A computer cooled by a fan contains eight printed circuit boards (PCBs), each dissipating 12 W of power. The height of the PCBs is 12 cm and the length is 17 cm. The clearance between the tips of the components on the PCB and the back surface of the adjacent PCB is 0.3 cm. The cooling air is supplied by a 10-W fan mounted at the inlet. The temperature rise of air as it flows through the case of the computer is not to exceed 10°C. The properties of air at 25°C are rho = 1.184 kg/m3, k = 0.02551 W/m·°C, v = 1.562 × 10–5 m2/s, cp = 1007 J/kg·°C, and Pr = 0.7296.
Determine the flow rate of the air that the fan needs to deliver
Determine the fraction of the temperature rise of air that is due to the heat generated by the fan and its motor.
Determine the highest allowable inlet air temperature if the surface temperature of the components is not to exceed 70°C anywhere in the system. Is evaluating the properties of air at a bulk mean temperature of 25°C a good assumption?