- Title: FRANCE: Exploding droplets explain why raindrops are different sizes
- Date: 14th August 2009
- Summary: AIX-MARSEILLE UNIVERSITY, MARSEILLE, FRANCE (RECENT) (REUTERS) PROFESSOR EMMANUEL VILLERMAUX, AIX-MARSEILLE UNIVERSITY, DESCRIBING EXPERIMENT APPARATUS VARIOUS OF APPARATUS VARIOUS OF PROFESSOR EMMANUEL VILLERMAUX AT HIS DESK (SOUNDBITE) (ENGLISH): PROFESSOR EMMANUEL VILLERMAUX, AIX-MARSEILLE UNIVERSITY SAYING "There is a topological change of the drop from the spherical shape to a pancake shape which then evolves towards a kind of a balloon shape, a bag shape, which bursts giving rise to polydispersed fragments in size." VARIOUS OF PROFESSOR VILLERMAUX AND A STUDENT CONDUCTING AN EXPERIMENT (SOUNDBITE) (ENGLISH): PROFESSOR EMMANUEL VILLERMAUX, AIX-MARSEILLE UNIVERSITY SAYING "This will not impact much the vision we have about the climate, the precipitation and stuff. It brings a new light on a known phenomenon and it advances the knowledge we have about break-up phenomena in general in nature."
- Embargoed: 29th August 2009 12:06
- Keywords:
- Location: France
- Country: France
- Topics: Science / Technology
- Reuters ID: LVA5LULV3DGOTM05J4YKZBV15E04
- Aspect Ratio: 4:3
- Story Text: The traditional view of why raindrops are different sizes is overturned with the discovery that raindrops explode as they fall.
Why raindrops are different sizes has exercised scientific minds for more than a century but some new research from France has finally answered the question once and for all. The work overturns the accepted view that rain drops collide during their fall and merge. Now, we know these events do occur but they are not an important factor and are in fact rare.
Professor Emmanuel Villermaux and Benjamin Bossa, of the Natural Phenomena Research Institute at Aix-Marseille University, filmed the evolution of a droplet as it falls, revealing that it changes shape.
"There is a topological change of the drop from the spherical shape to a pancake shape which then evolves towards a kind of a balloon shape, a bag shape, which bursts giving rise to polydispersed fragments in size," said Professor Villermaux.
Once burst, raindrops do not break up again because the droplets remain small enough so that their surface tension forces are not overcome by the drag forces.
Their research is part of a bigger programme examining liquid fragmentation. They are trying to understand how droplets behave in different situations and applications from liquid propulsion and diesel engines to agricultural sewage.
They say the phenomenon of droplets changing shape was already known but had not been applied to rain.
"This will not impact much the vision we have about the climate," said Professor Villermaux, but "it brings a new light on a known phenomenon and it advances the knowledge we have about break-up phenomena in general in nature."
Raindrops form in clouds as water vapour sticks to dust and other particles in the atmosphere. They fall when their weight can no longer remain in suspension. - Copyright Holder: REUTERS
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