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

Abstract

In many processes, shear viscosity is often a key quality indicator and can be used as a controlvariable. The magnetic resonance imaging (MRI) and ultrasonic Doppler velocimetry (UDV)viscometers have been developed for in-line measurement of viscosity. From the velocity profileby the MRI and UDV methods with simultaneous measurements of the pressure drop, we cancalculate the local shear rate and shear stress, respectively. Thereby, the viscosity as a function ofshear rate can be determined over a range of shear rates from theoretically zero at the tube centerto maximum at the tube wall. This system was tested on the flow of corn syrup and tomatoconcentrate. The samples were pumped though a flow loop composed of nominal 2 PVC tubingwith the flow rates of 72 mL/s for the corn syrup and 73.6 mL/s for the tomato concentrate. TheMRI measurements were undertaken using 64 phase encoding steps and 64 frequency encodingsteps. 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 syrupand the tomato concentrate, respectively. . The UDV technique provided velocity profiles thatcompared well with the MRI method. The rheological properties (shear viscosity and yieldstress) obtained by UDV showed good agreement with those with MRI method, implying thatthe UDV method was applicable to characterize complex fluids.