Boundary condition effects on the flow stability in a toroidal thermosyphon

The toroidal thermosyphon is widely used in solar water systems, nuclear reactors and geothermal energy systems, etc. The flow stability has been the main research topic but little attention was paid to the influence of boundary conditions. An experiment was performed on a copper torus. The Lorenz-like chaotic flow was not observed in clear contrast to that in the usual glass torus. Numerical simulation showed that the axial heat conduction in the tube wall deformed the heat flux distribution. A one-dimensional model generally formulated the boundary condition effects on the Hopf bifurcation. The model suggested that the metal wall could efficiently eliminate temperature perturbation, decrease the driving force and hence stabilize the global flow. The model was also used to analyze the effect of torus tilt angle on flow stability, whose conclusion agreed with previous experiment.