Maximum heat flux and wetting delay during quenching of high temperature carbon steel block

Abstract

Jet impingement quenching shows promising potential of achieving high heat flux today. Most recent studies investigated thermodynamic behaviors during quenching of copper, brass and steel blocks by jet impingement and determined the effects of dominating parameters on the maximum heat flux and wetting delay. Generalized correlations for predicting maximum heat flux and wetting delay were also developed. These correlations can predict the experimental data very well for both of copper and brass blocks. Experimental data for steel block have different character and can not be predicted by the above correlations. Therefore, the present study has been focused to investigate separately to explore the characteristics of these two phenomena for the steel block that has been experimented recently in Saga University, Japan. These two phenomena have been analyzed under various test conditions which included the jet velocities of 3-15 mis, jet subcoolings of 5-80K and initial block temperatures of 250- 600°C. The surface temperature and surface heat flux was estimated by an inverse heat conduction technique using the measured temperatures at two depths of 2.1mm and 5.0 mm from the surface. The surface temperature decreased very slowly with time just after the jet impingement. After a certain time delay, the surface temperature decreased at a faster rate. The digitized images of flow movement were also analyzed in the present study. It was found that the liquid didn't wet the entire surface just after the jet impingement. After a certain time period, the wetting front started to move in the radial direction. The effects of experimental parameters on the maximum heat flux and wetting delay were also observed in the present study. The characteristics of maximum heat flux and wetting delay are strongly influenced by the jet velocity and liquid jet subcooling. The maximum heat flux increases with the jet velocity and also with liquid subcooling. For higher jet velocity and higher jet sub cooling, the wetting delay is decreased. Both the maximum heat flux and wetting delay are found to be almost independent of block initial temperature. Finally, for the two regions of radial positions (lO-20mm and 20- 35mm) correlations of maximum heat flux together with the dominating parameters are developed. The proposed correlations show the accuracy of maximum heat flux within 01025%and 01030%respectively for the block initial temperatures of 250-400°C.