A numerical analysis of the characteristics of interfacial waves on the onset of flooding in an inclined pipe

The purpose of the present study is to investigate the characteristics of interfacial waves on flooding phenomena in an inclined pipe. The effects of liquid velocity and contact angle on the waves at the onset of flooding are studied with a two-dimensional computational fluid dynamic model. Flooding in a 30° inclined pipe is observed by using the Volume of Fluid (VOF) method. It is found when the contact angle is equal to 120°, the pipe wall cannot form a uniform liquid film and the gas velocity required on the onset of flooding decreases as the contact angle and liquid velocity increase. For a detailed understanding of the effects of contact angle and liquid velocity, an analytical forces model is proposed on the flooding waves, including gravity F_gw, the pressure of the gas core F_pc, pressure variations in the liquid film F_pl, wall shear force F_ws, interfacial shear force F_ss and surface tension force F_σ. Through the quantitative calculation of all forces, it is found that the amplitude and length of the flooding wave increase with liquid velocity. As the contact angle increases, the crests become sharper. Further, through analyzing the histogram distribution of the forces, the increase of the contact angle will change the mechanism of flooding from carrying droplets to rising waves. It provides a theoretical basis for the development of mechanistic models to predict the onset of flooding in the future.