EFFECT OF THE HYDRODYNAMIC CONDITIONS ON THE VAPOR FILM DURING FORCED CONVECTIVE QUENCHING

摘要

To achieve the high cooling rates required during quenching processes, the parts are quenched in agitated liquid baths which modifies boiling phenomena at the part-fluid interface and, therefore, the thermal field evolution within the part. In spite of this, the interactions between fluid hydrodynamics and wetting front kinematics have not been investigated in detail. In this paper we studied the effect of vorticity and pressure gradients near the part surface on wetting front kinematics during forced convective quenching by means of a mathematical model which couples the velocity, thermal and phase fraction fields. The particular physical condition studied was that of water at 60°C flowing parallel to a flat-end cylindrical stainless steel probe, for which experimental results were already available. The computed pressure and vorticity fields show larger gradients near the probe end as the fluid velocity increases. This behavior favors a thicker vapor film near the probe base reducing heat transfer to the quenching bath locally. In contrast, low pressure and vorticity gradients occurring for low fluid velocities favor a uniform vapor film. A direct consequence of the non-uniform vapor film thickness occurring at high velocities is a significant thermal gradient along the probe axis which favors distortion.