Drop impact on heated surfaces
Effect of polymer additives
The impact of liquid
drops on hot surfaces is a complex phenomenon which is important in various
Engineering applications (spray cooling or quenching, firefighting, etc.).
The impact morphology depends mainly on the surface temperature (when it
exceeds the saturation temperature of the liquid), and the Weber number
(which compares inertia and surface forces), as shown in the following
qualitative map:
Very small amounts of
flexible polymers are known to change significantly the behaviour of liquid
droplets when they impact on a solid surface. This was observed for the
first time at Rhodia Recherche (
We have found that polymers also change the impact morphology
of drops on heated surfaces.
One of the most
spectacular phenomena that happen when a liquid drop hits a hot surface is
the scattering of smaller secondary droplets from the free surface. See an
example in the movie below on the left (T = 250°C; We = 40).
When we add to the liquid
a very small amount of polyethylene oxide (200 ppm), and we repeat the
experiment in the same conditions, secondary atomization completely
disappears, and the drop just rebounds on the surface (see the movie below
on the right).
For high Weber numbers,
drops break down into smaller droplets upon impact (splashing); this
phenomenon is enhanced by high temperatures of the surface. See an example
in the movie below on the left (T = 120°C; We = 220). Polyethylene oxide
(200 ppm) prevents the drop from breaking-down (see the movie below on the
right).
V. Bertola, K. Sefiane, Controlling
secondary atomization during drop impact on hot surfaces by polymer
additives, Physics of Fluids, vol. 17(10), article 108104, 2005.
V. Bertola, Drop impact on a hot
surface: effect of a polymer additive, Experiments in Fluids,
vol. 37(5), pp. 653-664, 2004.