ISSN Online: 2377-424X
ISBN Print: 978-1-56700-421-2
International Heat Transfer Conference 15
Nucleation Site Interactions in Upward Flow Boiling Experiments
Sinopsis
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.