Liquid film thickness in the slug flow pattern of gas–liquid flow in straight circular microchannels

Using N 2 ‐water and N 2 ‐glycerol aqueous solutions as working systems, this study systematically investigated the stable flow patterns of gas–liquid flow in a straight circular tube following a T‐junction, covering various circular tubes with different inner diameters (0.25–1 mm), gas flow rates ranging from 1 to 200 mL/min, liquid flow rates ranging from 1 to 10 mL/min. Firstly, a two‐phase flow pattern distribution map was explored to determine the slug flow region, clarifying its formation conditions. Then, the steel‐needle calibration method was proposed to achieve the liquid film thickness measurement, which is simple yet highly applicable, effectively eliminating the influence of tube curvature. Next, an empirical correlation was proposed to predict the film thickness based on force analysis. The flowchart for flow pattern demarcation and the adaptive measurement and universal prediction for liquid film thickness can help to get a deeper understanding of the gas–liquid performances in microchannels.