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  • Hurray for the Leidenfrost Effect

    Posted by Shannon Love on December 15th, 2008 (All posts by )

    I’m a bit absent minded. This morning in the kitchen, I absentmindedly grabbed with my bare hands a cake pan that had been heated in the oven to 450F(232C).  I had forgotten that I had taken off my oven mitt. I grabbed the pan firmly and picked it up on one side. I should have been severely burned but I escaped because of the Leidenfrost effect. 

    From Wikipedia:

    The Leidenfrost effect is a phenomenon in which a liquid, in near contact with a mass significantly hotter than its boiling point, produces an insulating vapor layer which keeps that liquid from boiling rapidly. This is most commonly seen when cooking; one sprinkles drops of water in a skillet to gauge its temperature—if the skillet’s temperature is at or above the Leidenfrost point, the water skitters across the metal and takes longer to evaporate than it would in a skillet that is above boiling temperature, but below the temperature of the Leidenfrost point. It has also been used in some dangerous demonstrations, such as dipping a wet finger in molten lead and blowing out a mouthful of liquid nitrogen, both enacted without injury to the demonstrator. The effect is also responsible for the ability of liquid nitrogen to skitter across lab floors, collecting dust in the process.

    I had taken my oven mitt off in order to scoop some batter out of a bowl with my bare hands. I washed my hand off and then, with it still wet, I turned around and picked up the very hot pan. I felt the water in contact with the pan turn to steam and bubble through the water close to my skin. It felt like sticking one’s finger into warm seltzer water. I felt no heat at all but realizing what had happened, I dropped the pan before the water evaporated and the heat of the pan could burn me. 

    Of course, without the water on my hand, I would have felt the heat of the pan and probably would not have grabbed it. Still, it’s a startling example of a very interesting natural phenomenon. 

     

    10 Responses to “Hurray for the Leidenfrost Effect”

    1. Ginny Says:

      Thanks.

    2. Robert Schwartz Says:

      If you do burn yourself like that, plunge the affected part into ice cold water and keep it there for a while, long past the point where it hurts because of the cold. This often minimizes the blister or eliminates it altogether.

    3. Andrew Garland Says:

      This is also how people walk across hot coals without burned feet. There is always some wet grass around the coal bed. Being nervous and sweaty also helps.

    4. James R. Rummel Says:

      You lucky bastich!

      James

    5. Mike Wilson Says:

      Ok, that’s pretty cool right there.

      I’m now going to have a real hard time with the “oh, c’mon, it’d be so cool to show off to friends if you could get it to work reliably” impulse that’s yielded so many hand and arm scars over the past 39 years.

    6. Phil Fraering Says:

      I guess the leidenfrost effect can be negated by the magic phrase “Here, hold my beer and watch this…”

    7. Nonnie Says:

      The important question is did you clean up the mess where you dropped the pan?

    8. Obloodyhell Says:

      > Ok, that’s pretty cool right there.

      Yeah, but he forgot the obligatory:

      “Don’t try this at home, folks!!”

      :oD

    9. Wade Says:

      My Chem prof blew liquid nitrogen out of his mouth – it got our attention.

    10. Jay Manifold Says:

      Played around with squirt-bottles of water and hot plates in chem lab in HS. Grabbed the wrong one once and thought the bouncing drops looked funny. Squirted some more. Still looked funny. Only then thought to read the label on the bottle. Acetone.

      Fortunately, I was not in a 100%-oxygen atmosphere at the time; “Bondarenko had been undergoing routine training in a pressure chamber, which was part of a ten-day isolation exercise. At the very end of the exercise he made a trivial but fatal mistake. ‘After medical tests,’ explained Golovanov’s article, ‘Bondarenko removed the sensors attached to him, cleaned the spots where they had been attached with cotton wool soaked in alcohol, and without looking threw away the cotton wool– which landed on the ring of an electric hot plate.'”

      Don’t try this anywhere.