Mountain Turned into a Chimney for Wind Turbines?

you go right ahead and start without me

"Given that wind turbines operate about 30% of the time, take up a lot of space, are repair difficult and location specific. "

Thats why we like putting them all over North Dakota. About the only downtime they see here is when the wind speeds are too high and they have to park them due to overloading problems.

As far as taking up space once installed many have a foot print of less than the average sized home which in a farmers field or cattle pasture that is measured in hundreds of square acres thats nothing.

Repair wise the crews around here seem to have no problem bringing in the high reach cranes and equipment and can have a damaged turbine down on the ground and repaired in 1 - 3 days at most which is way faster than most auto shops will get your vehicle fixed and back to you and they are at ground level in climate controlled garages.

"repaired in 1 - 3 days at most"

Some repairs are easier than others.

Here's a shovel--just go for it.

I'm pretty sure its cost.

Lets break it down. It would take a lot of additional construction to build structures to funnel the ground level wind into the drilled holes housing the turbines in the mountain. Wind direction also varies so the structures would have to ideally surround the mountain (or atleast in a wide arc). Wind strength and duration varies due to location and terrain so very efficient sites including existing mountains (or cliffs) would be even more limited than those for above ground wind turbines.

Then take into account having to mine out the shafts and the inefficiencies of the wind at ground level compared to wind at higher altitudes.

Now compare all this to a standard wind turbine on a pole, which is going to be cheaper to make and far easier to locate and place solution.

In the end the standard wind turbine on a pole our even solar tower would be a cheaper and more flexible solution.

How about this.

We drill the holes in the mountain, then put big electric fans at the bottom to blow the air up through the tunnels to the turbines.

The turbines generate the power for the fans, and the extra electricity generated by the turbines can power a couple of 100W light bulbs at the power house.

But, the fans only suck on one side.

On the other side, they blow.

We could supplement the turbines with solar cells in the daytime, to keep the lights on, and the fans running.

Oh, that's silly isn't it. You don't need lights in the daytime. That calls for a battery bank to store the excess energy.

Lyn, you forget that you have this tunnel driven into the side of the mountain. If you do not light it up how can the air find its way to the chimney?

Its a save and sound concept!

I really think the biggest problem is actually directing the wind into the hole in the mountain rather than going around it. I just feel the wind 'harvesting' efficiency is going to be so low as to be the real deal breaker for such a project.

I can think of ways to help fix the efficiency issue but they add FAR to much cost and complexity. The terrain will be working against not with any such project.

As long as you aren't expecting me to invest, you just carry on. I don't give permission.

Even if the tunnel was free (a huge smooth lava tube in just the right place, or maybe giant rock worm paths....whatever), and the wind is always blowing at the hole, it still isn't a good idea unless the ground happens to be significantly warmer than the air most of the time.

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Unless the ground is very warm, the air in the tunnel will be cooled and likely moisture will also be added. This will make the air more dense and therefore less buoyant compared to the air outside the tube near both openings. This will work against any flow up the tube.

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If smooth large bore holes in mountains were common and under utilized, and if the wind were cooperative, flow in the reverse direction would probably work better.

flow in the reverse direction would probably work better.

I had an on topic 'better to suck not blow' joke in the works but it was far to <ahem>, so you'all have to use your imagination instead.

"...and likely moisture will also be added. This will make the air more dense and therefore less buoyant compared to the air outside the tube near both openings"

NO! Moisture added to air makes it LESS dense, not more dense. Avg. Mol. wt. of air is about 29. Mol. wt. of H₂O is 18.

Nope. It does no good to just consider part of the approximating equation.

PV = nRT

n= mass / molecular weight

so...

density = mass/V = P*molecular weight/RT

change in T is going to drive the change in density.

When relative humidity is less than 100%, the latent heat of vaporization of water added to air causes a temperature drop, yielding colder more dense air.

If the relative humidity is at 100%, then any water added will be liquid in form, therefore resulting in a density increase.

"density = mass/V = P*molecular weight/RT" Agreed.

"change in T is going to drive the change in density." Why?

Each water molecule that replaces an air molecule (effectively pushes an air molecule into a different mole) represents an 18/29 or 0.62 reduction in density of that molecule. To counteract that would require a 0.62 drop in the temperature of that molecule. 0.62*300K = 186K, or -87°C, or -125°F. There is no way the temperature is more important than the molecular weight!

High altitude, high temperature, and high humidity all reduce the lift of an aircraft, and, when combined, occasionally prevent takeoff.

