中文摘要：

对方腔内液态金属钠层流自然对流换热过程进行了数值模拟，着重分析了不同热边界条件下瑞利数对方腔自然对流换热过程的影响，得到了腔体局部换热系数分布特点及规律。结果表明，当瑞利数较大时，如大于10。，瑞利数对方腔内液态金属钠自然对流换热过程的影响非常显著。随着瑞利数逐渐减小，无论是腔体侧边换热系数，还是腔体底边换热系数，均与纯导热情况下计算结果间的偏差逐渐减小，表明腔内换热机理逐渐以导热过程为主。

英文摘要：

The numerical simulation was performed on liquid sodium laminar natural convection in square cavity. The distribution characteristics of heat transfer coefficient were obtained, and the effect was emphasized on the analysis of the impact of Rayleigh number upon the natural convective heat transfer process in a square cavity under differ- ent thermal boundary conditions. The results show that the liquid sodium natural heat transfer process is greatly influenced by the Rayleigh number when Rayleigh number is large enough. While when Rayleigh number is smaller than, say 103 , the distributions of natural convective heat transfer coefficients on both the side walls and the bottom wall of the square cavity are almost the same as those of conductive heat transferprocess, respectively. This means that the mechanisms of heat transfer process mainly depend on heat conduction under cases with lower Rayleigh number.