A physics question~

[xyz]

Ok, I have a question that caused much debate between myself and a school teacher I used to have. Ok the class was related to HVAC and the question was "At what temp does steam form?"
I answered on a test that "It all depended upon the temp of the air around where the water was being heated." Well he said I was wrong, that steam formed at 212 degrees Farenheit. I told him that he better check his credentials if he was to teach that class because that was the boiling point of water, not when steam formed. I'm not no Einstein but water can boil at different temps depending on altitude and barometric pressures right? please tell me if I'm wrong, I'm not creating this thread to say I'm right or who's right, I only want opinions. this has driven me crazy for many years now and I've never gotten a definitive answer from anyone on this.

 

[tuthill]

Chemistry not physics

Yes, water vapor can form at many different temperatures. The phase that water exists is a function of BOTH pressure and temperature. If you bring a pot of water to the top of Mt. Everest (low pressure), it will boil at less than 100 degrees (no, you cannot do European FL sanitary cycles on the top of Mt. Everest). The following is a "phase diagram" showing the different phases of water under given pressure and temperature. XYZ ironically enough. Note the "triple point," the point where all three phases of water can exist simaltaneously.

 

[thor]

xyz

To clear this dilemma maybe we will have to differentiate between water steam and water vapor. I guess when ice slowly "melts" by sublimation inside the freezer compartment at 0 °F it really doesn't turn from frozen water into steam but it does turn into water vapor. What is usually known as steam is 212 °F water vapor (at normal atmosferic pressure). When we see fog we are really seeing water vapor and not water steam.

I hope this helps.
Emilio

 

[tuthill]

Triple point

Not the greatest picture, but you can see the water, ice, and steam.

 

[tuthill]

O and you were saying you wanted opinions...SORRY. This is concrete testable SCIENCE, no opinions allowed. (granted the scientific community was not founded this way and new research isn't done this way either, but for something as simple as vapor pressure, opinions don't exist.)

 

[xyz]

Well put Tuthill~ I understand the diference in steam and vapor but let me be a lil more specific on that question on the test. It pretty much was referring to what temp did steam form inside of a boiler like one would see in the heating industry that would send heat out to radiators in other buildings in a factory setting. Anyways in that case, I still refuse to believe that steam didn't form before the temp hit 212.

 

[xyz]

kinda related here but isn't absolute freezing 460 degrees below zero f? and it has never been acheived? close but never acheived? This is when all atomic matter ceases to move? Correct here or not? It's been along time since I played with physics but it is in my heart.

 

[tuthill]

Your test question is a very poor one at that. Shame on your teacher.

Yep, absolute zero is, in theory, when all molecular motion stops. -459.67 F to be exact. Weeeeeeeeeeeiiiiiiiiiiiiiiiiiiirrrrrrrrrrrrrrd things start happening when you get close... and it is IMPOSSIBLE to actually achieve absolute zero. This can be explained very simply. To cool something down you have to transfer heat energy from it to it's surroundings. If I have a liter of water at 20 C and a litter of water at 40 C and I combine them, the temp of the water will be 30 C. Because the new "cooled" temperature will always be an average of the two, it is impossible to actually get to zero.

 

[nasadowsk]

Meanwhile, about 80 miles south of me, in a big concrete box by the water, there's a vat of very pure water circulating at around 1,000 psi, with a bit of it boiling at around 500+ degrees, as it cools a few thousand metal tubes sitting in it. The steam's going off the spin a turbine, then it'll be pumped back into the vat to circulate and boil again.

The boiling temperature of water's a function of pressure - more pressure = higher temperature to boil the water.

(Bonus points to anyone who can guess where that box is, who made it, and what model of box and boiling water vat it is. And why it's special, among its type)

 

[maytagbear]

Just a guess.....

Could it be a boiling water nuclear reactor?

Lawrence/Maytagbear

 

[nasadowsk]

Oh it's a BWR, but it's special (there's another unit out there in the US like it, it's special too) for a few reasons.

