Effect of gas density and surface tension on liquid film thickness in vertical upward disturbance wave flow

Gas–liquid annular flows, such as the flow attached to the fuel rods of boiling water reactors, is a prevalent occurrence in industrial processes. At the gas–liquid interface of such flows, disturbance waves with diverse heights commonly arise. Because the thin liquid film between two successive disturbance waves leads to the dryout on the heating surface and limits the performance of the heating components, complete knowledge of the film thickness and disturbance waves is crucial. The properties of the base film and disturbance waves have been studied extensively through experimental and analytical approaches. However, most experimental data and analysis available in the literature are limited to the near atmospheric condition, and the liquid–gas density ratio under near atmospheric conditions is much higher than in practical nuclear applications. In this study, we use nitrogen gas and water under the system pressures of 0.2 and 0.4 MPa, as well as HFC134a gas and water under the system pressure of 0.7 MPa. Therefore, the density ratio can be varied between 32 and 434. Based on our experimental data, we report a direct link between the film thickness, wave height, and dimensionless numbers. The analysis indicates the Weber number which represents the ratio of the drag force to the surface tension force is critical for the film thickness behavior. To examine this, we perform the experiments using nitrogen gas and 95% (v/v) of aqueous ethanol solution under the system pressure of 0.2 MPa. Finally, two models are proposed to predict the averaged film thickness and wave height, which are then compared with previous data.