Rewetting and maximum surface heat flux during quenching of hot surface by round water jet impingement

The transient cooling of hot stainless steel surface of 0.25 mm thickness is done with round water jet impingement. Initially, the surface was heated up to the temperature of 800 °C before the water was injected through straight tube type nozzle of 2.5 mm diameter and 250 mm length. During impingement cooling, the surface temperature was measured up to 12 mm radial distance away from the stagnation point. The jet exit to surface spacing, z/d, and jet Reynolds number, Re, varied in the range of 4–16 and 5000–24,000 respectively. The surface rewetting and transient heat flux of the test-surface was studied for these operating parameters.During impingement cooling process the initial rewetting occurred at stagnation region with the lowest wetting delay period. In fact, the rewetting temperature, rewetting velocity and the maximum heat flux reduced for extreme spatial location. However, the wetting delay increased significantly for the locations away from the stagnation point. The surface rewetting and transient heat flux were increased with the rise in jet Reynolds number, resulting in the enhancement in rewetting temperature, rewetting velocity and reduced wetting delay. The maximum heat flux was obtained for 4–6 mm radial location. The effect of jet exit to surface spacing on the rewetting parameters is found to be marginal. A correlation has been developed which predicted the maximum heat flux within an error band of ±10%.