Trans Atlantic Tunnel?

[pdf27]

*raises eyebrow*
Are you certain? i'll have to check that quite thoroughly, then...

Yep. Vacuum is what I do for a living. Below a certain pressure you don't get liquid water, it's either solid or liquid. To transfer from one to the other takes heat, so what happens is the energy to break bonds and turn the liquid to gas comes from the rest of it freezing and releasing energy.
Hence the Armstrong limit - that's basically the point where liquid water can no longer exist at body temperature.

 

[dropbearabroad]

Nice phase diagram, much better than the one I was going to put up. Yes pdf27 is absolutely correct, at low pressure water won't liquify or boil, it freezes or sublimes. If you don't mind me asking, are you an engineer, physicist, physical chemist etc?

 

[Lleibi]

Ok but according to this phase diagram when you make the vacuum at 300K, you go into the vapor phase, not solid... right?

And in space, it's going to take a while before the body radiates enough heat to go below the 200K and freeze.

 

[dropbearabroad]

Yes, but the energy required to vapourise the water molecules will come from the body which then reduces its temperature. A person doesn't have to literally freeze into a block of ice (273K, or in reality a bit below that, not 200K) for them to die of course. I can't remember exact figues but if a human's core temperature drops more than 3 degrees Celsius or so then hypothermia can set in, and if it drops another 10-15 degrees below that it is usually fatal. I don't know what the thermal loss to a vacuum at whatever the temperature of a tunnel thermally equilibrated with the surrounding ocean would be in this case but I wouldn't want to experience it.

Mind you, that's all rather incidental to the problem of asphyxiation.

 

[pdf27]

Ok but according to this phase diagram when you make the vacuum at 300K, you go into the vapor phase, not solid... right?

Absolutely. But the latent heat of vaporisation still applies and has to come from somewhere. Unless you've got a gas fire burning inside you (or only have a tiny amount of liquid water exposed) you're rapidly going to get colder.

It's all a little incidental to Hypoxia (which will get the unfortunate inhabitants of this tunnel within seconds of a big leak), but it's a very creepy way to die. As seen by the kerfuffle over Fukushima, something doesn't have to be very dangerous at all to terrify large sections of the public and make such a tunnel unviable.

 

[King Augeas]

Yes, but the energy required to vapourise the water molecules will come from the body which then reduces its temperature. A person doesn't have to literally freeze into a block of ice (273K, or in reality a bit below that, not 200K) for them to die of course. I can't remember exact figues but if a human's core temperature drops more than 3 degrees Celsius or so then hypothermia can set in, and if it drops another 10-15 degrees below that it is usually fatal. I don't know what the thermal loss to a vacuum at whatever the temperature of a tunnel thermally equilibrated with the surrounding ocean would be in this case but I wouldn't want to experience it.

Mind you, that's all rather incidental to the problem of asphyxiation.

The deep ocean is cold, even at the equator. The bottom of the Atlantic would be about 4 degrees.

As I understand it, the water in an evacuated bell jar freezes because it experiences evaporative cooling because of the low pressure. Evaporation has the effect of cooling a liquid as the most energetic molecules (hence "hotter") are preferentially removed, leaving a liquid possessing less energetic and hence "colder" molecules. In the bell jar, the evaporation at low pressure is sufficiently intense that it removes enough heat from the water to freeze it. I frequently evaporate organic solvents under a stream of nitrogen and it's commonplace to see ice forming on the outside of the test tube, as the solvent experiences evaporative cooling to below 0 C.

So a human exposed to vacuum would experience feel his skin become cold as surface moisture evaporated. I'm uncertain whether there would be enough moisture for frostbite and freezing of the skin to occur though, with the exception of the eyes and mouth, although anxious sweating could (briefly!) create a feedback loop I suppose. But there certainly wouldn't be enough cooling effect to cause death by cooling of the core body. Instead, after the moisture is lost, then it's simply the slow process of a warm body cooling via radiation in a vacuum.

