Natural circulation systems are broadly used in marine environments. When accidents happen, these systems may work under inclined condition. In this paper, we conducted a series of experimental study on the thermohydraulics behavior of natural circulation in a symmetric two-circuit loop under the inclined angle from 0∼45°. A CFD model is also set up and predicts the results well in comparing with the experiments. Both experimental and numerical analysis show that with the increase of inclined angle, the total circulation flow rate decreases. When the loop inclines about the axis perpendicular to the circulation, one circulation is depressed while the other is enhanced; accordingly the disparity between the branch circulations arises and increases with the increase of inclined angle. The flow pattern of the circulation under larger inclined angle (45∼90°) condition is also studied by CFD model. At large inclined angle the circulation is mainly happens in one circuit. Also based on this model, the influences of flow resistance distribution and loop configuration on natural circulation are predicted. The numerical results show that to design the loop with the configuration of big altitude difference and small width are favorable to confine the influence of inclination; however too small loop width will cause sever reduction of circulation ability in large angle inclination.

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