A tall chimney to facilitate heat exchange in the atmosphere | Hacker News Reader

A tall chimney to facilitate heat exchange in the atmosphere

superchimney.org

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For those skeptical of the science, note that there are large caves that exhibit this property, such as: https://en.wikipedia.org/wiki/P%C4%B1narg%C3%B6z%C3%BC_Cave#...

It seems like if the inside of the chimney column had a spiral shape, similar to a screw socket, the upward air pressure might alleviate some of the stress and make the column more structurally feasible. Granted, it would also dissipate some of the energy as heat.

Caves like that presumably connect two areas of air that are not otherwise connected, and not in equilibrium with each other, no?

Unless I'm missing something, TFA suggests that you can take a big system that's generally in equilibrium, and run a tube from one part to another, and get a similar effect. This seems like a very different proposition from what's happening in caves like you mention.

The atmosphere is emphatically _not_ in equilibrium. Why would you think it was? There's a giant fusion engine pumping energy into it, resulting in a fuck of a lot of activity (wind).

In particular, the upper atmosphere would not be colder than the lower if it was at equilibrium. Think about it.

I didn't say the system was closed. Why would you think I did? All I meant was that energy is free to flow around the atmosphere if it wants to; any macroscopic flow that wanted to occur would have occurred already.

In other words, caves like the GP mentioned (presumably) connect two systems between which energy is not otherwise free to move. That is not the case for a tube connecting two different sections of the atmosphere. Make sense?

> In particular, the upper atmosphere would not be colder than the lower if it was at equilibrium. Think about it.

Temperature varies inversely with pressure for a volume of gas. If low- and high-atmosphere gas had the same temperature, despite being at different pressures, that would be an imbalance.

This reminds me of Solar updraft tower prototypes [1], which concentrates heat at the bottom of the chimney instead of expecting cold air at the top of the chimney.

There's still a delta of temperature between the top and the bottom, but instead of

    T_bottom_chimney  = T_hot_ambient_air_bottom
    T_top_chimney     = T_cold_ambient_air_top

it is :

    T_bottom_chimney  = T_much_hotter_than_ambient_air_top
    T_top_chimney     = T_ambient_air_top

Everytime I start reading things like this, I wish I had a home with similar 'magic', like Solar chimneys[2] and other techniques[3],

[1] https://en.wikipedia.org/wiki/Solar_updraft_tower

[2] https://en.wikipedia.org/wiki/Solar_chimney

[3] https://en.wikipedia.org/wiki/Ground-coupled_heat_exchanger

This may be relevant:

Free-standing inflatable solar chimney: experiment and theoryhttps://works.bepress.com/nima-fathi/9/

I was getting convinced by the comments below that this is a nutty idea, but then ran across this review by real researchers in a real journal (impact factor: 8) in which they discuss super chimneys and other methods. Abstract and links below:

Fighting global warming by climate engineering: Is the Earth radiation management and the solar radiation management any option for fighting climate change?

Abstract

The best way to reduce global warming is, without any doubt, cutting down our anthropogenic emissions of greenhouse gases. But the world economy is addict to energy, which is mainly produced by fossil carbon fuels. As economic growth and increasing world population require more and more energy, we cannot stop using fossil fuels quickly, nor in a short term. On the one hand, replacing this addiction with carbon dioxide-free renewable energies, and energy efficiency will be long, expensive and difficult. On the other hand, meanwhile effective solutions are developed (i.e. fusion energy), global warming can be alleviated by other methods. Some geoengineering schemes propose solar radiation management technologies that modify terrestrial albedo or reflect incoming shortwave solar radiation back to space. In this paper we analyze the physical and technical potential of several disrupting technologies that could combat climate change by enhancing outgoing longwave radiation and cooling down the Earth. The technologies proposed are power-generating systems that are able to transfer heat from the Earth surface to the upper layers of the troposphere and then to the space. The economical potential of some of these technologies is analyzed as they can at the same time produce renewable energy, thus reduce and prevent future greenhouse gases emissions, and also present a better societal acceptance comparatively to geoengineering.

Here are links to the paper: http://www.sciencedirect.com/science/article/pii/S1364032113... or the research gate link: https://www.researchgate.net/publication/278826192_Fighting_...

From http://www.sciencedirect.com/science/article/pii/S1364032113... 6.4. Super chimney The super-chimney imagined by Pesochinsky [150,154] consists in a huge vertical open duct at both ends, which works as a giant vacuum cleaner, transferring hot air from the sea level to the atmosphere 5 km higher, where temperature is 30 1C. The principle consists in the chimney effect based on the fact that hot air rises by buoyancy above cold air, because hot air is less dense and therefore lighter than cold air. But the process can be made more intense preventing the mixing of warm and cool air, so a chimney prevents inside air from mixing with the outside air until the air exits. The chimney stack effect needs a differential of temperature between the air inside and outside to run correctly. Moreover, the higher the chimney is, the more efﬁcient it is. It is a similar concept to previously described SCPP [148], except that there is no solar collector at the bottom of the tower, which usually couples the GH effect to the sucking effect of the chimney. According to Pesochinsky the temperature difference between the bottom and the top of the tower is sufﬁcient. Another difference with conventional SCPPs concerns the size, 5–10 times bigger: up to 10 km high with a diameter of up to 1 km. Even if these heights have never been reached by human buildings, some GE / CE projects reported in the initial part of this review envisioned similar heights [59–65]. Furthermore, some authors reported, with such a large duct and in certain atmospheric conditions, that a cold air inﬂow could occur at the top and as a result a layer of cold air could get out at the bottom of the chimney, the hotter air surface being just pushed up, with the creation of a thermal inversion. In terms of heat transfer the result is nearly the same: cold air down and hoIndeed, on some Pesochinskys designs, the tower is alongside a mountain slope or drilled inside a mountain (which seems too expensive) and numerous air pipes are connected on the sides. Di Bella [155] suggested a similar concept by using giant open pit-mines and also recycling waste-heat from power plants. This heat input could be useful to prevent cold inﬂow entering these large diameter chimneys. To illustrate the potential of these devices, according to Pesochinskys calculations [156] only 10 super chim-neys 5 km high can offset the heat surplus in the Earth atmo- sphere, which causes current global warming. This would mean that all the atmospheric circulation would be completely reorga-nized from only 10 points on the Earth’s surface: the climate induced perturbations could be much worse than what we want toavoid. Hopefully with smaller, cheaper and more numerous superchimneys, better distributed on the surface of the planet, thisdeleterious effect can be avoided. The calculations done are rather simple, and were conﬁrmed by Mudde [157] from Delft Universityof Technology. They are based on a difference of temperature of 50 1C and as the super-chimney will facilitate air convection bybringing masses of warm air up to 5 km, then when the heat from the air radiates out, as it will be already at high altitude, lessenergy will be reabsorbed by the atmosphere, due to a thinner layer of atmosphere to go through. Therefore, more heat will beleaving the atmosphere, thus reducing the global atmospherictemperature. The authors believe that more scientiﬁc studies areneeded to prove the concept, and that the techology still fairly mature to build 5 km high chimneys.Constructional generalities are given by Pesochinsky with no real details: tall skyscrapers already exist; unlike chimneys, build-ings entail much heavier construction because there are ﬂoors, ceilings, several ﬂuids and lifts going up and down, and all otherelements within buildings which are necessary to make it useful for humans. A chimney is just a cylinder, thus is a much lighterstructure and can be build a lot taller than any building with new “super-strong”materials, not even described by Pesochinsky

Take Home: Feasible or not, the authors do not dismiss this as quackery.

