Elongational Flows in Jets, Filaments, Films and Vortexes:  Rheology and Hydrodynamics

Professor Alex L. Yarin
Israel Institute of Technology
Haifa 32000, ISRAEL
The speaker will be introduced by Prof. Darrell H. Reneker of the Maurice Morton Institute of Polymer Science, University of Akron.
 
Sponsored by: The Center for Materials Research and Analysis and the Department of Engineering Mechanics

Date:  Wednesday, March 10, 1999
Time:  3:30 p.m.
Place:  W128 Nebraska Hall


The topics of the talk cover strong elongational flows in free liquid jets and films moving in the air, as well as in the horseshoe/hairpin vortexes in the boundary layer. Various theoretical and experimental aspects of these flows, as well as some applications are discussed. Thin free jets break-up due to capillary instability. Perturbation evolution is very sensitive to the rheological behavior of liquids. Elongational flows emerging in capillary break-up are strong. They lead to an enormous increase of elongational viscosity of dilute polymer solutions, which exceeds that of solvent by 3 to 4 orders of magnitude. Large elongational viscosity practically arrests growth of perturbations leading to appearance of the beads-on-string structure. This phenomenon is treated both theoretically and experimentally. Some results related with elongational rheometers for dilute polymer solutions are discussed.

Some additional relative phenomena are tackled: (I) capillary instability of free jets of concentrated suspensions leading to a 'sausage'-like break-up, and (II) evolution of the horseshoe/hairpin vortexes which is retarded or arrested by a small amount of polymer additives. In the latter case, a mechanism underlying turbulent drag reduction is considered. Mechanics of solid and hollow fiber spinning is considered including such topics as draw resonance in hollow fiber spinning and formation of internal structure of polarization-maintaining optical fibers. Free liquid films produced by a jet impinging upon a planar target or by a fan-spray nozzle, as well as cylindrical film specimens stretched by a gas pressure differential, manifest themselves as another example of strong elongational flows, which might be utilized for measurements of elongational viscosity of dilute and concentrated polymeric systems. Various theoretical and experimental aspects of these flows are discussed including their instability and atomization.