Experimental Investigation on Air-Water Two-Phase Flow Pattern and Pressure Drop in Vertical Upward Annulus

Abstract

In the present work, air-water two-phase flow pattern and pressure drop in vertical upward annular channel with different diameters are experimentally studied. Two concentric annular test sections with the same hydraulic diameter of 4.6 mm are used in the experiments. The outer diameter and inner diameter corresponding to the two test sections are 18.60 and 12.30, and 86.75 and 80.45, respectively. Bubble flow, cap-slug flow, cap-churn flow, and annular flow were found in both the test sections and the flow pattern map is developed. It is found that the superficial gas velocity has an important effect on the transition of the flow patterns. Pressure drop correlations are reviewed and a total of 12 correlations are collected, including 4 homogeneous flow model (HFM)-based correlations and 8 separated flow model-based correlations. The existing correlations for estimating pressure drop were tested against the measured data. The comparisons show that no correlation studied here provides satisfactory agreement with the whole database. The Chisholm correlation provides the best accuracy with 20.9% for the small test section and 21.5% for large test section. It is also found that the existing models based on separated flow method predict frictional pressure drop with higher accuracy than those based on HFM. The result of this study highlights the requirement of a new method for calculating the frictional pressure drop in annular channels.