Concept explainers
A mass of 10 g of nitrogen is contained in the spring-loaded piston–cylinder device shown in Fig. P4–54. The spring constant is 1 kN/m, and the piston diameter is 10 cm. When the spring exerts no force against the piston, the nitrogen is at 120 kPa and 27°C. The device is now heated until its volume is 10 percent greater than the original volume. Determine the change in the specific internal energy and enthalpy of the nitrogen.
FIGURE P4–54
The change in the internal energy of the nitrogen.
The change in the enthalpy of the nitrogen.
Answer to Problem 54P
The change in the internal energy of the nitrogen is
The change in the enthalpy of the nitrogen is
Explanation of Solution
Write the expression for the initial volume of nitrogen.
Here, the mass of the spring loaded piston cylinder device is
Determine the linear P-v process for spring loaded piston cylinder device.
Here, the system pressure is
Determine the specific heat constant value.
Substitute
From the Equation (IV), the final volume is 10 percent greater than the original volume;
Determine the final temperature of the nitrogen.
Here, the final pressure of the nitrogen is
Determine the internal energy of the spring loaded piston-cylinder device.
Here, the specific heat of constant volume is
Determine the enthalpy of the spring loaded piston-cylinder device.
Here, the specific heat of constant pressure is
Conclusion:
Write the conversion of unit for temperature of 20 C from
Refer Table A-2(a), “Ideal-gas specific heats of various common gases” to obtain the value of gas constant, specific heat of constant volume and pressure for nitrogen gas is
Substitute
Substitute
Substitute
Substitute
Substitute
Thus, the change in the internal energy of the nitrogen is
Substitute
Thus, the change in the enthalpy of the nitrogen is
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Chapter 4 Solutions
Thermodynamics: An Engineering Approach
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