N. Willenbacher et R. Hingmann, SHEAR AND ELONGATIONAL FLOW PROPERTIES OF FLUID S1 FROM ROTATIONAL, CAPILLARY, AND OPPOSED JET RHEOMETRY, Journal of non-Newtonian fluid mechanics, 52(2), 1994, pp. 163-176
Non-linear shear and elongational flow properties of the ternary fluid
S1 have been compared to those of a binary solution with similar line
ar viscoelastic properties. In contrast to the binary solution, fluid
S1 exhibits a flow instability. The onset of this instability in rotat
ional flow is characterized by a critical Deborah number De(c) = 13.5.
Secondary flow causes an irreversible decrease of zero-shear viscosit
y. A flow-induced degradation of the dissolved polymer has been proved
by different analytical methods. However, this effect is not sufficie
nt to account for the observed reduction of eta0, and it is speculated
that the irregular flow additionally gives rise to a phase separation
or demixing of the originally homogeneous solution. Up to now there i
s no direct experimental evidence for this hypothesis. Elongational fl
ow properties have been characterized by means of an opposing jet appa
ratus. Apparent elongational viscosity of fluid S1 increases strongly
with increasing apparent elongation rate epsilon and total strain epsi
lon. A strain-independent equilibrium value is not reached. In the cas
e of the binary solution eta(E) is independent of e and increases only
slightly with increasing epsilon. Strong fluctuations of the force si
gnal are observed in the case of fluid S1 when a critical flow rate is
exceeded, indicating secondary flow phenomena.