A Procedure to Predict Subcooled-Water-Flow-Boiling CHF in Uniformly Heated Tubes for High-Heat-Flux Applications

A model to predict critical heat flux (CHF) for high-heat-flux subcooled flow boiling in uniformly heated tubes is proposed. The present CHF model is based on the mechanism of wall-attached bubble coalescence. To take into account the enhanced condensation due to high subcooling and high mass velocity in small-diameter tubes, a mechanistic approach is adopted to evaluate the nonequilibrium flow quality and void fraction in the subcooled water flow boiling. Comparison of the model predictions against ~3100 subcooled water CHF data shows relatively good agreement over a wide range of parameters that covers the operating conditions of fusion reactor components. The operating ranges of the present database cover 0.33 D 37.5 mm, 0.002 L 4 m, 0.1 P 20 MPa, 0.37 G 134 Mg/m²s, 49 h_sub,in 1659 kJ/kg, -1.25 x_em < 0, and 1.05 q_CHF 276 MW/m².