A 0.6-m3 rigid tank is filled with saturated liquid water at 135°C. A valve at the bottom of the tank is now opened, and one-half of the total mass is withdrawn from the tank in liquid form. Heat is transferred to water from a source of 210°C so that the temperature in the tank remains constant. Determine (a) the amount of heat transfer and (b) the reversible work and exergy destruction for this process. Assume the surroundings to be at 25°C and 100 kPa.
(a)
The amount of heat transfer during the process.
Answer to Problem 73P
The amount of heat transfer during the process is
Explanation of Solution
Write the expression for the mass balance for a tank which acts as a system.
Here, mass of water entering the system is
Write the expression for the energy balance equation for a closed system.
Here, net energy transfer in to the control volume is
For steady state, the change in internal energy of system is zero.
Substitute 0 for
Here, amount of heat transfer during the process is
Write the formula to calculate initial mass in the tank
Here, volume of the tank is
Write the relation between the initial and final mass of the tank.
Write the formula to calculate final mass in the tank
Here, final specific volume of the water is
Write the expression to calculate the quality at state 2
Here, specific volume of saturated liquid is
Write the expression to calculate final internal energy
Here, internal energy of saturated liquid is
Write the expression to calculate the final specific entropy
Here, specific entropy of saturated liquid is
Conclusion:
Refer Table A-4, “Saturated water-Temperature table”, obtain the following properties of water at the temperature of
Refer Table A-4, “Saturated water-Temperature table”, obtain the following properties of water at the temperature of
Substitute
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Substitute
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Substitute
Substitute
Thus, the amount of heat transfer during the process is
(b)
The reversible work and exergy destruction during the process.
Answer to Problem 73P
The exergy destruction during the process is
The reversible work for the process is
Explanation of Solution
Write the expression for the entropy balance on the extended system.
Here, entropy generation is
Write the expression to calculate exergy destruction during the process
Here, dead state temperature is
For the given process, the actual work is zero, then the reversible work will be equal to exergy destruction.
Conclusion:
Substitute
Substitute
Thus, the exergy destruction during the process is
Substitute
Thus, the reversible work during the process is
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Chapter 8 Solutions
Thermodynamics: An Engineering Approach
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