 

[nurdlinger]

Babcock & Wilcox Three Mile Island Autograph Model?

 

[tuthill]

Nine Mile Point Nuclear Generating Station

1n 1991 a Sight Area Emergency occured at the plant, making it only the 3rd time a SAE had been declared in the United States?????????????????????????????????????????????????

 

[nasadowsk]

Oyster Creek, actually

Nine Mile is the other plant of it's type (BWR/2) in the US. They have a certain distinction among currently operating (hint, hint) plants in the US.

OC is known for something else - it's was GE's first 'turn key' nuke plant. Just about everything prior to it was a prototype.

I believe (I'm not sure) that it was also the first Mark I containment that GE built (another hint). Humboldt bay might have beaten it (never saw a cutaway of that place though - it's got something in else common with the new GE BWRs, though)

 

[neptunebob]

I think Oyster Creek might be the oldest nuclear plant in the nation that is still operating - and they plan to run it for another 20 years!

Now, to answer the question about pressure in the Westinghouse reactor, the water is so pressurized it doesn't boil at all even though it is 600 degrees.

Oh, and I got into a dispute with my heating and air conditioning instructor too over electricity being more efficient than gas.

 

[stevet]

Come on now..where have all your memories gone?

Now let me try to remember.. I took biology and physics back in 1967 and 1971 respectively and remember that in order to change water into steam at 212 degrees, you needed to heat the water to 212 degrees by adding one btu per pound of water to raise the temp of water one degree but needed to add 180 btus to change the water at 212 to steam vapor. That is why a steam burn at 212 degrees will casue more harm to you than water at the same temperature. There is more potential (heat) energy in that steam. And don't forget that when water expands into steam, it increases its volume by over 1700 percent!

Now why does that stay with me for all these years?

Are my numbers correct? Just off the top of my head(where there is little else!).

 

[volvoguy87]

I'm no expert but I am VERY familiar with steam locomoti

Water should not boil in a boiler. The pressure in a boiler prevents boiling, thereby allowing the water to rise in temperature well above 212 degrees. This allows the steam to contain more energy (hotter steam has more energy).

The water WILL boil if there is a drop in pressure, such as a breach in the boiler (a boiler explosion). Also, as you release the pressure, the temperature will drop.

A note on boilers and explosions: There are two main types of boilers, fire tube and water tube. In a water tube boiler, the round case contains the fire and exhaust while the tubes inside contain the water. This type of boiler is pretty common. A fire tube boiler (used on most steam locomotives) contains the water within the round case and the flue pipes contain the hot exhaust gasses and carry them from the firebox at one end to the smoke box at the other.

In a steam locomotive boiler explosion, what usually happens is the water level gets too low in the boiler and goes below the crown sheet (the top of the firebox). With the water no longer on top of the crown sheet cooling it, the crown sheet really heats up and gets soft. The steam pressure (in a locomotive it can be between 150 and 300 psi) is on one side of the softened crown sheet and there is roughly atmospheric pressure below in the firebox. The crown sheet then gets pushed down into the firebox and tears away from the staybolts (which normally hold the crown sheet firmly in place).

First, the crown sheet tears, causing a breach in the boiler. Second, the steam starts escaping into the firebox, where it goes through the flues expanding all the way. Third, the steam starts shooting out of the stack until the stack reaches capacity. Then, the front of the smokebox blows off (this is the round metal plate on the front of the locomotive). The flying smokebox door alone can destroy another locomotive. The escaping and expanding steam will often blow the doors off of the firebox, blowing the fire and scalding steam into the cab of the locomotive, usually killing the engineer and fireman instantly. In severe cases, the boiler can lift off of the locomotive's frame and travel up to a half mile at supersonic speeds. From the moment the crown sheet tears to when the boiler lands can be less than two seconds, all thanks to water under pressure well above 212 degrees flashing instantly to steam upon the release of the pressure.

