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Saturated flow boiling of water in a narrow channel: time-averaged heat transfer coefficients and correlations.

Author(s) : WEN D. S., YAN Y., KENNING D. B. R.

Type of article: Article

Summary

Time-averaged local heat transfer coefficients were measured during flow boiling of water at atmospheric pressure in a vertical channel of rectangular cross-section 2 mm by 1 mm for ranges of mass flux 57-211 kg/m² s, heat flux 27-160 kW/m², thermodynamic quality 0-0.3 and inlet subcooling 1-12 K. The heat transfer coefficients were found to increase nearly with the square root of the heat flux. There was little effect of mass flux at 107, 134 and 211 kg/m² s; lower heat transfer coefficients at 57 kg/m² s were probably due to transient local dryout. Local time-averaged quality and different inlet conditions of subcooling and compressibility had little effect. Conventionally, this behaviour would be interpreted as nucleate boiling and a dimensional expression correlated the data to ±20%. However, the heat transfer coefficients were considerably higher than would be expected for pool nucleate boiling and visual observation showed local time-sharing between nucleate boiling and thin-film evaporation without nucleation, with only small temporal changes in the heat transfer coefficient. Eleven correlations for conventional and narrow-channel boiling predicted the data poorly, ranging from 250% average over-prediction to 70% average under-prediction. This suggests that conventional methods of distinguishing between nucleate and convective boiling mechanisms are unreliable and that a better understanding of the mechanisms of boiling in narrow channels is necessary to guide the development of correlations.

Details

  • Original title: Saturated flow boiling of water in a narrow channel: time-averaged heat transfer coefficients and correlations.
  • Record ID : 2004-2736
  • Languages: English
  • Source: Applied Thermal Engineering - vol. 24 - n. 8-9
  • Publication date: 2004/06

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