Two-dimensional numerical analysis of a rectangular closed-loop thermosiphon

The study presents a numerical investigation of the dynamical behavior of a rectangular natural circulation loop with horizontal heat exchanging sections. The study has been developed in a two-dimensional domain considering uniform wall temperatures, UWT, at the horizontal sections and thermally insulated vertical legs as thermal boundary conditions. The governing equations have been solved using a control volume method solving the velocity-pressure coupling with the SIMPLER algorithm. The analysis has been performed for a fixed geometry of the loop and for various Rayleigh numbers, separating the values of Rayleigh for which the system manifests stable and unstable dynamics. In the last case, it is shown that the vortices are responsible for the birth of the oscillations and for the growth of temperature gradients.