The components of an electronic system dissipating 150W are located in a 1-m-long horizontal duct whose cross section is 15 cm x 15 cm. The components in the duct are cooled by forced air, which enters at 30°C at a rate of 0.4 m³/min and leaves at 45°C. 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 25°C, determine (a) the heat transfer from the outer surfaces of the duct to the ambient air by natural convection and (b) the average temperature of the duct. Natural convection 25°C 45°C 150 W Forced air 30°C

The components of an electronic system dissipating 150W are located in a 1-m-long horizontal duct whose cross section is 15 cm x 15 cm. The components in the duct are cooled by forced air, which enters at 30°C at a rate of 0.4 m³/min and leaves at 45°C. 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 25°C, determine (a) the heat transfer from the outer surfaces of the duct to the ambient air by natural convection and (b) the average temperature of the duct. Natural convection 25°C 45°C 150 W Forced air 30°C

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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The components of an electronic system dissipating 150 W are located in a 1 -m-long horizontal duct whose cross section is 15 cm X 15 cm. The components in the duct are cooled by forced air, which enters at 30°C at a rate of 0.4 m3/min and leaves at 45°C. 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 25°C, determine (a) the heat transfer from the outer surfaces of the duct to the ambient air by natural convection and (b) the average temperature of the duct.
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Liquid water flows in a thin-walled circular tube at a mass flow rate of 11 g/s. The water enters the tube at 60°C, where it is heated at a rate of 3.8 kW. The tube is circular with a length of 2.5 m and an inner diameter of 25 mm. The tube surface is maintained at a constant temperature. At the tube exit, a hydrogenated nitrile rubber (HNBR) o-ring is attached to the tube's outer surface. The maximum temperature permitted for the o-ring is 150°C. Is the HNBR o-ring suitable for this operation? The fluid properties at 100°C are cp= 4217 J/kg-K, k= 0.679 W/m-K, µ = 0.282 × 103 kg/m.s, and Pr = 1.75. Is this a reasonable temperature at which to evaluate the fluid properties?
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