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Heat transfer of condensation in smooth round tube from superheated vapor.

Number: pap. 2078

Author(s) : XIAO J., HRNJAK P.

Summary

Heat transfer of R134a condensing in a horizontal smooth round tube with 6.1 mm inner diameter is investigated in this study. The paper presents heat transfer measurement with mass flux from 50 to 200 kg m-2 s-1 and heat flux from 5 to 15 kW m-2, showing the effect of mass flux and heat flux on the heat transfer coefficient (HTC). All the measurement is taken at constant pressure of 1.319 MPa, which corresponds to a saturation temperature of 50°C. By connecting heat transfer result with flow characterization, the behavior of HTC is explained from the perspectives of both mathematics and physics. The result shows that for fixed heat flux and different mass flux, even though the liquid film for larger mass flux is much thinner in the condensing superheated (CSH) region, the HTC is not affected by mass flux. In the two-phase (TP) region, however, higher mass flux clearly yields higher HTC. Opposite behavior is found when heat flux is varied and mass flux is fixed. In the CSH region, the HTC increases with heat flux, while in the TP region, HTC does not change with heat flux. For both cases, a peak of HTC is presented at quality one, which seems to imply some counter-acting factors that always put heat transfer largest at quality one. The counter-acting factors, however, should not exist based on flow characterization. After mathematically explaining the behavior of HTC in the CSH region, a newly defined HTC named as film HTC (HTCf) is proposed and ready to serve as a tool in a unified heat transfer model throughout the entire CSH and TP regions.

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Pages: 9

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Details

  • Original title: Heat transfer of condensation in smooth round tube from superheated vapor.
  • Record ID : 30018981
  • Languages: English
  • Source: 2016 Purdue Conferences. 16th International Refrigeration and Air-Conditioning Conference at Purdue.
  • Publication date: 2016/07/11

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