Prediction of Gas-Liquid Two-Phase Slug Flow Characteristics in Vertical Small Diameter Pipes by a One-Dimensional Two-Fluids Model

The purpose of this study is to improve a two-fluid model applicable to gas-liquid two-phase slug flows in small diameter pipes. Experimental data on void fraction and frictional pressure drop were obtained for vertical upward slug flow in 5 and 9 mm i.d. circular pipes, and those on the interfacial friction force were obtained by substituting the above data into an equation derived from the one-dimensional two-fluids model. The test liquids were a Poly-oxy-ethylene lauryl ether water solution, a 72 wt% glycerin water solution and a tap water at 30 °C, while the test gas was air at near atmospheric pressure. In order to study the effects of liquid properties, surface tension of the test liquids against air was varied from 0.042 to 0.071 N/m, viscosity was 0.797 to 19.6 mPa·s, and density was 996 to 1184 kg/m3. The range of volumetric flux of the liquid was 0.1 to 2.0 m/s, and that of the gas was 0.1 to 22 m/s. In addition, the drag coefficient data of the large bubble was determined from the data on the bubble diameter, the respective void fractions of the liquid slug section and the large bubble one, the interfacial friction force and the length ratio of the large bubble to the total of the liquid slug and the large bubble. These data were used to validate representative two-fluid model codes. Since the prediction by the codes did not fit well the present data, a new drag coefficient correlation for the large bubble was proposed using 5 dimensionless parameters. The predictions by the new correlation and familiar ones in literatures have been tested against the present data, and the applicability of the new one has been demonstrated.