Hot air at atmospheric pressure and 80oC enters an 8-m long un-insulated square duct of crosssection 0.2mx0.2m and negligible thickness. The duct air passes through the attic of a house at a rate of 0.15m3/s. The duct surface is isothermal at 60oC. Determine the exit temperature of the air and the rate of heat loss from the duct to the attic space. Assume fully-developed flow in the duct throughout.