The sound of the slurry

The mining and minerals industry has long used flowing water as a cost-effective and safe way to move its waste tailings from their origin to a storage pond. (See the article in Physics Today, March 2009, page 31 .) And nuclear sludge such as that held in tanks at Hanford, Washington, in the US and at Sellafield in the UK can also be hydraulically transported for eventual treatment. But a hydraulic conveyor needs continual monitoring to avoid blockages, maintain pressures, and minimize corrosion. Many monitoring methods are in use, but the job quickly gets complicated when solid–liquid suspensions are difficult or dangerous to access as they tumble along a pipeline and when they consist of a range of particle sizes and densities. As part of his PhD work at the University of Leeds in the UK, Hugh Rice took an acoustic method that was previously used to characterize marine sediments and adapted it for optically opaque industrial flows. Using a pair of piezoelectric transducers operating at 2 MHz and 4 MHz, Rice and colleagues have obtained attenuation and backscattering coefficients for each of four particle types, ranging in size (40–700 μm), density (glass and plastic), and shape (spherical and jagged). Until now those coefficients were available only for quartz sand. Using a dual-frequency algorithm borrowed from marine science to invert the signals in flowing suspensions, the researchers tested the flow-measurement method in a pipe as shown here. The results showed particle segregation and different flows for different particles. Ultimately, Rice and company expect to use such measured coefficients to obtain concentration profiles and flow regimes in arbitrary industrial settings. (H. P. Rice et al., J. Acoust. Soc. Am. 136, 156, 2014, doi:10.1121/1.4883376 .)