Abstract:

The subcooled boiling flow of water in a vertical tube under high pressure and high subcooling condition was numerically simulated using the two-fluid model, in which the bubble diameter model was a key factor to describe the subcooled boiling process. The influence of bubble diameter on the wall heat transfer was revealed by comparing different bubble diameter models, and the model suitable for high pressure was determined. The influence of pressure and wall heat flux on the flow and heat transfer characteristics was investigated. The calculation results show that the bubble departure diameter decreases with increasing pressure,which leads to the increase in the proportion of single-phase convective heat transfer and the decrease in the surface heat transfer coefficient. Moreover,the extremely nonuniform distribution of bubbles strongly depends on the characteristics of high pressure and high subcooling. Bubbles are aggregated near the wall with the increase of wall heat flux, which has significant influence on heat transfer characteristics of subcooled boiling process.

摘要：

采用双流体模型对高压高过冷度下垂直圆管中水的过冷流动沸腾进行了数值模拟。通过对比不同气泡直径模型，揭示了气泡直径对于壁面传热方式的影响，确定了适合高压工况的气泡直径模型。考察了压力及壁面热通量对流动及传热特性的影响。计算结果表明，压力增加气泡脱离直径减小，单相对流传热所占比例增加，表面传热系数减小。高压高过冷度特征决定了气泡相分布极不均匀，随着热通量的增加，壁面附近容易形成气泡的密集，对过冷流动沸腾中的传热特性有重要影响。