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What is the reason that hot oil makes sound and explodes when water is poured on it?

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The liquid water changes phase when heated above the boiling point, namely it becomes a gas. When water vapor in cavitation bubbles escapes fast, it makes a mess. The sound of splashing aside, notice that nothing happens if the oil is cold.

Related fun fact: The pistol shrimp is so loud, it kills other fish by snapping with its claw.

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I downvoted by accident, but I cannot undo it, unless you do some editing ... even adding a single space. Sorry. Let me know if you edit by replying to this comment. – babou Jun 18 '15 at 7:36
@babou: You'll hear from my lawyer. – NikolajK Jun 18 '15 at 11:34
Please give him this incriminating evidence. – babou Jun 18 '15 at 11:47
@babou: I was being serious, you could get into Max Stirners works. – NikolajK Jun 18 '15 at 11:55
@babou: I don't understand what you say here. The s at the end is also not part of his name, did you even look at the linked page? – NikolajK Jun 18 '15 at 12:15

The essential basic fact is that the boiling temperature of oil is very much above that of water, known to be $100^\circ\;\mathrm{C}$ at atmospheric pressure (by definition).

For oil, the boiling point varies, but is very often above $200^\circ\;\mathrm{C}$: $197^\circ\;\mathrm{C}$ for olive oil, $246^\circ\;\mathrm{C}$ for corn oil (depending on quality, it can vary significantly), and around $300^\circ\;\mathrm{C}$ for refined motor oil. Actually, organic oil may smoke, i.e., decompose chemically, much before it boils, but nevertheless at very high temperature such as $191^\circ\;\mathrm{C}$ for olive oil (extra virgin, higher for other qualities).

Thus hot oil may mean much hotter than the boiling point of water. Whatever the heat capacity of oil, or more precisely its specific heat, which is actually about half that of water, the very high temperature can provide considerable heat that will cause an instant change of state from water to steam, creating instantly a considerable change in pressure, thus in volume, i.e. an explosive behaviour for each drop of water.

Following on a comment by mikuszefski, there is also an issue of relative density, water being denser than oil. The effect depend on the amount of water being poured. If it is only a few drops, they either vaporize instanly, of are kept buoyant by the steam pressure as the bottom vaporizes first.

However, if the amount of water is more important, the buoyance will be insufficient (it is proportional to the square of the water blob size, while the weight is proportional to the cube), and the denser water will fall into the oil, while continuing its explosive vaporization, which may then carry some of the oil with it.

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Can you add to you answer the influence of specific weight. Namely, if water would stay on top, it would just evaporate, but as it sinks into the oil (oil goes on top of water) the rapid volume change results in an explosion "ejecting" oil. Otherwise, I think this is the most complete answer. – mikuszefski Mar 12 '15 at 14:30
@mikuszefski Thanks for the remark and edits. I did not keep all the edits, as my feeling is that pressure is the first to increase, thus producing the change in volume. My idea is that you need the pressure to move the molecules so that they will occupy more volume, if the enclosure will let them. – babou Mar 12 '15 at 15:28
Pressure change leads to volume change; agreed. – mikuszefski Mar 15 '15 at 17:14

Oil heats up faster than water because it has a lower specific heat capacity. As it reaches past boiling point of water as the water is denser than oil so its at the bottom. Then it turns into steam and the steam expands splashing the oil everywhere.

As for dropping water into already being hot oil its pretty much the same. Its interface determines the rate of heat flow.

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You were the next person to join this site after me, "23120". – centralcharge Sep 22 '13 at 12:07

Oil boils at a higher temperature than water which means that when water is poured into boiling oil it is heated to, and past, the boiling point very quickly. Oil is also less dense than water meaning that the water will sink to the bottom of the pot.

Water at the bottom of the pot being heated very rapidly forms a gas at the bottom of the pot underneath all of the oil. The gas takes up much more volume than the water previously did and also is now less dense than the oil and so it shoots up creating a fountain of oil and steam out of the pot.

This fountain creates a fine mist of the very hot oil, this greatly increased surface area coupled with the already hot oil causes it to ignite which then ignites surrounding droplets until the entire batch of oil that was displaced from the pot is a huge fireball.

You can also find pretty cool videos on youtube about this exact thing

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Shrapnel. The oil is analogous to the container that holds the explosive (water-->steam) .

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Yes, its pretty much the same. More precisely, its due to the difference in their temperature and due to vigorous transfer of thermal energy from hot oil to cold water where water instantly changes its state into vapour.

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The water heats up and expands as it is falling through the oil, due to density. the water is covered up and expands into steam blowing the oil away. boom.

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Due to abrupt transference of heat energy from hot oil to cold water drop.

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This really isn't much of an answer; it would be better if you could expand this to cover what heat transfer does (e.g., the rapid change indicates X). – Kyle Kanos Mar 12 '15 at 14:38

protected by Qmechanic Mar 12 '15 at 14:20

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