超临界压力水在水平同心套管间自然对流换热研究

通过数值计算深入分析了超临界压力条件下水的强烈的物性变化及对流换热的边界条件对水平同心套管间自然对流换热的影响规律，并为高新技术的发展提供一定的理论基础。采用求解原始变量的有限差分法，并利用大型通用计算程序ＰＨＯＥＮＩＣＳ，对控制方程组进行了数值求解。分析了在内、外管表面均为等壁温边界条件或内管为常热流、外管为等壁温边界条件下，同心套管间的流场和温度场；研究了强烈的变物性、内外表面温差及内管壁面上的热流密度等对内、外管壁上自然对流换热系数的影响规律。结果发现：在内管表面热流密度相同的条件下，不同的外管表面温度所对应的内、外管表面温差及对流换热系数有比较大的差异；在某些条件下，随着热流密度的升高，尽管套管内自然对流流速增大，但是自然对流换热能力却下降。

Natural convection heat transfer of water at super-critical pressures in a horizontal annulus

In order to provide a theoretical basis for new technology development. The influence of the sharp variation of thermophysical properties of super critical water and the boundary conditions on the natural convection heat transfer in an annulus was studied. The differential equations for steady state laminar natural convection of water at super critical pressures in a horizontal annulus were solved numerically using the finite difference method and PHOENICS. The flow fields and temperature fields were presented for different boundary conditions. The influence of variable fluid thermophysical properties, the temperature difference between the inner and outer cylinders and the heat flux on the inner cylinder surface on the natural convection heat transfer was analyzed. The results show that for a given heat flux at the inner surface, varying the outer surface temperature can cause significant variation of the temperature difference between the inner and outer surfaces and the convection heat transfer coefficients on both surfaces and for some conditions, the natural convection heat transfer will decrease as the heat flux on the inner surface increased although the natural convection velocities increase.