Simulations of Droplet Interactions with Lattice Boltzmann Methods

• Author / Creator

  Shardt, Orest

• Interactions between droplets were studied using two lattice Boltzmann methods (LBMs). The Shan-Chen LBM, in which repulsive forces between fluids maintain phase separation, was used to simulate systems with three immiscible components. The simulations demonstrated the three equilibrium configurations of two droplets in a third fluid: adhering, separated, and engulfed. Simulations of adhering droplet pairs, called Janus droplets due to their two-sided structure, in shear flow revealed the structure of the internal flow and the dependence of the rotation rate on the orientation of the droplet. A second type of interaction between droplets was simulated with the free-energy binary-liquid LBM: binary droplet collisions in confined simple shear flow. The conditions for coalescence were quantified and the effects of geometry and the parameters of this Cahn-Hilliard-type phase field model on the critical conditions were examined. Two parameters of the phase field model, the thickness of the diffuse interface and the mobility of the phase field, are important. Simulations with highly-resolved droplets, with radii spanning 200 lattice nodes, were used to determine the minimum film thickness before coalescence, its relationship to the interface thickness, and the effect of the mobility on the evolution of the minimum distance between the droplet interfaces during collisions. The critical conditions for coalescence in these simulations were compared with published experiments with polymers. Unlike the experimental polymer system, the interfaces of interacting droplets are often charged, as in the case of oil-water emulsions. To simulate such liquid systems, the free-energy binary-liquid LBM was coupled with an iterative finite difference solver for the linearized Poisson-Boltzmann equation that describes the electrostatic potential near a charged surface in an electrolyte solution. Simulations of collisions between charged droplets with constant zeta potentials in a sheared electrolyte showed the effects of surface charge on the critical conditions for coalescence.

• Subjects / Keywords

  • Poisson-Boltzmann
  • Lattice Boltzmann Method
  • Coalescence
  • Droplet
  • Phase field
  • Simulations
  • Janus droplet

• Graduation date

  Fall 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3FX7449N

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.