Okay, this is both convoluted and far-fetched and is likely gonna be shot down in flames, but I am placing this into G.Q. because I’m hoping it really does have a solid answer coming its way. Here goes.
I envision a power generating station of a type I’ve not heard of before. I saw a photograph of the wind generators, they are the lovely fields of tall shafts, topped with white blades. AFAIK, they turn turbines, generate electricity. All well and good.
This idea is based on something I remembered, as I looked at the photo of those huge wind trappers.
130 years ago, people could create a vacuum by hand-cranking a vacuum generator. Keep this in mind.
If you took the MECHANICAL energy of those rotating blades, and used them to pump air out of immense tanks? Water boils at a MUCH lower temperature in a vacuum. Instead of trying to generate power directly from those blades, use them to make the water used in boiling water reactors exist in a vacuum.
That way, it’d take MUCH less coal or oil or gas to boil a set amount of water, and you could essentially boil water/turn your turbines using much less raw energy sources. That would make electricity cheaper to generate, since the water would boil at a lower point.
Is this possible, and is this being done? Why wouldn’t it be possible? And, would it be a finer use of the mechanical energy trapped by the rotating fan blades?
It takes energy to create a vacuum. You are essentially pushing the air out into the atmosphere which is no different than pushing air into a tank uder pressure. This part isn’t free.
Yes, you can boil water at lower temperatures if the atmospheric pressure is lower but so what? You’ve got water vapor at room temperature but it’s at a significantly lower pressure than the normal atmosphere.
So you’ve got your less-than-atmosphere-pressure cold “steam.” The only way you can push something with it, turbine or piston or whatever, is if the pressure on the exhaust/outside is lower than the “steam” pressure. Unless you pumped all the air out of the atmosphere making it a lower pressure still your steam turbine will suck instead of blow.
It takes energy to create a vacuum. You are essentially pushing the air out into the atmosphere which is no different than pushing air into a tank uder pressure. This part isn’t free.
Yes, you can boil water at lower temperatures if the atmospheric pressure is lower but so what? You’ve got water vapor at room temperature but it’s at a significantly lower pressure than the normal atmosphere.
So you’ve got your less-than-atmosphere-pressure cold “steam.” The only way you can push something with it, turbine or piston or whatever, is if the pressure on the exhaust/outside is lower than the “steam” pressure. Unless you pumped all the air out of the atmosphere making it a lower pressure still your steam turbine will suck instead of blow.
Say you have a windmill which produces 1 Kw of mechanical power at the output shaft. You can probably convert 80 - 85% of that quite easily into electrical energy just by turning a generator. Now pray tell me where and how your system “multiplies” the energy. I think you fail to grasp even the most basic concepts. It would be like saying you can take a dollar, convert it to Yen, then to euros, then to pounds and then to dollars and you end up with two dollars. It ain’t gonna happen.
What you will find is, by creating the lower entropy state of the vacuum, you will not be able to transfer as much energy to turn your turbine. At best you will get the same efficiency out of your generator if you essentially expend all your energy in keeping the vacuum.
Think of it this way: in order to keep a vacuum you have to expell the atmosphere. The water will “boil” in order to create an atmosphere which you will then have to expell in order to keep the water boiling at this lower temperature.
It was worth a shot… not exactly an idea out of left field because operating certain kinds of generators in vacuums IS used in order to eliminate friction and resistance. However, thermodynamics ultimately has you beat on this one, I’m afraid.
I have heard of a theory in which turbines would pump air into an air-tight abandoned salt mine, storing air pressure, during off-peak hours during the night.
During the peak daytime hours, the pressurised air would be released, driving the turbines to produce electricity
No need to get nasty with epithets. Cartooniverse asked a straightforward question that seemed logical. Anyone can say that the idea won’t work but our mission at SDMB is to combat ingorance. Explaining why the idea won’t work in layman’s terms is a bit trickier. It wouldn’t be incorrect for me to say “can’t be done, second law of thermodynamics” but that would cheat the OPer of a good answer. The second law is probably one of the most misunderstood and misused things in physics. Won’t be combating ignorance if I stop there.
Cartooniverse I’m not sure I even answered the question adequately but I think it’s a start.
Padeye nailed it. Basically, chemically-fueled power plants convert chemical bond energy in oil or coal to heat, then to mechanical energy, then to electrical energy. Vacuum evaporation just adds a step to the process.
You would need much more throughput of low temperature, low pressure steam to extract the same energy that you would get from high temperature, high pressure steam. Adding the extra step would just drop the efficiency of the cycle as a whole.
The New York Power Authority does this with water at its pump-storage facility at the Gilboa reservior.
They have a small reservior excavated out of the top of a hill and they use hydro turbines to pump water into it from the main body during off-peak hours. During peak hours they let the water fall and use the turbines to generate power.
The low pressure water will form steam at a lower temp. due to the heat of vaporazation. This gives us some possibilities.
1 OK you can use it for cooling the ‘exhaust’ side of the turbine of a conventional (or nuke) PP which will allow it to produce more energy.
2 You can use the low temp water directly for cooling instead of a AC.
3 - Hi Opal
The 1st one would most likely take more energy then you would get from it but should work. The 2nd might be more efficient then a conventional PP plus the AC.
As an alternitive could you use a vacuum maker as a power sorce by itself?
