Simulating creaming behavior in an emulsion using the lattice Boltzmann method

Abstract

Oil-in-water emulsions are very common in industrial processes, and understanding the fac- tors governing emulsification and de-emulsification is crucial. A mechanism through which de-emulsification commonly takes place is coalescence, being the act of two dispersed-phase droplets coming together to create a single larger droplet. Due to density differences, it is common for dispersed phase droplets to form a creaming layer at the top of the emulsion, in- creasing the likelihood of coalescence and therefore de-emulsification. The goal of this thesis is to use the lattice Boltzmann method to simulate the rising of a dispersed phase oil droplet towards a creaming layer due to buoyancy effects and to quantify the effect of the viscosities of both phases on the velocity with which aforementioned droplet rises. This is done using the Shan-Chen psuedopotential method. After introducing gravity into the simulation the the droplet is allowed to reach a terminal velocity vt. This is done for independently varying viscosities for both the dispersed phase and continuous phase (νd and νc respectively). A weakly inverse relation was found between vt and νc. An estimation for the terminal velocity of a droplet rising due to creaming behavior is found by cancelling drag force found from Stokes’ law against the buoyancy force. Found results were not in agreement with said estimation. Different explanations for this discrepancy are varying droplet diameters, varying droplet densities, droplet deformation and high velocity fluctuations. The terminal velocities were also compared to the ratio between the viscosity of both phases, but no correlation was found.