A fan is to be selected to cool a computer case whose dimensions are 12 cm X 40 cm X 40 cm (Fig. 5-56). Half of the volume in the case is expected to be filled with components and the other half to be air space. A 5-cmdiameter hole is available at the back of the case for the installation of the fan that is to replace the air in the void spaces of the case once every second. Small low-power fan-motor combined units are available in the market and their efficiency is estimated to be 30 percent. Determine
(a) the wattage of the fan-motor unit to be purchased and
(b) the pressure difference across the fan. Take the air density to be 1.20 kg/m3.