Hydrodynamic forces acting on pipe bends in gas–liquid slug flow

•A transient, isothermal model has been developed to predict the forces.•The model is based on the unsteady-state momentum equation.•Validation of the one-dimensional, transient theoretical model has been done.•The predictions agreed well with our experimental result for air–water slug flow.•The physical reasoning explains the experimental results from the literature. In this paper, a one-dimensional, transient theoretical model, the Piston Flow Model (PFM), based on momentum analysis, is proposed to predict the time dependent forces acting on horizontal pipe bends in slug flow. Our experimental apparatus is described and results there from are presented. The PFM has been validated by comparing its predictions with our experimental results for air–water slug flow. The pressure traces, force traces and maximum force predicted agree well with our measurements.