Liquid Film Thickness Prediction in Elbows for Annular Flows

In many industrial applications such as oil and gas production systems and heat exchangers, annular flow is a frequently observed flow regime. A lot of experiments and analysis have been carried out in the last decades in order to determine the thickness of the liquid film in annular flow and in straight pipes; however, published liquid film thickness models and experimental data in bends are scare. This paper presents a model for predicting average liquid film thickness in bends according to the correlations obtained for calculating dimensionless interfacial friction factor as well as dimensionless liquid film thickness in bends. Correlations were obtained based on analysis carried out using a control volume of gas core and utilizing experimental data available in the literature for liquid film thickness in bends. Furthermore, liquid film thickness distribution at the inner and outer bends of elbows were investigated, and a simple analytical model has been developed for predicting film thickness at the outer and inner radii of a bend. It is shown that, the average film thickness calculations from the current model agree with experimental data and results show that the model can predict the film thickness changes based on the flowrates and properties of liquid and gas phases.