A heat exchanger for cooling electronic components is fabricated with two aluminum plates separated by aluminum fins (rather like corrugated cardboard). The plates are 8.04 inches wide by 10 inches long and 0.60 inches thick. Each plate has a heat load of 100 watts. There are 73 fins, each 0.80 inches high by 10 inches long and 0.010 inches thick. The fins are spaced on 0.110 inch centers. Room air at a rate of 250 ft3/min is delivered by a fan to a plenum at the inlet end of the heat exchanger. The air discharges from the heat exchanger into the room where the temperature is 68°F and the absolute pressure is 29.92 inch-Hg. Determine the required gauge pressure for the inlet plenum, assuming all surfaces are smooth and the loss coefficients (based on tube velocity) for the inlet and outlet are 0.7 and 0.6, respectively.