Less severe boiler failures on locomotives did happen, and people sometime lived, but the scalding caused excruciating pain, long recoveries, etc. etc. If the crew died in the explosion, it was so fast they never would have known what hit them. If they lived, they often had to wait to be pulled from hot wreckage.

Many people have perished in boiler explosions, and it is essential to ALWAYS respect your boiler. Keep it well maintained, insect it regularly, and operate it safely. A boiler is one of the most dangerous (and useful) things man has ever created.

Keep warm, but safely,
Dave

 

[nasadowsk]

Yeah Westinghouse's PWR runs at about 2X the pressure of GE's design.

Westinghouse also pioneered the concept of the containment - Shippingport had one. GE of course had one too - the VBWR (I think that was actually power reactor license #1!) had something close, Dresden had the stylish (but impractical) sphere, as did Yankee Rowe, Big Rock Point, and San Onofre #1.

On nuke power plant built in the early 60's didn't have a containment. It only operated for a few years, and to date, is the only commercial (well, almost, it wasn't fully comercial) nuclear plant ever built without one.

Anyone know what plant it is? And why its designers argued it didn't even need one?

 

[tolivac]

Babcock & Wilcox also built PWR nuclear boilers for the commercial power industry.
the first nuke plant I heard of was built outside of soux Falls SD in the fifties.It was used to replace the Hydroelectric power plant that originally powered the Soux Falls electric system.I remember reading about this when I was at the visitor center in soux Falls,SD.The containement building for the nuclear reactor there was spherical.The plant was converted to coal.For US power reactors the containment buildings were required by safety codes.and they had to be strong enough when the codes were written to withstand a direct airplane strike.And no one was allowed in the containment building when the reacter was in use.

 

[volsboy1]

Yep he is Wrong..It depends on Thermodynamics and what the pressure is.Most Us nuclear plants pressurize the water to raise the boiling point.I am talking about p.w.r. reactors not the BWR types.I would have gone and got me a cup of coffee if I rember they are steaming and not boiling.You are right.Now if you really want to piss him off like I did quote some quantaum thermodynamics and superfluidity,Equilibrium Thermodynamics and Non-equilibrium thermodynamics.Your taking H.v.a.c. does he not know about the Carnot cycle?I went to the head of the department on my final that he graded and he was wrong.I was not taking H.v.a.c though this was in particle physics.

 

[peterh770]

But is "steam" the same as "vapor", the same as "fog", the same as "mist". Sound more to me like some definitions are needed. Isn't steam the result of water that is vaporized at the boiling point? If so, then steam forms from water at 212 degress F...

 

[xyz]

But Peter, cannot steam rise from a cup of coffee that is a mere 120 degrees or so? Or is that mist? or smoke or fog or whatever else some may like to call it. What about your your bathtub water or shower water's steam? I know it's not at 212. Not trying to be a smartass, just asking opinions and I sure got some good ones. Thanks.

 

[xyz]

My baby brother and I used to go to Kindergarten and the school was located on the banks of a rather large pond. We lived 5 blocks from the school and when we went to the car to go to school there would be no fog in the air. When we would approach the pond and school we always saw fog on the water and could, as my baby brother callled it, "blow smoke out our mouths. I know the difference in these things but really, what temp does steam form at? I guess it all depends huh? I'm sure the temp and dew point was different at our house 5 blocks away. So the pond would be considered a microclimate?

 

[neptunebob]

This would have been the right answer in a physics or enviro

But the question I had a debate with was over whether electric heat was 100% efficient. I said no, because gas or oil or a fossil fuel would have to boil water in a power station and some the heat goes up the chimney so wouldn't that be less efficient than if you burned gas in a gas furnace? Correct me if I am wrong. I'm surprised Professor Rich the Sudsmaster hasn't said anything yet.

I do know that the boiling point of water is directly proportional to the pressure, that is, the lower the pressure the lower the boiling point to where in outer space, water would instantly freeze and never be a liquid and would eventually gasify. In fact, I think that is how they make freeze dried instant coffee. So glad I was interested in the space program when I was young.

