Solidification time of a casting will be more if
A. Thermal diffusivity of the moulding sand is more
B. Specific heats of molten metal and sand are low
C. Thermal conductivity of moulding sand is less
D. None of the above
Please scroll down to see the correct answer and solution guide.
Right Answer is: C
SOLUTION
Concept:
Thermal diffusivity of material is given as \(α = \frac{k}{{ρ c}}\)
where k is thermal conductivity in W/m-k, ρ is density in kg/m3 and c specific heat capacity in J/kg-K
It is the property of the material. Larger the value of α, faster heat will diffuse through the material. A high value of α could result either from a high value of thermal conductivity or low value of thermal heat capacity ρc. Thermal diffusivity α has units of square meters per second.
unit of \(\alpha =\frac{\frac{W}{m-K}}{\frac{kg}{m^3}\frac{J}{kg-K}}=\frac{m^2}{s}\)as Watt is J/s.
Hence from the option the correct answer is
unit of \(\alpha =m^2/hr\)
- For high thermal diffusivity, solidification time is less.
- For less specific heat of molten metal, solidification time will be less due to less heat storage capacity.
- Solidification time is high if thermal conductivity is less due to slow heat dissipation.