 

[Cymraeg]

Can I point out that the middle of the Atlantic is dominated by the Mid-Atlantic Ridge, along with a hell of a lot of transverse faults? Any tunnel is going to have to be magma-proof. Even if you get it to Iceland, go overland from there and then head towards Nova Scotia, there's still a significant risk from volcanoes and the divergent rift.

 

[Lleibi]

Absolutely. But the latent heat of vaporisation still applies and has to come from somewhere. Unless you've got a gas fire burning inside you (or only have a tiny amount of liquid water exposed) you're rapidly going to get colder.

It's all a little incidental to Hypoxia (which will get the unfortunate inhabitants of this tunnel within seconds of a big leak), but it's a very creepy way to die. As seen by the kerfuffle over Fukushima, something doesn't have to be very dangerous at all to terrify large sections of the public and make such a tunnel unviable.

Yes, it's true, i hadn't thought of that, all the surface water (sweat, eye lubrication, spit) is going to evaporate almost instantly, and that heat has to be provided by something. But as long as you are still alive (this was a triumph), you will still be producing a lot of heat... maybe it's enough not to instantly freeze.
Has it been tested on humans? j/k

 

[Alternate History Geek]

Can I point out that the middle of the Atlantic is dominated by the Mid-Atlantic Ridge, along with a hell of a lot of transverse faults? Any tunnel is going to have to be magma-proof. Even if you get it to Iceland, go overland from there and then head towards Nova Scotia, there's still a significant risk from volcanoes and the divergent rift.

Exactly why a trans-Atlantic tunnel is impossible.

And you'd also have to dig a tunnel several miles underground - which is several times deeper than the deepest anyone has ever dug or drilled.

And the tunnel would have a significant downward slope for HUNDREDS OF MILES. Meaning that in the case of a general mechanical failure the train will go to terminal velocity in the tunnel. Wrecking it when it hits the flat part of the tunnel.

 

[Dr. No]

You don't have to worry about depths and tectonics if you build a submerged floating tunnel.

 

[Alternate History Geek]

You don't have to worry about depths and tectonics if you build a submerged floating tunnel.

How would you anchor the wires to a seabed miles below the tunnel?

 

[Dr. No]

Submarine robots.

 

[Ironstark]

Could be attached to floaters on the surface, though probably unstable

 

[MattII]

Submarine robots.

Assuming 1 set of cables per km, and an average (almost certainly underestimating it here), then you're looking at 10,000 km of cable and 10,000 archors. Bringing it down to 1 set per 100 metres and an average depth of 2 km, you're up to 200,000 km of cable and 100,000 anchors. Even the groundwork required is extortionate.

 

[Lleibi]

Assuming 1 set of cables per km, and an average (almost certainly underestimating it here), then you're looking at 10,000 km of cable and 10,000 archors. Bringing it down to 1 set per 100 metres and an average depth of 2 km, you're up to 200,000 km of cable and 100,000 anchors. Even the groundwork required is extortionate.

And that's not the worst of it... i understand that in long suspending bridges with heavy traffic, the steel cables have to be maintained (repainting, repairing or replacing) very very frequently, to the point that someone is working on them at all times, 24/7. The maintenance of the anchorages of the floating tunnel could be just staggering.

It would be a lot better to make a suspension bridge between the US and Europe... hanging from the... orbital rings system! The train stations would be space elevators! and with ... uhmmm... cables made of carbon nanotubes! Weather wouldn't matter because the the bridge tube would be built with ... uh... graphene layers!

And it would be powered with ponies!

Haha, sorry, but the more i think about the "technical problems" of the tunnel, the more impossible it sounds, even though i quite liked the idea at first.

 

[dropbearabroad]

"You don't have to worry about depths and tectonics if you build a submerged floating tunnel."

But as already discussed you have to worry about stability. A floating tunnel is much more at the mercy of currents, tides and sea conditions etc than a fixed structure and you also have to worry about something (a ship, a sub, or even just the large mass of rubbish that can be found floating in the middle of the Atlantic) running into it. Combining a high speed train with a flexible floating tunnel presents serious safety issues, let alone if you try to run the thing in a vacuum.

