中文摘要：

为分析不同热工参数对强迫循环向自然循环过渡过程及稳定自然循环阶段传热及流动特性的影响,在内径为6mm的竖直实验段内开展实验,研究不同入口过冷度、热流密度及初始流量对强迫循环向自然循环过渡过程以及稳定自然循环过程的影响。实验结果表明：入口过冷度及热流密度对自然循环向强迫循环过渡过程及稳定自然循环过程的换热能力有明显影响,而初始流量对该过渡过程及稳定自然循环的换热能力的影响并不显著。

英文摘要：

In order to analyze the influence of different thermal parameters on the characteristics of heat transfer and flowing during the transition from forced circulation to natural circulation and during the stable natural circulation,the experimental study was carried out in a vertical test section with 6 mm inner diameter.The experiment was carried out under different thermal-hydraulic conditions,including different inlet subcoolings,heat fluxes and initial mass fluxes.The experimental results show that the inlet subcooling and heat flux have great effect on the characteristics of flowing and the heat transfer during the transition from forced circulation to natural circulation,and also during the stable natural circulation period.However,the effect of the initial mass flux is not significant.