We've all experienced the fluid-dynamics phenomenon known as the "teapot effect." Every time you pour out a nice relaxing cup of tea, a little of the elixir dribbles down the outside of the spout of the teapot, dampening your doily and your spirits.
It happens because liquid clings to the lip of the spout instead of exiting neatly, especially at low rates of flow.
Cyril Duez and his team of fluid dynamicists could not tolerate one more dribble. They have identified the root cause, a "hydro-capillary effect" that makes the tea fail to leave the spout material gracefully. Two techniques can be used to combat this.One is to simply use a spout made of thinner material, which gives the wayward beverage less purchase. Metal teapots, for instance, like we see at Chinese restaurants, tend to drip less than pudgy-walled ceramic ones.
The other, cooler approach is to coat the spout with one of a class of super-hydrophobic materials, which repel any attempt by the tea to cling to the spout instead of going where it's supposed to. Some of these materials can be activated and deactivated electrically, raising the exciting possibility, as Technology Review points out, of a hilarious gag teapot with a drip/no-drip switch. It would go nicely with your Fraunhofer Perfect Mug.
The puzzling part is that the team of exacting tea scientists are not British, but French.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.