Explaining how a Vortex Tube works

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SUMMARY

The discussion focuses on the mechanics of vortex tubes, emphasizing their unique design that creates a standing acoustic wave through tangential air inflow. A well-functioning vortex tube produces a loud howl, indicating effective operation. The outlet nozzle positioned at the anti-node allows for higher pressure, adiabatically compressed warm air to exit, while cooler air flows in lower pressure periods. The spiral flow increases the effective length of the "flute," impacting the frequency of the sound produced.

PREREQUISITES
  • Understanding of fluid dynamics principles
  • Familiarity with thermodynamics concepts, particularly adiabatic processes
  • Knowledge of acoustic wave behavior in fluid systems
  • Basic experimental design for verifying physical theories
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Engineers, physicists, and students interested in fluid dynamics, thermodynamics, and acoustic phenomena will benefit from this discussion on vortex tubes.

rentier
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I have an interesting(IMHO) approach to explaining how the vortex tube works.
There are a few explanations on wiki, but not a simple and convincing final one.
https://en.wikipedia.org/wiki/Vortex_tube

Normally a vortex tube, that runs well, howls very loud.
It is a kind of aerodynamically peculiarly shaped, twisted and folded "flute" (tangential air inflow, etc.), i.e. standing acoustic wave. If we have an outlet nozzle at the anti-node, more air comes out at higher pressure, adiabatically compressed, i.e. warm, and in periods of lower air pressure, there is less flow of the colder air. I.e. on average, more warmer air comes through.
Therefore the remaining air that flows further (or back, in the middle) is net colder.
The rotation, the spiral-shaped flow, essentially increases the length of the "flute", i.e. affects frequency.

(this could be verified experimentally in a linear assembly, I think.)

  • Is it a sane approach?
  • Does a vortex tube work, if the return flow goes through an additional insulated central tube? (guess yes)
 
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