A piston-cylinder device initially contains 0.08 m3 of nitrogen gas at 150 kPa and 200°C. The nitrogen is now expanded to a pressure of 80 kPa polytropically with a polytropic exponent whose value is equal to the specific heat ratio (called isentropic expansion). Determine the final temperature and the boundary work done during this process.

Respuesta :

Answer:

[tex]V_2 = 0.125 m^3[/tex]

Work done =  = 5 kJ

Explanation:

Given data:

volume of nitrogen [tex] v_1 = 0.08 m^3[/tex]

[tex]P_1 = 150 kPa[/tex]

[tex]T_1 = 200 degree celcius = 473 Kelvin[/tex]

[tex]P_2 = 80 kPa[/tex]

Polytropic exponent n = 1.4

[tex]\frac{T_2}{T_1} = [\frac{P_2}{P_1}]^{\frac{n-1}{n}[/tex]

putting all value

[tex]\frac{T_2}{473} = [\frac{80}{150}]^{\frac{1.4-1}{1.4}[/tex]

[tex]\frac{T_2} = 395.23 K = 122.08 DEGREE \ CELCIUS[/tex]

polytropic process is given as

[tex]P_1 V_1^n = P_2 V_2^n[/tex]

[tex]150\times 0.08^{1.4} = 80 \times V_2^{1.4}[/tex]

[tex]V_2 = 0.125 m^3[/tex]

work done [tex]= \frac{P_1 V_1 -P_2 V_2}{n-1}[/tex]

[tex]= \frac{150 \times 0.8 - 80 \times 0.125}{1.4-1}[/tex]

                  = 5 kJ

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