a)
The rate of heat transfer to the air.
a)
Answer to Problem 142P
The rate of heat transfer to the air is
Explanation of Solution
Write the expression for the energy balance equation for closed system.
Here, rate of net energy transfer into the control volume is
Conclusion:
The rate of change in internal energy of the system is zero at the steady flow system.
Substitute 0 for
Here, mass flow rate is
The specific heat at constant pressure
Substitute
Thus, the rate of heat transfer to the air is
b)
The outlet temperature of the air.
b)
Answer to Problem 142P
The outlet temperature of the air is
Explanation of Solution
Write the expression to calculate the mass flow rate of air.
Here, volume flow rate of air at inlet is
Write the expression for the rate of heat transfer output.
Here, heat gained by the air is
Conclusion:
Substitute
Heat loss by the exhaust gases is equal to heat gained by the air.
Substitute
Thus, the outlet temperature of the air is
c)
The rate of entropy generation
c)
Answer to Problem 142P
The rate of entropy generation is
Explanation of Solution
Write the expression for the entropy balance in the heat exchanger.
Here, rate of net input entropy is
Conclusion:
Substitute
Here, mass flow rate at entry 1 is
Substitute
Thus, the rate of entropy generation is
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Chapter 7 Solutions
THERMODYNAMICS: AN ENGINEERING APPROACH
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