Effect of jet diameter on the rewetting of hot horizontal surfaces during quenching

A horizontal stainless steel surface of 0.25 mm thickness and at 800 ± 10 °C initial temperature was cooled by a round water jet. The water jet at 22 ± 1 °C temperature impinged onto the hot surface through tube type nozzles of 250 mm length. The experiments were performed for the jet diameters in the range of 2.5–4.8 mm and the jet Reynolds number remained within 5000–24,000.The transient cooling performance of the test surface was determined on the basis of rewetting temperature, wetting delay and the rewetting velocity. A rise in the rewetting temperature and the rewetting velocity has been observed with the increase in jet diameter and jet Reynolds number, leading to decline in the wetting delay.The results of the steady state cooling are in agreement with the findings of other investigators. The correlations have also been developed to evaluate the stagnation and the local Nusselt number for the steady state cooling condition. These correlations predict 80% experimental data within an error band of ±10%.

► Round water jet impinge onto a hot surface.
► Effect of jet diameter on surface cooling is examined.
► Larger jet diameter has higher heat transfer rate.
► Transient cooling is analyzed on the basis of surface rewetting.
► Surface rewetting is enhanced with rise in jet Reynolds number.