The effect of nozzle height on cooling heat transfer from a hot steel plate by an impinging liquid jet

Abstract

The effect of nozzle height on heat transfer of a hot steel plate cooled by an impinging liquid jet is not well understood. Previous studies have been based on the dimensionless parameter z/d. To test the validity of this dimensionless parameter, and to investigate gravitational effects on the jet, velocity measurements were made in a liquid jet with a stagnation point, and heat transfer from a hot steel plate was investigated. Also, the critical instability point of a laminar liquid jet was examined over a range of flow rates. The experimental velocity data for the liquid jet were well correlated with the dimensionless number 1/Frz2 based on height. It was thought that the z/d parameter was not valid for heat transfer to an impinging liquid jet under gravitational forces; unsteady cooling experiments showed that the heat transfer was independent of z when 1/Frz2<0.187. A finite enhancement of heat transfer was observed when 1/Frz2=0.523. The discrepancy between these results and previous research is likely due to the instability of laminar liquid jets.