temp of steam

[Whammo]

I have heard that the temperature of steam over boiling water can reach 300 degrees yet boiling water can not reach above 212 degrees. Where does this extra energy come from?

[StrTrkr777]

212 degrees causes water to boil, at least at sea level, above or below has different temps to do so.

Going much above 212 causes the water to boil rapidly and then eventually it turns to steam. Steam is definitely hotter than the boiling water, but I am not sure to what temp it can become. But if you hold a solid object like a pan lid over the steam it will collect and eventually cool to the point of the boiling water and then drop back down into the pan.

Tip: Do not hold your arm or anything else above a steaming pot, it will burn you.

Jeffery

[ChiefScott]

The temperature of steam depends on how much pressure the steam is under. The steam in high pressure steam lines regularly exceeds 500 degrees.
Great for making ships go!!

[Sofa King]

H2O, like all basic compounds and elements, has at least three phases: ice, water, and steam. Then there's plasma, but we're talking science, not science fiction, right? All are related to temperature, pressure, and volume.

Science has known for years that the elements can be combined in different ways to form different compuonds. Earth combined with water, for example, makes mud. Similarly, water combined with air makes club soda. Water, air, and fire makes a gin and tonic. Hmm. I think I'm thirsty.

[Undead Dude]

Well, steam can be many temperatures-- at normal sea-level air pressure, it can't be any colder than 212 F, but it can be much hotter.

However, if you have a pot of boiling water sitting on your stove, you are not going to find any 300 F steam above it. Actually, you will briefly find 212 F steam, but that steam is going to cool in the air of the room and condense back into water very quickly.

So I think the real answer to your question is that what you heard is wrong. You can heat steam up to 300 F, but it isn't going to get that way by itself in a normal house with a normal pot of boiling water.

[Undead Dude]

And let me elaborate a little more on what ChiefScott was saying.

You might have a pipe of really hot water that is under pressure. When water is under pressure, it actually can be hotter than 212 F and still remain as water. This pressurized pipe could contain water that is 300 F. If you cut a hole in the pipe, the pressure would be released and the water would quickly boil. The steam coming out would be the same temp as the water-- 300 F.

So that is an example of a rather unusual senario in which you could have 300 F steam coming off of boiling water.

[Whammo]

undead dude, thank you! this is what I was wanting to hear. I couldnt understand how the steam above boiling water could be hotter then the water. Now Im even further convinced (now that someone agrees with me) that what I heard was wrong!

[HeadlessCow]

They might be referring to the fact that steam, while no higher in temp than the water, contains much more heat energy. This is due to the fact that the change from water to steam involves adding an amount of energy, called the heat of vaporization, which is released when the steam cools into water on your skin. That's why steam burns more than water at the same temp.

[Undead Dude]

It is true that steam has substantially more energy at equal termperatures, but it seems to me that the only reason a steam burn might be worse than water burn is due to circumstance. You might be more likely to have a greater amount of steam hit you. If one man dunked his head into 212 F water, and another fellow dunked his head into 212 F steam, I have a feeling that the person who had their head underwater would do much worse. Since water is far more dense, it would have more opportunity to transfer heat. As a matter of fact, while a gram of steam would have more energy than a gram of water at the same temperature, I'm willing to wager that the water would have much more energy per unit volume.

And of course getting burned isn't really about energy content. It's about energy transfer. The rate of transfer is dependent on the nature of the materials involved, the nature of the contact between the two materials and the difference in temperature between the two materials. The total thermal energy content is not important.

[NanoByte]

Yes, I go with this last post of UndeadDude. Steam can be dry or wet with water vapor (droplets suspended in steam and air), both at the same temp. Water has much higher heat conductivity to the skin, whose tissues / nerve endings must be raised in temp to be burned / to sense "ouch".

Ray

[MrKnowItAll]

Here's a scenario where you might have steam at 300 F or higher. Use a pressure cooker. In a pressure cooker, the water has to get hotter that the normal 212 to boil (as was previously alluded to). Steam escaping from this kind of cooker could very well be much higher.

