An experimental study on pressure drop of air-oil flow in horizontal pipes using two synthetic oils

Abstract

This study focuses on the frictional pressure drop in gas-liquid two-phase flow, characterized by nonlinear behavior under various flow conditions due to complex two-phase phenomena. The experimental investigation involves an air-oil mixture flowing through horizontal pipes with diameters of 20 mm and 40 mm, aiming to observe the flow patterns and quantify the pressure drop. Two oils with different thermophysical properties are used as the liquid phase. The operating temperature and pressure of the test pipes are controlled within the range of 24–44°C and 1–3 bar, respectively. Seven air-oil flow patterns are identified based on visualization results: stratified smooth, stratified wavy, annular, plug, slug, bubbly, and dispersed bubble flows. On analyzing 1043 data points from the experiment, this study explores the effects of total mass velocity, flow quality, pipe diameter, operating temperature, operating pressure, and oil type on the frictional pressure gradient. Particular attention is given to the variation of the frictional pressure gradient concerning operating pressure, and its relationship with total mass velocity, flow quality, and flow pattern is discussed. Additionally, the study examines predictions from 55 previous correlations against the current pressure drop data. The predictive capability of these correlations is evaluated for the entire dataset and its subsets, categorized by oil type, pipe diameter, operating pressure, flow condition, total mass velocity, flow quality, and flow pattern. Evaluation metrics include mean absolute errors and the proportions of data points within 30% and 50% of absolute error. In addition, average and standard deviation values are calculated for each dataset to provide a comprehensive assessment.