Dynamic characterization of a single phase square natural circulation loop

Natural circulation loop (NCL) has many applications in the energy sector as a passive heat transfer system. The passive nature of its operation increases the reliability of natural circulation loops and makes them crucial for the safety of the system. However, depending on the operating conditions, the dynamics of the system can vary significantly. For this reason proper analysis of the fluid flow dynamics in the NCL is very important. In this paper instability associated with the loop fluid flow in the NCL is investigated from a dynamical systems perspective with the help of phase plot, Fast Fourier Transform (FFT), correlation dimension and largest Lyapunov exponent. From the numerical analyses it is found that with the increase in heater power, dynamics of the fluid flow in the loop changes significantly. Loop characteristics remain steady up to a certain heater power level but with the increase in heater power level first it shows periodic oscillations and then it shows chaotic behavior. The existence of periodic and chaotic regimes is established using tools of dynamic systems analysis.