Multiphase numerical modeling and investigation of heat transfer for quenching of spherical particles in liquid pool

Quenching is a widely applied heat treatment process for metallic materials in order to adjust the microstructure and material properties by means of intensive cooling. Depending on the cooling rate attained with respect to the operating conditions as well as the cooling medium, specific material properties such as hardness can be adapted to engineering applications. One of the major constraints for intensive cooling remains with the selection of suitable process parameters. An imprudent selection will end up with sample distortion and cracks. The process being highly complex involving solidification, liquid pool immersion phenomena, rotation, the Leidenfrost effect and vapor formation emerging from liquid for these "millimeter" ranged particles, which make the complete process difficult to analyze by experimental investigations alone. In order to tackle this challenge, a multiphase numerical modeling based on a Eulerian framework is developed and experimentally validated in this work for analyzing the cooling rate of high temperature semi-solid spheres quenched in water. This model simulates particle quenching in liquids, where the source and sink terms of the conservation equations are modified to accommodate the phase transfer effects. To validate modeling results, a high temperature molten metal droplet generator is used to generate the droplets from Al 4.5-wt.% Cu with a diameter of about 1 mm which are quenched in water during the semi-solid state. The formation of dendritic structure within the solidifying droplet is highly sensitive to its cooling rate. This allows to calculate the cooling rate corresponding to the operating condition from SDAS (Secondary Dendrite Arm Spacing) and compare with numerical simulation. Finally, we investigate the influence of the particle Reynolds number (flow velocity) and pool temperature on heat transfer with this validated model.