Subcooled flow boiling heat transfer of water in a circular tube under high heat fluxes and high mass fluxes

Subcooled flow boiling under high heat flux and high mass flux (HHHM) conditions is commonly encountered in nuclear power engineering, for example, the heat removal technology for divertors in the International Thermonuclear Experimental Reactor (ITER). In the present study, subcooled flow boiling heat transfer of water was carried out experimentally in a uniformly heated vertical circular tube with an inner diameter of 9.0 mm under HHHM conditions. Heat transfer coefficients were presented from single-phase convection to fully developed nucleate boiling. The effects of parameters, including mass flux (G = 6000, 8000, and 10,000 kg/m2 s), heat flux (q = 5-12.5 MW/m2), system pressure (P = 3, 4.2, and 5 MPa), and thermodynamic vapor quality (xth = −0.5 to −0.03), were discussed. Many previous heat transfer correlations available in the literature were assessed against our experimental data. Most of these correlations cannot predict the experimental data very well. A modified Chen correlation was developed, which predicted the total heat transfer coefficients with a mean average error of 1.11% and a root-mean-square error of 6.45%. A modified Lahey model was proposed to determine the contribution of nucleate boiling in the total heat transfer coefficient under HHHM conditions.