If you follow the citations, the authors and those whom they cite are obviously failing at due diligence.

IANAP, but there's glaring difference between the super chimney and real working chimneys, like solar chimneys, geothermal chimneys, and regular old firebox chimneys.

It would be helpful if you would specify the differences, and explain how they are relevant to the practicality of the superchimney idea.

A Wacky Waving Inflatable Solar Chimney!

It kind of lost me when they started talking about the expected power output, though. A kilometer-tall tower seems like a very expensive and fragile way to generate ~200MW, compared with solar panels. I guess if you're primarily using it as a climate-engineering system, though, the free power is a bonus.

If water collection idea is a thin that can happen, that might have interesting implications too.

They almost got funding to build one that was going to be 1km high right next to my home town [1] in rural Australia.

[1] https://en.wikipedia.org/wiki/Mildura_Solar_Concentrator_Pow...

Back in the day dad and I figured out we would easily see the tower from home, and the shadow would cross our house. Also it would be possible to see the curve of the earth from the top, so there was talk of allowing tourists up there.

Can you really see the curve of the earth from 1km? I can't really even see the curve of the earth from an airplane (or can people with 20/20 vision see the curve from commercial aviation altitudes?)

The declination of the horizon is a couple degrees at altitudes that commercial flights fly at. It can be measured with standard carpentry tools.

Now how did you get carpentry tools into an airplane?

Disguise them as 100ml bottles of liquid...

Like this obviously: https://www.youtube.com/watch?v=6nNUEU8gnf4

I can't tell if this is satire. We're well into Poe's Law territory here.

Step 1: get a private pilot certificate.

I can see the curve of the Earth at the beach. Or maybe I'm just imagining it in the knowledge that it's there.

I can't see it at the beach, the sea is always too rough, but I can definitely see it on a still large lake.

A Solar Concentrator Power Station is neither of [1], [2] or [3] posted above.

So my question is "why wouldn't this just rip in half from the forces it's under?"

The upward force for the 20m chimney is calculated at ~600 tons. 600 tons is not a lot for a building to support in the downward direction, but quite a bit for a fabric tube to support, in tension. It's the rope/(space) elevator problem - you need a super material to handle that much force, don't you?

But aside from worrying that our wacky inflatable tube of death will rip free from its tethers and tumble freely in the wind, killing thousands, I actually really like this idea, as geo-engineering. It is a process that can be stopped and started relatively cheaply, unlike a lot of other proposals. If the tube has unforseen effects, it could be deflated and reeled in, unlike eg throwing particulate into the upper atmosphere.

Perhaps such a chimney could be built inside the shaft of a space elevator, canceling out the forces.

I'm only being half serious, but it is nevertheless interesting that the required structural challenges act in opposite directions.

So five kilometers of flailing inflatable tube man.

I get that the upwards wind force can sustain the fabric structure, but it is hard to imagine that it could also carry a bunch of huge turbines, as well as the cabling required to carry the generated electricity. Not to mention safety concerns. Does this seem unrealistic to anyone else?

Also, would it be possible to do a proof-of-concept using an existing man made structure like Burj Khalifa class skyscrapers? Presumably it would be easier to deploy a tube off the top of one of these than to build one from scratch.

The turbines are at the base of the mushroom; the rest of the structure will essentially be a giant tube man as you said

Its unrealistic in that it assumes wind doesn't really blow.

"The inside and outside air will be rising up. However, the air outside will be cooling adiabatically, so its temperature will be dropping. The air inside will be not affected by adiabatic cooling and will maintain its energy, so it will be warmer and less dense than outside air."

Is this a joke, or a crazy person? Air in the tube will expand and cool just like air outside the tube does.

From the FAQ. His answer is:

> Air inside the chimney is not affected by adiabatic cooling. Unlike freely rising parcel of air, the air in the chimney is restricted in its horizontal expansion and thus, it is not free rising. When air rises in the chimney, it also expands but only into upper direction. It compresses the layer of the air above it, heats it up and loses its own heat. At the same time the air below does the same thing. And that how it goes all the way until the chimney exit: layers of air are being pushed and push themselves. That results in maintaining the same amount of heat in every layer of air, and that is why the chimney works.

Sounds like complete bullshit to me. Expanding upwards will accelerate the air above, not compress it.

Why not both?

And why can't you state your analysis without calling other analyses offered in good faith bullshit?

This site is pretty much on the same level as sites advertising perpetual motion machines. I don't need every little detail to observe that it's bullshit.

Unless you confine a parcel of air in all directions, it will match the pressure of the surrounding air. Consider an arbitrary cubic meter of air at 15°C at sea level at the base of the tube. Now raise it 1,000m inside the tube. That air now occupies roughly 1.12 cubic meters and is at a temperature of roughly 5°C, the same as if it had risen 1,000m outside the tube.

The tube will work sometimes, but only when the atmosphere is unstable. Since the chimney is 5km tall, that means thunderstorm conditions.

You can only extract energy from a tube like this if there's some energy potential between the two ends. The atmosphere is constantly erasing differences in energy potential, so large-scale differences are ephemeral.

>You can only extract energy from a tube like this if there's some energy potential between the two ends.

The difference in temperature between the air at the bottom of the tube and the top of the tube is that potential.

It's not, because it's canceled out by the pressure difference. The net energy change of raising a parcel of air in the atmosphere is roughly zero. (Depending on the exact temperature profile of the atmosphere at any given moment, of course.)

Consider either a thermoelectric generator[1] or sterling engine[2]. Either of these can produce power given a hot and cold reservoir. Of course neither device is appropriate for this specific application (the temperature differential between 'surface' air and air in the high atmosphere), but they demonstrate the concept that any temperature gradient represents a form of potential energy.

Whether or not this specific design is an effective way to capture usable energy, I am not sure about. But, having something hot on one end, and cold on the other is a form of potential.

[1]https://en.wikipedia.org/wiki/Thermoelectric_generator [2]https://en.wikipedia.org/wiki/Stirling_engine#Theory

Both of those involve effectively closed systems where heat transfer can only occur at a point where you can extract work.

But what makes ambient air at the ground preferentially rise through the chimney?

Real solar chimneys, as posted elsethread, have a greenhouse at the bottom. Air at the bottom of the chimney, heated by the sun, preferentially rises up the chimney because it's constrained within the greenhouse.

If it were possible to "bootstrap" the system with an initial kick so that it became self-perpetuating with solar energy alone, notwithstanding changes in weather patterns, then I would think we'd also see standing hurricanes and tornados. But we don't because, I assume, these phenomena develop precisely because they're highly efficient at dissipating energy; and they dissipate it faster than a stable system can setup which preserves the initial constraints which developed (e.g. large scale climatic pressure differentials, boundary layers, etc).

Sure, you can potentially exploit the differential with other sorts of devices. But you can't do it using the same fluid that already contains the temperature difference, and attempting to use that temperature difference to drive motion in the fluid.

A generator that runs on heat differentials works by transferring heat from hot to cold and arranging it so that transfer does something useful. In a stable atmosphere, air rising through an open tube doesn't transfer heat, because it cools as it rises at the same rate that the surrounding atmosphere cools.

Why do you keep denying the principle when people have already pointed out that solar updraft towers (which exploit the exact same principle) exist and work? https://en.m.wikipedia.org/wiki/Solar_updraft_tower

That link doesn't support the article's thesis at all. It describes a system where the low-lying air has been heated up to be significantly warmer than surrounding atmospheric air. The energy being extracted is coming from solar power, not from the temperature difference at different levels of the atmosphere.

