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.