Granted, I don't know how much hotter, but under enough pressure, 300 sounds reasonable.

[rowrrbazzle]

Re the pressure cooker: I can't find my pressure cooker manual right now, but IIRC, at its maximum pressure, 15 lbs, the temp goes up to 240 degrees, which is hot enough to avoid botulism when canning.

Mr. Wizard (on one of the shows that still air occasionally on Nickelodeon) piped steam through a coiled metal tube and heated the coil with a propane torch. Paper held about an inch from the end of the tube in the invisible stream of superheated steam obligingly caught fire.

[Squid Vicious]

Well I just can't pass this one up. Sorry Chief, ex-Navy nuclear engineer turned chemist turned biophysicist here.

First of all, it is entirely possible for steam from boiling water, in an open pot, on your stove, at sea level, on earth to reach temps greater than 212 degrees F. When you heat water to a boil small bubbles start to form on the bottom (or closest to the heat source) of the pot. The bubbles form at nucleation sites usually consisting of imperfections or scratches in the metal (or glass). If the steam forms a bubble, you can rest assured that the pressure inside the bubble (not counting added pressure from the depth of the water, which is negligible) is at 1 atmosphere. Therefore the temp of the steam should be 212 deg F. If, however, you really crank the heat up so that the water is roiling (or, as we say in the biz..bumping) it is more than likely that the steam is superheated. How hot depends on your heat source. So, it is possible (and damn likely too if you cook like me) for steam to be greater than 212. 300? why not?

Be that as it may; that is generally not the reason steam burns are more serious. It's due to you acting as the heat sink for the latent heat of vaporization which is imparted to you as the steam condenses.

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"If you stick your finger in a pie, whatever is in the pie will be on your finger, and whatever is on your finger will be in the pie...unless you wear a rubber glove"----some demented old lady

[Undead Dude]

So, it is possible (and damn likely too if you cook like me) for steam to be greater than 212. 300? why not? -- Squid Vicious

Well, because that would be rather extreme. :)
It is true that there really can be a little variation in the temperature, but 300 F would be a little hard to believe. First and foremost, that would require the pot itself, which is constantly being cooled by 212 F water, to be at least 300 F. Second of all, it would require the nucleation to be extremely rare-- you'd need an almost perfect surface.

Between these two factors, I will confidently say that the improbability of this senario is low enough to be neglected in the real world.

It's due to you acting as the heat sink for the latent heat of vaporization which is imparted to you as the steam condenses. -- Squid Vicious
And I am confident that this is a misnomer. The idea that steam has much more energy than water at the same temperature assumes an equal mass of steam and water. But the reality is that when steam contacts your skin, the mass that covers a given area is going to be much smaller than the mass of water that would cover that same area. The density difference will be far more important than the difference in thermal energy/mass unit. If need be, I'll look up the heat of vaporization of water and the density of water and steam at standard pressure. That should settle it.

Now I'm not saying that steam burns aren't worse. I'm just saying that this isn't why. Perhaps the typical water burn is like a splash, while the typical steam burn is like a continuous hose spray.

[Temujin]

Then there's plasma, but we're talking science, not science fiction, right?
I thought fire was a plasma. Same with lightning.

[Undead Dude]

I thought fire was a plasma. Same with lightning. -- Temujin

Fire is not a plasma, but lightning is. Indeed, plasma is quite real. Plasma is any ionized gas, which includes the air that lightning travels in, the gas in neon signs and fluorescent lights, as well as the gases that are so hot that the electrons can't hold onto the nuclei (like on the Sun or in a nuclear fusion reactor).

[Omniscient]

I'll weigh in too. Undead is basically right. The steam cannot be hotter than 212 degree above an open pot. If you place a lid over the pot you will gain a few more degrees, if you use a pressure cooker the steam will get much hotter, as will the water. I don't have a phase diagram chart, but i imagine that 300 would not be unreasonalble. I can think of no reason that a rolling boil will cause the steam bubbles to reach a higher pressure (ergo temp.) than a simple boil. All that changes is the rate of evaportation. Also, he is correct that the heat of vaporization is small compared to the low density in steam. In short, listen to what UD said.

