Heavy liquid metals are proposed as coolants for subcritical assemblies such as accelerator-driven systems. Particularly lead-
bismuth eutectic is a superior candidate due to its low melting temperature. In that context, fluid- and geometry-specific
thermal-hydraulic experiments play a major role for the design and operation of such systems.
In this work a bundle with 19 rods (8.2 mm in diameter) in a hexagonal lattice with a pitch-to-diameter ratio P/D = 1.4 was
tested in the existing THEADES loop at Karlsruhe Liquid Metal Laboratory of KIT. This vertical test section (870 mm heated
length) includes three grid spacers, where localized instrumentation for both temperature and pressure drop is mounted. For this
geometry and with reactor-representative operating conditions (temperature, velocity, heat flux) forced-convective tests
applying a heat power density up to 100 W/cm2 have been performed.
Based on these results, it can be concluded that within acceptable engineering accuracy, the heat transfer performance for this
case can be well predicted by existing dimensionless correlations originally developed for other fluids, mainly sodium
