THE IMPACT OF DIFFERENTIAL WALL TEMPERATURES ON THE TRANSPORT PHENOMENA DURING THE SOLIDIFICATION OF A SUPER-EUTECTIC BINARY SOLUTION

摘要

The casting of binary alloys is one of the main industrial applications in the solidification phase change. The transport phenomena of the liquid binary alloy during solidification, such as thermosolutal convection, can affect the material quality of solidified ingots. This study focuses on the effect of three different differential wall temperatures between two vertically lateral walls on the transport phenomena of a super-eutectic aqueous ammonium chloride solution during solidification. Shadowgraph and particle image velocimetry (P1V) techniques were employed to observe the flow development and measure the flow velocity of the binary solution in the liquid. The transient temperature distribution within a rectangular test cell was measured by type-T thermocouples. The experimental results revealed that lighter and colder water-rich fluid ascended continuously through the mushy layer, migrating into the liquid zone during solidification with various differential wall temperatures and resulting in one double-diffusive layer that started to develop on top of the enclosure and moved downward continuously. Two circulations separated by the double-diffusive layer also grew gradually in the liquid zone. The case with smaller differential wall temperatures accelerated the rate of flow development, including the double-diffusive layer and its accompanying circulations. However, it could cause more A-segregates in the solidified ingots, unfavorable to the material quality. Although the case with larger differential wall temperatures can reduce the formation of A-segregates, it could overly slow down the crystal growth within the mushy layer.