Evaluation of Different Methods for Determining the Entrance Pressure Drop in Capillary Rheometry

• Published in: Applied rheology (Lappersdorf, Germany) Vol. 18; no. 6; pp. 63258-1 - 63258-5
• Main Authors: Aho Johanna, Syrjälä Seppo
• Format: Journal Article
• Language: English
• Published: De Gruyter 01-12-2008
• Subjects: bagley correction; capillary rheometer; entrance pressure drop; orifice die
• ISSN: 1617-8106
• DOI: 10.1515/arh-2008-0022

Two approaches for determining the entrance pressure drop in capillary rheometry were compared with low-density polyethylene and polystyrene melts as test fluids. Direct measurements with the orifice die were found to yield higher values for the entrance pressure drop, and hence lower values for the wall shear stress, than the Bagley correction method. This was postulated to be caused by the sticking of the melt to the wall of the outlet region of the orifice die. The additional pressure drop created in the outlet region of the orifice die, when the flowing material fills it completely, was also evaluated by means of numerical flow simulation.