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International Heat Transfer Conference 15

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

Nucleation Site Interactions in Upward Flow Boiling Experiments

Coen H.M. Baltis
Department of Mechanical Engineering, Eindhoven University of Technology, Den Dolech 2, 5612 AZ Eindhoven, The Netherlands

Cees W. M. van der Geld
Department of Mechanical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands

DOI: 10.1615/IHTC15.tpb.008598
pages 8331-8344


KEY WORDS: Two-phase/Multiphase flow, Boiling and evaporation, Nucleation site interactions

Abstract

The influence of vertically aligned nucleation sites on each other in upward flow boiling, which has never been investigated before, is the main topic of this paper. A setup was constructed to facilitate a vertical up-flow of deminiralized water under saturation conditions. The main test section is a glass channel with a set of vertically aligned bubble generators. Each bubble generator is operated independently, where power and wall temperature are registered and the vapour bubbles are visualized by a high-speed camera. During the experiments, the downstream bubble generator (BG1) power is kept constant, while the power fed to the upstream bubble generator (BG2) is incrementally increased. Two main trends have been identified. The first trend is dominated by added convection from one site to the other. Both bubble frequency and detachment diameter on BG1 increase with increased power fed to the upstream bubble generator. This effect decreases with increasing inter-site distance. When vapour bubbles start nucleating from BG2, these vapour bubbles actually prove to be inhibitive for bubble nucleation at a downstream bubble generator and can even lead to deactivation of this nucleation site. This second trend is only weakly dependent on inter-site distance, since the inhibition originates from bubbles flowing past BG1 in close proximity. Both trends become less significant if the bubble frequency of the downstream nucleation site is increased. This is easily understood from the fact that bubbles from BG1 divert both heat and approaching bubbles from BG2 away from the wall.

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