Hot air at 60°C leaving the furnace of a houseenters a 12-m-long section of a sheet metal duct of rectangularcross section 20 cm * 20 cm at an average velocityof 4 m/s. The thermal resistance of the duct is negligible,and the outer surface of the duct, whose emissivity is 0.3,is exposed to the cold air at 10°C in the basement, with aconvection heat transfer coefficient of 10 W/m2?K. Taking thewalls of the basement to be at 10°C also, determine (a) thetemperature at which the hot air will leave the basement and(b) the rate of heat loss from the hot air in the duct to thebasement. Evaluate air properties at a bulk mean temperatureof 50°C. Is this a good assumption?

Hot air at 60°C leaving the furnace of a houseenters a 12-m-long section of a sheet metal duct of rectangularcross section 20 cm * 20 cm at an average velocityof 4 m/s. The thermal resistance of the duct is negligible,and the outer surface of the duct, whose emissivity is 0.3,is exposed to the cold air at 10°C in the basement, with aconvection heat transfer coefficient of 10 W/m2?K. Taking thewalls of the basement to be at 10°C also, determine (a) thetemperature at which the hot air will leave the basement and(b) the rate of heat loss from the hot air in the duct to thebasement. Evaluate air properties at a bulk mean temperatureof 50°C. Is this a good assumption?

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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