Investigation of Churn and Annular Flow Transition Boundaries in Vertical Upward Gas-Water Two-Phase Flow

Abstract

Flow patterns are crucial in studying two-phase flow in vertical upward pipes, predicting phase distribution, flow transitions, and stability. Presently, studies on the transition boundaries between churn flow and annular flow mainly focus on flow rates, physical parameters, pressure, and temperature, often overlooking the influence of pipe diameter. This study addresses this gap by examining investigates the transition boundaries between churn flow and annular flow using a multiphase pipe flow experimental setup under varying pipe diameters, gas flow rates, and liquid flow rates. Experimental results indicate that with a constant liquid flow rate, as the pipe diameter increases, the gas flow rate required to form annular flow increases; higher gas flow rates lead to greater pressure gradients and smoother fluctuation amplitudes. With a constant gas flow rate, as the pipe diameter increases, the liquid flow rate required to form annular flow decreases; lower liquid flow rates result in smaller pressure gradients and smoother fluctuation amplitudes. With constant gas and liquid flow rates, smaller pipe diameters make it easier to form annular flow; smaller pipe diameters lead to smaller pressure gradients but larger fluctuation amplitudes. Based on the mechanical analysis of the liquid film and the principles of interface fluctuation, considering the shear force of the gas on the liquid film, surface tension, gravity of the liquid film, viscous force of the liquid film, and pressure gradient force, a novel churn-annular flow transition boundary model was developed. The new model and six traditional transition boundaries were evaluated using 276 sets of experimental data from public literature and 528 sets from this study. The prediction accuracy of traditional transition boundaries ranges from 53.92% to 86.27%, while the new model's prediction accuracy is above 98.19%. This new model incorporates the impact of pipe diameter, enhancing its applicability and accuracy across varying diameters.

Keywords: Two-phase flow, Flow pattern transition boundary, Pipe diameter, Churn flow, Annular flow