Study of the cooling of a metal plate at high temperature by water spraying

Abstract

Experiments to cool a steel plate at high temperature by spraying water droplets were carried out using four different nozzles (TG-SS1, TG-SS3, TG-SS5, TG-SS10), in order to assess their effectiveness. Two plate thicknesses were studied. The surface temperature was measured at several points positioned diagonally on the plate: in the centre, near the edge and in between, using K-type thermocouple wires welded directly to the surface of the plate with a separate contact. This technique ensures accurate temperature measurement throughout the cooling process. The spray nozzles have been characterised to obtain an average droplet velocity Vmean and a Sauter mean diameter (D 32). Prior to spraying, the plate was heated by a radiant panel to reach steady-state temperatures, ranging from 120°C to 650°C. During cooling, the plate continued to be heated by the radiant panel. Heat flux ( Q ˙ ) and heat transfer coefficient (HT C) were calculated from the temperature data. It was found that high levels of critical heat flux (MW.m−2 ) were achieved in the centre of the plate, ranging from 0.86 MW.m−2 , for the TG-SS1 nozzle to 3.58 MW.m−2 , for the TG-SS10 nozzle. In the same time, the convective heat transfer coefficient also reached high values ranging respectively from 5.5 kW.m−2.K−1 (TG-SS1 nozzle) to 27 kW.m−2.K−1 (TG-SS10 nozzle). It was concluded that the mass flux of water is the parameter with the greatest influence on cooling efficiency.