Determination of unidirectional heat transfer coefficient during unsteady-state solidification at metal casting–chill interface

Abstract

In this study, the interfacial heat transfer coefficient (IHTC) for vertically upward unidirectional solidification of a eutectic Al–Si casting on water cooled copper and steel chills was measured during solidification. A finite difference method (FDM) was used for solution of the inverse heat conduction problem (IHCP). Six computer guided thermocouples were connected with the chill and casting, and the time–temperature data were recorded automatically. The thermocouples were placed, located symmetrically, at 5 mm, 37.5 mm and 75 mm from the interface. As the lateral surfaces are very well heat isolated, the unidirectional solidification process starts vertically upward at the interface surface. The measured time–temperature data files were used by a FDM using an explicit technique. A heat flow computer program has been written to estimate the transient metal–chill IHTC in the IHCP. The experimental and calculated temperatures have shown excellent agreement. The IHTC during vertically upward unidirectional solidification of an Al–Si casting on copper and steel chills have varied between about 19–9.5 kW/m2 K and 6.5–5 kW/m2 K, respectively.