Skuzzy61 wrote:The more I think about it, the more I am convinced it cannot work. The mere act of moving air over a surface creates friction and thermal energy which must be dissipated. Compress the air, and more thermal energy is created. The cones would have to act like heat sinks without imparting any of the heat back into the stream.
At these velocities, thermal energy from friction will be minimal, and that's without considering a friction reducing boundary layer.
Minimal compression, minimal thermal increase.
And then the thing is, there are two paths to take that heat away.
- ...the blowing wind would dissipate collected heat from the outside surface of the sheet.
- The heat can be conducting/radiating from compressed-air to plastic bottle to the air surrounding the bottle, and with the wind blowing the air around the bottle away, that air would be getting renewed to ambient, keeping a temperature differential for continued heat transfer - but how much...
Is it enough to do what they claim... not likely, but... without numbers to show what is really going on, it's still in the possible/plausible camp.
And it's not a lot of compression, so not a lot of thermal energy into the air flow. If only part of that airflow has part of its thermal energy dropped through the side of the bottle, then upon expansion...
People are having this discussion because there are thermal paths and design that don't inherently violate the laws, such that without numbers to prove the final claim of -5C is impossible, the damn thing has to count as possible (possibly plausible). Which is what makes it such a very crafty device or a very very crafty "story".
Even if you look at a boundary layer on the inside of the bottle, there's how thick, how much turbulent flow, how thermally conductive - or convective within the boundary layer - as a thermal path from the compressed airflow through to the side of the bottle to the cooling refreshed ambient air on the outside of the bottle.
Hats off to them, one way or the other.
Video games are giving kids unrealistic expectations on how many swords they can carry.
... but don't harm the red dragon that frequents the area from time to time. He and I have an agreement.