The University of Southampton
Engineering and the Environment

Thermal and shear interactions between nano- and micro-particles in an acoustic field Seminar

Date:
16:00, 14 November 2017
Venue:
Building 13 Room 3017

Event details

ISVR Engineering Research Seminar Series 2017-2018

The interaction of an acoustic field with small particles (micrometre or nanometre size) in a liquid creates thermal and shear effects in the locality of the particle, within a range of a few microns of its surface at MHz frequencies. These thermal and shear waves dissipate energy, causing attenuation of the longitudinal pressure wave, but they may also interact with any neighbouring particles which are sufficiently close, thus modifying the temperature, velocity and pressure fields. The interactions are of interest for two applications: for characterisation of particulate suspensions by ultrasound (a linear technique), and for acousto-fluidic particle manipulation (a non-linear technique). The linear and non-linear effects are closely linked, and the shear interactions defined in models of linear scattering contribute to the streaming effects in non-linear fields.

Recent work has focussed on developing a modified multiple scattering model for linear propagation through suspensions of particles that includes these thermal- and shear-wave contributions. We have developed analytical forms for the dominant scattering contributions for emulsions and suspensions and investigated their dependence on the dimensionless shear and thermal wavenumbers. Numerical calculations demonstrate the contribution of the additional multiple scattering effects to the compressional wave speed and attenuation through the emulsion or suspension. The predictions of the model have been compared with experimental measurements for aqueous suspensions of silica particles using two different spectroscopy techniques. These indicate the regimes of success for the model and conditions where it still breaks down.

In addition, finite element simulations have recently been developed to investigate the thermal and shear effects around a particle in an acoustic field, and to explore their effect on particle interactions. A comparison of the simulations with an analytical scattering model for a single spherical particle will be presented, along with simulations of pairs and small clusters of particles.

Speaker information

Valerie Pinfield, Loughborough University. Valerie Pinfield studied Natural Sciences (theoretical physics) at the University of Cambridge, graduating in 1990 (MA, 1994). She worked for two years at The Welding Institute on electron beam welding, before joining the University of Leeds Food Science Department where she completed her PhD in 1996. Her research programme related to computational modelling of emulsion instability and ultrasonic propagation in scattering systems. After three years in research and development in the confectionery industry, Valerie returned to academia as a post-doctoral researcher at the Universities of Leeds and Nottingham, working on ultrasound propagation and scattering in a variety of inhomogeneous materials. Valerie is a Senior Lecturer and Head of the Chemical Engineering Department at Loughborough University, having joined as a Lecturer in 2012. She is a Fellow of the Institute of Physics, a Chartered Physicist and Member of the Acoustical Society of America. She currently leads an EPSRC-funded research project on ultrasonic characterisation of aggregated particle suspensions in collaboration with the Universities of Leeds and Manchester. The project encompasses theoretical, computational, and experimental investigations of ultrasound propagation with a particular focus on the shear and thermal interactions between particles in an acoustic field.

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