A technique that is an extension of an earlier approach for marine sediments is presented for determining the acoustic attenuation and backscattering coefficients of suspensions of particles of arbitrary materials of general engineering interest. It is necessary to know these coefficients (published values of which exist for quartz sand only) in order to implement an ultrasonic dual-frequency inversion method, in which the backscattered signals received by transducers operating at two frequencies in the megahertz range are used to determine the concentration profile in suspensions of solid particles in a carrier fluid. To demonstrate the application of this dual-frequency method to engineering flows, particle concentration profiles are calculated in turbulent, horizontal pipe flow. The observed trends in the measured attenuation and backscatter coefficients, which are compared to estimates based on the available quartz sand data, and the resulting concentration profiles, demonstrate that this method has potential for measuring the settling and segregation behavior of real suspensions and slurries in a range of applications, such as the nuclear and minerals processing industries, and is able to distinguish between homogeneous, heterogeneous, and bed-forming flow regimes.

The scattering and attenuation of megahertz frequency acoustic backscatter in liquid suspensions, is examined for a range of fine organic and inorganic particles in the Rayleigh regime, 10 -4 < ka < 10 0 (where k is the wavenumber and a the particle radius) which are widely industrially relevant, but with limited existing data. In particular, colloidal latex, mineral titania and barytes sediments, as well as larger glass powders were investigated. A manipulation of the backscatter voltage equation was used to directly measure the sediment attenuation constants, . Decoupling of the combined backscattering-transducer constant, allowing explicit measurement of the backscattering constant, ks, was achieved through calibration of the transducer constant, kt. Additionally, the methodology was streamlined via averaging between a number of intermediate concentrations to reduce data variability. This approach enabled the form function, f, and the corresponding total normalized scattering cross-sections, , to be determined for all species. While f and are available in the literature for large glass and sand, this methodology allowed extension for the colloidal organic and inorganic particles. Specific gravity normalisation of f collapsed all data onto a single distribution, with the exception of titania, due to scattering complexities associated withagglomeration. There was some additional variation in , with measured values of the fine particles up to of magnitude greater than the density-normalised prediction at low ka . Mechanisms accounting for these variations from theory are however analysed, and include viscous attenuation effects, the polydispersity of the particle type and increasing influence of the solvent attenuation.Additionally, thermoacoustic losses appeared to dominate the attenuation behaviour of the organic latex particles. This study demonstrates that particles close to the colloidal regime can be measured successfully with acoustic backscatter, and highlights the great potential of this technique to be applied for in situ or online monitoring purposes in such systems.

Of the various transition velocities that delineate flow regimes in multiphase pneumatic and hydraulic conveying, the critical deposition velocity is important because it separates depositing and non-depositing flows. However, no distinction has been made between the dependence of the critical deposition velocity on physical parameters and flow conditions at low solid volume fractions and in the limit of zero volume fraction, which are distinct mathematically. Here, the two cases are analysed separately, and a general functional form in terms of the particle Reynolds number and Archimedes number is proposed that is valid up to volume fractions of several per cent. An ultrasonic method for determining the critical value of the particle Reynolds number is presented, and results for four particle types at several nominal volume fractions (0.5, 1 and 3 % by volume) are combined with a number of data from the literature. The resulting expressions are found to compare well with several similar correlations for the critical deposition velocity and other transition velocities, and, unlike a recent best-fit approach for the pick-up velocity, incorporate an explicit dependence on volume fraction, to which the critical deposition velocity is most sensitive at very low volume fractions. Lastly, it is found that the functional forms for the critical deposition velocity in the literature are unable to reproduce the available data at higher volume fractions, and a number of suggestions are made for resolving this issue.

This is a repository copy of Concentration profiling of a horizontal sedimentation tank utilising a bespoke acoustic backscatter array and CFD simulations.

Measurement of particle concentration in horizontal, multiphase pipe flow using acoustic methods: limiting concentration and the effect of attenuation AbstractAn acoustic dual-frequency concentration inversion method, in which the backscattered acoustic signal received by transducers operating in the megahertz range is used to determine the concentration profile in suspensions of solid particles in a carrier fluid and which was originally developed for environmental applications, is applied to arbitrary suspensions of general engineering interest. Two spherical glass and two non-spherical plastic particle types with a range of size distributions and densities are used. Particle concentration profiles in horizontal turbulent pipe flow at Reynolds numbers of 25 000 and 50 000 -below and above the critical deposition velocity, respectively -and nominal concentrations of 0.5, 1 and 3 % by volume are presented for the four particle species, using measured backscattering and attenuation coefficients. In particular, the effects of particle size, density and flow rate on the transport and settling behaviour of suspensions are elucidated. The results demonstrate the potential of this method for measuring the degree of segregation in real suspensions and slurries across a range of challenging application areas, such as the nuclear and minerals processing industries. The limitations of the method are explored in detail through an analysis of the acoustic penetration depth and the application-specific maximum measurable concentration, both of which can be used to determine the most appropriate acoustic frequencies and measurement Highlights Marine model for measuring suspended solid fraction adapted for general use. Glass and plastic particles tested at several fractions in horizontal pipe flow.  Clear differences observed between species and settling and non-settling flows. Limiting concentration and penetration depth derived to inform future experiments. Method has potential for use in several engineering applications.