Requirements of high heat flux for fusion reactors components. Revised models and correlations to predict critical heat flux in subcooled flow boiling

The present paper provide an analysis of available experimental data on critical heat flux (CHF) of subcooled flow boiling in water, in the ranges of interest of fusion reactors thermal-hydraulic conditions, i.e. high inlet subcooling and velocity, and small channel diameter and lenght. The aim of the study was to identify a new correlation based on a structure representing the relation of heat balance and using a non-linear regression analysis of the available data-set. The reference data-set covers a wide range of operating conditions in the frame of present interest (0.1 < p < 5.5 MPa; 0.3 < D < 15 mm; 10 < L < 30 cm; 2000 < G < 40000 kg/m2ùs; 90 < DTsub,i < 230 K). In a previous study several correlations were analysed with a reduced data-set respect the present one, and others correlations were recently analyzed by Celata et al., Nariai et al. and Caira et al. Three correlations for critical heat flux, providing a consistent prediction of most of the data-set, were selected, namely Macbeth, Macbeth-Thompson and Gunther correlations. A new correlation, based on the same structure of above and providing a sensible improvement in predictions (an RMS of 15.8% on the entire data-set of 544 points was obtained) was identified and analyzed with respect to various parameters influencing the CHF phenomenon.