PNNL

Abstract

We have developed an on-line computer-controlled sensor, based on ultrasound reflection measurements, to determine the product of the viscosity and density of a liquid or slurry for Newtonian fluids and the shear impedance of the liquid for non-Newtonian fluids. A 14-MHz shear wave transducer is bonded to one side of a 45°-90° fused silica wedge and the base is in contract with the liquid. Twenty-eight echoes were observed due to the multiple reflections of an ultrasonic shear horizontal (SH) wave within the wedge. The fast Fourier transform of each echo is obtained for a liquid and for water, which serves as the calibration fluid. The reflection coefficient at the solid-liquid interface is obtained by plotting the natural logarithm of the ratio (amplitude for liquid/amplitude for water) versus the echo number and determining the slope. Because the slope of this line is not affected by changes in the pulser voltage and/or system electronics, the sensor is self-calibrating and a very accurate measurement of the reflection coefficient results. Data were obtained for 11 sugar water solutions ranging in concentration from 10% to 66% by weight. Since these solutions are Newtonian fluids, the data obtained from reflection coefficient measurements yield a value of the viscosity-density product. In tests, the viscosity values are shown to be in good agreement with those obtained independently using a laboratory viscometer. The data acquisition time is 14 seconds and this can be reduced by judicious selection of the echoes for determining the reflection coefficient. The measurement of the density results in a determination of the viscosity for Newtonian fluids or the shear wave velocity for non-Newtonian fluids. The sensor can be deployed for process control in a pipeline, with the base of the wedge as part of the pipeline wall, or immersed in a tank.