1. Determine the net electric power produced by the fuel cell-fan system, Pnet = P - Pf .
2. Consider the effect of attaching an aluminum (k = 200 W/m · K) finned heat sink, of identical top and bottom sections, onto the fuel cell body. The contact joint has a thermal resistance of R"t,c = 10-3 m2 · K/W, and the base of the heat sink is of thickness tb = 2 mm. Each of the N rectangular fins is of lengthLf = 8 mm and thickness tf = 1 mm, and spans the entire length of the fuel cell, Lc = 50 mm. With the heat sink in place, radiation losses are negligible and the convective heat transfer coef- ficient may be related to the size and geometry of a typical air channel by an expression of the form h = 1.78 kair (Lf +a)/(Lf · a), where a is the distance between fins. Draw an equivalent thermal circuit for part 2 and determine the total number of fins needed to reduce the fan power consumption to half of the value found in part 1.