From that article:

> The chimney had a height of 195 metres (640 ft) and a diameter of 10 metres (33 ft) with a collection area (greenhouse) of 46 hectares (110 acres) and a diameter of 244 metres (801 ft), obtaining a maximum power output of about 50 kW.

That's not a super chimney. It's a normal chimney. People believe in normal chimneys! You have a temperature difference between the bottom and the top of the chimney, but it is so short tat you can assume that the pressure of the surrounding air is constant, and that the pressure of the air in the chimney is constant.

When the chimney is very high, the pressure inside and outside the chimney changes with the height, so the temperature inside and outside changes with the height. So to compute the difference in the temperature you have to adjust it. They are implicitly using that the temperature changes outside and ignoring that it will change inside too.

Also, the design/experiments in Wikipedia use a large glass bell or something similar to trap the solar heated air and send it to the chimney. So they are replacing a good fire of firewood with solar power. But they ignore the HUGE glass bell in the project and in the video. They expect that the hot air will go spontaneously into the chimney instead of trying to go up in another path.

Trying to harvest some of the energy and also using the air column to keep the column up will make the hot air in the surface prefer to go in another path and ignore the chimney. Unless you put a huge glass bell to force the air path.

By the way, the design/experiments in Wikipedia use self porting towers, they don't use the same air to keep the structure up. I think that the idea of using the flow to keep the structure up is very fishy, but my handwaving is not powerful enough to be sure it's wrong, I'd like to see some calculations. But you surely need the glass bell too.

"They are implicitly using that the temperature changes outside and ignoring that it will change inside too."

I just want to point out that they are quite explicit about this. That's what prompted my original comment, and I quoted it there. That's why I can't figure out why it's not obvious to everyone that it's full of crap. They all but come right out and say, "This idea is full of crap because it's based on a terrible assumption which you can see right here."

Imagine a normal 200m solar updraft chimney at elevation 0km; it sustains enough updraft to work, and spans 0 to 0.2km. Now imagine another 200m chimney at elevation 0.2km; it too is self-sustaining and spans 0.2km to 0.4km. If we stacked these 2 chimneys on top of each other, it would be a self-sustaining 400m chimney. Repeat this for 5km, and it's a self-sustaining super chimney. But according to you this physical mechanism somehow breaks between 200m and 5km...

The glass bell may be necessary for a 5km chimney but I don't see why this would invalidate the physical principle behind it.

It's not self sustaining, it's sustained by the sun. When the sun goes down, the chimney quits.

For a 200m chimney that supports itself physically, that's fine. For a 5km chimney that relies on continuous airflow to hold itself up, that's substantially less fine.

"it's sustained by the sun."

That's what I meant. But you fail to explain why, if the principle works for a series of 200m chimneys at different elevations, it would somehow stop working if these chimneys were connected/stacked on top of each other.

I'm not arguing about the engineering difficulty of building a self-supporting chimney made of fabric, or whether or not it works at night. Just the thermodynamic aspect of it even working during the day.

Because it doesn't stop working. A tall chimney still works.

It works during the day just fine, as long as the atmosphere is sufficiently unstable, or you can concentrate sunlight to get excessive heating at the base of the chimney.

But the web site linked here claims that their super-chimney can work forever by exploiting the temperature difference between the bottom and top of the chimney. This is nonsense. It justifies this by saying that the air in the chimney somehow doesn't expand and cool as it rises the way that air outside the chimney does. This is bullshit.

Your logic seems to make sense but how would you explain the purported chimney effect that has been observed on https://en.wikipedia.org/wiki/P%C4%B1narg%C3%B6z%C3%BC_Cave#... which is a cave with openings at low and high elevations and the difference in temperature is claimed to create "constant wind of up to 166 km/h"?

I'd need more information to say, but I bet it's not actually constant. I had trouble digging up any concrete info on the nature of this cave's wind.

In a chimney there is a difference between the pressure at the bottom and at the top. If you move some "isolated" block of air from the bottom to the top, the reduction of pressure makes it cooler, because you can assume that there is very few heat interchanged and it's an adiabatic process.

(It doesn't matter too much if the air is in the real chimney, or in an imaginary chimney nearby, or in a very soft balloon, ...)

In a normal chimney the difference of pressure is small, and the difference in temperature is small. So you can usually just ignore them. If you have hot air at the bottom, you can simply subtract the temperature of the surrounding air that is essentially equal at the top or at the bottom and be happy with that result.

If you put a lot of this chimneys together, the difference between the temperature of the air that enter at the bottom and the air that exits at the top is big enough that it can't be ignored. I don't have hard numbers now, but assume that in a 200 chimney you have a ~1% difference that you can safely ignore. With 25 chimneys (5000m/200m) you have a ~25% difference in the temperature that you can't ignore.

So you can't compare the temperature of the air that enters the chimney at the bottom, with the temperature of the air that is surrounding the top of the chimney.

The chimney can work if the corrected temperature at the top after the expansion in the chimney is bigger than the temperature of the air around the top of the chimney. [You probably need more difference, 0.000001°C will not be enough.]

The physics doesn't change, but if the chimney is short you can ignore the correction.

Because "the principle" involves operating 24/7 to support itself based on the temperature difference between the top and bottom, and handwaving that the air inside will somehow magically not expand and cool like it would outside.

Obviously solar updraft towers work, but they exploit the temperature difference between air at the base of the chimney and air outside the chimney. Completely different.

Thunderf00t has debunked similar concepts its late now i'd go into more detail but people can look up thunderf00t waterseer

Waterseer is a different impossible idea: They ignore that they need to remove a lot of heat to transform water vapor into liquid vapor. And that there is not so much water in the air anyway. [Clouds are huge.]

SuperTallChemney: They ignore that in equilibrium the column of air is has different pressures and temperatures that are related by the adiabatic process laws.

Anyway, it's interesting that both project try to be people friendly and offer a lot of water for the desert. In the SuperTallChimney it's not very clear if the plan is to put it in the middle of a dessert [1] or nearby a wet place that usually has no so big temperature variations.

[1] As another user commented, desserts are very hot during the day and very cold at night. What is the plan to keep the chimney working at night?

That explanation doesn't make any sense. If you put that in a Physics exam midterm the T.A. give you an F-.

One classic error is to try to analyze each part separately using handwaving to estimate how strong is each effect and get the result you wish.

It's always better to use conservation rules to analyze the global effects altogether, in this case the Bernoulli Equation and the adiabatic process laws.

The pressure in the chimney is not constant, because it's very high. Air is actually a good insulator, so you can assume that there is not heat transfer between the layers of air. All the heating and cooling is due to the work in the adiabatic decompression. So the air will not be at a constant temperature.

As a former atmospheric science T.A., I'd give that a D for at least knowing the word adiabatic. I'd expect adiabatic cooling from air expanding as it rises up the tube. Expansion is in the vertical direction of course. Nothing magic is going to affect atm pressure inside the tube; it's the weight of the column of air above it, just like everywhere else.

I'm not so sure that the benefits of removing mixing would be significant compared to slowing from having a boundary layer all the way up. Does it work because insolation on the chimney itself heats the air inside warmer than its environment? Maybe I should just look at the paper.

> I'm not so sure that the benefits of removing mixing would be significant compared to slowing from having a boundary layer all the way up.

For practical purposes, the expansion of a rising thermal can be treated as adiabatic, because the mixing is not large in comparison to the volume.

One consequence of the flawed argument presented on the website is that this system will not run continuously, but only when the lapse rate is that of adiabatic expansion (dry or wet, depending on the relative humidity) - i.e. the same condition as for natural convection (and if there is condensation in the tube, that complicates the matter.) On the other hand, I suppose, if the proposal has some validity, that pumping air into the tube to raise it through an inversion might allow convection to start where it has not done so naturally, or to trigger conditional convection (where the air is buoyant only once saturated, on account of the release of latent heat as it rises further.))

