Design of a Natural Circulation Experiment to Investigate Flow Stability

A numerical methodology for the study of the stability characteristics of natural circulation systems using molten salts as working fluid is currently under development. This numerical methodology is intended as an aid tool for the design of passive decay heat removal systems for Molten Salt Reactors (MSRs). This paper presents the design of a natural circulation experiment that will be used to test this novel numerical methodology. The experiment has been designed to obtain 2D-like Rayleigh-Bénard cells with laminar flow. Moreover, the experiment will allow to obtain flow conditions close to those encountered in a natural convection system with an internal heat source. As the focus of the methodology is placed on its capability to accurately describe the dynamic behavior of the system, the experiment has been designed to cover a significant range of operational conditions (Rayleigh number) and to obtain distinguishable flow states and the transitions between them. The experiment design robustness has been investigated by performing numerical studies considering various potential bias and uncertainties. In the presented case the principal bias and uncertainties are related to the heating and cooling mechanisms, the wall materials effects and the possible non-negligible interaction with the environment. Results from this study show that an experimental configuration using a flat-cavity geometry will provide meaningful results and a sufficiently complex behavior for testing the methodology without resorting to a system with a turbulent or highly 3D dynamic. Finally, the experiment can operate with a conventional fluid while retaining key phenomena specific to the molten salts.