American Society of Agricultural and Biological Engineers

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Comparison of Viscosity Measurements using Magnetic Resonance Imaging and Ultrasonic Doppler Velocimetry.

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  016119,  2001 ASAE Annual Meeting. (doi: 10.13031/2013.4056) @2001
Authors:   Y. J. Choi, R. L. Powell, M. J. McCarthy
Keywords:   Magnetic Resonance Imaging (MRI), Ultrasonic Doppler velocimetry (UDV), shear viscosity, yield stress

In many processes, shear viscosity is often a key quality indicator and can be used as a control variable. The magnetic resonance imaging (MRI) and ultrasonic Doppler velocimetry (UDV) viscometers have been developed for in-line measurement of viscosity. From the velocity profile by the MRI and UDV methods with simultaneous measurements of the pressure drop, we can calculate the local shear rate and shear stress, respectively. Thereby, the viscosity as a function of shear rate can be determined over a range of shear rates from theoretically zero at the tube center to maximum at the tube wall. This system was tested on the flow of corn syrup and tomato concentrate. The samples were pumped though a flow loop composed of nominal 2” PVC tubing with the flow rates of 72 mL/s for the corn syrup and 73.6 mL/s for the tomato concentrate. The MRI measurements were undertaken using 64 phase encoding steps and 64 frequency encoding steps. The UDV parameters for the velocity measurement were a main frequency of 5 MHz, pulse repetition of 5 kHz and sampling frequency of 1.2 MHz and 1.3 MHz for the corn syrup and the tomato concentrate, respectively. . The UDV technique provided velocity profiles that compared well with the MRI method. The rheological properties (shear viscosity and yield stress) obtained by UDV showed good agreement with those with MRI method, implying that the UDV method was applicable to characterize complex fluids.

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