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

Abstract

The transient critical heat fluxes (transient CHFs) in SUS304circular tubes with various twistedtape inserts are systematically measured for mass velocities (G = 3988–13,620 kg/m2s), inlet liquid temperatures (Tin = 287.55–313.14 K), outlet pressures (Pout = 805.11–870.23 kPa) and exponentially increasing heat inputs (Q = Q0 exp(t/د„), exponential periods, د„, of 28.39 ms to 8.43 s) by the experimental water loop comprised of a multistage cannedtype circulation pump controlled by an inverter. The SUS304circular 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 (خ´â€‰= 0.5 mm) with average surface roughness (Ra = 3.89 خ¼m) is used in this work. The SUS304 twistedtapes with twist ratios, y [H/d = (pitch of 180 deg rotation)/d], of 2.40 and 4.45 are used. The transient critical heat fluxes for SUS304circular tubes with the twistedtapes of y = 2.40 and 4.45 are compared with authors' transient CHF data for the empty SUS304circular tube and a SUS304circular tube with the twistedtape of y = 3.37, and the values calculated by authors' transient CHF correlations for the empty circular tube and the circular tube with twistedtape 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 twistedtape inserts are given based on the experimental data. The correlations can describe the transient CHFs for SUS304circular tubes with various twistedtapes of twist ratios (y = 2.40, 3.37, and 4.45) in the wide experimental ranges of exponential periods (د„ = 28.39 ms to 8.43 s) and swirl velocities (usw = 5.04–20.72 m/s) obtained in this work within −26.19% to 14.03% difference. The mechanism of the subcooled flow boiling critical heat flux in a circular tube with twistedtape insert is discussed.