Entry flow behaviour of viscoelastic fluids in an annulus

Developing and fully developed velocity profiles in the entrance region of an abrupt 2-to-1 annular contraction were measured for a number of visco-elastic polymer solutions. Experimental results were obtained for Reynolds number and flow behaviour index in the range 9.8 ? Re ? 355 and 0.372 ? n ? 0.55 respectively. A momentum-energy integral technique was employed in the boundary layer analysis. The deviation from inelastic behaviour was indicated by the ratio of elastic to inertial forces, Ws/Re. Within the limits of confidence of the experimental results, good agreement with theoretical predictions was obtained and very little deviation from inelastic behaviour was observed for Ws/Re < 0.08. For the test fluids investigated, the entrance length was found to be longer than that predicted for the corresponding inelastic fluids of the same n.