Transient Critical Heat Fluxes of Subcooled Water Flow Boiling in a Short SUS304-Tube With Twisted-Tape Insert

The transient critical heat fluxes (transient CHFs) in a short SUS304-tube with twisted-tape insert are systematically measured for mass velocities (G = 3997.79 to 13419.8 kg/m²s), inlet liquid temperatures (T_in = 293.55 to 300.85 K), outlet pressures (P_out = 825.19 to 860.95 kPa) and exponentially increasing heat inputs (Q = Q₀exp(t/τ), τ = 26.85 ms to 8.42 s) 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 = 59.4 mm), effective length (L_eff = 49.4 mm), L/d (= 9.9), L_eff/d (= 8.23) and wall thickness (δ = 0.5 mm) with average surface roughness (Ra = 3.89 μm) is used in this work. The SUS304 twisted-tape with width (w = 5.6 mm), thickness (δ_T = 0.6 mm), total length (l = 372 mm) and twist ratio, y [= H/d = (pitch of 180° rotation)/d], of 3.37 is used. The transient CHFs for a short SUS304-tube with twisted-tape insert are compared with authors’ steady-state CHF data for a short SUS304-tube with various twisted-tape inserts, their transient CHF data for the empty SUS304-tube and the values calculated by authors’ steady-state CHF correlations for the test tubes with various twisted-tape inserts and their transient CHF correlations for the empty test tubes. The influences of twisted-tape insert, heating rate and swirl velocity on the transient CHF are investigated into details and the widely and precisely predictable correlations of the transient CHF for the test tube with twisted-tape insert are given based on the experimental data. The correlations can describe the transient CHFs for a short SUS304-tube with twisted-tape of y = 3.37 obtained in this work within −27 to 7.9 % difference.