Study on flow instability in natural circulation loop with parallel channels under moving condition.

• The additional forces caused by motion are considered in the instability model. • The natural circulation instability will be slightly extended affected by motion. • Inclination and rolling tend to destabilize the parallel channels system. • The loop flow fluctuation does not contribute much to the parallel instability. In this study, the mathematical models suitable for natural circulation, parallel channels, and general forms of additional force under moving conditions were established. An analysis code was developed using SIMPLE algorithm. Based on the validated code, the natural circulation and parallel flow instability under typical moving conditions such as inclination, rolling, heaving, and coupled motion were discussed, and the corresponding flow instability boundaries were obtained. The results show that under the moving conditions, the natural circulation flow change is manifested as the superposition of the two-phase instability fluctuation and the motion-induced fluctuation. The heaving condition has the most drastic effect on flow rate with fluctuation amplitude exceeding 30%, but the average flow rate remains unchanged. The boundary of natural circulation flow instability will be slightly extended affected by motions and the variation of the boundary quality is less than 0.03. The inclination and rolling tend to destabilize the parallel channels system and reduce the boundary quality by more than 0.1, whereas the effect of heaving on the parallel instability is not significant. For the parallel flow instability, the adverse effect is mainly attributed to the decrease of the mean flow rate at the entrance of the parallel channels caused by the motions, while the flow re-distribution between parallel channels and natural circulation flow fluctuation induced by the moving conditions do not contribute much. [ABSTRACT FROM AUTHOR]