Droplet dynamics in confinement

N Ioannou,H Liu,Y.H Zhang

doi:10.1016/j.jocs.2016.03.009

N Ioannou, H Liu + Show 1 more

Open Access

https://doi.org/10.1016/j.jocs.2016.03.009

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Abstract

This study is to understand confinement effect on the dynamical behaviour of a droplet immersed in an immiscible liquid subjected to a simple shear flow. The lattice Boltzmann method, which uses a forcing term and a recolouring algorithm to realize the interfacial tension effect and phase separation respectively, is adopted to systematically study droplet deformation and breakup in confined conditions. The effects of capillary number, viscosity ratio of the droplet to the carrier liquid, and confinement ratio are studied. The simulation results are compared against the theoretical predictions, experimental and numerical data available in literature. We find that increasing confinement ratio will enhance deformation, and the maximum deformation occurs at the viscosity ratio of unity. The droplet is found to orient more towards the flow direction with increasing viscosity ratio or confinement ratio. Also, it is noticed that the wall effect becomes more significant for the confinement ratios larger than 0.4. Finally, the critical capillary number, above which the droplet breakup occurs, is found to be mildly affected by the confinement for the viscosity ratio of unity. Upon increasing the confinement ratio, the critical capillary number increases for the viscosity ratios less than unity, but decreases for the viscosity ratios more than unity.

Highlights

Emulsions consist of immiscible fluids commonly found in production processes in food, chemical, and pharmaceutical industries
The droplet dynamics in a shear flow was successfully simulated by the former three models or their variants [31,32,33,34,35,36], none of them has systematically examined the impact of viscosity and confinement ratios on the droplet deformation and breakup, which is the focus of this work
The influence of capillary number, viscosity ratio and confinement ratio have been systematically studied for droplet deformation and breakup in a simple shear flow

Summary

Introduction

Emulsions consist of immiscible fluids commonly found in production processes in food, chemical, and pharmaceutical industries. Complementing theoretical and experimental studies, numerical simulations have been extensively used to investigate the droplet deformation and breakup in a simple shear flow [3,4,20,21,22,23,24] Among these works, Janssen and his co-workers [3,23,24] used the boundary integral method (BIM) to study the effect of viscosity and confinement ratios on droplet deformation and the critical capillary number. The droplet dynamics in a shear flow was successfully simulated by the former three models or their variants [31,32,33,34,35,36], none of them has systematically examined the impact of viscosity and confinement ratios on the droplet deformation and breakup, which is the focus of this work. The colour gradient LBM is used here because of its advantages such as low spurious currents, high numerical accuracy and strict mass conservation for each fluid which have been demonstrated in our recent works [37,38]

Numerical method

Results and discussion

Droplet deformation

Droplet breakup

Conclusions