this post was submitted on 08 Sep 2023
236 points (94.4% liked)
Asklemmy
43833 readers
770 users here now
A loosely moderated place to ask open-ended questions
Search asklemmy π
If your post meets the following criteria, it's welcome here!
- Open-ended question
- Not offensive: at this point, we do not have the bandwidth to moderate overtly political discussions. Assume best intent and be excellent to each other.
- Not regarding using or support for Lemmy: context, see the list of support communities and tools for finding communities below
- Not ad nauseam inducing: please make sure it is a question that would be new to most members
- An actual topic of discussion
Looking for support?
Looking for a community?
- Lemmyverse: community search
- sub.rehab: maps old subreddits to fediverse options, marks official as such
- !lemmy411@lemmy.ca: a community for finding communities
~Icon~ ~by~ ~@Double_A@discuss.tchncs.de~
founded 5 years ago
MODERATORS
you are viewing a single comment's thread
view the rest of the comments
view the rest of the comments
If we somehow remove the friction of air on train body. Then maglev would be zero friction transport.
Edit : Oh my. My little joke comment has ballooned into a full on debate. And I'm not even aware of any of these things they're all saying.
I just made a comment guys, I'm not serious or not in any agenda.
Atmospheric Railway and Hyperloop bullshit all over again. Unless you're in space, this isn't feasible.
Its already been done
Sure on a small test track. As soon as it was meant to be scaled up, every attempt has been whittled down. Either it fails completely (Look up Brunel's Atmospheric Railway) or has been so expensive and impractical that it gets reduced to cars in tunnels.
If you are most concerned with efficiency, then building the cheaper HSR infrastructure to get freight off of roads and passengers off of planes as fast as possible should be the first priority. Holding even a partial vacuum in tubes hundreds of miles long just to eke out a little more energy efficiency is laughable. Everything leaks. Maintaining cabin pressure in a 73-meter plane is a completely different beast from maintaining vacuum in miles of tube. It's likely that maintaining the tubes will end up costing so much that any efficiency gains acquired from the vacuum will evaporate.
The vegas loop is its own dumb thing, its not relevant.
For the leak thing, dont just assume whatever wild claim that benefits your side. Heres a DoE study, if you search leak youll find an estimated power usage profile, with large spikes for acceleration, and a sliver of an orange bar across the profile as the baseline load for maintaining vacuum against leaks https://www.energy.gov/eere/vehicles/articles/effect-hyperloop-technologies-electric-grid-and-transportation-energy
When I'm talking about leaks, I'm not talking about the extra energy required to constantly run vacuum pumps. I'm saying that HSR infrastructure needs inspection and occasional repair, but not nearly to the extent that a vacuum tube based solution would. Any savings made via efficiency are pissed away by having to pay more maintenance crews and material cost to maintain the infrastructure. The tubes are also much less likely to be able to be automatically inspected like rails can be using inspection cars because any train moving through the tube can only inspect the interior walls. Besides, rail already exists across much of the US for use as freight infrastructure. These same rails, if inspected and tested properly, can be used for high speed rail much more immediately than waiting for tubes to be built. Besides all of this, more aerodynamic trains can and have been built, but are not in use in the US. Instead, we send bricks down the rails. The "immense" efficiency gain from 0.5 atmospheres of air pressure is likely significantly less impressive when compared against well designed trains with regards to aerodynamics.
All of this is also completely ignoring how dangerous tunnels are for fires. Even with proper safety precautions, fires in tunnels are exceptionally dangerous. By venting out the smoke that kills people, you increase the intensity of the fire that also kills people.
Oh man yeah welded joints are just falling apart every week, it takes a fortune to upkeep some stationary metal.
I dont think you understand air's role in aerodynamics. At half atmosphere...you've plainly removed half the friction, there is half the air molecules to collide with the train. To give some perspective, all of the fastest manmade vehicles, by crazy high magnitudes of difference, are space vehicles. The ISS is whizzing around at nearly 5 miles a second in low earth orbit. Air is the limiting factor in speed. Its the only reason any additional fuel needs burning to maintain speed.
Finally...youre not gonna have a fire in a vacuum tube
if only this was a proposed technology
You mean that hyper idiotic Hyperloop idea thatβs just a warmed up remix of the vacuum train idea from the 1920s and will efficiently kill all passengers if a little thing goes wrong (if you can get a hundreds of kilometres long vacuum chamber airtight anyway)?
its a big topic, just be aware that "vacuum" in the real world is a sliding scale of air pressure. vacuum tube doesnt automatically mean conditions on a spacecraft in sci-fi when a hole is shot through a window. You can cut air pressure to half of atmospheric, and have an extremely weak vacuum, and still get amazing efficiency gains. We already have routine transit of pressurized cabins in the form of planes.
Still means 0.5 bar overpressure if something breaks, which is deadly. Also the proposed pressure for the Hyperloop was 0.1 atmospheres iirc. If there is a weakness in the tube it will fail catastrophically and a pressure wave kills anyone in it. Watch the video where the mythbusters implode that huge tank.
You basically bring a lot of the problems with space travel down to earth.
"vacuum tube doesnt automatically mean conditions on a spacecraft in sci-fi "
Half atmosphere is less pressure difference than normal passenger planes.
The direction of pressure difference is important
Its the same? Pressurized cabin in a lower pressure environment
The problem is the high pressure environment outside the low pressure environment