Out-of-phase flashing-induced instabilities in a natural circulation two-phase system with parallel channels

For the first time flashing-induced out-of-phase oscillations are observed in a natural circulation loop operated at low pressure. Both regular (symmetric) and irregular oscillations patterns have been found. Simulations with the best-estimate thermal-hydraulic code ATHLET (developed by GRS, Germany) have been performed to get deeper insight in the phenomenology of the instability.
The main characteristics of the flow oscillations are illustrated and the relation between fluid travelling time and oscillation period is studied.