I am also wondering about the Venturi effect, and the assumption that the tube will support itself against outside pressure with a 300mph wind blowing through it - though that figure comes from what appears to be a fatally flawed calculation.

If you can bootstrap the thing at all, the air in the tube can only expand and cool by going up the tube. If it expands at the base, it runs into air at the same pressure. If it didn't already have upward momentum, that might be the end of it, but if it's already moving upward into a region where the outside temp/pressure is lower, if it tries to expand, it can only do so upwards. Since air inflow at the bottom has to equal air out the top in equilibrium, that expansion can only push air through the tube faster, which helps the concept's viability. Granted, this is a slightly different theory of operation, but it uses the same basic logic of exploiting the pressure difference by limiting the ability of the air to expand freely.

He does say a lot of things that are goofy (you can't just assume the outside air is rising, still air is a thing that happens), and the theory I'm putting forward is a bit different than his, but I'm just saying I'm not sure you can dismiss the whole concept on thermodynamic grounds. IANAPhysicist, so I'm open to clarification on any point.

Air will accelerate as it moves up the tube, but that doesn't do anything useful for us. If the pressure drops in half then your speed will double, so a 1m/s inflow produces a 2m/s outflow, but you can't exploit that to produce energy. Or rather you can, but only by slowing the flow. You'll either slow it to a stop, or you need a source of heat to keep it going.

Maybe the plan is to put a large pot of boiling water at the bottom.

Elsewhere in the thread, there's a variation mentioned that collects solar energy to accomplish this.

There is a source of heat -- the sunlit Earth.

It sounds like the basic idea is to get that hot air off the surface where it can radiate energy to space with less reabsorption.

I agree that extracting work for power generation would limit the amount of air that's moved, so there's a tradeoff you'd have to make.

Part of the idea is that the tower supports itself on the venting air, which means it has to be running non-stop. Even at night, when there's no sunlit Earth to drive it.

Yes, there are many days where a structure like this could operate for several hours off of solar heating. But that's not what's being described here.

If you do some mountaineering, you'll notice that the elevation temperature difference is persistent day and night. It is always cooler higher up at the desert latitudes described. If the sun stopped shining for a few days, then yes, the surface temperature differential would produce less and less potential.

This idea requires some creativity, but it's among the most interesting I've heard. And the science that you question is definitely sound -- the only real issue I see is finding a material to handle the stresses.

If you do some glider flying, you'll notice that atmospheric convection almost always stops well before sunset.

Yes, it's almost always cooler at higher altitudes. That's because air pressure is lower, making the air less dense. When air expands, it cools.

Because of this, merely having warm air below cold air isn't enough to make the warm air buoyant. The temperature difference needs to be big enough that it will still be warmer when it has risen to the altitude of the cold air and expanded to match the pressure there.

To state it with some jargon, the temperature difference must exceed the altitude difference multiplied by the adiabatic lapse rate, otherwise the warm air doesn't go anywhere.

So: warm air at the bottom of the chimney will rise in the chimney if and only if the temperature at the top of the chimney is a lot colder. For a 5km chimney with dry air (moisture complicates the numbers but doesn't change the principles at work), the temperature at the top needs to be 50°C lower than the temperature at the bottom just to be in equilibrium. In order for air at the bottom to experience any force upwards, it will need to be a fair bit more than 50°C warmer than the air at the top.

The web site here says that this is not an issue because the air within the chimney does not experience adiabatic cooling as the air outside the chimney does. Which is complete nonsense.

> The web site here says that this is not an issue because the air within the chimney does not experience adiabatic cooling as the air outside the chimney does. Which is complete nonsense.

As I posted elsewhere, whether or not you can conceptualize it, there are real examples of this phenomenon in the world, such as this large cave network in Turkey. https://en.wikipedia.org/wiki/P%C4%B1narg%C3%B6z%C3%BC_Cave#...

Even if the temperature differential needs to be a bit higher to make this consistently effective, there are certainly ways that can be done. Such as channeling heat via thermal conductors and radiative materials at night, or consuming waste heat from industrial processes that would be happening regardless. I think it's worth exploring.

I can't find much information about those caves, but I bet the wind isn't constant.

It's worth exploring chimneys, and indeed people are. It's not worth exploring chimneys which generate airflow 24/7 without a heat source because they magically suppress adiabatic cooling of the air within.

"if it tries to expand, it can only do so upwards."

There also can be an inversion inside the tube. For example, air might cool more on the shadow side of the tower, and start going down there.

I think it is 'obvious' that that will happen if you make the chimney wide enough (as a thought experiment, make it 2000 km wide, treat the outside of the chimney as the inside of a chimney with diameter of close to the circumference of the earth, or consider the case of a kilometer high wall on the equator with air intakes at the bottom. You argument that air must go up on both sides of it)

Question is whether the proposed chimney is wide enough for that to happen, and to what extent.

My fav part is—"the air outside will be cooling adiabatically, so its temperature will be dropping"

No shit, sherlock.

Ummmmmmmmm.... You do know about thunderstorms and other clouds with unstable vertical develompment, right? Because that's how they work, by warm humid air violently rising into cool drier air.... Don't forget about the latent heat of condensation. This is just a thunderstorm in a sock.

.... That does however mean it would need humidity to operate... The adibiatic cooling alone would be a wash, I'm pretty sure. Perhaps differences in radiative cooling between altitudes would be a help.

But.... Even if the self powering potential is not there to maintain the chimney by itself, what's to stop us from putting 1gw of solar panels and powering the thing with fans? If the heat transfer numbers aren't wrong.... That could still be a very useful characteristic.

The system described operates continuously and supports itself with that constant airflow. Unless you live in a place where thunderstorms happen all day every day, it won't work.

If the column of air is really moving at 300 MPH, they'd better diffuse that at the bottom so people (and things) aren't sucked into the chimney (it would suck to be ejected at the top without a parachute but you could probably sell a ride to the top to the wing-suiters).

Nice debunking write up here:

http://climateboy.blogspot.com/2009/04/super-chimney-that-wi...

I don't find the debunking article persuasive. It says, "Imagine you take a blob of warm air from the surface up to some height... this transformation has to change the temperature of the air in the blob."

No it doesn't.

The nearest it gets to supporting that claim is, "It turns out to be very easy to derive an equation that says that the temperature decreases by 10 degrees C per about 1000 m of height with no vertical motion. That explains why the air above the surface is colder than the air at the surface."

I'd like to see the assumptions of deriving that equation. Without seeing how the equation is derived we can't jump straight to the "That explains why" part. I guess the equation he's talking about assumes the atmosphere is static and is simply deals with how the upper atmosphere is colder because it can radiate into space, whereas the lower atmosphere can only exchange radiation with warm ground or the cold-but-still-warmer-than-space upper atmosphere. If so, it says nothing about what happens when you "move a blob of warm air".

Maybe building these things is not feasible or maybe the effect is not significant, but it doesn't look physically impossible to me.

The air cools down when raising in the chimney because the air pressure decreases, leading to adiabatic expansion.

when any gas expands, it does work in expanding against the outside "surface" of the control volume, which comes from the internal energy - temperature - of the molecules.

The equations are commonly derived in thermodynamics undergrad courses. look up adiabatic expansion.

here's a video:

https://www.youtube.com/watch?v=ObnWb7yspxA

Good point. I stand corrected.

I still think that the radiating-into-space effect I mentioned is real. I imagine this is part of the reason there is convection in the atmosphere. But I'm out of my depth.

