Chapter 9, Problem 9.45P

At the end of its manufacturing process, a silicon wafer of diameter $D=150\text{mm}$ , thickness $\delta =1\text{mm}$ , and emissivity is at an initial temperature of $T_i=325°C$ and is allowed to cool in quiescent, ambient air and large surroundings for which $T_{\infty }=T_{\text{sur}}=25°C$ .

(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.