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

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

Flow boiling visualization of R-134a in a vertical channel of small diameter / Claudi Martín-Callizo in Journal of heat transfer, Vol. 132 N° 3 (Mars 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 3 (Mars 2010) . - pp. [031503-1/8] Titre : Flow boiling visualization of R-134a in a vertical channel of small diameter Type de document : texte imprimé Auteurs : Claudi Martín-Callizo, Auteur ; Björn Palm, Auteur ; Wahib Owhaib, Auteur Article en page(s) : pp. [031503-1/8] Note générale : Physique Langues : Anglais (eng) Mots-clés : Flow  boiling  Two-phase  Flow  patterns  Microchannel  Refrigerant  R-134a Index. décimale : 536 Chaleur. Thermodynamique Résumé : The present work reports on flow boiling visualization of refrigerant R-134a in a vertical circular channel with an internal diameter of 1.33 mm and 235 mm in heated length. A quartz tube with a homogeneous Indium Tin Oxide coating is used to allow heating and simultaneous visualization. Flow patterns have been observed along the heated length with the aid of high-speed complementary metal oxide semiconductor (CMOS) digital camera. From the flow boiling visualization, seven distinct two-phase flow patterns have been observed: isolated bubbly flow, confined bubbly flow, slug flow, churn flow, slug-annular flow, annular flow, and mist flow. Two-phase flow pattern observations are presented in the form of flow pattern maps. The effects of the saturation temperature and the inlet subcooling degree on the two-phase flow pattern transitions are elucidated. Finally, the experimental flow pattern map is compared with models developed for conventional sizes as well as to a microscale map for air-water mixtures available in literature, showing a large discrepancy. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Flow boiling visualization of R-134a in a vertical channel of small diameter [texte imprimé] / Claudi Martín-Callizo, Auteur ; Björn Palm, Auteur ; Wahib Owhaib, Auteur . - pp. [031503-1/8]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 3 (Mars 2010) . - pp. [031503-1/8] Mots-clés : Flow  boiling  Two-phase  Flow  patterns  Microchannel  Refrigerant  R-134a Index. décimale : 536 Chaleur. Thermodynamique Résumé : The present work reports on flow boiling visualization of refrigerant R-134a in a vertical circular channel with an internal diameter of 1.33 mm and 235 mm in heated length. A quartz tube with a homogeneous Indium Tin Oxide coating is used to allow heating and simultaneous visualization. Flow patterns have been observed along the heated length with the aid of high-speed complementary metal oxide semiconductor (CMOS) digital camera. From the flow boiling visualization, seven distinct two-phase flow patterns have been observed: isolated bubbly flow, confined bubbly flow, slug flow, churn flow, slug-annular flow, annular flow, and mist flow. Two-phase flow pattern observations are presented in the form of flow pattern maps. The effects of the saturation temperature and the inlet subcooling degree on the two-phase flow pattern transitions are elucidated. Finally, the experimental flow pattern map is compared with models developed for conventional sizes as well as to a microscale map for air-water mixtures available in literature, showing a large discrepancy. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]