
a)
The total entropy change and exergy destruction by treating the mixture as an ideal gas.
a)

Answer to Problem 71P
The entropy generated is
The energy destroyed is
Explanation of Solution
Write the entropy balance equation to obtain the expression of entropy generation in terms of
Here, mass of
Write the expression to obtain the energy destroyed during a process
Here, initial temperature is
Conclusion:
Refer Table A-2b, “Ideal gas specific heats of various common gases”, obtain the specific heat at constant pressure of
Obtain the value of
Here, constant pressure specific heat is
The partial pressure of
Substitute
Obtain the value of
The partial pressure of
Substitute
Substitute 6 kg for
Thus, the entropy generated is
Substitute 293 K for
Thus, the energy destroyed is
b)
The total entropy change and exergy destruction by treating the mixture as a non ideal gas using Amagat’s law.
b)

Answer to Problem 71P
The entropy generation is
The energy destroyed is
Explanation of Solution
Write the expression to obtain the initial reduced temperature of
Here, critical temperature of
Write the expression to obtain the initial and final reduced pressure of
Here, critical temperature of
Write the expression to obtain the final reduced temperature of
Here, critical temperature of
Write the expression to obtain the initial reduced temperature of
Here, critical temperature of
Write the expression to obtain the initial and final reduced pressure of
Here, critical temperature of
Write the expression to obtain the final reduced temperature of
Here, critical temperature of
Write the expression to obtain the entropy change for
Write the expression to obtain the entropy change for
Here, number of moles of
Write the expression to obtain the surrounding entropy change
Here, surrounding heat is
Write the expression to obtain the entropy generation
Write the expression to obtain the energy destroyed during a process
Here, initial temperature is
Conclusion:
Substitute 160 K for
Substitute 5 MPa for
Substitute 200 K for
Refer Figure A-30, “Generalized entropy departure chart”, obtain the value of
Substitute 160 K for
Substitute 5 MPa for
Substitute 200 K for
Refer Figure A-30, “Generalized entropy departure chart”, obtain the value of
Substitute
Substitute 0.75 kmol for
Substitute –4,745 kJ for
Substitute
Thus, the entropy generation is
Substitute 293 K for
Thus, the energy destroyed is
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Chapter 13 Solutions
Thermodynamics: An Engineering Approach
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