How does a capillary rheometer measure extensional viscosity?
When a twin-bore (Bagley corrected) test is performed, the data collected includes all the variables needed for calculating the extensional viscosity using the convergent flow (Cogswell) model. Extra care should be taken in the measurement of the orifice pressure drop, but the results from this method have been found to be in agreement with others and with other direct observations. A major advantage of generating extensional viscosity data by this method compared with alternative techniques is the ability to reach high extensional strain rates that are encountered in real production processes.
