Convection patterns and evolution of macrosegregation
during solidi®cation of hypereutectic and hypoeutectic
NH4CL-H2O binary systems in rectangular side
chilled ingots have been numerically investigated. Under
the conditions of pure thermal/solutal convection, without
a free surface, solidi®cation of NH4CL 70%-H2O hypereutectic
alloy is characterized by the formation of channels
and A-segregates, while solidi®cation of NH4CL 10%-H2O
hypoeutectic alloy is characterized by the formation of
circulation cells in the narrow melt and V-segregates.
Surface tension effects during solidi®cation of
NH4CL 70%-H2O results in establishing a counterclockwise
rotating cell at the cavity top, changing the number
and orientation of developed channels, and creating an
area of negative segregation at the cavity top. During
solidi®cation of NH4CL 10%-H2O, surface tension effects
increase the intensity of ¯ow and results in a higher degree
of macrosegregation.