Dispersed-Flow Film Boiling Heat Transfer Data near Spacer Grids in a Rod Bundle

A series of steady-state film boiling experiments have been conducted to show the effect of spacer grids on rod bundle heat transfer. Experiments were performed at the Oak Ridge National Laboratory in the Thermal-Hydraulic Test Facility, a pressurized water loop containing a 64-rod bundle, of which 60 rods are electrically heated. The bundle is equipped with detailed thermometry around two grids, which allows grid heat transfer effects to be studied. Rod surface temperature data show a 75 to 150 K temperature difference between measurements upstream and downstream of the grids, while heat transfer coefficients increase across the grids by 20%. Twenty to thirty hydraulic diameters are required for these effects to dissipate.