We've all seen steam coming from boiling water on a stove.  Why is a
large "plume" of steam emmited when the heat is removed?

You can see this for yourself by conducting this experiment:
1. Place pot of water on gas burner turned on high. (Dont' cover pot).
2. Allow water to boil for a minute or so.
3. Observe steam.
4. Turn off burner or remove pot from burner.
5. Observe a lot more steam for about 2 seconds.

Hey chrisstankevitz-ga,

I can't think of a search strategy for this, but I think I know the
answer. Steam is being created in the boiling pot because of the
difference in temperature between the surface of the water and the air
above it. When you turn off the heat and move the pan, you lower the
temperature of the air above the water. This increased gap in relative
temperatures would be a likely culprit in looking to explain "a lot
more steam for about 2 seconds."

"We boil at different degrees." - Emerson

Hope this help you get on "a roll" :-)

mmi-ga

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Request for Answer Clarification by chrisstankevitz-ga on 25 Jun 2002 19:16 PDT

Hi mmi,

Thanks for providing an answer, I've wondered about this for a long
time (This google thing is great!).  I like your thought about the
temperature differential between water and air and it's relation to
the steam we see with our eyes.  I personally do not "move the pot off
the burner" as I posted, I just provided that option for those using
electric burners that don't cool immediately.  Because I don't "move
the pot," I don't think the air temperature above my pot is really
changing that much.  Therefore, I am not sure if the phenomenon I am
seeing is explained by your answer.  I will take a closer look at the
air temperature when I return home tonight.

Thanks!

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Clarification of Answer by mmi-ga on 25 Jun 2002 19:33 PDT

Hey chrisstankevitz-ga,

Perhaps when the stimulus of the heat from the burner is removed, the
relatively colder air that continuously sinks into the pan no longer
gets heated as much, creating a billow of steam from increased
relative temperature differences.

At least that's my story and I'm stickin' to it! :-)

mmi-ga

In this case, I believe the commenter dr_lap provided a more
'satisfying' answer, but nevertheless mmi was first on the scene and
pointed me in the right direction.  Thanks everyone!

Hi Chrisstiankevitz,

That is an interesting observation. However, what you are observing is
not the steam itself, which is invisible, but rather condensing water
vapor. Properly speaking, steam is just water vapor, which we can't
see. What we can see is the water droplets that condense, as in a
cloud. (This is from my own knowledge, but for them that likes links,
here goes: http://www.zetatalk.com/energy/tengy16f.htm ).

My guess as to what you are observing is a sudden condensation of the
moisture-saturated air above the pot after reducing the heat input
(steam) into the air. Since the boiling water is largely controlling
the temperature and moisture in the air above, essentially creating a
microclimate, the observed plume should be fairly consistent
regardless of the overall weather.

In the case of moving the pot, there should also be condensation from
the input of steam into the cool air above, but the intensity of the
plume would be dependent on the water vapor and temperature of the
air.

Sounds like a fun thing to experiment with!

I would tend to go with the commenter as being correct. The cloud is
condensation of the steam.  When you eliminate the heat I would assume
that the temperature of the steam and the air above the water would
drop to where the steam quickly (closer to the water) loses heat and
there for condenses in a more confined area where the water molecules
have more sites to condense onto.  I would also guess that when the
boiling stops, that the effects of the surface tension of the
non-boiling water has something to do with it as well.

the flame under the pot is also causeing a jet stream up around the
pot and carrying an increased air flow.  the increased speed of air
captures the steam and carries it away. heat is a catalyst for
brownian movement.  (dense objects tending toward less dense areas.)
when the flame is extinguished, this current dwindles and the
assistance to go to a less dense area ends.  Now , van der walls
forces take over(like materials are attracted to like, each other) the
molecules colide and cool (lack of flame) simultaneously becoming
visible.

hope this helps.