Abstract
We propose a rheometry using ultrasonic velocity profiling (UVP) that visualizes and evaluates quantitatively opaque complex fluids in a cylindrical open vessel performing unsteady rotation. The methodology termed “ultrasonic spinning rheometry (USR)” is expected to provide details of various rheological properties. In our study of USR applications, an enhancement in measuring some rheological properties was achieved for three different non-Newtonian fluids. For quantitative evaluations, we focused on momentum propagation in unsteady shear flows from an oscillating cylindrical container. In such flows, this propagation is represented in the radial profiles of the phase lag of velocity fluctuations. The phase lag information is obtained by a discrete Fourier transform of the spatio-temporal velocity distributions measured using UVP and indicates that the phase lag changes substantially as rheological properties change in a test fluid. As the primary rheological property, a local effective viscosity that is representative of the Newtonian viscosity in the bulk of a measurement volume is determined using UVP. In addition, the shear stress distribution, yield stress, spatial viscosity profile, and shear modulus are obtained as secondary rheological properties.
Highlights
Like two wheels of a bicycle, rheometry together and suitable rheological models have importance in evaluating rheological characteristics in the fields such as polymers, biology, food processing, and dispersion systems
The phase lag information is obtained by a discrete Fourier transform of the spatio-temporal velocity distributions measured using ultrasonic velocity profiling (UVP) and indicates that the phase lag changes substantially as rheological properties change in a test fluid
To provide a visualization and quantitative evaluation of opaque and complex fluids, which are commonly encountered in industry and nature, we have proposed a rheometry using UVP, termed ultrasonic spinning rheometry (USR), which permit measurements to be taken of fluids in an open cylindrical vessel undergoing unsteady rotation
Summary
Like two wheels of a bicycle, rheometry together and suitable rheological models have importance in evaluating rheological characteristics in the fields such as polymers, biology, food processing, and dispersion systems. Shiratori et al [21] proposed a model-free USR for a quantitative evaluation of the shear-rate-dependent viscosity without adopting any rheological model This was achieved through a combination of UVP and axial torque measurements in a doublecylinder system as a general circular Couette flow. We developed an ultrasonic visualizer of the rheological characteristics [23]; here the spatio-temporal velocity field of test fluids in an oscillating cylinder are measured using UVP, from which the distributions of velocity, strain rate, and deformation are calculated and thereby provide in an intuitive manner features of the fluid characteristics. The proposed USR will provide rapid qualitative evaluations of rheological characteristics and quantitative estimates of such properties in local bulk volumes (cylindrical measurement volume of UVP), principally the effective bulk viscosity of complex fluids. The range of applicability of USR is determined by that of UVP, and cases of very viscous fluids, for example, larger than 100 000 cSt, and highly concentrated multiphase media would be outside this range because the attenuation of ultrasonic waves in the media is appreciable
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