The commercial OSP double-wall concentric cylinder flow cell consists of a double-wall cup (translucent) and bob (purple).
Researchers at the National Institute of Standards and Technology (NIST) have addressed crucial calibration procedures for an advanced rheological technique that can make measurements on the structural dynamics of complex fluids, which is crucial to understanding and predicting the performance of a wide variety of materials ranging from everyday products like shampoos and shaving creams; to biological fluids, like blood and mucus; to food products such as yogurt; and to paints, inks and drilling fluids.
A technique called orthogonal superposition (OSP) rheology, which applies an oscillatory deformation perpendicular to a primary shear flow, allows researchers to gain information on the transient structures formed within complex fluids at the microscopic scale. Rheological properties such as the complex viscosity are quantified from the changes in stress as a function of deformation or the rate of deformation. OSP provides a sensitive measurement of the macroscopic rheology in the complex flow, and this offers insight into the microscale structures that govern these properties.
The OSP technique is now accessible to general rheology experts as a commercially available geometry. Given the complicated flow design, a protocol to quantify measurement error, sources of error, and sensitivity are critical to successful use of the geometry. Unfortunately, many calibration procedures described in the literature are specific to each geometry design and not immediately applicable to the OSP commercial geometry.
The velocity field undergoing within the OSP flow cell undergoing steady shear or an orthogonal oscillatory shear for a Newtonian fluid using CFD simulation.
In a new paper, Ran Tao and Aaron Forster from the Materials Measurement Laboratory describe a detailed calibration procedure for Newtonian fluids and validate the sources of experimental error through computational f ..
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