Rheological measurement of suspensions without slippage: experimental and model

Abstract

Rheological measurements of suspensions are often performed using a rotational rheometer.In this type of rheometer, the tested fluid is sheared between two surfaces, one of which is rotating to generate a laminar flow of the fluid between the surfaces (i.e., a Couette flow). Manufacturers of commercially available rheometers generally recommend the use of a standard oil of known viscosity to verify that the rheometer is operating correctly. However, in the case of concrete rheometers, this approach would require large volumes of oil and was deemed not economically During the certification of SRM 2493, it was found that differences in rheometer geometry affect the accuracy of the rheological measurements. In order to gain fundamental insight about the impact that different rheometer geometries have on measurements of suspensions, a comprehensive analysis was conducted on three different rheometer families. The analysis included both experimental testing and computer simulation. The comparison between the model and rheological results showed that the increased viscosity due to the addition of the 1 mm beads to SRM 2492 was significantly higher in the Couette model than in the experimental data. It was also determined that some geometries, such as a double spiral, resulted in a higher viscosity than a simple serrated cylinder or vane. This finding led to the inference that slippage should also be considered. Ultimately, this report highlights that industrial rheometers experience slippage issues caused by their choice of geometry and their internal boundary conditions (free surfaces), and discusses the most accurate alternative available for calibrating rheometers.i ______________________________________________________________________________________________________ This publication is available free of charge from: https://doi

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