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Novel characterisation of concentrated dispersions by in situ acoustic backscatter systems

Bux, Jaiyana (2016) Novel characterisation of concentrated dispersions by in situ acoustic backscatter systems. PhD thesis, University of Leeds.

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Abstract

A range of concentrated dispersions were characterised via a novel in situ acoustic backscattering technique. nowledge of suspension dynamics and concentration is critical for the optimisation of processes which incorporate dispersion systems. The ability to measure and understand these parameters is challenging. Acoustic Backscatter Systems (ABS) offer in situ measurement capability in laboratory and industrial suspensions, where the application of other devices is negated due to high concentration or intrusive probe configurations. A robust analytical protocol was established via the ABS, for the characterisation of arbitrary particle types, in any concentration range up to the associated acoustic penetration depth limit. ABS measurements were analysed via the Rice method (Rice et al., 2014), which was varied herein for relatively larger scale dispersions. This approach enabled quantification of the sediment attenuation constants for a range of particles; barium sulfate (inorganic mineral), oil-in-water emulsions, latex beads and aggregated latex beads, for the first time here, as well as spherical glass beads. A calibration protocol was established for backscattering transducers, with improved data quality and a reduction in experimentation times, relative to published protocols (Betteridge et al., 2008). This facilitated the decoupling of the transducer constant Kt, from the system constant KsKt, enabling quantification of the sediment backscattering constants Ks, for the aforementioned particles. The measured constants for all particles were compared, highlighting the differing scattering influences dominating particles with contrasting physical properties. Importantly this information was extracted via a direct measurement approach, which didn't require exhaustive derivation of the form function f and the total normalised scattering cross-section x. f and x for all particles were normalised with respect to particle density to enable direct comparison. These data highlighted that f and x do not follow the assumed trend in the lower range of the Rayleigh scattering regime. The ABS was calibrated for a barium sulfate dispersion, to extract the relationship between measured signal, in the G function form from the Rice method, and concentration. This overcame the nonlinearity between concentration and directly measured attenuation. Importantly for the first time, this reference relationship facilitated the qualitative characterisation of an analogous dispersion within an industrial scale tank. Specifically, the tank system utilised impinging jet ballasts to resuspend settled sediment, and air-lifts to homogenise a non-active dispersion, analogous to a radioactive system at Sellafield Ltd (Cumbria, UK). The Rice analysis method proved to be a powerful technique for understanding the mixing and settling dynamics of a complex, large scale processes. The corresponding information was invaluable for mediating operational optimisation, and modelling for future decommissioning operations, of an inaccessible radio-toxic system. The characterisation of legacy waste suspensions comprising organic flocs, is a current challenge in the nuclear industry. Indeed, aggregated dispersions are abundant, yet their acoustic response is not yet well characterised. A robust, efficient, novel process was established for the manufacture of low density organic Latex particles on a litre scale, within a `controlled' jetting regime. The dispersions were readily aggregated, and marked differences were observed in their acoustic response with respect to un-aggregated beads. Very complex behaviour was observed, owing to the highly networked structure of the thermally attenuating particles.

Item Type: Thesis (PhD)
Keywords: acoustic backscatter, ultrasound, instrumentation, concentrated suspensions, settling, fluid mixing, impinging jets
Academic Units: The University of Leeds > Faculty of Engineering (Leeds)
The University of Leeds > Faculty of Engineering (Leeds) > School of Chemical and Process Engineering (Leeds)
Identification Number/EthosID: uk.bl.ethos.694440
Depositing User: Dr Jaiyana Bux
Date Deposited: 03 Oct 2016 12:33
Last Modified: 25 Jul 2018 09:52
URI: http://etheses.whiterose.ac.uk/id/eprint/14306

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