Numerical Study of the Free Surface Flow in a Centrifugal Gas-Liquid Separator

This work presents a numerical investigation of the free surface flow in a gas-liquid separator with a cylindrical expansion chamber using Computational Fluid Dynamics. The centrifugal flow is set through a tangentially oriented nozzle at the chamber wall and is modeled using an inhomogeneous Eulerian-Eulerian multiphase flow model with the free surface approach to capture the phases interface. Fluid dynamics is examined for a range of fluid viscosities and flow rates for a single-phase liquid flow at the inlet. Liquid-gas bubbly-flow at the inlet is also considered to investigate some aspects of the phases separation inside the cylindrical chamber. Analysis of the flow field reveals that the impact of the fluid at the chamber wall combined with the centrifugal movement push part of the fluid upwards, stabilizing a liquid level above the nozzle. Near the inlet, the flow dynamics is characterized by a strong centrifugal motion, which decreases continuously below the entrance position due to gravity and viscous effects. The liquid level over the chamber wall and the centrifugal intensity increase with the flow rate, but decrease with viscosity. Viscosity also tends to enlarge the liquid layer thickness over the chamber wall and diminish the residence time of the liquid from the inlet down to the chamber’s bottom exit. Investigation of liquid-gas bubbly-flows in this equipment shows that separation occurs mainly near the chamber entrance due to the sudden expansion and the formation of a thin fluid layer over the chamber wall. In a percentage basis, phases tend to be more effectively separated for higher inlet gas volume fractions, lower liquid viscosities and bigger gas bubbles. These conclusions give technically interesting information for dimensioning hydrocyclones for gas-liquid flow separation.