Water Sprays Cooling of a Hot Metallic Plate

Abstract

In the present work, spray cooling experiments of a hot steel plate were carried out with three different nozzles in order to provide accurate experimental data for the modellers. Special attention was paid to for both the measurement of the surface temperatures and the characterization of the sprays. Firstly, the surface temperatures were measured using K-type thermocouple wires welded directly to the surface of the plate in a separate contact. This technique provides an accurate measurement of the surface temperature during the cooling. Secondly, the spray characteristics of each nozzle were also thoroughly investigated. It was found that the droplet size and velocity distributions of each nozzle followed a log-normal law. The corresponding Sauter mean diameter (SMD) and mean velocity ranged from 170 to 230 µm and from 5.6 m s⁻¹ to 22.4 m s⁻¹, respectively. Spray cooling was started after heating the plate between 500°C and 600°C using a radiant panel. Cooling rates were very high and the time to reach ambient temperature varied from 4 s to 1 min depending on the nozzle used. Heat Flux (\({\dot{q}}^{{\prime}{\prime}}\)) and Heat Transfer Coefficient (HTC) were calculated from the temperature data. It was found that high levels of critical heat flux (CHF), around 9 MW m⁻², were achieved for two of the three nozzles studied, including the one with the lowest flow rate of only 1.6 L min⁻¹. Finally, the results obtained in this study could be used to validate numerical codes such as FDS and FireFOAM, which are commonly used in fire safety engineering.