Concept explainers
A piston–cylinder device contains steam that undergoes a reversible
The net work done and net heat transfer by piston cylinder device.
Answer to Problem 175RP
The net work done by piston cylinder device is
The net heat transfer by piston cylinder device is
Explanation of Solution
Write the expression to calculate the mass of the steam in the cylinder.
Here, mass of the steam is m, initial volume is
Write the expression for the volume at state 3.
Here, volume at state 3 is
Write the expression to calculate the heat transfer in for the isothermal expansion process 1-2.
Here, heat transfer in for process 1-2 is
Write the expression to calculate the work done out for the isothermal expansion process 1-2.
Here, work done out for process 1-2 is
Write the expression to calculate the work done in for the isentropic compression process 2-3.
Here, work done in for process 2-3 is
Write the expression to calculate the work done in for the constant pressure compression process 3-1.
Here, work done in for process 3-1 is
Write the expression to calculate the heat transfer out for the constant pressure compression process 3-1.
Here, heat transfer out for the process 3-1.
Write the expression to calculate the net work done by piston cylinder device.
Here, the net work done is
Write the expression to calculate the net heat transfer by piston cylinder device.
Here, the net heat transfer is
Conclusion:
Refer to Table A-6, “Superheated water”.
Obtain the value of internal energy state 1
Write the formula of interpolation method of two variables.
Here, the variables denoted by x and y are temperature and internal energy.
Show temperature and initial internal energy values from the Table A-6.
Temperature | Internal energy |
300 | 2805.1 |
350 | ? |
400 | 2964.9 |
Substitute
The value of internal energy state 1
Refer to Table A-6, “Superheated water”.
Obtain the value of initial molar volume
Show temperature and molar volume values from the Table A-6.
Temperature | Molar volume |
300 | 0.65489 |
350 | ? |
400 | 0.77265 |
Substitute
The value of initial molar volume
Refer to Table A-6, “Superheated water”.
Obtain the value of entropy at state1
Show temperature and entropy values from the Table A-6.
Temperature | Entropy |
300 | 7.5677 |
350 | ? |
400 | 7.9003 |
Substitute
The value of entropy at state1
Similarly,
obtain the values of internal energy at state 2
Obtain the values of internal energy at state 3
Substitute
Substitute
Substitute
Substitute
Substitute
The heat transfer during the process is zero, since isentropic compression process, entropy remains constant.
Substitute
Substitute
Substitute
Thus, the net work done by piston cylinder device is
Substitute
The negative sign indicates that the heat transfer occurs from system to surroundings.
Thus, the net heat transfer by piston cylinder device is
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Chapter 7 Solutions
THERMODYNAMICS
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