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It is a little observation i did when i was boiling the water.

what i observe is that when i turned off the stove on which the water was boiling i could see more steam coming out from it than the steam which was coming before the stove was turned off i.e. the amount of steam coming out per second was more when the flames which waere giving heat to the water is turned off

Why is that so?

Anni
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  • I tried it with an electric kettle, and there is no positive difference in steam when the heat is turned off, though the boiling stops immediately. I will try it with a flame later in the day. The only thing I can think is that the sharp cutoff of heat might synchronize the last rising steam bubbles to break out at the same time and seem to give off more steam. – anna v Jan 22 '16 at 05:46
  • Is it still sitting on the hot burner after you turn off the electricity? – Chet Miller Jan 22 '16 at 15:52

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So steam is caused when you have a supersaturated water vapor that cools and forms large suspended water droplets in the air. This is governed by the kelvin equation which you can read more about here:

https://en.wikipedia.org/wiki/Kelvin_equation

To get larger water droplets, or in your case a denser looking steam, you have two options: 1. you increase your partial vapor pressure or 2. you decrease the temperature. Without knowing more details, my guess would be your flame was also supplying a substantial amount of heat to the air around the water vapor. When you turned the heat off, the air cooled much more rapidly than the water and caused the vapor to condense more rapidly.

One easy way to think about this is breathing in the winter. When you blow hot moist air out of your mouth, you see steam. When you are in a warm building, you don't.

Greg Petersen
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