DTA

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Tesi etd-11202023-173544

Type of thesis
Corso Ordinario Secondo Livello
Author
REGOLI, IACOPO
URN
etd-11202023-173544
Title
Experimental Study of Boiling: Effect of artificial cavity on the microlayer and contact line dynamics at bubble growth in nucleate boiling
Structure
Cl. Sc. Sperimentali - Ingegneria
Course
INGEGNERIA - INGEGNERIA
Committee
relatore Prof. CIARAMELLA, ERNESTO
Relatore Dott. TECCHIO, CASSIANO
Membro Prof. SOLAZZI, MASSIMILIANO
Membro Prof. CIPRIANI, CHRISTIAN
Membro Prof. FONTANA, MARCO
Membro Prof.ssa niero, monia
Membro Prof. ODDO, CALOGERO MARIA
Membro Prof. SABATINI, ANGELO MARIA
Keywords
  • Boiling
  • Bubble Dynamics
  • Microlayer
  • Near-Wall Phoenomena
  • White Light Interferometry
Exam session start date
15/12/2023;
Availability
parziale
Abstract
We report an experimental study on the near-wall phenomena during the growth of a single bubble in saturated pool boiling of water at atmospheric pressure. Our focus is on the dynamics of triple contact line and liquid microlayer that can form between the heater and the liquid-vapor interface of the bubble. The microlayer thickness, the wall temperature distribution and the bubble shape are measured simultaneously and synchronously at 4000 fps by white light interferometry, infrared thermography and side wise shadowgraphy, respectively. In order to address the effect of cavities we perform two experiments using different heaters. In the first experiment, the bubble grows on a smooth surface of nanometric roughness whereas in the second the bubble growth occurs on a cylindrical artificial cavity of 25 micrometer diameter and 50 micrometer depth fabricated by focused ion beam. With the artificial cavity, the results show that the required wall superheating to trigger the bubble growth is decreased by a factor three. The radii of macroscopic bubble shape, microlayer and dry spot were reduced by half. The macroscale bubble dynamics is also slowed down. The initial microlayer thickness is thinner and detectable in a large portion of its extent. Based on the absence of interference fringe near the contact line (due to high interfacial slopes) and on recent numerical simulations we understand the microlayer profile consisting of two regions: a growing over time dewetting ridge near the contact line followed by a flatter and wider region that thins over time. The microlayer can be seen as a film deposited by the receding meniscus and its profile is thus controlled by the viscous and surface tension effects; its thinning over time is due to evaporation only. The ridge is a result of liquid accumulation due to contact line receding and strong viscous shear in the film.
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