Parametric Study on Transient Pool Boiling Heat Transfer Using Metal Rodlet

The transient pool boiling heat transfer of zircaloy and stainless steel rodlets was investigated using a quenching method. The influences of quenchant temperature, test specimen size, and material property were examined. The groove-structured surface was also prepared and tested, which could be a valuable attempt to study the effect of a machined surface structure of a vertical rodlet on the rapid cooling heat transfer performance. A test specimen with a small volume-to-heat transfer surface area and small heat capacity showed a shorter quenching time. In the low quenchant temperature condition, a stable film boiling regime was likely to be hardly observed. The grooved surface appeared to have a shorter quenching duration, which could be due to its small volume-to-area ratio. In addition, the groove-structured portion seemed to help the liquid make contact with the heated wall earlier than the plain portion. Based on this work, it was found that the quenching duration and the position of vapor film rupture can be controlled by the surface structure.

Heat Treatment Process and Parameter Design in Manufacturing

The heat treatment operation which is carried out post manufacturing is optimized. Simulation of the carburizing and quenching processes with parameter optimization are combined to attain the desired surface hardness with controlled distortion of final products. Parameters of interest for optimization include, the carbon content of gas, carburizing dwell time, material temperature before quenching, quenchant temperature and the heat transfer coefficient. The response surface method is used to obtain closed-form models of the objective (surface hardness) and the two constraints (hardness variance and physical distortion) in terms of the design variables. A finite element simulation tool is used to predict the material response (volume fraction of different phases, temperature and stress/strain) during the carburizing and quenching processes. This paper summarizes the methodology that is used to optimize the carburizing and quenching processes of an axisymmetric disk.