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Transfert de chaleur d'évaporation d'un film d'eau tombant sur des tubes de transfert de chaleur de type "projection pyramidale" : effet du coefficient de transfert de chaleur sur le flux thermique et la visualisation des configurations d'écoulement.

Falling film evaporation heat transfer of water on pyramidal projection type enhanced heat transfer tubes: effect of evaporation heat transfer coefficient on heat flux and visualization of flow patterns.

Auteurs : TAKAHASHI H., KOYAMA S.

Résumé

The paper presents the experimental results of the falling film evaporation heat transfer of water on enhanced heat transfer tubes with pyramidal projection pitches of 19 and 26 projection lines-per-inch (ppi). The heat transfer performance test was carried out at evaporation vapour pressure of 0.8 kPa in water, outlet chilled water temperature of 5 to 7°C and refrigerant mass flow rate per unit length of 0.75 and 1.50 kg/(m.min). The outside heat transfer coefficient of the 26-ppi tube increased with a decrease in refrigerant mass flow rate, and also increased with an increase in heat flux. The outside heat transfer coefficient of the 19-ppi tube was lower than that for the 26-ppi tube at the low refrigerant mass flow rate, but increased with an increase of refrigerant mass flow rate in the high flux range. The liquid refrigerant flow conditions at the top of the tested tubes were observed at a frame rate of 500 frames per second using a high-speed video camera. It was confirmed from the visualization that the refrigerant formed a thinner liquid film on the projection top of the tested tubes when the liquid refrigerant fell on the tube surface and its falling speed at projections groove for the 19-ppi tube was higher than that for the 26-ppi tube.

Détails

  • Titre original : Falling film evaporation heat transfer of water on pyramidal projection type enhanced heat transfer tubes: effect of evaporation heat transfer coefficient on heat flux and visualization of flow patterns.
  • Identifiant de la fiche : 2007-1102
  • Langues : Anglais
  • Source : ACRA-2006. Proceedings of the 3rd Asian conference on refrigeration and air conditioning.
  • Date d'édition : 21/05/2006

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