You forget that water vapor is around 1% of the mass of air at typical temperature and humidity range. Additional moisture will be some fraction of a percent typically. So the change is temperature were held constant, is not a 30% reduction in density. That is two orders of magnitude too large.

More importantly, consider the huge latent heat of vaporization for water ....over 2100 kJ/kg in typical atmospheric conditions as compared to the specific heat of air roughly 1 kJ/kg per degree Celsius.

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See how easy it is for the cooling effect of that tiny amount of water to overwhelm the minute change due to molecular weight?

Simplified:

Adding 1% mass of water to air....10 grams water added to 1 kg of air assuming no initial temp difference.

Molecular weight reduction in density is less than 0.4%

22kJ heat of vaporization equating to a temperature reduction of roughly 22 C or K

22/300 is more than a 7% reduction in volume...so more than a 7% increase in density from temperature reduction alone.

The temperature reduction effect is an order of magnitude larger and reliably dominates changes in density with water addition to air at typical atmospheric temperatures and pressures.

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Do you concede?

"Do you concede?" I'm quite willing to admit I'm wrong when convinced of that fact, but that condition hasn't been met just yet...

You are assuming that all of the heat of vaporization to evaporate the water comes from the air. That is pretty close to the truth when the air is clearing from fog on a cloudy day, but not so in the other situations I can think of at the moment.

If a molecule of water on the surface of a droplet sticking to the side of the tunnel acquires enough energy to escape the liquid phase and become part of the air, what is the source of most of that energy? The answer has to be from other molecules within that droplet. Any liquid water molecule has MUCH more intimate contact (collisions) with other liquid water molecules within the same droplet, than it does with the much more widely dispersed air molecules, whose average velocity is along the tunnel, so a very small fraction of the air molecules actually strike the water surface.

So that molecule escaping effectively cools the liquid from which it escaped. Now that cooler water will increase its rate of energy absorption from other nearby objects. Since the water has much more intimate contact with the rock than with the air, most of the energy will come from the rock. Over time, there will obviously be some cooling of the air from contact with the now cooler water and rock, but only a tiny fraction of the heat of vaporization will come directly from the air.

Nothing could be more intimate with the molecule than itself.

Examples abound of the significant temperature drop that occurs when moisture is added to air. The evaporative cooler thread was pretty recent.

Look, don't let my razing you about conceding get your hackles up and throw you off.

You can consider this any number of ways and arrive soundly at a fairly unambiguous conclusion.

First, take out of context of this problem, we were talking about changes to density when air in contact with liquid water results in an increase in humidity roughly around STP. From that perspective, there is additional water heat sink under consideration.

But...we did have context that is important. We were specifically discussing changes in density related to water in the earth surrounding the tubes contacting the air flowing in the tubes causing an increase in humidity.

You suggest that the heat of vaporization for particular molecules will have a preference for heat transfer from previously neighboring molecules it just left behind as still liquid.....

That seems pretty hard to support. Convection is typically a more efficient mode of heat transfer than conduction. Since change of state is occurring at the surface, it is safe to bet that at least as much heat come from the moving air, than the relatively static liquid water.

But here is the thing, even if we assume that the heat vaporization creates an instant temperature reduction in then remaining liquid water surface, that doesn't change the fact that the air will bec9me cooler and more dense.

Since the water surface has good contact with the moving air, any reduction in temperature at the water surface will drive heat transfer from the air to the cooler water. Remember it takes more energy for water to go from liquid to gas than it does to increase a liquid just above freezing to a liquid just below boiling.

What is more, is that many of those now cooler neighbor molecules right at the surface are the ones that will next undergo a phase change and increase the airs humidity.

Even if you could get the heat of vaporization to come from the exclusively the remaining liquid molecules, it would just make the tunnel surfaces cooler which would, of course cool the air in the tunnel, making it more dense.

Remember the magnitude of the effect is 20 times large for temperature reduction than for the change to molecular weight. That means, just to break even, over 95% of the heat of vaporization would would have to be made up from somewhere.

Thanks for taking some significant time to answer. I'm not at all angry, but neither am I convinced! I sure wish that someone else would come in and add credence either to my reasoning or to yours...

"Nothing could be more intimate with the molecule than itself." What does that mean or imply?

"Examples abound of the significant temperature drop that occurs when moisture is added to air." No question about that, as long as the water is being evaporated by heat coming from the air. Moisture is being added to the air just above my pressure cooker, and that moisture certainly isn't cooling the air, but the other way around (the air is cooling the water, and being heated in the process).

