Heat transfer and critical heat flux of subcooled water flow boiling in a short horizontal tube

The steady-state turbulent heat transfer (THT) due to exponentially increasing heat inputs with various exponential periods (Q=Q₀exp(t/τ), τ=6.55 to 21.81 s) were systematically measured with the flow velocities, u, of 4.15, 7.05, 10.07 and 13.50 m/s by an experimental water loop flow. Measurements were made on a 6 mm inner diameter, a 59.2 mm effective length and a 0.4 mm thickness of HORIZONTAL Platinum (Pt) circular test tube. The relation between the steady-state turbulent heat transfer and the flow velocity were clarified. The steady state nucleate boiling heat transfer (NBHT) and the steady state critical heat fluxes (CHFs) of the subcooled water flow boiling for HORIZONTAL SUS304 circular test tube were systematically measured with the flow velocities (u=3.94 to 13.86 m/s), the inlet subcoolings (ΔT_sub,in=81.30 to 147.94 K), the inlet pressures (P_in=786.29 to 960.93 kPa) and the increasing heat input (Q₀ exp(t/τ), τ=8.36 s). The HORIZONTAL SUS304 test tube of inner diameter (d=6 mm), heated length (L=59.4 mm), effective length (L_eff=48.4 mm), L/d (=9.9), L_eff/d (=8.06) and wall thickness (δ=0.5 mm) with surface roughness (Ra=3.89 μm) was used in this work. The NBHT and the steady state CHFs of the subcooled water flow boiling for the HORIZONTAL SUS304 test tube were clarified at the flow velocities u ranging from 3.94 to 13.86 m/s. The steady-state THT data, the NBHT ones and the steady state CHF ones were compared with the values calculated by authors' THT correlation, their NBHT ones and their transient CHF ones against outlet and inlet subcoolings based on the experimental data for the VERTICAL circular test tubes with the flow velocities u ranging from 4.0 to 42.4 m/s. The influences of test tube orientation on the THT, the NBHT and the subcooled flow boiling CHF are investigated into details and the widely and precisely predictable correlations of the THT, the NBHT and the transient CHFs against outlet and inlet subcoolings in a short HORIZONTAL circular test tube are derived based on the experimental data. The THT correlation, the NBHT ones and the transient CHF ones for the HORIZONTAL test tube can describe the THT data, the NBHT ones and the subcooled flow boiling CHF ones for the wide ranges of ΔT_sub,in, u and τ obtained in this work within ±15 % difference. (author)