A new transient model for motion and variation of gas phase in pipelines applying collocated multi-grid method with the Eulerian-Lagrangian approach

Abstract This paper investigates the gas phase, including bubbles' and gas pockets' migration and evolution in gas-liquid flow in the pipelines, where the safe operation is severely influenced by the gas accumulations. To investigate the formation, as well as location and amount of these gas accumulations, a new transient model applied with the Population Balance Model (PBM), gas pockets capturing and tracking model are proposed, which are discretized and calculated in the collocated multi-grid with Eulerian-Lagrangian coupling scheme. The flow field of the pipeline is modeled with the Eulerian scheme, while the bubbles' migration, gas pockets' capturing and tracking can be modeled in the Lagrangian mesh. To couple the description of bubble-dimension and that of pipe-dimension, the Rayleith-Plesset equation and the Smooth Particle Hydrodynamics (SPH) are applied, thus, the changeable characteristics of bubbles along the pipes can be described. Based on that, the bubbles' transition to the gas pocket under specific conditions can be predicted. And the subsequent capturing and tracking process will work with the help of the collocated multi-grid, which provides the accurate and parallel calculation. The relative parameters are extracted from the published experimental data, and the simulation results are in good agreement with the measured results. Meanwhile, the case studies show the model has the prediction ability of the gas phase's migration and evolution, as well as the formation and location of gas accumulations in the pipeline.