S. Ma, M. Md., J. Chaves, R. D. Sisson, Jr., Worcester Polytechnic Institute, Worcester, MA

Summary: The effect of oxide formation on the cooling rate and heat transfer coefficient as a function of temperature of 4140 steel probes has been experimentally and numerically investigated using the CHTE Quench Probe System. Time-temperature data has been collected for 4140 probes oxidized in air for 0, 5, 20 and 80 minutes oxidation times and then quenched in mineral oil-Houghton G. The heat transfer coefficient as a function of temperature has been estimated using inverse calculation by steepest descent method. The results indicate that a thin layer of oxides on the probe surface enhances the cooling rate by providing more nucleation sites for the bubble formation. However, when the oxidization time is prolonged to 20 and 80 minutes, the insulating effect is found more prominent, which is due to the low conductivity of iron oxides and the calculated heat transfer coefficient decreases.