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Natural convective heat transfer near the critical state.

Author(s) : GORENFLO D., BAUMHOEGGER E., HERRES G.

Summary

The use of carbon dioxide (CO2) as refrigerant has stimulated increased interest in heat transfer near the critical state. In general, experimental results for this region differ significantly from those far from it because some fluid properties - e.g. density or specific enthalpy - vary much more near the critical state than in greater distance at a given isobaric driving temperature difference. In this paper, measurements for natural convective heat transfer from an electrically heated copper tube with 25 mm O.D. to refrigerant R125 are discussed for fluid states very close to the critical point and in greater distance, and for both, two-phase or single-phase heat transfer at pressures slightly below or above critical. Particular attention is given to circumferential variations of the isobaric wall superheat in different regions of the fluid state. It is shown that heat transfer for film boiling slightly below or for free convection slightly above the critical pressure are very similar, because the same great variations of the important properties are dominating in both cases at small superheats of the wall, and because also at high superheats, variations of the properties between bulk fluid and heated wall are similar. From an additional comparison with former experimental data, it can be concluded that the principle of corresponding states in its simplest form is perfectly suited to directly transfer the results to CO2.

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Pages: 2009-5

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Details

  • Original title: Natural convective heat transfer near the critical state.
  • Record ID : 2009-1914
  • Languages: English
  • Source: 3rd Conference on Thermophysical Properties and Transfer Processes of Refrigerants
  • Publication date: 2009/06/23

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