对自然循环系统矩形通道内临界热流密度进行实验研究。研究发现:实验本体增加功率后,环状流液膜蒸干,壁温出现持续快速上升,实验本体出口发生沸腾临界。根据壁温的上升趋势和出口处流体的临界含汽率可以判断自然循环系统出现的临界热流密度(CHF)类型为干涸(Dryout)型。当自然循环系统沸腾临界出现时,自然循环流量出现明显的上升。根据理论分析可知:沸腾临界发生时导致自然循环流量上升的主要原因是环状流转变成弥散流,附在加热壁面的液膜消失,摩擦压降迅速减小。 The critical heat flux density in a rectangular channel of a natural circulation system is experimentally studied. The results show that after the experimental body increases the power, the annular fluid film evaporates and the wall temperature continuously and rapidly rises, and the boiling of the experimental body occurs at the outlet. According to the rising trend of the wall temperature and the critical vapor content of the fluid at the exit, the type of critical heat flux (CHF) appearing in the natural circulation system can be judged as Dryout type. When the circulation of natural circulation appears critical, the natural circulation flow increases obviously. According to the theoretical analysis, it can be seen that the main reason that the natural circulation flow rises when the critical boiling occurs is that the annular flow changes into a diffusive flow, the liquid film attached to the heating wall disappears, and the frictional pressure drop decreases rapidly.