Numerical Model of the Critical Gas Velocity for Liquid Displacement from the Lower Section of an Upward-Sloping Pipe

Abstract

Mobile pipelines are the most efficient and reliable tools for transporting a large amount of oil over long distances in combat, emergency rescue and disaster relief situations. In the completion of oil transfer or pipeline maintenance, the oil in the pipe is usually displaced by air. In the process of evacuation, due to the influence of terrain, working conditions and gravity, the gradual deposition of oil from upward-sloping pipeline sections to low-lying parts of the pipeline occurs, resulting in the formation of fluid deposits, which results in the incomplete drainage of the pipeline, directly affecting the recovery efficiency of the pipeline. According to the theory of gas–liquid two-phase stratified flow, the tail flow of a liquid membrane in an upward-sloping pipeline is analyzed as part of the gas-carrying oil flow process in an upward-sloping pipeline in this paper. The gas superficial velocity, which is the minimum velocity that can carry the accumulated liquid in the pipeline, is called the critical gas velocity of the gas-carrying liquid. A gas-carrying oil critical gas velocity model in an upward-sloping pipeline was established, and the change law of the critical gas-phase velocity in the upward-sloping pipeline was analyzed under the conditions of different tile angles, initial oil layer thicknesses and pipeline diameters. It was found that the tile angle had the greatest influence on the gas-carrying oil flow in the upward-sloping pipe, and the initial retained oil thickness had less of an influence on the gas-carrying oil flow in the upward-sloping pipe. When the pipeline diameter was small, the flow of the gas-carrying oil in the upward-sloping pipe was greatly affected by the pipeline diameter, but when the pipeline diameter was larger, the influence of the diameter on the gas-carrying oil flow in the upward-sloping pipe decreased gradually. The model developed can provide a useful means for the analysis and containment of accumulated liquid.