[Temujin]

Fire is not a plasma, but lightning is.
So what's fire then? I know this is unrelated to the original topic, but now I'm curious. thx.

[Undead Dude]

So what's fire then?
Fire is a chemical reaction. It is the rapid combination of various substances (most notably carbon and hydrogen) with oxygen. As oxygen combines with a flammable material, the chemical reaction obviously yields a great deal of heat. The glow of flame is a result of gases combining with oxygen with such a yield of heat that the gas becomes "incandescent".

Normally, the radiation given off by warm objects in invisible. It is of a lower frequency, generally in the infrared range. When an object gets hotter, the spectrum that it radiates widens into visible light. When this spectrum reaches the point that it produces visible light, the hot object is referred to as being "incandescent".

So flame appears as a light, for the same reason that a hot poker glows. It is really, really hot.

[Temujin]

Re: whether fire is a plasma. These folks say it is: http://www.hmco.com/college/chemistry/resourcesite/digests/chemedl/cednov96/msg00256.htm
I'm not a scientist, so I don't know the answer, but I'm pretty sure my teachers told me fire was an example of plasma. Has this been a topic of ongoing scientific debate?
(Maybe this should be a separate topic.)

[Coach]

Ok.. Fire is the quintecential oxidation of a substance. Take a log, burn it in a controlled environment and it will weigh more than when you started burning it. This is due to Oxidation or the addition of oxygen molecules to the structure molecule. We're talking basic chemistry 101.

Plasma is the dis-orientation of atoms in a steady state (debatable). While fire rearanges molecular structure, plasma (high heat) rearanges molecules and atoms themselves. "Fire" could relate to all of these, but I'd hold it to the norms of what happens on Earth for now; you never know what some "Joe" will think up next.

[Temujin]

... Fire does indeed contain ions and is correctly called a plasma. ...
Roland Stout, Ph.D.Physical Sciences
UNC-Pembroke
Pembroke, NC 28372-1510
(910) 521 6672 (voice & voice mail)Stout@nat.uncp.edu
(cut and pasted from the Houghton Mifflin Co. message board)
So this guy is wrong then. Right?

[sunbear]

You guys forgot phlogiston. It explains everything.

[CatInHat]

Back to the original topic ...

It seems unlikely that the steam above an open pot is much hotter than 212F. That's because the steam is being cooled both by the 212F water below it, and by the (much cooler) air above it. So at steady-state, the steam might be a little hotter, but not much. I'm also assuming that the air pressure inside and outside the pot is the same; i.e., that it is open at the top.

This hypothesis is based on a year of college-level thermodynamics, so it's not entirely a WAG.

------------------
The Cat In The Hat

[Sofa King]

A plasma is a gas that is so energetic the particles knock electrons off of each other and the gas itself therefore conducts electricity. Or as it was much more eloquently put above, an "ionized gas."

Plasma is made by combining fire and air, and a few more gin and tonics, please.

Know those cute little teapots that whisle when they come to a boil? That clear part just at the tip of the whisle is steam while the cloudy water vapor is... water vapor. Since the whistle is made by overpressure within the pot, it is safe to assume that that little clear jet is much hotter than 212 F @ s.l. Once it vaporizes, it is back to 212 and below.

I think you guys are somewhat misinterpreting B_Line's question. I agree in essence with Squid; if a sufficiently powerful heat source is applied to the bottom of the container, it would become hot enough to 'flash' the water molecules to steam at a temperature somewhat hotter than 212 degrees. Squid said to disregard the effect of overcoming the water pressure -- I say this is probably the decisive factor that permits the steam to reach ~ 90+ over 'normal' boiling point just above the surface of the water.

