Yuanzineng kexue jishu (Jul 2024)
Numerical Analysis of Effect of Hydrogen Migration on Steam Condensation Heat Transfer
Abstract
The condensation heat transfer of steam containing non-condensable gases is crucial for safety analysis in the event of severe accidents in the containment vessel. Previous studies have focused more on the heat transfer characteristics of condensation containing air, while less attention has been paid to the hydrogen-air conditions. The mechanism by which hydrogen migration affects condensation heat transfer is not yet clear. Numerical simulation methods were used to investigate the applicability of the multi-component diffusion coefficient equation under condensation phase change conditions in the paper. Based on experimental data, an effective steam diffusion correction model suitable for hydrogen-air conditions was proposed. Through the validation of experimental data from different scholars, 97% of predicted values have a relative deviation from experimental values maintained within ± 20%. Based on this, the hydrogen migration characteristics near the wall of the heat transfer tube and its effect on the condensation heat transfer coefficient were studied. The results indicate that there are three flow patterns of gas near the condensation surface, namely gravity flow, separation flow, and buoyancy flow. As the relative concentration of hydrogen increases, the gas flow pattern gradually changes from gravity flow to separation flow and buoyancy flow. The change in gas flow pattern will significantly affect the convective mass transfer rate of gas near the condensation surface, which has a stronger impact on condensation heat transfer than diffusion mass transfer. Ultimately, the condensation heat transfer coefficient shows a pattern of first decreasing and then increasing with the increase of relative hydrogen concentration. When the flow pattern of gravity flow is formed near the condensation surface, and an increase in the relative concentration of hydrogen gas will reduce the convective mass transfer rate of the gas near the condensation surface, while also increasing the diffusion mass transfer rate of steam in the mixed gas. The change in convective mass transfer rate plays a dominant role. Therefore, the condensation heat transfer coefficient will exhibit a negative correlation with the relative concentration of hydrogen gas. The condensation heat transfer coefficient is the lowest under the separated flow pattern. When a buoyancy flow is formed near the condensation surface, the convective and diffusive mass transfer rates of gas will increase with the relative concentration of hydrogen, and the heat transfer coefficient shows a positive correlation with the relative concentration of hydrogen. The study results are of great significance for evaluating the heat transfer characteristics of steam condensation after hydrogen release in serious accidents.
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