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.