Beer foam prevents the spilling over

Foam of the beer flower counteracts the spilling over

02/24/2015

The foam of the beer prevents, to a certain extent, the spilling over of the beverage, while liquids without foam coating run more easily over the edges. An American-French research team led by French researcher CNRS Saint-Gobain, Alban Sauret, has now studied the effect of foam on fluid movement within a container and found that even a thin layer of foam significantly dampens fluid dynamics.

When a container is set in motion, the free surface of the liquid begins to vibrate inside and, in case of doubt, to overshoot. „However, beer does not spill over as easily as water, which means that foam can be used to prevent it from spilling over“, This is the approach of Alban Sauret and colleagues in the trade magazine „Physics of Fluids“. The thought of the investigations had come to him while drinking a frothy Guinness, which hardly swirled over even with stronger movements of the glass, reports Sauret.

Effects of foam padding on fluid movement
Together with Emilie Dressaire from New York University and other colleagues at Princeton University in New Jersey, Alban Sauret has analyzed the phenomenon of foam absorption in the current study. Specially prepared rectangular containers were filled with a surfactant solution and air was pumped through the liquid from below with a fine needle. It created a foam of uniformly large bubbles. Now the researchers began moving the container and filmed the behavior of the liquid or foam using a high-speed camera. They realized that even a few layers of foam bubbles are sufficient to significantly dampen the dynamics of the liquid in the containers or their vibration.

Already a thin foam layer is sufficient for damping movement
According to the scientists, the friction of the foam bubbles on the vessel wall is decisive for the energy-absorbing effect of the foam. Foam bubbles without contact with the wall, however, would have little effect on the movement of the liquid. Furthermore, Sauret and colleagues explain that already five layers of foam bubbles are sufficient to achieve a comprehensive damping of the movement. Since the upper layer of the foam bubbles barely move, additional foam could cause no significant additional reduction in movement.

Numerous industrial applications possible?
While most people are well aware of the dampening effect of the foam on the movement of the liquid, rather than beer, latte macchiato, or cappuccino, the froth, according to the researchers, could unfold its true value elsewhere. For example, they are thinking about the transport of oil and LPG in tank trucks. Because here, the slosh dynamics can exert considerable pressure forces on the walls of a container and in the worst case lead to its destruction. For the foam numerous industrial applications are possible, so the conclusion of Sauret and colleagues. Not least, the foam can also be used for the safe transport of rocket fuel - and all that, thanks to the sight of a perfect beer flower. (Fp)

Picture: Tim Reckmann