Mathematical Model of Air Pocket Evolution during Water Filling a Long-Slope Pipeline and Its Application to Air Removal Prediction

Abstract

During water filling a long-slope pipeline, air pocket is very likely to be entrapped at peak point. In order to track air movement and predict air removal conditions, a mathematical model of air pocket evolution, including its formation, compression, and entrainment, is proposed in this paper. The simulation results were compared with the engineering field data and the two are basically consistent. Furthermore, the two most important factors which play a great role in the removal of air pocket, i.e., the terrain category and the inlet flow rate, are analyzed in detail. It is concluded that the removal conditions reach three outcomes: air pocket compressed and partly removed, compressed and completely removed, and compressed without any removal. In this paper, the terrain which leads to the last outcome is called the “Dangerous Terrain.” And for the “Dangerous Terrain,” it is of great importance that the inlet flow rate should be strictly confined within a certain level. While for the other two categories of terrains, an increased flow rate is in any respect beneficial to the removal of air pocket.

​Experimental investigations on characteristics of water-air two-phase flows during water fillings in undulation pipelines

“…The research showed that the water-air interface remained stable without obvious fluctuations for the low water-filling velocity case; for the medium water-filling velocity, the water-air interface experienced significant fluctuations, leading to the formation and discharge of small bubbles along with the water flow until the pipeline was completely filled with water; for the high water-filling velocity case, the water-air interface fluctuated violently, causing water to entrain the air pockets and flow downstream. Chen et al [19] investigated the dynamic characteristics of water-air twophase flow in the declination pipeline (observed from the flow direction) in the U-shaped pipeline system during the water-filling and air exhausting process. Initially, as water filled the pipeline and reached the low point of pipelines, a water slug was formed.…”