As for fire being plasma -- which is hardly 'science fiction', Sofa King, where'd that come from? -- wellllll, it's stretching a point. 'Fire' as we might conventionally think of it coming from the burner of a gas stove may contain some ions, but it's certainly not predominately composed of ions. I think it would be more scientifically accurate to say 'fire contains individual plasma molecules/atoms', but the most reliable test (to me) would be, can you contain the gases in question (or at least control their motion) with a magnetic field?

And Coach, just FYI, the word you meant to use is 'quintessential'.

[Undead Dude]

I agree in essence with Squid; if a sufficiently powerful heat source is applied to the bottom of the container, it would become hot enough to 'flash' the water molecules to steam at a temperature somewhat hotter than 212 degrees. -- DIF
Yes, slightly perhaps. But the important thing to remember here is it can't heat the steam to a temperature hotter than the pot itself! There is no way that that pot (on a normal stove at least) is gonna get up to 300 F, while it is full of 212 F water!

[Undead Dude]

Re fire being a plasma--

After reading some of those articles, I am going to say that I guess fire can be called a plasma. Multiple folks there claim that flame has a noted increase in electrical conductivity. This is the first time that I have heard of a flame described as such. It is probably much less ionized than your typical plasma tho.

Yes, slightly perhaps. But the important thing to remember here is it can't heat the steam to a temperature hotter than the pot itself! There is no way that that pot (on a normal stove at least) is gonna get up to 300 F, while it is full of 212 F water! --Undead Dude
==========================================
Agreed, but I believe that averaging the temperature of the pot bottom is where you introduce the error -- e.g., on the spot of the bottom where a gas flame's hottest point (what's the name for that, BTW?) might be adjusted to be, that point will alternately (millisecond to millisecond, I suppose) vary from hundreds of degrees to ~212 (as the bubbles form and detach, allowing more water to rush in and reheat).

[Mr Thin Skin]

I just conducted a little experiment in the kitchen. I heated a kettle of water to boiling, inserted a food grade thermometer through the whistle hole, and held it for quite a while. The temperature stabilized at 100 C. I was careful to keep the tip of the thermometer out of the water.

Let's talk about physics now:

To boil water, you must supply sufficient energy to raise the temperature of the water to about 100 C. Now, more energy has to be provided to push the water from liquid to gas. This is the heat of vaporization. Numerically it's 539.55 cal/gm. That's a considerable amount of energy.

Now, on to condensation, the heat of vaporization must be given up before water vapor can condense. The vapor condenses to 100C water, with the extra energy being absorbed by you, the heatsink.


The burn you receive from sticking your hand in steam comes not from the temperature of the gas, but the energy given up in the state transition from gas to liquid. Set your oven to 100 C and stick your hand in. I bet you could keep it there for quite some time.

So, since the vapor is 100C with loads of energy available with a state transition, why did the thermometer I used in my experiment not show a temperature above 100C--because the actual physical thermometer was coated with water at equilibrium with the vapor. Suppose a molecule of water condensed on the thermometer. It would deposit its energy into the water coating. You could consider it as raising the temperature above 100C. With this new energy, a water molecule could escape the water coating and join the vapor. The physical thermometer also conducts heat out of the kettle, into my hand. The thermometer drops below 100C, some vapor condenses, and raise the temperature back to 100C.

Ok finally, in terms of energy absorbed per some unit of time, what worse, bathing in 100C water vapor, or 100C water? Back to the stove! From a number of trials, I found that it took on average 12 seconds to raise the thermometer’s temperature from 10C to 100C when submerged in the boiling water and about 14 seconds on average for vapor only measurements. I performed four trials of each, interleaving the tests. I would have used a piece on meat on the thermometer to simulate my flesh, but I fresh out of the stuff.

Now as I mentioned in another topic, I am an expert magnet. An expert on the topic will now appear, call me an idiot, and give you another story.