Anyone here could run a super tall chimney software simulation ?

I'm super interested in seeing someone confirm or debunk this. Anyone else interested, upvote please

Probably nearly impossible. Fluid dynamics simulations are horrendously time consuming even at low resolution and small scale. This is bound to be more of an engineering stunt than a scientific endeavor.

GPUs are dime a dozen these days.

We need ChimneyCoin!

We need a new Godwin's law for cryptocurrency.

Engineering issues aside, to evaluate if a super chimney would be energetically viable you need to understand the concept of "Convective available potential energy" or CAPE--https://en.wikipedia.org/wiki/Convective_available_potential.... CAPE has dimensions of energy/mass and a describes how much energy is released by raising a mass of air to some higher elevation.

CAPE is used to forecast storm development, as updrafts can more likely spontaneously form when there is more energy released by the updraft. CAPE values can also be zero or negative, in which case there would be no available energy to sustain an updraft. From my understanding, CAPE is the only factor that would determine if a super chimney could work at a given time.

I have not found a good resource on global CAPE patterns including daily patterns, but it seems very likely that there is any fixed location and fixed elevation that always has a positive CAPE value. It would be an absolute requirement to find such a location for this project to work.

You should also be able to calculate a crude bound on the maximum updraft velocity simply as a conversion of potential energy to kinetic energy. Wikipedia says that exceptionally high CAPE values proceeding extreme thunderstorms are around 5kj/kg, which would accelerate a mass from rest to 100m/s (220mph). Of course this is an extreme value, typical values are more like 1kj/kg, which correspond to a velocity of 44m/s (100mph).

Here is a really good paper on CAPE and atmospheric convection heat engines: http://journals.ametsoc.org/doi/pdf/10.1175/1520-0469%281996...

thank you

The short story "Shortstack" by Walt Richmond and Leigh Richmond depicts this idea and was published in Analog in '64. Likely coincidental, but amusing to see '60s science fiction apparently made flesh.

The scifi novel "Omega" by Jack McDevitt also had this.

For the 5km chimney it needs to hold on 500km/h winds. For scale a category 5 hurricane is 250 km/h. Is it even possible to have that kind of structure with existing materials?

I'm not a real engineer, but most structures don't have the ability to flex like this tube could.

Rich Homie Quan couldn't even flex like this tube could. Making really tall stuff is hard.

While I am generally skeptical of this idea, 500km/hr winds occur at much higher altitudes - the force is much less than it seems because there is much less air doing the pushing. If a human can get to the edge of space and freefall safely, I imagine that will not be the sticking point.

The falling human is free to move with the wind. No shear forces. Unlike a tower attached to the ground.

They are proposing a fabric chimney. For sure that has its own challenges, but shear force isn't as much a problem, from I would intuit the setup to be.

http://www.wavyads.com/images/skyfly-dancer-yellow2.jpg

I've tried to simulate 1km chimney in Comsol, but I cannot make it converge to a solution. If anyone is interested, the model is here https://mega.nz/#!jFgBxI6J!jdxloYFwcuk_YyGcIMlOmJTKcPbxyD2B4... (may be I'm doing something wrong with simulation parameters, help would be very much appreciated!)

I don't have Comsol. Does it make nice graphics? Can you post a screenshot (in imgur)?

[Disclaimer: I think this idea doesn't work. If you wish to make it work try adding a huge glass bell like the one explained in other comment.]

Yes, it does, the problem is, the basic setup isn't converging to solution so nothing to plot, which is unusual and probably means I choose wrong boundary conditions or something.

This will also function as a hell of a bird vacuum.

The input is at the ground level, and obviously you'd have grates and such to prevent things other than air being consumed.

(That's assuming the thing would work at all, which it wouldn't as far as I can tell.)

Here's my analysis from maybe wrong principles. If you have slightly more dense air beneath slightly less dense air, the air will experience a net force upwards. If this net force is stronger than gravity, then the air will experience upwards acceleration. This will continue as long as there is a difference strong enough. At the top of the tube, there is no more force since the density will be the same since the air will spread out after exiting. (If it's not already at the same density after going through the tube).

Looking at it this way this seems sound to me, am I wrong?

It is a bit different than that.

Air is compressible. And because of that the mass of air that is being pulled toward Earth by the gravitational attraction of the rest of the planet means it compresses as much as it can as close to the surface as it can get, and then becomes less and less dense as you increase the distance from the center of the Earth.

This is nominally a stable state. Air doesn't move.

When you inject energy into air, that increases the kinetic energy of the air molecules. They bounce off each other and push themselves apart. As a result they have "more space" between them that air molecules than ones that aren't currently heated. What will happen then is the 'less energetic' molecules will 'fill in the spaces' left by the more energetic ones bouncing apart. You might visualize this like sand filling in a hole you are digging by throwing other sand up into the air.

If you do nothing, more energetic molecules end up higher up, and less energetic ones end up lower. Colloquially, "hot air rises". And if you constrain it in an envelope of some form (a balloon for example) then you can create a mass of air that has a lower average density than the air around it and that results in a lifting force.

Here is the rub, as long as you put heat into the air it will stay less dense and your balloon will stay in the air. However, stop adding heat (energy) and the balloon cools and begins to sink. Finally, there is a point where you cannot add any more energy to the air to get it less dense than the air around it. In balloonist terms that is your balloon's ceiling height. 2004 record was 4.1 miles[1]. This is a balloon where you have a super hot flame shooting up into it, and it won't go up any more because you have reached the point where you cannot put enough energy into the air to make it less dense than the surrounding air.

As a result, if you surround a column of air, it might initially rise because energy inside the column is unable to diffuse into the air around the column, but it will only do that until it reaches a new equilibrium point. Early on in the process not being able to spread out allows the air to keep its heat, but at it moves up in the tower/chimney the chimney prevents it from becoming less dense, so relative to the air above it, it gets heavier and heavier per cubic foot. These two effects balance out and the air stops moving.

[1] https://en.wikipedia.org/wiki/Flight_altitude_record#Hot-air...

But isn't the idea that you would end the column well before the air in it reaches equilibrium, and that way you would have a major temperature pressure gradient from the exit into the surrounding atmosphere, which would create a continuous flow?

Sure you would want to, but there aren't any solutions to the equations where those conditions are met.

Think if it in terms of energy in versus energy out. Where does the energy come from? Well the author is attempting to use the latent heat in the air. So you have to ask how much energy is there? You can start with Carnot and his principles of heat engines, but you also have to consider the ideal gas law, the temperature of the air goes down with a decrease in pressure. How much? Well if you look at the typical math the loss in temperature from the decrease in pressure between the top and the bottom of the chimney is exactly equal to the temperature difference measured at the top and bottom of the chimney. That situation is true because there is no net input of energy to raise the temperature of the air. So this relationship holds from altitude 0 to the bottom of the stratosphere. At the start of the stratosphere the atmosphere gets hotter as you go up[1].

Solar energy due to ground warming is contributed evenly for a first approximation across solid ground (note that cities are hotter than vegetation etc). There is no way to 'preferentially capture' just the warm air at the base of the chimney (see Maxwell's Demon[2])

At the end of the day, there is no "excess energy" to harvest there.

