The cross section of the rectangular duct of the heating system is 15 cm x 20 cm (figure shown below), with 6-m-long section of an air heating system of a house passes through an unheated space in the basement. Hot air enters the duct at 100 kPa and 60°C at an average velocity of 6 m/s. The temperature of the air in the duct drops to 54°C as a result of heat loss to the cool space in the basement. Determine the rate of heat loss from the air in the duct to the basement under steady conditions. Also, determine the cost of this heat loss per hour if the house is heated by a natural gas furnace that has an efficiency of 80 percent, and the cost of the natural gas in that area is $0.70/therm (1 therm = 100,000 Btu = 105,500 kJ).
The cross section of the rectangular duct of the heating system is 15 cm x 20 cm (figure shown below), with 6-m-long section of an air heating system of a house passes through an unheated space in the basement. Hot air enters the duct at 100 kPa and 60°C at an average velocity of 6 m/s. The temperature of the air in the duct drops to 54°C as a result of heat loss to the cool space in the basement. Determine the rate of heat loss from the air in the duct to the basement under steady conditions. Also, determine the cost of this heat loss per hour if the house is heated by a natural gas furnace that has an efficiency of 80 percent, and the cost of the natural gas in that area is $0.70/therm (1 therm = 100,000 Btu = 105,500 kJ).
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