Comparison of the dynamical behaviour of rectangular natural circulation loops

Abstract

This paper presents a comparison of the dynamical behaviours manifested by two singlephase experimental natural circulation loops. Both of the loops are rectangular and symmetric, with a heat source and a heat sink placed respectively at the bottom and at the top of the loop. The main differences between the two loops are their height and width, the inner diameter of their pipes and the length of the heating and cooling sections. In order to emphasize the differences in the dynamical evolution, the comparison was performed considering the same operating conditions. A phase space representation was chosen, so as to guarantee an adequate representation of the complex non-linear process dynamics. The proposed analysis, which is based on the morphological description of the attractors and on the evaluation of their correlation dimension, aims to give a preliminary characterization of the behaviours of the natural circulation loops under comparison. The proposed approach allowed it to be demonstrated that the differences of geometry lead to substantial changes in the dynamics that the two experimental loops may manifest for the same operating condition, defined by the heat power supplied to the fluid. In particular, reported results show that for some values of the heat power one of the experimental loops displays periodic oscillations whereas the other is governed by chaos.