  In this study, identical experiments of bottom-cooled solidification fluidic
mixtures that exhibit faceted and dendritic microstructures were performed. The
strength of compositional convection was correlated with the solidifying
microstructure morphology, with the help of separate Rayleigh numbers in the
mushy and bulk-fluid zones. While the dendritic solidification experienced a
monotonic decrease in the bulk fluid temperature, solidification of the faceted
case revealed an unconventional, anomalous temperature rise in the bulk liquid,
at the initiation of the eutectic phase. Based on the bulk-liquid temperature
profile, three distinct regimes of heat transfer were observed in the liquid
over the course of solidification, namely - convection-dominated, transition,
and conduction-dominated. The observations were analyzed and verified with the
help of different initial compositions, as well as other mixtures that form
faceted morphology upon freezing. The observed temperature rise was further
ascertained by performing an energy balance in an indicative control volume
ahead of the solid-liquid interface. The plausible mechanism behind the gain in
temperature of the liquid during freezing was further generalized with the help
of a simplified one-dimensional numerical model, and was extended to metals
which are low Prandtl number mixtures. The study sheds new insights into the
role of microstrostructural morphology in governing the transport phenomena in
the bulk liquid.