"Convection is typically a more efficient mode of heat transfer than conduction." Only IF the heat needs to be transferred relatively large distances. My home heating system does used forced convection to transfer the energy from the flames to the various rooms, but that involves relatively large distances. I commonly melt solder in a few seconds with a hot soldering pencil or soldering gun (conduction). To melt the same solder on the same circuit board using a hot air gun (convection) takes a large fraction of a minute or more, even though the hot air temperature is higher than the tip temperature.

I'm a big believer in experiments, even if they are mental ones. Imagine lining a wet rock tunnel at temperature X with thin sheet metal, and blowing warm air at temperature Y through it. Do you think the sheet metal would be closer to X or to Y? Now that I think about it, I've already done that experiment, in transportation tunnels. Unless the air is way above STP and very dry to start with, there will be dew on the metal. The conduction (which is occurring in solids and liquids) keeps the metal very close to the rock temperature. The convection (occurring in gasses, whose molecules are vastly farther apart and traveling more slowly) is only able to raise the temperature of the metal slightly.

From Wikipedia: "Sound travels faster in liquids and non-porous solids than it does in air. It travels about 4.3 times as fast in water (1,484 m/s), and nearly 15 times as fast in iron (5,120 m/s), as in air at 20 °C". There is a close relationship between sound travel and heat travel. Both involve collisions between molecules.

"...the air will bec9me cooler and more dense." This is true whether any water evaporates or not, due to contact with the cooler rock. Water vapor molecules being added then lower the density.

"Remember the magnitude of the effect is 20 times large for temperature reduction than for the change to molecular weight. That means, just to break even, over 95% of the heat of vaporization would would have to be made up from somewhere." I haven't yet taken the time to verify your math.

I'm still not convinced... Please someone - help us out!

When you have a moment, vet the following simplification:

At around 300 K, a change of 1 K (C) causes a change in volume and inversely density of around 1/300....so about 0.33%

The mass of water in atmosphere is usually in the neighborhood of 1%, sometimes lower, sometimes as much a 3%. Let's use 3% to see the largest change decrease density effect that displacement of lower mw water molecules could have. Let's assume water is an easy round 60% the mw of air to give it the best chance.

That leads to a cap of about 1.8% decrease in density. Let's give it the benefit of the doubt and call it 2%.decrease in density for 3% mass water vapor displacing air.

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So, what change in temperature is needed to exceed that cap on what might typically occur in the atmosphere? A 7 C drop would exceed that if we use the initial 0.33%.

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About what mass percentage of water added to dry air has enough heat of vaporization to motivate a 7C drop at around typical conditions?

The removal of roughly one kilo joule of heat from a kilogram of air corresponds to a one degree centigrade drop around STP.

One gram of water, i.e. 0.1% of a kilogram of water requires over 2.2 kilo joules to change from liquid to vapor. Let's use 2 to handicap the effect and make the math simple.

So that equates to a 2 C drop for roughly a 0.1% mass addition of liquid water being changed to vapor.

So, a 7 C drop would take roughly a 0.35% mass addition of liquid water being vaporized.

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Even being generous with the handicapping of this comparison, the heat of vaporization is still stronger than that of molecular weight by roughly an order of magnitude.

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Another opinion would be helpful, but you can verify this without help.

Density Altitude Calculator - English/Metric

Density Altitude Calculator and Pressure Compututation at ...

Density Altitude Calculator - PilotOutlook

The calculator linked is for humidity already present in the atmosphere, not for changes to density with the addition of vapor from contact with a liquid. There is no account of the temperature drop related to vaporization.

You keep insisting that the energy to evaporate the water comes entirely or principally from the air. That is just not the case here. I guess we have to agree to disagree.

I haven't been insisting that the heat comes primarily from the air. To the contrary, your argument depends on heat transfer from the air including the vapor being excluded.The heat comes from the surroundings which in the case of liquid water being vaporized in air has a significant part that is the air. Any reduction in temperature at one point will drive heat transfer to equalize the temp.

There is no need for the heat transfer to come predominantly from the air. Just 1/8 of the heat needed for vaporization is still enough to exceed the effect of molecular weight.

Thanks Lyn.

My current situation:

You can see that calculator neglects the cooling effect and is comparing density of air already at specific conditions, not the effect of moisture addition as we were discussing.

I erred in my assessment that you placed a higher value on understanding than feeling right. You have the necessary information. Believe what you will.

