Warm air at 65C, 3 m/s enters into a square (25 cm) duct made up of steel metal. The un-insulated duct is 10 m long and is in contact with the atmospheric air at 25C. If the heat losses to the atmosphere by natural convection then what will be the exit warm air temperature from the duct. It may be assumed that the natural convective flow at one surface does not affect the others as the two surfaces are horizontal, one at the top and at the bottom, and the two surfaces are vertical. Calculate the heat transfer coefficient for the obviously forced convection inside of the duct.