Abstract
Numerical simulation using computational fluid dynamics (CFD) has been carried out to study air and water two-phase flow in a small horizontal pipe of an inner diameter of 8.8mm, in order to investigate unsteady flow pattern transition behaviours and underlying physical mechanisms. The surface liquid film thickness distributions, determined by either wavy or full annular flow regime, are shown in reasonable good agreement with available experimental data. It was demonstrated that CFD simulation was able to predict wavy flow structures accurately using two-phase flow sub-models embedded in ANSYS-Fluent solver of Eulerian–Eulerian framework, together with a user defined function subroutine ANWAVER-UDF. The flow transient behaviours from bubbly to annular flow patterns and the liquid film distributions revealed the presence of gas/liquid interferences between air and water film interface. An increase of upper wall liquid film thickness along the pipe was observed for both wavy annular and full annular scenarios. It was found that the liquid wavy front can be further broken down to form the water moisture with liquid droplets penetrating upwards. There are discrepancies between CFD predictions and experimental data on the liquid film thickness determined at the bottom and the upper wall surfaces, and the obtained modelling information can be used to assist further 3D user defined function subroutine development, especially when CFD simulation becomes much more expense to model full 3D two-phase flow transient performance from a wavy annular to a fully developed annular type.
Highlights
Two-phase annular flow in a horizontal pipe is of great importance in a wide range of industrial applications, including chemical process, heat transfer system, steam generator and pipeline transportation[1,2]
The primary objective of this study is to model flow pattern and transient process experimented by Schubring and Shedd[6,11] by using modern computational fluid dynamics (CFD) approach to investigate air and water two-phase flow behaviours the annular wavy flow distribution characteristics and the base film thickness
The initial water film at the pipe inlet was defined using wavy annular flow function (ANWAVER-user defined function (UDF)), where the bottom and the top base film thicknesses are set to 0.1938mm and 0.125mm, respectively
Summary
Two-phase annular flow in a horizontal pipe is of great importance in a wide range of industrial applications, including chemical process, heat transfer system, steam generator and pipeline transportation[1,2]. The two-phase flow behaviors can have profound effects on overall system device performance; because non-. This is an Open Access article published by World Scientific Publishing Company. It is widely known that two-phase flow in a horizontal circular pipe can produce different flow patterns, which is required to be clearly distinguished. This gives arise an attention for researchers/engineers to develop effectively numerical and experimental methods that are able to accurately predict twophase flow transient regimes. Whole system performance can be improved via detailed design and optimization processes
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