Instability of Single-phase Natural Circulation Under Double Loop Systemfn1

Abstract The natural circulation in a single loop system has been studied by many researchers. In a multiple loop system, the instability of natural circulation is more complicated because of the interaction between the loops. In this study, the effects of the multiple loops on the natural circulation instability were investigated numerically. The double loop system with one heating tube and two cooling tubes were evaluated. The one-dimensional energy and momentum equations were solved using the Finite Difference Method. The flow regimes of the instability were evaluated with variations in the heat flux and the initial velocity condition. In a double loop system, the observed flow was classified into five regimes, namely, steady, transient–CS, transient–CS⧹CL, transient–CL and complex chaotic regimes, which were more complicated than those observed in single loop system. The flow regimes were qualitatively explained by the stability of the attractor in the phase space. The complexity of the regime was caused by the coexistence of two attractors.