4 ms·

>The "materials science" problem I call out is in the tube's lateral thermal expansion. I admire your method of argumentation. The comment I replied to said n

>The "materials science" problem I call out is in the tube's lateral thermal expansion. I admire your method of argumentation. The comment I replied to said nothing at all about thermal expansion. Your original comment, which I wasn't replying to, was mostly strange references to pressure ratios, and a single line about thermal problems, with no numbers cited. In that comment you did link to the Space Power Facility... as an argument against Hyperloop One! You did something similar downthread: https://news.ycombinator.com/item?id=15459777 https://news.ycombinator.com/item?id=15459777 But by asserting that you addressed the problem in your original comment, you make the person you're arguing with look like a bully, without having to actually address their points. Very efficient. >The best solution I've come up with for that is to take a regenerative rocket engine [1] and make it a tube. Pumping fluid in spirals along kilometers of a vacuum tube isn't easy, but it isn't as hard as trying to invent a material that won't deform when the top gets hotter than the bottom, or the east side gets hotter than the west. Using the phrase "regenerative cooling" in this context is another headscratcher. Regenerative cooling in rocketry is running propellant through channels in the nozzle, then either dumping it overboard, using it to power a gas generator, or burning it in the rocket. It's a great way to get rid of megawatts of heat. None of these things would be useful for a hyperloop tube? You don't want to run kerosene/liquid oxygen/hydrazine/whatever through a cooling jacket then dump it on the ground, you don't need a gas generator for anything, and there's no way to feed the heated propellant to the actual hyperloop car. And if you could, you wouldn't want to, since if you combusted it in the car it would just dump the exhaust in the tube, killing the vacuum. Presumably active cooling of a hyperloop tube would use a closed refrigerant cycle, which has little to do with regenerative cooling, besides the idea of cooling channels. Talking about regenerative cooling in this context isn't wrong, exactly, it just betrays a rather shallow understanding of the problem at hand, as seen in your first comment.

JumpCrisscross 9y ago
> Regenerative cooling in rocketry is running propellant through channels in the nozzle, then either dumping it overboard, using it to power a gas generator, or burning it in the rocket "Regenerative cooling" is a rocket term. It came to mind because I used to be an aerospace engineer. There's no requirement in the definition of regenerative cooling for the coolant to be dumped. > Presumably active cooling of a hyperloop tube would use a closed refrigerant cycle I don't think one can just presume that. You've already got lots of pumps for pumping air. Given (a) the seal on the tube will be periodically broken (for entry, exit and maintenance) and (b) a safety factor, you'll have more pump capacity than you'll need. Filtering and then compressing atmosphere, running it through a heat exchanger, and then letting it expand through the cooling channels before dumping it doesn't seem obviously worse than having kilometers of refrigerant running around. > which has little to do with regenerative cooling, besides the idea of cooling channels See above. Also, I assumed if you did this you'd use it to boost SpaceX's nozzles' economies of scale.
- sbierwagen 9y ago
  >"Regenerative cooling" is a rocket term. It came to mind because I used to be an aerospace engineer. There's no requirement in the definition of regenerative cooling for the coolant to be dumped. ? Regenerative cooling in rocketry uses propellant. Propellant is always dumped overboard, because it's propellant. Please show me a rocket that uses closed loop cooling of the rocket nozzle. >Filtering and then compressing atmosphere, running it through a heat exchanger, and then letting it expand through the cooling channels before dumping it doesn't seem obviously worse than having kilometers of refrigerant running around. My turn to be pedantic about definitions: this sure sounds like closed loop cooling to me! The working fluid is air, you draw it from a big reservoir, (the atmosphere) cool something with it, then return it to the reservoir. (Something you can't do with open-loop regenerative cooling of a rocket nozzle, since the coolant gets burned at the end of the cycle) However, maintaining the air dryers and replacing the filters sounds like it wouldn't be any cheaper than conventional phase-change cooling, and having to build custom vacuum/compressor pumps for the hyperloop project is going to be more expensive than buying COTS vacuum pumps.
  - JumpCrisscross 9y ago
    > Please show me a rocket that uses closed loop cooling of the rocket nozzle The most famous one is the under-development SABRE [1], which includes a closed-loop helium cycle. For cryogenic rockets, closed-loop cooling of the nozzle has been explored [2] to avoid hydrogen embrittlement and oxidation of the nozzle channels, as well as to simplify plumbing. In any case, we've devolved into arguing semantics. > My turn to be pedantic about definitions: this sure sounds like closed loop cooling to me! I was figuring on dumping the air once done versus worrying about a reservoir. That said, I haven't done any math on the benefits of saving the return piping (and reservoir cost and maintenance) versus using something traditional. > maintaining the air dryers and replacing the filters sounds like it wouldn't be any cheaper than conventional phase-change cooling, and having to build custom vacuum/compressor pumps for the hyperloop project is going to be more expensive than buying COTS vacuum pumps Fair enough. As you observe, it's a problem I haven't seen a suitable solution to (apart from burying, which trades the thermal problem for, in my view, the better water management problem and the scarier land-use problem.) [1] https://en.wikipedia.org/wiki/SABRE_(rocket_engine) https://en.wikipedia.org/wiki/SABRE_(rocket_engine) [2] https://www.google.com/patents/US3516254?dq=closed+loop+rocket+engine&hl=en&sa=X&ved=0ahUKEwjwr4XF8uvWAhUm54MKHeXHAdUQ6AEINjAC https://www.google.com/patents/US3516254?dq=closed+loop+rock...

