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Caractéristiques du transfert de chaleur en ébullition convective d'ammoniac à l'intérieur de tubes de faible diamètre.

Flow boiling heat transfer characteristics of ammonia in horizontal small diameter tubes.

Numéro : pap. n. 240

Auteurs : CHEN S. W., TAKABAYASHI S., SAITO K., et al.

Résumé

In this study, the two-phase flow boiling pressure drop and heat transfer coefficient of ammonia refrigerant is examined, with horizontal small channel tubes, owing to its high efficiency and in consideration of environmental issues. Ammonia refrigerant is known to be environmentally friendly, having zero GWP and zero ODP, but has a high COP. This study involves experiments at evaporation temperatures from -10°C to +5°C, 10 to 40 kW/m2 heat flux, and 40 to 120 kg/m2s mass flux, with 1.0, 3.0 and 0.5 mm internal diameter tubes. The purposes of this study are to show the pressure drop and heat transfer coefficient of ammonia in two-phase conditions, such as those in slug flow, wavy-annular flow and bubble flow and then compare the results with reported correlations. It was found that the pressure drop has relationships with mass flux, evaporation temperature and heat flux, which has only a weak relationship with diameter. The heat transfer coefficient has a weak relationship with heat flux, mass flux, and evaporation temperature for the 3.0 mm tube, but has a strong relationship with heat flux and evaporation temperature for the 1.0 and 0.5 mm tube. The flow pattern images of the ammonia refrigerant, which were taken by a high-speed video camera, show that annular flow dominates from the low vapor quality region in the 1.0 mm tube.

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Pages : 8 p.

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Détails

  • Titre original : Flow boiling heat transfer characteristics of ammonia in horizontal small diameter tubes.
  • Identifiant de la fiche : 30004544
  • Langues : Anglais
  • Source : 10th IIR-Gustav Lorentzen Conference on Natural Working Fluids (GL2012). Proceedings. Delft, The Netherlands, June 25-27, 2012.
  • Date d'édition : 25/06/2012

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