Concept explainers
A piston–cylinder device contains 6 kg of H2 and 21 kg of N2 at 160 K and 5 MPa. Heat is now transferred to the device, and the mixture expands at constant pressure until the temperature rises to 200 K. Determine the heat transfer during this process by treating the mixture (a) as an ideal gas and (b) as a nonideal gas and using Amagat’s law.
a)
The heat transfer during the process by treating as an ideal gas.
Answer to Problem 72P
The heat transfer during the process as an ideal gas is
Explanation of Solution
Write a closed system energy balance for the gas mixture.
Here, input energy is
Write the expression to obtain the mole number of
Here, molar mass of
Write the expression to obtain the mole number of
Conclusion:
Refer Table A-1, “Molar mass, gas constant, and critical point properties”, obtain the molar masses of
Substitute
Substitute
From the Table of ideal gas for
Substitute
Thus, the heat transfer during the process as an ideal gas is
b)
The heat transfer during the process by treating as non-ideal gas.
Answer to Problem 72P
The heat transfer during the process by treating as non-ideal gas is
Explanation of Solution
Write the expression to obtain the initial reduced temperature of
Here, critical temperature of
Write the expression to obtain the initial and final reduced pressure of
Here, critical temperature of
Write the expression to obtain the final reduced temperature of
Here, critical temperature of
Write the expression to obtain the initial reduced temperature of
Here, critical temperature of
Write the expression to obtain the initial and final reduced pressure of
Here, critical temperature of
Write the expression to obtain the final reduced temperature of
Here, critical temperature of
Consider hydrogen as ideal gas
Write the expression for molar enthalpy difference of hydrogen
Write the expression for molar enthalpy difference of nitrogen.
Conclusion:
Substitute 160 K for
Substitute 5 MPa for
Substitute 200 K for
Refer Figure A-30, “Generalized entropy departure chart”, obtain the value of
Substitute 160 K for
Substitute 5 MPa for
Substitute 200 K for
Refer Figure A-30, “Generalized entropy departure chart”, obtain the value of
Substitute
Substitute
Substitute
Thus, the heat transfer during the process by treating as non-ideal gas is
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Chapter 13 Solutions
Thermodynamics: An Engineering Approach
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