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MTGamer t1_j5vapv3 wrote

Reply to comment by radioactive_dude in How hot is the steam coming out of nuclear power plants? by ivy-claw

Wait, can steam exist at 50C, 1atm? Doesn't it have to be at least 100C to not just be a liquid?

Or in this case is it not really steam and just water vapor like breath in the winter?

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Ausoge t1_j5vy30m wrote

"Steam" is evaporated water - that is, water in gas form. It is colourless and invisible. What you see as a steam cloud is actually cooled, recondensed, liquid water droplets.

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BuffaloBoyHowdy t1_j5wfkzm wrote

This. You can't really see steam itself. All that white stuff is water vapor. Look closely at a kettle with boiling water. As the mist comes out of the spout, there should be a clear space at the opening, that's the steam. It quickly condenses into water vapor, which is what you see. Don't stick your finger in it.

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ramriot t1_j5x57pm wrote

Yup, this is why Live Steam is so damn dangerous. If a high pressure steam line develops a crack the escaping steam can sound like a banshee on heat but is also completely invisible. The jet is just hanging out there waiting to slice off your limbs or scald you do death.

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Rangoras t1_j5yyang wrote

If we ever had a super heated steam leak in the engine room we were trained to grab a broom or other stick and wave it in front of you from floor to above your head while moving slowly. When the broom was cut in half by the invisible steam jet you found the general leak location.

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unclepaprika t1_j5wiewo wrote

2 steps forward, 1 step back. Didn't we just establish that steam IS water vapor?

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lurkandpounce t1_j5ym84p wrote

Steam is water in a gaseous form and invisible.

Water vapor is made up of water droplets that are so light they are carried by the air currents.

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BuffaloBoyHowdy t1_j5zc5xr wrote

Steam is water vapor; water vapor is not steam. A square is a rectangle; a rectangle is not a square. Both are parallelagrams; but a parallelagram isn't a square or a rectangle. A thumb is a finger but a finger is not a thumb. Things are just like that sometimes.

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[deleted] t1_j5wmz6o wrote

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TrappedInASkinnerBox t1_j5wy37c wrote

On the engineering side at least the gaseous phase is definitely referred to as "steam" not "water vapor"

Saturated steam, superheated steam, etc

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mightyn0mad t1_j5x4ezm wrote

Seconded. Steam is steam, we do not call it water vapour. Depending on conditions it can be saturated steam (the one that looks white) or superheated steam (the colourless one)

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Angdrambor t1_j5wob3l wrote

>Steam is droplets of liquid water suspended in the air which appears white due to light scattering.
>
>Vapor is colorless and transparent. You cannot see it.

When I took thermo in my country, we refered to it the other way around. Steam is the invisible gas phase, "vapor" is the white cloud of liquid droplets.

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lichlord t1_j5wrrfh wrote

Was it thermo taught by scientists or engineers?

Thermo in chemistry and physics usually simplifies steam into gaseous water.

In engineering thermo courses the focus is less in phases and equations of state, and more on work and transformations. Engineering thermo will often distinguish between wet, dry, and superheated steam.

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CYWNightmare t1_j5x2odw wrote

I thought rainbows were water vapour with light hitting it so wouldn't I see water vapour to an extent?

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Tarhish t1_j5x63jz wrote

I got started at a nuclear plant as a computer/instrumentation guy, and was a little surprised at first by the term, 'dry steam' that got thrown about, though it makes perfect sense in retrospect.

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Become_The_Villain t1_j5z553g wrote

>got started at a nuclear plant as a computer/instrumentation guy

Homer Simpson that you?

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[deleted] t1_j5yw5hf wrote

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Rangoras t1_j5yxvzt wrote

Sea water needs to be desalinated before being used in a boiler. If you only just filtered it for solids the salts in the water would form a nasty layer of scale on the water side of the boiler tubes quickly resulting in poor heat transfer and failure of the boiler tubes. When we make our boiler water on my ships we only use water where salinity is under 5 PPM

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crujones43 t1_j606k33 wrote

Even the highly filtered lake water has enough particulate to build up calcium and sludge inside the boilers after only 2 or so years. I have been on a few water lancing jobs where we install and operate remote tooling to reach between the hundreds of boiler tubes and use a 9000psi water jet to break all the sludge and calcium up.

