The components of an electronic system dissipating 180 W are located in a 4-ft-long horizontal duct whose

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The components of an electronic system dissipating 180 W are located in a 4-ft-long horizontal duct whose cross section is 6 in × 6 in. The components in the duct are cooled by forced air, which enters at 85°F at a rate of 22 cfm and leaves at 100°F. The surfaces of the sheet metal duct are not painted, and thus radiation heat transfer from the outer surfaces is negligible. If the ambient air temperature is 80°F, determine

(a) The heat transfer from the outer surfaces of the duct to the ambient air by natural convection

(b) The average temperature of the duct. Evaluate air properties at a film temperature of 100°F and 1 atm pressure. Is this a good assumption?

Natural convection 100°F 80°F 180 W 4 ft 85°F 22 cfm

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Fundamentals of Thermal-Fluid Sciences

ISBN: 978-0078027680

5th edition

Authors: Yunus A. Cengel, Robert H. Turner, John M. Cimbala

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