Transient Critical Heat Fluxes of Subcooled Water Flow Boiling in a Short Vertical Tube Caused by Exponentially Increasing Heat Inputs

Abstract

The transient critical heat fluxes (CHFs) of the subcooled water flow boiling for the flow velocities (u=4.0–13.3m∕s), the inlet subcoolings (ΔTsub,in=68.08–161.12K), the inlet pressures (Pin=718.31–1314.62kPa), the dissolved oxygen concentrations (O2=2.94ppm to the saturated one), and the exponentially increasing heat inputs (Q0exp(t∕τ), τ=16.82msto15.52s) are systematically measured with an experimental water loop comprised of a pressurizer. The SUS304 tubes of the inner diameters (d=3mm, 6mm, 9mm, and 12mm), heated lengths (L=33.15–132.9mm), L∕d=5.48–11.08, and wall thickness (δ=0.3mm and 0.5mm) with the rough finished inner surface (surface roughness, Ra=3.18μm) are used in this work. The transient CHF data (qcr,sub=6.91–60MW∕m2) are compared with the values calculated by the steady state CHF correlations against inlet and outlet subcoolings. The transient CHF correlations against inlet and outlet subcoolings are derived based on the experimental data. The dominant mechanisms of the subcooled flow boiling CHF for a high heating rate are discussed.

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

“…The transient CHFs, q cr,sub , are almost constant for the exponential period, τ, higher than around 800 ms and they become higher with the decrease in the τ. Those show nearly the same trend of dependence on transient CHF data for empty SUS304-tubes of d=3, 6, 9 and 12 mm with the exponentially increasing heat input (13)(14)(15) , although the SUS304 twisted-tape of width (w=5.6 mm), thickness (δ T =0.6 mm), total length (l=372 mm) and twist ratio (1) and (2). The transient CHF experiments with rapidly increasing temperature are very severe for test tube and these SUS304 tubes were not the same serial number but the same manufacturer.…”

“…Equation (23) can also describe these ratios for the p* ranging from 48.21 to 5.196×10 3 (49 points) within ±50 % difference. Equation (23) was derived based on the experimental data on an empty SUS304-tube for the inner diameters of 3, 6, 9 and 12 mm and the heated lengths of 33.15 to 132.9 mm with L/d=5.48 to 11.075 at the outlet pressures of around 800 and 1100 kPa with the exponentially increasing heat input (13)(14)(15) . The transient CHF correlation against inlet subcooling for the test tubes with various twisted-tape inserts is derived due to the effect of boiling number based on swirl velocity, Bo cr,sw , and Weber number based on swirl velocity, We sw , on the basis of Eq.…”

“…First is to measure the transient CHFs for SUS304-tube with a twisted-tape of twist ratio (y) of 3.37 for the wide ranges of heating rates (τ), swirl velocities (u sw ) and inlet subcoolings (ΔT sub,in ). Second is to compare the above results with the steady-state CHF data for the SUS304-circular tubes with various twisted-tape inserts (10)(11)(12) and the transient CHF data for the empty SUS304-tubes previously obtained (13)(14)(15) . Third is to clarify the influence of twisted-tape insert, heating rate and swirl velocity on the transient CHF.…”

“…And the steady-state CHF correlations against inlet and outlet subcoolings for the test tubes with various twisted-tape inserts are derived as follows due to the effect of boiling number based on swirl velocity, Bo cr,sw , and Weber number based on swirl velocity, We sw . (5) and (6) (13)(14)(15) .…”

Transient critical heat flux for subcooled boiling of water flowing upward through a vertical small-diameter tube with exponentially increasing heat inputs

“…Celata et al (1992) experimentally investigated the power transient CHF for subcooled boiling in vertical tubes containing R-12 (dichlorodifluoromethane). Hata and Noda (2008) and Hata and Masuzaki (2010) conducted both steady-state and transient experiments on subcooled boiling of water flowing upwards in vertical tubes with various inner diameters while exponentially increasing the heat inputs. They clarified the effects of length-to-diameter ratio (L/d), inlet and outlet subcooling, and the e-folding time.…”