Chips of width L = 15 mm on a side are mounted to a substrate that is installed in an enclosure whose walls and air are maintained at a temperature of Tsur = T∞ = 25°C. The chips have an emissivity of ɛ = 0.60 and a maximum allowable temperature of Ts = 85°C.

   (a) If heat is rejected from the chips by radiation and natural convection, what is the maximum operating power of each chip? The convection coefficient depends on the chip-to-air temperature difference and may be approximated as h = C(Ts -T∝)^¼, where C = 4.2 W/ m. K^5/4.

   (b) If a fan is used to maintain air flow through the enclosure and heat transfer is by forced convection, with h = 250 W/m². K, what is the maximum operating power?