A computational fluid dynamics study on oil-in-water dispersion in vertical pipe flows

Abstract

A three-dimensional steady-state mathematical model for an oil-in-water dispersed flow was developed to study the effects of lift force on the dispersed phase behaviour in a vertical pipe. The Euler/Lagrange multiphase scheme implemented in CFD code ANSYS Fluent was used to investigate the interaction between the oil droplets (dispersed phase) and water (continuous phase). The flow field of the continuous phase was resolved by solving the Reynolds-averaged Navier–Stokes conservation equations with the k–ɛ turbulence model and standard wall function. The motion of oil droplets was obtained from the resolved flow field of the continuous phase as such that a two-way coupling was enforced to account for the influence of oil droplets on the water flow. Simulations were performed to model published experimental observation. The computational domain was a vertical pipe (3.2m in length and 38mm in diameter). Inter-phase forces (gravitational, drag, buoyancy and shear-lift) were taken into consideration where the shear-lift force is of our primary focus. Three different mixture velocities (1.5, 2.0, 2.5m/s) were simulated with oil fraction ranging from 0 to 0.5. Uniform droplet diameters of 0.5–6mm were tested. Here, droplet breakup and coalescence were not modelled. Comparison with experimental results was given in terms of the ratio of pressure gradient. The simulations show that the shear-lift force plays an important role in the overall force balance acting on the droplets and influences the radial distribution of the oil droplets (i.e. droplets tend to concentrate at the core of the pipe rather than near the wall). Oil droplets diameters are found to depend on the mixture velocity for the case under consideration.