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Investigation of pool boiling critical heat flux enhancement on a modified surface through the dynamic wetting of water droplets / Ho Seon Ahn in Journal of heat transfer, Vol. 134 N° 7 (Juillet 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 7 (Juillet 2012) . - 13 p. Titre : Investigation of pool boiling critical heat flux enhancement on a modified surface through the dynamic wetting of water droplets Type de document : texte imprimé Auteurs : Ho Seon Ahn, Auteur ; Joonwon Kim, Auteur ; Moo Hwan Kim, Auteur Année de publication : 2012 Article en page(s) : 13 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : pool  boiling;  critical  heat  flux;  dynamic  wetting;  microstructure;  nanostructure Index. décimale : 536 Chaleur. Thermodynamique Résumé : Dynamic wetting behaviors of water droplet on the modified surface were investigated experimentally. Dynamic contact angles were measured as a characterization method to explain the extraordinary pool boiling critical heat flux (CHF) enhancement on the zirconium surface by anodic oxidation modification. The sample surface is rectangular zirconium alloy plates (20 × 25 × 0.7 mm), and 12 µl of deionized water droplets were fallen from 40 mm of height over the surface. Dynamic wetting movement of water on the surface showed different characteristics depending on static contact angle (49.3 deg–0 deg) and surface temperature (120 °C–280 °C). Compared with bare surface, wettable and spreading surface had no-receding contact angle jump and seemed stable evaporating meniscus of liquid droplet in dynamic wetting condition on hot surface. This phenomenon could be explained by the interaction between the evaporation recoil and the surface tension forces. The surface tension force increased by micro/nanostructure of the modified zirconium surface suppresses the vapor recoil force by evaporation which makes the water layer unstable on the heated surface. Thus, such increased surface force could sustain the water layer stable in pool boiling CHF condition so that the extraordinary CHF enhancement could be possible. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000007 [...] [article] Investigation of pool boiling critical heat flux enhancement on a modified surface through the dynamic wetting of water droplets [texte imprimé] / Ho Seon Ahn, Auteur ; Joonwon Kim, Auteur ; Moo Hwan Kim, Auteur . - 2012 . - 13 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 7 (Juillet 2012) . - 13 p. Mots-clés : pool  boiling;  critical  heat  flux;  dynamic  wetting;  microstructure;  nanostructure Index. décimale : 536 Chaleur. Thermodynamique Résumé : Dynamic wetting behaviors of water droplet on the modified surface were investigated experimentally. Dynamic contact angles were measured as a characterization method to explain the extraordinary pool boiling critical heat flux (CHF) enhancement on the zirconium surface by anodic oxidation modification. The sample surface is rectangular zirconium alloy plates (20 × 25 × 0.7 mm), and 12 µl of deionized water droplets were fallen from 40 mm of height over the surface. Dynamic wetting movement of water on the surface showed different characteristics depending on static contact angle (49.3 deg–0 deg) and surface temperature (120 °C–280 °C). Compared with bare surface, wettable and spreading surface had no-receding contact angle jump and seemed stable evaporating meniscus of liquid droplet in dynamic wetting condition on hot surface. This phenomenon could be explained by the interaction between the evaporation recoil and the surface tension forces. The surface tension force increased by micro/nanostructure of the modified zirconium surface suppresses the vapor recoil force by evaporation which makes the water layer unstable on the heated surface. Thus, such increased surface force could sustain the water layer stable in pool boiling CHF condition so that the extraordinary CHF enhancement could be possible. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000007 [...]

