a thin-walled, uninsulated 0.4-m-diameter duct is used to route chilled air at 0.07 kg/s through the attic of a large commercial building. the attic air is at 37°c, and natural circulation provides a convection coefficient of 4 W m2K at the outer surface of the duct. if chilled air enters a 16-m-long duct at 7°c, what is its exit temperature (°c) and the rate of heat gain (w)? properties of the chilled air may be evaluated at an assumed average temperature of 300 k.
