HEAT TRANSFER AND CRITICAL HEAT FLUX OF SUBCOOLED WATER FLOW BOILING IN A SUS304-TUBE WITH TWISTED-TAPE INSERT

The subcooled boiling heat transfer (HT) and the steady-state critical heat fluxes (CHFs) in a short SUS304-tube with twisted-tape insert are systematically measured for mass velocities (G=4016 to 13950 kg/m(2)s), inlet liquid temperatures (T-in=285.82 to 363.96 K), outlet pressures (P-out=764.76 to 889.02 kPa) and exponentially increasing heat input (Q=Q(0) exp(t/tau), tau=8.5s) by the experimental water loop comprised of a multistage canned-type circulation pump controlled by an inverter. The SUS304 test tube of inner diameter (d=6 mm), heated length (L=59.5 mm), effective length (L-eff=49.1 mm), L/d (=9.92), L-eff/d (=8.18) and wall thickness (delta=0.5 mm) with average surface roughness (Ra=3.89 mu m) is used in this work. The SUS304 twisted tape with twist ratios, y [=H/d=(pitch of 180 degrees rotation)/d], of 2.39, 3.39 and 4.45 are used. The relations between inner surface temperatures and heat fluxes for the SUS304-tubes with various twisted-tape inserts are clarified from non-boiling to CHF. The subcooled boiling heat transfers for SUS304-tubes with various twisted-tape inserts are compared with our empty SUS304-tube data and the values calculated by our and other workers' correlations for the subcooled boiling heat transfer. The influences of the twisted-tape insert, the twist ratio and the swirl velocity on the subcooled boiling heat transfer and the CHFs are investigated into details and the widely and precisely predictable correlations of the subcooled boiling heat transfer and the CHFs for turbulent flow of water in the SUS304-tubes with twisted-tape inserts are given based on the experimental data. The correlations can describe the subcooled boiling heat transfer coefficients and the CHFs obtained in this work within -25 to +15 % difference.