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Build vertical tubes (400 ft in diameter) high enough to reach prevailing winds in order to create a lower pressure gradient inside the "straws" drawing air up from the bottom driving turbines. Like blowing across the end of a straw.
Unlike Solar Chimneys, Windstraws don't need a solar collector
or any temperature difference to cause draft. Each tube contains hundreds of turbines inside and up the length of it's shaft (should they counter-rotate or does that matter?). That way you'd use less acreage for the footprint.
acreage=amount of land needed
http://www.enviromi...ect/video/video.htm
[brattleboro, Apr 13 2006]
[link]
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<dumb kid>What's 'acreage'?</dk> |
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This seems good, but I'm sure that there are some hidden flaws that you haven't thought of. Wouldn't the high winds break the tower? And what about fixing damage to the it? I'm sure that it would require more energy to build than it would produce. |
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Neutral until these are addressed. |
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How is enclosing a specific column of air going to make the enclosed air act any differently than the unenclosed air just outside the tube? |
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how is the sucked up air
converted to energy? With
turbines? If you are already
building the tower why not put
a windmill on to of it, the
swept area (a mesure for how
much energy it can harvest) is
much higher than your drinking
straw pointing into the air. |
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I like these kind of ideas (except the hundreds of turbines bit). |
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I think the venturi effect could be used to draw air up the duct, tube, whatever, and be used to get ventilation in a building. Only useful in certain regions, I suppose.
To improve the idea, the duct should trap the sunlight, to get the stack effect. |
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Finally, I think the straws idea is similar to ducting light using fiber-optics. Although the friction of air will be a big disadvantage. |
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>dbmag9<"Wouldn't the high winds break the tower? And what about fixing damage to the it? I'm sure that it would require more energy to build than it would produce." |
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The straws are built of carbon fiber nanotubes, very strong. Install maintenance elevators. Have to update my research on cf nanotech to get an estimate of amount of energy needed to fabricate- I'll get right on it. |
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>GC<"How is enclosing a specific column of air going to make the enclosed air act any differently than the unenclosed air just outside the tube?" |
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The straws are open at each end. Picture nuke plant cooling towers tall enough to reach prevailing winds with turbines installed horizontally. As the winds blow across the tops of the Windstraws it creates low pressure inside the straw drawing air in from the bottom up the shaft (openings at the bottom allowing air to rush in). This way there could be a number of turbines instead of only one at the top. |
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Again, why does a cylindrical volume of air just on the outside of the tube act any differently than the identical volume of air on the inside of the tube? Is there an elbow joint at the top pointing into the wind or something? |
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Imagine a nuclear power plant cooling tower (sans the nukes) rising up through the clouds high enough to reach prevailing winds (6,000 ft?). These towers have openings around the base. As the prevailing winds flow across the top of each tower it creates low pressure inside creating an updraft which spins the turbines inside the tower. The turbines are positioned horizontally inside the tower. |
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To echo [nietsch]'s query: It it is that high, why not just install windmills up top? |
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[Galbinus_Caeli] I think they actually use a system like this, although much smaller, as a kind of air conditioning system in some homes in the Middle East. |
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If I remember correctly a rotating cap sits on top of the chimney. One end is open and the other end is pointed so that the open end is directed away from the wind creating suction and moving air through the chimney. I think jars of water are placed at the bottom of the chimney to help cool w/ evaporation. |
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I wasn't able to find exactly what I said with a quick search of my books, but I did find the exact opposite. (I think they might use both ways). A tracking wind chute funnels the air down the chimney. A fin is placed opposite the chute on the tracking cap. |
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The cooling towers on a power plant, nuclear or conventional, have a heat source at the bottom. Convection causes air flow from the bottom to the top. Elevated roof vents, like those mentioned by Zimmy, also work because the air inside the chimney is warmer than that outside, so it rises. |
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Basically you have not mentioned what power source is driving the air flow through your tubes. You need to do something to the air inside to make it act different from the air outside. |
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[Galbinus_Caeli] You are right about Nuclear Cooling towers. The heat source in question is the heated water that is being cooled. There is a layer of plastic honeycomb at the bottom that the water trikles through and comes in contact with the air that cools it. The shape of the towers also enhances this effect by increasing the velocity of the air exiting the tower. |
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As to this Idea I think 1st that the stresses involved are massive. This thing would need litterally Miles and Miles of cable to stay upright(as jet stream winds are more than 2 miles high) Also I think the benefit from this effect will be minimal as the windmills will dampen the flow of air, then combine the effects of gravity as the air column cools it will want to fall back on itself in the tube. I think a windmill would work a lot better. Bone. |
