Equiaxed dendritic solidification with convection: Part III. Comparisons with NH₄Cl-H₂O experiments

This third article on equiaxed dendritic solidification is intended to provide experimental validation of the multiphase model developed in part I. Numerical and experimental results are presented for the solidification of a NH₄Cl-70 wt pet H₂O solution inside a square cavity cooled equally from all sidewalls. The numerical simulations were performed using the numerical procedures developed in part II. The experiments were conducted to measure the temperature histories via thermocouples and to record the images of the solidification.process using a shadowgraph system. Preliminary validity of the multiphase model is demonstrated by the qualitative agreement between the measurements and predictions of cooling curves as well as of the evolution of the crystal sediment bed. In addition, several important features of equiaxed dendritic solidification are identified through this combined experimental and numerical study, including the grain generation and growth behaviors in the presence of liquid flow, the sedimentation of equiaxed crystals, the formation of a crystal sediment bed, and a bottom zone of negative segregation resulting from the countercurrent solid-liquid multiphase flow. Quantitative comparisons between the numerical simulation and experiment reveal several areas for future research.