Sunday, February 10, 2013

The Leidenfrost Effect

I've observed this many times but haven't really thought about what is happening.  When you drop water on a stove burner that is at the right temperature, they form little beads that skitter around on the burner and only slowly get smaller.  What is happening is referred to as the Leidenfrost effect.  When a liquid comes in contact with a mass significantly higher than its boiling point, a layer of vapor insulates the liquid and prevents it from boiling, at least for a little while.

I came across this interesting video demonstrating the effect when dropping a red hot metal (Nickel) ball into water.  For a while you can see a thin layer of vapor surrounding the ball.  Eventually, the insulating effect is overwhelmed as the ball cools and the water is not vaporizing instantaneously. After this the water boils furiously.

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