Experimental simulation of high-temperature and high-pressure annular two-phase flow using an HFC134a–ethanol system: Characterization of disturbance wave flow

Nuclear power, recognized as a critical component in achieving a carbon-neutral energy society, relies heavily on understanding the thermal-hydraulic phenomena in boiling water reactors (BWRs). Among these phenomena, steam-water annular flow near fuel rods is vital for reactor safety, yet direct visualization and precise measurement of liquid film characteristics at actual BWR conditions (285 °C and 7 MPa) remain challenging due to extreme operating conditions. To address this, we used an innovative HFC134a–ethanol simulant system operating at low temperature and pressure (40 °C, 0.7 MPa) to simulate the BWR steam-water system. Utilizing the constant electric current method and high-speed visualization, liquid film characteristics, including the base, average, and maximum film thickness, disturbance wave height, velocity, and frequency of HFC134a–ethanol system were obtained and systematically studied. Our results demonstrated that base film thickness predominantly depends on interfacial shear stress acting on the base film rather than surface tension. A new predictive correlation for base film thickness was derived, significantly improving accuracy over existing correlations and offering enhanced prediction accuracy crucial for modeling dryout phenomena in reactor thermal-hydraulic analysis. Additionally, this study provides comprehensive benchmarking data for validation of thermal-hydraulic codes and CFD models, thus directly contributing to improved reactor safety assessments and optimized nuclear reactor designs.