Transient Critical Heat Fluxes of Subcooled Water Flow Boiling in a SUS304-Circular Tube With Various Twisted-Tape Inserts (Influence of Twist Ratio)

Abstract

The transient critical heat fluxes in SUS304-circular tubes with various twisted-tape inserts are systematically measured for mass velocities (G = 3988 to 13620 kg/m2s), inlet liquid temperatures (Tin = 287.55 to 313.14 K), outlet pressures (Pout = 805.11 to 870.23 kPa) and exponentially increasing heat inputs (Q = Q0exp(t/τ), τ = 28.39 ms to 8.43 s) by the experimental water loop comprised of a multistage canned-type circulation pump controlled by an inverter. The SUS304-circular tube of inner diameter (d = 6 mm), heated length (L = 59.4 mm), effective length (Leff = 49.4 mm), L/d (= 9.9), Leff/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 tapes with twist ratios, y [= H/d = (pitch of 180° rotation)/d], of 2.40 and 4.45 are used. The transient critical heat fluxes for SUS304-circular tubes with various twisted-tape inserts are compared with authors’ transient CHF data for the empty SUS304-circular tube and a SUS304-circular tube with twisted-tape of y = 3.37, and the values calculated by authors’ transient CHF correlations for the empty circular tube and the circular tube with twisted-tape insert. The influences of heating rate, twist ratio and swirl velocity on the transient CHF are investigated into details and the widely and precisely predictable correlations of the transient CHF against inlet and outlet subcoolings for the circular tubes with various twisted-tape inserts are given based on the experimental data. The correlations can describe the transient CHFs for SUS304-tubes with various twisted-tape inserts obtained in this work within −27 to 7.9% difference.