Single-point correction for representative shear rate and strain in parallel plate rheometry derived from energy-dissipation rate analysis

초록

In this study, a single-point correction is investigated for determining representative shear rate and strain magnitude in parallel-plate rheometry, where shear stress is inherently non-uniform due to spatial variations in shear rate and strain. The correction is derived from the flow quantification approach based on the energy-dissipation rate. The correction factor of 0.765 to the tip shear rate and strain is found to coincide with the previously reported geometric one-point correction factor corresponding to the representative radius, at which the local shear stresses of a Newtonian and a non-Newtonian (power-law) fluid are equivalent. The correction has been validated for steady shear viscosity and large amplitude oscillatory shear measurements with four different non-Newtonian fluids: two aqueous xanthan gum solutions of 1 and 2 wt%, two aqueous PEO solutions of 2 and 4 wt%. The accuracy was assessed in comparison with measurements with the cone-and-plate fixture. The steady shear viscosity data exhibits the average relative errors less than 4.5% (in case of PEO solutions) and 10% (xanthan gum solution) for a wide shear rate range from 0.01 to 1000 [1/s]. The LAOS test data shows the average relative errors in both storage and loss moduli are limited to 4.2% (2 wt% PEO solution) and 7.85% (4 wt% PEO solution) for the strain magnitude range from 0.03 to 1000%.

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