Laminar natural convection with a pair of hot and cold tube in a closed cubic cavity is carried out. This configuration can be founded in performance of nuclear power plant containment passive residual heat removal system. The basic government aquations are sloved by means of finite volume method. The effect of Ra number (103–106), shape of tube and spatial position on local and mean heat transfer characteristics is studied. It is found that the Nu number increased when raising Ra number. The Nu number is higher when the shapes are circle and triangle. In adddition, it is founded that the heat transfer has a better effect when the cold tube locates above the hot tube among the five spatial positions. The results provides theoretical basis for performance of nuclear power plant containment passive residual heat removal system.

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