This metal ball may not look like hot stuff, but it can travel through water in a flash. When hot objects move quickly through a fluid, they exhibit something known as the Leidenfrost effect, where cavities of air form around them. Unlike previous research, where balls were passed through liquid inside a small bubble, the researchers aimed to make the largest cavity they could.
By heating some balls to absurdly high temperatures-400oC-and dropping them into 90oC water, the 20-millimeter-diameter balls were encapsulated by a tear-shaped cavity that was five to 15 times their size, which cut through the water like a hot knife through butter.
In other trials, balls were coated in a material that repelled water, which generated a similar cavity without the need for the high temperatures. When the balls were raced against a similarly weighted tear-shaped piece of plastic, the treated metal balls had 90% less drag, the team reports today in.
The researchers say that this “Cavitation” could help decrease drag in watercraft.