Heat Transfer via Laminar Jet Flow from Upward-facing Triple-pipe System onto Hot Moving Thin Steel Sheet

With the primary objective of investigating the effect of varying the nozzle interval and steel sheet temperature on the heat flux distribution within the jet impact region, the boiling heat transfer characteristics of three upward-facing water jets impinging on a moving hot thin steel sheet were studied as a fundamental phenomenon of run-out table (ROT) cooling in a hot rolling mill. Using water as a test coolant and a stainless steel sheet as a test piece, the intervals between adjacent nozzles were varied from 8 to 12 to 16 mm and experiments were conducted over a steel sheet temperature range of 300–700°C and at a moving velocity and volume flow rate of 1.5 m/s and 960 ml/min, respectively. Three-dimensional inverse heat conduction analysis was used to evaluate the heat flux distribution based on the temperature profile of the steel sheet captured by a thermal imaging camera. It was found that three high-heat flux regions were present in the jet impact region, with the heat flux highly dependent on the temperature of the steel sheet associated with the boiling mode. In addition, it was found that, because of the effects of the two side jets on the flow formed by the center jet, the high-heat-flux region associated with the center jet was dependent on the nozzle interval. As a result of this dependence, decreases in the nozzle interval reduced the degree of heat removal by the center jet.