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.

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.

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.

This is a repository copy of Multiscale modelling of ceramic nanoparticle interactions and their influence on the thermal conductivity of nanofluids.

This study determines the thermophysical properties of nanofluids using ultrasonic techniques. Using an acoustic test cell, fitted with 4 MHz high-temperature transducers, measurements of the speed of sound in an aqueous dispersion of alumina nanoparticles (Al2O3, 99.9%, spherical, dp = 50 nm) are made at volume fractions from 1-5 vol% over the temperature range 20-90°C. The observed relationships between the measured parameters and speed of sound variation are presented. Available theoretical approaches are reviewed and applied to the data of the study. The speed of sound data together with measurements of density and predictions of thermal conductivity, derived from Lagrangian particle tracking (LPT) simulations, are used to determine