Flow transients have been investigated in a wide range of thermohydraulic situations employing Refrigerant-12. Six pressures (including the reference to PWR and BWR characteristic liquid to vapour densities ratios), several periods of the flowrate transients coast-down during the simulated flow decays, and different specific mass flow rates have been studied.
The experimental data have shown a complete inadequacy of steady-state critical heat flux correlations in predicting the onset of boiling crisis during fast flow transients (half-flow decay time, t_h <5.0÷6.0 s). The time interval from the start of the flow rate transient to the onset of dry-out has been experimentally determined for all the runs. Data analysis for a better theoretical prediction of the phenomenon has been accomplished, with the introduction of describing parameters.