Analysis of the local heat transfer of quenching of moving metal sheets made of different materials using flat spray nozzles

Abstract

Experimental investigations have been performed for the cooling of hot moving metal sheets of thickness 2 mm and 5 mm with the initial temperature of 500 °C to 800 °C by two flat spray nozzles. Tap water at room temperature is used as a coolant. Experiments are carried out for nickel, nicrofer, and aluminum alloy AA6082 with varying sheet velocity( 5,10,15 mm/s) and nozzle inclination angle (45°,65°,90°). The temperature distribution on the backside of the sheet during the cooling is recorded with a high-speed infrared camera. The recorded thermal data are used in the inverse heat conduction analysis to estimate the local heat fluxes and temperatures on the quenched surface. The thermal images obtained are used to analyze the length of the pre-cooling, transition boiling, and nucleate boiling. The maximum heat flux, the DNB temperature, and the rewetting temperature are presented for researched parameters. The nozzle inclination angle has a weak influence. The higher the velocity and the thickness of the sheet are, the higher the maximum heat flux and the shorter the pre-cooling region. The reason is that the position of the max. heat flux is shifted downstream near to impingement region.