Modelling air and water two-phase annular flow in small horizontal pipe

Abstract

Numerical study using Computational Fluid Dynamics (CFD) has been carried out to investigate flow behaviours and underlying physical phenomena associated with air/water two-phase flow inside a small horizontal tube of an inner diameter 8.8mm. The base liquid film thickness distributions, determined by either wavy or full annular flow regime, are compared with available experimental data. CFD simulation has successfully predicted the wavy structure applying a user defined function, which has coupled in ANSYS-FLUENT solver to correlate with other two-phase flow models under the Eulerian–Eulerian framework. Results from liquid distributions and two-phase flow behaviours have indicated the presence of strong gas/liquid interferences. This can largely contribute towards the thickening of the liquid film coverage along the top pipe wall surface for a fully developed annular flow, compared to those occurred in the wavy annular flow regime. This is due to possible earlier droplets broken down thus the liquid wavy front can travel from the low part of the pipe to the upper wall surface. Some discrepancies between CFD prediction and experimental data could be due to the limitation of CFD model as only a simplified 2D variant is adopted, rather than a full 3D transient two-phase flow model.</p