30 September 2013

The Leidenfrost Effect is endlessly fascinating

I've written about it before (see "How to dip your hand into liquid nitrogen") and was delighted to find at Nothing to do with Arbroath the above video, in which students at the University of Bath used the effect to create directional movement by droplets of water.

Today I also found a description of the effect from 1868:
Mr. Davenport informs us, that he saw one of the workmen in the King’s Dockyard at Chatham immerse his naked hand in tar of that temperature [220°]. He drew up his coat sleeves, dipped in his hand and wrist, bringing out fluid tar, and pouring it off from his hand as from a ladle. The tar remained in complete contact with his skin, and he wiped it off with tow...

Mr. Davenport ascribes this singular effect to the slowness with which the tar communicates its heat, which he conceives to arise from the abundant volatile vapour which is evolved ‘carrying off rapidly the caloric in a latent state, and intervening between the tar and the skin, so as to prevent the more rapid communication of heat.’..

The workmen informed Mr. Davenport, that, if a person put his hand into the cauldron with his glove on, he would be dreadfully burnt, but this extraordinary result was not put to the test of observation. 
And found that the eponym comes from a German physician:
"During his lifetime, Leidenfrost published more than seventy manuscripts, including De Aquae Communis Nonnullis Qualitatibus Tractatus (1756) ("A Tract About Some Qualities of Common Water") in which the Leidenfrost effect was first described (although the phenomenon had been previously observed by Herman Boerhaave in 1732)."


  1. Mythbusters used this effect to dip their wet fingers into a pot of molten lead: http://www.youtube.com/watch?v=yTOCAd2QhGg

  2. Two observations.

    1.) It is not temperature that burns skin; it is heat flow.
    2.) In 1992 I bought a copper-clad stainless pan set. They REALLY heated up fast, which I knew intellectually, but in the kitchen they still kept catching me off guard, burning butter and olive oil mostly. One day I spilled a little water in an over- pre-heated pan and learned about the Leidenfrost Effect, though it was 15 years later that TYWKIWDBI gave me the name.

    The small water droplet beaded up but did not boil. It floated like an air hockey puck. It also did not appear to boil away. It took around 10 minutes for it to get small enough to finally boil away. I spun it around and around in the pan, as fast as I could.


    A. The pan must be spotless.
    B. The pan must be HOT - medium hot is not good enough. When the temp drops below the Leidenfrost temperature, the droplet dissipates rapidly and "normally."
    C. With multiple droplets they will bounce off each other more often than merge.

    I've had single droplets last as long as 15 minutes.


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