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[deleted] t1_j5vbsyx wrote

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graebot t1_j5yj1aq wrote

Clouds are water vapour, but I wouldn't refer to them as steam. Technically, steam is invisible, and exists above 100 C at 1 atmosphere. Only once it drops below the vapour point (100C @ 1 Atm) does it start condensing into water vapour. Water vapour is not steam, it's just liquid water droplets suspended in air.
When steam is used to do work, it starts as high pressure, high temperature, and as it does work, the pressure reduces, and the temperature with it, and after doing work you're usually left with water vapor as the spent product.

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blanchasaur t1_j5yrprq wrote

No, that's not quite right. Water vapor is definitely a gas, you can't see humidity. Clouds are a suspension of liquid water in the air, not water vapor.

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bigbaltic t1_j5vg5s3 wrote

What you see coming out from stacks is not steam. It's more like a cloud of extremely humid air

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braize6 t1_j5vy5fo wrote

In power plants, water is under pressure. Increasing the pressure, also increases the boiling point. The water at my plant is around 800 degrees Fahrenheit, yet still a liquid. We do this through a series of enclosed heaters, which actually increases pressure as steam is released, which in turn makes the steam condense back to water at a higher temperature. Our plant does this 3 times. Which then the water goes into the boiler. This process is called superheating. Or known as "superheated steam."

Our throttle pressure is 3500psi. So you can imagine just how hot our water can get before it turns into steam (there's a chart out there if you're curious about pressure and temperature of liquid and steam.) Now let's add that water expands about 1600 times from liquid to steam. The result, is a massive amount of energy.

Edit- I appreciate the feedback, and yes, there are many different processes that are going on, in order to generate power, and the boiler process. I'm trying to simplify, because to explain the entire process I'd need about 50 more pages, as it seems many here also know.

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racer_24_4evr t1_j5wyztb wrote

Superheating is when you take steam that is at the boiling point for the given steam pressure, and heat it further. I believe what you described is preheating feedwater.

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Coomb t1_j5xc81d wrote

More likely it's a combination of preheat/superheat/reheat. If you follow a little packet of water through a plant with feedwater preheat, then superheat, then reheat, you get "three times" through the heater. But the description does leave something to be desired.

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racer_24_4evr t1_j5y59ny wrote

Yeah, in our plant, we have three boiler drums, each with preheating and superheating, as well as a reheat on exhaust steam from the high pressure side of the turbine, so there’s a lot of heat moving.

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braize6 t1_j5y905y wrote

Yes it leaves a lot to be desired, because well, there is. The entire process would take me the rest of the month to specifically explain. If someone is interested in all of that, the info is out there

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braize6 t1_j5y8vnx wrote

Basically, yes. With the result of the preheated feedwater going to the water walls, to the economizer, to the superheater to the..... Honestly I could go on for a while here as you seem to also know lol

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racer_24_4evr t1_j5yc8xx wrote

It’s cool to talk about, people don’t realize how much goes into operating a large high pressure version of a kettle.

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Angdrambor t1_j5wnycf wrote

What comes out of the towers, if it's visible, is water droplets suspended in air. Steam is clear in air, but it partially condenses into visible clouds of droplets if it cools down too much.

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lemlurker t1_j5ybumj wrote

It's not steam by the time it exits the tower. It's condensation like clouds

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DrunkenGolfer t1_j5ws4fu wrote

The boiling point is just the point at which a liquid can no longer remain a liquid. It can become a vapor at much lower temps, below freezing even.

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Old_comfy_shoes t1_j5za47o wrote

If you have some water and it touches something very hot, the water can't exceed 100C, because as soon as it does, it becomes steam. But the steam can be crazy hot. So with enough temperature difference, if you plunge something crazy hot into water, the vapour won't instantly escape, and the heat transfer could be very rapid creating larger pockets of really hot steam, only the outside of which would be cooled by the water. So, the steam can be much hotter. But the water must stay at 100C in order to be water.

Steam, should always be hotter than 100C, which is why it converted to steam. It's essentially water that is hotter than 100C at 1 ATM, by definition. But usually it would only be a little bit hotter in conventional use. 300C seems like a lot though. Idk anything about reactors, but I think they plunge massive insanely hot rods into water?

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Seraph062 t1_j63qqh0 wrote

> But usually it would only be a little bit hotter in conventional use. 300C seems like a lot though. Idk anything about reactors, but I think they plunge massive insanely hot rods into water?

You generally want steam for turbines to be pretty hot, the ones I'm familiar with usually run about 500°C. There are a few reasons for this, hotter steam is generally easier (and more efficient) to extract energy from, it's also better for the turbines because droplets can cause damage and higher steam temperatures help avoid droplet formation.

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