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Entropy generation during flow boiling of synthetic refrigerants.

Author(s) : REVELLIN R., BONJOUR J.

Summary

In general, enhanced tubes are used in evaporators in order to increase their heat transfer performances. Enhanced tubes also induce an increase of the pressure drop along the evaporator and, as a consequence, the decrease of the saturation temperature is higher than that observed with smooth tubes. An important question is therefore: "Are enhanced tubes thermodynamically always better than smooth tubes?" In order to answer this question, the relations (using the separated and the mixture models) developed by Revellin et al. (2009) for calculating the local entropy generation of a diabatic two-phase flow have been applied to an evaporator. Its length is fixed to 5 m; the fluid is R134a. The heat flux is assumed uniform along the evaporator and both smooth and enhanced tubes have been considered. It appears that enhanced tubes are not always thermodynamically the best solution. Furthermore, reducing the tube diameters seems to be a good solution for reducing entropy generation and, as a consequence, for reducing the refrigerant charge.

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Details

  • Original title: Entropy generation during flow boiling of synthetic refrigerants.
  • Record ID : 2009-1462
  • Languages: English
  • Source: RCR 2009. 1st IIR Workshop on Refrigerant Charge Reduction in Refrigerating Systems.
  • Publication date: 2009/04/06

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