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An 8-m-long, uninsulated square duct of cross section 0.2 m X 0.2 m and relative roughness...

An 8-m-long, uninsulated square duct of cross section 0.2 m X 0.2 m and relative roughness 10-3 passes through the attic space of a house. Hot air enters the duct at 1 atm and 100oC at a volume flow rate of 0.15 m3/s. The duct surface is nearly isothermal at 60oC. Determine the rate of heat loss from the duct to the attic space and the pressure difference between the inlet and outlet sections of the duct. Evaluate air properties at a bulk mean temperature of 80oC. Is this a good assumption?

Taking a bulk mean fluid temperature of 80oC based on the problem statement (this assumes that the air does not loose much heat to the attic), the properties of air are:

cp = 1008 J/kg?oC

k = 0.02953 W/m?oC

? = 2.097 × 10-5 m2/s

? = 0.9994 kg/m3

Pr = 0.7154

The rate of heat loss is ____W.

The pressure drop is ____Pa.

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