CONCENTRIC CYLINDER END EFFECTS AND FLUID INERTIA EFFECTS IN CONTROLLED STRESS RHEOMETRY - PART-I - NUMERICAL-SIMULATION

In a commercially available CSR controlled stress rheometer, the theor etical formulae for calculating the shear viscosity and complex viscos ity of a fluid in a recessed concentric cylinder geometry, do not take into account end effects. The first part of this paper is concerned w ith a theoretical prediction of end effects on steady shear viscosity measurements of Newtonian fluids in a recessed concentric cylinder geo metry. Fluid inertia effects are included in the theory and the releva nt equations are solved using a perturbation analysis which is valid f or low Reynolds number hows. The perturbation equations are solved num erically using a finite difference method. From this theory, correctio n formulae are produced to compensate for end effects and second order fluid inertia effects in steady shear flows on a CSR rheometer. End e ffects are also investigated for shear thinning fluids using the Polyf low package, and results show that they are less significant than thos e for Newtonian fluids. The second part of this paper is concerned wit h a theoretical prediction of the end effect of a recessed concentric cylinder geometry on complex viscosity measurements of a generalised l inear viscoelastic fluid. The theory will include a first and second o rder fluid inertia perturbation analysis and the relevant equations ar e solved using a finite difference method. Using this theory, the exis ting oscillatory shear formulae which include second order fluid inert ia effects, are modified to compensate for end effects. (C) 1998 Elsev ier Science B.V. All rights reserved.