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Global and local statistics in turbulent emulsions

Published online by Cambridge University Press:  05 February 2021

Lei Yi
Affiliation:
Center for Combustion Energy, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing100084, PR China
Federico Toschi
Affiliation:
Department of Physics and Department of Mathematics and Computer Science, Eindhoven University of Technology, 5600 MBEindhoven, The Netherlands CNR-IAC, Via dei Taurini 19, 00185Roma, Italy
Chao Sun*
Affiliation:
Center for Combustion Energy, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing100084, PR China Department of Engineering Mechanics, School of Aerospace Engineering, Tsinghua University, Beijing100084, PR China Physics of Fluids Group, Max Planck-University of Twente Centre for Complex Fluid Dynamics, University of Twente, 7500 AEEnschede, The Netherlands
*
Email address for correspondence: [email protected]

Abstract

Turbulent emulsions are complex physical systems characterized by a strong and dynamical coupling between small-scale droplets and large-scale rheology. By using a specifically designed Taylor–Couette shear flow system, we are able to characterize the statistical properties of a turbulent emulsion made of oil droplets dispersed in an ethanol–water continuous solution, at an oil volume fraction up to 40 %. We find that the dependence of the droplet size on the Reynolds number of the flow at a volume fraction of 1 % can be well described by the Hinze criterion. The distribution of droplet sizes is found to follow a log-normal distribution, hinting at a fragmentation process as the possible mechanism dominating droplet formation. Additionally, the effective viscosity of the turbulent emulsion increases with the volume fraction of the dispersed oil phase, and decreases when the shear strength is increased. We find that the dependence of the effective viscosity on the shear rate can be described by the Herschel–Bulkley model, with a flow index monotonically decreasing with increasing oil volume fraction. This finding indicates that the degree of shear thinning systematically increases with the volume fraction of the dispersed phase. The current findings have important implications for bridging the knowledge on turbulence and low-Reynolds-number emulsion flows to turbulent emulsion flows.

Type
JFM Papers
Copyright
© The Author(s), 2021. Published by Cambridge University Press

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