An assessment of cogswell's method for measurement of extensional viscosity

Abstract Cogswell's method for measurement of extensional viscosity by determining the entry pressure loss in capillary viscometry is critically examined. Comparisons are made between extensional viscosity values introduced in finite element calculations as input data and predictions based on the calculated entry pressure losses for polymer melts. The calculated pressure losses are in good agreement with experimental data by Laun and Schuch. An equation proposed by Cogswell and another by Binding are used in the extensional viscosity comparisons. The slope of the extensional viscosity versus stretch rate is predicted rather well, but the calculations can shift the results above or below the true values.