The components of an electronic system dissipating 150 W are located in a 5-ft-long horizontal duct whose cross section is 6 in x 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. The ambient air temperature is 80°F. Use the property tables to calculate the properties of air at the film temperature. Assume the fan fails and thus all heat generated inside the duct must be rejected to the ambient air by natural convection through the outer surfaces of the duct. Evaluate air properties at a film temperature of 120°F and 1 atm pressure. k= 0.01576 Btu/h-ft-°F v= 0.1923 x 10-3 ft²/s Pr = 0.723 NOTE: This is a multi-part question. Once an answer is submitted, you will be unable to return to this part. 80°F 85°F 22 cfm Natural convection 150 W 100°F

The components of an electronic system dissipating 150 W are located in a 5-ft-long horizontal duct whose cross section is 6 in x 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. The ambient air temperature is 80°F. Use the property tables to calculate the properties of air at the film temperature. Assume the fan fails and thus all heat generated inside the duct must be rejected to the ambient air by natural convection through the outer surfaces of the duct. Evaluate air properties at a film temperature of 120°F and 1 atm pressure. k= 0.01576 Btu/h-ft-°F v= 0.1923 x 10-3 ft²/s Pr = 0.723 NOTE: This is a multi-part question. Once an answer is submitted, you will be unable to return to this part. 80°F 85°F 22 cfm Natural convection 150 W 100°F

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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Required information
The components of an electronic system dissipating 150 W are located in a 5-ft-long horizontal duct whose cross section
is 6 in x 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. The ambient air temperature is 80°F. Use the property tables to calculate the properties of air at the film
temperature. Assume the fan fails and thus all heat generated inside the duct must be rejected to the ambient air by
natural convection through the outer surfaces of the duct. Evaluate air properties at a film temperature of 120°F and 1 atm
pressure.
k = 0.01576 Btu/h-ft-°F
v= 0.1923 x 10-3 ft²/s
Pr = 0.723
NOTE: This is a multi-part question. Once an answer is submitted, you will be unable to return to this part.
80°F
85°F
22 cfm
Natural
convection
150 W
100°F
Determine the average temperature of the duct. Calculate for one iteration and evaluate the result.
The average temperature of the duct is 101.37 °F.

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