I am MUCH more a scientist than a touchy-feely. As I indicated before, I'm quite ready to admit I was wrong, IF the math or the experiment proves it so. My own math just proved me wrong on a totally unrelated concept just last week, and I have advised the interested parties that I was totally wrong.

Everything we have been discussing is partially based on assumptions that have neither been proven true nor false. We are both comfortable with the standard gas laws. It is the energy transfer where we seem to differ.

I will refer back to Kariba power station shaft which is the nearest you will get to a working example of what you are proposing. There are some important differences. In the gorge at the base of a hydro dam the air humidity is 100% due to the spray from the outfall. I will assume the the air at the top of the dam has 0% humidity so the air density based on humidity alone is 1.14% lower at the bottom than the top. You don't have a humidity differential so this can be ignored in you case. The height of the dam is nominally 305m so based on height alone the air density at the top is 3.5% lower than the bottom. This assumes the same temperature but temperature drops by 1°C for every 1000ft so in your case that would increase the density the top relative to the bottom by based on temperature alone by 0.035%. So for every 100ft (305m) of shaft you have a Δp of 3.2mb. this would give you a wind speed of 0.73m/sec or 1.61mph. Not enough to drive a wind turbine. Because of the thermal mass of the water passing through the turbines the temperature in the gorge at the Kariba outfall stayed at 8ºC day and night but at the top of the dam the temperature fluctuated widely. In the Kariba case we were generating wind speeds of 4.5m/sec or 10mph in the hottest part of the day when the ambient was 40ºC and 2m/sec or 4.5mph at night when the ambient temperature dropped to 0ºC. The bus bars raised the ambient in the shaft by 30°C. Most of the power comes from the Δt and very little from the Δp. If there was not input from the bus bars, at night when the top temperature drops below 2°C the pressure effect would be totally cancelled out.

I apologize for suggesting that your motivation was ego and not understanding. An ad hominem attack is a logical fallacy, and my use of such betrays my frustration at not being able to communicate this in a way that someone who obviously has the capacity to understand it, does.

Thank you for having the maturity to not respond in kind to my childish outburst.

If I haven't soured you to this discussion; when you have time, review the simplified version I detailed and let me know what you see as incorrect assumptions of if it makes sense.

Thanks!

One of these days I do hope to find time to do some more in-depth thinking and calculations. That will include reviewing that 'simplified version'.

This has become a comedy.

But, I realize that everyone has to believe something.

I believe I'll have another drink.

What about mounting one of those mountains on a barge and making a self-locating sail boat out of it with a few bed sheets for sails? It could travel to where the wind is on its own, tack up narrow rivers or bays, etc. and generate electricity as it traveled and also was at anchored. I can just see it now--> "The Mountain Top Chimney Yacht Club will be holding it's annual Electrical Generation Regatta on April 1st of this years. The entrant to generate the most power will be declared the winner. Contestants must supply their own calibrated and certified watt meter as per the racing committee."

I'm selling my big sloop and buying a mountain! Come-about helmsman! Jibe for a starboard tack! Trim the genoa! Get that watt meter reading higher! Keep a weather helm!

Good Luck, Old Salt

Sooo a floating man made island with its own mountain just to generate power, don't think that would work. Why not just build an inflatable solar tower, teether it to the ground and hold it up with balloons.

Being serious here, Kite power would be far better for that.

http://en.wikipedia.org/wiki/SkySails

I agree. Everybody knows there is no way you are going to get a 4M (Man Made Maritime Mountain) up on a plane without kite sails. I mean, maybe it could work for a molehill, but not to move a mountain...and who wants to be stuck wallowing about in a regular displacement hull while you generate electricity.

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Many have hit on the key obstacle holding back this stupendous project...drilling the holes. So it is probably better if we don't go the route of modifying one of the pre-made/preexisting mountains into the necessary hull and mountain shape.

We should just use some pre-cleared holes. There are quite a few in my area that seem to go pretty much all the way up. Now with the expensive holes sourced, it's just the regular old mountain stuff we need to fill in the rest.

Anyone want to contribute some mountain stuff?

Why not combine the 3 ideas and make a more efficient electrical generation tubular pneumatic wind generated kite assisted with supplemental balloon support with solar assistance power station. I can see it now----------> 81 Mississippi River size barges tied together in a 9 x 9 configuration. A small mountain or large mole hill constructed around a horizontal feed tunnel to a vertical draft generating tunnel bore. Above the top of this would be a 1,000 ft (if FAA permits, 400 ft if not) fabric, preferably Kevlar, tube extending the effective height to somewhere around 800 ft when the helium support balloons are filled. Around all this solar panels could be mounted to generate even more electricity on sunny days.

