An optimize empirical correlations for liquid film thickness and interfacial friction factor in vertical gas-liquid annular flow

Background: The annular flow regime is one of the most prevalent two-phase flow regimes, occurring throughout a broad range of gas and liquid flow rates. This flow pattern is distinguished by a thin layer of liquid around the walls and a core of quickly flowing gas in the middle.Methods: Using image recording and processing methods, the generation of an annular flow pattern in a countercurrent two-phase flow in a vertical transparent pipe was explored in the current experimental study. In this regard, the range of air (bottom to top) and water (top to bottom) velocities for annular flow was 20.94-3.66 m/s and 0.3-1.06 m/s, respectively.Significant findings: In this paper, the liquid film thickness is provided as a novel five-variable correlation function of gas phase superficial velocity, liquid phase velocity, pipe diameter, Weber number, and Froude number, with an R2 value of 0.98. In addition, the interfacial friction factor (liquid and gas phases) is provided as a fivevariable correlation based on gas flow Reynolds number, liquid flow Reynolds number, pipe diameter, liquid film thickness, and Froude number with coefficient of determination of 0.97. The sensitivity analysis of the acquired experimental findings reveals that the liquid film thickness and the interfacial friction factor are most sensitive to changes in the superficial velocity of the gas phase and the Reynolds number of the liquid phase, respectively. Also, for the thickness of the liquid film and the interfacial friction coefficient, the experimental values and suggested correlations deviate by a maximum of 3.15 percent and 4.56 percent, respectively.