On the mechanism of pool boiling critical heat flux enhancement in nanofluids / Hyungdae Kim in Journal of heat transfer, Vol. 132 N° 6 (Juin 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061501-1/11] Titre : On the mechanism of pool boiling critical heat flux enhancement in nanofluids Type de document : texte imprimé Auteurs : Hyungdae Kim, Auteur ; Ho Seon Ahn, Auteur ; Moo Hwan Kim, Auteur Article en page(s) : pp. [061501-1/11] Note générale : Physique Langues : Anglais (eng) Mots-clés : Critical  heat  flux  Evaporating  meniscus  Nanoparticle  deposition  Wetting Index. décimale : 536 Chaleur. Thermodynamique Résumé : The pool boiling characteristics of water-based nanofluids with alumina and titania nanoparticles of 0.01 vol % were investigated on a thermally heated disk heater at saturated temperature and atmospheric pressure. The results confirmed the findings of previous studies that nanofluids can significantly enhance the critical heat flux (CHF), resulting in a large increase in the wall superheat. It was found that some nanoparticles deposit on the heater surface during nucleate boiling, and the surface modification due to the deposition results in the same magnitude of CHF enhancement in pure water as for nanofluids. Subsequent to the boiling experiments, the interfacial properties of the heater surfaces were examined using dynamic wetting of an evaporating water droplet. As the surface temperature increased, the evaporating meniscus on the clean surface suddenly receded toward the liquid due to the evaporation recoil force on the liquid-vapor interface, but the nanoparticle-fouled surface exhibited stable wetting of the liquid meniscus even at a remarkably higher wall superheat. The heat flux gain attainable due to the improved wetting of the evaporating meniscus on the fouled surface showed good agreement with the CHF enhancement during nanofluid boiling. It is supposed that the nanoparticle layer increases the stability of the evaporating microlayer underneath a bubble growing on a heated surface and thus the irreversible growth of a hot/dry spot is inhibited even at a high wall superheat, resulting in the CHF enhancement observed when boiling nanofluids. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] On the mechanism of pool boiling critical heat flux enhancement in nanofluids [texte imprimé] / Hyungdae Kim, Auteur ; Ho Seon Ahn, Auteur ; Moo Hwan Kim, Auteur . - pp. [061501-1/11]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 6 (Juin 2010) . - pp. [061501-1/11] Mots-clés : Critical  heat  flux  Evaporating  meniscus  Nanoparticle  deposition  Wetting Index. décimale : 536 Chaleur. Thermodynamique Résumé : The pool boiling characteristics of water-based nanofluids with alumina and titania nanoparticles of 0.01 vol % were investigated on a thermally heated disk heater at saturated temperature and atmospheric pressure. The results confirmed the findings of previous studies that nanofluids can significantly enhance the critical heat flux (CHF), resulting in a large increase in the wall superheat. It was found that some nanoparticles deposit on the heater surface during nucleate boiling, and the surface modification due to the deposition results in the same magnitude of CHF enhancement in pure water as for nanofluids. Subsequent to the boiling experiments, the interfacial properties of the heater surfaces were examined using dynamic wetting of an evaporating water droplet. As the surface temperature increased, the evaporating meniscus on the clean surface suddenly receded toward the liquid due to the evaporation recoil force on the liquid-vapor interface, but the nanoparticle-fouled surface exhibited stable wetting of the liquid meniscus even at a remarkably higher wall superheat. The heat flux gain attainable due to the improved wetting of the evaporating meniscus on the fouled surface showed good agreement with the CHF enhancement during nanofluid boiling. It is supposed that the nanoparticle layer increases the stability of the evaporating microlayer underneath a bubble growing on a heated surface and thus the irreversible growth of a hot/dry spot is inhibited even at a high wall superheat, resulting in the CHF enhancement observed when boiling nanofluids. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]

A review on critical heat flux enhancement with nanofluids and surface modification / Ho Seon Ahn 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) . - 13 p. Titre : A review on critical heat flux enhancement with nanofluids and surface modification Type de document : texte imprimé Auteurs : Ho Seon Ahn, Auteur ; Moo Hwan Kim, Auteur Année de publication : 2012 Article en page(s) : 13 p. Note générale : Heat transfer Langues : Anglais (eng) Mots-clés : Boiling  Heat  transfer  Nanofluidics  Surface  phenomena Index. décimale : 536 Chaleur. Thermodynamique Résumé : Recently, there has been increasing interest in boiling nanofluids and their applications. Among the many articles that have been published, the critical heat flux (CHF) of nanofluids has drawn special attention because of its dramatic enhancement. This article includes recent studies on CHF increasing during the past decade by various researchers for both pool boiling and convective flow boiling applications using nanofluids as the working fluid. It presents a review of nanofluid critical heat flux research with the aim of identifying the reasons for its enhancement and the limitations of nanofluid applications based on various published reports. In addition, further research required to make use of the CHF enhancement caused by nanofluids for practical applications is discussed. Finally, the surface modification method with micro/nanostructures to increase the CHF is introduced and recommended as a useful way. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000002 [...] [article] A review on critical heat flux enhancement with nanofluids and surface modification [texte imprimé] / Ho Seon Ahn, Auteur ; Moo Hwan Kim, Auteur . - 2012 . - 13 p. Heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 2 (Fevrier 2012) . - 13 p. Mots-clés : Boiling  Heat  transfer  Nanofluidics  Surface  phenomena Index. décimale : 536 Chaleur. Thermodynamique Résumé : Recently, there has been increasing interest in boiling nanofluids and their applications. Among the many articles that have been published, the critical heat flux (CHF) of nanofluids has drawn special attention because of its dramatic enhancement. This article includes recent studies on CHF increasing during the past decade by various researchers for both pool boiling and convective flow boiling applications using nanofluids as the working fluid. It presents a review of nanofluid critical heat flux research with the aim of identifying the reasons for its enhancement and the limitations of nanofluid applications based on various published reports. In addition, further research required to make use of the CHF enhancement caused by nanofluids for practical applications is discussed. Finally, the surface modification method with micro/nanostructures to increase the CHF is introduced and recommended as a useful way. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000002 [...]