[1] "Within the stratosphere temperatures increase with altitude (see temperature inversion); the top of the stratosphere has a temperature of about 270 K (−3°C or 26.6°F).[5] This vertical stratification, with warmer layers above and cooler layers below, makes the stratosphere dynamically stable: there is no regular convection and associated turbulence in this part of the atmosphere." -- https://en.wikipedia.org/wiki/Stratosphere

[2] https://en.wikipedia.org/wiki/Maxwell%27s_demon

That doesn't quite add up to me. After all, we extract energy from heating differentials all the time in the form of windmills. This really just seems like a scheme for channeling what is basically the same air circulation. The argument being that ground-warmed air doesn't typically rise in a straight line, and so by preventing lateral convection, you'll get a much faster flow up the chimney.

The use of it for wind energy is less interesting to me, though, than the idea of getting hot air radiating further from the surface of the Earth. If that is indeed significant in how the greenhouse effect works, that alone seems worth considering.

My layman's understanding is that wind is caused by pressure differences that result from different regions on the ground heating up differently in the sun. But the pressure difference between the ground and air higher up is just right to balance out gravity, so on average you should expect no movement at all.

Additionally, windmills work without any kind of tunnel, so you should expect this tower to work just as well if you just pointed a few wind turbines downward on a pole. But I think the horizontal winds would be much stronger, so you should readjust the direction a bit, which leaves you with a really tall windmill.

My understanding is that this balancing out with gravity would be true, but for horizontal mixing that occurs, as well as downdrafts of cold air and radiation (which is significant enough to motivate the chimney idea, according to the author). So you have this very complex voyage of ground-heated air upward, which is responsible for most of what we think of as local weather.

I understand the idea is to streamline the updraft, essentially controlling weather in the immediate vicinity.

I feel like a bunch of people are skirting right around this but this was unclear to me.

The design calls for an absolutely enormous taper at the bottom called the collector. That land area is covered surface, so there is a huge volume of hot air that isn't mixing around the column near the base. I assume this is how they get around the symmetry issues of a uniform cylinder.

I had to go to one of the publications to find a close up photo with much clarity, maybe this will help others to notice.

There are sites promoting that idea, but TFA (or the video on the front page, anyway) claims the idea will work without any kind of energy collector at the base.

Presumably you just lay a pipe that goes up the side of Everest and free power!

I wonder if the author asked the question "Why don't we have tornadoes all the time?"

If they had, that would have lead them to the physics of tornadoes. In my case it was the physics of so called 'dust devils' in the desert which are much smaller phenomena but based on the same ideas. Warm air rising through cooler air.

You might ask, but why don't we have them all the time? And the answer is that as air goes up, it spreads out, and as it spreads out it becomes less dense, and the lack of density is perceived as a colder 'temperature' even though the air molecules still have more kinetic energy and are thus 'hotter'.

In the video the tube is supposed to constrain the air (which it will) and the warmer air will rise inside of it, but without an energy source the warm air rises until its 'weight' is equivalent to the un-risen air underneath it, at which point it stops rising and the system is stable. If you were to cool off the bottom the air would start sinking again.

This has been experienced time and again by inexperienced makers of fires in their fireplaces. If you don't put enough energy into the air to make it rise, it comes back down the chimney and fills your living space with smoke. A fireplace is a remarkable little machine, where the fire heats the air, which pulls in more air as the air above rises, which puts more oxygen into the fire and increases its energy output etc. But without the fire burning in the fireplace the air stops moving.

Tornadoes benefit from a mass of really cold air sitting on top of warm air. This does two things, one the cold air above pushes down on the warm air to pressurize it, and two when a "hole" begins forming in the cold air mass it operates like an inverted tub drain and the warm air starts draining out of the tub. The energy source for a tornado is the temperature differential that is set up by the result of moisture condensing out of the air and super cooling the air around it.

Similarly a hurricane is powered by the temperature differential between the ocean and the air above it.

All three systems (fireplace, tornado, hurricane) share a common theme, there has to be a source of energy for them to operate. Without it, the air reaches equilibrium and just sits there. No magic allowed.

That said, if instead you built a tunnel, then you could connect two different air masses and extract energy from two different pressure differentials. The most interesting ideas have a tunnel under the Rockies or under the Sierras between the Mojave desert on one side and the milder (and moister) climate on the other. To the delta you can get from that is linear with respect to distance and/or a geographic feature that can inhibit the natural balancing of the air masses (like a range of tall mountains).

Sadly neither super chimneys nor lighter than air vacuum balloons are workable ideas.

Edit: It occurs to me that if you could make the chimney high enough you could put the top in the underside of the jetstream, then you could suck air up using the venturi effect.

I think I'm missing something here. How is the temperature differential between a fireplace and the top of that chimney different than the temperature differential between the ground and the top of the super chimney?

The fireplace is dumping BTUs of energy into the air above it, the ground doesn't do the same.

Isn't that just a difference of degree, not in process?

I do not know if this works, but I can say that if heat is allowed to get higher in the atmosphere, then when it radiates freely, more will escape into space than if it radiates freely at ground level.

No. The thing you have to understand is that the air from sea level to the stratosphere, to a first approximation in stable conditions, has the same energy. There are local discontinuities where some air is slightly warmer than other air and so it goes up but by and large its a stable system.

That said when you have a boundary layer between two areas with different thermal properties you get wind between them. If you like to go sailing as I do you will recognize this as 'lake effect' wind where the sun sets and the water dumps heat more slowly than the land, so you get an offshore breeze. Or in the morning when land heats up faster than the water and you get an onshore breeze. That occurs because there is a net energy differential between the two masses. There is no energy differential between higher altitude air and lower altitude air absent other weather effects (like water condensing from vapor to liquid or liquid to ice)

>first approximation in stable conditions, has the same energy <

Nonsense, unless maybe you mean the same mass of air (are you including water vapour, particulates, hire are you accounting for differences in constituency [eg ozone levels]); even then it seems highly unlikely.

Or by stable conditions do you mean ones that don't exist in reality (and in which case how is that useful as a model for the real atmosphere?).

The air at the top of the chimney is cold because it has expanded due to lower atmospheric pressure. The air inside the chimney undergoes this exact same expansion, and loses the exact same temperature.

A fireplace chimney is different because the air at the bottom starts out hotter than the ambient temperature. When it comes out the top, it has cooled but is still hotter than the ambient temperature at that altitude.

I see what you're saying wrt the difference. Thank you.

The air once at the top wouldn't experience any expansion if it was the same density as the outside air, but what about the energy it picks up from expanding? Wouldn't it still have that? Of course it will have lost some from fighting gravity.

In a stable atmosphere, all the various effects cancel out.

But it's not a stable system, it's being driven with heat from the base.

A simple hydrodynamic [physical] model should be easy to build in the lab.

The chimney described here supports itself with the airflow it generates, which means it has to operate 24/7. That means it has to operate in stable air. It can't.

So if you had mirror arrays pointing at the bottom of the super chimney, the sun would be the energy source, so it could work?

at which point, wouldn't it be better to use the solar energy more efficiently as either a source of power (thus eliminating CO2), or use it to grow plants to absorb CO2 (as a sink)?

This has no bearing on TFA, but it was my impression that the physics of tornadoes and dust devils were actually known to be pretty different. Also the mechanism you describe doesn't sound like any of the proposals I've heard of. Do you have a digestible source for that? I'm just really curious about tornado formation.

Hmm I wonder if there is a lecture to go along with these slides: http://www.physics.indiana.edu/~dermisek/CM_13/Tornado_Physi...

So many signals suggesting this is a wild physics-defying idea that could never work, e.g. how many websites claiming 'this one neat trick solves global warming' really hold the key to solving global warming?

I hope that's not the case and by this time next decade we're all laughing about that century and a half where we put so much carbon in the atmosphere wow wasn't that a hoot...

Realistically, I am sympathetic to the idea that geoengineering, massive structures and engineering projects enabled by modern materials, etc. deserve more thought.

