An Experimental Investigation of Flow in the Die Land Region of a Capillary Rheometer

Abstract

A Laser Doppler Anemometer and a high speed data logging system are used to study the details of flow in the die land region. An abrupt entry cylindrical glass die, 6 mm I.D. and 210 mm long, is used. A 9.7 poise Newtonian Silicone Oil and a highly elastic polymer solution are investigated under low Reynolds number flow conditions (N_Re < 1).

The results indicate that, for the Newtonian fluid, the axial velocity distribution is fully developed at 1 mm from the die entry plane and is independent of the Reynolds number within the range studied. Some unusual effects are observed for the elastic fluid. In particular, it is found that a form of vena contracta is formed immediately downstream of the entry which leads to acceleration-deceleration effects. At higher flow rates, the axial velocity distribution becomes asymmetric followed by the development of instability. Under unstable flow conditions, the velocity at the wall of the die is non-zero indicating a slip flow, in addition.