flat5

When making soup if I have the flame very high and stir I may notice no steam rising or feel the steam. When I then lower the flame I suddenly see steam rising and it may really heat up my hand.

Why more steam when I lower the temperature?

shakran

When you lower the flame you're lowering the air temperature above the pot. Steam then condenses into water vapor, which is much more visible than steam. So you're not actually seeing more steam - you're seeing a miniature cloud forming over your pot.

flat5

So steam is not necessarily water vapor?

I can now understand why my hand feels the heat more.
The cooler air above tends to keep the hotter "air" compacted/pushed against my hand.

I'll buy that :-)
Thank you, shakran!

shakran

no problem.

And you're right - technically, steam is not water vapor. In fact, steam is not generally visible. What you see coming out of the pot is water vapor, aka condensed steam.

flat5

Definitions of steam on the Web:

In physical chemistry and in engineering, steam refers to vaporized water. It is a pure, invisible gas (for mist see below), which at standard atmospheric pressure often has a temperature of around 100 degrees celsius, and occupies about sixteen hundred times the volume of liquid water (steam can of course be much hotter than the boiling point of water; such steam is usually called superheated steam).
en.wikipedia.org/wiki/Steam

ok, wikipedia.org does not mean the definition is correct :-)

The vapor phase of water, unmixed with other gases.
www.cleaver-brooks.com/GlossRW.html

Water vapor at a temperature greater than the boiling point.
amsglossary.allenpress.com/glossary/browse

The invisible vapor into which water is converted when it boils.
park.org/Philippines/pinatubo/page7.html

Visible mixture of condensation and water vapor in air. Product of boiling water.
http://www.stuffintheair.com/Blowin_...ogWeather.html

If it is not water vapor, what else can it be?

As I see it, it is very hot H2O.

krwlz

Actually steam feels "hotter", and can actually burn you worse than the same temperature air because of its specific heat (Which is higher than air). That specific heat is the amount of heat (Usually in joules or BTU's) needed to raise one gram of the substance by one degree centegrade (or the english eqivalent F). (Or in the opposite direction, the amount of heat released in the cooling process.)

Therefore, when that steam hits your hand, it condenses, releasing all that heat into your hand, which will rise in temperature faster than strict water.

.... God I love engineering school.

kutulu

You were right about everything except one thing there: You have a phase change going on so it's the heat of vaporization, not the specific heat (KJ/kg).

iamnormal

I think with the flame set on high it creates a layer that lacks O2 to burn next to the pan. This creates a insulation effect.
Try riseing the pan higher from the burner to increase the burning of the fuel under the pan.

krwlz

Good point. The heat released into you when the vapor condenses is due to heat of vaporization. Thank you for pointing that out. Heat of vaporization is mildly linked to specific heat as though, as per comparing steam to... Say the vapor comming off dry ice. (Which sublimates, so it's a bad example, but none the less)