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Dryout-type critical heat flux in vertical upward annular flow : effects of entrainment rate, initial entrained fraction and diameter

Wu, Zan LU ; Wadekar, Vishwas; Wang, Chenglong LU and Sunden, Bengt LU (2017) In Warme - Und Stoffubertragung
Abstract

This study aims to reveal the effects of liquid entrainment, initial entrained fraction and tube diameter on liquid film dryout in vertical upward 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 water and organic liquids including n-pentane, iso-octane and R134a. Effect of the initial entrained fraction (IEF) at the churn-to-annular flow transition was also investigated. A transitional Boiling number was proposed to separate the IEF-sensitive region at high Boiling numbers... (More)

This study aims to reveal the effects of liquid entrainment, initial entrained fraction and tube diameter on liquid film dryout in vertical upward 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 water and organic liquids including n-pentane, iso-octane and R134a. Effect of the initial entrained fraction (IEF) at the churn-to-annular flow transition was also investigated. A transitional Boiling number was proposed to separate the IEF-sensitive region at high Boiling numbers and the IEF-insensitive region at low Boiling numbers. Besides, the diameter effect on dryout vapor quality was studied. The dryout vapor quality increases with decreasing tube diameter. It needs to be pointed out that the dryout characteristics of submillimeter channels might be different because of different mechanisms of dryout, i.e., drying of liquid film underneath long vapor slugs and flow boiling instabilities.

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author
organization
publishing date
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Contribution to journal
publication status
epub
subject
in
Warme - Und Stoffubertragung
pages
10 pages
publisher
Springer
external identifiers
  • scopus:85023756779
ISSN
0947-7411
DOI
10.1007/s00231-017-2099-z
language
English
LU publication?
yes
id
22ac37a7-b7b1-428b-9dd2-6141a24e6f0e
date added to LUP
2017-07-27 09:54:52
date last changed
2017-07-27 09:54:52
@article{22ac37a7-b7b1-428b-9dd2-6141a24e6f0e,
  abstract     = {<p>This study aims to reveal the effects of liquid entrainment, initial entrained fraction and tube diameter on liquid film dryout in vertical upward 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 water and organic liquids including n-pentane, iso-octane and R134a. Effect of the initial entrained fraction (IEF) at the churn-to-annular flow transition was also investigated. A transitional Boiling number was proposed to separate the IEF-sensitive region at high Boiling numbers and the IEF-insensitive region at low Boiling numbers. Besides, the diameter effect on dryout vapor quality was studied. The dryout vapor quality increases with decreasing tube diameter. It needs to be pointed out that the dryout characteristics of submillimeter channels might be different because of different mechanisms of dryout, i.e., drying of liquid film underneath long vapor slugs and flow boiling instabilities.</p>},
  author       = {Wu, Zan and Wadekar, Vishwas and Wang, Chenglong and Sunden, Bengt},
  issn         = {0947-7411},
  language     = {eng},
  month        = {07},
  pages        = {10},
  publisher    = {Springer},
  series       = {Warme - Und Stoffubertragung},
  title        = {Dryout-type critical heat flux in vertical upward annular flow : effects of entrainment rate, initial entrained fraction and diameter},
  url          = {http://dx.doi.org/10.1007/s00231-017-2099-z},
  year         = {2017},
}