A 5 - m long section of an air heating system of a house passes through an unheated space in the basement, Figure 1. The cross section of the rectangular duct of the heating system is 20 cm x 25 cm. Hot air enters the duct at 100 KPa and 60 oC at an average velocity of 5 m/s. The temperature of the air in the duct drops to 54 oC as a result of heat loss to the cooling space in the basement. Determine : a) The rate of heat loss from the air in the duct to the basement under steady conditions. b) The cost of this heat loss per hour if the house is heated by a natural gas furnace that has an efficiency of 80%, and the cost of the natural gas in that area is $1.6/therm (1 therm = 105,500KJ). Given data for air: CP = 1.007 KJ/Kg K
A 5 - m long section of an air heating system of a house passes through an
unheated space in the basement, Figure 1. The cross section of the rectangular
duct of the heating system is 20 cm x 25 cm. Hot air enters the duct at 100 KPa
and 60 oC at an average velocity of 5 m/s. The temperature of the air in the duct
drops to 54 oC as a result of heat loss to the cooling space in the basement.
Determine :
a) The rate of heat loss from the air in the duct to the basement under steady
conditions.
b) The cost of this heat loss per hour if the house is heated by a natural gas
furnace that has an efficiency of 80%, and the cost of the natural gas in that
area is $1.6/therm (1 therm = 105,500KJ).
Given data for air:
CP = 1.007 KJ/Kg K
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