DROPLET SIZE AND VELOCITY MEASUREMENTS AT THE OUTLET OF A HOLLOW CONE SPRAY NOZZLE

During the course of a severe accident in a nuclear pressurized water reactor (PWR), hydrogen may be produced by reactor core oxidation and distributed into the containment. Spray systems are used in order to limit overpressure, enhance the gas mixing, avoid hydrogen accumulation, and wash out fission products. In order to simulate these phenomena with computational fluid dynamics codes, it is first necessary to know the droplet size and velocity distributions close to the outlet nozzle. Furthermore, since most of the phenomena relative to droplets (condensation, gas entrainment, and collisions) are of particular importance in the region just below the nozzle, accurate input data are needed for real-scale PWR calculations. The objective is, therefore, to determine experimentally these input data under atmospheric conditions. Experimental measurements were performed on a single spray nozzle, which is routinely set up in many PWRs. This nozzle is generally used with water at a relative pressure supply of 3.5 bar, producing a mass flow rate of approximately 1 kg/s. At a distance of 20 cm, in which under ambient conditions atomization is just achieved, it is found that the geometric mean diameter varies from 280 to 340 mu m, the Sauter mean diameter varies from 430 to 520 mu m, and the mean axial velocity varies from 14 to 20 m/s. The radial velocity is around 7 m/s, whereas the orthoradial velocity is almost equal to zero at this distance of the nozzle. Gas velocity measurements around the spray are also performed.