlet temperatures of 30 °C and 40 °C, the smooth-wall channel shows higher mass transfer rates at the highest coolant inlet temperature of 58 °C. Both absorption limited and residence time limited conditions are observed with variation of weak solution flow rate at fixed vapour flow rates. DEWEY : 621.5 ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S0140700710001829 [article] Heat and mass transfer characteristics of a constrained thin-film ammonia–water bubble absorber = Absorbeur à bulles à ammoniac-eau aux pellicules minces limitées: caractéristiques du transfert de chaleur et de masse [texte imprimé] / Ruander Cardenas, Auteur ; Vinod Narayanan, Auteur . - 2011 . - pp. 113-128. Génie Mécanique Langues : Anglais (eng) in International journal of refrigeration > Vol. 34 N° 1 (Janvier 2011) . - pp. 113-128 Mots-clés : Absorber  Microchannel  Bubble  Ammonia–water Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : A study of absorption of ammonia vapour bubbles into a constrained thin-film of ammonia–water solution is presented. A large-aspect-ratio microchannel constrains the thickness of the weak solution film and ammonia vapour bubbles are injected from a porous wall. A counter flowing coolant in a minichannel removes the generated heat of absorption. Experiments and a simple one-dimensional numerical model are used to characterize the absorber performance at a nominal system pressure of 6.2 bar absolute. Effect of varying the mass flow rate of the weak solution, vapour flow rate, solution inlet temperature, and coolant inlet temperature on absorption heat and mass transfer rates and exit subcooling are discussed. Two absorber channel geometries, each of 600 μm nominal depth, are considered: 1) a smooth-wall channel, and 2) a stepped-wall channel that has 2-mm deep trenches across the width of a channel wall. Results indicate that the reduction in coolant inlet temperature significantly enhances the mass transfer rates in both absorber geometries. While the stepped-wall geometry exhibits higher mass transfer rates at lower coolant inlet temperatures of 30 °C and 40 °C, the smooth-wall channel shows higher mass transfer rates at the highest coolant inlet temperature of 58 °C. Both absorption limited and residence time limited conditions are observed with variation of weak solution flow rate at fixed vapour flow rates. DEWEY : 621.5 ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S0140700710001829

Submerged jet impingement boiling of water under subatmospheric conditions / Ruander Cardenas in Journal of heat transfer, Vol. 134 N° 2 (Fevrier 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 2 (Fevrier 2012) . - 08 p. Titre : Submerged jet impingement boiling of water under subatmospheric conditions Type de document : texte imprimé Auteurs : Ruander Cardenas, Auteur ; Vinod Narayanan, Auteur Année de publication : 2012 Article en page(s) : 08 p. Note générale : Heat transfer Langues : Anglais (eng) Mots-clés : Boiling  Heat  transfer  Jets  Surface  roughness  Water Index. décimale : 536 Chaleur. Thermodynamique Résumé : An experimental study of jet impingement boiling is presented for water under saturated and subcooled conditions. Unique to this study is the documentation of boiling curves of a submerged water jet under subatmospheric conditions. Data are reported at a fixed nondimensional nozzle-to-surface distance of H/dj = 6 and for a fixed surface-to-nozzle diameter ratio, dsurf/dj, of 23.8. Saturated jet impingement experiments are performed at three subatmospheric pool pressures of 0.176 bar, 0.276 bar, and 0.478 bar with corresponding saturation temperatures of 57.3 °C, 67.2 °C, and 80.2 °C. At each pressure, jet impingement boiling at varying Reynolds numbers are characterized and compared with pool boiling heat transfer. The effect of surface roughness and fluid subcooling is studied at the lowest pressure of 0.176 bar. Boiling curves indicate a strong dependence of heat flux on jet Reynolds number in the partially developed nucleate boiling region but only a weak dependence in the fully developed nucleate boiling region. At a fixed wall superheat, fluid subcooling is found to shift the boiling curve to the left thereby enhancing heat transfer performance. Critical heat flux is found to increase with increases in pressure, surface roughness, and Reynolds number. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000002 [...] [article] Submerged jet impingement boiling of water under subatmospheric conditions [texte imprimé] / Ruander Cardenas, Auteur ; Vinod Narayanan, Auteur . - 2012 . - 08 p. Heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 2 (Fevrier 2012) . - 08 p. Mots-clés : Boiling  Heat  transfer  Jets  Surface  roughness  Water Index. décimale : 536 Chaleur. Thermodynamique Résumé : An experimental study of jet impingement boiling is presented for water under saturated and subcooled conditions. Unique to this study is the documentation of boiling curves of a submerged water jet under subatmospheric conditions. Data are reported at a fixed nondimensional nozzle-to-surface distance of H/dj = 6 and for a fixed surface-to-nozzle diameter ratio, dsurf/dj, of 23.8. Saturated jet impingement experiments are performed at three subatmospheric pool pressures of 0.176 bar, 0.276 bar, and 0.478 bar with corresponding saturation temperatures of 57.3 °C, 67.2 °C, and 80.2 °C. At each pressure, jet impingement boiling at varying Reynolds numbers are characterized and compared with pool boiling heat transfer. The effect of surface roughness and fluid subcooling is studied at the lowest pressure of 0.176 bar. Boiling curves indicate a strong dependence of heat flux on jet Reynolds number in the partially developed nucleate boiling region but only a weak dependence in the fully developed nucleate boiling region. At a fixed wall superheat, fluid subcooling is found to shift the boiling curve to the left thereby enhancing heat transfer performance. Critical heat flux is found to increase with increases in pressure, surface roughness, and Reynolds number. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000002 [...]