Investigation of unsteady flow in liquid-liquid hydrocyclone using Eulerian-Lagrangian approach

Abstract

The considerable influence of inflow variations within hydrocyclones on separation efficiency and the time required to achieve steady-state flow made the examination of the transient behavior of two-phase flow crucial. This study investigated the overall progression of two-phase flow, starting from the injection of oil droplets until reaching a steady state in a de-oiling hydrocyclone simulated using the open-source software OpenFOAM v5. Furthermore, the impact of sinusoidal variations in the inlet flow was examined, as vibrations on oil platforms significantly affected the inlet flow of hydrocyclones, thereby influencing their efficiency. To assess the improvement in efficiency over time, the analysis focused on the variations in efficiency from the initial introduction of oil droplets into the hydrocyclone until maximum efficiency was achieved. This examination revealed three key time spans (Start-Up, Semi-Stable, and Fully Stable) where the efficiency trend underwent noticeable changes. Notably, the initial time span (Start-Up) was the most critical, showing an 80% increase in efficiency within the first two seconds. Additionally, the study examined the breakup and coalescence of droplets during transient oil injection at three different time intervals. Sinusoidal variations of 10% in the inlet flow led to a decrease in efficiency from 91% to 82%. This decrease in efficiency was caused by extreme variations in the inlet flow rate, which disrupted the vortices in the core of the flow responsible for carrying droplets to the overflow. During the first and second cone time spans of each cycle, the disruption resulted in a decrease in efficiency that was recovered by the return flow in the second half of the cycle.