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Effect of Entrainment on Liquid Film Dryout in Vertical Upward Annular Flow

[+] Author Affiliations
Zan Wu, Bengt Sundén

Lund University, Lund, Sweden

Vishwas Wadekar

PS2E Institute, Jouy-en-Josas, France

Paper No. HT2016-7042, pp. V002T08A001; 8 pages
  • ASME 2016 Heat Transfer Summer Conference collocated with the ASME 2016 Fluids Engineering Division Summer Meeting and the ASME 2016 14th International Conference on Nanochannels, Microchannels, and Minichannels
  • Volume 2: Heat Transfer in Multiphase Systems; Gas Turbine Heat Transfer; Manufacturing and Materials Processing; Heat Transfer in Electronic Equipment; Heat and Mass Transfer in Biotechnology; Heat Transfer Under Extreme Conditions; Computational Heat Transfer; Heat Transfer Visualization Gallery; General Papers on Heat Transfer; Multiphase Flow and Heat Transfer; Transport Phenomena in Manufacturing and Materials Processing
  • Washington, DC, USA, July 10–14, 2016
  • Conference Sponsors: Heat Transfer Division
  • ISBN: 978-0-7918-5033-6
  • Copyright © 2016 by ASME


This work aims to investigate the effect of liquid entrainment on liquid film dryout in annular flow for flow boiling. Entrainment and deposition rates of droplets were included in mass conservation equations to estimate the local liquid film mass flux in annular flow, and the critical vapor quality at dryout conditions. Different entrainment rate correlations were evaluated using flow boiling data of n-pentane, iso-octane and water. Effect of the initial entrained fraction (IEF) at the churn-annular transition was also investigated. A transition Boiling number was proposed to separate the IEF-sensitive region at high Boiling numbers and the IEF-insensitive region low Boiling numbers. Besides, the diameter effect on dryout vapor quality was studied. The dryout vapor quality increases with decreasing tube diameter. A possible reason is that there is less droplet entrainment in smaller tubes, as evidenced in numerous flow pattern visualization studies. It needs to be pointed out that the dryout characteristics of submillimeter channels to be different because of different mechanisms of dryout, i.e., drying of liquid film underneath long vapor slugs and flow boiling instabilities.

Copyright © 2016 by ASME



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