The tunnels would be constructed prior to placement of the mountain materials since current large tunnel boring prices sometimes start, without overruns, around $1,000,000,000 US$

Replacement of the displacement hull with a planning hull could be done at a higher cost. Problem is though where are there any tug boats with planning hulls to tow it? Don't forget that it will have to comply with all US Coast Guard regulations and 49CFR. To avoid water pollution a chemical or catalytic porta-potti could be installed. Next project is the design of the sails. Maybe nylon, Dacron, a modern synthetic, etc.

Keep the ideas coming. Maybe the whole mouth could be filled with tongue-in-cheek suggestions.

Good Luck, Old Salt

You don't need to force wind into the mountain. Atmospheric pressure will accomplish that. Stack effect formula will provide proof. Why would you need to use fans to push air up, don't you have a chimney or understand how it works. Is there somewhere I can go to ask an engineer about this?

Yes. Use a search engine to "ask an engineer".

Be prepared for disappointment when you do.

Okay, I initially decided not to query you on the stack effect your referenced. Since it seems not to be just a buzzword you threw in, but instead a phenomena pivotal to what you see as the viability of this scheme, let's discuss this stack effect.

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An important question to ask is what is necessary for a stack effect to induce some non-negligible flow? Knowing what drives the effect is key here. The kinetic energy of flow is not conjured from nothing just because a tall tube is situated vertically.

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Does a hole in a mountain, in and of itself necessarily have what is needed to induce upward flow? If upward flow were initiated by some outside means, would the thermal mass of and the moisture content of the mountain around the hole help of hinder upward flow typically?

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What questions exactly would you like answered about this scheme you have suggested?

Is there somewhere I can go to ask an engineer about this?

Right here. Ok, now I am starting to understand what you are asking.

Disregard comments regarding adding fans, they just relate to the comments regarding the difficulty of getting the air to flow up the hole rather than around or over the mountain alone.

This all comes back to effectively trying to create a solar updraft tower system (including the required solar collector area to get the hot air to maximise the stack effect - don't forget about that!) using a mountain instead of building the tower. Ok.

So the question simplifies to "can you make a solar updraft tower out of a mountain cheaper than building one"?

My answer would be - possibly if the mountain had an existing straight(ish) vent hole you could exploit, and the surrounding area was suitable for the large collection area (large flat area), and the local weather conditions were favourable.

Possible but very limited in the number of potential sites this would work in my opinion. And I still think the costs of excavation and land flattening around the mountain would be more expensive than just building the tower in a more suitable site.

Jack - Wind and Solar Power Engineer (among other things)

Lest you embarrass yourself further, read this:

Stack effect - Wikipedia, the free encyclopedia

What happens if the wind is blowing from the opposite direction of the bottom hole?
Keep trying.

Lest you embarrass yourself further, read this: Stack effect - Wikipedia, the free encyclopedia What happens if the wind is blowing from the opposite direction of the bottom hole? Keep trying. LYN Apparently one of us is missing something. Where in the stack effect formula does wind direction become a consideration. The wind generated in the mountain comes from atmospheric pressure. This works like a giant chimney.

Keep dreaming.

This reminds me of others who come here with insane ideas and want us to direct them to someone who will buy into their ridiculous notions.

Do you know joe.fordham? kastrupsky?

Maybe all three are the same??

The idea of coring and tunneling is so like what my dream man cave would look like.

Get a parcel of land with a nice hill or peak on it, quarry a core down into the hill ending up with a pile of material for the rock fortress on top of the hill, tunnel in at the bottom to reach the core and have a personal batcave style tunnel door....way cooler than Wayne Manor.

So... this dream man, he has his very own cave, does he?

:-)

Cost is why, I assume.

From here: http://www.windustry.org/how_much_do_wind_turbines_cost

'The costs for a utility scale wind turbine range from about $1.3 million to $2.2 million per MW of nameplate capacity installed. Most of the commercial-scale turbines installed today are 2 MW in size and cost roughly $3-$4 million installed.'

An example: http://en.wikipedia.org/wiki/Clem_Jones_Tunnel

Cost of 4.8 km of tunnel: $3.2 billion

Dont know how big a mountain you are proposing, but your final $/kWh figure is going to waaay more expensive drilling a hole in a mountain, than it will be plonking a turbine in a field.

