Rewetting Velocity of High-Temperature Vertical-Narrow-Annular Flow Passages Under Counter-Current Flow Condition

Quenching of a thin gap annular flow passage by gravitational liquid penetration was examined experimentally by using R-113. The outer wall was made of copper. The inner wall was made of copper or glass. The inner diameter of the outer wall of the annular flow passages was 40 or 41 mm and the annular gap clearance δ was 0.5, 1.0, 2.0 and 5.0 mm. The outer wall was heated initially up to 250 °C and also the inner wall was heated when the copper inner wall was used. The quenching was observed in δ ≥ 1.0 mm. When δ = 0.5 mm, the wall was just gradually cooled down. The relation between the wall superheat and the heat flux during quenching process was similar to the boiling curve of pool boiling. However, the peak heat flux as well as the heat flux in the film and the transition boiling was lower than those in the pool boiling. These heat fluxes became lower as the gap clearance became narrow. The rewetting velocity became slow as the gap clearance became narrow. The rewetting velocity seemed to have a unique relation for the Peclet number Pe = (ρ_SC_Sδ_SU/λ_S) and the Biot number Bi = $hδs/λs$ ; Pe ∝ $Bi$ which was the same as that of the Yamanouchi correlation. A decrease in the heat flux (the heat transfer coefficient) in the rewetting front region, which corresponds to the peak heat flux, results in a decrease in the rewetting velocity as the gap clearance becomes narrow.