Nano scale Porous Hydrophobic Coatings for Energy Efficient Creation of Stable Vapor Film to Reduce Drag
Drag reduction, Low energy creation of stable vapor film
Formation of a vapor film on a solid surface reduces the drag coefficient. However the formation of a stable vapor film layer requires large input energy. The vapor film is established when the nucleate boiling regime changes to the film boiling regime. In nucleate boiling, individual isolated bubbles grow at and detach from discrete location on the boiling surface, while the majority of the surfaces stays wetted. On the other hand, in film boiling a stable continuous vapor film completely covers the surface, so there is no contact between the liquid and the surface. The transition from nucleate boiling to film boiling is commonly known as critical heat flux (CHF). For most normal surfaces CHF occurs at about 1000 kW/m2 for water at atmospheric pressure, requiring substantial energy to develop a surface vapor layer.
This technology allows formation of a stable vapor film on an object’s surface with substantially less energy by reducing CHF by orders of magnitude. The CHF for surfaces prepared with the coatings is as low as 20-40 kW/m2, requiring 96-98% less heat to sustain the vapor film. The coatings performance is the result of engineered porosity and hydrophobicity.
Achieving stable vapor film with low input energy
Professors Jacopo Buongiorno (Department of Nuclear Engineering),
Dr. Thomas J. McKrell (Department of Nuclear Engineering),
Professor Robert E Cohen (Department of Chemical Engineering),
Professor Michael F. Rubner (Director of Center for Material Science and Engineering),
U.S. Patent Application Serial Number 61/706401, filed on September 27, 2012
Last revised: April 3, 2013
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