JumpCrisscross 9y ago

> Regenerative cooling in rocketry is running propellant through channels in the nozzle, then either dumping it overboard, using it to power a gas generator, or burning it in the rocket "Regenerative cooling" is a rocket term. It came to mind because I used to be an aerospace engineer. There's no requirement in the definition of regenerative cooling for the coolant to be dumped. > Presumably active cooling of a hyperloop tube would use a closed refrigerant cycle I don't think one can just presume that. You've already got lots of pumps for pumping air. Given (a) the seal on the tube will be periodically broken (for entry, exit and maintenance) and (b) a safety factor, you'll have more pump capacity than you'll need. Filtering and then compressing atmosphere, running it through a heat exchanger, and then letting it expand through the cooling channels before dumping it doesn't seem obviously worse than having kilometers of refrigerant running around. > which has little to do with regenerative cooling, besides the idea of cooling channels See above. Also, I assumed if you did this you'd use it to boost SpaceX's nozzles' economies of scale.

sbierwagen 9y ago
>"Regenerative cooling" is a rocket term. It came to mind because I used to be an aerospace engineer. There's no requirement in the definition of regenerative cooling for the coolant to be dumped. ? Regenerative cooling in rocketry uses propellant. Propellant is always dumped overboard, because it's propellant. Please show me a rocket that uses closed loop cooling of the rocket nozzle. >Filtering and then compressing atmosphere, running it through a heat exchanger, and then letting it expand through the cooling channels before dumping it doesn't seem obviously worse than having kilometers of refrigerant running around. My turn to be pedantic about definitions: this sure sounds like closed loop cooling to me! The working fluid is air, you draw it from a big reservoir, (the atmosphere) cool something with it, then return it to the reservoir. (Something you can't do with open-loop regenerative cooling of a rocket nozzle, since the coolant gets burned at the end of the cycle) However, maintaining the air dryers and replacing the filters sounds like it wouldn't be any cheaper than conventional phase-change cooling, and having to build custom vacuum/compressor pumps for the hyperloop project is going to be more expensive than buying COTS vacuum pumps.
- JumpCrisscross 9y ago
  > Please show me a rocket that uses closed loop cooling of the rocket nozzle The most famous one is the under-development SABRE [1], which includes a closed-loop helium cycle. For cryogenic rockets, closed-loop cooling of the nozzle has been explored [2] to avoid hydrogen embrittlement and oxidation of the nozzle channels, as well as to simplify plumbing. In any case, we've devolved into arguing semantics. > My turn to be pedantic about definitions: this sure sounds like closed loop cooling to me! I was figuring on dumping the air once done versus worrying about a reservoir. That said, I haven't done any math on the benefits of saving the return piping (and reservoir cost and maintenance) versus using something traditional. > maintaining the air dryers and replacing the filters sounds like it wouldn't be any cheaper than conventional phase-change cooling, and having to build custom vacuum/compressor pumps for the hyperloop project is going to be more expensive than buying COTS vacuum pumps Fair enough. As you observe, it's a problem I haven't seen a suitable solution to (apart from burying, which trades the thermal problem for, in my view, the better water management problem and the scarier land-use problem.) [1] https://en.wikipedia.org/wiki/SABRE_(rocket_engine) https://en.wikipedia.org/wiki/SABRE_(rocket_engine) [2] https://www.google.com/patents/US3516254?dq=closed+loop+rocket+engine&hl=en&sa=X&ved=0ahUKEwjwr4XF8uvWAhUm54MKHeXHAdUQ6AEINjAC https://www.google.com/patents/US3516254?dq=closed+loop+rock...