Detection of subcooled boiling heat transfer regimes up to critical heat flux by accelerometric equipment

The design of the plasma-facing components of the Next European Torus-International Thermonuclear Experimental Reactor fusion reactor has been addressing the highest requirement in the field of heat transfer thermal hydraulics. The more promising heat transfer technique, among those possible using water as coolant, is based on the subcooled boiling thermal hydraulics in the fully developed regime, with the highest heat transfer coefficient, but avoiding the reaching of the critical heat flux (CHF) and its consequent dangerous burn-out. To this aim an experimental activity was launched in order to optimize the material, the physical parameters and the structure geometry. Among others, an objective of this work is the development of an experimental system for the detection of the subcooled boiling phenomenon covering the whole heat transfer regime, on externally heated cylindrical channels, from the single phase up to the CHF. The principle is based on the recording, by using quartz accelerometers, of the bubble implosion noises transmitted by the structure in the proximity of the collapsing regions.