
A tall chimney to facilitate heat exchange in the atmosphere - chr1
http://www.superchimney.org
======
lend000
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#...](https://en.wikipedia.org/wiki/P%C4%B1narg%C3%B6z%C3%BC_Cave#Wind)

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.

~~~
fenomas
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.

~~~
koverstreet
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.

~~~
fenomas
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.

------
vmarsy
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](https://en.wikipedia.org/wiki/Solar_updraft_tower)

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

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

~~~
grecy
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...](https://en.wikipedia.org/wiki/Mildura_Solar_Concentrator_Power_Station)

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.

~~~
jdavis703
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?)

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

~~~
codecamper
Now how did you get carpentry tools into an airplane?

~~~
lucisferre
Like this obviously:
[https://www.youtube.com/watch?v=6nNUEU8gnf4](https://www.youtube.com/watch?v=6nNUEU8gnf4)

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

------
saalweachter
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.

~~~
rlpb
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.

------
the_rosentotter
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.

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

------
mikeash
"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.

~~~
andrewflnr
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.

~~~
mikeash
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.

~~~
acjohnson55
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.

~~~
mikeash
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.

~~~
lend000
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.

~~~
mikeash
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.

~~~
lend000
> 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#...](https://en.wikipedia.org/wiki/P%C4%B1narg%C3%B6z%C3%BC_Cave#Wind)

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.

~~~
mikeash
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.

------
smoyer
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).

------
robocat
Nice debunking write up here:

[http://climateboy.blogspot.com/2009/04/super-chimney-that-
wi...](http://climateboy.blogspot.com/2009/04/super-chimney-that-will-save-us-
all.html)

~~~
abainbridge
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.

~~~
kashkhan
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](https://www.youtube.com/watch?v=ObnWb7yspxA)

~~~
abainbridge
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.

------
yohann305
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

~~~
microcolonel
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.

~~~
TeMPOraL
GPUs are dime a dozen these days.

~~~
pbhjpbhj
We need ChimneyCoin!

~~~
rapind
We need a new Godwin's law for cryptocurrency.

------
datadata
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...](https://en.wikipedia.org/wiki/Convective_available_potential_energy).
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...](http://journals.ametsoc.org/doi/pdf/10.1175/1520-0469%281996%29053%3C0572%3ANCAAHE%3E2.0.CO%3B2)

~~~
SubiculumCode
thank you

------
jcrawfordor
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.

~~~
desertrider12
The scifi novel "Omega" by Jack McDevitt also had this.

------
humanfromearth
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?

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

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

------
gtt
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...](https://mega.nz/#!jFgBxI6J!jdxloYFwcuk_YyGcIMlOmJTKcPbxyD2B4Hvuo1OIoFM)
(may be I'm doing something wrong with simulation parameters, help would be
very much appreciated!)

~~~
gus_massa
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.]

~~~
gtt
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.

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

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

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

------
foota
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?

~~~
ChuckMcM
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...](https://en.wikipedia.org/wiki/Flight_altitude_record#Hot-air_balloons)

~~~
neltnerb
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.

~~~
fenomas
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.

------
ChuckMcM
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.

~~~
foota
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?

~~~
mikeash
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.

~~~
foota
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.

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

~~~
pbhjpbhj
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.

~~~
mikeash
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.

------
Tarrosion
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.

~~~
erikpukinskis
Your critique of the proposal is ascientific.

~~~
vermilingua
And your lack of justification is ascientific.

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

------
scythe
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...](http://www.engineeringtoolbox.com/natural-draught-ventilation-
d_122.html)

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).

------
shoefly
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.

------
desireco42
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.

------
pdonis
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.

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

~~~
pdonis
Ah, ok.

------
mbfg
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?

------
mbfg
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.

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

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

~~~
Thetawaves
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.

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

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

~~~
pbhjpbhj
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?

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

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

~~~
tempestn
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.

~~~
kpil
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.

------
codecamper
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.

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

~~~
LeifCarrotson
Hyperloop needs vacuum, not pressure.

~~~
erikpukinskis
Pressure can be efficiently converted to vacuum I believe.

~~~
wolfgang42
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.

------
chroem-
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.

~~~
bognition
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.

~~~
chroem-
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.

~~~
hn_throwaway_99
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.

~~~
guscost
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?

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

------
unabridged
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.

~~~
Tharkun
Global warming is _already_ a problem.

------
foota
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.

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

------
pmoriarty
How much will one of these cost?

~~~
iokevins
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](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](http://www.superchimney.org/build.html)

~~~
zyb09
Its 125 billions, not 1250 billions. Also US deficit is around ~500 bil now
(way less then 1250b, but more then 125b)

~~~
iokevins
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#/...](https://en.wikipedia.org/wiki/United_States_federal_budget#/media/File:U.S._Total_Deficits_vs._National_Debt_Increases_2001-2010.png)

[2]
[https://web.archive.org/web/20131210100653/http://superchimn...](https://web.archive.org/web/20131210100653/http://superchimney.org/build.html)

------
hossbeast
Unreadable on mobile

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

~~~
chiefalchemist
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?

~~~
stephengillie
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.

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

~~~
undersuit
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.

------
ryanobjc
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.

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

