PeriodicExperiments: #15: Leidenfrost Effects

What if I told you that you could safely stick your fingers in molten lead (621 ℉). Or that you can submerge your hand in liquid nitrogen (-321 ℉) without being harmed. Better yet, what if I said that water can flow uphill? Remarkably, all of these things are possible thanks to a certain scientific concept. That concept: force fields. While they can't deflect giant laser beams, force fields actually exist in real life. However, they go by a different scientific name: Leidenfrost effects.

Discovered in 1756 by Johann Gottlob Leidenfrost, the Leidenfrost effect is a little-known phenomenon of science. Since I discovered it about a week ago, the concept has fascinated me. My interest in it eventually led me to perform some experiments. Seeing as I didn't have any molten metal or liquid nitrogen to play with, I had to settle for some simpler demonstrations. My first experiment involved dropping a red-hot steel ball into water. While the procedure was easy, it took a couple tries to film it right. When I did get a good shot, the results were amazing.

Upon examining my amateur slow-motion footage, I noticed something peculiar about the metal ball as it entered the water. The sphere became surrounded by a bubble. As you have probably seen, water evaporates when it comes in contact with a heated surface. However, if a surface is extremely hot, things get a little strange. Sometimes, if a liquid is vaporizing faster than it can escape, the gas builds up and forms a barrier. The thing to note here is that gases can't transfer heat nearly as well as liquids can. It is for this reason that the gas bubble slows down further evaporation. This is the essential idea behind the Leidenfrost effect.

In my second experiment I did something quite different. To show the Leidenfrost effect once again, I started by heating an empty frying pan. As it sat over the stove flame, I used a small pipette to shoot water at it. Initially, the water quickly boiled away as expected. However, after about five minutes, something very interesting happened. The water drops from the pipette stopped vaporizing. Upon landing on the skillet, each droplet began to skitter around wildly. While they did evaporate eventually, the droplets seemed impervious to the pan's extreme heat.

Similar to the steel ball, the metal pan was beyond hot enough to vaporize any water that touched it. Surprisingly, this is exactly what kept the pipette drops around for so long. As soon as the droplets hit the pan, their underside instantly evaporated. Due to the fact that this happened so quickly, their own vapor became trapped beneath them. And just like before, their vapor insulated them from the hot skillet. As a result, they were able to ride around on a cushion of air like miniature hovercrafts. To see more Leidenfrost magic, click the links below!