Experimental investigations of gas-liquid two-phase flow in a horizontal mini pipe: Flow regime, void friction, and frictional pressure drops

Experimental studies of air-water two-phase flows in a mini tube with an inner diameter of 3.12 mm have been conducted in terms of the flow pattern, void fraction, and pressure gradients. The fluid velocities range from 0.065 to 21.78 m/s and from 0.109 to 1.835 m/s, respectively. A right-angle prism is applied to capture images simultaneously from two perpendicular directions. Three-dimensional gas-liquid interfaces are reconstructed with the obtained images from two directions. The gas void fraction is investigated using this method, which is experimentally validated with the quick closing valves method. Three flow patterns are obtained in the present work, which is bubbly, slug, and annular flows. The Probability Density Functions of the cross-sectional void fraction show that the intermittent flow has two peaks and the annular flow has only one peak. Volumetric void fraction is affected by the flow pattern and the flow rate. However, at very high gas velocities, volumetric void fraction is independent of the liquid rate. A new frictional pressure drop correlation is proposed based on the experimental data.