A common (universal?) feature of industrial metal chimneys/smoke stacks, affixed to the outer surface of their top few metres. Presumably they function in the following manner:

  1. industrial process generates hot gaseous emissions
  2. emissions are directed toward the chimney intake
  3. emissions warm the chimney as they rise within it
  4. chimney warms the air immediately surrounding it
  5. this air rises and encounters the spirals
  6. spirals set up a vortex
  7. vortex extends ?high above the upper limit of the chimney
  8. emissions emerging from the top of the chimney encounter this vortex
  9. chimney becomes functionally equivalent to a much taller spiral-less chimney, delivering the emissions much higher into the atmosphere.

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