COMPLEX FLOW OF VISCOELASTIC FLUIDS THROUGH OSCILLATING PIPES - INTERESTING EFFECTS AND APPLICATIONS

In the present communication, the flow of liquids through a straight pipe which is oscillating longitudinally about a mean position is examined. The basic flow is generated by a constant pressure gradient and the effect of the superimposed oscillations upon the flow is analyzed with particular attention to the flow rate. In the viscous case as well as for an elastic fluid with constant viscosity, no variation in the flow rate is present. This is in agreement with the theoretical analysis. Nevertheless, for viscoelastic fluids, increases in the flow rate of up to twenty times are possible when compared to purely rectilinear flow. This effect is examined for various viscoelastic fluids and relations are found with that basic properties of such fluids. The complex flow situation is analyzed using flow visualization techniques. As a result, the flow appears to be dominated by a shear-thinning effect. A numerical solution using a power-law fluid predicts increases in flow rate which agree qualitatively with the experimental data but are quantitatively different. It is therefore concluded that a more general model must be used for agreement between experiments and theory. In the light of the experimental results, applications are being presently undertaken for the flow of polymer melts in situations of industrial interest. © 1979.