At the end of its manufacturing process, a silicon wafer of diameter D = 150 mm, thickness δ = 1 mm, and emissivity ε = 0.65 is at an initial temperature of T_i = 325°C and is an owed to cool in quiescent, ambient air and large surroundings for which T_∞ = T_sur = 25°C.

(a) What is the initial rate of cooling?

(b) How long does it take for the wafer to reach a temperature of 50°C? Comment on how the relative effects of convection and radiation vary with time during the cooling process.

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5 sin 24 = 273 + To, (K) 0<1<12h ) T, o(K) = 273 + 11 sin 24 12