Concept explainers
A 0.5-m3 rigid tank contains refrigerant-134a initially at 200 kPa and 40 percent quality. Heat is transferred now to the refrigerant from a source at 35°C until the pressure rises to 400 kPa. Determine (a) the entropy change of the refrigerant, (b) the entropy change of the heat source, and (c) the total entropy change for this process.
a)
The entropy change of the refrigerant.
Answer to Problem 43P
The entropy change of the refrigerant is
Explanation of Solution
Write the expression to calculate initial specific volume of the refrigerant.
Here, initial specific volume is
Write the expression to calculate the initial internal energy of the refrigerant.
Here, initial internal energy is
Write the expression to calculate the initial entropy of the refrigerant.
Here, initial entropy is
Write the expression to calculate the final specific volume of the refrigerant.
Here, final specific volume is
Write the expression to calculate the final internal energy of the refrigerant.
Here, final internal energy is
Write the expression to calculate the final entropy of the refrigerant.
Here, final entropy is
Write the expression to calculate the mass of the refrigerant.
Here, mass of the refrigerant is m, volume of the tank is
Write the expression to calculate the expression for the entropy change of the refrigerant.
Here, entropy change of the refrigerant is
Conclusion:
From Table A-12, “Saturated refrigerant 134a– pressure table”, obtain the following properties at saturated pressure of
Substitute
From Table A-12, “Saturated refrigerant 134a– pressure table”, obtain the following properties at saturated pressure of
Substitute
From Table A-12, “Saturated refrigerant 134a– pressure table”, obtain the following properties at saturated pressure of
Substitute
Specific volume remains constant for a rigid tank
From Table A-12, “Saturated refrigerant 134a– pressure table”, obtain the following properties at saturated pressure of
Substitute
From Table A-12, “Saturated refrigerant 134a– pressure table”, obtain the following properties at saturated pressure of
Substitute
From Table A-12, “Saturated refrigerant 134a– pressure table”, obtain the following properties at saturated pressure of
Substitute
Substitute
Substitute 12.37 kg for m,
Thus, the entropy change of the refrigerant is
b)
The entropy change of the heat source
Answer to Problem 43P
The entropy change of the heat source is
Explanation of Solution
Write the expression for the energy balance equation for closed system.
Here, energy transfer into the control volume is
Write the expression to calculate the entropy change of the heat source.
Here, source temperature is
Conclusion:
Substitute
Here, heat transfer input is
Substitute 12.37 kg for m,
Heat transfer for the source
Substitute –1058 kJ for
The entropy change of the heat source is
c)
The total entropy change during the process.
Answer to Problem 43P
The total entropy change during the process is
Explanation of Solution
Write the expression for the total entropy change during the process.
Here, total entropy change during the process is
Conclusion:
Substitute
Thus, the total entropy change during the process is
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Chapter 7 Solutions
THERMODYNAMICS
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