The cost is hard to envision but probably would be horrendous, the project requires a number of technological leaps (all do-abole but it takes time and funding), but for me the real killer is the issue of what happens if there's an accident or even just a power failure. If your train breaks down on land you can still breath and probably get to a secure shelter and medical attention and wait for the repair crews to turn up. If the same thing happens in a vacuum filled tunnel under the sea, 2000 miles from help then you've got a big problem. And that is just for a simple breakdown, what happens if there is a major leak, a derailment, a collision etc?

 

[Lleibi]

The anchorage system actually seems pretty stable. I wouldn't worry about the stability as much as the fact that the tunnel is supposed to be able to make up for, somehow, the yearly widening of the Atlantic Ocean from the dorsal.

 

[dropbearabroad]

No, I think the lateral stability problem is far greater than the small annual growth in the width of the Atlantic. The solutions to the latter problem are much easier to come up with than for the stability issue. The anchorage of tether cables to the ocean floor may be stable, at least until there is a subocean earthquake or landslide which could be a problem. But the problem is that the tunnel itself would be swaying and twisting in the ocean some km above the ocean floor.

Take a kid's helium baloon outside and you will see it bob around dramatically in even a slight breeze. Now picture your trans-Atlantic tunnel also bobbing around, while trying to maintain a vacuum across tens of thousands of articulated connections and with a train weighing several thousand tons moving at several hundred/thousand kph. The Atlantic contains many different ocean currents moving in different directions and with different speeds. The weather and tides change the local behaviour of some of these currents. As a result the tunnel will adopt a series of continually moving curved paths. In current rail systems, the tracks are set and if they ever move it usually results in a crash. Although this Atlantic tunnel wouldn't have conventional tracks its path is going to be constantly changing and that presents some serious safety issues.

An analogy was made earlier in this thread to think of the train as being like a bullet in a barrel. I suggest you know think of that barrel as being wobbly, moving around and made of thin plastic. Would you feel safe using it now?

 

[Lleibi]

No, I think the lateral stability problem is far greater than the small annual growth in the width of the Atlantic. The solutions to the latter problem are much easier to come up with than for the stability issue. The anchorage of tether cables to the ocean floor may be stable, at least until there is a subocean earthquake or landslide which could be a problem. But the problem is that the tunnel itself would be swaying and twisting in the ocean some km above the ocean floor.

Take a kid's helium baloon outside and you will see it bob around dramatically in even a slight breeze. Now picture your trans-Atlantic tunnel also bobbing around, while trying to maintain a vacuum across tens of thousands of articulated connections and with a train weighing several thousand tons moving at several hundred/thousand kph. The Atlantic contains many different ocean currents moving in different directions and with different speeds. The weather and tides change the local behaviour of some of these currents. As a result the tunnel will adopt a series of continually moving curved paths. In current rail systems, the tracks are set and if they ever move it usually results in a crash. Although this Atlantic tunnel wouldn't have conventional tracks its path is going to be constantly changing and that presents some serious safety issues.

An analogy was made earlier in this thread to think of the train as being like a bullet in a barrel. I suggest you know think of that barrel as being wobbly, moving around and made of thin plastic. Would you feel safe using it now?

It might be just me, but i don't see much problem with that. According to the video, the anchors would be tight, but with enough room to wobble slightly. Think that the structure of both cables with the ground between them form a triangle, you can't deform it much.
Yes, there will be currents, but that's why it has a small room to wobble, to adapt to those changes. It's not going to be like a balloon that is sustained by a single thread. For example, take the helium balloon, tie it with 2 threads, and glue those threads to a table forming a triangle. Now, perpendicular to the plane of that triangle, place something in front and behind of the balloon, to account for the other segments of the tube. Now try blow some air against it, poke it softly, etc... it really won't move that much.

At least that's how i see it

 

[Henriksson]

I would move this to Future History.

Cool idea, I think.

To ASB, you mean.

They're kind of the same thing.