Heat transfer during transient cooling of high temperature surface with an impinging jet

An experimental study of transient boiling heat transfer during a cooling of a hot cylindrical block with an impinging water jet has been made at atmospheric pressure. The experimental data were taken for the following conditions: a degree of subcooling of ΔTsub = 20 - 80 K, a jet velocity of uj = 5 - 15 m/s, a nozzle diameter of dj = 2 mm and three materials of copper, brass and carbon steel. The block was initially and uniformly heated to about 250°C and the transient temperatures in the block were measured at 8 locations in r-direction at two different depths from the surface during the cooling of hot block. The surface heat flux distribution with time was evaluated using a numerical analysis of 2D-heat conduction. Behavior of the wetting front, which is extending the nucleate boiling region outward, is observed with a high-speed video camera. A position of wetting region is measured and it is correlated well with a power function of time. The changes in estimated heat flux and temperature were compared with the position of wetting region to clarify the effects of subcooling, jet velocity and thermal properties of block on the transient cooling.