[Squid Vicious]

OK, OK. Undead Dude I concede your point..sorta. Being a "scientist" I decided to rely on empirical evidence. So, while you guys have been arguing, I did an experiment. I put 1 liter of water in a 3 liter erl. flask and started heating it. The temp of the steam (as measured by a temp probe suspended into the steam) never exceeded 212 deg. F; UNTIL almost all of the water was gone. The temp then rose dramatically and leveled off to around 250 deg F. I blame this on my heat source. I used a rather small hot plate. So I'll stand by my statement that if you impart enough energy to flash the water into steam it can become superheated. However, practically speaking, the steam is around 212 deg F.

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"If you stick your finger in a pie, whatever is in the pie will be on your finger, and whatever is on your finger will be in the pie...unless you wear a rubber glove"----some demented old lady

[Undead Dude]

I must say that I am impressed with the initiative of the empiricists! Who wants to volunteer to collect eveidence for relativity? ;)

The burn you receive from sticking your hand in steam comes not from the temperature of the gas, but the energy given up in the state transition from gas to liquid. Set your oven to 100 C and stick your hand in. I bet you could keep it there for quite some time. -- Mr Thin Skin
The reason that you don't get burned quickly if you stick your hand into a 100 C oven that contains only air, is because air is of a very low density, and has little ability to transfer energy to you.

I really think that the role of vaporization heat is overblown a lot in this thread. Certainly it is there. Certainly it is important. But I don't think it is nearly as important as has been frequently suggested.

It may very well be the case then when you stick your hand in 100C steam that most of the energy imparted to your hand will be the heat of vaporization. That is to say, the energy to convert the steam to water might be (I haven't actually tried to calculate this yet) more than the energy to to reduce the condensed water droplets from 100C to skin temperature. However, I bet that a lot more energy would be transferred if your oven was filled with 95 C water.

So, since the vapor is 100C with loads of energy available with a state transition, why did the thermometer I used in my experiment not show a temperature above 100C--because the actual physical thermometer was coated with water at equilibrium with the vapor. -- Mr Thin Skin
Well, no the reason that the thermometer did not show a temperature above 100C is because the vapor/steam is 100C! Heat transfer cannot occur from a colder object to a warmer object. That is fundamental to the concept of temperature. Once the thermometer reaches 100C it no longer causes condensation.

From a number of trials, I found that it took on average 12 seconds to raise the thermometer’s temperature from 10C to 100C when submerged in the boiling water and about 14 seconds on average for vapor only measurements. -- Mr Thin Skin
Of course condensation sets in very quickly when the steam hits cool air, so much of what would contact your thermometer would have already condensed beforehand. Unfortunately a definitive experiment of this nature would be rather hard to do without special equipment. A good test would involve putting a thermometer into a sealed container of dry steam, and comparing that to a thermometer put into a sealed container of water at the same temp.

[Undead Dude]

So I'll stand by my statement that if you impart enough energy[...] However, practically speaking[...] -- Squid
I'm with you here. A lot of the fun of science is considering the impractical, yet non-impossible. :)

[Undead Dude]

that point will alternately (millisecond to millisecond, I suppose) vary from hundreds of degrees -- DIF
You really think the variation would be that high? This is a judgement call, but I think that with a pot made of a normal material, a hot spot would become a haven for nucleation (thus cooling the pot) long before the hot spot would get very far above 212F. Keep in mind that most of the cooling of the pot is taking place while the bubble is expanding (as this is when vaporization occurs).

[Mr Thin Skin]

Ok Undead, riddle me this:

If 1 gram of water vapor condenses on you, how much energy is absorbed by you?

63 calories because the water is 100C to start and you ar 37C to start.

539 calories because of the state transition.

That's almost a ten-fold difference.


About air density. Dry air is more dense than steam. The barametric pressure is greater on cold humid days than it is on hot dry days.

Look, I'm not saying that immersion in boiling water is less dangerous that immersion in steam, I'm saying that with a sufficient flux of steam they're close to equivalent.

Also, my equilibrium description is correct. Molecules don't know the temperature of anything. They land, they leave. That's how it is.

Sorry, got to go have surgery now. Bye

[Undead Dude]

Well, that's clear then that most of the heat from steam would come from the heat of vaporization . I guess my attacks on heat of vaporization were really kinda irrelevant to what you were saying.

