A physics question~

[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.