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Communication Dans Un Congrès Année : 2012

Experimental investigation on the local curvature of bubble interface during boiling on a single nucleation site

Résumé

The current study presents an investigation on the local curvature of the bubble interface and its relation to local bubble growth regimes and bubble detachment. An experimental facility has been built in order to produce bubbles by nucleatingon a 180 micrometer diameter artificial nucleation site on a horizontal copper surface. The copper surface was heated from bellow with a copper rod which was equipped with thermocouples in order to measure the heat flux and the surface temperature. The whole test sample was immersed in a large volume of saturated degassed n-pentane at atmospheric pressure. In order to observe and analyse the boiling phenomenon, high speed videography was used. A short focal objective was employed in order to accurately capture the bubble contour. An image processing code has been developed using Matlab commercial software. It allows the determination of the local curvature of the bubble interface through the two main radii of curvature. The bubble volume and the height of the center of gravity were also measured as a function of time. The different phases of bubble growth were thus identified for the analysis of the interface curvature. The evolution of the curvature at the apex of the bubble reflects the evolution of the vapour pressure inside the bubble. The relation between the vapour pressure evolution and the growth phases of the bubble is investigated. It is shown that inertia plays a negligible role and that bubble growth is dictated by thermal diffusion considerations. The measured curvature profile along the bubble has been compared to the hydrostatic Young-Laplace curvature relation. The theoretical relation predicts a linear and almost constant curvature profile along the vertical axis, with a higher curvature at the apex of the bubble. Such a curvature profile is observed during the first instant of the bubble growth. After 20 % of the total growth time, for all different superheat conditions, the bubble starts forming a neck. The presence of the neck imposes a higher curvature at the base of the bubble, close to the triple contact line. The curvature profile is thus strongly modified, showing a constant curvature only on the upper part of the bubble with an increasing curvature when approaching the bubble base. Just prior to bubble departure, the measured curvature close to the bubble base suddenly increases and seems to diverge. The observation is relevant with regard to the mechanism of bubble detachment. The departure of the bubble is more strongly related to a break-up of its neck than to a detachment of the triple contact line. A deeper analysis of this break-up mechanism is needed in order to provide an accurate prediction of the bubble departure volume.
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Dates et versions

hal-01025474 , version 1 (17-07-2014)

Identifiants

  • HAL Id : hal-01025474 , version 1

Citer

Samuel Siedel, Serge Cioulachtjian, Sergio Di Bari, Anthony Robinson, Jocelyn Bonjour. Experimental investigation on the local curvature of bubble interface during boiling on a single nucleation site. ECI 8th International Conference on Boiling and Condensation Heat Transfer, Jun 2012, Lausanne, Switzerland. pp.13. ⟨hal-01025474⟩
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