- Tubeless siphon
The siphon phenomenon is normally conducted by a tube. Polymer melt can suck
the liquid into the tube even if the tube end locates high above the liquid surface,
because of a significant viscoelastic effect. Such a flow is also called Fano flow
(Fano 1908 ). Another situation is the pouring of the viscous polymer melt from a
cup. Once the flow starts, the polymer melt can be continuously poured out, even if
the liquid surface inside the cup becomes lower than the cup edge, as illustrated in
Fig.7.16. So far, a clear theoretical description of this phenomenon is still lacking.
- Drag reduction
Adding a small amount of high molecular weight PEO or poly(acrylate amine) into
high-speed flows can effectively suppress the occurrence of turbulent flows, and
thus reduce the drag force. Application of such a drag-reduction agent can raise at
least one-fold exalting height of fire water, reduces the number of pumping stations
on the oil pipeline, or raises the efficiency of oil extraction by expelling the oil from
the leaks of rocks. So far, since we know little about turbulent flows, the mechanism
of drag reduction is still unknown.
Fig. 7.15 Illustration of Barus effect for the transverse swell due to the slow-down of the flow at
the exit of extrusion die
Fig. 7.16 Illustration of tubeless siphon and continuous pouring of polymer melt
142 7 Polymer Flow