1 The easiest way would seem to let replacement water in and let it expand through a turbine.
2 Lets look at this possibility. Take the water and reduce pressure> Water boils and temp drops. Take this low temp water and expose to ambiant air through heat exchanger. Temp/ pressure of the low pressure steam goes up - perhaps forming water vapor which isn’t going to get you very far. What you would want to do is increase the temp while maintaining the low pressure.
Nope I really can’t do that much with that right now - maybe later.
Yeah but … steam doesn’t provide all that energy to turn turbines just because the water boiled to make it. The energy came from the heat added to the water in order to change its state from liquid to vapor. The water boiling is more or less incidental.
At low pressure, like a reasonably good vacuum, the water will boil without adding any energy to it at all so the only energy contained in the vapor is that in the cool water to start with. Changing its state back to liquid will not result in the recovery of any energy unless you cool the resulting water below its beginning temperature. And how do you do that?
Pumped storage is fairly common. As Exgineer said, water is kept in a reservoir, called a forebay at the outlet of the main dam, during the hydro plant’s normal operation. Then during slack times on the grid, the generator-turbine combination is turned into a pump to pump the once-used water back up into the main reservoir at its higher level.
Those in northern California, Oregon and Washington are on alert for any attempt to export their water elsewhere, but the pumped storage idea does just that. Take the San Luis Dam in the San Joaquin Valley. During the day water goes out the turbines generating electricy and is kept in the forebay. Then at night the turbines pump the forebay water back up behind the dam using electrical power drawn from the grid. In order to do this, more water than would otherwise be used has to run out through the turbines in northern California, Oregon and Washington. In effect, a fraction, depending on the process efficiency, of that excess water has been transferred to the San Luis reservoir. Ha Ha.
The entire point of heating the water with combustible fuel is to create high pressure steam to run the turbine.
Simply opening a large hole in the top of the boiler would allow the water to boil much more easily. But, all the energy to drive the turbine would go out the top.
Using a wind turbine to draw a partial vacuum in the boiler would be worse than simply putting a large hole in the top. If the wind turbines did their work fast enough you might spin the generator turbines backwards due to the partial vacuum causing backflow through the system. At that point, you might as well get rid of the water and the heat and just use the wind turbine to draw air throught the generator turbine.
Hey, folks, it was just a thought. I learned a littlebitta Physics here, and now I understand why it was not the most brilliant idea I’ve ever had. Freakin’ windmills. They oughta be good for something. I wonder if one could grind wheat into flour using one…
Now, that concept of an adhering surface that would work in high humidity, bitter cold, water, vacuum of space…boy, if only I’d been able to figure out the details on THAT little invention.
This is not some flaky left field idea. Although it does seem to be difficult to implement, The National Energy Laboratory in Hawaii has a pretty big program devoted to making it practical.
Interesting, and it answers my question about how you cool things down to start the cycle again. It’s true that in principle if you have a temperature difference you can extract energy from it somehow.
If you had two large caverns both completely air tight this could work. You fill one cavern almost completely with water and connect the two caverns with a small tunnel at the top. In the tunnel you put the turbine and a air tight door. In the second cavern you pump out the atmosphere. Then open the door.
The small amount of air from the other chamber expands and fills the avaiable space which would also start the turbine turning. At that point the water would start to boil and the pressure differential would turn the turbine. The only problems would be the windmills keeping up with the rising pressure to keep the system running. You may have to close the door now and then to re-lower the pressure in the one cavern.
Evetually of course the remaining water would freeze and you would have to add more energy to the system. Also two air tight caverns of the size required are a practical impossibility. Leakage would doom the system.
Whether this would be an improved system from just driving the turbines directly by the wind I don’t know. But until the water freezes you would be getting “free” thermal energy from the water into your system.
I am going to go out on a limb here and guess Degrance is not an engineer or a physicist.
>> Whether this would be an improved system from just driving the turbines directly by the wind I don’t know
Anyone who paid attention in high school physics knows the answer is “no”.
> But until the water freezes you would be getting “free” thermal energy from the water into your system
That’s wrong but you could correctly phrase it thus: When hell freezes over we will get a lot of free thermal energy coming from there.
>> Also two air tight caverns of the size required are a practical impossibility. Leakage would doom the system
Ah, so that’s the problem! What is the size required? And why is it an impossibility? And why does it only work in large scale?
>> You may have to close the door now and then to re-lower the pressure in the one cavern
What’s so difficult about closing a door?
Your post makes absolutely no sense to anyone who knows just a bit about energy and work.
As I said in the beginning: You have a windmill which puts out X kilowatts of mechanical energy at the shaft and you have an electrical generator which takes mechanical energy and converts it to electricity with some losses. There is NO way in the world you can insert any system between the output of the windmill and the input of generator which will make things better. A direct coupling between the shafts has an efficiency close to 1 or even one if you look at it that way. Anything which takes X kilowatts and delivers more than X kilowatts is getting energy from somewhere. The idea that you can take X kilowatts and shift them around a bit and end up with more than X kilowatts shows ignornce of the most basic principles of physics, thermodynamics and every day common sense.
Anyone defending such a machine, please provide some numbers of where the energy comes and goes.
No there isn’t and no one, including me or the OP, said you could. The question was and has been, "Could you create a vaccuum using the power from the wind turbines and use that vaccuum in such a way that would allow you to use less coal/oil to boil the water used in driving a steam turbine. I posted a means by which the thermal energy in the water could be freed with out burning any oil/coal.
You see that was what the posted asked.
Don’t know why I would possibly answer the original question.
Guess it was just a lark.