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Title: Experimental study on bubble dynamics and wall heat transfer arising from a single nucleation site at subcooled flow boiling conditions – Part 2: Data analysis on sliding bubble characteristics and associated wall heat transfer

In this second of two companion papers presents an analysis of sliding bubble and wall heat transfer parameters measured during subcooled boiling in a square, vertical, upward flow channel. Bubbles were generated only from a single nucleation site for better observation of both the sliding bubbles’ characteristics and their impact on wall heat transfer through optical measurement techniques. Specific interests include: (i) bubbles departure and subsequent growth while sliding, (ii) bubbles release frequency, (iii) coalescence of sliding bubbles, (iv) sliding bubbles velocity, (v) bubbles size distribution and (vi) wall heat transfer influenced by sliding bubbles. Our results showed that sliding bubbles involve two distinct growth behaviors: (i) at low mass fluxes, sliding bubbles grew fast near the nucleation site, subsequently shrank, and then grew again, (ii) as mass flux increased, however, sliding bubbles grew more steadily. The bubbles originating from the single nucleation site coalesced frequently while sliding, which showed close relation with bubbles release frequency. The sliding bubble velocity near the nucleation site consistently decreased by increasing mass flux, while the observation often became reversed as the bubbles slid downstream due to the effect of interfacial drag. The sliding bubbles moved faster than the local liquid (i.e., ur<0) atmore » low mass flux conditions, but it became reversed as the mass flux increased. The size distribution of sliding bubbles followed Gaussian distribution well both near and far from the nucleation site. The standard deviation of bubble size varied insignificantly through sliding compared to the changes in mean bubble size. Lastly, the sliding bubbles enhanced the wall heat transfer and the effect became more noticeable as inlet subcooling/mass flux decreased or wall heat flux increased. Particularly, the sliding bubble characteristics such as bubble growth behavior observed near the nucleation site played a dominant role in determining the ultimate level of wall heat transfer enhancement within the test channel.« less
Authors:
 [1] ;  [2] ;  [3]
  1. Idaho National Lab. (INL), Idaho Falls, ID (United States)
  2. Texas A & M Univ., College Station, TX (United States). Dept. of Mechanical Engineering
  3. Texas A & M Univ., College Station, TX (United States). Dept. of Mechanical Engineering, Dept. of Nuclear Engineering
Publication Date:
Report Number(s):
INL/JOU-16-38275
Journal ID: ISSN 0301-9322; PII: S0301932215302251
Grant/Contract Number:
AC07-05ID14517; AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
International Journal of Multiphase Flow
Additional Journal Information:
Journal Volume: 84; Journal Issue: C; Journal ID: ISSN 0301-9322
Publisher:
Elsevier
Research Org:
Idaho National Lab. (INL), Idaho Falls, ID (United States)
Sponsoring Org:
USDOE Office of Nuclear Energy (NE)
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; boiling heat transfer; bubble coalescence; bubble size distribution; bubble sliding; single nucleation site; sliding bubble velocity; subcooled flow boiling
OSTI Identifier:
1357617
Alternate Identifier(s):
OSTI ID: 1326697