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Flow modes and mode transitions for falling films on flat tubes / Xiaofei Wang 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) . - 09 p. Titre : Flow modes and mode transitions for falling films on flat tubes Type de document : texte imprimé Auteurs : Xiaofei Wang, Auteur ; P. S. Hrnjak, Auteur ; S. Elbel, Auteur Année de publication : 2012 Article en page(s) : 09 p. Note générale : Heat transfer Langues : Anglais (eng) Mots-clés : Drops  External  flows  Film  flow  Flow  instability  Flow  visualisation  Jets  Laminar  to  turbulent  transitions  Liquid  films  Pipe  flow  Two-phase  flow Index. décimale : 536 Chaleur. Thermodynamique Résumé : Flow mode transitions for a liquid film falling over flat tubes are studied for a wide range of conditions. Hydraulic oil, ethylene glycol, ethylene-glycol-water mixtures (at three different volume ratios), and water are used as working fluids in experiments conducted under adiabatic conditions, without an imposed vapor flow. The flow modes are observed over a range of flow rate and tube spacing. The flow modes are more complex but similar to those manifested on round tubes, and include the sheet, sheet-jet, jet, jet-droplet, and droplet modes. However, the transitions at Ga1/4 <= 16 (mainly for hydraulic oil, ethylene glycol) are very different from those on round tubes: there is no sheet-jet mode during transition between the sheet and jet flow modes. Moreover, at all Ga, the Re range over which the jet mode occurs is narrower than that for round tubes, and the hysteresis in mode transitions is not as pronounced as for round tubes. The transitional Re increases slowly with tube spacing, also in contrast to observations of round-tube falling films. The flat-tube falling-film flow regimes are described, and new correlations are provided to relate the transitional Re number to Ga and geometry. By analyzing repeated experiments, it is shown that the standard deviation of the measurements from the correlations is less than 5.2%. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000002 [...] [article] Flow modes and mode transitions for falling films on flat tubes [texte imprimé] / Xiaofei Wang, Auteur ; P. S. Hrnjak, Auteur ; S. Elbel, Auteur . - 2012 . - 09 p. Heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 2 (Fevrier 2012) . - 09 p. Mots-clés : Drops  External  flows  Film  flow  Flow  instability  Flow  visualisation  Jets  Laminar  to  turbulent  transitions  Liquid  films  Pipe  flow  Two-phase  flow Index. décimale : 536 Chaleur. Thermodynamique Résumé : Flow mode transitions for a liquid film falling over flat tubes are studied for a wide range of conditions. Hydraulic oil, ethylene glycol, ethylene-glycol-water mixtures (at three different volume ratios), and water are used as working fluids in experiments conducted under adiabatic conditions, without an imposed vapor flow. The flow modes are observed over a range of flow rate and tube spacing. The flow modes are more complex but similar to those manifested on round tubes, and include the sheet, sheet-jet, jet, jet-droplet, and droplet modes. However, the transitions at Ga1/4 <= 16 (mainly for hydraulic oil, ethylene glycol) are very different from those on round tubes: there is no sheet-jet mode during transition between the sheet and jet flow modes. Moreover, at all Ga, the Re range over which the jet mode occurs is narrower than that for round tubes, and the hysteresis in mode transitions is not as pronounced as for round tubes. The transitional Re increases slowly with tube spacing, also in contrast to observations of round-tube falling films. The flat-tube falling-film flow regimes are described, and new correlations are provided to relate the transitional Re number to Ga and geometry. By analyzing repeated experiments, it is shown that the standard deviation of the measurements from the correlations is less than 5.2%. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000002 [...]