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Q & A: boiling water without losing steam

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Most recent answer: 03/24/2014
Q:
I want to boil water in a pot but have the mass still be the same. (So I'm thinking there is either no vapor or vaporization happens but it comes back to water and falls back in the pot.) What should the temperature of the heat or temperature of the outside should be?
- Erica (age 20)
St. Louis
A:

When you boil the water you're converting it to vapor (steam). Steam takes up much more volume than liquid if you keep the pressure fixed. So in order to not let any steam escape, you need for the pressure to go up. Pressure cookers let you do that some. Once the pressure reaches the maximum the pressure cooker can take, any further boiling has to be balanced either by letting steam escape or by having it condense back to liquid. The condensation will mostly happen at the coolest point, the lid, from which the liquid will fall back in the pot. So you could keep the water boiling, without requiring any steam release, by using a very low burner setting so that the heat flow in can be balanced by the heat flow out of the lid. That means you won't have a powerful rolling boil but just a very gentle boil.

Mike W.


(published on 03/24/2014)

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