Experimental investigation on droplet size in post-dryout region

• Visualization experiments is conducted to investigate droplet size under PDO conditions. • Existing droplet size correlations are assessed with obtained data and literature datasets. • A new droplet size correlation is developed based on the droplet Weber number. • The proposed correlation well predicts droplet size across varying fluids, pressures, and mass fluxes. Due to the limited availability of experimental data on droplet size in dispersed flow under post-dryout (PDO) conditions, and its critical role in accurately predicting PDO heat transfer, this study designs and conducts a visualization experiment to investigate droplet behavior in PDO regime. A square flow channel with a centrally positioned electrically heated tube is constructed, installing multiple observation windows on both side walls to provide optical access to the droplets. Experiments are conducted under heat fluxes exceeding the critical heat flux (CHF), ensuring the observation area within the PDO regime. Droplet motion in the vapor flow is recorded by the high-speed camera through transparent windows. The droplet size and their distributions are extracted and analyzed under various operating conditions. The obtained data are combined with literature datasets to evaluate existing droplet size correlations. The results show that current droplet size correlations do not accurately predict the data. Therefore, a new droplet size correlation based on the droplet Weber number is developed, demonstrating good predictive performance over a range of operating conditions.