Suroto, Bambang Joko (2014) Bubble activation from a hydrophobic spot at “negative” surface superheats in subcooled boiling. Applied Thermal Engineering, 88. pp. 1-7. ISSN 1359-4311

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Abstract

We present experimental results on the controlled bubble generation from a single PTFE (polytetrafluoroethylene) spot—with diameter varying from 2 mm to 6 mm—deposited on a flat polished copper surface that was submersed in subcooled pure water. The static contact angle of the PTFE coating was measured to be over 120°, which conveniently produced a clear contrast with the copper substrate in terms of wettability that ensured controlled bubble nucleation. By making use of a high-speed camera, statistical details about the bubble formation that include the departure frequency and diameter have been obtained at various surface temperatures. An interesting observation was made of repeated cycles of bubble nucleation and detachment at nominally negative surface superheats (i.e., the wall temperature being below the saturation temperature at the system pressure), which featured particularly long bubble growth time and seemingly no waiting time. The vertical temperature distribution inside the bubble, which was measured by a micro-thermocouple of about 250 μm in diameter, suggests a relatively stable bubble composition of water vapor and dissolved air. A heat-pipe analogy was drawn to describe the internal heat transfer mechanism of bubble growth on a mixed wettability surface under subcooled conditions. Keywords :Bubble dynamics; Mixed wettability; Single bubble; Dissolve air; Subcooling

Item Type:	Article
Divisions:	Fakultas Matematika dan Ilmu Pengetahuan Alam (FMIPA) > Prodi Fisika
Depositing User:	Marbiyah . Siti
Date Deposited:	22 Aug 2016 02:19
Last Modified:	22 Aug 2016 02:19
URI:	http://repository.lppm.unila.ac.id/id/eprint/326

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