In this study, it Splitomicin is firmly confirmed that the steady-state CHF correlations against outlet and inlet subcoolings, Eqs. (21) and (22), can delineate not only the authors’ published CHF data (3206 points) for the HORIZONTAL and VERTICAL SUS304 test tubes with the wide ranges of inlet pressures (Pin = 159 kPa to 1.1 MPa), inner diameters (d = 2–12 mm), heated lengths (L = 22–150 mm) and flow velocities (u = 4.0–13.3 m/s) [17], [18], [24], [25], [26], [27], [28], [29] and [30] within ±15% difference for 30 K ? ΔTsub,out ? 140 K and 40 K ? ΔTsub,in ? 151 K but also the flow transient CHF for the circular tube of 6 mm inner diameter obtained in this work within −34.1% to 15.4% and −39.7% to 0.55% differences, respectively. We have supposed that the expressions of flow velocity map (ucr/ucr,st versus α) and critical heat flux one (qcr,sub/q0 versus α) at flow transient CHF against steady-state critical heat flux would be very useful to discuss the mechanism of the transient critical heat flux of subcooled water flow boiling caused by a rapid decrease in velocity, which would occur due to the hydro-dynamic instability suggested by Kutateladze [31] and Zuber [32] or due to the heterogeneous spontaneous nucleation at the lower limit of the heterogeneous spontaneous nucleation temperature [33]. The ratios of flow velocity at flow transient CHF point to flow velocity calculated from Eq. (22) with initial heat flux, q0, by a try-and-error method, ucr/ucr,st, and ossification of flow transient CHF, qcr,sub = q0, to steady-state critical heat flux calculated from Eq. (22) with the flow velocity at flow transient CHF point, (qcr,sub/qcr,sub,st), for the SUS304 circular test tube of d = 6 mm and L = 59.5–59.7 mm with inlet liquid temperatures, Tin, of 290.12–308.51 K at the initial flow velocities, u0, of 6.9, 9.9 and 13.3 m/s are shown versus the deceleration caused by a rapid decrease in velocity, α, at initial heat flux, q0, which is equivalent to the CHF at the flow velocity of 4 m/s, (qcr,sub,st)u=4m/s, in Fig. 18. The experimental data of ucr/ucr,st and qcr,sub/qcr,sub,st for the SUS304 test tube of d = 6 mm with the rough finished inner surface can be expressed for the α ranging from −7.357 m/s2 to −0.326 m/s2 by the following correlations:equation(26)ucrucr,st=-0.275α+0.794forα≤-0.75m/s2equation(27)ucrucr,st=1for-0.75m/s2<α<-0.326m/s2equation(28)qcr,subqcr,sub,st=0.05α+1.038forα<-0.75m/s2equation(29)qcr,subqcr,sub,st=1for-0.75m/s2<α<-0.326m/s2