Open Siphon or Fano Flow

As seen in Video A, the liquid continuously climbs up in an "open siphon" as the drum at the top rotates.  The elastic stresses stored in the fluid by the long relaxation times of the extended polymer molecules allow the fluid to "strain harden" in extension. The video clearly shows that, beyond the initial "collection region", the filament is of a constant radius as the strain hardening prevents the filament "necking down", a primary form of failure in the spinning of simpler fluids. This effect can be utilized to understand, and improve, the commercial spinning of threads and fibres.  A Newtonian fluid would not be capable of this behaviour.

Figure A

Figure B
A. Tubeless Siphon
B. Die swell


Video A. Open siphon

Video B. Tubeless siphon


  • A brief explanation of these phenomena and description of the demonstration setup.
  • The full video files of the movies above can be downloaded at their original locations in the old group website.
     Open siphon
     Tubeless siphon and die swell