4 ms·
Why not, instead of using an almost-vacuum and a separate means of propulsion, create a stream of air similar to that of bank tubes and just use that for propul
by mangeletti 10y ago
Why not, instead of using an almost-vacuum and a separate means of propulsion, create a stream of air similar to that of bank tubes and just use that for propulsion?
Fans inside of the tube would pull air in the direction of travel, and it could be circulated or pumped in from / out to the outside at the ends. At the end of the tubes a main fan system would be the primary work horse, creating vacuum forces on the arrival end and pushing forces on the departure end.
In the last mile, the fan system could shut down and use the pressure to help stop the vehicle and even store some of the pressure to help start the system in the opposite direction later (i.e., regenerative breaking).
- kinofcain 10y agohttps://en.m.wikipedia.org/wiki/Beach_Pneumatic_Transit https://en.m.wikipedia.org/wiki/Beach_Pneumatic_Transit Among other things it's more efficient to send electricity than to send air.
- mangeletti 10y agoI don't mean as a means to maximize efficiency, but to avoid a lot of the problems (e.g., the risks of a vacuum, the cost of engineering one, etc.).
- kinofcain 10y agoInstead of the air resistance of a train-sized object (about a quarter mile long) you'd have air resistance equivalent to a train 300 miles long (think of the tunnel as an inside out train). It's inefficient by several orders of magnitude.
- mangeletti 10y agoAh, I see what you mean :/ EDIT: Wait, if the walls were made to be near frictionless, then the aggregate energy, minus what's lost to hear from turbulence, would be used for motion, right?
- brandmeyer 10y agoAir has viscosity. Even for extremely smooth surfaces, you would expect the flow to be fully turbulent over such a distance.
- mangeletti 10y agoWhat I mean is that the energy wouldn't be lost. The turbulence wouldn't result in a net loss of energy, except that which was lost as heat through the walls (a 1cm layer of vacuum would insulate against that). Am I thinking if this wrong?
- brandmeyer 10y agoTotally wrong. All of that turbulence goes into heat, which must be sunk through the walls (or something else), and is therefore lost. "Fully turbulent flow" is a reference to the transition away from (low-friction) laminar flow. Flow gets to be fully turbulent by experiencing high internal fluid friction due to its own viscosity. Air's viscosity is low relative to water, but it still isn't zero. 500 mph flow through a big long tube is extremely lossy.