Spheres of Water on Hot Pan

Nailed that answer particluarly well....

Very good answer, but I thought is was Sessile effect.

I'm not sure if sessile droplets are exhibiting the same behavior. Don't have time to investigate right now...sorry.

<...What force keeps water sphere from collapsing?...>

Surface Tension keeps the droplet together. Pool boiling is taking place close to the interface between the hot surface and the droplet. The droplets are "dancing" because they are floating on a turbulent layer of steam at this interface. Combined heat and mass transfer transfer is the phenomenon that limits the rate of reduction in size of the droplets.

These phenomena can be studied as fundamentals during an undergraduate course in Chemical Engineering.

This means that the surface tension ofrce of water is so much that even the turbulent flow of steam & bouncing of the sphere cannot collapse it.

By the way, is it anything to do with hydrophobicity?

Actually, I believe you mean to say film boiling. The heat flux from the heated surface is so high that it immediately flashes the water to steam and prevents the water from wetting the surface.

Any liquid molecule has it's "Tension" on surfdace like the water drop on the water lily's leave, it keeps moving in pressed ball shape, and this features was used a lot in our daily life like "TNF" coloth.

Theroy is to reduce the polarity of one solid subject, so that the water drop will not be "attracted " by the solid surface and when the surface tension of water drop can cover the "attraction " from the solid surface, this water drop will keep the shape without collasping. By using this theory we can do some special treatment to use chemical way to reduce the fibres' polarity so that the water drop will not stay on the cloth's surface and keeps sliding down.

Thanks jasonzen

That was a nice little bit of additional information.

Can you give us some examples?

BAB

In apparel industry or Bag's indurstry we call this "Water Repellent", which is different from "Waterproof". It gives the fabric light weight and will not get wet when rains.

Such as wax polishing on the car so the raining drops will not stay on the car.

Such as 3M Scotch dealed Cloth for Raining Jacket.

It was called surfactants .

It is not just only make the surface to be shining ( you may do the shining work of your car by cloth but you can not make the rain go away quickly ), all is about to make the water drops keeps it surface tension and without stick to the other surface . A simple theory of Universal Gravitation, two objects attract each other, light one goes to heavier one, in this case is same, surface has lots of polarity , the strength of polarity is decided by the Molecular Weight, The Molecular Weight is bigger, then the Polarity will be bigger too.

Many thanks.

BAB

This entertaining phenomenon occurs because the water evaporates fast enough to support the liquid water on a current of water vapor.

Evaporation is greatly accelerated by heat radiated from the surface of the pan.

Surface tension pulls the suspended water into spheres, which have the least surface area per unit volume of any geometric solid.

The only thing I was going to add was that it's because of the radiant heat is enough to cause the surface boiling. Generally when you fry things the heat transfer is through the conduction via contact of your juicy steak to you iron fry pan. But if you get the iron fry pan hot enough then the radiant heat flux will increase to such a level that you get the surface boiling.

Other metals like Aluminium will create the same effect at lower temperatures because the emissivity is higher so the radiant heat flux is higher at lower temps.

Hello ESO

One should never cook in Aluminium pans, pots etc, nor use the "non-stick coated" articles, because these have long-term toxic effects.

Cast Iron, Stainless steel are OK, with no bad long-term effects for the body.

Kind Regards....

As a fun little aside, the Leidenfrost effect is also what keeps your feet from burning when you (or hopefully someone else) walks across hot coals. I remember watching a video in my high school physics class that starred a local college professor explaining how it works and then he walked across the hot coals. I guess the whole secret is being nervous enough before hand that your feet sweat.