Recently-reported data suggest that bubble nucleation on surfaces with nano-sized features (cavities and posts) may occur close to the thermodynamic saturation temperature. However, according to the traditional theory of heterogeneous bubble nucleation, such low nucleation temperatures are possible only for surfaces with micro-scale cavities. Motivated by this apparent contradiction, we have used infrared thermometry to measure the nucleation temperature of water on custom-fabricated nano-to micro-scale cavities (from 90 nm to 4.5 µm in diameter) and posts (from 60 nm to 5 µm in diameter), machined on ultra-smooth and clean silicon wafers using electron beam lithography. Our cavity data are in agreement with the predictions of the Young-Laplace equation, thus re-affirming the correctness of the classic view of heterogeneous bubble nucleation, at least for the water-silicon system investigated here. The data also suggest that individual posts of any size have an insignificant effect on bubble nucleation, as expected from theory.
Nucleation, growth and detachment of steam bubbles during nucleate boiling of a water pool at atmospheric pressure is experimentally investigated using a combination of synchronized high-speed video (HSV), infrared (IR) thermography and particle image velocimetry (PIV). The heater is a thin (<1 m), horizontal (20×10 mm 2), resistively-heated, indium-tin-oxide (ITO) film, vacuum-deposited on a sapphire substrate (250 m thick), which allows for unobstructed optical access from below the boiling surface. This approach enables detailed measurement of the phase, temperature and velocity distributions on and above the boiling surface. The database reported herein is for isolated bubbles, exhibiting nucleation temperatures 107-109C, bubble departure diameters 3.0-3.8 mm, frequencies 4.7-15.00 Hz, wait and growth times 52-200 ms and 15-16 ms, respectively, at average heat fluxes 29-36 kW/m 2. The database is most useful for validation of modern simulations of nucleate boiling in which the phase, temperature and velocity distributions within and around bubbles are resolved using interface capturing methods such as Volume Of Fluid (VOF), Level Set (LS) and Front Tracking (FT).
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