Surface heat flux of upward circular water jet impingement on a moving hot steel sheet

Abstract

This study experimentally investigated the boiling heat transfer characteristics of a circular upward water jet issued from a 7-mm-diameter nozzle impinging on a moving hot 0.3-mm-thick stainless-steel sheet. The moving velocity (1.5, 3.0, and 4.4 m/s), temperature (100-590℃), and water flow rates (2.5, 3.0, and 3.5 L/min) were varied during the test. The surface heat flux in the jet impact region depended significantly on the initial temperature of the solid. The surface heat flux increases as the solid temperature increases, attains a peak value (∼30 MW/m²) before decreasing, and reaches a valley value before increasing again. Furthermore, the moving velocity of the solid influences the cooling characteristics, considering that the duration of water contact of a local point on the test sheet is shorter for larger velocities. Moreover, the maximum value of the surface heat flux in the jet impact region can be roughly correlated with the local temperature of the solid. The maximum heat flux peaked at approximately 190℃ and reached a valley at approximately 370℃. Three empirical correlations for predicting the maximum heat flux in the nucleate, transition, and film boiling are built as functions of the local temperature. The equations in the transition and film boiling can predict the results within a ±20 % error margin.