Concept explainers
A piston–cylinder device initially contains 0.6 m3 of saturated water vapor at 250 kPa. At this state, the piston is resting on a set of stops, and the mass of the piston is such that a pressure of 300 kPa is required to move it. Heat is now slowly transferred to the steam until the volume doubles. Show the process on a P-V diagram with respect to saturation lines and determine (a) the final temperature, (b) the work done during this process, and (c) the total heat transfer.
(a)
The final temperature of the piston cylinder device.
Answer to Problem 41P
The final temperature of the piston cylinder device is
Explanation of Solution
Write the expression for the energy balance equation.
Here, the total energy entering the system is
Substitute
Here, the mass of the piston cylinder device is
Write the expression for the mass of the system.
Here, the initial volume of the system is
Determine the final specific volume of the piston cylinder device.
The final volume of the piston cylinder device is
Conclusion:
From the Table (A-4 through A-6), obtain the value of initial specific volume, the specific internal energy at initial pressure of
Substitute
Substitute
Unit conversion of final pressure from kPa to MPa.
Refer to Table A-6, “Superheated water”, obtain the below properties at the final pressure of 0.30 MPa using interpolation method of two variables.
Write the formula of interpolation method of two variables.
Here, the variables denote by x and y are temperature and specific volume.
Show the temperature at
S. No |
specific volume |
Temperature, |
1 | ||
2 | ||
3 |
Calculate final temperature at final pressure of 0.30 MPa for liquid phase using interpolation method.
Substitute
From above calculation the final temperature is
Repeat the above statement for the final specific internal energy.
Thus, the final temperature of the piston cylinder device is
(b)
The work done during the piston-cylinder process.
Answer to Problem 41P
The work done during the piston-cylinder process is
Explanation of Solution
Determine the work done during the constant pressure process.
Here, the final pressure is
Conclusion:
Substitute
Thus, the work done during the piston-cylinder process is
(c)
The heat transfer during the piston-cylinder process.
Answer to Problem 41P
The heat transfer during the piston-cylinder process is
Explanation of Solution
Conclusion:
Substitute
Thus, the heat transfer during the piston-cylinder process is
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Chapter 4 Solutions
Thermodynamics: An Engineering Approach
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