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Are these intended to reach that high? I think structures only 1/5 that height have been built so far. |
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The same principle that pulls gasoline out of a carburetor jet is what makes Windstraws work. Or maybe some of you remember sitting at the soda shop playing with your straw by blowing across the end and watching the liquid being sucked up and sometimes out of the straw. Or the way autobody paint sprayers use a stream of pressurized air blowing across the end of a tube pulling and atomizing the liquid paint inside canister. |
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As the prevailing winds blow across the top of the Windstraw tower it speeds up causing low pressure to form in the stack drawing air in and up from the bottom. I guess it's a combination of the Venturi and Bernoulli effects. The tower is not a closed cylinder at the base, it has opening allowing air to rush in. |
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As for the material used to build the towers, they are made out of carbon nanotubes (not too far in the future... or ARE they?). |
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As for the lone turbine sitting atop, it's a waste. You have this perfectly good cylindrical tower with huge volumes of air being sucked up and out the top by the prevailing winds. So stack the turbines horizontally one atop the other all the way up the shaft. The blade span of the turbines is the same as the diameter of the tower. There is no central hub, the blades rest on an outer ring fixed to the inside of the tower. Of course you'd have to limit the number of turbines according to the amount of draft produced by the prevailing winds but if you get more than one you're still ahead of the game. |
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It has nothing to do with hot air rising, it has to do with rivers of air blowing across the top of the straw sucking air in from the openings at the bottom. |
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Zimmy's idea of the rotating cap at the top might make the straw more efficient. They rely on winds spinning the vented cap (sort of like a squirrel cage fan lying on it's side) using angled blades to pull the air out of the tower. You could also take advantage of that motion too. Or perhaps large deflectors placed around the top edge of the tower can be extended or lowered in order to increase the efficiency of the Bernoulli effect. |
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>GC>"You need to do something to the air inside to make it act different from the air outside." |
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It's a simple principle, speed the air up across the top of a tube and anything inside will be pulled up the length and out in a futile attempt to equalize the pressure difference. Of course you'd have to install screens in the openings at the bottom to keep birds from being sucked up and out. Gotta save the birds! |
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Ok, I think we are suffering from a misunderstanding of how venturi tubes work. |
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The tubes used in carberators are short and small. Long and wide will not work. Basically if there is enough diameter to allow a vortex there will be no suction. |
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Here, think of this example. Do you have a fireplace? What happens when you try to start a fire in a windstorm? Right, the smoke blows right into the room until the chimney heats up enough to begin to draw. |
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Or try this. Take a short length of pipe with you on a drive. At least 1" diameter. Ok, drive down the road and extend the tube out the open window. Which way does the wind flow? In if you tilt the tube into the flow, slightly out, if you tilt it back, but not very much. |
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(I am dripping this at this point. Either I have a lousy understanding of physics, or I am unable to clearly communicate my objections.) |
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I don't intend to appear obstinate, but how else are we going to solve the world's problems? Have you seen the video link? |
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Brattleboro.. there is no harm in positing ideas the problem is that the physics of what you are discussing are simply not going to work in your favor. |
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In order to generate suction in a tube you need to have a lot of air flow and a sufficiently small opening to create an area of low pressure. Your typical snowfence works on a similar principal and thier zone of effect is within Yards of the Fence. For this to have any effect the tube would have to be quite small. Otherwise the air hits the tube, bounces up and then flows right back down on top of the open part of the tube completely negating the the effect you are after. |
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In order to pull the air up you need to create suction to lift the column of air enclosed in the tube. Thats just to lift the air(how much does a column of air 400ft wide weigh per foot). Now you need to get that air column to do work on the blades of the turbines. Though you may think this is insignificant it actually requires a lot of force to generate power. Your typical wind turbines have like 60 meter prop spans in order to turn them efficiently and even then they do not just spin like crazy, they are going slow and steady. |
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Wind turbines are very efficient and are well developed technology. |
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Finaly there is one other major issue with your idea here. The jet stream(which is what I assume you mean by prevailing wind) moves constantly. It is not a static feature. And so your straw(if it could work) would only have air flow some of time. |
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Also I need to correct myself from before. The Jet stream is not 2 miles up it is actually 7 miles up in the atmosphere. It is simply not within the realm of modern engineering to construct such a structure. Even if constructed of Carbon Nano Tubes the tube alone would weigh litterally Millions of Tons without even considering the Turbines or the generators or the support cables. |
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