Your critique of the proposal is ascientific.

And your lack of justification is ascientific.

Unfortunately no concrete concern was voiced that could be addressed other than vague comparison to hoax websites.

These geoengineering proposals should be understood as mitigation strategies to be implemented after we have reduced carbon emissions, since even then we still have a problem. But this one seems very dubious.

>Speaking in terms of thermodynamic, we can say that chimney prevents adiabatic cooling of a rising parcel of air. Normally, when hot air freely rises in atmosphere, it expands as it gets higher and pushes the surrounding air. That causes surrounding air to heat and rising air to cool. That process continues until equilibrium is reached. At that point air stops its ascending. Unlike freely rising parcel of air, the air in the chimney is restricted in its horizontal expansion and thus, it is not free rising. When air rises in the chimney it also expands but only into upper direction. It compresses the layer of air above it, heats it up and loses its own heat. At the same time air below does the same thing. And thatâ€™s how it goes all the way until the chimney exit: layers of air are being pushed and push themselves. That results in maintaining the same amount of heat in every layer of air, and that is how the chimney works.

This explanation ignores gravity. Air above you exerts more pressure on you than air below you, albeit by a tiny amount. But when the only thing moving is air in a 5-kilometer chimney, you can't get something for nothing. For intuition, just imagine the chimney is full of water. The water at the bottom is obviously under more pressure than the water at the top. The chimney faces the same consideration, but the ideal gas law applies.

Furthermore, the equation used in the "Calculations" section:

>q = Π dh2 /4 [ (2 g (po - pr) h ) / ( λ (l pr / dh) + ∑ξ pr ) ]½

is sourced from this website:

http://www.engineeringtoolbox.com/natural-draught-ventilatio...

which rather obviously works from the assumption that the chimney is placed inside of a heated house.

This all seems to be a sort of Sokal effect in climate science, I'm afraid. The paper 'SubiculumCode cited does not really analyze the thermodynamics used for the chimney and points more to the unrealistic dimensions (1 kilometer diameter and 10 kilometers high).

Whatever we do, it's important that we learn how to control the "ingredients" of our atmosphere. There are so many things that could go wrong with our atmosphere and result in mass extinction. Global warming, ice ages, massive volcanic eruptions, etc. If we can find a way to quickly filter out the crap and rebuild our atmosphere... well, this technology could be used for protecting our Earth and future pursuits in space.

I think this, however flawed some of the explanation of the effect might be, is something we can try and experiment with fairly easily. Either it can be done, or not. And I believe it can.

Now, we can't let Musk do all the cool things, maybe someone else could step in and fund a project to explore application of updraft towers.

We already have something that does the same thing as this claims to (facilitate heat transfer from the surface to the upper atmosphere): it's called the hydrologic cycle.

Yes and he goes into that in the video. The argument is that this accelerates that cycle.

Ah, ok.

Given this, if successful, is creating storms at the top, won't it continually and repeatedly be hit by lightning? And given that it is some kind of fabric, cause havoc?

If you search 'solar tower' on youtube, you will see all kinds of videos of existing installations of things that are similar, albeit most are not as tall, nor are they flexible. But the basic concept appears to be the same. Quite a few of them are from many years ago. So it would seem the idea works to some extent, and perhaps the the idea of a much taller, and flexible variant is the crucial difference that will make a big difference.

Wouldn't such a chimney take off like a Chinese lantern?

Would the radiant heat from the ground be enough to continue this effect at the same rate during the nighttime?

This line of inquiry is the key to proving or debunking this. Apparently a few here think that the chimney will fall over when the sun goes down.

This analysis fails to capture the fact that the upper troposphere also cools when the sun goes down - resulting in a maintained differential between the input and the output.

Watched the video. Sounds miraculous :) Anyone here knowledgeable of atmospheric thermodynamics?

This model must be able to be simulated somehow! To Minecraft!

Well we have pipes that go up the side of mountains, open both ends, add a skirt to the bottom, measure if there's a temperature rise at the top?

Then you can start working on viability of materials and such, no?

Would it be possible to make these into skyscrapers to house people and businesses? That would handle the financing part of it.

Is it really a good idea to move more water vapor, a potent greenhouse gas, significantly higher up in the atmosphere?

Doesn't water vapor high in the atmosphere reflect more energy upward than downward? I recall another geo-engineering proposal that involved autonomous ships that would spray water up into the atmosphere to reflect the sun's energy.

As far as I know, it gets colder on the ground when there is a clear night.

Presumably the radiation is absorbed by the clouds and the heat stays in the atmosphere.

I have absolutely no idea how it compares to reflective clouds during the day.

Hate to be a downer, but out of 157 comments so far, nobody has mentioned ocean acidification. If there was a way to build these chimneys... we could then go on burning fossil fuels & so then the oceans would become more acidic, possibly leading to the inability of krill to form exoskeletons, removing a one of the main oceanic bottom of the food chain food sources.

Would this be an efficient source of air pressure for the Hyperloop?

Hyperloop needs vacuum, not pressure.

Pressure can be efficiently converted to vacuum I believe.

I'm not sure why this is being downvoted. The method that immediately comes to mind is using the Venturi effect, though admittedly I don't know the efficiencies involved.

Couple the tower to an enormous array of venturi tubes.

Whether the vacuum generated from the flow is adequate for hyperloop use, and how to actually connect the vacuum lines from the absurd contraption to the hyperloop tube in a structurally sound manner are left as exercises for the reader.

Are you suggesting that the hyperloop built 5km up?

Also no, as LeifCarrotson mentioned, the hyperloop is removed air to reduce drag.

Whoever made this assumes that the chimney wall would be a perfect insulator, which absolutely cannot be the case if it's supposed to be a thin cloth or film barrier. The air would cool to the same temperature as the surrounding atmosphere.

This will not work.

It only has to be a reasonably good insulator. And anything that can stand up to winds at kilometer altitudes will do fine.

I doubt it has to be a good insulator. The air is travelling up the tube at high speed and there isn't time for it to cool significantly before it emerges.

No, it would have to be a very, very good insulator. You're talking about three miles of tubing exposed to high speed winds and large convective heat losses. Anyone who's taken a course on thermal power systems would know that this is absolutely preposterous.

I'm not saying it's feasible or anything, but he's talking about moving air at over 100 miles per hour. It would only take a couple of minutes to get to the top.

Right, plus it's a 30 metre diameter tube. The bulk of the air moving up the centre would be insulated by the outer layers of air near the inner skin of the tube.

That's not how convection works. It won't be moving quickly in the first place if it cools off. This whole farce of a thread is really tempting me to sink time into calculations to prove that this is absolute bullshit.

The author also states in the FAQ that the air in the chimney will not undergo adiabatic cooling. If that were possible it would also not undergo expansion and would remain denser than the surrounding atmosphere.

Chimneys do not require perfect insulators otherwise no chimneys would work. The biggest thing they do is prevent air mixing which in turn prevents a lot of energy exchange. This could work.

You realize that other chimneys have an outside energy source and that this essentially amounts to a free energy device, right?

I can scarcely believe that this is an actual level of argument that's occuring on HN.

I am not qualified to evaluate the actual possibility of this device, and there are many points that don't seem plausible to me.

However, the author is not arguing free energy. That would be like arguing wind turbines are "free energy". It's very clearly a solar powered device, with solar energy providing the heat that drives the air movement.

I'm not qualified either but this is an important point, the energy is definitely available and photoelectric semiconductors are merely one way to harness it.

Regarding the practical issues, what happens at night? Does it collapse under its own weight? How do you get it up in the sky in the first place?

