Hybrid quasi-steady thermal lattice boltzmann model for investigating the effects of thermal, surfactants and contact angle on the flow characteristics of oil in water emulsions between two parallel plates

Abstract

In this work, a two-dimensional hybrid quasi-steady thermal lattice Boltzmann model with temperature-dependent interfacial tension, surfactant and contact angle modules, is used to study the combined multi-physics effects on oil in water (O/W) systems flowing between two-parallel oil-wet plates. The proposed model is used to execute a parametric study for investigating the effects of the droplet radius, source terms, temperature, and surfactants parameters such as concentrations, elasticity, and diffusion coefficients on the flow characteristics of oil in water (O/W) emulsions inside microchannels. Flow conditions such as droplet Reynolds number0.41≤Re≤48, Webber number0.041≤We≤28 dimensionless surfactant surface concentration0.1≤Γ∗≤0.5, and surface Péclet number0.011≤Pes≤31are used in the simulations. The presence of surfactant noticeably enhances the droplets' transportation inside the channel, due to increased droplets' contact angle and deformation. Contaminated droplets with surfactant retain a greater bulk mass center velocity than clean ones to the tune of 2–5 times depending on the simulation conditions. The rise in temperature has a major impact on improving the suspended phase bulk velocity and power number ratio (system's efficiency indicator) for cases with and without surfactant. However, the presence of surfactant at elevated temperatures ameliorates the amount of useful work absorbed by the droplets from the flow significantly. Using specific conditions from the parametric study such as high temperature and surfactants characterized by low diffusion coefficient, results in an effective droplets breakup. The daughter droplets depart from the channel walls by shear lift, which enhances the suspended fluid transportation and increases the power number ratio up to 5.7 times.