Study on characteristics of water film breakdown on the corrugated plate wall under the horizontal shear of airflow

摘要

The corrugated plate (CP) dryer is a very important component for the steam-water separation in the steam generator because the separation efficiency influences the overall thermal efficiency of a nuclear power plant. Carryover and breakdown phenomena of the water film at the corner of the CP have a great impact on the steam-water separation effect. The study of the complicated steam-water separation mechanism is beneficial to improving its efficiency. Breakdown and flow characteristics under horizontal shear of water film falling down from the vertical CP is studied. Water and air are used as the two phases in the study. This paper derives and validates a model for calculating the critical airflow velocity of water film breakdown at the corner of the CP. On the basis of the hydrodynamics theory and applying the image processing method, the relationship between water film thickness and critical airflow velocity of water film breakdown is investigated through an experiment. Additionally, the water film thickness is measured with the application of the Charge Coupled Device (CCD) high-speed camera acquisition system. The Planar Laser Induced Fluorescence (PLIF) method is applied for the water thickness measurement in the experiment. Results reveal that the critical airflow velocity of water film breakdown is related to the CP structural parameters, properties of the two phases and water film thickness. Comparison of the experimental result and the result calculated by the model is performed as well. The results calculated by the developed model are in good agreement with the obtained experimental results as the water film thickness is large in a certain range. The results show that the critical airflow velocity of water film breakdown and the water film thickness are negatively correlated. In order to analyze the factors contributing to the critical airflow velocity of water film breakdown, three novel parameters are introduced firstly. In particular, the results reveal that a larger value of parameters is better to the increase of the critical airflow velocity of water film breakdown. And when the flexural angle of the CP corner is approximately 27 degrees, the steam-water separation performs best. It recommends that the flexural angle of the CP corner should not exceed 43.2 degrees.