Identification of Gas Void Fraction and Flow Patterns in Upward Direction of Vertical Pipes

Abstract

Experiments on gas-liquid two-phase flow were conducted at three positions of upward section in a vertical pipe with diameter of 101.6 mm. In this study, probability density functions (PDFs) and local distribution of gas void fraction were applied to identify the possible flow patterns that can be formed in a vertical upward orientation. It was observed from the shape of PDFs that bubbly, intermittent and annular flows are the dominant types. These flow structures were significantly influenced by gas and liquid superficial velocities. Bubbly flow was formed at low gas flowrates, which was characterized by discrete bubbles distributed in a liquid continuum. The bubbles were uniformly distributed in the pipe center with similar shape and size. Intermittent flow was formed due to gradual increase of gas flowrate, where large bubbles tend to collide and coalesce with the smaller ones. The bubbles are noted to occupy the greater part of the pipe's cross-section. Fluctuations of gas flowrate led to distortion and breakdown of the large bubbles immediately. Further increase of gas flowrate was attributed to formation of annular flow regime. In this type, the liquid phase flows along the pipe walls in the form of liquid film, while the gas phase flows in the center of the pipe. Further attempts were also performed by examining the local distribution of gas void fraction which confirmed the achieved above-mentioned results.