A long, partially-evacuated tube with a piston of air at atmospheric pressure coming from one end will probably develop a supersonic shock wave ahead of the gas piston. That's the basic mechanism of a shock tube.
I got suckered into doing some computer simulations of these back in school, on a chemical kinetics program that used shock tubes. About an arm's length from me I probably can find a box of old Fortran punch-cards with the code.
Hyperloop Technologies
Re: Hyperloop Technologies
I'd guess that that would kill everyone in the first car since I don't think they will be robust enough. I'm not sure about the deceleration - just hitting a Mach 2 relative air stream might be survivable (should be <6 g based on accelerating the swept cylinder of air to capsule speed for 1.4m^2 frontal area and 15 ton capsules). But, as Tom mentions, they are in a tube so it will probably be more of a sound brick wall than barrier.
The coming cars should be okay since emergency breaking should start as soon as ground movement goes above a certain threshold with repressurization starting at the same time (or at least when the tube is breached). It would therefor require a big earthquake with rapid large ground acceleration and an epicenter close to the track. Those conditions might kill you just as well on a train (high speed or not). Or in your car on the freeway/in a landing aircraft if a crack opens up in the wrong place. Ships are probably fine though
The coming cars should be okay since emergency breaking should start as soon as ground movement goes above a certain threshold with repressurization starting at the same time (or at least when the tube is breached). It would therefor require a big earthquake with rapid large ground acceleration and an epicenter close to the track. Those conditions might kill you just as well on a train (high speed or not). Or in your car on the freeway/in a landing aircraft if a crack opens up in the wrong place. Ships are probably fine though
Re: Hyperloop Technologies
I think an encounter with the shock wave could be made survivable, but it is one more thing to deal with. Most of the energy would probably reflect off and send the shock wave back down the tube. The shock wave does heat the air a bunch, but it is over fast. And the reflected shock wave will hit the gas piston again, reflect off, and come back even faster and hotter. That happens in shock tubes.
I think you'd need to slow the vehicle down as much as possible before the main piston of air hits, though. That's gonna hurt.
The heating problem could be pretty severe. Assuming you have rarefied gas at room temperature (300 K) and 0.7 Torr (rough vacuum) and suddenly rush in air at ambient pressure, you might be raising the pressure by 1000x or more. So the simpleminded approach says the temperature will go to ... well, hot. I don't think you'd really achieve 300,000 k but I'd not want to be exposed to it.
If you've ever been briefed on the hazards of using oxygen, one of the hazards is opening a valve from a pressurized O2 source too quickly. This can produce a hot shock wave that can ignite any fuel present in the lines, and even the lines themselves. That includes metal tubing.
I think you'd need to slow the vehicle down as much as possible before the main piston of air hits, though. That's gonna hurt.
The heating problem could be pretty severe. Assuming you have rarefied gas at room temperature (300 K) and 0.7 Torr (rough vacuum) and suddenly rush in air at ambient pressure, you might be raising the pressure by 1000x or more. So the simpleminded approach says the temperature will go to ... well, hot. I don't think you'd really achieve 300,000 k but I'd not want to be exposed to it.
If you've ever been briefed on the hazards of using oxygen, one of the hazards is opening a valve from a pressurized O2 source too quickly. This can produce a hot shock wave that can ignite any fuel present in the lines, and even the lines themselves. That includes metal tubing.