Project ForgeEqual amounts of a liquid metal at the same temperature are poured into three identical cylindrical moulds made of steel, copper and aluminium (outside mould temperature stays near atmospheric during solidification). Thermal conductivities: steel 60.5, copper 401, aluminium 237 W/m·K. Specific heats: steel 434, copper 385, aluminium 903 J/kg·K. Densities: steel 7854, copper 8933, aluminium 2700 kg/m³. The sequence of solidification in the mould, from fastest to slowest, is
- ACopper - Steel - Aluminium
- BAluminium - Steel - Copper
- Copper - Aluminium - Steel
- DSteel - Copper - Aluminium
Explanation
By Chvorinov-type reasoning, solidification rate depends on the mould's ability to draw heat away, governed by thermal diffusivity/effusivity of the mould material — higher thermal conductivity relative to volumetric heat capacity (ρc) drains heat fastest. Ranking the moulds' heat-absorbing capability from the given properties gives Copper fastest, then Aluminium, then Steel slowest.
Source: GATE ME 2016 Set-3 (2016)
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