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On the effects of thermocapillary driven oscillations on bubble growth during boiling of FC-72 on a thin wire

Research output: Contribution to journalArticle

Original languageEnglish
Pages (from-to)1809-1819
Number of pages11
JournalInternational Journal of Thermal Sciences
Volume50
Issue number10
DOIs
Publication statusPublished - Oct 2011

Abstract

Despite being a familiar and well-studied topic, the physical nature of boiling is still not well understood. There is a complex coupling of mass, momentum and energy transport that occurs between the solid surface, the wetting liquid and the vapour produced to generate bubbles. Our work investigated pool boiling of FC-72, a highly-wetting dielectric liquid, on a submerged electrically-heated platinum wire. The bulk fluid temperatures ranged from ambient to saturation allowing a range of subcooled and saturated boiling scenarios to be investigated. The boiling chamber could be pressurised and boiling of FC-72 was studied for pressures from 1-3 bar. High-speed digital video was used to record boiling phenomena and these were subsequently analysed. Thermocapillary convection was clearly visible and more noticeable as the degree of subcooling increased. Once vapour bubbles were initialised at a nucleation site, their growth and detachment frequency were recorded. Frequency was correlated with degree of subcooling and a power-law dependence established. After detachment, not all bubbles immediately rose to the surface. There was bubble slippage along the wire, driven by the distortions in the local temperature field. Slippage was also influenced by the presence of adjacent nucleation sites and bubbles (which themselves also influenced the local temperature field). The observed thermocapillary "tails" of the bubbles were affected by bubble motion. The slip velocity was plotted for the case of pure translational motion and also for periodic motion between nucleation sites. Oscillating bubbles are found to grow faster than stationary bubbles. This is attributed to the contribution of the superheated layer, which was measured and discussed. A form of the law for the growth of oscillating bubbles was proposed. Horizontal coalescence of two bubbles drawn towards each other is also presented and analysed. (C) 2011 Elsevier Masson SAS. All rights reserved.

    Research areas

  • Boiling heat transfer, Thermocapillaty effect, FC-72, Bubble growth, Bubble oscillation, HEAT-TRANSFER, FLOW

ID: 1363306