Eli5: Why is that water doesn’t evaporate immediately on a very hot surface?
In: Physics
It takes time for the heat to transfer into the water. The water droplets also heat up bottom first (since that’s where they touch the hot thing) and it can result in a thin heat insulating layer of steam that the water can coast around on.
It does if the surface is hot enough! If you’ve ever put a hot frying pan under running water that’s exactly what’s happening.
It can, if it’s hot enough. Instantly converting liquid water into a gas can cause explosions, though.
It’s called the leidenfrost effect. Basically as soon as the water touches the surface, a tiny portion turns into stean almost instantly, and that steam then forms an insulati layer that the rest of the water droplet sits on, preventing it from touching the hot surface directly.
The same effect also works with liquid nitrogen, and it’s why a persons hand can **briefly** come into contact with liquid nitrogen without receiving freezer burns
Others have mentioned the Leidenfrost effect, which does insulate the water from the hot surface on a layer of steam, but that’s only part of it.
The other part is that when water evaporates, it takes its heat with it. Heat is just energy and evaporation is just water molecules with enough energy to leave the liquid. It’s why sweating cools you down.
So not only do you have to deal with an insulating layer of steam, but you also have to transfer enough heat into the rest of the water while lost of that heat is being taken away by the evaporating water, massively slowing down the rate at which the rest of the water heats up.
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