Why silhouette takes a drop of coffee or milk after impacting the breakfast table is sometimes circular, sometimes starry? The answer is related to the intricate conditions that determine when a droplet hits a solid substrate maintains its integrity after the crash or fragments into many smaller pieces, experiencing what is known as the transition to splash.
“We have shown that the ‘splash’ only occurs when vertical velocities inducing seemingly irrelevant presence of the gas atmosphere on the extremely thin and fast film fluid is ejected after the impact, exceeding the rate of shrinkage caused by the forces cohesive liquid,” reports professor Jose Manuel Gordillo.
Together with fellow professor of the Research Group: Fluid Mechanics at the University of Sevilla Guillaume Riboux, conducted a study chosen by the editors of the journal Physics Review Letters as suggested readers web work and home.
Helium and low pressure to remove the splash
One of the most striking consequences of the theory of Riboux and Gordillo is that, for the first time, you can explain the known experimental observation indicates that the splash can be suppressed when the air is replaced by helium or when the atmospheric pressure is reduced.
To explain the phenomenon of these researchers have had to modify the expression of classical aerodynamic lift force and adapted to tiny length scales that characterize the sheet, taking into account the effect of the gas forces on the lubricating fluid.
These additional forces are surprisingly very dependent free path between gas molecules. The length scale is typically a million times smaller than the diameter of the drop.
Studies on the impact of the drops have implications for technological applications, from printing ink to the combustion or spread of pathogens in plantations.