Look, I'm not saying that immersion in boiling water is less dangerous that immersion in steam, I'm saying that with a sufficient flux of steam they're close to equivalent. -- Mr Thin Skin
And I would agree with that. It goes along with what I said about circumstance, rather than heat of vaporization.

Also, my equilibrium description is correct. Molecules don't know the temperature of anything. They land, they leave. That's how it is. -- Mr Thin Skin

Well, no. You can't discuss temperature and vaporization and then turn around and tie that to the nature of individual molecules. That crosses the line from thermodynamics to quantum mechanics. Concepts like vaporization and temperature are meaningless outside of the context of large agregates.

Let's put it this way. When your thermometer reaches 100C, an equilibrium between vaporization and condensation will be reached resulting no net increase in condensation. That is what I meant by "no longer causes condensation".

[Omniscient]

Well done UD, I see no error in your logic, reasoning, and most importantly facts. One can pretend that a couple of molecules over a hot nucleation site at the bottom of a pan (contradicting the fact you expressed saying temperature is a non-issue when dealing at a molecular level), but it doesn't relate to the question at hand. The very hot steam at those points will transfer all the excess heat into the water as it rises to the surface. So even if you could measure heat at a molecular level, it wouldn't propose a possible situation where 300F steam at the surface of the pot can exist.

[Lumpy]

Sorry to change the subject again, but I had to put my 2 cents worth in on the subject of flame:

When you see a red, orange, yellow, or white flame, what you're seeing is soot particles boiling off the flame source, being briefly incandescent before being oxidized. A flame with complete combustion produces only that blue glow like you get in gas stoves. An ordinary flame like a candle flame is actually inefficient; it has to "smolder" enough for you to see a luminescent flame.

You can prove this, if you want to spend a few bucks: go out and buy a gas mantle, the kind that go in camping lanterns. Follow the directions on the box for priming it. Then presuming you have a gas stove, light the burner and put the gas mantle on it.

You will get a blindingly bright light as the heat of the flame makes the mantle incandescent. The mantle will probably quickly burn out, since they weren't intended to take that much punishment, but it demonstates the principle.

[Undead Dude]

Ya know, Mr Thin Line, now that I look back at your previous post, I see that you were already talking about the equilibrium of water and vapor. Geez. Why didn't I see that? I guess I was just rushing to the issue of heat transfer. So it looks like although I reacted to much of what you said, there really isn't anything that I should have been disagreeing with.

[sunbear]

How to enjoy steam up to 212 deg F in the sauna: http://www.sauna.fi/pages/recomm.htm

I seem to remember sauna thermometers going to 120 deg C, but most people leave the room at 90 deg C. The steam is generated by hot rocks, so not much to do with the boliling kettle problem.

Have you guys applied the ideal gas law (PxV=nRT) to figure out what pressure is needed for 300F? You deal with deg Kelvin!

[Squid Vicious]

Sunbear, The ideal gas law is not really usefull in this situation. For one thing water is far from an ideal gas. However it would work as a close enough approximation as long as you stayed within the gas phase area of the phase diagram. Also, we're not talking about a closed system. The pressure is constant at 1 atm and the volume of the water increases about 1000 times from water to steam. The easiest way to find the saturation pressure of water at a certain temp is to use either a steam table or a phase diagram. Once again though, for practical purposes you would apply them for a closed system. It doesn't work for this system.

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"If you stick your finger in a pie, whatever is in the pie will be on your finger, and whatever is on your finger will be in the pie...unless you wear a rubber glove"----some demented old lady

[sunbear]

Well, use any table then.

Continuing with steam/sauna, I have a report of 120 deg C in a sauna.Nobody was in it, but it broke the thermometer at that point. They used to kill lice in the Finnish army(about 1940) with this method, from clothing, not people.

[Undead Dude]

Geez. And of course I meant Mr Thin Skin, not Mr Thin Line. Our A/C was out for a few days, and I think all this talk about heat was making me loopy. :)