中文摘要：

本文通过数值方法对三种热边界下管内SCO_2的换热特点进行了研究,结果表明,不同于常物性流体,SOO2在三种不同的热边界下局部换热性能有明显差异。研究发现,第一类热边界（恒定壁温）下流体的温升明显快于第二类（恒定热流密度）和第三种热边界条件（与H2O耦合换热）,而第二类和第三种热边界条件虽然壁面热流分布有差异,但SCO2的温升过程及沿程的换热系数分布具有一定相似性。以SCO2为工质,在对管壳式换热器管侧进行简化时,与定壁温边界相比,采用定壁热流边界与实际的双流体耦合换热工况更加接近。

英文摘要：

The flow and heat transfer characteristics of SCO_2 in a vertical tube under three different thermal boundary conditions are numerically studied.It is found that the temperature raise of bulk fluid in a tube is much quicker under the first type thermal boundary condition（constant wall temperature boundary） than under the second type and third kind thermal boundary conditions（constant wall heat flux boundary and two-fluid coupled heat transfer boundary）.Although there are differences in the wall heat flux distribution,the temperature raise process and heat transfer coefficient of SCO_2 along the flow direction have some similarities under the second type and third kind thermal boundary conditions.When using SCO_2 as working fluid,the assumption of constant wall heat flux is more accurate than constant wall temperature in the numerical study of heat exchanger in engineering applications.