Cost would be offset by efficiency since wind would be constant and a wind turbine "plopped" in the middle of the field is productive at about 30% of the time. To power New York City , a land area equal to the size of Connecticut would be needed. Using a mountain and vertically placed turbines, a small mountain around 5000 ft, you could conceivably put hundreds of turbines in one location. The bottom opening although shorter than the vertical shaft would be more expensive since the vertical shaft could be fracked (Can you tell I have spent too much time in the oil fields?) incrementally and debris could be removed from horizontal opening.

No, I could not, and still cannot tell that you have spent time in the 'oil fields'. Do you see 'fracking' as a useful way to excavate....but only vertically?

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As far as I know, hydraulic fracturing is used on wells oriented vertically as well as on those oriented horizontally. For tunnels meant to stay open to allow air flow, it does not seem like fracturing the material that is to form the walls of your tunnel would be a very good idea....structurally speaking.

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I am open to the possibility of being wrong and appreciate learning something new, especially if it is completely contrary to what I had understood up to that point. So please, thrall us with your acumen.

In series. So after horizontal tunnel is in place , you drill vertically and frack the bottom 2% and removed debris via horizontal opening.

So you will have x ammount of air in m^3 initially moving at x velocity in m/s, & that mass of air will have x ammount of kinetic energy you will be extracting to turn into electrical energy? And there will be hundreds of turbines in series?

Yes. Stack effect formula provides wind speed, wind turns turbine. Giant chimney.

Please provide the 'stack effect formula' you reference.

You have a fundamental misunderstanding if you believe atmospheric pressure in and of itself will motivate flow up a vertical chimney.

Imagine a very large diameter tall chimney. How would the 'stack effect' know which side was the inside?

Not understanding it yet? Imagine a chimney so large it too up half the surface of the earth, so that half of the Earth's surface is on one side of the chimney and half on the other. Which is the inside and which is the out? On which side will the chimney effect create an updraft?

There is a pressure difference between the outside air and the air inside the building caused by the difference in temperature between the outside air and the inside air. That pressure difference ( ΔP ) is the driving force for the stack effect and it can be calculated with the equations presented below.[2][3] The equations apply only to buildings where air is both inside and outside the buildings. For buildings with one or two floors, h is the height of the building. For multi-floor, high-rise buildings, h is the distance from the openings at the neutral pressure level (NPL) of the building to either the topmost openings or the lowest openings. Reference[2] explains how the NPL affects the stack effect in high-rise buildings. For flue gas stacks and chimneys, where air is on the outside and combustion flue gases are on the inside, the equations will only provide an approximation and h is the height of the flue gas stack or chimney. \Delta P =\; C\, a\; h\; \bigg(\frac {1}{T_o} - \frac {1}{T_i}\bigg) SI units: where: ΔP = available pressure difference, in Pa C = 0.0342 a = atmospheric pressure, in Pa h = height or distance, in m To = absolute outside temperature, in K Ti = absolute inside temperature, in K U.S. customary units: where: ΔP = available pressure difference, in psi C = 0.0188 a = atmospheric pressure, in psi h = height or distance, in ft To = absolute outside temperature, in °R Ti = absolute inside temperature, in °R

Temperature difference will exist from floor to mountain top. Even near where I live the mountains (Tehachapi) although only less than 2000 feet there are always a few degrees cooler than valley floor. Once again nothing special, just taking advantage of what is available.

Are you aware that the air both inside and outside your chimney cools due to decreasing pressure with increasing altitude?

As Lyn correctly said, you need a heat source to force the air up the chimney. The energy has to come form somewhere.

I'm far more concerned by the lack of sufficient flow/velocity in this air stack to do ANY work at all.

Betz' Law says that at best you get 59% of the power put in to the wind turbine back out as useable energy.

We haven't even looked at generator efficiency, yet.

I jus can't go on.

Sure, pressure is lower at greater altitude, pretty much wherever you go.....so in your experience, have you noticed an updraft pretty much everywhere you go? Why would air in a tube behave differently than outside if there were no heat source or heat sink on one side. Isn't the outside of a tube compared to the inside, analogous to the inside compared to the outside? A tube is just a vertical barrier.

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If you really want to understand you need to stop insisting you understand this, because you have the concept wrong. Enough people have told you. If it was advice you came for, you have it. If it was praise and support, you will need better idea and a willingness to be wrong in order that you might actually learn something.

DAVEWISOR, doesn't "really want to understand". He already KNOWS he's right and no amount of logic and reality will convince him otherwise!
This follows a familiar pattern:

To Save the Globe with Floating Energy Barges (FEB) Early on this #2 sets the tone.

sufficiently to offset the resistance created by the tunnel walls and curvesNot only it should as well compensate gravity.

