Consider an array of vertical rectangular fins, which is to be used to cool an electronic device mounted in quiescent, atmospheric air at T∞ = 27°C. Each fin has L = 20 mm and H = 150 mm and operates at an approximately uniform temperature of Ts = = 77°C.

(a) Viewing each fin surface as a vertical plate in an infinite, quiescent medium briefly describe why there exists an optimum fin spacing S. Using Figure 9.4 estimate the optimum value of S for the prescribed conditions.

(b) For the optimum value of S and a fin thickness of t = 1.5 mm, estimate the rate of heat transfer from the fins for an array of width W = 355 mm.

Quiescent air, T.