Characterisation of non-newtonian fluids using a back-extrusion technique

Abstract

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.At present standard rheometers provide sufficiently precise measurements characterising behaviour of non-Newtonian materials. In practice, this accuracy is not always necessary, and the methods providing relatively cheap, fast and sufficient measurements of the rheological characteristics are fully acceptable. Back extrusion - representing one of these methods - is based on plunging of a circular rod into an axisymmetrically located circular cup containing the experimental sample. Formerly this method was applied for a characterisation of power-law, Bingham and Herschel-Bulkley fluids. The aim of this contribution is to present a sufficiently simple user-friendly procedure how to determine the individual rheological parameters appearing in the Vočadlo model (sometimes called Robertson-Stiff one) - yield stress, consistency parameter and flow behaviour index.