Heat Transfer Characteristic of Slit Nozzle Impingement on High-temperature Plate Surface

Abstract

Heat transfer mechanism of a slit jet impingement was thoroughly studied to improve capacity and uniformity of a hot steel strip/plate during its ultrafast cooling or quenching. The impact angle has a significant influence on the heat transfer characteristics of the stationary slit jet impinging process. Heat transfer capability and rewetting front propagation, which include such parameters as q_max, t_MHF, and T_MHF, differ significantly between the upstream and downstream regions. Parallel flow and intense sputtering in the downstream region are apparent for the forward-moving inclined slit jet impingement cooling process. The antiparallel flow in the upstream region is thinner, and the sputtering is reduced and is relatively stable. As the plate moves forward, the wetting front expands and forms almost a straight line with synchronized and uniform heat transfer. The inclined angle increases from 0 to 45°, which significantly increases the heat transfer intensity and shortens the time to nucleate boiling stage as well as the width of the transitional boiling region. A higher moving velocity reduces and promotes q_max moving to the downstream region.