1-122 A4-m-long section of an air heating system of a house passes through an unheated space in the attic. The inner diam- eter of the circular duct of the heating system is 20 cm. Hot air enters the duct at 100 kPa and 65°C at an average velocity of 3 m/s. The temperature of the air in the duct drops to 60°C as a result of heat loss to the cool space in the attic. Determine the rate of heat loss from the air in the duct to the attic under steady conditions. Also, determine the cost of this heat loss per hour if the house is heated by a natural gas furnace having an effi- ciency of 82 percent, and the cost of the natural gas in that area is $0.58/therm (1 therm = 105,500 kJ). Answers: 0.488 kJ/s, $0.012/h 4 m Hot air 60°C 65°C 3 m/s FIGURE P1-122

1-122 A4-m-long section of an air heating system of a house passes through an unheated space in the attic. The inner diam- eter of the circular duct of the heating system is 20 cm. Hot air enters the duct at 100 kPa and 65°C at an average velocity of 3 m/s. The temperature of the air in the duct drops to 60°C as a result of heat loss to the cool space in the attic. Determine the rate of heat loss from the air in the duct to the attic under steady conditions. Also, determine the cost of this heat loss per hour if the house is heated by a natural gas furnace having an effi- ciency of 82 percent, and the cost of the natural gas in that area is $0.58/therm (1 therm = 105,500 kJ). Answers: 0.488 kJ/s, $0.012/h 4 m Hot air 60°C 65°C 3 m/s FIGURE P1-122

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

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