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.