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The efficiency of most industrial plants depends crucially
on water vapor condensing on metal plates, or condensers,
and how easily the condensed water can fall away allowing
for more droplets to form. Typically on a flat-plate
condenser water vapor quickly condenses to form a thin
liquid film on the surface reducing the condensers ability
to collect more water and ultimately acting as a barrier to
heat-transfer. By creating hydrophobic surfaces, either
through chemical treatment or surface patterning,
researchers have been able to prevent this problem by
encourage water droplets to form and fall away. Now a
team of MIT researchers have taken this process a step
further by making surfaces that are patterned at multiple
scales. A group from MIT's mechanical engineering
department found that the energy released as tiny droplets
of water merged to from larger ones is enough to propel
the droplets upward from the surface. The removal of
droplets doesn't depend solely on gravity, droplets don't
just fall from the surface, they actually jump away from it.
Using this information their new process produces a surface
that resembles a bed of tiny, pointed leaves sticking up from
the surface. These nanoscale points minimize contact
between the droplets and the surface, making the release
easier. After the leaf-like pattern is created a hydrophobic
coating is applied using a solution that bonds itself to the
patterned surface without significantly altering its shape.
This patterning can be made on a film that can be applied
to a variety of surfaces including the copper tubes and
plates commonly used in commercial power plants. This
technology could also be useful for other processes where
heat-transfer is important, such as in dehumidifiers and for
heating and cooling systems in buildings.