Analysis of friction models during simulations of filling processes in single pipelines

The analysis of filling processes in pressurized pipelines has been conducted using a steady friction model in the implementation of governing equations. This research is focused on the case of a filling process of a single pipeline without an air valve. Three equations were used to represent the phenomenon: (i) a rigid water column approach, which describes the water movement along the water system; (ii) a piston flow model, which assumes a perpendicular air-water interface to the main direction of the pipe; and (iii) a polytropic model for representing the thermodynamic behaviour of an entrapped air pocket. This research studies the filling processes occurrence using equations of steady and unsteady friction models, where Moody, Wood, Hazen-Williams, and Swamee-Jain equations are analysed. The analysis is applied to a case study of a single pipe of a total length of 1000 m with an internal diameter of 595 mm variation of pressure surges in the implementation of these formulations. Results confirm that there is a minimum discrepancy between steady and unsteady friction models since values of pressure surges pattern are similar.