Ultrasonic techniques for measurement of coal slurry viscosity

The authors present a technical evaluation of ultrasonic methods as applied to the measurement of slurry viscosity. The four ultrasonic techniques examined were measurement of attenuation, acoustic impedance, relaxation, and acoustic streaming and cavitation. Acoustic impedance measurements are more sensitive to slurry viscosity than to any other fluid parameter. The three other techniques measure acoustic attenuation, but in different frequency ranges. The direct attenuation measurement technique suffers from the difficulty of extracting the viscous contribution from other effects, especially the thermal effect. The relaxation method requires an operating frequency near 10⁹ Hz, which is difficult to achieve at present. Finally, the streaming and cavitation method has not been carefully examined because the technique is based on nonlinear acoustic effects which are not well understood. Results from this study indicate that it is feasible to develop an online ultrasonic viscometer based on the measurement of either acoustic impedance or acoustic streaming and cavitation. The authors describe the design and performance of an ultrasonic shear-wave wedge for acoustic impedance measurement