Flow of hot air through uninsulated square (a = 0.15m) ducts of a heating system in the attic is considered. 10 m 70C Air 85C 0.1 m/min S Steady operating conditions exist. The inner surfaces of the duct are smooth. Air is an ideal gas with constant properties. The pressure of air is 1 atm. Determine if the flow is fully developed and the exit temperature and the rate of heat loss. Assume the critical Reynolds number is 2000, the air properties are shown: p = 1.009 kg/m k=0.0297 W/m.C v=2.06 105 m/s C = 1008 J/kg.C Pr = 0.706 The Nusselt number for turbulent flow is: hD Nu= = 0.023 Re8 Pr03