Difference in density in a gravitational field is the phenomena this heat engine works around. It isn't quite right to suggest gravity must be compensated for, when gravity acting on fluids of different densities is what converts the difference in temperature into a more readily usable fluid flow.

I think if you do not have full information about this you can contact professional chimney experts in long island, as they are best at what they do. You can take relevant suggestions and solution from the.

Install a lot of wind turbines in chimneys, do they?

Thanks for the reply. What I wanted to determine was why couldn't a mountain be hollowed out and be used as a chimney. Everything I have learned so far points to yes. Air speed would be constant but lower than optimum for standard turbines at 28.8 miles per hour. I will contact the experts you suggested. Thanks for your input.

Of course. Have you done any sort of theoretical calculations as to how much energy you think you may be able to extract? I saw a windspeed of 18 Miles/hr? Do you anticipate that the windspeed will be constant over the entire length of the chimney when it is passing through 100's of turbines along the way?

'Velocity will change with cross sectional area and density. But if there are no leaks or flow additions in the tube, the mass flow rate steady state should be the same for any place in the tunnel, excluding very short time scale changes from pressure waves/flow instabilities.

If that weren't the case there would be areas where pressure was falling or rising due to a mismatch in goes-ins versus goes-outs.

Thanks, I wasnt asking you to think about it though, your not proposing a series of wind turbines be installed in series in a tunnel dug from a mountain.

No I don't think wind speed will remain at 18mph. How wind speed would be affected by different sized generators , as in would it be better to have 200 smaller generators as opposed to 50 larger ones is an area I have looked at yet.

You need to work out how much energy you anticipate will be travelling through the chimney first, before you can specify a number of turbines. It will be a theroetical number based on all the variables, of which there will be very very many. I wish you all the best in your endevour.

First you should see what is atmospheric pressure.

It is in fact the effect of gravity on the air column. Inside or out side the " chimney" conditions are the same at same levels so that nothing will happen if a temperature difference (as in the stack equation) will be imposed by an external energy source.

The temperature gradient as one goes higher is not a movement generator on the vertical as neither the pressure gradient will be.

OK, build your tunnel in the mountain. When it is working, discover the mountain is gold ore and remove it. Doesn't the "stack effect" still work, without the mountain? Where I live, where the land is flat, we call these free energy generators thunderstorms or even tornadoes. There are some minor problems. What goes up comes down, so the updrafts are accompanied by destructive downdrafts, and the whole energy system moves, making it difficult keep the wind turbines under the tornado.

Why don't you consider the Michaud wind turbine system that actually roots the vortex (tornado) to one spot, and does so very reliably. The vortex extends very high up according to the write up on this. One can utilize enhanced ground solar absorption (black field or dark field) if there is no local waste heat to dissipate.

Also costs could be lowered by using existing tunnels and adding vertical shaft. Took the time to read about the Clem Jones Tunnel, all I can say is WOW! Talk about money down the tube.

100's of turbines in one location......in series? Or do you envision an VERY large diameter hole? Yep.....impressive tunnel, but defnitely a lot of money down the gurgler

In 1979 I worked for 6 months at the Helms Storage Project. I worked in the kitchen as a relief cook. The contractor was Granite/Ball &Groves. From what I remember, there were over 15,000 workers involved. The machine used to bore the tunnel was about 200 ft tall, 2 giant fans about the size of 3 747 engines each, were used for ventilation, a mine type of train was used to move people and debris in & out of the tunnel. It was a 24/7/365 operation. I think it would be far cheaper to build a wind farm in North Dakota.

Maybe cheaper to build a wind farm in North Dakota, but the line voltage drop from there to civilization makes it somewhat costly.

'Costly'!?

Nope, you don't get to use that word in the same thread you suggest boring large diameter holes through mountains to improve flow to wind turbines might be financially justified, and still retain a chance of being taken seriously.

The prospect of being taken seriously ended with the original post.

The cost of boring is negligible, because to reduce line voltage drop costs, he is actually proposing to construct a 5000 foot high mountain next to New York City. You can just leave the tunnels and vertical tube empty.

Two words................Katabatic winds.........................funny how that pesky air density works.

But then drawing downward thru a hole you'd just have to set the turbines for it.

Katabatic winds would not be a hindrance, but a benefit. It would just add to the atmospheric conditions that we are taking advantage of. Pressure comes in through the bottom and out through the top. Like a chimney.

