CHF behaviour during pressure, power and/or flow rate simultaneous variations

The present paper deals with the results of an experimental investigation on critical heat flux in forced convective flow boiling during transients caused by simultaneous variations of pressure, flow rate and/or thermal power. The three parameters were varied according to an exponential law for the flow rate and the pressure decrease, and to a ramp and a step law for the input power increase. Experiments were carried out employing a tubolar test section which was electrically and uniformly heated. Test parameters included the flow rate half-flow decay time, several values of the initial power (before the transient) and the final power (at the end of the transient) in the case of step transients, and the slope of the ramp in the case of ramp transients, and the depressurization rate. An analysis of the experimental data was performed using the local conditions approach, and applying the quasi-steady-state method. The effect of the simultaneous variation of two or three main parameters on the time-to-crisis was also analysed for transients in which only one of the parameters was varied