Experimental and numerical studies on spray cooling of a downward-facing surface under partial coverage of multi-nozzle sprays

Abstract

A new experimental study (aka SPAYCOR-S2) on multi-nozzle spray cooling of a downward-facing heater surface is conducted on the SPAYCOR facility at KTH, to provide data assessing the feasibility of spray cooling for in-vessel melt retention (IVR) in light water reactors. It is intended to investigate the potential for reducing the number of nozzles for spray cooling of an 80 mm × 120 mm surface, from the 2 × 3 nozzle array in the previous study (Bandaru, 2021) to a 2 × 2 nozzle array in the present study. Given the same heater surface, the pitch-to-diameter ratio is enlarged in a 2 × 2 nozzle array, resulting a partial coverage of the spray cones of four nozzles, in contrast with the 2 × 3 nozzle array where the heater surface was fully covered by six-nozzle spray. The tests focus on the cooling performance of such partial coverage of multi-nozzle spray and the effects of heater surface’s inclination angle. The experimental results reveal that the inclination angle of the heat surface has a negligible impact on cooling capacity, although it is slightly higher on the surface inclined at 90° than on the surfaces inclined at 45° or 60°. The maximum steady heat flux of the 2 × 2 nozzle array at its minimum spray flowrate is determined as 1.96 MW/m2. A numerical study on the spray cooling of the 2 × 2 nozzle array is also performed with models in OpenFOAM, which are extended from our previous development (Fang, 2023) by adding models for thin-film boiling and conjugate heat transfer in solid. For validation of the numerical study, the spray cooling of the heater surface inclined at various degrees is simulated, and the results are compared with those of experiment. The simulation generally shows good correspondence with experiments.