Find the solidification time of the two iron castings when both are poured (with no superheats) into the sand molds at initial temperature 28°C.

(i) A slab shaped casting of 10 cm thickness, (ii) a sphere of 10 cm in dia. Iron: freezing temp: 1540°C; L= 272 kJ/kg; density = 7850 kg/m3 Sand: c = 1.17 kJ/kg-K; k = 0.865 W/mk; density = 1600 kg/m3

Air enters a horizontal, constant-diameter heating duct operating at steady state at 290 k, 1 bar, with a volumetric flow rate of 0.25 m°/s, and exits at 325 k, 0.95 bar. the flow area is 0.04 m2. assuming the ideal gas model with k = 1.4 for the air, determine (a) the velocity at the inlet and exit, each in m/s, and (c) the rate of heat transfer, in kw flow rate, in kg/s, (b) the mass kg 0.3