
a)
The change in enthalpy and entropy of water vapor using departure charts.
a)

Answer to Problem 70P
The change in enthalpy and entropy of water vapor using property table are
Explanation of Solution
Write the mean change in enthalpy
Here, enthalpy of ideal gas at temperature of 280 K is
Write the mean change in entropy
Here, gas constant is R, initial pressure is
Write the reduced temperature
Here, critical temperature is
Write the reduced pressure
Here, critical pressure is
Write the reduced temperature
Here, critical temperature is
Write the reduced pressure
Here, critical pressure is
Write the change in enthalpy
Here, change in enthalpy of ideal gas is
Write the change in entropy
Here, change in enthalpy of ideal gas is
Write the change in enthalpy
Here, molar mass of water vapor is
Write the change in entropy
Here, molar mass of water vapor is
Conclusion:
Refer to Table A-4E, “saturated water temperature table”.
Obtain the value of initial pressure
From the ideal gas properties of water vapor table A-23E, select the enthalpy of water vapor at temperature of 860 R and 1260 R as
Substitute
From the ideal gas specific heats at various common gases table A-23E, select the gas constant of steam as
From the ideal gas properties of water vapor table A-23E, select the entropy of water vapor at temperature of 860 R and 1260 R as
Substitute
From the Nelson-Obert generalized compressibility chart A-15, select the initial state of compressibility factor
Substitute 860 R for
Substitute
Substitute 1,260 R for
Substitute
From the Nelson-Obert generalized compressibility chart A-15, select the initial state of compressibility factor
Substitute 0.07213 for
Substitute
From the molar mass properties table A-1, select the molar mass
Substitute
Thus, the change in enthalpy
Substitute
Thus, the change in entropy
b)
The change in enthalpy and entropy of water vapor using property table.
b)

Answer to Problem 70P
The change in enthalpy and entropy of water vapor using property table are
Explanation of Solution
Write the change in enthalpy
Write the change in entropy
Refer to Table A-4, “saturated water temperature table”.
Obtain the initial enthalpy
Refer to Table A-4, “saturated water pressure table”.
Obtain the final enthalpy
Conclusion:
Substitute
Thus, the change in enthalpy
Substitute
Thus, the change in entropy
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Chapter 12 Solutions
Thermodynamics: An Engineering Approach
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