Temperature Effects on Interfacial Area Concentration and Void Fraction in LBE-N2 Bubbly Flow

Temperature-dependent local two-phase flow parameters in lead–bismuth eutectic (LBE)–gas bubbly flows are essential for validating the closure models used in safety analyses of steam generator or heat exchanger tube rupture accidents in lead-cooled fast reactors. However, published measurements are limited to temperatures of 250 °C and below. Therefore, separate-effects experiments on LBE–nitrogen bubbly flow were conducted in the SZU-LEAF loop using a four-sensor conductivity probe, extending the experimental database to 400 °C. The local void fraction (α), bubble frequency (fb), bubble velocity (vb), equivalent bubble radius (Rb), and interfacial area concentration (IAC) were measured at three axial locations at 200, 250, and 300 °C under four gas–liquid flow rate conditions. Except for the low-gas/low-liquid baseline, the cross-sectionally averaged IAC increased by 28–78% over 200–300 °C. The increase in IAC exceeded that expected solely from gas expansion, suggesting that temperature-dependent liquid properties may modify bubble dynamics. This temperature effect may be associated with turbulence-related flow conditions: IAC was nearly temperature-insensitive at the lowest flow rate but increased by 78% at the highest. The Shen–Hibiki IAC correlation agreed reasonably well with the measurements at 200 and 250 °C but underpredicted the IAC at 300 °C and insufficiently captured its temperature dependence. Additionally, local void fraction distributions were measured at the enhanced temperature range of 325–400 °C. The cross-sectionally averaged void fraction increased systematically relative to its value at 300 °C, with the magnitude of the increase being broadly consistent with that expected from gas thermal expansion. These measurements extend radial void fraction data for LBE bubbly flow to 400 °C and provide benchmarks for high-temperature two-phase flow models.