A Rostami - Department of Polymer Engineering, Amirkabir University of Technology, Mahshahr Campus, Mahshahr, Iran
B Kaffashi - Department of Chemical Engineering, Faculty of Engineering, University of Tehran, Tehran, Iran
A.A Gholipour - Department of Polymer Engineering, Amirkabir University of Technology, Mahshahr Campus, Mahshahr, Iran

The elongational viscosity can significantly affect the flow of nanocomposites in manufacturing processes such as film blowing, blow molding and fiber spinning, therefore anaccurate knowledge of the elongational viscosity is require. The strain rate in direct measurement methods cannot be controlled and most experimental data on elongational viscosity is limited to low strain rates. Due to the unsteady nature of elongational flow, the flow in a channel withcontraction has been used for an estimation of elongational viscosity [1]. In abrupt contractions, the elongational flow becomes dominant. Cogswell [2] obtained the followingequations for estimation of elongational viscosity for a circular symmetric flow: ean  P 3( 1)4  2 ,8 3( 1) een  P (1) , (2)where  e is elongational viscosity,  is strain rate and a is the apparent shear rate. Cogswell used the power law model for shear viscosity.