Concept explainers
1 kg of oxygen is heated from 20 to 120°C. Determine the amount of heat transfer required when this is done during a (a) constant-volume process and (b) isobaric process.
FIGURE P4–62
The amount of heat transfers to constant-volume process.
The amount of heat transfers to isobaric process.
Answer to Problem 62P
The amount of heat transfers to constant-volume process is
The amount of heat transfers to isobaric process is
Explanation of Solution
Write the general expression for the energy balance equation.
Here, the total energy entering the system is
Simplify Equation (I) and write energy balance during a constant-volume process.
Here, the heat to be transfer into the system is
Take the oxygen as the system.
Substitute
Here, the mass of oxygen is
Rewrite the Equation (I) and write energy balance during a constant-pressure process.
Here, the heat to be transfer into the constant-pressure process is
Since, the quasi-equilibrium process during a constant pressure
Determine the change in temperature.
Here, the initial temperature oxygen is
Write the expression for linear interpolation method.
Here, the result of constant-pressure of specific heat is
Conclusion:
Substitute
Substitute
From above calculation the constant-pressure of specific heat is
Substitute
From above calculation the constant-volume of specific heat is
From the Table A-2b “Ideal-gas specific heats of various common gases”, obtain the value of constant-volume specific heat of air at 300 K temperature as
Substitute
Thus, the amount of heat transfers to constant-volume process is
Substitute
Thus, the amount of heat transfers to isobaric process is
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