
Concept explainers
The cost of energy “vented out” by the fans in 1 h.

Answer to Problem 148RP
The cost of energy “vented out” by the fans in 1 h is
Explanation of Solution
Determine the density of air at the indoor conditions.
Here, the house maintain a pressure is
Determine interior volume of the house per hour
Here, the width of the house is
Determine the mass flow rate of air vented out.
Determine the rate of energy loss by the ventilating fans.
Here, the specific heat of air at room temperature is
Determine the amount of electric energy loss by “vented out”.
Here, the fan takes time is
Determine the amount of cost of the heat “vented out” per hour.
Conclusion:
From the Table A-1, “Molar mass, gas constant, and critical-point properties” to obtain the value of gas constant of air as
From the Table A-2a, “Ideal-gas specific heats of various common gases” to obtain the value of specific heat of air at room temperature as
Substitute 92 kPa for
Substitute
Substitute
Substitute
Substitute
Substitute
Thus, the cost of energy “vented out” by the fans in 1 h is
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Chapter 6 Solutions
Thermodynamics: An Engineering Approach
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