Cold conditioned air at 12°C is flowing inside a 1.5-cm-thick square aluminum (k = 237 W/m·K) duct of inner cross section 22 cm * 22 cm at a mass flow rate of 0.8 kg/s. The duct is exposed to air at 33°C with a combined convection-radiation heat transfer coefficient of 13 W/m2·K. The convection heat transfer coefficient at the inner surface is 75 W/m2·K. If the air temperature in the duct should not increase by more than 1°C determine the maximum length of the duct.

Cold conditioned air at 12°C is flowing inside a 1.5-cm-thick square aluminum (k = 237 W/m·K) duct of inner cross section 22 cm * 22 cm at a mass flow rate of 0.8 kg/s. The duct is exposed to air at 33°C with a combined convection-radiation heat transfer coefficient of 13 W/m2·K. The convection heat transfer coefficient at the inner surface is 75 W/m2·K. If the air temperature in the duct should not increase by more than 1°C determine the maximum length of the duct.

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter7: Forced Convection Inside Tubes And Ducts

Section: Chapter Questions

Problem 7.4P

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Question

Cold conditioned air at 12°C is flowing inside a
1.5-cm-thick square aluminum (k = 237 W/m·K) duct of
inner cross section 22 cm * 22 cm at a mass flow rate of
0.8 kg/s. The duct is exposed to air at 33°C with a combined
convection-radiation heat transfer coefficient of 13 W/m2·K.
The convection heat transfer coefficient at the inner surface
is 75 W/m2·K. If the air temperature in the duct should not
increase by more than 1°C determine the maximum length of
the duct.

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