The upper troposphere cools as well, resulting in a maintained differential.

This is absolutely not a free energy device. It may be bunk, but it is an attempt at a heat engine. Or rather, an attempt to make an existing heat engine more efficient/ faster/ controlled. There is outside energy and it is already doing work. We want more heat transfer and more controllable weather.

where is the outside energy source? If it's ambient solar light, then it hit (mostly) evenly, so can't possibily be an energy source for this chimney!

More light is absorbed at the bottom than at the top. This energy is already doing work as weather.

If the air under the chimney needs to be warmer than the air beside it,this could be achieved with mirrors or a broad greenhouse.

Things like this are the reason I don't think global warming will ever be a problem. Even if this example turns out to be a pipe dream, we will eventually figure out a way to lower the temperature or remove co2 from the atmosphere.

Global warming is already a problem.

Any idea how tall one of these would need to be in theory to support itself? I think that would be a cool sight to see and a great way to prove feasibility.

its bunk science i have no clue why this got top of hacker news

How much will one of these cost?

Video says at the end that one 20m diamater chimney would cost 5MM and that 25k chimneys would solve global warming.

Video is from 2013.

I guess nobody really knows although the author touches the subject here: http://www.superchimney.org/build.html

From another page:

PRICE

It is difficult to estimate the price at this point. Materials should be more expensive than those used for hot air balloons, since they have to be multilayered. Even if they are ten times as expensive the price should be under 10/ m2 (see http://www.alibaba.com/showroom/hot-air-balloon-fabric.html). To build 20 m diameter chimney would require as much fabric as 300,000 m2 of fabric or $3,000,000. Outside roping, mushroom cap, ground base, labor and machinery to inflate will increase the price. However, I do not see it bringing above $5 million.

Thus, if 25,000 chimneys of such size are enough to stop global warming, the investment will be less than 1,250 billions (annual US budget deficit). Furthermore, as we get more experienced with building super chimneys, we can make them more powerful by making them taller and wider.

The benefits will be millions of acres of arable land in deserts around the world, fresh water, electricity etc. It is quite possible that we can end up making profit on solving Global Warming problem.

Link: http://www.superchimney.org/build.html

Its 125 billions, not 1250 billions. Also US deficit is around ~500 bil now (way less then 1250b, but more then 125b)

Wikipedia[1] reports deficit was ~1,250 bilions in the 2011-12 timeframe, dropping significantly in 2013. Wayback machine[2] seems to indicate the author wrote the page in the 2013 timeframe, so the figures probably need updating.

[1] https://en.wikipedia.org/wiki/United_States_federal_budget#/...

[2] https://web.archive.org/web/20131210100653/http://superchimn...

Apparently people didn't watch the video. The author estimates $5M

Unreadable on mobile

This embedded 10-minute Youtube video contains the core ideas: https://www.youtube.com/watch?v=BfITeN76Thc

Notes:

- Warm air naturally moves up, and cool air naturally moves down. A chimney is like a hot air balloon

- The taller the chimney, the faster the smoke rises. Exponentially.

- The temperature drops 10 C every 1000 meters we go up. This is because there is more heat at the ground than in the sky (Transcriber's note: Dense air at the surface can store more heat than thin air near space can.)

- Consider a 5km chimney - the air at the base will be 50c warmer than at the top. This will cause dramatic airflow, up to 300 mph. While the air inside will be like the air outside, it will be hotter inside, due to the lack of Adiabatic cooling. When air rises, it pushes on the air it's passing, causing it to exchange heat with the air it's passing.

- By contrast, the chimney compresses air and causes it to gain heat and rush up, cooling the chimney.

- When warm air exits the top, the hot air causes precipitation in the cool air it's entering. AKA sudden clouds for deserts, or Oasis_aaS.

- Deserts are ideal, as they allow year-round operation. (Transcriber's note: Does that mean the ground and the upper atmosphere are less than 50C difference in northern areas?)

- The rains will cause carbon fixing, as more plants consume it and biodegrade into dirt.

- Global warming isn't caused by the planet receiving more heat, but by the planet storing more heat. (Transcriber's note: As an amateur astronomer, I disagree slightly. Part of the problem is how even our orbit is, which will change over the next 100,000 years.)

- This is basically a heat pump for the planet, like a reverse hurricane.

- There's less atmosphere between the upper atmosphere and space, than there is between the surface and space, so more heat will be radiated away by the air in this way. And the thinner atmosphere will reabsorb less of that heat than the denser atmosphere near the surface would.

- The chimney will be suspended entirely by the buoyancy of the air leaving it - it will have a "mushroom cap" which will direct exiting air downward, to push the chimney upward.

- They're expecting to use Hot Air Balloon fabric, and that it will be sturdy enough to be 3 miles (5 kilometers, 1640 story building) tall, and withstand winds and other shearing forces.

- Close the mushroom caps, and use hot air balloons, during initial inflation; then open the mushroom caps once it's fully inflated.

- 20 meter diameter chimney is estimated to cost ~ $5000.

- 25k super chimneys needed to completely address global warming, estimated cost $125,000,000.

- Total global economy estimated at $71,277,000,000,000, so this is a 0.17% global GDP investment opportunity. (Transcriber's note: IANAL nor fiduciary.)

  There's a table included too, it's not easy to reproduce:
  
  Height m - 2000 - 3000 - 4000 - 5000 - 5000 - 5000 - 
  Diameter m - 500 - 500 - 700 - 1000 - 10 - 20 - 
  Air Temperature at the base ?C - 30 - 30 - 30 - 30 - 30 - 30 - 
  Air Temperature at the upper end ?C - 10 - 0 - -10 - -20 - -20 - -20 - 
  Air Speed m/s - 52.7 - 80.4 - 109.2 - 139 - 139 or 500km/h or 300mph - 139 or 500km/h or 300mph - 
  Air Flow kg/s - 12,034,838 - 18,379,911 - 48,938,418 - 127,292,000 - 12,729 - 50,916 - 
  Producing electric power Mega Watt - 4447 - 15790 - 77542 - 327,786 - 32.8 - 131.1 - 
  amount of water condensate/precipitation kg per second - 0 - 73,520 - 327,887 - 929,231 - 93 - 371 - 
  CO2 uptake by irrigated desert tons - 0 - 147835 - 946,146 - 1,478,354 - 148 - 592 - 
  number of super-chimneys needed to cool the atmosphere - 224 - 99 - 27 - 10 - 100,000 - 25,000

Edits complete.

Re:" Dense air at the surface can store more heat than thin air near space can.)"

So, in theory, if we made the Earth's atmosphere less dense, we'd cool the planet. Correct? Any idea how much less dense?

It can be a function of either temperature or density - you can make it "cooler" by sucking all of the air out of the room. Because then, there are fewer air molecules, but they each have the same quantity of heat.

lets say it works, and makes the clouds. the clouds which rain down, and cool the surface. now your temperature differential is gone, no?

the main usefulness of this is to make places like sahara livable, electricity generation is just a nice side effect.

If a constant air flow is needed to keep the chimney upright, what will happen during the night, when the desert cools down?

That is a very good question. I was wondering about this myself but guessed that the upper atmosphere will still be significantly colder.

The video shows the chimneys mostly being built in deserts and their table has an example of 2km tall chimneys working on only a 20 °C difference. If you're building in a place where the winters or nights are particularly cold you should just built higher to exploit the colder temperatures further in the troposphere.

A spelling error makes it hard for me to take the proposal seriously.

For something as important as this, the details count. A loose approach to spelling is disturbing.

It's clear from reading that English is not the author's first language. This isn't a case of sloppiness.

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