Nuclear and even fossil fuel power stations are pressurized becuase the steam must be very forceful to spin the turbogenerator so there temperature is up to 600 degrees.

Oh, and speaking of power stations, the new Westinghouse AP1000 has a special cooling system that actually fills the outside of the reactor vessel with water to prevent a meltdown or an explosion. Seems to be a good idea, I just wished the place didn't look like a dunce cap.

http://ap1000.westinghousenuclear.com/ap1000_safety_ircd.html

 

[sudsmaster]

I know that one of the earliest semi-commercial nuclear reactors was a small one built near Sunol, California. I don't think it had a containment building, but it's been a while since I read up on it. It was decommissioned years ago but I think the site is still off limits. It's also situated very near the aqueduct that carries water from Yosemite to San Francisco.

 

[nasadowsk]

You're getting closer - the California was was the (in)famous SRE reactor. It could put power to the grid, though as a bonus, it was an experiment, really. But it's successor was designed from day one as a power plant, and it didn't have a containment, either.

Anyone know what plant that was? And what was the coolant - and why they felt a containment wasn't needed (though today, no doubt, it would be with this technology)?

 

[Cybrvanr]

cooling loops

The idea behind a boiler (and your automobile's radiator system) is to raise the pressure, and thus raise the boiling point of the water. Now, in a closed-loop steam engine, similar to what's used in a power plant, or in a steamship, the boiler boils the water under pressure. That water, under pressure to about 250 PSI or more, then travels to the engine where it's pressure is reduced, flashing the water to steam, and powering the apparatus. The low-pressure steam (usually about 25 psi or so now) goes to a condenser, where it is changed back into water, and it flows back to the boiler.

My big question is however, is what makes the water go back INTO the boiler? If the pressure is about 25 PSI, and the pressure in the boiler is at 250 PSI, then I would think that the water would not flow, but the system would just equalize in pressure and not do anything. Is there a pump or something to force the water back into the boiler against the internal pressure?

 

[tolivac]

In the case of power plant boilers-nuclear or fossil fueled-the intake to the boiler isn't pressurized.The water from the low pressure section of the turbine (most of these LP turbines are what is called "condensing"the steam is converted to water at the exhaust of the turbine)In other turbines(non condensing) this is not the case-the exhaust goes to the plant coolers where it turns back to water-then is pumpted back into the boiler intake with very large pumps-mainly the QUANTITY of water being handeled.The pumps can have motors or small turbines that are up to 4000Hp.The only excpetion on the boiler intakes is on fossil fueled plants they have a three stage turbine system on the generator-And the boiler has two stages.It has a high pressure output(up to 6000PSI!) and a low pressure up to 3000PSI.Most operate around 3000-4000PSI.The steam flow in these fossil plants-first the high pressure steam goes thru the High pressure turbine-next the the water goes back into the boiler where it is reheated again to the medium pressure and passed thru the med pressure turbine. After that there is a crossover pipe from the medium pressure turbine to the low pressure stages.Than the water goes back to the boiler.Nuclear plants have simpler steam systems-nuclear boilers don't have reheat as the fossil fueled ones do.At a nuclear plant-the steam isn't heated to as high a pressure as the fossil fueled plants-the fossil fueled plants boilers run at higher temparatures.Nuke turnbines have a high pressure turbine(up to 2000PSI)than a crossover pipe to the low pressure turbines.After the low pressure turbines the water is cooled in the cooling tower system and then back to the boiler.
On locomotive boilers the water had to be pumpted into the boiler under pressure-a small steam powered reciprocating pump was used.And the steam loco's had steam powered air compressors to pump up the brake system.If you listen to an idling steam locomotive you can hear the steam powered air compressor going if the crew has it activated-it makes a rythimec "Click-Clack" sound.And if you look at the compressor-on the side of the loco-you can see the piston go up and down-the boiler pump works like this.