Nonlinear analysis of a rectangular natural circulation loop

The aim of this paper is to present a novel approach to the analysis of the dynamical evolution of a rectangular natural circulation loop heated from below. During an experimental phase nonlinear temperature oscillations were detected at different location and for various unstable operating conditions of the loop. The experimental time series were intially filtered using wavelet packet approach. Afterwards, Singular Value Decomposition (SVD) was applied, so to reduce the filtered signals to their dominant features, and the calculation of the Average Mutual Information (AMI) function was performed. Both these approaches were adopted in order both to take into account the intrinsic nonlinear behavior of detected temperatures and to obtain a simplified phase space representation of the dynamics of the system. Such a representation was used to determine the System Dimension, whose knowledge represents the first step in the analysis of any dynamical system. Finally, phase space representations of various operating conditions show the presence of dynamical behaviors characterized by different values of the system dimension, pointing out the possible existence of chaos in the system in study.