Determination of Rewetting Velocity During Jet Impingement Cooling of a Hot Surface

An experimental investigation has been carried out to study the cooling of a hot horizontal stainless steel surface of 0.25 mm thickness, which has 800 +/- 10 degrees C initial temperature. A round water jet of 22 +/- 1 degrees C temperature was injected over the hot surface through a straight tubes type nozzle of 2.5 mm diameter and 250 mm length. The experiments were performed for the jet exit to target surface spacing in a range of 4-16 times of jet diameter and jet Reynolds number in a range of 5000-24,000. The rewetting velocity during transient cooling of hot surface was determined with the help of time variant surface temperature data and with the captured thermal images of the hot surface as well. The effect of Reynolds number, Re, jet exit to surface spacing, z/d, on the rewetting velocity has been determined for the different downstream spatial locations. A correlation has also been developed to determine the rewetting velocity, which predicts 75% of experimental data within an error band of 610%.