Already done, if you think about it. A deep mine has vertical ventilation shafts and there is the added bonus of hot air in the mine. Well at least the mine i was in had very warm air. Ask yourself the question; does the ventilation shaft outlet need an extraction fan? Why?

Quote" Kariba North power station on the north bank of the Zambezi river"

WOW!! I haven't heard of that project for years. I designed some of the power transformers for that project which were very innovative in order to save weight and size to be able to transport from the ships to the site over somewhat a primitive rail system. I designed a special tank bracing scheme, special type windings, had custom bushings built by Pittsfield, and was to my knowledge the only Schnabel car transformer ever built in Rome, Ga. We had to send an engineer over to travel the route with a plywood cutout of the transformer to be sure we could get it to the site and inside to the final destination. The cost reductions were so great that we had to drop some of them because it would have raised our cost reduction budgets too high in the future. I haven't heard of this project for a lot of years and wasn't even sure whether or not it was even completed. I remember pouring over the project documents and being amazed at the different and innovative things that were done. I also remember the changes in government around the project and how that effected things. This sure triggered some memories

Thanks, this is what I was looking for.

I believe it would be possible but probably not cost efficient.

The cost to bore a hole large enough in diameter and at the proper length to take advantage of the induced air flow horizontally then vertically up through a mountain would be extreme.

The tunnel would have to be slip formed with concrete cement & steel to keep falling debris from being induced into the air stream and causing damage to the fan blades.

Dealing with unseen rock formations is especially hard on the boring equipment and slows the process significantly.

We have had short 100-250 foot in length, 30 foot diameter tunnels bored at some of our sites through relatively soft dirt with the cost ranging at $5k - $15K per foot.

Adding the cement and steel required for installing a liner in the tunnel raises the cost up to $25K - $35K per foot depending on the thickness and strength of concrete required by the area soil composition and type of overburden present.

Acquiring the environmental permitting required to cut the equipment service road(s) into the area for installation and maintenance would also be extremely time consuming and costly. (Legal fees. Engineering documents. Administrative costs. ?)

Building a power line into the area at the top of the mountain for power distribution would also be extremely expensive as it would be in a very harsh and remote area with difficult access.

My WAG on the cost per foot for engineering, permitting, boring a tunnel, forming and pouring/pumping the concrete, installing the fan and generator equipment then building a power substation and distribution line would be in excess of $500K per foot.

You must have been using those disappearing drugs when you came up with this.

It seems that your thinking may be a little cloudy and you are partly in the dark here. I hate to rain on your parade, but my vision of this is a little snowy.

Very clever (Witty) Lyn - I did not suggest it would work in all weathers!

Just be cheap to build and work in principle. (I hope)

The cladding panels could be solar, heat retaining glass, (coated) whatever.
I just chose corrugated sheet as very cheap, heat absorbing-transferring to inside air.
A sort of vertical "hot box" - with a chimney on top.

Many thanks to the 4 who supported my idea, cannot get my hat on now!

jt.

ps... I do not do (illegal) drugs - it was only a joke. (settle for alcohol)

An old Marine Pilot sat down at the Starbucks, still wearing his old USMC flight suit and leather jacket and ordered a cup of coffee.
As he sat sipping his coffee, a young woman sat down next to him. She turned to the pilot and asked, `Are you a real pilot?'
He replied, 'Well, I've spent my whole life flying planes, first Stearmans, then the early Grummans.... flew a Wildcat and Corsair in WWII, and later in the Korean conflict, Banshees and Cougars. I've taught more than 260 people to fly and given rides to hundreds, so I guess I am a pilot, and you, what are you?
She said, 'I'm a lesbian. I spend my whole day thinking about naked women. As soon as I get up in the morning, I think about naked women. When I shower, I think about naked women. When I watch TV, I think about naked women. It seems everything makes me think of naked women.'
The two sat sipping in silence.
A little while later, a young man sat down on the other side of the old pilot and asked: "are you a real pilot?"
He replied, 'I always thought I was, but I just found out I'm a lesbian.'

I like your humor.

I've told this one before. Stop me if you've already heard it.

Two engineering students were riding across campus when one said, "Where did you get such a great bike?"

The second engineer replied, "Well, I was walking along yesterday minding my own business when a beautiful woman rode up on this bike. She threw the bike to the ground, took off all her clothes and said, 'Take what you want.'"

The first engineer nodded approvingly, "Good choice; The clothes probably wouldn't have fit."

[I don't think DAVEWISOR is in to humor.]